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· Registered
3 Posts
Discussion Starter · #1 ·
Hello from the 49th state and thank you in advance for any suggestions for troubleshooting this frustrating issue as I am working in the dark as temps hover around zero.... :roll:

Pertinent Background Info: 2000 Sierra 4x4 1500 5.3 Vortec 200,000 plus org miles
Owner had a service engine light come on several months back but took no action. Light is still on.
Not owning a reader, no codes have been identified YET but will resolve this issue soon and update.
In the past 12 months owner had noticed intermittent slow starts and occasional flat or sluggish response upon acceleration.
Several weeks back truck suddenly will not start, and I am recruited to fix it!
Fuel pressure (zero), spark at all cylinders and lack of audible pump activation tests indicated faulty fuel pump.
Fuel pump was replaced w/ oem ACDelco and new 4 prong flat wiring connector that matched factory wiring was installed and verified correct orientation.
Oem fuel filter and fuel pressure regulator were also installed and verified no leaks and proper operation.

Now here is where the conundrum really begins.........

Ignition is turned on but not started. Proper fuel pressure is verified.
Truck starts right up and runs, maintaining proper fuel pressure.

I am thinking this is a done deal, wrap it up. Wrong. :evil: I try to restart it later and the truck won't start again.

So I check the obvious...all fuses and inspect the relay. Everything looks ok. Check ground on frame under bed where fuel pump ground wire and tank neck ground strap attach and they are fine.

I Jump terminals 30 to 87 while i have the ignition keyed and the pump fires right up.

I switch out the FP relay for one of the other 3 identical ones in the under hood fuse block.
( POSSIBLE CLUE?: owner mentioned a previous issue in last 12 months with some moisture getting into that under hood fuse block and having some possible corrosion build up...this seems to have resulted in the horn becoming stuck on until the relay was removed. It was later dried and connections cleaned off and relay reinstalled without further incident.)

With the swapped relay, the truck once again starts and runs fine, going on 10 mile test drive with no problem. Thinking problem solved,and I will replace the bad relay. Wrong again.

Fast forward a day. Truck starts fine and warms up for 5 minutes no problem. Step on gas, truck dies. Attempt to restart fails. Swapping relays with either of the remaining 2 good relays both fail. Again check all fuses....they are fine.

Test the FP relay connections in the under hood fuse box. Have constant power and ground to the 2 appropriate terminals. Test for 2 second prime when ignition is keyed shows that terminal is energizing properly.

When I remove the FP relay and jump terminals 30 and 87 the truck starts and runs fine.

So I know that has been pretty long winded but I have read a ton of threads and want to make sure I provide as much detailed info as I can.

Now I humbly ask for your knowledge and input to help make the proper and necessary repairs! What would cause this symptom? Truck starts and runs fine with fuel pump relay removed and jumper wire from terminal 30 to 87 but not with a know good FP relay installed. I tested the relays for click sound when power and ground applied to 30/86 and I get 0 Ohms on the multi meter when I probe 87 and 85

I plan to disconnect battery and remove the under hood fuse panel and inspect it.
I will be getting a hold of a code reader and posting those results.

I understand I also need to test the PCM and would appreciate any insight on that subject!

So based on all that, THANKS IN ADVANCE!!! for any suggestions and advice! Mahalos!

· Registered
96 Posts
Sounds like you're on the right path!

I agree; pull codes ASAP and let the computer give you a hand. At this point it looks like you have it nailed down, but there also might be another system affecting it that the codes might point to.

As for the Relay, you say you know it's good, but might not handle the current? Probably not the case, but keep it in mind. As for the jumper working but not the new relay, you might have intermittent connections between the relay and the fuse panel. The panel is fairly easy to remove, so I'd give it a good look over and check all of the connections for rust/corrosion and physical fit. The jumper might have been making the connection better than when the relay was inserted.

Give those a try, keep us updated, and good luck!


· Registered
3 Posts
Discussion Starter · #3 ·
Good day! Thanks for the reply Epyon!

Got a hold of a code reader, but a bit doubtful it will lead me to the trouble.....
Pulled 4 codes:

P0157 Both are O2 sensor codes unlikely effecting the fuel pump
P0446 pd (pending)
P0446 EVAP Evaporative Emmission Control System Vent Control Circuit
So this makes sense....easily could have damaged a vacuum line or could be from filling tank with motor running ( we never do that in AK :mrgreen: )
But again, does not look like anything on that EVAP circuit would cause the problem I am having.......
I will be inspecting the under hood fuse block and tracing wires looking for anything causing intermittent issues...As Epyon remarked, there seems to be a strong likelihood this is a short or open circuit.

Been searching googler but having ahard time finding solid info on the PCM location or testing procedures.....If anyone has any links on this subject may I ask you to please share them!
Again, starts and runs fine w jumper wire instead of FP relay
Testing w test light at relay coonection shows constant power and ground as well as 2 second prime upon ignition being keyed....
With the relay in place, the fuel pump never fires at all, even for the 2 second prime.

Thanks again! I'm doing my best to stay positive!

· Registered
3 Posts
Discussion Starter · #4 ·
As it warmed into the teens today, I decided I better motivate and deal with this problem.

I pondered on Epyon's comments as well of advice from a friend with a past similar issue and decided K.I.S.S. :shock:

I don't mind repairing things but I think I speak for a lot of folks who just kind of cringe at deep electrical troubleshooting

So I had an extremely delicious dab of a Girl Scout Cookies variety......waited a few minutes and had another.......finally ready to track this nightmare down.....

Well it did not take long to indeed identify the of the Fuel Pump relay connectors in the under hood fuse block had become slightly compromised, undoubtedly when forcing in the test light probe or multi-meter probe during my previous troubleshooting prior to the Fuel Pump replacement.....Ahhhhh K.I.S.S.!

So the problem is now resolved, truck running fine......Thanks for giving me a place to talk it out, and thanks for the encouragement Epyon!

Does anyone know how to remove the "change engine oil" indicator that is flashing prematurely?
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