Help diagnosing intermittent EFI start problem

[Jambi]

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. However 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.

 

[pcf_mark]

After driving and it sits for 10-20 minutes rthen ead the fuel pressure. I bet it drops to near zero. My EFI conversion has similar behavior with terrible hot starts then rough running for a few minutes then it clears up and runs just great.

The fuel pressure drops, the intake, fuel rail and injectors get heat soaked. With no fuel pressure the fuel boils in the rails turning to a vapor / liquid mix. When you re-start the engine is trying to run on this and can't re-start until the fuel pressure stabilizes.

A good test (and how I start my hot truck) is to turn the key to run, wait 3 seconds, turn it off. Repeat this three times. This runs the fuel pump a few seconds several times and this build pressure in the fuel rail pushing the vapor back to the tank and putting liquid fuel behind the injectors.

This could be the regulator or the check valve in the fuel pump letting the fuel leak back to the tank. In my case the regulator is problem I just have not replaced it yet.

OR you could have a leaking injector that is draining the fuel into the engine but that would start super rich and smoke I think.

 

[Jambi]

I've been out of town with no internet accessibility for the last week. So how long should it take the fuel pressure gauge to drop back down to zero? Mine appears to be dropping to zero within 15-20 minutes.

 

[OX1]

I've been out of town with no internet accessibility for the last week. So how long should it take the fuel pressure gauge to drop back down to zero? Mine appears to be dropping to zero within 15-20 minutes.

Easy to see if that is a problem. Turn key on and off several times, running pump/lines back up to pressure, then start. I doubt that is your problem.

I'm guessing weak TFI module and/or weak voltage to EEC or TFI.
I extended wiring on main power wires for EEC in my dads hotrod and it
did exactly as you describe. Even .4-.5 volts drop between battery and EEC power @ processor, was enough to give it fits.\
Used larger guage wire on my extension, and problem went away. This led me to believe that that voltage, or even minor reduction
of it, was very finicky to the EEC upon even wamr starts (even though cold starts where fine, EVERY time).

 

[EFI Guy]

Since you're in Denver come see me one weekend, we'll get her figured out quickly.

 

[pcf_mark]

That is really nice of EFI Guy! An OEM set up can stay weeks at 40 psi.

 

[Jambi]

I resolved the 53 code by replacing the TPS. For some reason the TPS I had on wasn't measuring the correct voltage and the spring-loaded piece inside wasn't spring-loaded anymore.

I'm no longer getting the 96 code, but I will sporadically pull a 95 code, which is odd to me. Following every test I do or after every drive (when I do get the Bronco started) I run the code reader again and sometimes it will pull a 95 and sometimes it won't, which doesn't make sense to me.

There's no fuel in the regulator vacuum line. I'm going to try and check some other things in the fuel pump circuit, but I'm running out of ideas.

 

[OX1]

I resolved the 53 code by replacing the TPS. For some reason the TPS I had on wasn't measuring the correct voltage and the spring-loaded piece inside wasn't spring-loaded anymore.

I'm no longer getting the 96 code, but I will sporadically pull a 95 code, which is odd to me. Following every test I do or after every drive (when I do get the Bronco started) I run the code reader again and sometimes it will pull a 95 and sometimes it won't, which doesn't make sense to me.

There's no fuel in the regulator vacuum line. I'm going to try and check some other things in the fuel pump circuit, but I'm running out of ideas.

Well, progress anyway. Glad to see you got some of it worked out.

 

[Jambi]

Well, here it is February and I still don't have this issue resolved (although I did take a break from it for about 4 months out of frustration). The only two codes I'm pulling at this time are 51 and 67 so I don't know if those are contributing or not.

My particular harness was made for an EFI conversion for a classic Mustang with a T5 manual transmission, but I have a C4 in my Bronco. On my EFI harness there's a round, 2-pin hard shell "neutral sense connector" that I don't have connected to anything, which is probably the reason for the 67 code, but would that cause my start then no start problem? Is there a way for me to jumper the connector or something so I can at least eliminate the 67 code?

 

[OX1]

This thread might help...........................


https://www.stangnet.com/mustang-forums/threads/efi-wiring-help-on-86-5-0-pin-30-46.832635/

 

[pcf_mark]

Did you verify your fuel pressure after shutting the truck off? If you shut off with 40 and it slowly goes down (or quickly) your regulator is probably bad.