I was getting up to 230 at stops so I thought I might pull the thermo and start the car to see if it was bad,,, this is where it gets ugly, the car ran for 2 minutes then started to sputter badly then completely shutting down and would not start. I promptly returned the thermostat and it started right up but now runs very rich and has lost 50-75hp, exhaust smells horrid. I have spent about $2,500 trying to have it fixed, number of mechanics have tested it with scanners and I have sense changed plugs, wires, and the whole opti spark unit.
car mods are
HPP3
JET piggyback stage2
underdrive pullys
msd coil
4:10 rear
I also have tried removing the HPP and the jet chip with no change in cars condition

 

No trouble codes present? The temp sensor in the water pump feeds the pcm info. If it is messed up, it can make the car run rich like you describe.

 

Absolutly no codes present and all sensors are showing up on the Snap-On Scanner as if they are running in perfect GM specifications. The techs I have taken it to are stumped or say something dumb like " I dont think there is anything wrong with it"

 

my money's on the intake leak. High temps will make it open up like that and get real ugly.

1) check the rear of the intake manifold / engine block seam to see if there's oil seeping out (might be baked on pretty good). The area along side the EGR tube is where it commonly happens.

2) unplug the MAF and start the car. It'll be running speed density without problems unless the leak is a HUGE problem.

Next time this happens and the car won't start, try #2 and you should be fine.

Ideally though, get the manifold put on properly. Use HIGH temp RTV on the seam, and do NOT follow the directions for a "fast cure" by running the car. Let it sit overnight and set-up slowly. As soon as you start the car with fresh RTV, the EGR tube will start boiling it out.

Let us know what you find.

 

Does your coolant level stay constant?

If not you might have an issue in your heads, or maybe a gasket. If the exhaust smells bad then something is probably getting in there (unless it is just rich, which i think smells wonderful) and it might be coolant leaking from your heads.

You might think about getting the compression checked and the heads checked too. Just a thought.

If the heads are leaking coolant, then it will cause the thermo to open at a much hotter temp. Coolant leaks in the heads could also cause it to run leaner and hotter due to air escaping into the cylinders with boiling temps.

Im kinda talking out of my *** right now, its almost 4 am.

Good luck,
Stu

 

I have seen this happen with a 94 before. Can you get it running next time and see if the fans are coming on. If they are not coming on turn on the A/C and see if the fans come on then. If so you have a problem with your PCM.


JK

 

running rich does sound like a sensor problem and keep in mind I dont know much about the modified car but, have you tried unplugging your piggy back module and running off the stock PCM. If your ppiggyback is trying to modify your settings and trick the PCM it could be bad or causing the problem. On Our FI bikes we use power commanders and if you start having problems the first place you start is by unplugging the power commander and see if it goes away. Especially where all of your readings with the scan tool seem correct.

 

I checked oil and coolent im not missing any. Over heating is not the issue as far as I can tell the car ran super until I started it with out the thermostat, the OBD1 shut the car down. I was really just trying to get a cooler running car for free =( When I say smelly I mean super rich, leaving black deposits on my bumper. I have removed all after market programming and piggybacking and still runs the same "I think that stuff is a rip-off"
I had compression checked and something called ohms test on ignition?
thanks for replys

 

opps forgot to say the fans are coming on at the correct points.
and
) unplug the MAF and start the car. It'll be running speed density without problems unless the leak is a HUGE problem.

Will this further decrease performance of my car or trip sensors, or should I try this.

 

Check your Temp sensor while the scan tool is plugged in. Pull the wire and ground it see if the temp changes if not I am not sure but it does sound like you have a bad PCM. It is getting the correct settings is the O2 crosscounts high what is the Block Learn

 

Id bet its a leak somewhere. Maybe exhaust leak from the manifolds or an intake leak.

Leaks dont always throw codes, but will make your car run bad. Good to hear your heads are fine, i was kinda worried about that.

 

I would think if it was that bad out the tailpipe it would throw a code from the O2 sensor. Are you still using o2 sensors I have seen guys on here with the things that fool them

 

Yes im still using stock O2s and i have the cat on the car but the guts are gone. The snap on scanner shows the o2s bouncing all over just like they should in fact right in accordance to the gm specs.
thanks

 

Well if it was reading right and running rich, then its probably either your o2's or you have an exhaust leak. A leak will put more air in your exhaust making the sensors read lean, then it will add gas so the sensors read right. That will cause it to be rich and fool the computer.

 

But could this happen just from removing the thermostat? Thats all I did before I took that thing out it was running like a top. Just got off the phone with chevy " they have the car atm" he said there is no intake leak and seems to be nothing worng witrh the heads, and he says he dont see anything wrong with it running like it is. However I'm the only one that knows how it ran and I know somehting is wrong to cause this problem.