85T GL won't rev past idle

[roger.svoboda]

85 Turbo GL. Changed plugs, wires, dizzy cap and rotor,new fpr and chased down all the vacuum leaks we could find. Idles fine around 20" mercury vacuum. New chts. Changed the maf. verified ecu in my 86T runs fine. Verified wiring to the maf with vom off the wiring diagram. car will start and run at 2000 rpm cold and drops off to 800 when hot. When you give the engine some additional throttle it runs dies runs dies. Won't die completely keeps on running but can't get any power or additional revs out of it. My best guess is that injectors aren't opening for every cycle or that one bank is working intermittently. When idling the engine is smooth and even with no vibration or oddities. when more air is admitted no run too good. vroom die, vroom die, keeps doing that but doesn't quit completely.

 

How many times do you need to ackowledge the new rules before you can post?????

[m4xwellmurd3r]

Have you checked things like the TPS?

[roger.svoboda]

yep tps won't do that it only leans things out at idle. ran the codes nothing.

[DeleriousZ]

it almost sounds like your timing is off, but who knows. Have you taken a MAF from a working car and tried it? What do the plugs look like?

[roger.svoboda]

maf we changed out came from a runner. Happened suddenly. Running liked a striped babboon at 1800. Try to start the next morning around 0730 and nothing. When idling she sounds perfect no vibration, no miss just smooth as silk. Hold open the throttle a bit and it tries to rev then dies back like the ecu is cutting off the fuel and then giving it back.

[roger.svoboda]

Yes it was the tps even tho we had verified it three weeks earlier. Another case of assumption biting one on the butt.

[SC_300ZX_86]

Ok, this is going to sound really strange, but before you jump on me for my answer, try it. I'm betting your car will not REV past 2200 RPMs then it starts bucking sputtering and dying... right?

 

Well, if it's an auto, look in the back where the spare tire is mounted. Behind that mounting point is a small box with 2 plugs in it. It's the ATCM. With the car turned off, unplug both plugs at the same time, then plug them back in. It doesn't matter the order you unplug them as long as they are both out at the same time. This for whatever reason seems to cure the problem. It's happened to mine about 4 times under different conditions. The first time was after a brushless car wash, the next time was after driving on a sunny SC day for about 20 mins at highway speed then it sat while I ate dinner. When I came out it wouldn't go past 2200 RPMs.

 

The last time around I cleaned the contacts on both plugs, the put a light coating of vaseline around the outside edge of the conntectors and haven't had the problem since.

 

I have been all over the service manuals and can't seem to find a reason for this interation. So, for those of you a lot smarter than me, PLEASE put your 2 cents in!

 

I hope this helps!

 

 

PS: Now my problem is under WOT the car will die at 4000 RPMs like I hit a wall, won't shift, but if I ease my way up under 1/2 throttle it will ease past 4000 with some minor skips... any ideas?

Edited September 15, 2009 by SC_300ZX_86
Had I side thought...

[zylephone]

i would check the wires cap and rotor and plugs.

[roger.svoboda]

Meant to post the answer but we had other problems also. The above problem was that the tps stuck altho we had checked it less than two weeks previous so the ecu thought the car was supposed to be at idle and would cut the fuel back even tho the throttle was open. So the answer is don't depend on what it was last week - recheck. After that however the speed limiter device went south and the car wouldn't go over 2000 rpm but unlike a bad maf it would rev to the redline if you weren't moving. cut the purple wire at pin 29 and solved that problem. The combination of things going out at once was fairly frustrating as kept checking and kept getting the right answer but the car still not running. She doing fine now.