Intermittent Lift pump?

[tdsub]

I'm a new member with a question: can a lift pump quit and then work intermittently? My '98 Suburban (120K miles) wouldn't start after sitting a couple of weeks. We cracked an injector when cranking and got no fuel, so suspected the lift pump. Activated that with a code-reader and it started right up. Replaced the fuel pump relay just in case, but that wasn't it, since the next time it sat, it wouldn't start again. Here's the kicker--did nothing further but let it sit a couple of more weeks and then it started right up.

Should I replace the lift pump on the theory it's going bad but intermittently working? Thanks for any ideas. TOM

[Robyn]

If you can get it to "NOT" work then test to see if you have 12V to the LP at that time.

If no 12V then the issue is not the LP but another problem.

The LP should run upon activating the key switch to the start position and then run full time once the engine makes oil pressure.

The Oil pressure switch could be shot too.
The 98 has the LP controlled by the ECM rather then the OPS as in earlier years but the OPS still needs to send a signal before the LP will run after engine startup.

With no start its likely a bad LP especially if its the original.

Check these things out and keep us posted.

OH BTW Welcome to TDP :D:):D

Missy Robyn

[tdsub]

Thank you very much for the advice. I've been out of town and, wouldn't you know, after sitting another 2 weeks it starts right up with one turn of the key (after glowing). Does the ECM you refer to act intermittent when gonig bad? If I can't get it to NOT start, I guess I could just replace everything: LP, ECM, OPS, but that seems excessive. I'm thinking the OPS is probably the least likely culprit, since once it starts, it always runs well. TOM

[simon]

Thank you very much for the advice. I've been out of town and, wouldn't you know, after sitting another 2 weeks it starts right up with one turn of the key (after glowing). Does the ECM you refer to act intermittent when gonig bad? If I can't get it to NOT start, I guess I could just replace everything: LP, ECM, OPS, but that seems excessive. I'm thinking the OPS is probably the least likely culprit, since once it starts, it always runs well. TOMA good idea would be to install a electric or mechanical fuel gauge in the T valve hose and run it in the cab,+ a toggle switch to bypass the OPS.This will let you monitor fuel pressure,and the bypass switch helps you diagnose a bad LP, OPS,or exessive vac/plugged sock in the tank. in case of a failing OPS the switch lets you get home,if you have one of these critters that wont run without a working LP(most do).

In a no start situation,check for 12v at the fuel shuttoff solenoid.
It might be the ignition switch is failing.(worn contacts).Wriggeling the wiring harnass under the steering collom will often restore power.

I would also check/clean the engine grounds on the rear pass side head as well.