It's a 93 z28 with some headers,ud pulley,cia. I am not seeing any kr, but the short term fuel trim is way down ,like to 97 or something and the long term is at 108 ?, 02 sens are 5 months old(gm) why or what could cause this ,it feels like it lost about 50 ftlbs of tq after it is in closed loop.it runs great in open loop but other than the above mods its a stock m6 car. thanks for any help

 

I wonder if you're running rich due to leaky injectors or something that's adding too much fuel. Got any codes?

 

That wouldn't have in closed loop, check your o2's while in open loop and see what they read, then also check for exhaust leaks, then prolly try cleaning the maf.

 

No MAF on a 93. You know that man!

FBody1, if you're using Datamaster, send me the datalog and let me take a look.

 

It is a 93 it does not have a MAF no there is no codes I will check the 02's in open loop. Any other suggestions?

 

burnt o2 sensor wires was my case it ran like crap surged and hesitated off idle in gear, wouldent hurt to check if they are shorting out or burnt the coating aroudn the wires

 

ok I will look at the 02 sens wire's and trace them back into the harness to see if they look ok. could this be the reason for the fuel trim #'s I am seeing? no I have datamaster on mine (94z) this is a freinds car(93z) I dont think my version of datamaster(3.4.1) will work on his? thanks guy's what about the fuel reg,his is stock and reads 50 psi w/ vacume hose off ? sounds kinda high to me , could this be the reason that the fuel trim are so low ?

 

The only thing that changes in closed loop is the usage of the o2 sensors.. So double check that.

Heated O2's are a good idea also.

 

Don't spread misinformation. That doesn't help anyone. If you don't know all the information, then don't tell someone it CAN or CAN'T happen. Just leave a suggestion, and point out that you aren't 100% sure, and leave it open for someone with more knowledge on the subject.

O2 sensors measure oxygen. If one cyl is running very lean or very rich due to an injector stuck closed or open, it can mess up the O2 readings for the whole bank. As such, once it hits closed loop, the engine will try to compensate and give the rest of the bank either too much or too little fuel.

An engine can run pretty well with one cyl running out of spec, but once a whole bank starts getting the wrong amount of fuel, it can suddenly start to run like CRAP.

Thus, due to a single injector malfunction, you can have this "running like crap only in CLOSED loop symptom."

Misfiring spark plugs, and arcing plug wires can actually cause the same symptom, if the condition happens enough to really mess with the O2 readings enough to make the STerms spike.

If the condition persists for long enough, then the LTerms will also drift away from where they should be, at which point, it might even start to run bad in open loop. But the drift will always be worse in closed loop (while the false lean/rich condition persists), as both the potentially out of spec LTerms AND the out of spec STerms will both be added to the fuel table values. (In open loop, only the LTerms are added, while the STerms are set to 128).

And to the original poster: THIS TOPIC HAS BEEN COVERED EXTENSIVELY IN THE PAST. PLEASE USE THE SEARCH FUNCTION NEXT TIME!

Ps. If your engine is running too lean, you can burn up valves, burn holes in the heads, block, etc. If your engine is running too rich, the excess fuel can wash the lubrication off cyl walls (not good); worse still, it can drain down into the sump, reducing the lubricating properties of all the oil in your engine. As a result, you could spin bearings or have other catastrophic engine failures occur... Clearly neither condition is good, and as such, you should not drive the car if it is running too rich or too lean. If it is too rich, you might want to smell the oil for gas, and if you smell any, you should probably change it before you drive the car again..

 

KainZ, who died and made you god of the LT1?? You need to ease up man. Bunker knows what he's talking about and made a suggestion. It's not as cut and dry as you may seem to think. A single leaking injector can easily cause the car to run terribly at all points. You may have posted some good information above, but dang man, take a chill pill.

FBody1, what are you using to look at the computer?? Handheld, Datamaster, ect????

 

Your version of Datamaster won't work because it is 3.4.1 EE and he would need 3.4.1 DA. You need to figure out some way to see the voltage put out by the O2 sensors.

 

I don't know why you think I only have $EE, but I have both versions (see sig, I own two 93's).

 

I was refering "you" to the originator of the thread. My mistake if I seemed like I directed that towards you. Also, what does it matter if you own 2 93's. They're both DA versions of Datamaster aren't they?

 

Yes, a single leaking injector CAN make the car run bad at all points, as I already mentioned, if you actually read my whole post. But, it can also make the car run really bad ONLY in CLOSED loop, as I also pointed out. Bunker doesn't know what he's talking about, because he said that a single leaking injector wouldn't cause the symptoms this guy is seeing, and that is misinformation.

His suggestion to check for exhaust leaks was valid, as would be checking the O2 sensors, and I didn't rag on him for those, I only said that he shouldn't say that someone else's (Kevin Blown 95 TA's) suggestion wouldn't happen only in closed loop, when he clearly doesn't know enough to be saying that definitively. It CAN happen only in closed loop, for the reasons I mentioned, and explained.

I never implied that it was cut and dry, or that those examples WERE the cause of his problems, only that they COULD be, thus, he should CHECK them. Bunker's other suggestions were also on the money, and clearly the guy should be checking those.

I never said I was the god of LT1s, nor do I think that I am. Many people on this board know much more than I do, about many different things, and I often learn new things from reading their posts. This is a topic which I happen to understand, and can make logical statements about.

I believe in using logic to diagnose problems, rather than spreading misinformation/rumor/hearsay. My logic in this case is sound, and so I am posting about it. How about you stop worrying about my attitude and start worrying about helping people diagnose their problems correctly?

 

Yep, Bunker should have rephrased his post regarding the possible injector fault. The FBody1 originally said that his BLM was 108 and that is the limit for taking out fuel, so he has a persistant rich condition, and there's only so many things that could cause that, injector leakage being one of them. Also, a rich condition will be less evident in a colder engine and get worse as a the engine warms up, in addition to the reasons that kainZ stated.