hesitation at high RPM?

[oh my psi]

Okay so it's a 1987 Sundance T1, I just bought it a week ago. The car has a slightly stumbly idle, first of all. But my main concern is that the engine gets very stumbly and resistant around 5k RPM. I have yet to actually try and take it all the way to 6k because the car seems very angry with me. It's like the engine has invented a new redline for itself. Now, I certainly don't need to hit the 6k redline in order to enjoy this car, but it seems odd because it pulls strong and runs well at all other areas in the rev range. No problems reaching full boost in the low/middle rev ranges. I want to turn up the boost someday so I'd like to get this cleared up.

The previous owner said that the muffler may not be doing so well, and he thinks it may be clogged with some chunks from the precious catalytic converter as it was dying.

The car has recent plugs and wires, I have yet to pull the plugs for a closer look.

Any thoughts or ideas? Any things I can check or consider replacing?

I am planning to replace the whole catback exhaust and muffler. The car has a test pipe now and I need to put on a cat for VA inspection, so I may as well go to a bigger diameter overall.

[NAJ]

Since there are concerns of a Restricted Exhaust I would certainly start there.
If you have the Test Port that threads in where the O2 Sensor goes you can check Exhaust Backpressure,MAX of 2 PSI at 2000 RPMS.
If you do not get your Exhaust Replaced as you planned and see if the problem still exists.

[Moparbishi]

check the tps switch had this prob on my shadow

[dodge89shelby]

i had a tII engine that did exactly that but it was caused by a damaged wire in the injector harnes. it ran good. just sounded odd and rightfuly so cause it was running without #3. try to wiggle your wires around and see if it clears up. and oh yeah. i didnt get a code either when it was doing that though i really think i should have.

[oh my psi]

Okay I checked it today for codes, none found (gave me a 55, all clear). I will try some of the things you guys mentioned. I assume tps is throttle position sensor? I will do a search, but it would be helpful if you clarified for me.

[oh my psi]

I messed around with the injector wires and harnesses, no change.

[lancer117]

i have the same problem with my car . but seams like its missing a little around 4500 to 5500 it seems to miss about 3 or 4 times . mine has new plugs ,wires , coil . hopefully we can kill to birds with one stone . thanks

[Moparbishi]

yes sorry for the delay. tps is the throttle position. i would really check it and make sure it is ok. might now throw a code. mine didn't and it was thye culprit. almost like a 5300 rpm rev limiter.

[oh my psi]

yeah the car atually seems to hiccup at or above 5000.

How do I check the tps, with voltage? Or am I looking for something visual? Where is it on my car? Is it somewhere near the throttle body? Remember I have the suck through turbo.

[EvilcowRoland]

TPS is on the throttle body. I'm not as familiar with the older style systems, but it should be a flat black sensor that has 2 Torx bolts attaching it to the throttle body (it's similar to the later style one but smaller for future reference). It should have 3 wires coming out of it that run about 5-6 inches and then into a connector towards the driver's side strut tower. If the TPS is bad, it will only throw a code if it reads lower than 0.16V or greater than 4.7V. I don't know what it should read in between per RPM, but with the key on and the engine off, move the throttle plate and test the voltage output. If you see it drop off anywhere and pick back up it may have a dead spot.

[oh my psi]

I did some routine stuff today... gapped spark plugs, they all looked clean, but all of them were a bit tight, so I widened the gaps a bit to get them around 0.035-0.040.

I also cleaned the throttle body with TB cleaner spray, and cleaned the ends of some of my vacuum lines.

I also revved the car while out of gear, and it will go clear to redline with no hiccups. So whatever my problem is, it has something to do with the car when it's under load. It sounds to me like an ignition problem. The wires on the car are new, and the plugs look good, so I'm not sure what to do next.

It could still be exhaust related, since the car is not under boost when freely revving, which could be why it revs fine when parked.

[jim34]

Just be careful you could be experiencing a lean condition, how did the plugs look any speckeling on the porcelain or melted electrodes ?
A fuel pressure gauge temporarily taped to the window will save your engine if you are goin lean the pressure will drop at high load high fuel demand

[oh my psi]

Yeah i was wondering if it might be lean. For now i will just keep it away from the RPMs that cause me trouble. I wonder if it's a clogged injector, or something else related to flow.

I found some injectors from a 2.5 turbo I, these are the bigger ones like those on the T2's. Could I swap these in now, since they are cheap, or will I have any sort of fuel calibration problems? I may convert to T2 eventually, so this wouldn't really be a waste of money even if it doesn't solve my problem. (the junkyard ones i found are from a low mileage Sundance, so they are probably much better condition than mine).

[EvilcowRoland]

Did you have any trouble getting those injectors out? I can't believe someone let that car go to the yard. It was so clean!

With the bigger injectors, you might get a little bit of overfueling in cylinders 1 and 2 since the old log intake setup gave those extra fuel anyways (bad intake design so they programmed the computer to compensate). It shouldn't be horrible though. Just plug them in and go.

[jonnymopar]

Ok, this might be a stretch, but I did have this same problem with a non-turbo Daytona I had almost a decade ago. I was fiddling around under the engine bay back when I was still learning and I had inadvertently disconnected a vacuum line. The car would rev to about 4000rpm and start popping and farting, but it would be fine if I drove it uner 4000rpm, no matter how much throttle. It did not give me a check engine light either, which was weird.