6.0 Knock/misfire, NOT PISTION SLAP!

**Sayety** · 11-19-2008, 05:26 PM

Hello everyone I am new to the site but did search this topic before posting a Q.

My problem is this: (fyi the truck is a 2000 2500LD with the 6.0, 125K on the clock)

I was towing my camping trailer (about 6000#) to the storage building today when (going up a steep grade) I the motor started to knock. It was definatly the top end of the motor...sounded like valves knocking from cheap gas. i eased up a bit and it quited down somewhat. When i got to the top the service engine light started flashing (i assume that indicates a misfire) Pulled off the road, shut the motor off and restarted...NO NOISE NO LIGHT. the next hill same thing. Got the camper to the storage lot and came home....NOT A SOUND or LIGHT the whole way home. Get home put it on my OBD2 computer NO CODES! I don't know where to start to troubleshoot a problem like this....if i can't get it to knock then i can't fix it. I don't know how much it has to do wiht the issue but this is the first i have towed (anything heavy) in such cold weather before, about 20F.

Fuel related?
Temp related?
OR bigger problems?
any advice, help or sugustions are very welcome.

**EagleTalons** · 11-19-2008, 06:06 PM

Which octane grade are you using?

**Sayety** · 11-19-2008, 06:11 PM

Originally Posted by EagleTalons

Which octane grade are you using?

89...same as always. I towed 10K miles this summer on 89 without issue. However that was wiht summer blend gas...could winter be THAT different?

**04sierracrewcab** · 11-19-2008, 07:04 PM

welcome!

hopefully we can help you resolve this!

to me it dosent sound like anything to do w fuel .. esp if i didnt do it on the way home

**EagleTalons** · 11-19-2008, 07:40 PM

Well, with an older VW engine if you are using too low of octane and are climbing a hill it will detonate.

**CoolBlueSS** · 11-20-2008, 01:01 PM

You were putting alot more strain on it than you usually do. UIt might have just been a fluke. Bad tank of gas, sensor freak out, ect. I'd keep an eye/ear on it for a while, though.

**vncj96** · 11-20-2008, 01:31 PM

distributer (coil packs), wires and plugs check em all out

**Sayety** · 11-20-2008, 09:23 PM

I was able to get it to misfire with the OBD computer hooked up. It was the #7 cyl. I took the plug out and the electrode was completely gone. replaced with a new plug and the computer was still showing a misfire, though it was running much smoother. I swaped the coil pack with one from another cyl and then the computer showed no more misfire.

Hopfully this is the end of the problem....Or perhaps the electrode got blasted because of antifreeze in the cyl? Time will tell...

**EagleTalons** · 11-21-2008, 12:00 AM

Wow! Good thing you found that out though!

**dogger** · 11-28-2008, 11:04 PM

one problem that # 7 has is the injector being at the end of the fuel rail get junk built up in it and starts clogging the injector and that can cause the problem. if it comes back see about swapping the injector's and see if the problem goes away or moves. #1 #7 #2 #8 all can get junk built up in them. the problem doesn't have to be constant either I chased the same problem down one time for 2 weeks because it came and went. btw how often do you change your fuel filter? gm put out a service notice to change filter's ever 30k because of this problem and I think owners manual say's every 60k.