I've never met an electrical problem I can't solve - until now, so advice is desparately needed. Here's the situation:

I have a '95 Windstar with a 3.8L engine. It won't start, but the starter turns it over just fine. There's good spark - but no fuel pressure.

First I checked the fuse and the relay in the relay box next to the battery. Both were OK. Then I checked voltage (with key 'on') at the inertia switch infeed: 12 V, as expected. And, I I tested the interia switch too; it was OK. Next I opened the connector where the leads to the fuel pump connect to the leads to ground and to the inertia switch. The ground wire gave zero resistance back to the battery, so it is good. And, with the inertia switch connected, I get 12 V (with key 'on) at the pink+black wire. So, I assumed I had a bad fuel pump.

I removed the tank and got the pump out, but it bench tested OK (that is, it runs fine whenever connected directly to 12V power). So, I tested the wires between the pump and the end of the pump harness leads. They test OK (zero resistance) also. That is, none of my testing found any indication of a problem.

But, since it is such a pain to take out the tank and I have 110K on the car, I replaced the pump anyway (along with the undercar fuel filter and the in-tank filter) and put everything back together only to find I still had precisely the original problem. So I also replaced both the relay in the relay box (next to the battery) and the other fuel pump relay in the expensive PCM power relay (an enclosed multi-relay box) next to the radiator. Neither of these replacements had any impact on the problem.

Further testing with ammeter, voltmeter, and ohmmeter indicates that when there is any appreciable load on the fuel pump circuit, no power gets through (i.e., some relay doesn't work?), but when there is no load, the same circuitry manages to deliver 12V consistently. This is made more baffling by the fact that I have checked the internal resistance of both the old and new fuel pumps. The original pump has a 2 ohm resistance, while the new pump has a 30 ohm resistance across its terminals.

Can it be possible that even a 2 ohm resistance is enough to keep one of the relays from working properly? Is a fuel pump supposed to have as little as 2 ohm resistance (or as much as 30 ohm, like the new pump?) Is there any way that the PCM itself (rather than the PCM power relay, which is a separate module) could play a role in this problem? Does anyone have any ideas or advice about what I can test or replace next to try to solve this problem? I'm already on my second event of removing the gas tank, and that's enough!

Greatful for any ideas anyone of you might have,

Matt Klionsky
klionsky@megsinet.net

 

I answered in the 67-79 forum but just in case you missed it
Check for corrosion in the power wire/connectors for the pump circuit. I have seen this before, usually in trailer light circuits. You can measure 12volts ok, but as soon as you put a load on the circuit all the voltage is dropped on the corrosion.
You can also run a 12volt line direct to the pump, if the pump runs I guess 30 ohms is ok, but it does seem quite high for a pump motor. I would expect more like 10 or less, I mean you are only measuring windings, so even 10 would seeem high.

Sparky

"Further testing with ammeter, voltmeter, and ohmmeter indicates that when there is any appreciable load on the fuel pump circuit, no power gets through (i.e., some relay doesn't work?), but when there is no load, the same circuitry manages to deliver 12V consistently. This is made more baffling by the fact that I have checked the internal resistance of both the old and new fuel pumps. The original pump has a 2 ohm resistance, while the new pump has a 30 ohm resistance across its terminals."

 

I feel your pain Pon. Went thru the same drill with an 88 Bronco a while back. Had good cranking and spark but no fire. Turned out the EEC lost ground. This shut down the fuel pump and injectors but still provided spark. The culprit was a corroded connector. The EEC gets its ground from a fine wire conected directly to the negative battery cable lug. When the in-line connector (by the radiator support) broke down the mystery was on. The big clue in my case was the pump did not run momentarily when the ignition key was turned on. If you are not hearing the pump whine briefly to pre-pressurize the fuel rail, a computer problem nay be a possibility. Look forward to hearing what the fix was. HTH
Good Luck,
FL Panhandle