6500RPM wall, I can't redline under load
 

I frequently hit a wall at 6500 RPM under load (but not when revving in neutral, it happily flies by 6500 then), it feels like fuel cut, it will lurch terribly, and I don't have the nerve to keep the gas pedal down to find out what happens. '87 TII, COMPLETELY stock. Air filter is fairly clean, plugs and wires are new and all the injectors are supposed to be new, and I recently adjusted the TPS back to spec. The fuel filter is new and was changed AFTER the gas tank was cleaned and coated. Injector cleaner hasn't seemed to do anything. Any suggestions? I do have the 3800RPM hesitation which I plan on fixing soon, could the 6500RPM problem be caused by ground issues?

i had this same problem, mine was due to poor grounding, after running some ground wires from the ecu and some other locations in the engine bay mine went away. may or may not be a problem

well it's very likely that my grounds are generally poor, so maybe tomorrow I'll have to spend some time fixing them. I really want to autocross the '7 for the first time this weekend and having the 3800RPM hesitation and this cutout at 6500RPM would be awesome.

i'd say just check the stock ones and pick up some 14 guage wire at checker or wal mart (wal mart is cheaper) and some ends, and run some of your own on top of the stock ones, i have a full "circle earth" type setup i did on my car.

The primary ECU ground under the intake manifold (somewhere) is a common cause of the problems. When you're doing the vacuum lines, you should clean up any wiring you see under there. Also add a ground from the ECU side of the ground cables to the ground.

Circle grounding does nothing if the ECU doesn't have a good ground to begin with.

-=Russ=-

thats my point, i grounded the ecu bracket, the bracket that holds the ecu and its bracket, and pin 2c on the ecu (check which pin you should be grounding in the FSM) and then several in the engine bay including leading and trailing coils, block, stock injection harness ground, and tranny bell housing ground, connected all together and with one from the negative battery terminal.

Well, while replacing my faulty Rtek chip today I ran all four ECU grounds to the bracket and left them also attached to their original locations. This did nothing to solve my 6500RPM wall.

HOWEVER, now that I have an A/F gauge I could tell a little bit about what's going on when I hit that wall. It looks like I'm leaning out completely when it hits, and I went ahead and tested if I could somehow push past this wall by keeping the throttle open, but it just bucked like a slow-reacting rev limiter: lean, rich, lean, rich, lean, rich. No passing it. I do suspect my battery is a bit weak, but it was brand new last summer. I did some basic voltage checks and the whole car certainly isn't getting quite enough power. While running and no accessories are turned on, the battery only runs at about 12.7V. I recently installed an S5 alternator, so it's brand new and I wired it properly. It looks like there's a .5V drop from the positive terminal on the alternator and the positive terminal on the battery. With the car off I turned on the headlights and checked the battery voltage, it was about 11.6V

Could these things be related? Should I be checking the voltage at my fuel pump while driving (because I suspect maybe the resistor pack is to blame)? Anything else I should try?

Probably Fuel Cut.

Theres little chance that this is your issue, but my car had the same symptoms, and it ended up being that something had hit the downpipe and drastically reduced the size of the pipe.

It seems that way, but why would it be cutting fuel? That's what I can't figure out...

I also replaced my battery today with one that pushes 800CCA at 0 degrees F, mainly because startup has been sluggish. So far so good, and my voltage is ok. 12.6V at 700RPM, but 14V at 850RPM, so I figure that battery will do at least better than the last two ~450CCA batteries I had. However, I tested it again after changing the battery and it certainly isn't a system voltage issue as the problem is still present exactly as it was before.

The good news is that I got to replace my Rtek 1.7 chip with the stumble fixed chip. It works very nicely, but I did encounter one situation where it leaned out when I don't think it should have, but I will have to do more testing to see if I was correct or if I just misjudged how far open I had the throttle.

Oh and Jason, I have a straight through exhaust now, had a stock setup when I bought the car, and this issue has remained the same the whole time. So it couldn't be that.

i know what it is i'd put money on it, yone of your secondarys isnt working, the inkector connector may have poped off or be corroded ect. happened to me twice

If that were the case then I would think I shouldn't be able to push 10psi of boost at 6000RPM without blowing my motor...

It doesn't blow right away. I would guess that your secondary injectors are either clogged or aren't working properly.

It shouldn't be the secondary injectors themselves, as when I bought the car it had only a few thousand or less miles on all the injectors. The PO replaced them, and I could visually verify that when I installed 720cc secondaries (used, but they've been working wonderfully as well). This problem has followed two pair of secondaries, two ECU's and an Rtek fix, regrounding of the ECU and engine bay, alternator, starter, two batteries, a higher flowing fuel pump, MBC, and exhaust upgrades.

I do appreciate the help so far, I still need some more ideas to try.

do what everyone said and check the grounds. also check your entire fuel system.

it sounds to me as the pump is on its way out. sending the injectors out to be professionally cleaned isnt a bad idea either. and replace the fuel filter also.

but then it also sounds like something else is ready to go..... check your fuel pressure regulator as well

With the RTEK there should have been no fuel cut. My bad.

The voltage is too weak. There's an alternator problem. That MIGHT cause too low a fuel pump voltage at high rpm/high load.

The alt should be putting out more. Something like 13.5vdc if you have headlights on. I'd be interesting to run a digital meter to the large blue wire on the fuel pump connector with some long meter leads where you could SEE the pumps voltage when boosting. It'll read approx 9.5vdc when under no load. With load it should be in the 12vdc and above range for sure.

I suspect the voltage was weak due to a weak battery and not the alternator:
"I also replaced my battery today with one that pushes 800CCA at 0 degrees F, mainly because startup has been sluggish. So far so good, and my voltage is ok. 12.6V at 700RPM, but 14V at 850RPM, so I figure that battery will do at least better than the last two ~450CCA batteries I had. However, I tested it again after changing the battery and it certainly isn't a system voltage issue as the problem is still present exactly as it was before."
Now today, after about 100 miles of driving, some using the stereo and headlights, it's still starting up as strong as it did when I first installed the new battery. When I did a "headlights on while running" and a normal running test, the headlights dropped the battery voltage about .5V, so I figure with the new battery the voltage probably sits right at 13.5V when they're on. I will test this again now that the battery is replaced, but I doubt that or the alternator is the issue.

I will definitely check the voltage at the fuel pump asap. I should note that this higher flowing fuel pump was a brand new TRE Performance pump when I installed it and now only has probably 1500 miles on it. I think I said earlier that I suspect my fuel pump resistor pack is faulty. I will get on that test asap. I'll of course take other suggestions until I get this fixed.

I believe I've covered these issues in this thread already:
1) already checked AND regrounded all major grounds
2) pump was brand new when installed about 1500 miles ago
3) problem has followed the nearly new injectors when I got the car to the used secondaries I installed a couple months ago.
4) the fuel filter was also replaced by the PO shortly before I got the car

im just gonna throw this out there, you have checked every thing would except 2 things

-ground to fuel pump
-spark plug wires (its actually a fact the more you remove them the worse they get)

sorry speed, my reading comprehension is a bit lacking so forgive me i am also dyslexic to a certain degree. being out of school for 6 years does a lot

The plug wires are brand new as of last month as well, which were replaced to clear up the trailing coil from arcing across itself (and they did in fact fix that problem).

So yeah, the next thing is to check the wiring at the fuel pump. Now, when I replaced the pump I made sure I soldered all new connections securely and whatnot, but I didn't check the existing connections and not while running either.

cptpain, don't sweat it :)

Rewiring your fuel pump would be a good idea. Check the wires to your secondary injectors. If one or both are not firing you will get this problem.

The battery has nothing to do with voltage to the fuel pump. Once the car is started, the alt takes over and you can unplug your battery and the car will keep running. If your alt is going, that could be your problem.

Just throwing this out there, but could your tach be out of calibration? You could actually be going 7500 rpm when you think you are going 6500 rpm. I have never really felt the rev limiter in a stock turbo II (<- almost an oxymoron, a STOCK Turbo II), but if it is like my NA, it will rev to crazy speeds (like 8500 rpm that my one friend was doing in first gear just because "rotors are bulletproof") when unladen, and when loaded, it stops at 7500 just about right on the nose.

The only other thought I had was noise on the CAS, but that would make the engine run strangely throughout the power band.

Hope you get it fixed

I don't think it would lean out like that just because it was hitting redline... +1 on the fuel pump grounding/wiring check and get the alternator tested, I think you said it was new, but was it a re-man, or is it ....new? I've had a re-man crap out on me within the first two months of owning it.