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Discussion Starter #1
I’ve done some searching and think I need to pull codes but I’ll share the car and the symptoms to see if I’m missing something.
92 LX 5.0 AOD with 27k. Car is all original with the exception of exhaust and cold air. It’s been garage kept since new and I’ve had it 4 years. It sees about 600 miles a year, basically perfect day only driving and local car shows. This past summer, on its last drive it ran perfect and pulled in the garage and sat for a couple months.
Went to start it and it just cranked. Did not hear fuel pump and no rail pressure.
Swapped the two relays under the MAF and tried again. This time, the fuel pump stays running constantly (fuel at the rail) but cranks and no start. The check engine light
 

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the check engine light? what?

if it is on

go ahead and change the ecm, then tell us if it is fixed, if not fixed we can start diagnosing

oh, what are the relays you changed, and why change them?
 

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Discussion Starter #3
The check engine light is on at half brightness with the key on no crank. Just glanced at it so maybe nothing. I swapped the fuel pump relay with the relay beside it bolted to the side of the shock tower. That came from a search. I will pull codes next as that is proper but I thought I’d post to make sure I’m not missing something else. The first symptom was no fuel pressure. Swapped relay and fuel pump stays on continuously. Verified pressure at rail. Did not verify spark but the fuel pump running continuously is not normal. Battery is less than a year old and is fully charged. The condition of everything on the car is like new. It ran like a top last time driven. Zero hiccups.
 

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since the relay, fuel pump and ecm all require electricity, what electrical tests did you do to support the theory that the relays were bad?

no fuel pressure, or pump coming on, does not mean change the relay...... i am pretty sure there are no credible searchs that say 'change ' parts before testing

test light?, DVOM voltage drop tests, anything like that?
 

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since the relay, fuel pump and ecm all require electricity, what electrical tests did you do to support the theory that the relays were bad?

no fuel pressure, or pump coming on, does not mean change the relay...... i am pretty sure there are no credible searchs that say 'change ' parts before testing

test light?, DVOM voltage drop tests, anything like that?
When will the parts cannon come into play?
 

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Discussion Starter #6
I’ve re-read my posts and the replies and I understand the sarcasm.
First of all, there isn’t going to be a parts cannon thrown at the car. I’m not that guy so we can just go ahead and put that behind us.
Second, you are correct in asking the troubleshooting methods. That’s where I am now. The initial problem was no fuel pump or pressure. I checked the inertia switch and it is not tripped. So I moved onto the next possible cause and spent 5 minutes swapping the relay. It was then this current situation presented itself. The fuel pump now works continuously with fuel pressure at the rail. Yet no start. So I left it alone and posted here.
My next step Is asking where I should go from here.
Had swapping the relay shown no change, my next steps would have been grab a DVOM and start tracing the fuel pump circuit and see where that led me. But instead the pump does now run and with good fuel pressure, but no start. The relays I swapped matched and I read others diagnosed their issue doing the same. So I did shortcut to find root cause a bit but felt it was logical. Not my first car where a failed relay caused the same symptom.
I plan on checking spark, and injector signal but this is where I need to make sure I’m headed down the right troubleshooting path.
I’ll admit this is out of my normal Fox knowledge. My other car (91 GT with a microsquirt driven 351) never gave me this type of symptom since I bought it stock in 95 and modified it over the years.
 

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well since you recognize your ways

re install the old relays, so not to introduce another problem

then fire the DVOM and test light up

how much of the start system do you know?
 

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Discussion Starter #8
well since you recognize your ways

re install the old relays, so not to introduce another problem

then fire the DVOM and test light up

how much of the start system do you know?
Not much And this is where I could use some experience to isolate the root cause. I can’t guarantee how fast I’ll be jumping on it due to work schedule but will get the relays put back as soon as I can. When I do, I will post back. I do appreciate the help.
 

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Shall we run down system design?

it is imperative to know what to expect testing wise, so then your result will have proper meaning
 

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Discussion Starter #10
Ok. Swapped relays back to original.
no fuel pump key on. Verified before I swapped them that it works via pump noise and strong pressure from rail.
 

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OP, you are going to wish a scary, angry midget jumped out of a closet and kicked you square in the nuts if you keep asking indy how to diagnose.

Here's my 2 cents.

It does sound like the EEC caps. Did you try to pull codes and did the fuel pump run with the code reader connected? The pump runs a self check at the beginning of the code reading. If the pump didn't run, it's either the pump, wiring, fuse or the eec.

You can energize the fuel pump relay and take voltage measurements at the connector above the fuel tank.

I would pull the EEC and check the caps.
 

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Discussion Starter #14
It’s been awhile since I’ve been on Corral. Shame on me.
Indy- I’m not an engineer so bear with me.
To answer your question, electrically I understand the basic fuel pump circuit consists of a relay, inertia switch, and the EEC. How the circuit itself is laid out is beyond my realm of understanding. I would think the key switch closes the relay to command power to flow to the pump, with the inertia switch acting as a fuse in the circuit. I may be off, but like i said- my knowledge here is limited.
That said, I did attempt to pull codes. I used a jumper wire with crimped spade terminals and jumped the small connector to the #2 port on the large connector. I do remember doing that once on my other foxbody years ago.
What I got was nothing. The check engine light illuminated dimly with the air bag light (I believe) was very bright. No flashes. Tried several times. When I attempted to crank, the check engine light went full bright (same as air bag light intensity) and the check oil light illuminated when cranking. Of course no fuel pump and no start. Battery was full charge and grounds are clean.
That’s where i am at.
 

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you are an engineer!!
see that

i think enjoy the ride would like to be that character in your closet.....i see a volunteer

back to it

you said that the CEL was illuminated during cranking the engine, correct??
 

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Discussion Starter #16
You are correct. The only thing that changed was the illumination intensity.
 

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we'll ignore ilumm intensity

FORDS.

in order for the ecm to ground the fuel pump relay to send power to the fuel pump and ground the injectors to fire them......the ecm NEEDS RPM SIGNAL

if the ecm is receiving the ecm signal the CEL light will go OUT, key diag check

if your light remains ON, that means the ecm is NOT receiving the rpm signal

guess what the rpm signal is?
 

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Discussion Starter #18
Hmm. I’m assuming the tfi? Pickup in the distributor?
But humor me. The fuel pump has no prime koeo. It did when I swapped relays but would run continuously. Perhaps the relays aren’t the same after all. More shame on me.
So back to needing rpm to ground the relay.. let me sleep on it. Every foxbody I’ve owned would prime the fuel pump with no cranking.
Thank you again.
 

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Discussion Starter #20
That sounds like a plan. To be sure, I verified again the check engine light stays on when cranking.
 
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