tlsmith1999

Hello,
I am new to 928's, my first one just arrived today and it is having a problem.

I am not much of a mech, but I can figured it out slowly with some help

My car is running smooth at idle, but has very poor acceleration. With the gas floored it will go about 50mph @ 3-3.5K rpm.

In neutral or park, it will run up to about 3.5-4K rpm quickly, with gas floored, but then it creeps up from there.

A friend suggested it might be a vacuum problem. I have searched nichols webpage and here, but I can't find a good diagram that shows where or what the vac lines look like that I need to check.

Thanks for any help,

blitz928

Had the exact same problem, exactly, it was my LH computer.

David L. Lutz

It doesn't sound like a vacuum problem to me either. But you ask for a diagram and this should get you started.




Good luck!

worf928

The bad news: There are about a hundred things that could all contribute to poor power. Depending upon the service history of your car you could have dozens of little problems all contributing.

The good news: You're in Austin; there are lots of 928 folks there. And you have an '89 with the diagnostic port that can be used by the Hammer or Spanner to give you a quick head start on finding some problems. These problems come to mind and can be diagnosed via the Hammer or Spanner:

Hall Sensor
Knock Sensors
Temp-II Sensor
EZK (ignition computer) faults
LH (fuel computer) faults
Protection Relay

Next, do a search on the following topics:
Thrust Bearing Failure / Flex-Plate Check
Cam Timing
Fuel Pressure and Pressure Hold testing
Mass-Air Sensor (MAF or MAS)

A number of scheduled maintenance items can lead to poor performance if left too-long:
Fuel Filter (***can get clogged and prevent fuel flow at high loads***.... )
Spark Plugs, Plug Wires, Rotors, Distributor Caps

Injectors also get clogged and/or get poor spray patterns that can lead to poor power.

waveflux

Again, Go into the footwell on the passenger side to the fuse panel. Do you see a green or red LED? The car should be running while checking.

SeanR

Getting lots of good answers so far. I suggested checking the vacuum at the dampeners because, from the phone call, it sounded more like a fuel delivery issue. From what I understand, the engine is not misfiring or in limp mode.

I did suggest it could be bad fuel filter/pump, or even bad gas.

tlsmith1999

No red or green lights.

tlsmith1999

yes, it is running smooth, just low power, no git-up-'n-go.

worf928

Fuel Filter

blitz928

Does the engine hit 4000 rpm and literally stop revving. Almost like you hit a rev limiter. and then SLowly creep up in revs even when you floor it. If this is true, see if you can get a good LH and swap them. It's quick and easy. You as was mentioned before by Dave C have the luxury of a Diagnostic port so you can check for faults as well.

SeanR

I think we have a new addict in our midst. LMAO.

tlsmith1999

Who me??

If I miss the Turkey because I am in the garage working on the car, then maybe.
But I have already joined two support groups. (rennlist and 928oc).

With the car parked and floored, it revs up to 3750 real fast and easy, then it creeps up slowly. if I let the revs drop, then floor it again quick, I get right back up to where ever I was last at before I let off last time. If I keep it floored long enough it will crawl up to 5K (1-2mins). I haven't been brave enough to keep it floored long enough to get it any higher than that.

tlsmith1999

It is not like any rev limiter I have seen before. The one on my bike cuts out the engine if you hit it. This car just sounds like you are flying wide open, but just can't go any faster.

the flyin' scotsman

Is the exhaust system stock?...............the cats are perhaps plugged.

blitz928

The rev limiter scenario was the only thing I could figure I could describe the symptom like. When I had this problem I had a hell of a time explaining it. I brought my mechanic friend out for a drive with me. and showed him exactly what I meant.

This is my post on the subject from last spring...


https://rennlist.com/forums/928-forum/438826-my-lh-brain-saga-thanks-rich-andrade.html