TerryKing
Newbie
Hi,
I've been chasing this for months... 92 GMC Yukon with 180,000 or so. Vermont. Chassis rust. Developed these symptoms about a year ago:
- Stumbles (irregular miss) at idle. Every second or two. ONLY when warmed up.
- Missing at more than 1/2 throttle, again mostly when warmed and especially after heavy loading like towing.
AND it was the same AFTER a new GM Crate motor and transmission.. so it was problems with the original TBI, Ignition etc..
CODES: High voltage on Coolant Sensor, High voltage on MAP sensor. Replaced sensors; same codes.
Finally got serious about GROUNDS.
- Added heavy copper braid cable from Engine block at Transmission to Frame. New clean surfaces/bolts.
- Added heavy copper braid cable from (above frame location) to Body next to original Ground stud below computer area.
THAT got rid of the sensor errors, and the missing was reduced a lot but not eliminated.
Had a tail-light problem that was bad ground so added a new ground bolt near back bumper, cleaned up frame metal. Fixed the tail light problems.
AND while I was in the pit looking at all this, I saw that the fuel pump had a separate ground bolt in the center of a cross member forward of the gas tank. And it looked really rusty. So, I cut the ground lead off, and added a #12 wire about 3 feet long to that new ground bolt near the rear bumper. I was about to take off pulling a camper trailer on a long trip, and so I did everything I could think of.
SUCCESS! Suddenly the missing went away and I could push very heavy throttle with good power and no missing!
SO: If you have an old favorite GMC/Chevvy with a lot of chassis rust, think about doing a serious regrounding job! Soon I'll put 10 amps through that old ground lug and see what the resistance really is..
Regards, Terry King
...In The Woods in Vermont, USA
terry at terryking dot us
I've been chasing this for months... 92 GMC Yukon with 180,000 or so. Vermont. Chassis rust. Developed these symptoms about a year ago:
- Stumbles (irregular miss) at idle. Every second or two. ONLY when warmed up.
- Missing at more than 1/2 throttle, again mostly when warmed and especially after heavy loading like towing.
AND it was the same AFTER a new GM Crate motor and transmission.. so it was problems with the original TBI, Ignition etc..
CODES: High voltage on Coolant Sensor, High voltage on MAP sensor. Replaced sensors; same codes.
Finally got serious about GROUNDS.
- Added heavy copper braid cable from Engine block at Transmission to Frame. New clean surfaces/bolts.
- Added heavy copper braid cable from (above frame location) to Body next to original Ground stud below computer area.
THAT got rid of the sensor errors, and the missing was reduced a lot but not eliminated.
Had a tail-light problem that was bad ground so added a new ground bolt near back bumper, cleaned up frame metal. Fixed the tail light problems.
AND while I was in the pit looking at all this, I saw that the fuel pump had a separate ground bolt in the center of a cross member forward of the gas tank. And it looked really rusty. So, I cut the ground lead off, and added a #12 wire about 3 feet long to that new ground bolt near the rear bumper. I was about to take off pulling a camper trailer on a long trip, and so I did everything I could think of.
SUCCESS! Suddenly the missing went away and I could push very heavy throttle with good power and no missing!
SO: If you have an old favorite GMC/Chevvy with a lot of chassis rust, think about doing a serious regrounding job! Soon I'll put 10 amps through that old ground lug and see what the resistance really is..
Regards, Terry King
...In The Woods in Vermont, USA
terry at terryking dot us
