Truck/Engine Shudder

[Marcos Beltran]

I have a 95 chevy V6 TBI and for the last 7 or 8 months the truck would shudder when turning it off. Only happened every once in a while so it didnt bother me but now its occurring about once in every 5 times i turn off the truck. Its not motor or transmission mounts cause i replaced them a little less than a year ago. Anyone have/ had the same issues?

 

[Supercharged111]

I have a 95 chevy V6 TBI and for the last 7 or 8 months the truck would shudder when turning it off. Only happened every once in a while so it didnt bother me but now its occurring about once in every 5 times i turn off the truck. Its not motor or transmission mounts cause i replaced them a little less than a year ago. Anyone have/ had the same issues?

Are you talking about run on? As in, you turn the car off and it keeps going for a second or more.

 

[Marcos Beltran]

Are you talking about run on? As in, you turn the car off and it keeps going for a second or more.

Yes, at least thats what it seems like.

 

[Supercharged111]

Yes, at least thats what it seems like.

My guess is either 82 octane fuel or a carbon buildup on your pistons/combustion chambers driving up the compression ratio. Or really retarded timing.

 

[Marcos Beltran]

Timing is set at factory specs. Had to reset it cause i replaced the timing chain a little over month ago. How do you get rid of carbon build up, use one of those additives like seafoam.

 

[Schurkey]

Number One cause of run-on is that the idle speed is too high. Verify your idle speed, and therefore the IAC valve operation.

Lesser causes are as said--crap octane, carbon in the chambers, a wiring fault where turning off the key doesn't actually kill power to the ignition/fuel injectors, etc. Overall, I'm surprised that a fuel-injected engine can "run on".



When I want to clean carbon from combustion chambers, I drizzle a "urine stream" of plain ol' water down the throttle bores at ~2000 rpm.

Water does an AMAZING job of removing carbon via "steam cleaning". Dirt cheap, effective. Might want to change oil 'n' filter afterward, due to moisture contamination.

And it doesn't cause the neighbors to call the fire department like dropping Seafoam or Top Engine Cleaner down the throttles.

 

[Supercharged111]

And it doesn't cause the neighbors to call the fire department like dropping Seafoam or Top Engine Cleaner down the throttles.

Now where's the fun in that?

 

[Steve A]

Might check the fuel pressure regulator for deteriorated / leaking gaskets. I've seen the TBI regulator units leak fuel which runs down the throttle bore. Rebuild kits are available and a lot cheaper than a Throttle Body if that's the case.

 

[Marcos Beltran]

Might check the fuel pressure regulator for deteriorated / leaking gaskets. I've seen the TBI regulator units leak fuel which runs down the throttle bore. Rebuild kits are available and a lot cheaper than a Throttle Body if that's the case.

Rebuilt the TB less than 2 months ago. The truck runs really well, really smooth. Just took it for an hr trip one way this weekend and have no issues with it. Its just this thing of staying on a little after turning it off. Doesnt happen all the time. I also did a tune up 2 weeks ago ( cap, spark plus, wires) and it helped quite a bit but not completely gone. Gonna clean out the egr valve and see if that helps.

 

[Schurkey]

Number One cause of run-on is that the idle speed is too high. Verify your idle speed, and therefore the IAC valve operation.

Lesser causes are as said--crap octane, carbon in the chambers, a wiring fault where turning off the key doesn't actually kill power to the ignition/fuel injectors, etc. Overall, I'm surprised that a fuel-injected engine can "run on".

Its just this thing of staying on a little after turning it off. Doesnt happen all the time. I also did a tune up 2 weeks ago ( cap, spark plus, wires) and it helped quite a bit but not completely gone. Gonna clean out the egr valve and see if that helps.

Have you connected a scan tool to verify idle speed, and IAC operation?

Have you checked the injector fuses to verify that there's no power with the key off?