Hello all -

I have a '91 L98 and recently had knocking issues during low speeds under load - like up a hill. I took it to a friend of my father's who is an expert mechanic- an hour and a half away - and they did a carbon treatment on the engine. The car ran like a top. However, a few weeks later, the knock returned along with a code 32. So the car went back. Long story short, they have chased this code by replacing the EGR soleniod, the EGR (twice), and the vacuum line to the EGR. The EGR ended up being the culprit. Seemed we were out of the woods but there was still a slight knock. We got a knock sensor code several months back so we figured, why not just go ahead and replace the knock sensor while we're at it? Done. Knock gone, ran great. So, my dad takes it out for a long test run, code 32 returns. They chase it again, no vaccum leaks, the EGR is operating like it should, there is no apparent reason this code should still be coming up. Just for the hell of it, they replaced the ECM - NO DICE!!!

We're beating our heads against the wall here. Any ideas? Like I said, I'm an hour and a half away from the car and with some cooler weather settling in around here, this is targa top off time - so I'd like the car back. I got to drive it on Saturday and it ran great, aside from the code 32. Any help would be greatly appreciated.

Thanks!

 

Do you have an aftermarket exhaust on the car? High flow exhaust
systems sometimes cause EGR issues. benny

 

DO the 91's have an egr temp switch?
I know they had them on the 86-89 cars but cant recall about the 90-91's.

They would throw false codes but not hurt anything.

Just suggesting in case it could be a possibility.Its been a long time since I worked on a 91.

 

benny - no, no aftermarket exhaust - all stock.
Aggravated4life - from what I've read and see in my FSM, 91's don't have the EGR switch.

Thx for the suggestions though!

 

The knocking is a symptom of insufficient EGR flow under load. The EGR is controlled by several inputs. For example, the park/neutral switch if misajusted or faulty can make the ECM think that the car is still in park thus no EGR flow is called for. The duty cycle is also calculated by inputs from the coolant temp., manifold temp, MAP and TPS. Since you have replaced the EGR and checked the vacuum lines it is possible that one of these items is preventing the ECM from sending the signal to the EGR thus knocking and Code 32. I would check each of these items to make sure that the ECM is getting the appropriate signal to turn on the EGR.

Hope this helps

 

Did you guys clear the codes correctly?
(Im assuming you did,but doesnt hurt to ask again)

Also,what is your base timing set at?Is your balancer and timing marks where they should be?Some of these balancers can slip with age and cause the base timing to be way off.

Thats a jump in the dark...see,alot of L98's dont hurt too much with the egr disabled.Im curious if your balancer could have slipped or you have too much timing going on,causing possible knock/ping.

Also,hows the plugs? Carbon treatment can foul them somewhat sometimes.

 

gmboileau - We know the park/neutral switch is okay as they've checked it. Not sure about the TPS or MAP - I'm going to send that to them. Thx for the suggestion!

Aggravated4life - we're set on the timing - they even played with it a bit prior to knock sensor replacement thinking that there was some wear. After we replaced that, the knock went away. They did find some odd marks in the cap showing that the spark was occuring just before the plate. That's corrected and a new distributor cap went on. They also pulled the plugs on Monday to check to make sure they weren't fouled and they were clean.

Thanks for the suggestions!