gatortruck

Hi guys, I have a 92 GMC seirra with a 95 camaro 5.7l LT1 engine in it. When I bought the truck I was having problems with it running lean. I replaced the throttle position sensor and the air temp sensor and nothing. Then I unplugged the air temp sensor. Now it runs great for about 10 to 15 minutes then starts to run lean. It has headers with no o2 sensors. I've heard that it takes about 10 minutes for the o2 sensors to come online. Ive also heard that my mass airflow sensor might be bad. Will the truck run right with no o2 senors. I am completely baffled by this problem I've tried everything I know. Anyone who can help or offer any kind of advice it would be greatly appreciated. Thanks in advance.

LearJet

no o2 sensors?? If you ran an open loop tune it would be doable. If it is running an open loop tune and it's lean you will need to adjust fueling in the tune. How do you know it's lean?

Injuneer

It only takes about 3.5 minutes for the PCM to enter closed loop, in a normally "sensored" engine. With no O2's, and disconnected IAT sensor the PCM lacks adequate info to fuel the engine correctly. Stop playing "parts replacement roulette", put a scanner on it, and see what's going on.

What modifications have been done to the engine, besides the headers? Who tuned it? Did they use a wideband to tune it? Were they aware it was going to run constantly in open loop?

gatortruck

All it has besides the headers is cold air. The engine is a awap. I had a scanner put on it and it threw several codes. The only ones that would effect the engine in this way were the o2 codes and the mass airflow code. I have no idea who tuned it or what they did. The guy I bought it from knew nothing about the engine or how much potential it had. Like me he couldnt figure out what was wrong. I just assumed its running lean (low idling,very sluggish acceleration,popping) If I turn the truck off for about a minute it starts off sluggish the runs fine for 10 to 15 min. Can any mechanic tune it. About how much does it cost. I am definently open to any suggestions. Thanks for the input guys. I apperciate it.

LearJet

well if it was mine I would weld up some O2 bungs in the headers and install o2 sensors to start. List the codes you got when you scanned it. where are you located?

meissen

So you're not even really getting a lean code, just guess-timating?

Give us a list of the codes that it's throwing and that'd help diagnose it. If it were really lean, it'd be throwing a lean code. If it really is lean, try checking your fuel pressure with a fuel pressure gauge. My dad's car was having problems with a lean code on one bank and it turns out it was just a dying fuel pump that was causing it.

gatortruck

Im located in Fort Walton Beach,FL about 40 miles east of pensacola. My first thought was also to weld up some o2 ports. Which I can do myself. Id have to take it up to my freinds shop when I get the time to get a list of the codes. Ill have him put a fuel pressure gauge on it while Im there. No, Im not really 100% sure that its running lean just a guess from the way it runs. It has very little acceleratrion at all. It drops about 300 -500 rpm's at idle and pops if you hit it to hard. Thanks again for the advice guys I really appreciate it.

LearJet

Unless someone tuned it to run without o2's it's not going to run well without o2's.

gatortruck

ok I put o2 sensors on the collectors and still the same problem? Has anyone else had this or a similar problem if you have please help!

Injuneer

If it didn't have O2 sensors before, it may have been tuned to run open loop. Adding the sensors doesn't mean they're doing anything. You need to get a scanner or scan software on it, and find out how the PCM is responding to the conditions.

gatortruck

OK Ill try that. Thanks for the help guys