fuel pump problom

[gn79]

I have been having problems with my fuel pump. It is like something is shorting it out. I have bought a new one and it still does it. I have changed the relay and they still short out. can any one help me out.

 

[Ken Cunningham]

What do you mean "shorting out"? What are the symptoms?

I have been chasing down a 'hard start' condition that has been with me for about 6 mos. Intermittently, my fuel pump will either not cycle on at all, or will just barely get a tickle of power at key on. Not enough to pack the fuel line with fuel. I replaced my relay under the hood with a brand new GM one, replaced my hot wire relay in the trunk, and took out my kill switch to try to clean up the power back to the pump. Still no better.

Then I got a little smarter and tried to be systematic about it. I ran a pair of wires back to the trunk so I could monitor the power on a little digital voltmeter I now keep on the console. 1st, I connected the power monitor wire to the hot wire after both relays, just before the wire exits the trunk to the pump harness. I noticed that, intermittently, I would show no voltage at key on. That finding eliminated the fuel pump as my source of problem. 2nd, I moved the power monitor wire to the trigger line (in my hot wire set up, this is the original fuel pump power line). That also shows an occasional lack of power, exonerating my hot wire relay. Next I should attach my volt meter to the power going into the under-the-hood fuel pump relay. But because it is a new relay, I by-passed that step and swapped in a new (used) ECM. Other people on this board have reported that a bad ECM can cause problems exactly like mine. I just did this today, so have no conclusions yet.

The moral of this too long post: don't be too fast to condemn the fuel pump because there are a lot of links in the chain.

 

[gn79]

Originally posted by Ken Cunningham
What do you mean "shorting out"? What are the symptoms?

I have been chasing down a 'hard start' condition that has been with me for about 6 mos. Intermittently, my fuel pump will either not cycle on at all, or will just barely get a tickle of power at key on. Not enough to pack the fuel line with fuel. I replaced my relay under the hood with a brand new GM one, replaced my hot wire relay in the trunk, and took out my kill switch to try to clean up the power back to the pump. Still no better.

Then I got a little smarter and tried to be systematic about it. I ran a pair of wires back to the trunk so I could monitor the power on a little digital voltmeter I now keep on the console. 1st, I connected the power monitor wire to the hot wire after both relays, just before the wire exits the trunk to the pump harness. I noticed that, intermittently, I would show no voltage at key on. That finding eliminated the fuel pump as my source of problem. 2nd, I moved the power monitor wire to the trigger line (in my hot wire set up, this is the original fuel pump power line). That also shows an occasional lack of power, exonerating my hot wire relay. Next I should attach my volt meter to the power going into the under-the-hood fuel pump relay. But because it is a new relay, I by-passed that step and swapped in a new (used) ECM. Other people on this board have reported that a bad ECM can cause problems exactly like mine. I just did this today, so have no conclusions yet.

The moral of this too long post: don't be too fast to condemn the fuel pump because there are a lot of links in the chain.

Hey Ken, thats the same problem I have. I have rule out the fuel pump, relays and now I trying to see if it is the oil pressure switch. I have put in a new one, but no luck. Let me know if the ecm worked. I have not tired it yet and the pump is still not getting the voltage it needs.

 

[Ken Cunningham]

So far it looks good. I've only driven the car twice since swapping in the new ECM, but the voltage hit at key-on-engine-off looks way stronger than before. The digital voltmeter is a little slow to respond, but with the old ECM even when it worked I would only see about 4-6 volts before the voltage disappeared. Now I see a good 10-12 volts before the cut off. It seems that the voltage is on longer, letting the el cheapo voltmeter register the hit.

It will take a couple of weeks of driving before I will be totally convinced that the ECM is to blame, but I didn't want to make you wait that long for my preliminary opinion.

 

[GN Bob]

Check the fuel pump primer pin on the ECM plug. You can get the pinout diagram off of the gnttype site.

My T-Top car had a water leak that dripped right onto the ECM plugs which face up, the plug and connector were wet and the connection was intermittant. Sometimes I would get no prime sometimes it would be OK.

Carefully remove the plastic plug locking retainers and ease out the plugs. Get some electronic contact cleaner and spray both the pins and the connector and while still wet, plug the connector in and pull it out a few times and spray again to clean out any corrosion. Alcohol and a Q-tip would work also.

A bit of dielectric grease on the pins helps too.

Good Luck.

 

[Ken Cunningham]

Thanks for the tips. You've already anticipated my next question: can I salvage the old ECM? I'll clean up all the connector pins and retry the unit before I trash it.