Fuel pressure & engine miss

[jpchris]

Have 95 Tahoe that has a slight miss when under a load in 2nd gear. Acts like it is starving for fuel. When hot, in starting runs for a little bit then dies, then :confused: takes several times before starting. Checked lift pump and is working fine. Dealer put new vacuum pump but has not taken care of this problem. Installed new injector pump a year ago.Occasionally check engine soon light comes on but when you give it fuel it goes off. Anyone else have this problem. Any suggestions.
jpchris@gdsys.net

[jimbo6.5]

i'ts probably your oil pressure switch, However you did describe starting and then dying which could also be a lift pump relay . first the relay
takes up the starting duties and then when the engine reaches oil pressure the relay passes the power to the oil pressure switch, I don't know how long it;s been for you and a oil pressure switch, but general motors suggest changing it with the lift pump. And really for the price it's worth the guessing game a relay is 10 or15 dol. and an oil pressure switch is only 20 bucks

[jpchris]

Originally posted by jimbo6.5:
i'ts probably your oil pressure switch, However you did describe starting and then dying which could also be a lift pump relay . first the relay
takes up the starting duties and then when the engine reaches oil pressure the relay passes the power to the oil pressure switch, I don't know how long it;s been for you and a oil pressure switch, but general motors suggest changing it with the lift pump. And really for the price it's worth the guessing game a relay is 10 or15 dol. and an oil pressure switch is only 20 bucks

[moondoggie]

Good Day!

Our '95 Sub was doing much the same recently; it would also stumble with WOT. I suspected the lift pump. As near as I can tell, the lift pump gets power two ways: through a relay (during cranking) or through the oil pressure switch/sender (during running). Here's what I did:

I have an old vacuum/pressure gauge, back from the days when folks used to analyze some engine problems with these. I connected a 3' hose between the vent port on the top of the fuel filter & this gauge. I then put the gauge where I can see it when I turn the key. I set the parking brake, put the truck in any position except park or neutral, & turn the key as though to crank the engine. This causes the lift pump to run, but the engine won't crank.

The second test was to shut off the key, put the truck in park, & start it.

On our Sub, I developed fuel pressure during cranking (1st test) & none during running (2nd test). I replaced the oil pressure switch/sender. Now I develop fuel pressure in both modes of operation. No more stalling after starting, no more stumbling on WOT.

This may not be what's wrong with your truck, but I can do these two tests quicker than I typed them out, so why not? If it doesn't help you, maybe someone else...

Blessings!

Brian Johnson, #5044

'82 6.2 1500 4X4 1/2T pickup, 4spd man w/ OD, bone stock, 335K+, "In Rust We Trust"
'89 6.2 4X4 1/2T pickup, bone stock, 145K+
'95 6.5TD 2500 4X4 heavy 3/4T pickup, Gear Vendors Aux. OD, 183K +
'95 6.5TD 1500 4X4 3/4T Suburban, Kennedy exhaust, 203K +

[Turbine Doc]

JP did you get this fixed, similar thing happened to me a recently changed <5000 mile fuel filter was the cause picked up some bad fuel somewhere, put in a new filter and problem was solved.