Would like input from some of you experts out there. My 94 Z28 (350 engine - LT1) runs great in the cold mornings. Once I leave work around 5 pm when its warmer out it misfires like crazy. Intermittent but real noticeable. Expecially on acceleration is will just bog down and almost stall. Runs like someone put a banana in my tailpipe .

Next morning its great again -even after running 30 min down the freeway. 5 pm - bad. Now I dont think anyone is putting water in my tank while I'm in the office (Thats what it seems like) so looking for feedback from people.

I know its always had a code- EGR code- dont remember which one but its had that for yrs and was planning on upgrading the exhaust and ripping all the EGR stuff out anyway so didn't worry about it.

Could be wires, optispark, and read on a forum it was likely an o2 sensor. I'm also wondering if the cat could be backed up because thats how bad in runs but why only when air temp warms up and not in morning after even driving 30 min?

It sometimes backfires as well when revving up. Also stalls out. It runs ok with cold air and hot engine but not ok with warm air and either cold or hot engine. Not sure on what codes it has recently because my car has a obd2 with obd1 connector and autozone/murrays, etc never has something I can use (Doesnt have the obd1 connector) and dont really want to spend the hundreds right now for the tool.

Any ideas? Thanks Dan

 

Its a known fact that a car will be faster in the winter time than in the summer time due to cooler incomming air so you will always loose a little power in hotter temps dont know the severity in your case though and sounds a little more than it should be. Also if it was the cat backed up then it would continually perform poorly. I know 02 sensors can go bad a produce poor gas mileage and a little power loss but when mine went out and i had a code also i still didnt notice a power difference just hurt my gas mileage. Well also a clogged air filter could do this id check and clean it anyways if possible actually thats the first thing i would check because this can cause surging of the engine and stalling.

 

Check the coolant temp sensor in the water pump. Sounds like it is telling the PCM the coolant is much cooler than it actually is. The lower temp will richen the mixture correctly when the engine is cold, but will cause it to run excessively rich when the engine warms up but the PCM doesn't know it.

Check what the PCM shows the sensor is reading, using a scanner, or measure the resistance of the sensor circuit. Shoebox has info on the temp sensor:

http://shbox.com/1/4th_gen_tech2.html#ect

 

I'll check that injuneer - I went out and playe dwith the car and found out the following. When pulling out the plugs spark looked strong and a sae a constant spark upon revving so I'm questioning if its the iginition circuit now. I DID notice A LOT of water coming out of the tailpipes when revving the engine (NOT coolant, Water). What could this mean? PS theres no water in the oil.

 

Oh by the way - the needle for the coolant temp on the dash seems to work fine which should say thats ok shouldnt it? Also I unplugged one by one the injectors and heard no difference in the engine running or in one engine from the next so it tells me at least its an overall engine-vs cyl specific- issue.

 

Nevermind on the water - it stopped- I'm belevin now it was condensation - but sure was a lot but still have the same problem.

 

IMHO, If it isn't the coolant or engine temp sensor, it may be a plug wire shorting against an exhaust manifold that gets worse under more heat. All the symptoms are ignition sounding. Have it scanned and save time.

 

Thought of that and looked hard - no wires shorting. I have an exhaust leak by the headers which could maybe throw off the o2 sensors but I dont think it would make it as bad as it acts - every time I drive I'm worried about being stranded. Thats how bad it is. Thanks for the input though.

I am wondering about what ingineer said and i understand the logic if you're talking looking at the air temp sensor but not the coolant sensor. This car misfires with warm air NOT a warm engine (Cold air and hot engine is fine but warm air and cold engine isnt so why are we talking about coolant temp vs air temp?)

 

Your 94 does not have an OBD-II PCM. It is OBD-I, and it has a usual 12-pin OBD-I ALDL connector. Who told you it was OBD-II?

That is, unless you have for some reason swapped in a 96/97 OBD-II PCM. But if that was the case, you logically would have swapped in the correct 16-pin OBD-II ALDL connector.

You need to add a "signature" with basic info about your car - year, model, engine, tranny and any major mods. Otherwise, you are just making it harder for people to help you.

 

Dude I thought you were knowledgeable. The 94 and 95 have OBD2 software with a obd1 connector. Do a google search on that. I'm not making things hard - You dont know what you're talking about concerning that.

 

Don't call me "dude"..... show a bit of respect.

You try a "search".... I have a 94 Formula, have owned it since new, and have written the online reference "bible" for scanning the OBD-I PCM, that many people on this site use.

You are the one who is seriously confused. 93 and 94 are OBD-I with a 12-pin OBD-I connector. 95 is OBD-I, with a 16-pin OBD-II connector. 96/97 are OBD-II with 16-pini OBD-II connector.

What a rude, inconsiderate person. Don't send me any more PM's asking for help in the future, because you are on my "ignore" list.

 

You are absolutely wrong, and you just offended the most knowledgeable person on this site concerning these cars.

 

Wow.... how could you make a statement like that. Totally incorrect. Serious case of "foot in mouth" disease. Time for a major apology.

 

At this point, this thread isn't serving any useful purpose, except to embarass the orignal poster. Let's shut it down.

 

I guess we'll have to reopen this. Apparently, from his PM to me, "dnapowersports"' still thinks he's right.
Pretty funny.