Question on the power to the fuel pump relay switch???????

flemdog28 · Nov 12, 2008

When you turn the key and you hear the relay for the pumps click, is it the computer that sends the power to the relay to turn it on? I am trying to figure out if the computer is bad, that is why i am not getting power to the fuel pumps or not. Somebody help!!!!!!!!!!!!!!!!!!!!!!!!!

IMenriched · Nov 13, 2008

when you turn the key on (not over to start), you should hear the fuel pump prime briefly.

the relay itself could be the culprit...whole lot cheaper than the ecm (engine computer).
not saying your isn't bad...but usually they don't have issues.
check ground wires and interia switch

Psychopete · Nov 13, 2008

The switch side of the fuel pump relay gets hot from the computer relay. The computer ground the order side of the relay at pin 22 to finally turn on the fuel pump. This is really a lot easier to see visually with a wiring diagram..

Here is a VERY generic one:
http://econtent.autozone.com:24991/znetrgs/repair_guide_content/en_us/images//0900c152/80/07/81/c7//large/0900c152800781c7.gif

The circuit you're diagnosing is on the left, right under the alternator box, just under the fuse links.

Keep in mind that both the computer and fuel pump main powers have fuses. Either one could be blown.

So both the computer relay and computer have to be functioning for the fuel pump relay to work. Could be maybe just the computer relay you're hearing?

Quick way to test computer circuit / relay / fuse is to check for spark or power on pin #1 (yellow) at the computer. That would narrow quite a bit down to it only being in the fuel pump circuit, or the computer might not be grounding the relay from pin 22.

Also, see the section in the EEC-IV diagnostics in the technical library regarding grounding the terminal at the test harness for testing the fuel pump circuit. Basically that grounds the relay as it would have from pin 22 on the computer.

Pete

flemdog28 · Nov 13, 2008

relay

we are getting power to the fuel pump relay, we ran a test light on it and there si power there. and we test the wire going to the inertia switch and we are getting power but the wire leaving the inertia switch to the pumps is not getting any power. does the computer turn the relays on we you turn the key?????????

Psychopete · Nov 13, 2008

flemdog28 said:
we are getting power to the fuel pump relay, we ran a test light on it and there si power there. and we test the wire going to the inertia switch and we are getting power but the wire leaving the inertia switch to the pumps is not getting any power. does the computer turn the relays on we you turn the key?????????

The whole thing starts when you put the key on Run. The diagram above shows that the computer relay trips from the signial from ignition switch. Ground is coming from the battery, no smoke and mirrors there.

FWIW, The fuel pump relay will turn on twice for 1-2 sec once the key is put on 'Run'.

If you have power directly BEFORE the inertia switch, but not after, you either need to reset it or it's just bad. Temporarily "jumper" it, if it runs, replace.

Pete

flemdog28 · Nov 13, 2008

switch

yea we get power to the switch but not after. so we will try and bypass it tonight and if that is the problem then i will order a new one, but then the computer is fine?????????????????

Psychopete · Nov 13, 2008

flemdog28 said:
yea we get power to the switch but not after. so we will try and bypass it tonight and if that is the problem then i will order a new one, but then the computer is fine?????????????????

If you're seeing power before the intertia switch, sounds like the computer is doing it's job by grounding the fuel pump relay..

If you're getting spark, and can run diagnostics, I would certainly say that everything seems to be functioning properly as far as the computer.

Pete

flemdog28 · Nov 13, 2008

Computer

Ok So The Wire That Goes To The Computer For The Fuel Pump Relay Is The Ground For The Relay And The Other Wires. Good My Friend Kept Telling Me That The Computer Is Prob Shot, And I Was Hoping It Wasn't, I Got This Truck From A Friend That Wehn He Was Driving Ti Down The Road The Truck Died On Him, He Spent Some Money For New Pumps And It Still Would Not Get Power So I Am Hoping That It Is Just The Switch Or The Connector To The Switch

Psychopete · Nov 13, 2008

Yes. The ground to the switching side of the fuel pump relay comes from the computer, this is how it controls it. Positive is from the completed computer relay circuit for it's main power. If the computer were not functioning properly, you wouldn't hear the relay click or see any voltage at all before the inertia switch.

People love to blame computers for problems. They do go bad, but it's not very common. It's on my last thing that I'd think was the problem list. :icon_thumby:

Pete

flemdog28 · Nov 13, 2008

COOL THANKS WILL BE TRYING IT OUT TONIGHT HOPING THAT EVERYTHING WILL WORK SO I WILL HAVE A TRUCK TO DRIVE FOR THE WEEKEND.

THANKS
ANY OTHER PROBS I WILL POST AGAIN ON THIS THREAD :rockon:

flemdog28 · Nov 13, 2008

thanks

well we worked on it tonight and the connector going into the inertia switch was shot, so we replaced it and now we have power thanks :headbang:

Question on the power to the fuel pump relay switch???????

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