89 Sierra 350 cutting out under load - HELP

[Cole K]

Okay so this truck is a k1500 with the 350 & 700r4. Truck for the longest time would have an occasional hiccup and cut out just once every blue moon. about a month ago it got really bad. Especially when overdrive kicks in, the whole truck shutters and cuts out (gets worse when you give it more gas) but will stay running. It also does it in the higher gears but not as badly. It also doesn't really do it with very light acceleration. I rebuilt the throttle body and that seemed to fix it for about a month. Just recently started doing it again really bad. I after quite a bit of research i decided i would replace the ICM, cap, and rotor. Got an expensive ICM. Didn't fix it, nothing changed. Any ideas or input is greatly appreciated! I need to get home for thanksgiving in a couple weeks & need this resolved!!

Additional info: When truck is cold, sometimes it will fire up but die immediately. Also when it is cold it runs like crap, coughing and sputtering. It clears up when truck is warm. Still can here an occasional cough at idle when warm but clears up about 98% Trans was rebuilt awhile ago, the shop had a difficult time getting overdrive to work and thought something was up with the computer. I think they by-passed something to get it to work. Not sure.

 

[RichLo]

Since it does it in neutral when cold you can probably rule out transmission issues

and Since it does it during times of high fuel consumption the worst (Cold startups and high load cruising) I would guess its fuel related. I would start by replacing the fuel filter. then if that doesn't work check fuel pressure

Also, are you sure its a 700r4 not a 4l60?

 

[jkeaton]

Also check for vacuum leaks.

 

[Gramps]

On an 89 there isn’t anything to do with overdrive or shifting that’s computer controlled. It’s all done by the detent cable off the throttle linkage. The only thing electronic in a 700r4 is the torque converter lockup.
That’s either controlled via a vacuum switch which is only supplied with voltage once a temp sensor reaches operating temp. But if there’s a vacuum leak, that probably won’t work well AND the engine will have issues running.

Otherwise it’s controlled by the ecm which will only allow it to activate the lockup once it’s up to temp and map sensor shows strong vacuum signal.


Start simple, check/replace plugs and wires. Look for a vacuum leak. (Check the egr valve to be either stuck open or blown) After that I’d check the idle air control motor or proper operation (and where it seats in the throttle body to be clean and unobstructed)

 

[Cole K]

I know for a fact its a 700r4. Truck has a new gas tank, sending unit, fuel pump, lines, and filter. Everything fuel related is new. Also has moderately new plugs and wires. Thanks for the replies everyone, i will check vacuum and the stuff gramps listed.

 

[Schurkey]

As usual, put a scan tool on the thing and see what the data stream is telling you.

Test fuel pressure. Test spark intensity--heavy load problems can be a weak ignition coil.

When my truck did about the same thing, it was the pickup coil in the distributor. Had a high-speed misfire that got progressively worse until it would occasionally die at idle.

 

[Cole K]

So i found that the EGR valve was shot. went ahead and replaced it, it still didnt change anything. Fuel pressure is fine, no vacuum leaks anywhere. Going to stop by orileys tomorrow and see if the scanner will say anything. More opinions would be great!

 

[jkeaton]

You have OBD1, you can pull the codes yourself with a paperclip. Oreillys most likely wont do that for you. Their scanners are usually for OBD2 vehicles.

 

[magimerlin]

You have OBD1, you can pull the codes yourself with a paperclip. Oreillys most likely wont do that for you. Their scanners are usually for OBD2 vehicles.

Our scanners will do obd1 aswell.. just gotta use the adapter plug..

The easiest way is with a paperclip or a short section of wire though.... weve all been doing that for years...lol..

Sent from my SAMSUNG-SM-G891A using Tapatalk

 

[jkeaton]

True, mine does both...just placing my bets that the kid behind the counter who tries to read the codes with an OBD2 scanner won't have a clue why the connectors are different....lol