SteveinNC

All,
Rebuilt my tranny and it has been running solid for almost a year and 10K miles. My baseline pressure was always a solid 80PSI cold or hot and never fluctuated. Reverse went to 130-140 PSI and when towing at 55-65 mph it ran at 190 PSI solid. Fluid is only a couple of months old and hasn't been over 210 F for more than a couple minutes. And that was only a couple of times towing. I installed pressure and temp gauges during the rebuild.

now on to my issue at hand....

Last week one day I saw my base pressure at idle was 85-90 PSI and everything else seemed normal. No extra noises, different shifting nothing. Didn't think much of it even though my baseline pressure has always been 80 PSI solid for a year.
Then about 2 days later I got in my truck stone cold start and base pressure at idle immediately went to 130-140 PSI and the needle jumps a lot so can't give a definitive pressure. Basically my overall pressure has increased 60 PSI through the entire gear range. I can rev the motor in neutral and get 250 PSI easy. baseline has stayed up at 130-140 PSI.
It not a faulty gauge as I can hear the pump whining and it does shift much harder in all the lower gears. I did have full range of gears 1-4 and lockup in 3rd and 4th both as confirmed using the brake pedal test and watching RPMs increase some.
Checking voltage on my TPS and its goes from .71v idle evenly up through to 4.60v at WOT. Went through the range several times and didn't see any spikes or dead spots. Pulled my Force motor out (brand new Borg Warner at rebuild along with all new ACDelco solenoids and wiring harness also). ohm tested it and got 5.0 ohms. Found my original Force motor that came out of it that was working when I pulled the tranny for rebuild and it ohm tests the exact same ohm reading. The screens in the end of the force motor looks clean. I used a jewelers loupe to confirm this.

any and all ideas are welcome!! any more info you need to help diagnose just let me know. I'm out of ideas.

Thanks in advance,
Steve

mrvedit

I would first suspect a sticking force motor (PCS); why not install the old one and see what you get.
At the same time you have the pan off, why not check the boost valve and the pressure control valve above it to make sure nothing is sticking. Maybe a little sliver of metal got in there.

jimmyblue

iTrader: (11)

I would try and look at the force motor current, and
for immature codes that might be pushing up the line
pressure commanded. I guess the main questions are
whether the force motor / PCS is responding properly
to commanded current, and whether there's something
commanding (or causing) more pressure (less current)
than before.

SteveinNC

All, I swapped my original force motor back in as suggested with no other changes and pressure dropped back down and stayed there. Went through the gears and pressure reacts how it should in all gears. Thanks for the help!
One thing I did notice is that my max pressure with this old force motor is now 220 to 230. The "new" solenoid never would go over 200 in any gear or rpm. Wondering if there wasn't a problem from the beginning? It was supposed to be a Borg Warner new solenoid, but there is zero markings on it and it didn't last very long. Makes me wonder what was really inside that BW box.

Thanks again for your help!
Steve

SteveinNC

Well, I just went back out and started my truck up to backup my initial test results from last night to make sure the numbers are matching up. They are NOT. Line pressures are back up. not as high as the other force motor but I never knew what the baseline pressure was with this EPC and setting either.
Back to the drawing board. Now I think I need to go along with JimmyBlue's thinking and check to see what the PCM is commanding the EPC solenoid to do and go from there. So 2 tests with this older EPC and one test showed 60 PSI last night and 110-120 a couple of minutes ago.
Got to wonder if the PCM isn't going. Time will tell once i do the voltage check per the ATSM manual procedure.

If you guys don't mind standing by for guidance it would be greatly appreciated.

Steve

mrvedit

The TPS voltage of .71V did give me pause. Did you use a volt meter and a scanner?
Do you have Hp Tuners or EFI Live?
With a scanner have you confirmed you have 0% throttle with the throttle closed?

Jimmy probably has more experience with high TPS voltage, but I started to have problems around .65V and therefore adjusted the TPS position (even with a drilled throttle plate) until I got it down to .50V

In any case, as Jimmy mentioned, the next step is to see what the PCM is commanding. High current -> low pressure; low current -> high pressure.

SteveinNC

I will mess with this TPS also. Seems outside of having debris floating around making valves stick it seems everyone is going along the lines of an electrical issue somewhere. And I would agree with that when 1 turn of the key gives you test results ABC and 12 hrs later the next turn of the key gives completely different results with zero other changes. and both test were stone cold starts.
The .71v to 4.6v TPS test mentioned above was with a volt meter probing into the TPS wiring harness itself. I don't have any after market tuner software or means of scanning to gather data any other way right now. This is a '93 truck with OBD1. Tuning is something I wanted to get setup to do within the next year after I get all the windows replaced in my house. Money don't grow on trees.
I will get the volt meter back out and gather some data and we can go from there. Thanks again for your help so far!

Steve

mrvedit

My concern about the .71Volts applies to LS1 PCMs like the "411". I don't know anything about the earlier OBD1 stuff.
Is the '93 PCM controlling the trans?

clinebarger

The TBI PCM's where pretty bad about the EPC drivers being flaky or giving up completely. They will scan perfectly normal but Commanded AMPS will be different than Actual AMPS.

SteveinNC

Sir,
How should I go about trying to get voltages readings from the PCM to the force motor? I tried pulling the electrical connection from the passenger side of the tranny and using paperclips to get contact with my volt meter with the key on. But I must have done something wrong and the transmission fuse blew and I could never get any good numbers on my meter either.
Electronics is my weak point. I can deal with mechanical stuff and figure it out all day long. But volt meters and electronics isn't a strong suite. Any help or links would be appreciated.

FYI: I did get a brand new BW EPC solenoid and the original high pressure symptoms are still present. So we know it is NOT the force motor.
Would it simply be easier to swap out the PCM with a known good 8625 PCM and see if the EPC driver issue you mention is the problem rather than dealing with getting voltage readings? Open to any and all suggestions.

Steve

SteveinNC

All, I'm open to any and all suggestion to resolve this issue. As it stands right now, I'm back to my original symptoms of higher pressure throughout the entire gear range with a brand new EPC solenoid installed, new fluid and filter. Check to make sure the boost valve was still properly seated and no debris in the pan except for STD clutch and band residue which looked like normal levels to me.

I see OReillys has MasterPro brand ECMs for my truck (8625 version). If everyone seems to think the ECM is the issue..... is this MasterPro brand worth it? Any experience or other suggestions?

Thanks,
Steve
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mrvedit

I've been very happy with ebay seller "SpareECM" who might have an ECM for your truck.
With LS PCMs (at least) he will pre-program your VIN, enable or disable VATS and a few other basic options.

SteveinNC

All,
Follow-up with the issue finally resolved. It was my PCM. Specifically a 8625. Got a reman'd one and swapped over my PROM/CALPAC and bingo. All my pressures go back to normal and everything has stayed like that for a couple days and several turns of the key. I beleive we have it licked this time.

Mr Clinebarger nailed that one on the head!

mrvedit, thanks again for your help. Your suggested contact didn't have my specific PCM so had to go elsewhere. But thanks for the help and guidance none the less.

Steve

mrvedit

Glad to hear you got it fixed. And THANK YOU for taking the time to update your thread here.