OK, weird title, but it's a weird problem (to me, anyway).
I'm the original owner of a '96 Cobra. Engine's been overhauled twice, but it's always been naturally aspirated, with stock pistons/rods. IMRC's have been deleted. I live on the Gulf coast and never had the cooling TSB installed, but never had problems with overheating. (Even now, I don't think it's a true overheating prob, but temps might be related.)
The (mis)behavior I'm experiencing is that if I get on the freeway and run at speed for an extended period (~15-20 min), I'll start to notice the air conditioner get a little warmer and a little humid. It doesn't quit completely--it's just...not right. When this happens, there's no change in engine feel as long as I'm just cruising, but if I downshift and gun it, instead of pulling cleanly to redline, the engine will pull for a short time then acts like it hits a rev limit--really awful misses and the tach just stops climbing. (This is on the freeway in traffic at speed, and this usually happens when I'm trying to maneuver, so I'm not really looking at the tach to see where the needle is.) There are no codes thrown when this happens.
My shop (just a normal car repair place; not a Ford dealer, speed shop, or Mustang specialty shop) has been struggling for months to troubleshoot and fix this. Part of the problem is that it's a bit of a chore to reproduce; the only consistent way I've found to do it is extended driving at speed. Not quite what the valet in Ferris Bueller does with the Ferrari, but maybe closer to that than my shop's techs are comfortable doing in a customer's car. Since normal city driving doesn't expose the issue, I'm also not entirely certain when the problem was introduced.
So far, my shop has checked/repaired the alternator and battery connections to try to rule out electrical contributions and replaced the temp sensor. The most recent engine overhaul was about a year ago, and of course I got new plugs and wires at that time, so they're still pretty new.
Prior to the temp sensor replacement, I'd correlated this behavior to the temp gauge climbing past the M in NORMAL. This seemed pretty consistent--as long as the needle stayed below the M, the a/c stayed cold and the engine would rev smoothly to redline. After the temp sensor was replaced, the needle stays lower on the gauge, but the behavior still occurs, so now I see it happen between the O and R.
The shop did purchase an ECU programmer and used it back when they installed the IMRC delete (and gave it to me afterward; I've left it in the box since then). I don't know exactly what they changed with it, but that was also years ago and the car didn't behave like this back then.
Any suggestions for how to methodically hunt this down and fix it? Should I be looking for a place that "knows Mustangs" instead of letting my local shop continue to chase this?
I'm the original owner of a '96 Cobra. Engine's been overhauled twice, but it's always been naturally aspirated, with stock pistons/rods. IMRC's have been deleted. I live on the Gulf coast and never had the cooling TSB installed, but never had problems with overheating. (Even now, I don't think it's a true overheating prob, but temps might be related.)
The (mis)behavior I'm experiencing is that if I get on the freeway and run at speed for an extended period (~15-20 min), I'll start to notice the air conditioner get a little warmer and a little humid. It doesn't quit completely--it's just...not right. When this happens, there's no change in engine feel as long as I'm just cruising, but if I downshift and gun it, instead of pulling cleanly to redline, the engine will pull for a short time then acts like it hits a rev limit--really awful misses and the tach just stops climbing. (This is on the freeway in traffic at speed, and this usually happens when I'm trying to maneuver, so I'm not really looking at the tach to see where the needle is.) There are no codes thrown when this happens.
My shop (just a normal car repair place; not a Ford dealer, speed shop, or Mustang specialty shop) has been struggling for months to troubleshoot and fix this. Part of the problem is that it's a bit of a chore to reproduce; the only consistent way I've found to do it is extended driving at speed. Not quite what the valet in Ferris Bueller does with the Ferrari, but maybe closer to that than my shop's techs are comfortable doing in a customer's car. Since normal city driving doesn't expose the issue, I'm also not entirely certain when the problem was introduced.
So far, my shop has checked/repaired the alternator and battery connections to try to rule out electrical contributions and replaced the temp sensor. The most recent engine overhaul was about a year ago, and of course I got new plugs and wires at that time, so they're still pretty new.
Prior to the temp sensor replacement, I'd correlated this behavior to the temp gauge climbing past the M in NORMAL. This seemed pretty consistent--as long as the needle stayed below the M, the a/c stayed cold and the engine would rev smoothly to redline. After the temp sensor was replaced, the needle stays lower on the gauge, but the behavior still occurs, so now I see it happen between the O and R.
The shop did purchase an ECU programmer and used it back when they installed the IMRC delete (and gave it to me afterward; I've left it in the box since then). I don't know exactly what they changed with it, but that was also years ago and the car didn't behave like this back then.
Any suggestions for how to methodically hunt this down and fix it? Should I be looking for a place that "knows Mustangs" instead of letting my local shop continue to chase this?
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