Gear selector silly question

[Dariusz Salomon]

That sounds like a fuel pump issue....or the electrical circuit for it.

That is my first culprit-circuit-will look closer into it on saturday. But I just wanna maje sure I'm not missing something-I couldn't 100% say i.e"there's no power from ecm" if,let's say shifter was also responsible by design for preventing power to get to relay-I hope it makes sense what I'm trying to say. So now that I know shifter stops cranking if it's not P or N I know it has nothing to do with the pump. I will look at other reasons.

 

[Dariusz Salomon]

My 1999 'Burb won't crank if in anything other than P or N.
Cranking but no start is unlikely to be selector IMO.

What are you basing your 'pump not priming' diagnosis on - lack of sound (where you can normally hear it - unlike my 'Burb where the tank is so far back)? If so, thoroughly check the wiring. On mine, the pump had been replaced and the pigtail was connected poorly with crimps. From memory, your Tahoe has the tank forward of the axle - but the same could have happened.

The other thing that caused me no-starts was a stuck fuel pressure regulator. When we run on LPG the FPR will be wide open returning all the petrol to the tank. That I think makes them prone to sticking wide open and negating the pump's ability to hold pressure for starting (though it'd be useful to know if the prime is stopped after X amount of time or when pressure has built). You can check this by turning the key to prime then depressing the pintle in the pressure test port. If there's a dribble there then the pump took fuel up from the tank. Repeat to check.

NB a healthy pump and FPR will squirt fuel from there and it will land on the dizzy - do not attempt with a hot engine or attempt a start if this happens.
No fuel whatsoever - not even a dribble - says pump not engaging.

Yeah-on sound and the fact it then refuses to start. The pump always primes the moment I turn the key when I first start it on the day.
I do think it's electrical and it happens with no warning-recently I was to go tp the friend's garage to replace radiator and those AN oil lines-she wouldn't start day before. Then,on the day, my wife went to started(cause she got in her head the truck likes her and will start for her) and,of course,she started. She would work all day as needed-start everytime-took me home. Following day I though"gotta test those new lines-se if there are any leaks,top up coolant if necessary". Zip-zero-"no sir,I don't feel like going nowhere"-and she ain't started since. Saturday gonna be my first day off after 4 days of 12 hrs shifts so I'll have time to play-we meant to go to a car show on sunday,but it may not materialise. And my tank is full-will have to buy some 20 l jerry cans and drop that fuel to drop the tank too. Joy.

 

[Dariusz Salomon]

Hook up a fuel pressure gauge and check for pressure when it cranks, but not fire up.

I don't have any-will have to get some.

 

[stutaeng]

Absolutely will need a pressure guage. I feel like it needs to be a standard item that should come with any gmt400 purchase...

Check fuel pressure first. If you don't have any pressure, then look into electrical side. Also, double check your pressure guage to make it's good. Check for power at the pump connection, continuity, relay, etc.

No sense looking into ECU if pump is dead (or intermittently failing), power wire broken or corroded, etc.

Let us know how it goes.

 

[Pinger]

For this, you can get a good enough idea of what's going on just by pressing the pintle on the test port.

Yeah-on sound and the fact it then refuses to start. The pump always primes the moment I turn the key when I first start it on the day.
I do think it's electrical and it happens with no warning-recently I was to go tp the friend's garage to replace radiator and those AN oil lines-she wouldn't start day before. Then,on the day, my wife went to started(cause she got in her head the truck likes her and will start for her) and,of course,she started. She would work all day as needed-start everytime-took me home.

Mine was like that when the FPR was sticking. I'm just wondering if a pump working (or really not working very hard) against an open FPR would still be as audible as you expect?
Bear in mind you can 'jump' all the circuitry and feed 12V directly to the pump at the fuse box (the one in the engine bay). See Haynes wiring diag as to which connections to bridge. You can also put a MM across that connection and earth and check for open or short circuit in wiring and/or pump.

And my tank is full-will have to buy some 20 l jerry cans and drop that fuel to drop the tank too. Joy.

When I had the sticky FPR and the dodgy wire my tank was around 1/4 to 1/2 full and I was loathe to drop it. That resistance though helped me find the real problems. That and an invoice for a recently fitted new pump!

 

[Cadillac Bob]

Yup them gear shifters get slop after yrs of use and setting your hand on them as you switch radio stations lol but you should know what gear it’s in due to position over time of driving and knowing your vehicle

 

[someotherguy]

Pump not priming sometimes-old story. It gotten more serious recently. Result is crank not start. I'm trying to understand all ways affecting that kind of fault and eliminate one by one before I tear into the pump and pigtail. But also I'd like to know more.

Small block Vortec notorious for not starting when fuel pressure is even marginally low. This is why your #1 go-to here is a fuel pressure test. Spec is 58~62 psi; if it's down into the mid or low 50's that is low enough to make many of these trucks not start reliably. Suspects will be filter, pump, injectors ("spider"), or regulator.

Richard

 

[HotWheelsBurban]

Small block Vortec notorious for not starting when fuel pressure is even marginally low. This is why your #1 go-to here is a fuel pressure test. Spec is 58~62 psi; if it's down into the mid or low 50's that is low enough to make many of these trucks not start reliably. Suspects will be filter, pump, injectors ("spider"), or regulator.

Richard

Mine, if it sits a while, or overnight, starts faster if we prime it a few seconds. I'm sure the injection parts are all original, at 211K. We bought the truck with 130K on it and I haven't replaced anything up there.....
Most of the hot slow crank issues it was having got fixed with the new starter and battery. Amazes me how it decided to quit, right there in the shop!

 

[Dariusz Salomon]

For this, you can get a good enough idea of what's going on just by pressing the pintle on the test port.

Mine was like that when the FPR was sticking. I'm just wondering if a pump working (or really not working very hard) against an open FPR would still be as audible as you expect?
Bear in mind you can 'jump' all the circuitry and feed 12V directly to the pump at the fuse box (the one in the engine bay). See Haynes wiring diag as to which connections to bridge. You can also put a MM across that connection and earth and check for open or short circuit in wiring and/or pump.

When I had the sticky FPR and the dodgy wire my tank was around 1/4 to 1/2 full and I was loathe to drop it. That resistance though helped me find the real problems. That and an invoice for a recently fitted new pump!

I jumped it temporarily the other time,whenit did that-and the pump did work. So I think either control(I spliced the killswitch into the wire-maybe it corroded) or pump is getting "stuck" somehow?

 

[Dariusz Salomon]

Absolutely will need a pressure guage. I feel like it needs to be a standard item that should come with any gmt400 purchase...

Check fuel pressure first. If you don't have any pressure, then look into electrical side. Also, double check your pressure guage to make it's good. Check for power at the pump connection, continuity, relay, etc.

No sense looking into ECU if pump is dead (or intermittently failing), power wire broken or corroded, etc.

Let us know how it goes.

I tried again ti start her up-to no avail. I cranked her around 7-8 seconds and nada. Imma get my hands dirty tomorrow.