High HCs on Emissions

[Arctic91]

Hopefully some of the emissions gurus out there can identify this as a "classic" symptom of a particular problem...

Had to submit to an emissions test and HC levels were WAY above limit. CO levels were close to limit, but still under. Summary and trace reports are incuded below, if those help.

My first thoughts were that (1) the injectors need to be replaced (believe they are the originals), (2) I have a vacuum leak (pump seems to run longer than I remember it running when first purchased and I occassionally get a high pitched "squeal" for a sec on start-up - think it started after the last oil change, so I may have disturbed something down there), or (3) the plugs were old and combustion was less than optimal. The idle has always been a little rougher than I would have liked, but after installing new plugs the idle smoothed out considerably (FYI - I replaced Bosch platnums with AC Delco 41-800 plantums gapped at .035). 24 hours later, the idle is has become a little more rough like it was before and there is more carbon on the new plugs than I would have expected (there was quite a bit on the old plugs). Plan for the next week is to probably troubleshoot the vacuum and price new accel injectors. I would think that if those are the violators, I wuoldn't keep getting the carbon on the plugs.

One other issue that concerns me is that there are traces of fresh oil around the base of the plugs and the threads... both old and new. Is that fairly common or should I worry much about it? It wasn't a lot... but the fact there was some bothers me.

Anything that you guys think I might have overlooked?

Thanks,
Scott


http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Report.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Report.jpg)

http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Trace.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Trace.jpg)

[GOLDCYLON]

Hopefully some of the emissions gurus out there can identify this as a "classic" symptom of a particular problem...

Had to submit to an emissions test and HC levels were WAY above limit. CO levels were close to limit, but still under. Summary and trace reports are incuded below, if those help.

My first thoughts were that (1) the injectors need to be replaced (believe they are the originals), (2) I have a vacuum leak (pump seems to run longer than I remember it running when first purchased and I occassionally get a high pitched "squeal" for a sec on start-up - think it started after the last oil change, so I may have disturbed something down there), or (3) the plugs were old and combustion was less than optimal. The idle has always been a little rougher than I would have liked, but after installing new plugs the idle smoothed out considerably (FYI - I replaced Bosch platnums with AC Delco 41-800 plantums gapped at .035). 24 hours later, the idle is has become a little more rough like it was before and there is more carbon on the new plugs than I would have expected (there was quite a bit on the old plugs). Plan for the next week is to probably troubleshoot the vacuum and price new accel injectors. I would think that if those are the violators, I wuoldn't keep getting the carbon on the plugs.

One other issue that concerns me is that there are traces of fresh oil around the base of the plugs and the threads... both old and new. Is that fairly common or should I worry much about it? It wasn't a lot... but the fact there was some bothers me.

Anything that you guys think I might have overlooked?

Thanks,
Scott


http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Report.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Report.jpg)

http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Trace.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Trace.jpg)


All of the above but replace the 02 sensors as well. Cheap fix and new set of plugs has to have helped. Before you move on to the injectors

[tccrab]

My vote is on leaky fuel injectors.
A vacuum leak would make it run lean causing higher CO & NOx but lower HC.

TomC

[tf95ZR1]

Do you have an after market chip in? I put my stock one back in
for testing. And IMHO, the shotgun approach of replacing everything
could get very expensive instead of isolating the problem first. Now how
to do that is another question for those who know more than I do.
Good Luck!

[ZR1Vette]

Rather dry read but has some good info in it>>>

http://www.colostate.edu/depts/NCVECS/converters/az.html

Might lead you to some issues for you to consider...like the CATS..

I think the carbon build up is a key indicator... suggesting injectors...concerning having a chip...I just passed the Virginia emissions test with a Haibek chip installed and I think that helped since that chip tends to run the LT5 a bit leaner
Michael

[tomtom72]

Hi Scott,

Here's a few more thoughts for ya.

Squeal could be the serp belt, or any of the driven devices & tensioner.....my $ is on serp belt. It might want to be relieved of duty, or it may have gotten wet somehow.

Oil @ base of plugs & on plug threads is a bit tough for me to justify saying that the O-rings on the cam covers are failing. You don't mention an oil trail from anywhere above the plugs. Shine a light down one of the holes and see with the plug wire out if ya see anything. I use a bit of motor oil on my plugs when I change'em to prevent any corrosion between the steel & aluminium.

Carbon build up on just a few plugs? Do they match up to a particular coil? That's one way to chase down an ignition issue on the wires & the coils. Could also be the injector at those cylinders, leaking or bad spray pattern.

Carbon build up on all the old plugs? Unlikely that all the coils fail at once, but ya never know. Test for good spark. How old are the plug wires? Again, suspect injectors if the ing sys is okay.

Carbon build up on just a few of the new plugs? Then I check the wires, coil(s), and suspect injectors at those locations. Same drill, test for good spark, maybe ohm out a wire pair + that coil. Over at Mr. Haibeck's site, zr1specialist.com, is a bunch of how to's...even ohmming out the injectors thru the ECM....great stuff.

Rough idle, does she smell rich or lean? If rich, could be ignition and or injectors. Obviously a scan at idle & in closed loop would give ya the fuel numbers and a fairly good idea what's up. Or again test for good spark at those holes. A scan will also tell ya if the O2 sensors are getting lazy, cross count #'s. Section 6E in the FSM, Driveability and Emissions chapter has alot of great stuff that helps....or at least it helped me get a handle on this 'puter controlled stuff.:redface:

Lastly, please don't take this the wrong way, new air filter & PCV's? I'm not ready to point at he cats just yet, but they're in the running....it's just that the rough idle + the carboned up plugs make me want to see the other stuff first. JMHO.

:cheers:
Tom

[Paul Workman]

I'm gonna start sounding like a broken record, but IMO a scanner should be included with every Corvette sold!:wink: But, I digress...

Based on similar symptoms I had once, my money is on one or both of the O2s is lazy. A bad O2 may or may not trip a code, but you might check for a code. And, before doing a wholesale parts change-out, see if one of the parts stores will do a static and a dynamic scan and give you a print-out (as you may see something later after the first glance at the data).

If the plugs were carboned up, whether the O2s are faulty or not, the (dynamic) readings will give you a good push in the right direction:

At idle in closed loop, normally the O2 voltage will cycle from lean to rich continuously, crossing over the "mid" point between "rich" and "lean" (called a cross count) with every cycle. Both O2s should be behaving approximately the same. If not, there is a problem...

If a single O2 that is reading low on average (below 450 mV), it is indicating lean. And, if the other O2 is "normal", chances are high the lean O2 is bad. Its signaling "lean" to the ECM and the ECM is increasing the injector dwell time on that side of the engine; riching the mixture in attempt to bring the average reading up. This would cause you HC to read high, plugs on that side of the engine to foul, and gas mileage would suffer. (FWIW, I've never seen O2s that have gone bad indicate "rich". I suppose it could happen, but every one I've see indicate "lean" when they go bad.)

If BOTH O2s read "lean" and the plugs are fouling, it is possible both O2s are bad, but the chances just got pretty slim, unless something like silicon got introduced into the oil or the air vent (space between the wires going into the O2s) got plugged. (I had a case where a mechanic used to seal up the wires with silicone RTV to keep oil contamination out. As result, the new O2s "went bad" (lean) after only a couple thousand miles...twice, and plugs would foul something awful, mileage went down. Replacing the valve cover gaskets and leaving the O2s free to "breath" and (voila!) the problem was solved!)

Again, in closed loop mode, if one or both O2s are reading high (rich), then I would suspect something else is wrong and the O2s are not indicating incorrectly, but rather they are correctly indicating a too rich situation. (Course, it is foolish to assume, so one my be smart to eliminate (test) the O2s to verify they are OKay (which they probably are!).)

A fuel pressure leak-down test would confirm a leaking injector(s). However, beyond hard starting accompanied initially with some black smoke, an injector or a few would have to be leaking really badly. And, keeping in mind that more (or all?) plugs are fouling would sort of dismiss (for the moment) a leaking injector - not likely they ALL would be leaking; highly unlikely, I would think.:wink: But, a leak-down test is easy enough to do.

As for the (secondary throttle plates) vacuum pump running excessively, it is easy to do a vacuum leak test on the secondary actuators and connections. But, even if there is a leak or the plates are not opening, I doubt the plugs would foul as result. However, if there is an air leak, when in closed loop, the ECM will attempt to maintain the proper mixture by adding more fuel. This will result in the idle increasing. (Try pulling the power brake booster hose off while it is idling (in closed loop) and see this phenomenon for yourself.)

I guess my point in all of this is getting that rascal scanned is the first step to eliminating a lot of "could be this or could be that" guessing. If nothing else, you will find out what stuff is not the problem, and that helps a lot! After a mechanic gave me that "no problem found" line after having my '95 Vette for two weeks, yet the problem persisted, I bought my first scanner some 6 years ago. It was the best money I ever spent on the Vette!;)

Good luck! let us know what the scan showed and I'm sure someone on this board will be able to put a finger on it!

P.

P.

[Zr1 Destroyer]

Hopefully some of the emissions gurus out there can identify this as a "classic" symptom of a particular problem...

Had to submit to an emissions test and HC levels were WAY above limit. CO levels were close to limit, but still under. Summary and trace reports are incuded below, if those help.

My first thoughts were that (1) the injectors need to be replaced (believe they are the originals), (2) I have a vacuum leak (pump seems to run longer than I remember it running when first purchased and I occassionally get a high pitched "squeal" for a sec on start-up - think it started after the last oil change, so I may have disturbed something down there), or (3) the plugs were old and combustion was less than optimal. The idle has always been a little rougher than I would have liked, but after installing new plugs the idle smoothed out considerably (FYI - I replaced Bosch platnums with AC Delco 41-800 plantums gapped at .035). 24 hours later, the idle is has become a little more rough like it was before and there is more carbon on the new plugs than I would have expected (there was quite a bit on the old plugs). Plan for the next week is to probably troubleshoot the vacuum and price new accel injectors. I would think that if those are the violators, I wuoldn't keep getting the carbon on the plugs.

One other issue that concerns me is that there are traces of fresh oil around the base of the plugs and the threads... both old and new. Is that fairly common or should I worry much about it? It wasn't a lot... but the fact there was some bothers me.

Anything that you guys think I might have overlooked?

Thanks,
Scott


http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Report.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Report.jpg)

http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/th_Trace.jpg (http://i256.photobucket.com/albums/hh193/Arctic91/ZR1/Trace.jpg)Eeeeerrr...i had the same HC issue with mine here in colorado! I replaced o2's, oil, plugs ,added two bottles of gar. to pass and ran the holy living crap out of it, but still didn't pass...got closer but no pass!

Soooo, I tried a few other things like turning my lpe fuel pressure regulator down to like 20 or 25(can't remember exactually) and got even closer, but still nooooooo dice!

I almost gave up until i did a leak down test on all 8 cylinders and found i had a rear cylinder that only held 2 pounds of air (which i later found out some one must of dropped a tiny srew or something down this cylinder at some point). Not wanting to do a rebuild on the 368 yet i decided to order a B&B and use the flowmaster system that came on my car for an E test system only(i'll post some pics). I went and purchased two of the cheapest/low budget converters toward the forward front of the system and found a larger one to put in place of the center resonator area...had my buddy nj weld them inplace for a total of 5 converters under the Z.

(Keep in mind this system is for E testing only)......so for one last try i drove down to my local testing place to see my good buddies and she passed with flying colors with my new 5 cat system and this was the ONLY way i could get my fancy little 368 to pass! I have since done a 415 cube build with way larger ports then my little drm 368 and also held between 96-99% on a leak down test and can't wait to see my buddies at the E test station again with my newly modded flowmaster system that i made to fit the headers for a total of three very low flow junk converters!

I'll take pictures of my schweet guarantied to pass flowmaster system and i'm done with breakfast!:wave:

[Zr1 Destroyer]

Pics as promised...ignore my old B&B off of my 90z with that wicked dr.gas xpipe from back in the day!
http://i43.photobucket.com/albums/e396/ry368/Zr1%20top%20end/Nova-Zr1shots073.jpg
http://i43.photobucket.com/albums/e396/ry368/Zr1%20top%20end/Nova-Zr1shots075.jpg
http://i43.photobucket.com/albums/e396/ry368/Zr1%20top%20end/Nova-Zr1shots074.jpg
http://i43.photobucket.com/albums/e396/ry368/Zr1%20top%20end/Nova-Zr1shots077.jpg
http://i43.photobucket.com/albums/e396/ry368/Zr1%20top%20end/Nova-Zr1shots076.jpg
This is my big phuck you to colorados E testing bs....lol!:mrgreen:

[Sgreg]

Squeal is probably pilot bushing. Can't pass emissions about half the time so can't help there. :confused:

[Jeffvette]

(2) I have a vacuum leak (pump seems to run longer than I remember it running when first purchased


I'm not quite sure why people get all worked up about that damn pump cycling. It is a sealed system. It has no effect on anything else, just hte secondary activation, and only then when it is commanded on. You can unplug the pump and drive the car around and still have secondary activation just from the vacuum from normal engine operation.


I occassionally get a high pitched "squeal" for a sec on start-up - think it started after the last oil change, so I may have disturbed something down there),

Belt slipping. Replace belt, Get the goodyear belt.


the plugs were old and combustion was less than optimal. The idle has always been a little rougher than I would have liked, but after installing new plugs the idle smoothed out considerably (FYI - I replaced Bosch platnums with AC Delco 41-800 plantums gapped at .035). 24 hours later, the idle is has become a little more rough like it was before and there is more carbon on the new plugs than I would have expected (there was quite a bit on the old plugs).

Are the plugs showing a lean condition? As a lean misfire will cause you to fail emissions?


One other issue that concerns me is that there are traces of fresh oil around the base of the plugs and the threads... both old and new. Is that fairly common or should I worry much about it? It wasn't a lot... but the fact there was some bothers me.

So where is the oil coming from? Internal, or is it leaking from the cam cover seal down to the plug?

[Arctic91]

OK... sorry it took a little while to get back on the board. I checked a few things out yesterday afternoon and couldn't get out of work until late this evening:

1. Checked the vacuum between the pump and the plenum - pump works like a champ and the system held solid at 12 on both ends (pump end and plenum end), so I think vacuum is good.

2. Checked fuel pressure at the rail - steady 43 psi with the system pressurized (key on) and at idle, but it dropped to the 34-32 psi range within moments after turning the motor off. If the pressure is within spec (or close enough that it wouldn't affect the diagnosis), that would seem to indicate leaky injectors, right? Could it also indicate a failed check valve in the fuel line? I didn't see one mentioned in the FSM, but not sure if there is one between the pump and rail? I still don't understand the other method of checking resistance between the ECM and injectors that was described, but I can understand a simple drop in pressure. If the pressure test is a definitive indicator that the injectors are leaking, then I'll go ahead with the replacement.

3. Finally got the second u-joint that I needed to get the #8 plug out and put in the new one. Seems to run slightly smoother but still rougher than I would like, due to the rich mixture I assume. Plugs are definately indicating a rich mixture. Can't seem to isolate it to particular cyl or bank.

4. The high-pitch that I sometimes hear on start-up is the electric a.i.r. pump, not the vacuum pump or belt. I changed the oil a couple of days before going into for the emissions test and think that the ramps may have pushed up on the front spoiler and disturbed the seating of the pump somehow. Pretty embarassing - I guess I need some ramps with a lower angle. The pump is running quite a bit more than it has in the past and I can hear/feel airflow around the seals. Could be the cause for some of the elevated readings? Seems to be a likely contributor, now that I know what it does.

5. The oil around the base of the plugs seems to be coming from somewhere deeper down than the cam cover. I'm not getting much on the plug boot and none on the electrode. I would have to say it's from an external source since it appears to be heavier on the outside base of the plugs. It's not bad, but I've never had that on any previous car, so it struck me as being odd. I'll have to check the oil level in the morning and see if I'm using.

A few thoughts came to mind as I was driving home tonight: (1) I really DO need a scan tool, (2) I also need a 5-cat exhaust system while I'm at it (can I borrow that if all else fails? Seriously, can I borrow that if I need it?), and (3) is there a way to manually lean the fuel/air ratio? I would hope the ECM automatically adjusts for altitude.

Big thanks to all those who have chimed in so far!! :worship:

[tomtom72]

Scott,

Those fuel numbers look to be okay, but on the low side. Those numbers maybe pointing to another possible issue, but not relayed to the emissions' test failure. I think there is a device called a "pulser" in the pump plumbing in the tank and that could cause an issue with a leak down test...if it is n/g it allows fuel in the feed line to flow backwards once the pumps are off....I think I may have that right? When was the F/filter last changed?

Or the drop in static pressure is an indication of injectors that have crud on the nozzle & are leaking fuel....that would also explain the rich condition of the plugs. Are your injectors OEM?

My guess would be you are dumping fuel, thru bad injectors and that is making the HC's fail.....I don't know if the O2 sensors could pull enough fuel out to compensate for leaking injectors...sorry. A scan would help at this point or you could pull up the plenum to get the fuel rails up in the air and do another fuel pump test(KOEO) with the injectors unseated to see if they leak.

JMHO
:cheers:
Tom

Oh, if the air pump is making that squeal....the bearings in the electric motor are not long for this world. The oil leak I can't do anything but guess....I've never had my covers off so I have no idea from hands on exp where the likely oil leak points would be....sorry.

[Paul Workman]

2. Checked fuel pressure at the rail - steady 43 psi with the system pressurized (key on) and at idle, but it dropped to the 34-32 psi range within moments after turning the motor off. If the pressure is within spec (or close enough that it wouldn't affect the diagnosis), that would seem to indicate leaky injectors, right? Could it also indicate a failed check valve in the fuel line? I didn't see one mentioned in the FSM, but not sure if there is one between the pump and rail? I still don't understand the other method of checking resistance between the ECM and injectors that was described, but I can understand a simple drop in pressure. If the pressure test is a definitive indicator that the injectors are leaking, then I'll go ahead with the replacement.

For what it's worth: With the key on (not running), my static pressure is 46# (FSM said pressure would "peak" after cycling the ignition switch several times - I never tried it tho). With the key turned off, the pressure dropped a couple #, but did not leak down from there initially and only lost a couple # over a period of over 2minutes. So, in comparison, it seems to suggest there is a leak somewhere; beit one or more injectors or as you say, a check valve in the pump. Before I pulled the plenum, I would want to eliminate the pump side of the fuel system first. If the pump feed held pressure, then you know for sure one or more injectors are having issues. (I've never had to do that on an LT5; plenty of other cars, so someone will prolly have a specific procedure fixture idea that will help ya get that done.)


3. Finally got the second u-joint that I needed to get the #8 plug out and put in the new one. Seems to run slightly smoother but still rougher than I would like, due to the rich mixture I assume. Plugs are definately indicating a rich mixture. Can't seem to isolate it to particular cyl or bank.

Like you said, it really is time to have it scanned. (Wish you lived close by, and we'd run a few!)

5. The oil around the base of the plugs seems to be coming from somewhere deeper down than the cam cover. I'm not getting much on the plug boot and none on the electrode. I would have to say it's from an external source since it appears to be heavier on the outside base of the plugs. It's not bad, but I've never had that on any previous car, so it struck me as being odd. I'll have to check the oil level in the morning and see if I'm using.

This is apparently not that uncommon. As mentioned in the FSM and one other poster, it stems from leaking around the gasket surrounding the plug hole between the cam cover and the head. Perhaps re-torquing the cam cover would fix it, as gaskets tend to crush with pressure and heat over time.


PLs Keep us posted. Some of us have been fussin with cars "forever", but the LT5 is certainly unique. So, all info and troubleshooting results are what makes this board so rich!

P.

P.

[Arctic91]

So I was able to borrow a scan tool from a friend until I can get one for myself and here's what the real-time data scan provided (after bringing engine to a nominal operating temp with all accessories off):

No Error Codes Found
PROM ID: 281
Cool Temp: 210F
MAP Sensor: 0.99-1.01V
Throttle Sensor: 0.52V
Batt: 13.7V
Manifold Air Temp: 77.2F
Left O2 Sensor: 80-699mV (Fluctuated like crazy!!)
Right O2 Sensor: 80-699mV (Fluctuated like crazy!!)
Left Block Learn Value: 124-127
Right Block Learn Value: 128-131
Block Learn Cell: 0
Left O2 Cross Counts: 38-122 (settled to approx 72)
Right O2 Cross Counts: 148-252 (settled to approx 227)
Left Integrator Value: 126-136 (settled to 126)
Right integrator Value: 126-136 (settled to approx 126)
CCP Duty Cycle: 0.0%
Idle Air Meter Position: 26 Steps
Desired Idle: 650RPM
Spark Advance: 8.1-11.2 Degrees (settled at approx 10.1)
Engine RPM: 625-650 (mostly 650, but showed flashes of 625)
Knock retard: 0
Knock Sensor: 160
Throttle Angle: 0%
EGR Duty Cycle: 0.0%
4th Gear: Not Engaged
1st Gear: Engaged
A/C: Not requested
A/C Clutch: Disabled
A/C Forced Off: No
Battery Voltage High: No
CCP Purge: Off
Learn Control: Disabled
Loop Status: Closed
Fan 1: Off
Fan 2: Off

The tool was an EZ-Scan 6000, so it doesn't run all the same tests as a Tech1. I left out some of the data becuase it was clearly not applicable to the diagnosis (stuff like vehicle speed, etc.). I left some of the data in (like PROM ID) in case it was indicative of an aftermarket chip (believe OEM chip is in, but not sure).

The only things that seemed odd to me was the very rapid change in O2 sensor data (not sure if that would be considered "normal" and indicative of good response time, though?) and the cross counts (I assumed they would be additive and not decrease, but I saw fluctuations in the values and a big difference between right/left).

Everything else seemed to be in spec, or very close. Even the interogator and block learn codes are not far away from the desired values of 128. Any smoking guns in the data to suggest bad injectors or O2 sensors? If not, I'm starting to suspect failure of the cats or the electric air pump? :icon_scra

[Paul Workman]

As you said, nothing really is jumping off the page, except maybe that left O2 sensor's cross counts. :icon_scra

As for O2 values fluctuating, THAT is normal and stems (in part) due to the individual exhaust pulses passing over the sensor in conjunction with when the voltage is sampled by the scanner. The "cross counts" are the number of times the O2 sensor voltage swings past the mid point. The cross count number can be an average over time, or an absolute count, depending on the mode the scanner is operating in. But, all things being equal, the O2s should be in close proximity as far as operation goes, and the left O2 certainly appears to be "lazy"; at least at this test. (However, after a little WOT running, I have seen O2s that looked a bit lazy initially come back to life and run fine.)

Running a data monitoring scan while driving might shed additional light on the subject. On one occasion I found an O2 that was crapping out when under load that would indicate little (if anything) when idling. Just a thought.

As for the AIR system, if it wasn't working, or the car was not completely warmed up, or if some injectors were fouled, HC tests would suffer. However, plugs would not be fouling w/ or w/o the air system running.

So, if you can, run a dynamic scan if you can and maybe another static scan to see if that left O2 doesn't straighten out. If it continues to be sluggish and not conform with the right side sensor's data then I would be confident that changing it would be the right thing to do, in any case.

Other than the left O2, the scan does not look all that out of whack. So, one of the things I am wondering about is the chip: Is it stock or has it's fuel tables been altered? (You asked about "leaning out" the mixture. There's no screws to twist, but the fuel tables are where the mix is determined - hence the question about the chip.) Another thing; some old school thinking was big on running cooler thermostats as a way of dealing with knock issues. A cold thermostat is an HC test killer - along with an engine that is not fully warmed up and "blown out" before the test. (In fact, I'd be curious as to what a effect a slightly warmer than standard 'stat would have on the HC test results...)

One other thing I notice is the PROM ID: Yours is #281, and mine is #8441 (car is a 90#1201). I have no idea what the difference that makes (if any).

Well, I hesitate to say more w/o being there as I fear I've prolly already sent you on enough of a cat and mouse chase as it is. But, run the snot out of it and then see if that left O2 conforms w/ the right one. If not, then I'd have NO compunction about replacing it. AND, there are some fuel injector cleaners that some have had success with to get the emissions test to pass.

Bottom line: It's running to rich and the question is why? (duh) Anywayz, see what happens after some WOT runs, and mebby do a dynamic (monitor) scan to see what is happening under normal driving conditions and let us know.

Good luck!

P.

[tomtom72]

Hi Scott, Okay this is where my skill is a bit thin. I usually have to combine my data with my nose & smell the exhaust! Oh how analog I still am!:o

Hopefully Jeff or one of the other guys that are fluent in scan tool interpretation will chime in soon & show the light.

FWIW, my read is the O2 sensors are just fine, not broke or lazy.
There seems to be a large(?) fuel imbalance across the motor. I get there from the by reading the left & right cross counts and the left & right block learn values. Now, this is where I have to defer to the senior guys with the skill....I'm not sure which bank has the suspect injectors, my apologies for my lack of real assistance. My only feeble answer, if it were my car, would be to examine the plugs from both banks and try to match up the plug condition to the scan data.....see how each hole is burning and which hole #'s give the worse carbon fouling and if there is a trend on a particular bank.

Sorry that's all I got!:redface:
Take heart one of the more versed guys will see this and help ya out.

:cheers:
Tom

[Zr1 Destroyer]

So I was able to borrow a scan tool from a friend until I can get one for myself and here's what the real-time data scan provided (after bringing engine to a nominal operating temp with all accessories off):

No Error Codes Found
PROM ID: 281
Cool Temp: 210F
MAP Sensor: 0.99-1.01V
Throttle Sensor: 0.52V
Batt: 13.7V
Manifold Air Temp: 77.2F
Left O2 Sensor: 80-699mV (Fluctuated like crazy!!)
Right O2 Sensor: 80-699mV (Fluctuated like crazy!!)
Left Block Learn Value: 124-127
Right Block Learn Value: 128-131
Block Learn Cell: 0
Left O2 Cross Counts: 38-122 (settled to approx 72)
Right O2 Cross Counts: 148-252 (settled to approx 227)
Left Integrator Value: 126-136 (settled to 126)
Right integrator Value: 126-136 (settled to approx 126)
CCP Duty Cycle: 0.0%
Idle Air Meter Position: 26 Steps
Desired Idle: 650RPM
Spark Advance: 8.1-11.2 Degrees (settled at approx 10.1)
Engine RPM: 625-650 (mostly 650, but showed flashes of 625)
Knock retard: 0
Knock Sensor: 160
Throttle Angle: 0%
EGR Duty Cycle: 0.0%
4th Gear: Not Engaged
1st Gear: Engaged
A/C: Not requested
A/C Clutch: Disabled
A/C Forced Off: No
Battery Voltage High: No
CCP Purge: Off
Learn Control: Disabled
Loop Status: Closed
Fan 1: Off
Fan 2: Off

The tool was an EZ-Scan 6000, so it doesn't run all the same tests as a Tech1. I left out some of the data becuase it was clearly not applicable to the diagnosis (stuff like vehicle speed, etc.). I left some of the data in (like PROM ID) in case it was indicative of an aftermarket chip (believe OEM chip is in, but not sure).

The only things that seemed odd to me was the very rapid change in O2 sensor data (not sure if that would be considered "normal" and indicative of good response time, though?) and the cross counts (I assumed they would be additive and not decrease, but I saw fluctuations in the values and a big difference between right/left).

Everything else seemed to be in spec, or very close. Even the interogator and block learn codes are not far away from the desired values of 128. Any smoking guns in the data to suggest bad injectors or O2 sensors? If not, I'm starting to suspect failure of the cats or the electric air pump? :icon_scraBump your tps down to 46 or 47ish just for emisions....i loosened mine and bumped it until the car started to idle and almost die and checked my scan tool....it read 42. I did indeed seem to help my e test!

[Jeffvette]

Any update?

[XfireZ51]

Arctic,

The trace shows that HC is moving up during decel. Maybe you need to cutoff fuel faster on decel. Could be a calibration change.

[Jeffvette]

Arctic,

The trace shows that HC is moving up during decel. Maybe you need to cutoff fuel faster on decel. Could be a calibration change.

And that is masking an issue. Not recomended. This car in good running condition should pass easily.

[Arctic91]

Hey Jeff... :wave: thanks for asking. Here's a quick update:

A couple weeks back, I made the mistake of bringing it into a local shop that has a good rep for diagnosing emissions problems. A week and $300 later, they were scratching their heads and claimed "internal mechanical problem" as the root cause. Still not throwing codes and everything seems normal. No mods to the car- bone stock - so it shouldn't be this difficult. Lesson learned: stick to those who own a Z to diagnose a Z.

Nitrous Junkie took a look at it for me and ran a leak down test with no issues noted, so I concluded that the other shop was grasping at straws (pretty hard to disprove that diagnosis). Next, I started changing the easy things. New fuel filter and O2s haven't made much of a difference - still running rich, partial throttle "stumbling" and what seems like an intermittent miss at idle. I have new injectors (accel) and ignition wires (MSD) ready to go, but won't be able to get to that until the 12th (with a little help/teaching on the finer points of under-plenum plumbing from Nitrous Junkie and Zr1 Destroyer).

I really hope that the new injectors will do the trick and that the cats haven't been wrecked from it running rich. I'm not sure how long the problem existed before I bought the car... could have had 4 or 40k miles worth of unburned crap filtering through there. I'm thinking that new cats would be the next move if the injectors don't solve the problem. Does that sound logical?

Scott

[guinnessdood]

Scott...if you don't get it to pass with the new injectors I'll be really surprised...but if it doesn't...borrow Ry's "emission exhaust" that is propped up to his fence next to his garage. After you pass...remove his exhaust and install a Corsa...or a B&B (with some aftermarket cats) if you prefer and a set of headers (I think Rod has a used set layin around)....now you'll sound like a ZR-1!!! :-)

[cope05]

headers laying around..........PM me please with the info if that is the case.

[Arctic91]

Uly,

I've had the same thought a couple of times... wish me luck once the injectors are in.