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Username Post: Failed emissions - very high HC at idle        (Topic#187176)
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-13-08 03:03 PM - Post#1410599    

So I took the '94 C2500 5.7 TBI in for inspection today, and she failed emissions - badly! The guy at the inspection station didn't put it up on the dyno (says he doesn't put trucks heavier than 1/2 ton on it), just did the two-speed test on it where they run it at around 2200-2800 RPM then at idle, testing emissions at both of those engine speeds.

The funny thing is she passed beautifully at the high speed test. What sucks is I don't have the failed test report with me, but here's basically what the numbers were on HC.

High speed test, HC allowable standard was 220ppm. Test turned in a clean 74ppm! Low speed (idle) test, allowable standard was also 220ppm, test turned in..... 500+ ppm!!! amazingly bad. We ran the test 3 times to be sure (this guy was really trying) and even keyed in different GVWR's (7200 and 8600; my truck is actually the 7200) just to see if it gave any leeway or affected the test results.

The engine is bone stock down to the air filter, 144K miles, base timing set at zero, fresh oil change yesterday, brand new O2 sensor yesterday. The ONLY and I mean ONLY non-stock part of the system is a gutted (hear me out first, next paragraph) catalytic converter with a Flowmaster 40 behind it, 3" in/out with a single turndown pipe.

I *expected* the gutted converter to likely cause it to fail the test. But shouldn't it fail all the way around, not just at idle? Shouldn't it have turned in an equally miserable number at the high speed test? Why such a disparity between the two numbers? What if I told you the high speed HC ppm number was EXACTLY the same as last year's test results, when the truck had a fully intact catalytic converter and base timing was retarded 4 degrees (I didn't set it this way; was how I purchased it.) By the way, previous year's low speed test number was right on the dot at the standard - 1 digit shy of failing.

When I got home I checked the CTS and got 360 ohms which should be between 158F and 176F for the coolant going by Chevytech's chart in the FAQ, so I *think* I trust the CTS (truck had been sitting a moment while I unloaded groceries). Oh, and while it was still running, I hit the thermostat housing with an IR thermometer and moved around until I got my highest reading of around 178F.

The truck SMELLS rich at idle. Before I replaced the O2 sensor yesterday I thought, hey, since the cat is gutted - maybe a good idea to convert to a 3-wire O2. Well duh, '94 has one from the factory, so we can rule that out.

Ideas?

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
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59 EWW 
Very Senior Member
Posts: 1871
59 EWW
Loc: Kansas City Kansas
Reg: 08-31-03
04-13-08 04:30 PM - Post#1410658    
    In response to someotherguy

I've always been a believer that engines run alittle dirtier at idle then at higher RPM's.

Combustion temperatures at idle being low, and with no cat to help cleanup the exhaust, with the miles you have, I'm not real surprised it failed at idle and passed at higher RPM.

I believe if you install a new cat, it would pass.
Ernie

59 Biscayne 2dr
65 Elcamino
97 Z71,K1500,5.7
06 GMC Canyon


 
Chevytech 
Subject Matter Expert - Senior Member
Posts: 3094

Loc: Twin Cities, Minnesota, U...
Reg: 04-25-04
04-13-08 04:32 PM - Post#1410659    
    In response to someotherguy

Hi Richard

I would try a 195 T-stat in it.

TBI systems run rich when below normal operating temperature. Both your ohms reading and your IR thermometer reading show it is on the cool side of normal.

TBI trucks do not seem to tolerate poor quality high ethanol fuel as well as port fuel vehicles. My 1993 idle poorly on the gas that some retailers sell here. Do you notice an occasional misfire at idle?
For those of you that are wondering why you are not getting replies to your thread:

Did you give the model, year, engine, fuel system type, and transmission information?

If the it has been altered from stock let us know about that too.


 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-13-08 04:47 PM - Post#1410664    
    In response to Chevytech

Ernie - yeahhhh, I *almost* agree with you on the new cat, except for a 500+ppm reading vs. the allowable standard of 220ppm? That's a LOT! I'm sure a new cat would clean it up a bunch but I wonder if it could clean it up enough - I get the idea there's another problem here and while a new cat might get me a passing score, I'd still be overlooking another contributor to the problem.

Chevytech - good suggestion; when I first hit the thermostat housing I got around a 160ish figure and immediately thought someone might have installed a 160F thermostat. A little probing around got me near 180F though so that made me reconsider. I know the reading the IR thermometer gets isn't going to be entirely accurate for the actual temp of the coolant; maybe I allowed too much wiggle room there? I definitely agree the stat should be a 195/196 for a TBI; it'll probably be the next thing I try.

Haven't really noticed a miss at idle on this truck yet but I have on other TBI trucks I've owned, so I know what you mean.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
Boosted 1 
Member
Posts: 179

Loc: Downey,Ca.
Reg: 10-25-06
04-13-08 10:55 PM - Post#1410888    
    In response to someotherguy

Just a thought here, Hows the tune-up ? Most of the time high HC will be an Ignition problem,CO fuel system, NOX EGR,Timing. I'm sure in your case a CAT will do the trick.
92 3500 toy hauler, 63,70,Nova,83 Shovel, Blown with N2o 90 step side


 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-14-08 05:37 AM - Post#1410992    
    In response to Boosted 1

Cap and rotor looked good so I didn't replace, wires looked good but I didn't test them for resistance, new AC CR43TS plugs along with the new O2 sensor, oil change, etc., replaced the coil wire as it had come loose and got corroded, cleaned the coil and cap terminals real good, base timing is factory spec - zero.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
elcamino 
Valued Contributor
Posts: 4997
elcamino
Loc: Lake Superior-Michigan US...
Reg: 03-30-00
04-14-08 06:23 AM - Post#1411018    
    In response to someotherguy

Have you ever though of running a fuel system cleaner thorough?

  • Quote:
Recommendations
Treat one full tank of gas up to 20 gallons with one bottle of P.i. For very large gas tanks, partially fill to 40 gallons and treat with two bottles of P.i. Using more than two bottles per treatment is not recommended. Treat gas every 4,000 miles or 100 hours of service. P.i. helps pass emission tests by running one tank of treated fuel through the engine prior to testing. Safe for use with catalytic converters, oxygen sensors, oxygenated gas and 10 percent ethanol blended gas. Not recommended for two-cycle engines.



P.i. Performance Improver Concentrate (API)

Might be worth a try before spending money chasing problems...........
Mike
2009 Cadillac CTS4 AWD Performance Sedan
2012 GMC Sierra AWD Denali 6.2L


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
04-14-08 06:25 AM - Post#1411019    
    In response to someotherguy

I've told this story here but it's been a long time since. What I've done all my life requires alot of idle time (boosting engines), or it did and now I've cut that back alot.

My first TBI rig was pretty impressive, super easy starts and virtually no pain involved, but I did notice it came with a sacrifice, they drink fuel at idle.

So then came my new 92 model, it was pretty much the same (thirsty at idle) so one dark but snowy Winter day, I set out to determine how much more fuel this 350 was burning than did my QJ 454.

Realize I think the efficiency of a perfect QJ and low RPM's is near impossible to beat, I have a pre-focused 18" long light I can send into many places, but into that idling 454's throat, you cannot see the fuel----basically running on vapors or atomized fuel to the point it's invisible. Equally impressive as long as you don't touch those back two, then you flush the toilet.

Two long cold days----I found that the TBI 350 was burning over 4 times the fuel at idle as was the 454. All that to gain an easy start in the worst weather, and a reliable one. My tests were pretty crude, borrowing a buddies JC Whitney inline flowmeter that was supposed to be "state of the art" for the day, also had to rig it up on the return side and subtract the difference. So how precise the outcome was, I really don't know, but there was little doubt that it used more idling, lots more.

IMO, I'd do the stat but I'd also be looking for another cat to put on, it needs it due to the ridiculous amount of fuel going thru.

If that didn't do it but only helped, those of mine that ran alot idling, sure did better with 44 plugs rather than 43's.

Of course, I've never had to pass the test either, likely won't.



 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-14-08 06:35 AM - Post#1411026    
    In response to CDAUSA

Ya know, seems like every TBI vehicle I've had smelled rich at idle, but I've had two recently with gutted cats so it may be coloring my memory a bit.

Interesting test you did and while it may not have been dead-on "scientific" I think that it has more value than just anecdotal evidence, and a lot more effort than most of us casual observers would go to!

I wonder if any of the custom chips for TBI's have addressed this issue?

I hear you on the 44's - I don't know what I was thinking on getting the 43's, other than they're the "original" plug. Seems like pre-FI I used to always get hotter plugs than original. If it called for a 43, I'd usually install a 45. I wonder what kind of other trouble I might be inviting if I went up two heat ranges?

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
04-14-08 06:58 AM - Post#1411035    
    In response to someotherguy

I think you'd probably only shorten plug life, in this situation. Alot more work than the cat, you could put a smog pump on and adapt a clutch to it so it would only run when you wanted, like at idle. Certainly more than I would be willing to do

Wonder what would happen if you found one of those afterburner exhaust tips (wrecking yard) like on the new diesels, and slipped it on? I've only looked at one, just seems to me that it uses a venturi effect to draw fresh air in to mix with.

 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
04-14-08 07:08 AM - Post#1411041    
    In response to CDAUSA

Only anecdotal info----if you ever run into any NOS R44T's, even 43T's, they are alot better plug than the CR's.

But.........given my hard head I'd do some research and likely find a crossover AC Plat that was a couple of heat ranges hotter. Nothing else but to see the difference.

Do they charge you each time you try to pass?

 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-14-08 07:45 AM - Post#1411077    
    In response to CDAUSA

Really? I thought the "C" was supposed to be commercial service; what's bad about them? I can't say I have enough experience either way to notice. I'd figure though as many engines as you service you've got a bunch of experience with different plugs.

I think before I did any of that other stuff, I'd just break down and put a cat on it. But before that I will be installing a new thermostat and I'll also consider bumping up the plugs. The sticker under my hood said to gap them at .035; I thought for sure they should have been .045. The plugs came out of the box somewhere in between, closer to .040 than anything else, I checked each one before installing and just left them alone as it was a happy medium between what I thought they should be and what the sticker said. Maybe I should widen them to .045.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
04-14-08 09:04 AM - Post#1411129    
    In response to someotherguy

  • Quote:
"C" was supposed to be commercial service

I thought so too, can't be though as the CR doesn't have half the guts of an R. When they dropped the R43T and replaced it with the CR, the lifespan was cut in half-----this in a severe duty situation with engines running 24/7, NG, and loaded down to 1 inch of vacuum. But pickups responded the same, just won't live with them.

Just from experience, I'd widen the gap "slightly", maybe .040" if you go to a hotter plug. They are somewhat self cleaning and the heat range would make up for it. Get any wider and with time, it starts working its way back to the wires and rotor, too much gap or load on that plug and it will blow thru the center of the rotor in a heartbeat.

 
chrisk1500 
Very Senior Member
Posts: 1817
chrisk1500
Loc: Saskatchewan, Canada
Reg: 10-30-04
04-14-08 10:46 AM - Post#1411206    
    In response to CDAUSA

  • CDAUSA Said:
Wonder what would happen if you found one of those afterburner exhaust tips (wrecking yard) like on the new diesels, and slipped it on? I've only looked at one, just seems to me that it uses a venturi effect to draw fresh air in to mix with.



Those tips are designed to bring in air to mix with the exhaust before exiting the tip using the venturi effect (as you suggest). The reason they are on the diesels is to cool down the air to a 'normal' temp - regen mode is toasty.

A venturi tip *might* dilute the readings a little...I am not terribly familiar with emissions testing because it doesn't exist up here. How far into the pipe is the 'sniffer' put?
07.5 DMAX 2500 HD ext cab, 4x4, Edge EVO Race, 4" straight pipe, PPE tie rod sleeves, bushwhacker pocket flares, etc...

06 Escalade


 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-14-08 10:57 AM - Post#1411217    
    In response to chrisk1500

  • chrisk1500 Said:
A venturi tip *might* dilute the readings a little...I am not terribly familiar with emissions testing because it doesn't exist up here. How far into the pipe is the 'sniffer' put?


Almost 12" so I'm guessing it wouldn't help.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
CDAUSA 
Needs to Get Out More Member
Posts: 12906

Loc: Texas Panhandle
Reg: 12-31-01
04-14-08 11:34 AM - Post#1411239    
    In response to someotherguy

The one I looked at was on a F@rd, it had "ports" beyond that, I'm pretty sure.

I've got to make a run---if I see one on a lot I'll stop and measure. Of course, if there's enough volume passing by to draw in clean air, and he stuck the sniffer in that area.........................................

 
patgizz 
Senior Moderator Member
Posts: 8341
patgizz
Loc: Cleveland, OH
Reg: 01-30-00
04-14-08 11:51 AM - Post#1411254    
    In response to CDAUSA

my dad's 90 burb just failed. last test 3 years ago the HC was 242 on a 250 limit...

this year the HC was 242.5 on a 166 limit.

i dunno what happened to ohio's testing.

time for commercial plates, exempt from emissions.

 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-19-08 06:48 AM - Post#1414897    
    In response to Chevytech

  • Chevytech Said:
I would try a 195 T-stat in it.

TBI systems run rich when below normal operating temperature. Both your ohms reading and your IR thermometer reading show it is on the cool side of normal.


Man.. talk about pegging it. Finally had a moment to pull the thermostat this morning and some surely well-meaning person installed a 160F thermostat in it!

I've got a 195F in there now and we'll see how it does. If I get a chance I'll run over and have the smog test re-run today.

While I was at it, I hit the stud and nut for the sensor grounds with a wire wheel on my drill; they were a little crusty. Shinin' now!

So far after warming up (via a little gentle power-braking) I'm getting temps off the housing of 195~200F depending on how close I shoot it. And my temperature gauge on the dash, which I just assumed was inaccurate, is now actually reading where it should be. Still smells rich but I guess the test will reveal the truth.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
Bishop 
Frequent Contributor
Posts: 1488
Bishop
Age: 27
Loc: DMV Area
Reg: 01-06-07
04-19-08 10:45 AM - Post#1415041    
    In response to someotherguy

when you guys replace the T-stat i've heard of people drilling a small hole in it, do you guys do this? if so what size?
Not only so, but we also rejoice in our sufferings, because we know that suffering produces perseverance
Romans 5:3


 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
04-19-08 11:05 AM - Post#1415053    
    In response to Bishop

I went with a 1/8" hole to help bleed the air out of the system. I've seen people suggest everything from a 3/32", pair of 3/32", 1/8", and 3/16". 3/16" seemed too large so I just went with 1/8".

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
HDSCSTEVE 
Member
Posts: 34

Loc: Lindsay, Ontario, Canada
Reg: 10-24-06
05-14-08 06:31 AM - Post#1432633    
    In response to someotherguy

BUUUMMMMPPPP! What happened here no reply after test??? I live up in Ontario, Canada here and the government up here is getting pretty sticky on these emission tests. I got an 88 SB SS with a stroker and 3" exhaust with no cats. I just got done completely restoring/rebuilding it in OCT, 07 (4-5 years of leisure work) and they just took out the 20 year rule in AUG 07. Now 88 and older has to get tested every two years for life. What the hell is that. Thanks gov of Ontario, my bum has been killin' me since. Emission testing sucks....

Steve

Edited by HDSCSTEVE on 05-14-08 06:32 AM. Reason for edit: No reason given.

 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
05-15-08 03:55 AM - Post#1433354    
    In response to HDSCSTEVE

Hey Steve, don't shoot me but I still haven't gone back for the emissions test. Since I'm currently "getting away with it" I haven't been in a huge rush to find out if my repairs fixed the problem. I am still curious though and would like to put the issue to rest, so I will have it re-tested - hopefully within the next week or so.

Sorry to hear they've made a retro-active emissions rule in your area. All the people I know here that have picked vehicles as projects based simply on them being outside of the emissions years, I warn them that those regulations are subject to change at any time, without notice.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
chrome_ashes 
Senior Member
Posts: 794

Loc: Columbus, OH
Reg: 11-27-02
08-05-08 02:20 PM - Post#1492993    
    In response to someotherguy

Did you ever get this figured out?

I went through the same thing with my '93 (click here for my post)

I can't remember what ended up being the cause, but it wasn't the cat.

If I remember correctly, it set off the SES light for the MAP sensor within a day or two of failing the test.

I think I ended up replacing the O2 sensor and MAP sensor, cleaning up the IAC valve and changing the oil.

Definitely change the oil right before you have it tested. HCs can get trapped in the oil over time and will cause higher readings in the exhaust.
'04 Suburban SLT, 5.3L
'55 Chevy 3200 - sold
'57 Chevy 3200 - sold


 
someotherguy 
Moderator
Posts: 25971
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
08-06-08 02:36 PM - Post#1493747    
    In response to chrome_ashes

I gotta tell you, I wish I had the chance to run back over and have this thing checked again. It seems I'm always running this way or that way, and when I have so-called "free time" it's when everyone else is closed, so I find myself going out into the shop to work on trucks some more.

There is one undeniable fact though; a 160F thermostat in these trucks is the WAY wrong part; 195F is what it needs. There's no way the computer was operating in closed loop, or if it did manage to reach operating temperature to get there, it wouldn't stay there. If it ever reached closed loop it was almost surely falling out of it when idling. The idle HC numbers were through the roof. I'm confident that after changing the thermostat I'm in good shape. It doesn't smell rich anymore, either.

I know, I know; not very scientific, but finding a 160F stat in there was the next best thing to a smoking gun in my case.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
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