97 Cobra no code misfire after eng replacement

BarnStang

Founding Member
Mar 2, 2001
1,261
3
39
Hagerstown, MD
Eng seized on the 97 Cobra. Found a 98 Cobra motor with 80k miles on it. Looked like brand new. Spotless. Not cleaned though. It came out of a car like that. Still had the inspection sticker on the back of the valve cover.
I couldn't make the 98 eng harness work so I swapped the 97 harness onto the motor. Way too many connectors didnt match up. But the 97 harness went on every connector except 1.
The air tubes in the front of the motor, there's only one section on the 98 instead of two on the 97. And the sensor is now on the drivers side. So I simply extended that sensor connector, making sure to match the 2 pins correctly.

Started right up. No codes. Runs and drives ok, but seems down on power. And has a slight shudder that wasn't there with the 97 motor. And sounds like it has a miss.
I can hear a rhythmic pop or thump from the exhaust out back, but cant discern which side its coming from.

I pulled each wire off the coil packs (oh swapped the coil packs from the 97, the connectors on the 98 packs were broke) one at a time. Each one arcs to the coil pack terminal when held close so each one appears to be firing its plug. Couldn't really tell any noticable change in rpm or engine sound when each one was lifted though. Was trying to find one that didn't make any change...
Has new plugs.
Everything else on the motor is what it came with. All 98 stuff. Coils are the only 97 parts added. So all the EGR and induction are 98. Including any sensors in the block.
Oh, I also swapped the drivers side coolant temp sender...the gauge was way off.

I'm pretty good with the 87-93 mustangs. So am familiar with the sensors and stuff. But this problem I think I need some help with, before I let a Ford dealer tell me they have no idea...which is what i expect I would get until I find someone who has worked on these cars a lot.

Any help would be greatly appreciated.
 
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I solved this some time ago. Even though they looked brand new, the #7 spark plug wire had failed. It finally threw a Cyl #7 missfire code. New plugs, wires, and coil packs and its screaming down the road again.