99 Mustang GT 4.6 Driveability Issues

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1999 4.6/5 speed Mustang GT with coil on plug ignition system experiencing severe stumble to dead mis under load below 2000 rpm. Idle is smooth and high rpm (above 2000) is smooth, makes good power with fuel economy in the 20-24 mpg (normal) range. Symtoms Get worse after warm-up. PCM sets no codes.

Ignition system appears fine, spark plugs new, none fouled, boot on coils are solid with no evidence of arcing, resistance and voltage checks of coils primary and secondary are within specs.

Could this problem be non ignition? Anyone experienced this situation?? :confused:

posted by  Phoenix568

I used the ACTRON CP9145 scanner and found no codes. I am aware of the
tendency of the intakes to crack on the late model 4.6 and did some quick
leak testing and did not find anything . I probably should go back and look again. The problem occurs mostly after engine warm up, which would expand any existing cracks and it also happens under engine load conditions where vacuum is the greatest. As far as TSB's go I have ordered 2 from Helm but they both seem to be related to ignition issues TSB# 2003-14 and TSB# 2004-16.
Anyway, thanks for your input....gives me something else to look at.

posted by  Phoenix568

My 1999 Mustang is doing the same. can you help

posted by  dennis yule

Check the recalls or sevice buletins on this one 'cause it sounds like a fairly common problem.

posted by  srober32

ford has a new manifold which is 1/3 aluminum.if it cracks underneath you will never see it.a vacuum gauge might help....ITS THAT FORD QUALITY.
i like the 97 explorer.

posted by  the lobster

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