No start this morning (pump didn't prime), it now starts

[67coupe]

First off, I have searched and was prepared to run through jrichker's list....until now.

This morning my car didn't start. It was fairly cold ~30F. The fuel pump would not prime. With what little time I had, I placed my hand around the pump relay and could not hear or feel anything when turning the key.

Just got home from work, the damn thing starts. I hate intermittent problems. Also, I can hear and feel the relay clicking.

Is it possible for cold weather to cause a relay to stick? I really don't want to get stranded (lucky the car was at home). Will I be okay only replacing the relay?

Thanks.

 

[2000xp8]

Unfortunately in this situation there is no 100% way to be sure it's the relay.
I'd but another relay and keep it in the glove box. If it happens again, pop on the new relay, if it starts you obviously found the problem.

 

[67coupe]

Sorry for not checking my thread. Work has been bad last 3 days.

Picked up a new relay. It's in the glove compartment. If it acts up again (fine so far), I'll pop the new relay in.

Thanks.

 

[67coupe]

It did it again!!!!!!!!!!

Well guess what popped up this morning. No start, pump would not prime. I popped in the new relay....from last time. Nothing....same thing. Ran inside and printed off jrichker's list.

4.) No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – Coupe & hatch cars hide it under the plastic trim covering the driver's side taillight. Use the voltmeter or test light to make sure you have power to both sides of the switch
B.) Fuel pump power relay – located under the driver’s seat in most stangs built before 92. On 92 and later model cars it is located below the Mass Air Flow meter. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) 86-90 models only: Blown fuse link in wiring harness. Look for 12 volts at the Orange/Lt Blue wire on the fuel pump relay.
91-93 models only Blown fuse link in wiring harness. Look for 12 volts at the Pink/Black wire on the fuel pump relay.
The fuse links for all model years 86-93 live in the wiring harness near the starter solenoid.
94-95 models only: 20 amp fuel pump fuse in the engine compartment fuse box. Look for 12 volts at the Dark green/yellow wire on the constant control relay module.
F.) Engine seem to load up on fuel and may have black smoke at the tailpipe. Fuel pressure regulator failed. Remove the vacuum line from the regulator and inspect for fuel escaping while the pump is running. If fuel is coming out the vacuum port, the regulator has failed. Check the regulator vacuum line for fuel too. Disconnect it from the engine and blow air though it. If you find gas, the regulator has failed.

Since the car sat untouched overnight. I didn't try A. Couldn't check B with the limited time I had this morning and I assumed both relays were bad since neither cut the pump on and neither clicked. I checked E and had 12V.

After looking at both relays: The factory one has 4 pins, and the one from Crapzone had 5 pins. Figured I got the wrong relay. So, I jumped B & E with a spare wire, pump came on and drove to work.

Went to Crapzone, he verified it was the correct relay and had nothing else we could try. He told me to check my oil pressure switch... Told me the car wouldn't start without oil pressure. I politely told him that my car doess not have an "oil pressure switch." He still looked it up anyway.

When I left autozone, I put the stock relay back in for S & G. The damn thing works.

So, I have reviewed the wiring diagram and have a few questions.

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

The only wires I see on the diagram remotely related to the FP relay are:

KAPWR - Fuse link is okay. Measured 12V.

1) Could it be the EEC Relay? No VPWR to FP Relay? Probably not, car ran fine once started.

2) Or is it an issue with the EEC (wire 22)? Wire 22 is a ground...right?

3) Is the inertia switch in-line btw the relay and pump? Or before the relay?

4) Next time it happens, should I measure for 12V at the VPWR terminal on the FP relay? Or should I measure wire 22 at the FP relay? Should be grounded with key on.... right?

Don't know if its coincidence, but it dropped to 27* last night. Might have something to do with cold weather?

Unfortunately, I probably won't be able to troubleshoot this until it acts up again. Just hoping to have a plan in place next time.

 

[HISSIN50]

When it acts up, check Pink/blk to see if it has 12 volts [but the pump isnt running]. If so, check the connector at the tank.

If lacking power at pnk/blk while you should have it (during the prime out), check VPWR for 12 V and 22 for continuity to ground (check this during the prime-out period). If both are present and pnk/blk is dead (and blk/or has 12V), the relay is at fault.

 

[67coupe]

When it acts up, check Pink/blk to see if it has 12 volts [but the pump isnt running]. If so, check the connector at the tank.

If lacking power at pnk/blk while you should have it (during the prime out), check VPWR for 12 V and 22 for continuity to ground (check this during the prime-out period). If both are present and pnk/blk is dead (and blk/or has 12V), the relay is at fault.

I firmly believe its something prior to the relay or the relay itself. Simply because it worked with a paper clip.

It's going to be tough to diagnose because it has only happened twice since November (daily driver). Both were on first starts of a cold morning. Strange thing is, it has never died while running/driving (in 8 years) and I'm pretty stumped how something could be THIS intermittent.

I have my DVM and wiring diagram in the car. At least I'll be prepared the next time it acts up. I will check VPWR for 12V and 22 for ground when it does acts up again.