Series 1 3800 PCM Transmission Bypass (Page 1/1)
statue4 FEB 17, 09:49 PM
I have been referencing this great page (http://www.gmtuners.com/fiero/transbypass.htm), but have a couple questions yet. The car is 1988, originally V6 getrag 5 speed. The donor car was 1992 Bonneville SSEi w/ Series I 3800SC. I am using the 5 speed, instead of the Bonnie's auto.

There are pretty much two things that must be bypassed: the transmission solenoids and the PRNDL selector.

The GM Tuners page says to put 194 bulbs in place of the TCC and shift solenoids. Easy enough. Here is my first point of confusion: The pin diagrams I used to make my harness are from very similar, but not identical to the actual wires I have. I think it is for a 91-93 L27 instead of 92-93 L67. Both the diagram and the car/engine/PCM have Tan/Black TCC Solenoid, Yellow/Black Shift B, and Light Green Shift A. The diagram I have shows a White TCC PWM Solenoid, but the actual car/engine/PCM has a different circuit there and no other white wire on that 32-pin connector. Will I have any problem doing the light bulb job with the three wires I do have, or do I need to also find a TCC PWM Solenoid circuit? I haven't been able to find a TCC PWM Solenoid on pin diagrams from later years.

Second question is about Transmission Range Position Switch bypass. The GM Tuners page mentions using a relay to tell the PCM that the transaxle is either in D3(drive) or N, using a clutch pedal switch or brake pedal switch. Can I not just wire it up so the PCM always thinks it is in D3 (would be easier and cleaner than running a wire up from the pedals), or would that cause problems?

Thanks! The swap is drivable, but I'm trying to get it daily-drivable.
Raydar FEB 18, 09:53 AM
When I swapped my 4.9 auto to a 5 speed, I just jumpered the wires to tell the PCM the engine was in drive.
I removed the PRNDL switch, retaining only the reverse light wiring.
I did not use a clutch switch. It will start in gear. But I learned to drive on manual cars that would start in gear. Just learned to be careful.
olejoedad FEB 18, 09:58 AM
Statue, perhaps you should contact Ryan at the website and ask for clarification.
statue4 FEB 18, 11:07 AM
Raydar, I'm hoping I can do the same. The starter motor still won't engage without the clutch pressed, and even if that wasn't the case I'm not too worried about starting it in gear. Will the PCM thinking it is in drive or in nuetral have any difference on fuel and spark to the engine and ultimately drivability?

olejoedad, I hadn't even thought of that. How do you think I could reach him?
olejoedad FEB 18, 11:12 AM
There is contact info on the website.....
Dennis LaGrua FEB 25, 12:03 PM
The ideal way to solve this would be to go into the program and delete the transmission code. The trouble with this is that there is very little software support for the series I ECM's but you may find it online Replacing the shift solenoid inputs with bulbs should trick the ECM into believing that the solenoids exist . I just don't see this as the ideal solution.
Ryans trick about sending a message to the ECM that the transmission is in drive is a unique solution but I am not certain how that might affect other ECM operation. It may very well work but having never tried it I just don't know. Perhaps Ryan has had overall good results doing it this way.
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[This message has been edited by Dennis LaGrua (edited 02-25-2022).]

Darth Fiero MAR 03, 02:11 PM

quote
Originally posted by Dennis LaGrua:

The ideal way to solve this would be to go into the program and delete the transmission code. The trouble with this is that there is very little software support for the series I ECM's but you may find it online Replacing the shift solenoid inputs with bulbs should trick the ECM into believing that the solenoids exist . I just don't see this as the ideal solution.
Ryans trick about sending a message to the ECM that the transmission is in drive is a unique solution but I am not certain how that might affect other ECM operation. It may very well work but having never tried it I just don't know. Perhaps Ryan has had overall good results doing it this way.



The 194 bulb trick I employed many moons ago was out of necessity since I did not possess tuning software at that time to disable the codes in the PCM tune. The old 92-93 3800 PCM I was working with at the time only ran electrical diagnostic checks on the shift and TCC solenoid circuits to see if they were connected. The newer computer systems go beyond this and actually look at transmission output speed vs. input speed (engine RPM) to determine if the transmission is actually operating in the desired gear and is not slipping. Obviously, with the enhanced diagnostic tests the newer PCMs employ, the 194 light bulb bypass trick won't work and the PCM will need a custom tune.

Getting a custom PCM/chip tune is the modern solution and the best method of making one of these computers work with a non-electronic automatic or manual transmission.

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More is more. Less is not enough.

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[This message has been edited by Darth Fiero (edited 03-03-2022).]