High HCs on Emissions

Originally Posted by Arctic91

(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!!

[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

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]

Originally Posted by Arctic91

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.)

Originally Posted by Arctic91

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!)

Originally Posted by Arctic91

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?

[Paul Workman]

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

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!

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!
Take heart one of the more versed guys will see this and help ya out.


Tom

[Zr1 Destroyer]

Originally Posted by 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?

Bump 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!

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.