1988 k1500 5.7 starts, but will only run if I pump the gas.

[7heGreatSloth]

Alright, got this 1988 K1500 5.7 from my father. It was sitting in a field in Idaho for a couple years. I put a new battery in it, and got it started. It would only stay running if I pumped the gas. I dropped it into drive and kept pumping, about 30 seconds later it throttled up and ran and drove perfect, idled perfect and I drove it 700 miles to colorado. I turned it off multiple times to get fuel, started and idled perfect and ran perfect every time.

I was almost home, a few exit ramps from mine it started bogging down. I pulled onto the next exit and it died. I did a roadside tune up (cap and rotor and plugs). I towed it home and have since been throwing parts at it. I've done both coolant temp sensors, both the oil pressure switch and sensor, a couple questionable vaccum lines, fuel filter, map sensor and replaced a frayed coolant temp sensor wire. Still doing the same thing, starts and only stays running while pumping the gas just like when it first started in Idaho.

I does show low oil pressure (hence the thought to replace the oil pressure sender and sensor), and it does backfire occasionally while pumping the gas. Figured I would post on here and see if anyone has any ideas on where to move on getting this thing running.

 

[7heGreatSloth]

Well damn.

 

[7heGreatSloth]

Anyone?

 

[jd33173]

Fuel pressure? May want to see what kind of fuel pressure you are getting, pump may not be happy anymore, it is 35 yrs old. And just like that, i am freaking old considering i graduated hs when our trucks rolled off the line..

 

[GoToGuy]

Since sat so long, how much grunge could be in the fuel tank? And your driving , pumping fuel has stirred it all up. Filled fuel filters, tank sock. Old tired fuel pump. Leaking degraded lines in fuel tank. Yep fuel pressure check . Did you download the free OE service manuals here in forum?

 

[Schurkey]

1988 K1500 5.7...
...have since been throwing parts at it.

Stop throwing parts, do real diagnosis.

Fuel pressure test, and connect a scan tool to verify EVERY sensor and computer output--spark advance, IAC position, EGR operation, etc.

Verify that the magnet on the distributor mainshaft is still intact. Cracked magnets are really common.

Cranking compression test would be a good idea.

 

[Erik the Awful]

A fuel pressure test is #1. If it's your fuel pump, don't even bother with a new TBI pump. Step right up and get the Vortec fuel pump. It's a perfect fit and far more capable.

 

[RichLo]

To me it sounds like a sticking IAC solenoid or plugged Idle passage.