97 yukon 5.7 vortec

[Yukon78]

Started with mis under load. No check engine light or codes.changed fuel pump,filter then plugs,wires,distributor and cap,then coil,knock and cam,temp,thermostat sensors..then maf,egr valve,fuel pressure fine.no vacuum leaks yesterday lastly changed spider. Now runs ruff at idle and throwing misfire on cyl 7 and 02 sensors.checked for leak at spider is none..120000 miles well maintained. Grasping at straws at this point.

[barry G]

must have a ground thief.

Try cleaning, like heavy duty stuff form a truck stop. The whole engine bay, top of tranny, hard to reach places.

 

 

A good sign would be verifying fuel is at 20mpg or less..

a lean condition may have shredded dangerous oxides (interacts with electric functions). that is very rare for a gm.. but it does need to be thought of.

The 5.7 will blow headgasket at #7 before any other spot. Most smallblocks do. The vortec is a real good one however.

 

there is also a map sensor. if you have live data on a cheap obd2, you can verify all kinds of things.

look for stable idle vacuum reading etc.

[bronyaur]

Also make sure the cam retard is within +/- 2. It won't turn on the CEL until it's about +/- 15, so if you're just under that you'll experience a miss at highway speeds and sometimes under a load. If you changed out the distributor, you need to check this. Requires a pro scan tool.