Help!!!.... I'm in PCM Hell!!!
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Help!!!.... I'm in PCM Hell!!!
I have a 96 385 stroker with 8.5:1 comp and a Vortech S-Trim pushing 14 PSI. I have yet to get this puppy to run right. I have just changed out the OBDII PCM with a OBDI PCM and still have the exact same problem. Anybody seen a St Term Fuel Trim split from Bank to Bank? I am getting a 50% Fuel trim on Bank1 and a 20% Fuel Trim on Bank2. My O2 numbers are just as strange: Bank1 O2mvs run 10mv to 30mv Bank2 300mv to 900mv. All Plugs are soaked with gas and glazed black from way Fat. I have changed and checked all of the obvious: new O2s, new wiring harness at the O2s, moved the O2s from bank to bank, MAF swapped out, switched injectors from bank to bank, tested resistance in the injector harness, checked for header leaks, removed the CATs, closed the plug gap to .035 (NGK TR55s). None of this has made a bit of difference. I know theres several guys out there running this setup or close to it and have it working like it should. If you have seen this before and have any ideas, I could sure use a helping hand! Thanks.....
Drifting
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From: Norcross GA
Re: Help!!!.... I'm in PCM Hell!!! (wicked96)
What are you running for injectors (size)?
I wonder what the ECM will see if you disconnect the O2 sensor. i.e. I'm wondering what, if anything it is seeing.
The ECM is a 165?
I wonder what the ECM will see if you disconnect the O2 sensor. i.e. I'm wondering what, if anything it is seeing.
The ECM is a 165?
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Re: Help!!!.... I'm in PCM Hell!!! (ZylaRace)
I am running MSD 50# with no FMU.
There is a baseline number when you unplug the O2s that the PCM should report ( I cant remember right now ) but I tried it and had the number exacty.
Its a 161 PCM ( auto car )
There is a baseline number when you unplug the O2s that the PCM should report ( I cant remember right now ) but I tried it and had the number exacty.
Its a 161 PCM ( auto car )
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Re: Help!!!.... I'm in PCM Hell!!! (DOCTOR J)
I see this at all RPMs. At idle after it goes to closed loop I get this. If I rev it and then hold at a stable RPM: during the rev it goes to correct numbers within seconds though the BLMs and O2s creep back to the previous activity. Water temp and oil temp are normal, headers get red hot like a very lean condition although it is choking you with gas fumes and black smoke. If you drive it it runs smooth and has all kinds of power. At WOT you get a big puff of black then it cleans up once the boost gauge goes +. The injector pulse width and fuel pressure have been reduced to the max. It ran even worse, throttle response was terrible. With the screw all the way backed out of the fuel pressure reg I get 36 psi so that as low as I went. That didnt make any diff......
Burning Brakes
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From: Greenwich, CT
Re: Help!!!.... I'm in PCM Hell!!! (wicked96)
FWIW, my first thought is that saturated injectors need a certain amount of rise-time to open, and this might be causing unstable operation at low pulse widths. (I was under the impression P&H injectors are more common once you get to this size range.) Was there no calibration data with the kit? Can MSD give you any info to compare timing on these injectors to the standard GM units? Got a shop nearby that could run a timing calibration for you?
What I'm thinking about is a curve like this one, so you would have some data to raise the LPWInjector Offset in the PCM:
http://cmillard.freeservers.com/Z28/...%20offsets.htm
Short-term, have you already tried cranking up the injector constant past 50#? That would help get the fuel flow down some.
BTW, since there is no FMU, how is the MAF compensated for boost? Did you have to re-scale all the load tables?
HTH
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Re: Help!!!.... I'm in PCM Hell!!! (DOCTOR J)
No, P&H injectors are the next step up. 72# and 96# are P&H. You also need aftermarket PCM since they are low resistance injectors and are not compatible with the factory PCM. I have had MSD on the phone quite a bit going over this issue to no avail.
Saturated are slower reacting ver P&H but the MSD 36# and 50# are racing type injectors that have a 1.5ms reaction time and are considered comparable to the P&H in performance. P&H will run cooler though.
Good idea on the injector constant, I have not tried that. I could move it up to a 60# injector and see what happens.
I have two monster fuel pumps that can feed over 1,000 hp. So there is no need to close off the return line with a FMU.
It has got to be something with the car I think I have settled on. The chances of me tuning this PCM the exact same as Fastchips did the OBDII would have to be unreal, but yet I have the exact same FT/BLM and O2 numbers. Its almost as if I fouled up and put the old OBDII back in it thinking that it is the new one, thats how close they are.
I didnt by the way:)
[Modified by wicked96, 4:05 AM 8/10/2002]
Saturated are slower reacting ver P&H but the MSD 36# and 50# are racing type injectors that have a 1.5ms reaction time and are considered comparable to the P&H in performance. P&H will run cooler though.
Good idea on the injector constant, I have not tried that. I could move it up to a 60# injector and see what happens.
I have two monster fuel pumps that can feed over 1,000 hp. So there is no need to close off the return line with a FMU.
It has got to be something with the car I think I have settled on. The chances of me tuning this PCM the exact same as Fastchips did the OBDII would have to be unreal, but yet I have the exact same FT/BLM and O2 numbers. Its almost as if I fouled up and put the old OBDII back in it thinking that it is the new one, thats how close they are.
I didnt by the way:)
[Modified by wicked96, 4:05 AM 8/10/2002]
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From: Sachse Texas
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Re: Help!!!.... I'm in PCM Hell!!! (wicked96)
headers get red hot like a very lean condition although it is choking you with gas fumes and black smoke.
Generally split BLMs are caused by an exhaust leak somewhere in the system prior to the O2 sensors. Are you sure you are plugging the O2 sensors into the correct plug. The '96 having 4 O2's it is easy to get them mismatched.
I would increase the injector constant slowly until the idle is not getting washed out with fuel. Have you got any diacom or datamaster files you could share? You might also want to look into a program called VE master. It is suppised to help dial in the car at RPM's below 3K and non WOT use.
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From: College Station Tx
Re: Help!!!.... I'm in PCM Hell!!! (DOCTOR J)
Sounds like there is a fundamental problem in the injector scaling, or one of your o2's is dead. 2 quick things - send me a copy of your OBDI program and I will check the basics - send it to chris@slowcar.net - also swap your o2's and see if fuel trims switch sides (stay with the sensor - indicates bad sensor(s)) or stays like it is (indicates some other problem).
Good think you got rid of your OBDII computer - at around 420g/sec it will cut your injector pulsewidths in half approximately (for no real reason), and you will go lean - quite a few engines have been lost this way. The only workaround is a frequency clamp (maf massager, etc.) or obdI swap.
The VE (load) tables are not used at all when the MAF is operational - the purpose of the Ve tables is to translate manifold pressure at a given set of conditions to airflow (as a percentage of an "ideal" engine). The MAF measures airflow directly, so doesn't need them.
The tables are in the pcm, but only referenced if the MAF is deleted (SD mode).
Good think you got rid of your OBDII computer - at around 420g/sec it will cut your injector pulsewidths in half approximately (for no real reason), and you will go lean - quite a few engines have been lost this way. The only workaround is a frequency clamp (maf massager, etc.) or obdI swap.
With my (limited) understanding of MAF, I would have thought that the changes made would require remapping to run well. Obviously I missed something here - how do the load tables handle this rangeability? Is this a calibration you bought from someone? Just curious, and trying to understand GM programs better.
The VE (load) tables are not used at all when the MAF is operational - the purpose of the Ve tables is to translate manifold pressure at a given set of conditions to airflow (as a percentage of an "ideal" engine). The MAF measures airflow directly, so doesn't need them.
The tables are in the pcm, but only referenced if the MAF is deleted (SD mode).
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Re: Help!!!.... I'm in PCM Hell!!! (Vette92)
Its plenty rich thats for sure, I dont doubt it that fuel is burning in the tubes. O2s are saying that it is way lean and the PCM is dumping the fuel to it.
Yes, I know that a exhaust leak will cause split FT numbers. I went as far as taking my Hooker headers off and reinstalled my stock manifolds.... No change with that either. I am using good gaskets also no cheep ones.
I have thought about getting long tubes just to satisfy me that the shorties are not the cause of this.
Yes, I know that a exhaust leak will cause split FT numbers. I went as far as taking my Hooker headers off and reinstalled my stock manifolds.... No change with that either. I am using good gaskets also no cheep ones.
I have thought about getting long tubes just to satisfy me that the shorties are not the cause of this.
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Re: Help!!!.... I'm in PCM Hell!!! (ChrisB)
Hey Chris! I have talked to you a couple of times about this on the phone. I just converted to OBDI and found the exact same behaviour as with the OBDII. I now have all the tools to scan and tune the OBDI and know enough about it to really be dangerous. I have a guy that has tuned other LT1s helping with the program part of it. We tried the first program on it and it barley runs. I have not had time to work on it. Last night I put the OBDII back in it because it still wont run as good with the OBDI in it and I wanted to see if any of the last round of changes made any difference. No such luck!
I have went through all the changing stuff from bank to bank. No change. (first post)
Sure, I can email the program to you. If you have a good base file for a blown stroker like this I would like to try it. The program I have is a first try. I had planned on working on it some more this weekend.
Sorry to be slow at replying guys! Been really tied up the last couple of days!!
I have went through all the changing stuff from bank to bank. No change. (first post)
Sure, I can email the program to you. If you have a good base file for a blown stroker like this I would like to try it. The program I have is a first try. I had planned on working on it some more this weekend.
Sorry to be slow at replying guys! Been really tied up the last couple of days!!