Strange Electrical Gremlins - Ignition

a91what · Aug 19, 2016

Have you tested the tps to see if it is working correctly? With a meter across pins 46 and 47 (on the tps harness with koeo, probe the wires with the DMM) you should see a very steady climb in the voltage as you depress the throttle. If the voltage does not move linearly or the tps does not return to within 10% of its value with each full close of the pedal then I would suspect it to be bad. The tps signal cannot exceed 5v +-10% due to the vref output being the maximum available potential.

a91what · Aug 19, 2016

You have other electrical issues I would inspect the harness and check continuity on the pins to ensure that the harness is not at fault.

I am not saying the ecu isn't at fault but judging from your previous posts the harness would be my main focus. Especially if the car tries to turn over on its own, the cranking signal is supplied by the ignition switch nothing else.

90sickfox · Aug 19, 2016

@a91what is the EEC iv electrical guru of this forum. He knows things about these cars we mortal humans could only dream of knowing. All hail Steve !!!!

You can decide not to listen to him if you want. I didn't listen and payed the price of looking like a dummy. I've learned that he knows what he's talking about. Follow his lead and your car will be fixed.....or face the dummy police [emoji117] [emoji61]

blistovmhz · Aug 19, 2016

90sickfox said:
@a91what is the EEC iv electrical guru of this forum. He knows things about these cars we mortal humans could only dream of knowing. All hail Steve !!!!

You can decide not to listen to him if you want. I didn't listen and payed the price of looking like a dummy. I've learned that he knows what he's talking about. Follow his lead and your car will be fixed.....or face the dummy police [emoji117] [emoji61]

Not arguing with anyone. Just asking questions.

a91what said:
Have you tested the tps to see if it is working correctly? With a meter across pins 46 and 47 (on the tps harness with koeo, probe the wires with the DMM) you should see a very steady climb in the voltage as you depress the throttle. If the voltage does not move linearly or the tps does not return to within 10% of its value with each full close of the pedal then I would suspect it to be bad. The tps signal cannot exceed 5v +-10% due to the vref output being the maximum available potential.

I'll have to check it again in the morning, but I did test it completely unplugged from the ECU/harness, and the progression was linear and looked good (based on other TPSs I've looked at). This is the thing. I'm not generally clueless about electronics, but this Mustang is just kicking my ass, and I'm still not positive I'm even looking in the right direction. I've found a few guys who insist that the TPS signal (green) will show 5V from the ECU (or anywhere from 1.5-5.0V) when the TPS is not plugged in. This doesn't make any sense to me, but if it's true, I'm totally chasing my tail here.

Blew up my front diff in the Jeep and won't have parts to fix it this weekend, so no wheeling and no Jeep fixin', so LOTS of time for the Mustang.

nandomart · Feb 25, 2019

blistovmhz said:
Not arguing with anyone. Just asking questions.

I'll have to check it again in the morning, but I did test it completely unplugged from the ECU/harness, and the progression was linear and looked good (based on other TPSs I've looked at). This is the thing. I'm not generally clueless about electronics, but this Mustang is just kicking my ass, and I'm still not positive I'm even looking in the right direction. I've found a few guys who insist that the TPS signal (green) will show 5V from the ECU (or anywhere from 1.5-5.0V) when the TPS is not plugged in. This doesn't make any sense to me, but if it's true, I'm totally chasing my tail here.

Blew up my front diff in the Jeep and won't have parts to fix it this weekend, so no wheeling and no Jeep fixin', so LOTS of time for the Mustang.

I was wondering if this was ever resolved. Im dealing with a similar issue. If I disconnect the tfi harness with the koeo the fuel pump cycles on and off and it tries to start for half a second. I rotate the distributor koeo and the fuel pump cycles again. I removed the coil spark plug wire and I see it throw spark when I rotate the distributor koeo. Really stumped

General karthief · Feb 25, 2019

nandomart said:
I was wondering if this was ever resolved. Im dealing with a similar issue. If I disconnect the tfi harness with the koeo the fuel pump cycles on and off and it tries to start for half a second. I rotate the distributor koeo and the fuel pump cycles again. I removed the coil spark plug wire and I see it throw spark when I rotate the distributor koeo. Really stumped

start a thread in the tech forum, hard to answer a question when we don't know the problem or what your working on. This is an old thread.

90sickfox · Feb 25, 2019

There is a pick up signal coming from the distributor. There is a sensor inside it below the rotor button. That sensor controls injector timing ( kind of ). If you turn the distributor with the key on it will think the car is cranking, cut the fuel pump on, and shoot spark. This is normal.

90sickfox · Feb 25, 2019

nandomart said:
I was wondering if this was ever resolved. Im dealing with a similar issue. If I disconnect the tfi harness with the koeo the fuel pump cycles on and off and it tries to start for half a second. I rotate the distributor koeo and the fuel pump cycles again. I removed the coil spark plug wire and I see it throw spark when I rotate the distributor koeo. Really stumped

This is a very old thread. Like the thief said....start a new thread and give us a little more info.

Also, go through the checklist earlier in this thread.... at some point you will be told to go through the checklist so might as well get a jump on it.

Strange Electrical Gremlins - Ignition

a91what

SendMeUrDataLog

a91what

SendMeUrDataLog

90sickfox

Wasn't a pretty sight...and I've got big hands

blistovmhz

nandomart

New Member

General karthief

wonder how much it would cost to ship you a pair

90sickfox

Wasn't a pretty sight...and I've got big hands

90sickfox

Wasn't a pretty sight...and I've got big hands

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Strange Electrical Gremlins - Ignition

SendMeUrDataLog

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Wasn't a pretty sight...and I've got big hands

New Member

wonder how much it would cost to ship you a pair

Wasn't a pretty sight...and I've got big hands

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