To paraphrase the author of the piece regarding EGR and timing, EGR slows down the cumbustion burn rate, therefore allowing the PCM to advance timing significantly. The tables in the PCM are for both EGR on and EGR off. If the PCM is adding timing based on input of EGR gas, and the EGR isn't providing the product, then the timing is way too advanced for the parameters of the engine, resulting in detonation/preignition/ping, etc. That's where I was going in my earlier post. As far as LSx not using EGR, the PCM is probably programmed to operate without any EGR. I would guess there's enough overlap in the cam to dilute the mixture. Tim sends

LT1 guys just swap their stock modules for an LT4 module. If you're using an LT1 PCM, this is the ticket.

For the record, didn't read the whole thread.

Got around to swapping the rails with injectors and regulator attached from another LT1. No change.

Also, if i disconnect the MAF then start the car, the car will run at idle but die if i give it any throttle.

Another thing i tried was increasing the injector constant to 26.5 instead of about 25. BLMs were still at 108 and still had knock retard

Got the laptop and datamaster working. Went out for a test drive just to get more data. Blms never go above 128 at anytime in any cell. I got constant maximum knock retard when driving about 30 mph. IAC is very low at idle, about 6-10.

i increased the injector constant to 27.1 lbs and no longer had 108 blms at idle. Blms were at 121 and 125 about. Still heard the audible ping when i reved on it though. I switched the constant back to 24.91 for now.

one step closer...pinging/detonation is gone

the last couple times i've been starting it, its been throwing DTC 33 code for the a couple seconds after startup. DTC 33 means high map or low vacuum. I checked out the data from the test drive and its like the map was acting really slow. The map wasn't chaning very much as the rpm changed. Searched all over for high map code on some LT1 sites and this never came up - a slow map. Anyway, swapped the MAP sensor from a good known LT1 and made a huge difference. Also got rid of the pinging/detonation. However still has low blms and spark retard at times.

Last nite i reset the battery and changed the oil and the blms at idle at cell 16 were 112/115 after letting it idle for a while, it may still drop to 108. This morning i decided to try it with the MAF unplugged and BLMS at idle were 135/138. I'm going to try swapping MAFs from another car but the other car has a de-screened MAF so i dont know if i can completely trust it.

Anyone have an explanation why the BLMs would go the other way with the MAF unplugged? I'm suspecting something with the MAF sensor but maybe its something else.

I barely tested it with the MAF unplugged but i revved on it once and it had a few degrees of spark retard.

edit: swapped MAFs, no difference between the two

okay I have the same problem. This is when car is in closed loop For one thing my lterm counts and sterms counts are in the pink. So it is running rich at idle. But also when I rev the engine it will detect spark retard depending on how high it revs but to atleast 2000rpm the Spark Retard was 15 then once it idled it was 0 constantly. Lower revving only yielded less Spark retard. Also when it gets the spark retard the sterm counts go 133 134.

But reading this post I noticed that it could be false knock. So I do know at the joint where the cat connects to the y pipe right under passenger seat it does leak exhaust there. And another thing I do have my egr valve removed and blocked off. Also I found out my fuel regualtor was toast, and the plugs were carboned up cause I took out one and it was carboned fouled. But I replaced the regualtor now. So the plugs are fouled and most likely the o2 sensors.

Also when the car is cold it does not stumble when I step on the gas cold (open loop) just closed loop it does this.

So I do not know what could be causing this

Thanks for any help

I think my problem was 1 blown head gasket and the other head gasket was about blown. I think I had or have false knock, not sure, I turned off the knock sensor and nothing bad happened but I checked everything out and I knew everything was fine, plus the only way I knew anything was wrong was because the computer said so, I could not tell by driving. I never got around to really testing for false knock after replacing the head gaskets but the LT1 runs like a top now and I have now parked the car for winter storage...

Ok, for your situation...

Start out by doing this. Fix all exhaust leaks. Replace the plugs if you think you need to, you could replace them with the 100,000 mile ac delco platinums but I like the NGK TR-55's because they are only about $1 a piece but they won't last near as long as the AC delco platinums but they provide a better spark. Try running 91-93 octane fuel.

Do you have a datamaster file recorded? I could look at it and see if any sensors are obviously bad or if something is obviously wrong. Otherwise, I'm going to write a book about everything you should test next if what I mentioned above doesn't fix it. Send me a PM if you want to do that: http://www.thirdgen.org/techboard/pr...=newpm&u=39056

And your saying you have a stumble? Explain that more. Your stumble might not be an open loop/closed loop issue but temperature related. Detonation or knock is more likely to happen as the temperature increases.

Here is some good reading: http://members.aol.com/InjuneerZz/ScanMast.htm

The stumble is only when it is warmed up or pretty close. When it stumbles I have to give the throttle a quick snap from idle and it does rev smoothly, rather it shakes for a sec seems like it wants to die then rpms pick up. Go to 1000rpm say and do the same and it revs nice. Same when it is cold it revs perfect picks up right away. And also it has a rough idle but smooths out up higher like over 1000rpm.

Alirght I sent a datamaster to your PM

Thanks for the help

Alright heres my datamaster files. I already know that it runs a bit rich that is because the o2 sensors are dirty. But I cleaned them and nothing changed with the stumble or rough idle.

soooo??? did anybody know the solution for the problem??? im having the same pain... when i run at WOT it feel like the spark plug timing inst working, or like a dead spark plug :S so i hace new wires, sparkplugs, coil, ICM, maf, iat, iac...

plz heeeelp im runung my camaro like having a 4 cilinders engine on it! :S

it is a lt1 1997 camaro

Well, I may have figured out what the problem might have been in my case. I customized my y-pipe and the exhaust hits or comes very close to the frame/body of the car in 2 or 3 spots. I haven't got around to fixing my exhaust yet so it doesn't come in contact with anything.

As a temporary solution, I programmed the knock sensor out. Not the safest thing to do but I knew everything was good and my fuel was good. Might be able to measure the electrical resistance of the knock sensor and put a resistor in its place.

The real solution will be to fix my exhaust routing.

For your issue, hard to say what it might be unless you can hook up a laptop and see for sure if the knock sensor is causing the pcm to pull timing. If the KS is causing the pcm to pull timing, its being caused by something else. Bad KS, bad knock module, something hitting the engine or exhaust, etc. It could also be something else entirely, like a fuel pump or bad optispark. Loss of power could be a lot of things.

Right!!! im going to fix my exhaust pipe, because the U bend of the diferential is touching the stabilizer bars, and when i am in a stop light with the brake pedal pushed, i feel some hiting or something like that, maybe bad motor mounts.

so you recoment to test or like a temporary solution to put a resistence that match te resistence of a good KS ?

the opti is good and the KS module is good too, im going to try the resistence solution..

Tnks!