Hey,

I had a re-program done on my 97 LT1 camaro by PCMforless a
couple of years ago and I had a couple of questions about it stemming from the fact that it just failed emissions.

As you can see in my sig, it has an LE1.1 emissions cam and the appropriate PCMforless tune. Last spring, it passed the emissions test fine here in Toronto.

Having done a scan at the local garage (I don't have a proper scanner), they are informing me that it never gets up to proper operating temp (it never gets above the 1/4 mark on the dashboard temp gauge) - and it is for this reason that computer is dumping extra fuel in and causing me to fail the HC emissions test at idle. The garage guys seem fairly convinced that it is the low temp (or stuck-open) thermostat.

Does anyone know what the warm idle is set to for this cam? (I have put the same question to PCMforless)?
With the current temp problem, I am seeing idle about 1150 or 1200 rpm and that seems to be contributing to the fact that my car is not passing emissions at the idle speed test.

I am informed that the idle speed may well be high because I may have a
few vacuum leaks, which I am going to look into but I wanted to check
what the requested idle speed actually was.

Also, the car currently has a 160 degree thermostat but I believe it is not opening so I thought I might switch back to the original 180 degree thermostat and also test the 160 unit and see if
it is opening at the proper temp. Will changing to the 180 degree unit
cause any problems with the tune other than having the computer perhaps
pull a bit of timing out? It appears fairly likely that the 160 thermo
is a good part of the problem.

The next question is if the low temp is causing the computer to dump extra fuel in which is causing the failure of the emissions test, then is it possible or likely that the same temp issue is causing the high idle - i.e. that I don't necessarily have any vacuum leaks at all, just the thermostat problem causing my emissions and idle issue?

Thanks for the input.

 

Well I don't have a cam, although I do have Aftermarket Y-Pipe, High Flow Cats, a PCMForLess.com Tune, 160 Deg Thermostat, and just passed emissions. (Basic Bolt-Ons + tune)

I HIGHLY DOUBT it's the Thermostat, unless it's actually bad. I'm willing to bet it would be more related to Vacuum Leaks or a bad Sensor (Temp, O2, etc...).

Also would say that the same combination passed previously without issue, so has anything changed, if not then something probably failed, and that's the culprit.

PS if your Tune is for a 160 Deg Thermostat, you really should stick at that temp...

 

The garage guys confirmed very specifically that both front O2 sensors were swinging back and forth exactly as they should. Also, the PCM temp sensor seems to be in agreement with the temp sensor in the head that feeds the gauge - they both are showing very low (in fact the fans never come on - at least in the couple of hours of driving and idling that I have been doing.

I agree that the 160 degree thermo initially was not a problem (since it passed last year with the exact same config.), but as you suggested, I am starting to believe that the thermo is bad. I let the thermo sit around for 6 months or so last year in the open air while the car was apart - maybe that allowed it to corrode(?) I don't know, but even with the electric fan, (which is supposed to cool better) the thermo should ensure that the engine is reaching correct operating temp., which it is not.

Then my next suspicion is that that low temp is causing not only the extra rich mixture, but also the elevated idle (the PCM still thinks it is in "cold idle" mode, if such a term exists). Certainly there is a reasonable chance that there are vacuum leaks in an 11 year old car that was reassembled by an amateur (me), but I think there is at least a fair chance that the defective thermo may be the only culprit here. Maybe some tuning gurus (including PCMforless) can confirm what the PCM would do to the idle if it saw that low temp coming from the sensor.

Anyway, I think I will put the 180 thermo back in, at least for emissions and see if that clears things up, since I have one sitting here.

THX for the input.

Edit: meant to say electric water pump, naturally we all have electric fans - Doh!

 

Going into closed loop is based on time and engine temp. You have to satisfy both conditions in order to enter closed loop. If you never achieve the temp required for closed loop operation, which is not out of the question I guess. Then you could be running rich due to open loop and the rich a/f ratios commanded for engine startup.

What kind of temps are you seeing?

 

The thermostat has absolutely nothing to do with the problem you describe (low engine operating temp).


A stuck-closed stat does not cause an engine to run cold.


If the fans never come on, it should be boiling over after extended idling, with either a 160 or 180 stat.


It is pretty much out of the question that the engine never reaches 140*F.

What the sensor is saying to the PCM, is a different matter...


Now there is the $20k question.

 

The mechanic says he is seeing mostly about 172 degrees F with a maximum of 176 degrees F. This corresponds quite closely with the dash gauge which never gets above the 1/8th position which corresponds to roughly 180 degrees F. That's as high as the temp gauge ever got and I just drove accross town in 90 plus degree heat. Sure looks like the thermostat is defective, no?

I am not sure what people think, but I am very tempted to put the 180 degree thermo back in, do my emissions test and go from there. Given that my tune is for a 160 degree thermo, do you think I can do any damage by doing this? I would doubt it, at least in the short term but would like some confirmation.

Merci.

 

176* is where a 160* thermo operates. It takes about 15 degrees from where the thermo is rated for full open. The rating on a thermostat is where it begins to open. There is no reason that running at 176* would cause you to stay in open loop, unless somebody made a huge fowl up with the tuning. But you said you passed before with everything else being the same.

 

The only thing I did this past winter was head gaskets (head porter screwed up and caused a leak which was welded up - much hassle and expense). Other than re-assembling the motor, I did replace the driver's side front O2 which was bunged up by all the coolant getting on it.

I'm thinking I should clean the MAF as well (?) - that just requires a Q-tip and some rubbing alcohol, correct? Last night I checked around the TB and tried to find some vacuum leaks (by squirting some oil at the hose junctions) but did not find any.

I think the next step is to find an F-body savvy shop in the Toronto area and see if they can pinpoint the issue with their scanner.

With the local garage scan we seem to have confirmed that both front O2s are swinging back and forth as they should and that the 160* thermo is actually working correctly (same thermo as last year).

Is it possible that my bad reading was simply because I had residual extra fuel in the engine/cats as a result of my earlier problems with the O2s right after re-assembly. (I also ran the car for an hour or so after putting it together without attaching the pass. front O2).

Is it possible I just need to run this thing long and hard before doing the test? Having said that, I does seem to me that the computer is dumping too much fuel in because the gas consumption seems to have gotten noticeably worse - which shouldn't happen with an LE1.1 Emissions cam and the appropriate tune (Isn't that correct?)

THX again.

 

Are they doing a tailpipe test with your car? The test stations around here just plug into the OBD2 port and look to see if all the self-tests passed or not, if it is 1996 or newer.

 

wow, just wow....
Tag

 

They test the exhaust at idle and at about 2100 rpm.

Last year the idle was a tad higher, simply due to the fact that the cruise control cable held the throttle blades open a bit and I did not adjust the cable until this spring. Last spring, I also had a good sized coolant leak on the driver's side bank that ruined that O2 sensor.

That O2 was just replaced (right before the most recent emissions test). I have read some other posts that indicate that the cat may have had a fair bit of unburnt fuel in it as a result of the O2 sensor issue and that that may have been a part of the high HC problem. Don't really know - I am taking it in to a shop this week.

THX

 

Maybe that cats are simply worn out. I agree, it doesn't seem like anything huge has changed here. And if there's no check engine light..

 

Maybe this will help someone in a simalar situation.

As you will recall, I failed emissions at idle with triple the allowable HC output, but the other exhaust gasses were ok and the HC output was fine at the 2100 rpm test. After getting the thing scanned at a local performance shop (mostly LS1 experience though) we determined that the idle was at 900 (which was the programmed idle setting), IAC was showing 75 counts (which I believe is on the high side), manifold vacuum was showing 16", shorth term fuel trims were at 10% and long term were at 14%. Injector pulse width at idle was 2.1 ms.

Anyway, after determining that my problem was more than likely either an exhaust leak before the front O2s or a missfire, I decided to pull the plugs and read them. Long story short, the plug on cyl 7 (the one that had the coolant leak in the intake runner) was clearly fouled and not firing. I put in a new set of platinum TR55s, did a resistance and visual check on the spark plug wires and did a compression test on a few of the cylinders on the drivers side. Rookie mistake - I clearly should have just replaced all the plugs (or at least the one in cyl 7) when I had the thing apart to have the coolant leak fixed.

It now goes like hell and passed emissions easily. Sure was painful getting to this point though.

 

Fix your vacuum leaks. They will throw off the fueling and even timing depending on how severe.