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1988 Chevy k2500 does not shift at hiway speeds

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New User

Apr 20, 2021, 12:46 PM

Post #1 of 3 (377 views)
1988 Chevy k2500 does not shift at hiway speeds Sign In

i have the following:

1988 K 2500 chevy truck 4x4 350 cid (5.7L) engine w/tbi

the problems that has arisen are as follows:

1) error code 44
2) rough running and stalls out at low rpm's, when accelerating truck would stall or bog down
3) will not shift at hiway speeds (45 mph or higher) with gas pedal all the way to the floor
4) all emission controls has been removed by previous owner
5) truck started out with rough idle then progressed into stalling, rough driving no in town driving speeds will run great at idle now

here is what i have done so far:

A) replaced the only 02 sensor (upflow) in the lower exhaust
B) replaced the coolant temp sensor
C) replaced all exhaust manifold gaskets
D) replaced thermostat
E) replace entire ECM unit and replaced ECM chip also
F) replace steering column also

i have been to alot of these forums but this one so far seems to be quite accurte this truck is my work truck i live on SSI, i am a disabled vietnam vet, there is a local radio show on saturday mornings called under the hood, and they tell me my problem maybe not fuel pressure, but rather fuel flow of course they cannot tell me how to measure actual fuel flow.
i need this truck to be road worthy as it is i cannot even drive in a 45 mph zone my truck does shift at 18, 27 mph as she should but not over 45-47 mph

Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Apr 20, 2021, 2:12 PM

Post #2 of 3 (369 views)
Re: 1988 Chevy k2500 does not shift at hiway speeds Sign In

This is a fairly basic system without a lot of electronics.
Code 44 is a lean code

There can be quite a few causes for this

vacuum leak
Bad 0/2 sensor or related wiring
exhaust leak upstream of the 0/2 sensor
low fuel pressure
clogged/inop fuel injector
Bad MAP sensor or related wiring
water in the fuel
Bad TPS sensor
Bad engine ground


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

(This post was edited by Hammer Time on Apr 20, 2021, 2:15 PM)

Tom Greenleaf
Ultimate Carjunky / Moderator
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Apr 20, 2021, 3:14 PM

Post #3 of 3 (359 views)
Re: 1988 Chevy k2500 does not shift at hiway speeds Sign In

Open book for this. I didn't see "fuel filter" on your list? If water just replace it anyway - careful I think it's on frame 1/2 way tank to engine like most. Careful if flare nuts if corroded lines will twist up lots younger than this.

If you do it or another dump it from inlet end into a glass container look for water. Not so common with use of ethanol in most areas not all.

Vacuum leak? If that bad and getting worse you may have lousy power assist to brakes. If so that's much too low to tell most transmissions to upshift will think it's under a heavy load and run like crap to.

I'll save the novel if you don't know how to find vacuum leaks ask I describe ways with few tools IDK what you would take on or send out?


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