'87 TBI lurching and surging

[TX87R10]

'87 R10 TBI. About 2 days ago I started feeling the truck seeming to misfire when not giving it gas but still in gear.

Yesterday it started "lurching" after it had been running for a bit. Starting up was fine, in gear it would feel like it was missing gas then it got a double shot of gas repeatedly. Truck has not died yet but it starts up good but after a few minutes starts running rough.

I changed spark plugs bc I found two that were not up to standard. I changed fuel filter and it was pretty gross. After changing both, no change in behavior. Still lurching and surging like it is starved for gas then someone hit the NOS (NAWS) button.

Going to check for leaks tomorrow but figured it might sound familiar to someone.

 

[Rickf]

Any backfiring through the exhaust?

 

[gmbellew]

I had a cracked torque converter control solenoid cause those symptoms once on my 1990 burb. but they only showed up after the converter locked once on a drive. I could drive around town fine as long as i never locked up. but if I locked the converter, it never fully unlocked and caused that when idling at a light.

 

[TX87R10]

Any backfiring through the exhaust?

None

 

[Frankenchevy]

I’d check injectors and fuel pump.

 

[TX87R10]

I’d check injectors and fuel pump.

I thought about the fuel pump but I have factory dual tanks and both were behaving this way. I haven't pulled the tanks before but each one should have it's own pump so I think I ruled that out.

I'll look up how to test the injectors

 

[fast 99]

Assume it isn't tossing codes otherwise you would mention it? Possible ignition missfire? Distributor caps are a problem on those, especially if any brand other than Delphi or GM is used, will crossfire within the cap. Check coil tower for corrosion. Another easy check is vacuum, if not steady mechanical areas should be looked at.

 

[TX87R10]

Assume it isn't tossing codes otherwise you would mention it? Possible ignition missfire? Distributor caps are a problem on those, especially if any brand other than Delphi or GM is used, will crossfire within the cap. Check coil tower for corrosion. Another easy check is vacuum, if not steady mechanical areas should be looked at.

Haven't seen any but I will check the codes again. I was thinking misfire but then after it happens I put it in park and sit there and the idle just climbs and climbs then drops and does it again. Just noticed that

 

[fast 99]

Grounds, excessive ac ripple try disconnecting alt, vacuum leaks. Could be more than 1 thing wrong.

 

[TX87R10]

I still haven't found the cause, checked all tubes all connections everything looks good.

In my annoyance I decided to drive it further to see if it would stall out. When I got home I realized the lights were dimming at the same time the lurching and surging was happening.

I parked and turned off the truck and the lights just kept going up and down. Definitely seems like alternator could be cause. It was really rainy today so going to check further tomorrow thanks everyone for the help and ideas

 

[TX87R10]

Grounds, excessive ac ripple try disconnecting alt, vacuum leaks. Could be more than 1 thing wrong.

It was ac ripple. Changed the alt and we are back in business.

Thanks again!

 

[fast 99]

It was ac ripple. Changed the alt and we are back in business.

Thanks again!

That bit me once really bad. Now I check it on every car with drivability issues. Very easy with a digital VM.

 

[TX87R10]

That bit me once really bad. Now I check it on every car with drivability issues. Very easy with a digital VM.

One if the problems was it would only happen in gear. I couldn't get it in gear and test or observe anything at the same time. Running a solo operation lol