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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: Butalla on March 31, 2012, 08:39:42 am
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I have an 86 C10 SB that originally had a 305ci engine code H with a 700R4. When I bought the truck, it had been switched to a 350ci with a 72 Quadrajet and a TH350 trans. I bought an 85 700R4 to put into it. My question is whether or not I can use the existing ECM that is still under the dash? Will it be looking for signals from the engine or carb that are no longer connected and then not control the TCC correctly? What sensors do I need to make sure I still have and where are they located? I'd like to make sure I know what I'm getting into before I start. Thanks in advance for any input!
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Welcome to the site.
Have you looked into the harness adapters from Painless, B&M, etc. that will allow you to wire for the lockup torque convertor?
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I have seen them and figured that they would be plan B if I can't use the original ECM. I can't really afford to spend any more than I need to right now.
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Here is a link for "typical" wiring. http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_computer_control_wiring.jpg (http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/81-87_computer_control_wiring.jpg)
There are people on here a whole lot more familiar with the 80's ECM that will be able to chime in, just give them some time.
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Thank you, that should be helpful. I'm in luck in the fact that all of the wiring was left in, I just need to see what is unconnected.
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700R4's are NOT controlled by the ECM. Lockup of the converter is all you have to worry about. Do a search there was a thread on this recently.
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I understand that the ECM does not control the shift points of the 700R4. However, if I understand correctly, it does control the torque converter lockup. What sensors is it looking at to do this? If anyone could please answer this i would appreciate it.
Thanks
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I've been told by transmission shops before that they can set the trans up mechanically to lockup the converter so it wouldnt need any electrical wiring for it.
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Alright, I've found out that the ECM is looking for the throttle position sensor and pulses from the distributor to determine TCC lockup, neither of which I have anymore. Therefore, i think I'll have to create the external circuit. Better to know now that find out when I'm into it already. It doesn't look terribly complex.
Also, Anyone know what the vacuum sensor is on the firewall just to the right of center? It doesn't look like it's connected to anything.
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Also, Anyone know what the vacuum sensor is on the firewall just to the right of center? It doesn't look like it's connected to anything.
Do you have a pic, or can you describe the shape color of the sensor ?
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It is black, cylindrical with the vacuum port facing toward the center of the firewall and the electrical connector at the opposite end.
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(http://img.tapatalk.com/d036569e-6c94-c441.jpg)
This one?
Sent from my T-Mobile G2 using Tapatalk 2
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That looks like the sensor for the anti-knock system. You can safely remove it if you want to clean up the engine bay. It is probably unhooked already but if not there is a thread on the board with detailed instructions.
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Yes, that's the one.
Thanks
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See, it does take a whole village. ;D
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I'm probably about to show my ignorance, which is o.k. Isn't that the low vacuum switch which is required to disengage the lockup torque converter (under low vacuum) that you are trying to get working? Also, isn't the knock sensor always in the block since it is essentially a microphone looking for a thud? No vacuum hose on a knock sensor???
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First off, an 85 C10 with a "H" 305 is the LE9. It won't have a "ECM" under the dash, it has a ESC (Electronic Spark Control) which controls timing to the distributor.
Depending on where the pictured Vac switch is located ( appears above the ESC locaton above the AC), it is the ESC Vacuum switch, and has nothing to do with the Transmission.
There is a another VAC switch just like this generally mounted to the booster bracket, it as jaredts pointed out is the low-vac switch so the converter will unlock in low vacuum situations. There is also a brake cancel switch which unlocks the converter when you hit the brake pedal.
Only on ECM 1987-up TBI motors is the control in the ECM and needs all the sensors you doesn't have and never had.
I am guessing you didn't take my suggestion and search for the answer. I found these that directly address this:
http://forum.73-87chevytrucks.com/smforum/index.php?topic=14209.0
http://forum.73-87chevytrucks.com/smforum/index.php/topic,7310.0.html
http://forum.73-87chevytrucks.com/smforum/index.php?topic=3925.0
http://forum.73-87chevytrucks.com/smforum/index.php/topic,21274.15.html
http://forum.73-87chevytrucks.com/smforum/index.php?topic=5947.0
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I've been told by transmission shops before that they can set the trans up mechanically to lockup the converter so it wouldnt need any electrical wiring for it.
Yes. I had a 700r4 built with a hydraulic lockup. No wires, no vacuum, just the TV cable.