Variable Valve Timing Woes

[Steevo]

I had a MIL going on and off on my Envoy XL with the 4.2 6 cyl engine a couple years ago.

The code was P0014. Exhaust Camshaft Over Advanced.

I changed the CPAS with a new GM part, and the problem seemed to subside. Light went out. The old one had signs of sludge on it when replaced.

Then the code returned.
I added a quart of Rislone in case the problem was engine sludge related. I left that in for one oil change cycle.
The problem seemed to subside again.

The Malfunction Indicator Light would occasionally come on, I pulled the codes and the were always that same code.
I never noted any running problems, in fact the only difference was the DIC would report dramatically better mileage when the light was on.
I liked the gas mileage increase!

For the next several oil changes I followed the same procedure, the next change I added a quart of Marvel Mystery Oil, and the next I added a can of Sea Foam. Trying different things to scavenge sludge

I received occasional MIL indications, and then it would go off on it's own.
For quite a while I didn't see any problems at all, maybe for 8 or 9 months.

Then last week things changed. I noticed a slight stumble at idle, and later that day I got a misfire and a blinking MIL. It went away and then got worse. I pulled the code, same one.

I took out and cleaned the CPAS with Carb cleaner. It wasn't too dirty but I cleaned it and put it back in.

The misfire reoccurred.

Yesterday, I did an old school engine flush procedure, dumped the oil and added ATF and let it run at idle for 1 1/2 hour, then changed the oil and filter.

I still have a slight rough running at idle. It stumbled but didn't die at a stop light last night.

No codes were there today, I just checked. The stumble and near stopping didn't store a code.

I am going to throw another CPAS at it this afternoon to see if that solves the problem.

I changed the spark plugs 3 months ago, I used the Bosch Platinum plugs.

Does anyone have any ideas to troubleshoot this problem?

 

[dfc739]

I'm surprised no one has said this yet, but these engines ONLY like the AC Delco 41-103 Iridium spark plugs. Anything else has been known to cause issues.

What code did you pull for the misfire?

A malfunctioning camshaft position sensor can also cause a stumble. When it's acting up trying unplugging it to see if it changes.

 

[Mooseman]

Definitely try replacing the camshaft position sensor. Hope that fixes it because the only thing left is the camshaft phaser itself, which means opening the top of the engine. I had to replace it couple years ago. No trouble since.

 

[Steevo]

I'm surprised no one has said this yet, but these engines ONLY like the AC Delco 41-103 Iridium spark plugs. Anything else has been known to cause issues.

What code did you pull for the misfire?

A malfunctioning camshaft position sensor can also cause a stumble. When it's acting up trying unplugging it to see if it changes.

P0300 for the misfire. Normal.

P0340 and P0014

The P0014 I have had off and on for a couple years but no running problems. Just the light and the code like I mentioned.
It just now started causing problems.

The P0340 is camshaft position sensor. But I think that is caused by an actual misposition caused by the part I changed today. I hope that improves with the new CPAS.

As to those Bosch plugs, they have been in there two or three months.
Could that really be a problem?

I did change the CPAS today- an hour ago, I haven't tested thoroughly yet. That's tomorrow.

 

[triz]

Did you clean all the oil off the connector?

 

[Steevo]

Did you clean all the oil off the connector?

It's not leaking so I don't think there is an oil problem. The original part that I changed a couple years ago was and had oil on it.

I'll take a look tomorrow.

I know the lock is broken. What a PITA.

 

[triz]

It's not leaking so I don't think there is an oil problem. The original part that I changed a couple years ago was and had oil on it.

I'll take a look tomorrow.

I know the lock is broken. What a PITA.

Ah ok. I thought it was recent as when I changed mine the connector was full of oil. I was just wondering if you cleaned the connector before installing the new one.

 

[Steevo]

Since I put the new CPAS in yesterday the misfire and stalling has not reoccurred. No MIL and no codes.

The slight rough running is still there.

The Bosch spark plugs have been in about 8 months, unlikely to be the problem but it feels ever so slightly funny, so that is next unless someone else has an idea.

 

[triz]

Since I put the new CPAS in yesterday the misfire and stalling has not reoccurred. No MIL and no codes.

The slight rough running is still there.

The Bosch spark plugs have been in about 8 months, unlikely to be the problem but it feels ever so slightly funny, so that is next unless someone else has an idea.

You would be surprised how picky this car is with parts. I would do plugs and the clean the TB.

 

[Steevo]

The saga continues.

Since last post I got a bad misfire, blinking MIL. I looked at the codes, P300, a generic misfire.
Not too helpful.

Finally I got a P304. Cylinder 4 misfire.
I got a coil and changed the coil on cylinder 4.
That might have been giving little failure warnings for 2 years.
The bad misfire went away, completely.

Then I got a P340, so I changed the camshaft position sensor.
That subsided, no further MIL or codes.

However, there is a vague loss of power, vague but noticeable.
And a very slight rough running. That kind of goes together.

I suspect another failing coil.
But I have not changed out the Bosch plugs that have been in there four months.
I did buy the recommended plugs.

But the problem is not bad enough to store a code so I cannot find out which coil is the problem.
Waiting for it to fail completely like the #4 is not a good solution.

I am thinking of finding someone with a scope to check for spark, see if that gives a clue and I can throw another coil at it.

Does anyone have any ideas as to steps to isolate this problem?

 

[BRomanJr]

The saga continues.

Since last post I got a bad misfire, blinking MIL. I looked at the codes, P300, a generic misfire.
Not too helpful.

Finally I got a P304. Cylinder 4 misfire.
I got a coil and changed the coil on cylinder 4.
That might have been giving little failure warnings for 2 years.
The bad misfire went away, completely.

Then I got a P340, so I changed the camshaft position sensor.
That subsided, no further MIL or codes.

However, there is a vague loss of power, vague but noticeable.
And a very slight rough running. That kind of goes together.

I suspect another failing coil.
But I have not changed out the Bosch plugs that have been in there four months.
I did buy the recommended plugs.

But the problem is not bad enough to store a code so I cannot find out which coil is the problem.
Waiting for it to fail completely like the #4 is not a good solution.

I am thinking of finding someone with a scope to check for spark, see if that gives a clue and I can throw another coil at it.

Does anyone have any ideas as to steps to isolate this problem?

Since you have the correct plugs put them in, I agree these engines are picky on plugs.

 

[Don37725]

I am thinking of finding someone with a scope to check for spark, see if that gives a clue and I can throw another coil at it.

Does anyone have any ideas as to steps to isolate this problem?

Buy a diagnostic program that works with a laptop or your smart phone - I bought an inexpensive $24 one from Amazon - ScanTool 423001 ElmScan 5 Compact OBD-II Scan Tool and OBDwiz Diagnostic Software - when I had a misfire I was able to see which cylinder it was - it showed the number of misfires for the problem cylinder.

And put the correct AC Delco plugs in. Bosch makes good plugs - I use them in my Jetskis because that is what the manufacturer recommends - I use AC Delco in my TB and Envoy for the same reason.

 

[Steevo]

Buy a diagnostic program that works with a laptop or your smart phone - I bought an inexpensive $24 one from Amazon - ScanTool 423001 ElmScan 5 Compact OBD-II Scan Tool and OBDwiz Diagnostic Software - when I had a misfire I was able to see which cylinder it was - it showed the number of misfires for the problem cylinder.

And put the correct AC Delco plugs in. Bosch makes good plugs - I use them in my Jetskis because that is what the manufacturer recommends - I use AC Delco in my TB and Envoy for the same reason.

I have a code scanner, there are no stored codes to read.
I have a friend who has a professional level thing like that on his laptop, and we did connect it.
There is nothing.

I may just change the plugs.

 

[kctrailblazer]

run the vehicle and disconnect the wire harness for the #4 coil and see if the vehicle runs worse..if there is no change then its probably a bad coil..before replacing the coil switch it with the #3 and and pull the harness if it gets worse then you know its the coil and not a harness issue.