Just finished installing the Hughes Engines plenum repair kit on my 2001 5.9L along with a 180 degree stat and a new 52 mm Fastman TB. Followed all the provided instructions as well as the write-up in the FAQ section of the forum. Torqued all fastners to spec, checked and rechecked all vacuum lines, throttle linkage, plug wires and fuel injector connectors. Since having done all that, my truck has developed a noticeable stumble. It is most noticeable at low-mid rpm range under load and the idle is somewhat sloppy, but under WOT, it hardly seems to miss a beat. It seems to me that it is possibly running on only 7 cylinders. I am open to any and all suggestions.

 

If your plenum had been leaky for awhile, then it is possible your plugs have gotten fouled. I'd start by pulling them, and checking. Also, check the routing of your plug wires to make sure you don't have one that has gotten burned or is arching across.

 

Make sure the connectors to the fuel injectors are connected tightly. Also how long have you driven it for? When I did mine it ran weird for a little while. It wouldn't hold idle at all. It might be that your computer is relearning everything.

 

If your looking for a little more performance from a set of plugs then consider an old trick used for a long time in racing. Take a basic set of plugs. Trim the curved tip so the electrode is even with the tip. Basically taking about an 1/8 inch off the curved tip. Reduce the gap by .01 This trick has been used for a long time to direct the combustion and would ad as much as 4-5 hp.

 

I checked all the plug wires and the routing. It all seems fine. Triple checked my fuel injection harness, that was my first guess. The plugs are only about 4 months old and they were fine up until two days ago when I installed the new plenum kit. It seems pretty rough for just the PCM relearning everything.

 

did you clean the fuel rails? did you yank the plugs yet? check for a gas smelling plug... also as suggested, they probably should have been replaced if your plenum was leaking (autolite 3923's).

 

oh, and did you yank or move the distributor? if so your injector sync could be off.

 

What would be the best way to check if I knocked the distributor out of sync?

 

you need a drb scan tool to check it. if you moved it at all, then your 1st option would be to rotate it one way or another to see if it improves your problem. if yes, then go get a shop to set it for you. I'd do this ONLY if it's original position has changed... otherwise it's probably where it should be.

 

Double check all of the connections on the TB.