Cutting out at 4200-4300 RPMs 87 SL

[newmember]

I have a 1987 Dodge Shelby Lancer with a 2.2 that's been bored, stuffed with forged internals, ported intake and exhaust manifolds, walbro fuel pump, +40 injectors, newer fuel rail and FPR, rebuilt T2 Garrett, full 3" exhaust, factory intercooler and airbox system and a Stage 5 FWD Performance cal in it. A couple weeks ago (I am not driving the car everyday) I had a problem with the car reaching 4200-4300 rpms then stuttering like it was bouncing off a rev limiter. The car starts up fine, reaches normal operating temperature, doesn't blow any smoke, and idles smoothly, and no CELs are on. I thought I was having spark break up and replaced the plugs, wires, entire distributor assembly, and coil from my 90 Daytona, which are all good parts and take the Daytona out to redline all the time(this did not fix the problem). I replaced all rubber fuel lines and fuel filter back in June, and didn't have any troubles with it immediately following. A few days of toying with the car and it's situation, and I noticed the boost was not stopping 18 lbs like it should and going into the mid 20's. Has anyone experienced similar problems? I haven't had time to go home to work on the car recently and was trying to get some ideas for the next time I get a chance to work on it. A fellow TMer was leaning towards the possibility of a computer related problem. Any thoughts?

[Young Gun]

TPS sensor or map sensor.

Don't take my word for it but i was told on my own diagnosis thread about those two going bad when your engine bogs down at 4k rpm's

[newmember]

Well I didn't think about that, I'll have to check that out. Thank you

[trannybuster]

Timing would be my first guess(cam then dist), any guages to make sure it isnt running lean, and whats your fuel base pressure set at? Make sure it isnt running lean would be the first priority, read your plugs, better yet wideband(??).

[roachjuice]

Plugs. What's the gap? How fresh? Champions work great. I had random cutting out like that with Ngk plugs. Swapped them to RN9YC plugs. Never had another problem like that. Except for some old plug wires. That's will do it too.

[DaveSkrab]

Does it do it every time? under accel? can you do it just free revving it? When the bottom end was done did you happen to use a new or inspect the intermediate shaft gear? I have a remarkably similar situation. I have found that the distributor rotor (ie shaft, down to oil pump gear and int shaft gear) has a lot of play, more so than on another engine that had NO issues running to the actual rev limiter. Gears are likely getting worn out and I bet there's a harmonic around that 4200-4500RPM range that's causing a little bit of spark scatter. I will let you know next week if that fixes mine.

[newmember]

trannybuster- i already removed the timing belt covers last time i was toying with it, just ran out of time to check the timing. Base fuel pressure is good, checked that already too, and the plugs are very nice looking.

roachjuice- plugs have maybe 2500 miles on them and were installed in the beginning of june, and Champion RN9YC's are all I've run in it. They are gapped to what they should be. I thought my magnacore wires were the culprit, but swapping them out for newer aftermarket wires from my Daytona gave me no change.

daveskrab- it does it everytime, under accel or even when i try to throw a hard downshift. I bought the engine from a friend who had it built by a very good machine shop, but sold the car he planned on putting it in. I know he wouldn't remember if it was inspected or new, but I'm going to see if that has excessive movement.

thanks for everyone's input so far, i appreciate it

[trannybuster]

Well if plugs look good, Id bump timing 2deg, go slow ,listen for knock, the forged slugs will handle it easily, its the head gasket that'll let loose IF the detonation is pretty bad. Id bet itll run good on just 2deg..

[glhs727]

Fuel pressure at idle doesn't tell you a whole lot since you aren't having an issue at idle, check what your fuel pressure is at 4300 rpm when you are having issues. Also check your map and tps voltage and see if anything wacky is happening at 4300 rpm.
+1 on the Ishaft teeth. One of my customers over on the "other" forum had a similar issue, and I told him to check the I shaft, and sure enough his teeth were worn. replaced the Ishaft and all was well again....

[trannybuster]

Fuel pressure at idle doesn't tell you a whole lot since you aren't having an issue at idle, check what your fuel pressure is at 4300 rpm when you are having issues. Also check your map and tps voltage and see if anything wacky is happening at 4300 rpm.
+1 on the Ishaft teeth. One of my customers over on the "other" forum had a similar issue, and I told him to check the I shaft, and sure enough his teeth were worn. replaced the Ishaft and all was well again....

Normally just replacing Ishaft wont fix it, the oil pump will be cooked as well, so both need changing, and if it jumped timing on the shaft they'll be hit. Also most of us dont have fuel pressure guage inside car so idle is all we have :) . Its sound advice though, check that Ishaft first and foremost becasue it could destroy the intermediate shaft bearings!

[moparman76_69]

Does it cut out hard to the point throws you forward? Always a consistant RPM?

http://www.turbo-mopar.com/forums/showthread.php?56724-Still-chasing-down-a-cutout-problem

Been chasing a similar 4000 rpm issue for a year. Finally swapped computers the other day, we'll see in a few days if that is it.

[glhs727]

Also most of us dont have fuel pressure guage inside car so idle is all we have :) . Its sound advice though, check that Ishaft first and foremost becasue it could destroy the intermediate shaft bearings!

well if you had an FWD-P fuel pressure test kit, you would hook it up to your shrader valve then run it out the cowl and put the gauge under the wiper blade so you could drive and see FP plus it isn't inside the car... LOL - I drove like that for a couple of weeks with my srt-4 a long time ago. I did get a few weird looks....

[trannybuster]

^^I was thinking that when I wrote it, then thought 'but then thought what a pita'....sometimes it is was it is!

[DaveSkrab]

Update, I have replaced the I shaft and oil pump with known good components, However I did find that the Cam timing was advanced 1 tooth. So with new components and proper cam timing the car runs beautifully. It may have only been the Cam timing on my engine, but there was considerably more wear on the shaft / oil pump gear teeth than what I replaced it with.
Hope this helps!

[trannybuster]

Well you'll know if its failing, cause itll be tore up pretty badly, and they dont last long once they start. Kool, you got it runnin good!