Code 18 loss of tach signal SOLVED

[tw205]

I’ve been working on an old abandoned 85 BII 2.8. Got it running a rolling and started working on drivability. No CEL but I looked anyway. I got 21,31,54,83,84,87 and continues men 18.41,54,63. I got them narrowed down to the 18 and 63 in continuous mem.
I’ve checked wire condition from the dizzy looks fine. It looks like the ECM has been replaced. Says 85 Bronco II 2.8 in yellow marker across the face. When I set timing to 10 degrees BTC and plug the spout back in, the idol picks up as it should. I shine my light on timing marks and see it has advanced and moves around if I rev the engine. All looks normal. Still drives like crap. No power, occasional backfire. Pull the codes and that 18 and 63 are back after I cleared them.
Here is my thought. If I’m crazy say so but be nice. The code 63 is TPS voltage too low. If I accelerate, the rpms begin to increase when the fuel from carb accelerator pump enters the cylinders. The TPS should be sending signal to ECU saying more fuel is being added but low signal from TPS will be conflicting with PIP from dizzy. Will this cause a code 18. I’m trying to figure this out without a parts cannon being fired at it. I haven’t put any new parts in it but I have swapped out some used ones with no significant changes. Dizzy got swapped as did the TPS. Changing TPS got rid of code 21 but 63 comes back with a drive so it’s signal is too low. As it’s simply a potentiometer I can understand it’s failing. Both dizzys with their own modules preform the same.

My big question now is. Will that bad TPS initiate a code 18.

 

[RonD]

21 Engine Coolant Temperature (ECT) sensor out of range – ECT

63 Throttle Position Sensor (TPS) signal too low TPS

From here: https://www.therangerstation.com/tech/obd-i-diagnostic-trouble-code-dtc-applications-2-digit-ford-codes/

Have to say I have not worked on many of the computer carb setups in a long long time

Yes, in the absence of Vacuum Advance the TPS is required so computer can change spark timing when accelerating, to match richer/faster burning air/fuel mix
So hesitation would be the result if TPS wasn't working as it should

I would assume TPS, like the ECT, would use +/- 5volts as reference voltage and share that same 5 volt wire from computer
I would start there and see if one of the 3 wires at TPS has 5v key on TPS unplugged, -5v is OK to
One of the other wires should be a ground reference
3rd wire is the return/signal wire back to computer, need to test that with TPS plugged back in, 0.5v to 4.5v, throttle closed and wide open

 

[AndyB.]

These will help.

 

[tw205]

21 Engine Coolant Temperature (ECT) sensor out of range – ECT

My bad Ron. should be code 23. TPS out of range.
Thanks for the reply.

 

[tw205]

Picked up a new TPS and installed. No more code 63. Still getting the code 18 loss of tach. Pulled the ECU and started checking wire. Spout tested good. Checked for resistance across IDM resistor. Nothing coming across resistor. Removed it and tested again. No reading. Did some research and found it should be 22k resistance. Can’t find one like it but I’m reading you can replace with a radio shack 22k 1/8 watt resistor. But I got a parts truck. Pulled that one off and tested. 21.7K. Perfect. Installed cleared codes and took her out. Ran codes when I got back. Success!!!! No more code 18.