SOHC to DOHC motor swap problems...

I recently did a full motor swap in my 2000 GT. The motor is from a '97 Cobra with lot's of goodies and ported heads and some nasty camshafts. The car was originally an automatic and now it has a T56. Oh, and the motor is having air forced through it with the aid of my Vortech JT trim.

Has anyone ever encountered a problem like this before?...

The car free revs to 7500+rpms but, when under load i.e. on the dyno or the street, it won't go past 6k????????? The fuel is definitely there and I think it might be an ignition problem. I have tried messing with the plug gaps thinking it could be spark blow-out but, I'm only seeing 14 pounds of boost. I tried switching out the coil-on plugs for a newer set, didn't really help. The only thing that was changed when installing the new motor was some wiring in the harness to get the wires to fit better that go to the coil-on plugs. I have checked over the wiring so many times now and haven't found any issues. I have also replaced the cam and the crank sensors a couple times...

Oh, and sometimes, randomly, the car will pull to 6800+rpms while under load but, 99.9% of the time it won't.

Does anybody know what the problem could be?

I am open to ANY ideas!!!!

rev limiter is set at 8500

fuel system was cleaned out (this was when I thought the problem was solved. It would rev to the moon but, only for two days. So, I cleaned it out again and back to the old same rev problem)

yeah i'd have gone to a Cobra computer...the work to get a 2v pcm to see the 4v right + the sc....my god.

yeah i'd have gone to a Cobra computer...the work to get a 2v pcm to see the 4v right + the sc....my god.
I guess I won't have to do that...other people have done the same motor swap and never changed out their computers. They had no issues. thanks

When I had the S-trim on my 357w it hit a wall at 5700 . . . lean. Are you sure your getting enough fuel?

When I first started reading your post I was thinking spark blowout, but you said you checked that. What is your plug gap?

What does the motor do when it hits 6k? Does it start popping like its hit the rev limiter? Thats what mine did, cost me a set of felpro's too.

When I had the S-trim on my 357w it hit a wall at 5700 . . . lean. Are you sure your getting enough fuel?

When I first started reading your post I was thinking spark blowout, but you said you checked that. What is your plug gap?

What does the motor do when it hits 6k? Does it start popping like its hit the rev limiter? Thats what mine did, cost me a set of felpro's too.

The gap is set at .020 and the air/fuel is perfect. It sort of sounds like the car is hitting the rev limiter. The fuel supply has been checked over a few times now and everything checks out ok. The fuel pressure is good and all that too.

What are you using to measure the afr's? I used a LM-1. What air/fuel ratio are you seeing?

What are you using to measure the afr's? I used a LM-1. What air/fuel ratio are you seeing?
It has been on the dyno several times with a wideband...seeing 11.8

its not a tail sniffer is it?

its not a tail sniffer is it?
no, it goes directly into the midpipe

If your wideband sensor goes into the "H" of an H-pipe then you may be getting false readings. I have not had this problem myself but when I was going to weld the O2 bung into the h-pipe of my car I was told not too, that the readings wouldn't be accurate. I had mine in a header collector. I know this only tells you what 1 side of the motor is doing, but thats where you have to rely on the plugs.

Speaking of plugs, how do your plugs look?

If your wideband sensor goes into the "H" of an H-pipe then you may be getting false readings. I have not had this problem myself but when I was going to weld the O2 bung into the h-pipe of my car I was told not too, that the readings wouldn't be accurate. I had mine in a header collector. I know this only tells you what 1 side of the motor is doing, but thats where you have to rely on the plugs.

Speaking of plugs, how do your plugs look?
plugs look good! If anything it is running a little rich...

Well now I'm stuck. I dont know what to tell you.

Have you gone to turbomustangs.com and done some research? I would bet that the answer your looking for is somewhere in the archives of info over there. Just use the big green search button and read away. If all else fails, ask.

Well now I'm stuck. I dont know what to tell you.

Have you gone to turbomustangs.com and done some research? I would bet that the answer your looking for is somewhere in the archives of info over there. Just use the big green search button and read away. If all else fails, ask.
cool, thanks for all the suggestions!