ugod02010

Okay so I been having a bad miss, cutting out w/my 95 formula. I changed icm,coil,opti, and just about everything else u can think of. It just won't go away !no codes, everything in datamaster looks fine no crazy timing being pulled l&sterms seem inline. I cannot figure this out. It feels like the spark is breaking up. It was shutting down changed icm since it only seemed to do it when warm so I thought I would start there. Seemed to stop stalling but still ran really really rough high in the rpm range. Next I wen to the opti since I bought a cheapo from eBay. Stuck my original back on and the car ran good for about a day just really low on power. Then today after work the car cold barely pull its own *** up the hill literally had to let it coast up the hill any gas more than just touching it had it missing and stumbling backfiring and everything. Limped home only code was EAS. (Think this is just smog). About a month ago I had to replace the fuel pump,tank and injectors,( put acell 24lbhr in since they were same as factory. Ran good then got screwy one day so I pulled it down and the rotor come off the opti (same one I just put back on) just replaced the wheel inside with the one from my eBay opti. (Thought if optics were shot the other had a good optic but bent wheel from rotor) sorry about bouncing around so much I am trying to get as much as possible. Any ideas I'm starting to think the ECM or maybe the injectors are junk. But that should make the timing pull and cause a funny reading in datamaster?

DTFB

I've been having the same problem. im starting to think its the PCM to

ugod02010

I've been thru everything I can think of. I was reading yesterday and I seem somewhere somone was saying the 94 95 obd1 computers break all the time something like the failure rate of those 2yrs is higher than all other lt1 years combined. But everyone on here seems to think the pcms rarely fail. Anyone else have any insight into this. I wish I could find the article but its lost in the emptiness that is the interweb. But the guy said he was talking to a gm bigwig and that's where he got the info.?

DTFB

you guys think it could be the knock sensor retarding the timing or something in that ball park!?!

Ed Wright

iTrader: (1)

Don't believe that crap.

Jdawson38995

I had a miss....turned out to be a timing chain.....

ugod02010

I know u know ur stuff. I wish I could find that page. It sounds like it makes some valid points. He was talking about the opposite people on here do going from ond1 to the ond2 since it has a better processor( well not a processor in a car but the equivalent). It computes at twice the speed of the obd1 computers. Guess today ill have to go thru my history and find it. Anyways as far as a knock sensor I haven't looked at those yet. How many knocks should I have when I have datamaster running. It's usually about 1000 to 3000 I think after a few minutes of running.? I will make a video tonite I know it's hard to diagnose something someone else is explaining.

ugod02010

Here's the post:
I was investigating the constant failure of the PCMs in my 94, and contacted everyone that I could find about the subject. It was an engineer at GM that clued me into the fix when he suggested that I use the OBDII computer vice the OBDI as the cure. Unfortunately, shortly after that, GM stopped talking to me. Hmmmm....was I on to something here? You betcha!

Here's the skinny on this. It seems that all of the OBDI computers used in all LT1 powered cars in 1994 and 1995, except for the Corvette (they used a different computer) will fail--this according to every rebuild company that I talked to. This particular PCM is responsible for more failures than ALL other power train computers combined (at the time). Hard to believe? I thought so, too. In fact, it was a year later that I took the chance and bought a known good OBDII computer in desparation. I studied the entire harness and all the connectors. There are only three differences and they aren't a problem. The OBDII PCM has a connector for crank triggered timing, a connector for the EGR and a connector for the third O2 sensor, that's it. The harnesses and connectors are otherwise identical. All the guy that loads the software into the PCM has to do is turn off that part of the software--just like turning off the CAGS.

The OBDII computer uses two 32 bit RISC processors, the OBDI uses two 16 bit RISC processors. That means that OBDII PCM computes mathmatical solutions about 3X as fast. It also has 3X the memory and can handle 15,000 more lines of code. Installing your OBDI software on this computer is just about like supercharging the engine since the OBDI software is based on a 16 bit language and uses, I think a 16 bit address vice 32 bit address in the OBDII. What's important to you is that GM rates this single change as worth 10 hp to the engine. This is solid and REAL hp.

It is amazingly easy to make the change. The hardest part is unbolting the old one, removing it and throwing it in the garbage can. PCMforLess.com can do the necessary software mods for you for about $100. Mine was the first and worked beyond all expectations. There is so much wrong with the OBDI that most people just accept the way the cars run as that is the way they are supposed to run. It ain't so. And yes, my car passed the SMOG test on a rear wheel dyno. Since the software was keyed to my VIN number and was correct for the car, nothing showed up on the SMOG computer.

It's just my opinion, but I think GM stopped talking to me, becuz they are aware of this problem. Being aware of it, they should replace all the defective PCMs, but that would cost a fortune and they don't want to pay for it. Better to just let those cars rust away in a wrecking lot and disappear inside a crusher. There should be a class action lawsuit against GM, but it will never happen.

ugod02010

I missed the post about the timing chain. I don't think it would be that the car idles just fine. Just when I try to go it gets screwy. When ur chain was off was your idle messed up also I think it would be. I thought about that when all this first started. But there's no smoke or anything now. I did have smoke b4 when my injectors failed.

Ed Wright

iTrader: (1)

I don't know who that is, but I think he is smoking crack. I also prefer the OBD2, but only for the OBD2 diagnostics. Neither one will run faster or make more power than the other. I have seen no more OBD1 LT1 PCM failures than any others. Most I have seen are from people that don't know whatbthey are doing trying to program them.

I don't know why so many put so much faith in wild crap like that they read on the Internet, which is a vast sea of mis-information. Much more bullshit than truth floating around.

shbox

I agree. That is the biggest load of crap I have read in a while. Don't be fooled.

RamAir95TA

iTrader: (2)

Post the username so I can point and laugh. Amazing.

bufmatmuslepants

iTrader: (3)

The 10hp gain was not from obd2, it was from using 2 cats instead of 1.

ugod02010

http://www.theformulasource.com/foru...hp/t15279.html

ugod02010

Ok that's where I found that at. I kinda figured the kid didn't really know what he was saying. Well while I have a couple of the biggest names in the ltx world do you guys have any idea where to go next or how I can troubleshoot my pcm short of tearing it out and buyin a new one for it no to change anything. I got a good video of the car acting up this morning I will put a link up maybe actually seeing/ hearing u guys can point me in a direction to try next

ugod02010

Here's the video from this morning you can hear at idle the car sounds good but soon as I press the gas it starts breaking up. Also how high should my knock count be on datamaster or another scanner I also have pcm communicator. It doesn't log but I can monitor all the vitals with it

ugod02010

Lots Of views but no Ideas C'mon guys I am going nuts chasing my tail here!!!
i just had pcm communicator hooked up and when i started the car it was at 4048knock count- After about 2or3 min I was up to 5134 then after about 4-5min it was up to about 5434. Sound normal or does that sound high or like that may have something to do with this? the Knock Retard the highest reading when just revving the car in park was .6-1.2 degrees.

DTFB

I'm still trying to figure it out myself we are in the same boat. I'm try putting a LT4 knock sensor in

duh

iTrader: (16)

I had a nice little conversation with Ion via email about my 93 doing almost identical issues. After looking at the log of what my car runs like, he said the only thing that stood out as wierd was my vss jumping to 180 mph. I told him that it registers at idle and will show anything from 10-40 mph on the dash while sitting at idle. He then told me that was a common problem when he repaired them was in the solder of the ECM. It would crack from the heat and vibration. He suggested a new ECM or reman if I can find one. I have one on its way, so I can report back after I install it. I think you might be on the right track, or at least I'm hoping this is the right track.

Ed Wright

iTrader: (1)

One test they taught us at the GM Training Center was a simple "slap test", start your data logger, then slap the ECM/PCM. If the car misses, you found it. If not stop the logger. Play it back and look for data spikes. If it gets extremely hot it could be the problem. High knock counts or mis-fires are seldom the computer.
Any competent tech could find a mis-fire. Injector driver issues are about the only thing in an LT PCM that would make one miss. Very easy to test with a DSO. Bad or missing wave forms will tell the tail.