5.7 Vortec missfire issues

[CKVortec]

My bad. Just had an issue like this on mine and I think the guy who swapped my injectors crossed 2 legs to the wrong cylinder

that's interesting, because my Snapon Solus scanner troubleshooting tips mentioned exactly that for "misfire under light load" and that is why I pulled the upper intake. all injector locations checked out so while i was in that far I decided to swap the whole assembly with a used spare I had on the shelf.

 

[geeeee89]

CMP offset. I had the exact issue. Mine ran perfectly aside from a miss/stumble at around 2300-2500 rpm. Lower and higher than that was perfect but it would hesitate while revving through that range. I was getting a sporadic CEL for “random cylinder misfire”

Give this thread a read.

https://www.gm-trucks.com/forums/to...s-with-98-yukon/?tab=comments#comment-2400209

I used the exact method as described using A Bluetooth OBD reader and the DashCommand app and paid for the extra reading as the guy described in that thread. Used that to read the engine data while adjusting the distributor. Mine was at over 11 degrees when it should be as close to 0 as possible. I was able to get it to -0.2 and it runs like a top now.

your snap-on scanner should be able to read this I would think.

 

[geeeee89]

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[Aarong23]

I skimmed over this, so I apologize if this has been asked or done already. Have you tried the distributor itself? On both of my 400s, they both developed a wonky misfire. Changed plugs, wires, cap, egr, etc. Didn't do anything. Had it hooked up to a really high end scanner and it showed the misfire was coming from all cylinders at different times. Changed the distributor and ran like a Rolex watch after that.

 

[CKVortec]

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Here are some pics of my 2000 pickup and 1999 Suburban called Optimus Primer. one is the best plow truck in my neck of the woods and the other is the best winter road ripper that I've ever driven. Don't try to keep up with me in the winter... it won't turn out well.

 

[SUBURBAN5]

Awesome looking suburban

 

[HotWheelsBurban]

Cool looking trucks! I didn't know that Suburbans were available without dark tinted windows. You don't see them down south like that LOL.

 

[SUBURBAN5]

I think on the plan Jane wt base trim... if you had ls and lt. Think tints were standard

 

[CKVortec]

CMP offset. I had the exact issue. Mine ran perfectly aside from a miss/stumble at around 2300-2500 rpm. Lower and higher than that was perfect but it would hesitate while revving through that range. I was getting a sporadic CEL for “random cylinder misfire”

Give this thread a read.

https://www.gm-trucks.com/forums/to...s-with-98-yukon/?tab=comments#comment-2400209

I used the exact method as described using A Bluetooth OBD reader and the DashCommand app and paid for the extra reading as the guy described in that thread. Used that to read the engine data while adjusting the distributor. Mine was at over 11 degrees when it should be as close to 0 as possible. I was able to get it to -0.2 and it runs like a top now.

your snap-on scanner should be able to read this I would think.

Please read the original post before jumping to conclusions, the CMP is set dead on zero degrees. and, yes, the snap-on scanner works to set this. Also, this is the 3rd engine replacement I have performed on the exact same drivetrain and none of the others had any issue.

 

[CKVortec]

I think on the plan Jane wt base trim... if you had ls and lt. Think tints were standard

This used to belong to the Alaska Railroad, so it was a base model with no frills except some funky 19.5 inch wheels and tires and HUGE running boards. It also used to be School Bus Yellow, couldn't stand it!
It has come a long way from the $2500 eyesore that I bought years ago.