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

[GOLDCYLON]

Originally Posted by 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

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/NCVEC...erters/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.

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.


Tom

[Paul Workman]

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

Originally Posted by 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

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!

[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!





This is my big phuck you to colorados E testing bs....lol!

[Sgreg]

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