Massive hesitation when turning left?

[sciphi]

This one has me thoroughly stumped. My Buick with its 3800 Series II V6 and 4T65 transmission has a massive hesitation when turning left. I have a ScanGauge II hooked up for real-time scanning, and the PCM is interpreting whatever's going on as knock. This results in 15-20* of timing being pulled, with the resultant drop in performance.

I've noticed this happens most repeatably and predictably when turning left at a sharp angle and accelerating from a stop/walking speed after the car has been sitting/inching forward for 5-10 seconds. Accelerating forward a little bit and then turning left does not result in the same loss of timing.

Any ideas what could be causing this?

 

[Eddie]

Knock sensor wire shorting out due to engine torque in a left hand turn?

 

[sciphi]

It's entirely possible. What should I be looking for to test that?

 

[mechtech2]

My first guess is fuel.
The pickup situation in the tank is causing it to suck air, or block off flow somehow.
But a loose motor mount may cause enough movement to short a wire or pull on a connection.

 

[Trav]

IIRC the knock sensors are located in the block coolant drains.

 

[eljefino]

I like the motor mount idea, but that it's bottoming out and something is causing the motor to vibrate oddly.

Bummer that it allows pulling that much timing. Were they expecting you to run the thing on kerosene?

If you have bad valve seals and are burning a little oil when the vacuum changes, and the oil is sloshing around in the head to get by those seals, that burning oil will cut your fuel octane.

 

[sciphi]

The fuel pump and fuel pressure regulator are less than 3 years old. The fuel filter was replaced last fall. I still could be lacking fuel pressure, since I don't have a fuel pressure tester.

The front and rear motor mounts are new. The side mounts are original.

 

[IndyIan]

Air leak maybe? If the air filter is on the body, the acordian section can get a tear that opens with engine movement.

 

[onion]

I agree that it sounds like a knock sensor wire is grounding out inermittantly- and that's something you won't likely find by checking with a meter. Personally I would find the knock sensors and check over the wiring harnesses... see if you can see a rubbed through, burned, or corroded area in the wiring.

And I suppose it's possible that one of the sensors could be bad internally. Try disconnecting them one at a time and see if the problem goes away. If so, then carefully inspect the wiring on that side. If the wiring looks ok, try replacing that sensor.

 

[sciphi]

I just moved the car around. I tried to get it to do it with a coldish engine, and couldn't. It did display 3* of knock turning left when the engine temperature was 145*F. It pulls a lot more timing when the engine is hot and after driving a few minutes than when it's cold.

 

[mechtech2]

Originally Posted By: IndyIan
Air leak maybe? If the air filter is on the body, the acordian section can get a tear that opens with engine movement.


also good

 

[sciphi]

Update: found the rear knock sensor wire soaked in leaking antifreeze and loose from a broken bracket. It got cleaned up, secured away from future leaks, a soaked ground point nearby dried off, and the antifreeze leak (leaking heater hose connection) fixed. I'll see what this does.

One motor mount had shifted, so it got tightened down. I'll check the others for movement once the weather improves.

And totally irrelevant, but since the tools were out anyways the oil got changed.