88 GMC K2500 Stalling Problem

Sure sounds pumpish to me. Had an 88 S-10 that had so little left by the time we got it home from 300 miles - that it barely moved - we definately had to avoid hills the last 20 miles or so. Do you run with less than 1/4 tank? Even though the return gas is supposed to wash over the pump, it's definately better cooled when over

1/4 tank full. Elliott

Tim Duerst wrote:

do you have any DTC?

-Bret

Bret,

Can you tell me what's DTC.....? Sorry to be ignorant.

He's referring to "Detected Trouble Codes" from your truck's computer. Usually they also set the Ceck Engine Soon light on the dash - but I think there are a few that don't. Some AutoZone's (not Advanced Auto) will read them for you, or any shop - though careful w/ the price it's a

15 m>

diagnostic trouble codes... on an 88 they'll be 2 digit codes that you get by connecting two pins (can't remember which off hand) on the ALDL connector and counting the flashing check engine light.

they're very helpful.

Bret

Thanks, will the procedure be in manuals like Chilton and so forth? or is there a tester that I could get? In the mean time would you even hazard a guess?

Thanks, Tim

Tim,

Sorry I wasn't paying attention to the year (pre 96 you can read without a special reader). The OBD1 diagnostic connector is by your knees in the driver seat. Pin A is ground and pin 5 is the Diagnostic terminal. I think these are usually the top right of the connector, unless it's mounted upsidedown (look for the tabs and key I depicted with the | and the _ characters): | F E D C B A _G H M_

And FYI the pins are: A = Ground B = Diagnostic Terminal C = AIR (if used) D = Check Engine light (if used) E = Serial data (requires a reader) F = TCC (if used) G = Fuel Pump (if used) H = Brake Sense speed input M = Serial Data (4 cyl only, requires a reader)

So to read your DTCs, put a paper-clip or some sort of jumper between pins A and B. Turn on the ignition and count the flashes. For example, a 42 would blink 4 fast, pause a moment and then blink

2 times. The sequence will begin and end with a 12. Each code repeats itself 3 times - so be patient.

You can report your codes back to the NG and posters here will tell you what they mean. You can also search on "OBD" and "Chevy" and you will find lots of info. For example:

Elliott

Tim Duerst wrote:

No, do NOT start the truck with the ALDL port grounded! A few more questions...............

1) Will it do this forever (start, stall) or does it eventually resolve and let you get moving? 2) When you tweak the skinny pedal, in neutral, do the revs come up smoothly or is it sluggish/rough 3) Manifold vacuum (in/hg) at idle in neutral? Manifold vacuum at 2,500-3,000 rpm in neutral?

Doc

Hi,

Thanks for the info, it worked well but, all it flashes is the number 12. Am I suppose to start the truck? All I did was turn the ignition on.

Tim

1: I think it's your EGR valve. 2: Starting the truck like that is generally considered a BAD thing. I have heard that it should NEVER be done, and I have also been told that it can. If your not getting any codes now though, then you wont get any if you start it. Even then, a fuel pump wont throw codes. 1A: If/when it was running JUST before this (I'm assuming it had a period of degradation) did it run just fine on the highway, but poor at low speeds and plain rotten at idle? If so have you checked your EGR valve for operation? If it gets stuck open (these might as well have been designed to get stuck open) then the exhaust gases being introduced into the engine will cause it to stumble at idle. It's a super simple R&R if that is the problem.

~KJ~

Hi,

Thanks, I figured ignition on meant what it said but, I'm new to this kind of troubleshooting and had to ask.

yes, forever when I put it in drive and apply the gas it dies after moving a short distance (5-10 ft).

You'll have to let me know what the skinny pedal is. It is smooth in neutral when I rev it though. It forever has idled rough until it warmed up. I kinda excepted it ( the rough idle )with what I've read in here over the years.

I'll have to get a gauge to test that. What should I see there for a range?

Thanks for everybody's help so far.

Tim

die like the ignition is switched or, a rough, stumbly kind of stall?

my 88 idles smooth until the engine warms up enough to let the EGR valve leak.... (that damn thing keeps getting pushed back on the to-do list)

the skinny pedal is the gas pedal.

an engine in good condition wil have a steady needle at around 17 in/mg at idle. go to a parts store and pick up a haynes manual for your truck, they have a decent section on using a vacuum guage to troubleshoot.

-Bret

Ah, skinny pedal kinda ...makes ...sense now LOL!

Like the ignition is switched off.

Tim

Tim, You say it dies like you shut off the key. Does it also do it in reverse or just drive? Does it also do it if you put it in drive and hold the brake? How about if you hold the brake and give it some throttle? From the description I'd almost think it was a problem with the wiring going to the ignition system from the firewall. Like a loose connection or a wire that is grounding out when you put it in gear. Does this vehicle have an security system?

You can ground the terminal after its running to put it into field service mode, I dont know when that was discontinued though.

Exactly, grounding it once it's running is ok, cranking it and running it when grounded is bad news.

Doc

>

You haven't noticed any 'effects' you say? It runs like absolute shit and you haven't noticed any ill effects? Bwahahahahaha. You passed up the opportunity to benefit from my knowledge LONG ago dear boy..............

Doc