David '96 993

After many parts tested and replaced, my car only goes to 5500RPM under certain conditions.

It is an intermittant problem in that it only happens under load (exiting turns) only in certain turns. This is a dedicated track car, so when this condition appears it is in the same turn on every lap. On some tracks it does not happen at all, but others it will happen on the same turn every lap.

It feels like the rev limiter is kicking in and I can't get it to go above 5500RPM.

I have replaced or switched the following:
AFM
Brain
Coil
Wires
Spark Plugs
Flywheel sensor

I tested the fuel pump for pressure, but have not yet replaced.

Any ideas????

I don't know where to look at this point

Zero10

What year 944?
Perhaps it's G-forces acting on the tach needle, and it just can't swing around past 5500?... Are we going by the factory instrumentation?

David '96 993

It is a 1987NA.

The car is clearly not pulling past 5500. Feels like a rev limiter and other 944's pull away from me with the same exit speed.

Campeck

check under the distrib. cap?

David '96 993

I did not see anything unusual under this distributor cap. Also, the spark plugs look the same when I pulled them all.

M758

Ok the key is that it appears to be G force related.

Same turn every lap you say. Which track and whay turn? Left or right?

You have replace much of the stuff that could fail. Seems to me that it maybe a wiring or maybe vacuum issue realted to the g-forces. For example something is moving at causing the problem.

Have you taken the corner in different gear and figured what happens?
Have you taken the same corner slower to see what happens?

Are you sure it is 5500 RPM or it at certain spot on the track. My car had fuel pick up issue that would cause my car to die on exit of 2 or 3 corners on one track (all same direction). Each lap this would happen at about the same spot. Turned out to be something in the fuel tank that blocked the pick-up.

Maybe a plug is coming out or hose is opening at the that spot on the track due to g-loads.

I'd would best to dermine if the issue is 5500 RPM or a certain type of g-load. Or even a certain g-load that causes a problem only at 5500 RPM?

If it is g-load RPM thing then you have to figure what could be happening that is RPM related.

What is different about 5500 vs 5400 RPM WOT?

Well you get more fuel at 5500 RPM.
Distributor cap & rotor move faster.
Speed sensor reads more RPM.
DME interprerts as more RPM.

Then figure which ones of these could be impacted by G-loads?

Could the speed sensor be moving every so slightly and losing signal?
Cap and Rotor issue?
DME electrical connection?

David '96 993

Joe,
You are a wealth of information. Did my first NASA event at Willow a couple of weeks ago, and did not have any of these issues. Nor do I have any issues at the Streets of Willow.

The issues came up at Laguna Seca in turn one (downhill, so not too much of an issue). It also happened at turn 5 so I would work around it by keeping my RPM higher than 5500 by left foot braking slightly. Both of these were left turns(One uphill and one downhill). Willow has very few left turns...Maybe you are on to something as I had huge issues at Vegas in many of the left turns. Not every left turn makes it happen. It may the g-force(how much) that triggers it.

I have an intermittant no start issue and had the flywheel sensor replaced. I still have the issue and the car will start up if I wiggle the sensor. I am going to have the connections checked. When it does not start, I have no spark. I don't know if there is any correlation or not.

M758

Hmm...
Lack of spark if occuring at speed could show as an RPM issue.


For the no-start issue... have you checked the coil or the plugs. The idea is to see if the problem is getting the coil to fire or getting the spark from the coil to the plugs. If you wiggle the flywheel sensor and the you get the car to start then I'd look there closely. Could be a loose connection electicaly or could also be the height of the sensor relative to the flywheel. If you lose signal from the speed and refernce sensors (BG and DG) then the DME does not know to tell the coil to fire.

It does seem strange that 5500 RPM is problem, but apparently not 5800 RPM.

Based on what I know I can't see why 5500 is so special other than may be some odd issue with the the number of teeth on the starter ring at 5500 RPM.

Campeck

i know of a 924 racer that on hard left or right turns would go lean/rich because of the G forces pushing the afm flap door out of whack....

maybe thats not lettign you rev to high? not sure. and if it was that. not sure how you would fix it. the racer turned it around so it only happened during accerlarationa nd braking.

David '96 993

Ashton,
Thank you for the idea, but I did swap the AFM thinking that the MAF door was sticking. I swapped it at the track and this issue still persisted.

Joe,
I think that I will dig into the sensors. I am hoping that there might be something there. I already swapped my coil with Dylan. That was the first change I made, as I have heard about coil issues under load.

Can a fuel pump be impacted by load?

nine-44

I am having the same problem with my 86 NA. I'm pretty sure it's weak valve springs causing valve float. Every now and then I hear a kinda "tink" noise while doing it. Unfortunately I beleive it's piston/valve contact.

nine-44

BTW, it acts like a soft rev limiter or like someone pulled a bunch of advance out of the timing. Mine normally does it about 5200-5500.

David '96 993

Andy,
Your comments mirror that of a racing buddy that had a simlar simptom. Once he had a valve job (ouch) the problem went away. I am looking at all options before I go that route.

Thanks.

StoogeMoe

That's an interesting theory Andy, but wouldn't it happen whether you are on a straight or in a corner? I wouldn't expect that to be g-related.

David, so you don't experience this at turn 9? That is pretty heavily loaded left turn also. The only difference is you usually aren't accelerating out of that corner. Do experience this through the whole turn or just coming out when you are getting on the throttle? If that is the case, I would suspect fuel starvation probably from the tank area. Does this happen on any level of fuel?

xsboost90

i dont think he said it had anything to do w/ cornering, just that cars are leaving him after the corner...no power. correct? I wonder if you have a bad fuel pressure regulator not opening up at WOT.