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Discussion Starter · #1 ·
Ive got a 89 mustang I recently turboed. Has everything needed from the qft 650 blow thru to the a1000 fuel pump etc. Ive recently had a prob with the car not wanting to rev past 4500. It starts what feels like cutting spark around 3k but like a full cut at 4500. Idles smooth and all. A/F ratios are not rich around 13 when this happens. Ive replaced to plugs and gapped them to 25 and even replaced the coil and distributor and still same prob. Car ran great for a day or so once finally got it all dialed in then went to fire up next day and this happens. Im stumped here. Checked resistance on plug wires and they check out. Not sure if the btm boxes are know to go bad or what. Hell its only 2 months old bought brand new.
 

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Discussion Starter · #3 ·
Check the rotor in the distributor . Could be loose.
The distributor that was in it when it started messing up was one that I locked the timing with and thinking something failed on it I got a new one and didn't modify it when I put it in. Everything on it is good thus far I checked the gap on reluctor wheel to make sure it was good and for shaft play.
 

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Ive got a 89 mustang I recently turboed. Has everything needed from the qft 650 blow thru to the a1000 fuel pump etc. Ive recently had a prob with the car not wanting to rev past 4500. It starts what feels like cutting spark around 3k but like a full cut at 4500. Idles smooth and all. A/F ratios are not rich around 13 when this happens. Ive replaced to plugs and gapped them to 25 and even replaced the coil and distributor and still same prob. Car ran great for a day or so once finally got it all dialed in then went to fire up next day and this happens. Im stumped here. Checked resistance on plug wires and they check out. Not sure if the btm boxes are know to go bad or what. Hell its only 2 months old bought brand new.


I have five 6AL boxes that just shut off when they died, the 1 6BTM I have had symptoms similar to yours, wouldn't rev, ran really ratty.


I put a Mallory 6.6 hyfire in and have had zero problems in almost 5 years. The mallory is nice because it will do as little as .1 degree of timing per psi, rather then the 1.0 degree per psi the 6btm does.


The MSD 6530 is a good option to if you are ok using a laptop to do changes. The Mallory has a hand held box to make changes.
 

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Ive got a 89 mustang I recently turboed. Has everything needed from the qft 650 blow thru to the a1000 fuel pump etc. Ive recently had a prob with the car not wanting to rev past 4500. It starts what feels like cutting spark around 3k but like a full cut at 4500. Idles smooth and all. A/F ratios are not rich around 13 when this happens. Ive replaced to plugs and gapped them to 25 and even replaced the coil and distributor and still same prob. Car ran great for a day or so once finally got it all dialed in then went to fire up next day and this happens. Im stumped here. Checked resistance on plug wires and they check out. Not sure if the btm boxes are know to go bad or what. Hell its only 2 months old bought brand new.
Try taking the rpm chip out and see what happens
 

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I had the same thing happen to my 6BTM box. Mine actually wanted to limit about 2000 rpm less than the chip. Took the chip out with no change. Called Summit and since it was within one year they sent me a new one. All good.
 

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Discussion Starter · #7 ·
I did take the chip out few days ago and checked and still did same thing. Swapped out the btm box for the 6t box that was on the car originally and still same thing. Im stumped here. Even put the locked distributor back in to see if maybe the new one was bad and still same thing. going down the road you can feel it surging alittle and seems to be worse when hot. Idk if I got a wiring prob but just weird how it all of a sudden started and the whole ignition is changed and no change in the problem.
 
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