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 Help diagnosing intermittent EFI start problem 
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Post Help diagnosing intermittent EFI start problem
The last couple days I've been trying to figure out a start issue I've been having with my EFI. I'll try to describe the symptom as best as I can and what I've done so far to troubleshoot it.

Symptoms: Bronco will generally start no problem on first attempt first thing in the morning. After driving it anywhere from 1/4 mile or beyond and then having the engine off for say more than 10 minutes, the engine has a very difficult time starting IF it starts at all. This happened Saturday when I drove to a friend's house that lives in my neighborhood and then I couldn't start it up again to go home. Had to leave my Bronco overnight at the friend's house. When I returned yesterday morning to try and start it, it did start, but took more effort than it should have. Then yesterday I drove around the neighborhood stopped back home, turned the engine off and left it off for like two minutes, tried starting it and it started back up immediately. Howeverl I then tried to restart like 10 minutes later and it would not start and wouldn't start the rest of the evening. The kicker is, up until this weekend, this start --> drive ---> stop ---> no restart has been intermittent. I've been left stranded places on a few occasions and I'm over it.

So, here's where I am at so far in my troubleshooting:

Fuel pressure is where it should be

I'm getting spark

KOEO codes are 53, 67
CM codes are 53,96

And now I'm trying to figure why the 53 code is showing up. I tested the TPS a little bit ago and am confused by my results because I am getting 5.7v on the voltage source wire (orange) and 5.7v on the sensor output (green) wire. Shouldn't the voltage source wire read around 5.0v and the sensor output wire read around 0.5v and then increase as the throttle opens? Not sure if this is the cause of my start problems, but I do need to resolve the 53 code right?


Mon Jul 17, 2017 9:26 am
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Post Re: Help diagnosing intermittent EFI start problem
I just replaced my fuel pressure regulator. It's too early to tell if it's my issue, but it was very intermittent as well.

Fuel pump relay? Can you hear the pump(s) running with the key on? I assume so since you say the pressure is good. What pressure are you seeing?

TFI module? Where is it mounted?

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1973 Bronco, 351 SEFI, Locked, discs, 35's ZF-5spd and Atlas 4spd. 235:1 Crawl Ratio. It may be ugly, but it's slow.
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Mon Jul 17, 2017 10:40 am
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Post Re: Help diagnosing intermittent EFI start problem
Fuel pump relay is new and good--pump kicks on at turn of the key and fuel pressure reads 35 psi. TFI module is located on the distributor, which I purchased new from Jeff's Bronco Graveyard.


Mon Jul 17, 2017 11:06 am
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Post Re: Help diagnosing intermittent EFI start problem
Code 67 could indicate an open signal return circuit which would affect the TPS, BP, ACT and ECT sensors. What computer and harness are you using?


Tue Jul 18, 2017 10:10 am
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Post Re: Help diagnosing intermittent EFI start problem
Viperwolf1 wrote:
Code 67 could indicate an open signal return circuit which would affect the TPS, BP, ACT and ECT sensors. What computer and harness are you using?


Computer is an A9L and the harness is one made from a place called Chuck's Roadster Electrics out of Nevada City, CA.


Tue Jul 18, 2017 10:44 pm
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Post Re: Help diagnosing intermittent EFI start problem
cplynn wrote:
Viperwolf1 wrote:
Code 67 could indicate an open signal return circuit which would affect the TPS, BP, ACT and ECT sensors. What computer and harness are you using?


Computer is an A9L and the harness is one made from a place called Chuck's Roadster Electrics out of Nevada City, CA.


You should check the signal return line to see if it is actually going to ground. The ECM should provide that ground but you can ohm between one of the sensors and pin 46 of the ECM connector. If you get continuity there the problem is likely inside the ECM.

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Wed Jul 19, 2017 10:40 am
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Post Re: Help diagnosing intermittent EFI start problem
Good luck- I jut got a headache looking at that diagram!!


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Wed Jul 19, 2017 3:26 pm
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