Need help troubleshooting a 4R70W - TCCoA Forums
 
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post #1 of 8 (permalink) Old 05-10-2006, 09:59 AM Thread Starter
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Need help troubleshooting a 4R70W

I know this is my first post, but I've searched everywhere and this seems to be a pretty active place for questions on these trannys.

Ok, short background. I transplanted a 4.6 and a 4R70W from a '93 Lincoln Mark VIII into a hot rod. I am using the PCM and tranny harness to operate the tranny only. The engine fuel and spark are on a stand alone system. I fed the PCM a TPS signal, a brake signal and the required grounds and power inputs and connected the tranny harness. The transmission WAS working, but there seemed to be a 2-3 slippage. After a short time I lost 3 & 4 all together, it would just rev up like neutral.

I just completed a tranny swap from another Mark VIII ('95). I have all four gears, but again, there is slppage going to 3rd. It catches if I back off the throttle.

I have a couple of specific questions that might help me.

1. How is line pressure controlled? What effect does the TPS have on it? Right now the TPS is shared with the EFI system and maybe that's causing a problem.

2. Are there any other inputs needed for the PCM to properly shift?

3. Is too low an RPM a problem? I'm running 2.79 gears and that make the engine RPMs very low for cruising. The car only weighs about 1,600#'s so I wouldn't think that it impose that great a load compared to a 4,000# car.

I know the first instict is I have two bad transmissions, but I don't want to put a good one in and ruin it too. I know the optimum setup would be an aftermarlet controller, but again, I'm not totally conviced that would solve the problem.

Any info would be appreciated.
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post #2 of 8 (permalink) Old 05-10-2006, 12:59 PM
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Yeah, you might want to use a separate TPS and see if that helps any.
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post #3 of 8 (permalink) Old 05-10-2006, 03:06 PM
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Wow...
Yeah, that is going to be a problem. The PCM uses a lot of other stuff to determine shifting based on spark, air temp, brake input, engine temp and such.
You will need to have all of the needed inputs hooked up for it to function properly. If you don't have an EDIS module and the computer wants that input then this may be part of your problem. I believe there was a truck that didn't have EDIS and used the 4R70W.
This issue might take a little work to get right.
Darrin

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post #4 of 8 (permalink) Old 05-10-2006, 07:00 PM Thread Starter
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Well, I hooked up the stock TPS and gave it another try. It's pretty much doing the same thing. I might even be skipping right to 4th, it's hard to tell, the car is so light and I'm afraid to get on the gas so i don't fry something.

Actually, I am using the EDIS, but it's controlled by the Megasquirt. I could hookup the PIP signal to the stock PCM. I was wondering if that might need engine RPM to figure shift points as well. I was just nervous that "sharing" the PIP signal between the Megasquirt and the stock ECU would fry something.

I'll keep at it, keep the ideas comming, thanks.

Hmmm, now that I think of it, engine RPM would be important for the PCM to know to maintain proper line pressure. But there is a "transmission speed sensor" and a "vehicle speed sensor", so I though that would be enough.
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post #5 of 8 (permalink) Old 05-10-2006, 08:19 PM Thread Starter
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Ok, it's looking better now, but still not right. I hooked up the PIP signal and the didn't do much, but it didn't seem to hurt either. I also powered up the Overdrive lockout. Now it shifts 1-2-3 pretty good. Took it for a nice easy ride around and there was no more neutral rev.

I guess I'm not used to such a sloppy shift though too. It does seem to hold on to second for a long time too, but that could be a function of the overdrive lockout being on. I could cruise in third at around 2000 RPM. If I gave it some pedal (not enough to downshift) it would rev up to 3000 RPM. Never seemed to get TC lockup either, but that doesnt bother me much.

So, I guess I need to look at the fixes for shfit problems that is prevelent with these. Hopefully, that is all it is. I'd gladly listen to any other input though, Thanks
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post #6 of 8 (permalink) Old 05-12-2006, 08:12 AM
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Why not choose another stand alone unit to run the trans like TCS/compushift/or the new TCI unit.

------------------------- Dan Gilsdorf ---------------------------
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post #7 of 8 (permalink) Old 05-12-2006, 08:38 AM
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Once I saw the car I realized how many parameters that the computer uses for the transmission functions are missing. You are going to have an issue since the computer uses MAF input to determine load as well. Also, what are you using for a speed sensor and is it giving the computer the correct info?
That is one nice car by the way. Keep plugging at it.
Darrin

01 F150 5.4L 4x4 and a 98 Mustang GT vert sitting engineless and without transmission or converter


All my vehicles tuned by BC Automotive (me)

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post #8 of 8 (permalink) Old 05-12-2006, 11:08 AM Thread Starter
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Well, I tried a couple more things last night with no success. The more I researched it, not having a MAF issue kept comming up too. I gave up and ordered a Baumann controller this morning. I figured it's something I need anyway, so I might as well go ahead and get it. I knew try to use the stock PCM was an experiment anyway, but I wanted to try. Thanks for the input, I'll let you know how it works.

Darrin, I guess you found me on the MD boards then, thanks. Yea, it LOOKS cool sitting in my garage
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