3.2 carrera rev limiter

[brit911]

Guys I need some help, seeing as this forum is so busy I though it wouldnt hurt to ask my question.

I have a 3.2 carrera which seems to hit a rev l,imiter when it feels like it, normally this is at 5400 although when quite hot this can be as low as 5000rpm. I have changed to plugs/leads/rotorarm/dist cap/engine earths/fuses/fuel filter/air filter

Any ideas would be very much appreciated, It has been suggested that the chip may have been changed in the dme control unit but i'm not sure if it has , I was thinking of changing the cylinder head temp sensor as this would be directly affected by heat, the engine also doesnt \feel that smooth when accelerating even slowly, again possible mixture fault, it idles fine, got the normal hunting when cold but apart from that its good,

I look forward to hopefully getting some replys

Thanks

[Dutchie]

it should only do that at 6200 rpm but i,m sure you know that. The man you need is Steve Wong he is the chip expert on this board. Try to bump this around 16.00 pm euro time again.

[brit911]

I have already e-mailed steve and taken his advise, just wondered if anyone else had had the same problem, as North America is the largest porsche market in the world I hoped someone hay have experienced the same problem and known the fix, thanx for reply

[ChrisBennet]

Is it really hitting the rev limiter or is it bucking in a fashion similar to hitting the rev limiter? You can fake out the head temp sensor with a resister to eliminate that as a possible cause without actually replacing it.
-Chris

[white87911]

Sounds like you may have a fuel delivery problem. You may be starving the engine for fuel, this could be caused by a bad fuel pump, clogged line or pick-up, pinched line, etc. Thats what I would check from here. If the rpm varies then it would not be the chip. The chip would be 1 rpm only.

[Peter Kelly]

Check the speed and reference sensors (get Bently manual if you don't have it already). If the nose of one of those sensors is dinged it can cause this problem. Even if the sensors look ok, replace them. ( 80 bucks or so each)

[Dan Owens]

Can you describe in a little more detail what it feels like when it hits the "limiter"? Does it cut out or is it just feeling flat like it's not getting enough fuel and has no power? Do the symptoms change when you're lite on the gas versus heavy on the acceleration? Sounds more like the AFM is going bad based on the limited description you've given so far but could be a number of things. When was your O2 sensor last replaced?

[bell]

is it possible you have a "slow" tach? or are you using an aftermarket one?
just a thought

[Steve W]

What everyone said is pretty applicable, although I do believe that what Peter Kelly says is probably the first thing I would check. Also, if the sensor gaps are off, it would artificially limit the rpms at the upper end.

[gerry100]

Two year ago, mine would run rough and suddenly "cut out" for an instant at around 5k rpm.

I replaced the CH temp sensor and the DME. I think the DME relay( 5 minutes, $50) did the trick.

CH temp sensor, is more of a PITA ( $65, 3-4 four hours if you are a hack like me).

I'd do both if I were you.

[masraum]

The stock rev limiter should kick in at 6520 rpm, the engine redline is 6250, they give you another 270 rpm's just in case.

I'd double check the accuracy of the tach, if it's accurate then I'd check the fuel system. Is it similar to a rev limiter or exactly like a rev limiter?

[BGCarrera32]

Head temp sensor or fuel pressure...if speed or ref sensor the signal should get stronger with an increase in rpm, not drop pulses causing this condition...

The only possibilty with the speed or ref sensor is that the sheathing on the leads to the sensors has become compromised by laying against the exhaust or hot engine tin, so you might want to chase them with your fingers and check leads.

[brit911]

Thanks for the tips, i thought i would spend the afternoon painting my wheels and generally pampering the little porker and in the engine bay on the left hand side are two wires, one that is brown with white stripe and another red with black stripe this plug is just hanging in the engine bay, I have looked for the engine temp sensor down by no 3 cylinder but cannot locate it, i think i must be a muppet. Should this sensor be easy to spot????

In response to Dan Owens & Chris Bennet It feels like it hits a limiter, as per other cars I have driven and I would certainly say its similar The engine hold back and wont rev any higher..

[Dan Owens]

If I'm understanding what you're saying here I don't believe the rev limiter works that way. I believe it cuts the electrical power signal and reconnects after the RPM's drop below that limit. It doesn't just stop your RPM and or hold at the RPM point preventing you from increasing the RPM. Someone more knowledgeable may jump in here and correct me if I'm wrong but that's how mine acts if I hit the limit.

[BGCarrera32]

When I hit my rev limiter I get a "bah-bah-bah-bah-bah"- a definite cutout in other words. The rythem is consistent.

[brit911]

Mine definatly goes bah-bah-bah, i think i have a fuel pump in the garage, i might give it a try, will at least rule out fuel, the filter has only covered 3000 miles!!!

Thanks for the posts.

[brit911]

Had another look this evening, still cant find the engine temp sensor, can anyone help with is location.

Thanks

[ChrisBennet]

Originally posted by brit911
Had another look this evening, still cant find the engine temp sensor, can anyone help with is location.

Thanks

The head temp sensor is on the front of the engine (front=closest to the front of the car) on the left. It's hidden behind a oval shaped rubber cap. Unless you have a very old sensor, a white wire will lead to it. You have to access it from underneath the car.

The connector for the head temp sensor is located in the engine compartment on the left and a little below the heater blower. There is a bracket with 3 connectors in a vertical row (hidden by the heater tube), the heat temp sensor is the white connector.

It's a bit a a pain to change and I wouldn't change it without testing it first. Measuring the resistance of the sensor isn't a very good test IMO because the failure mode for the early sensors is intermittant. Substituting a resistor in place the the sensor, say 270-300ohms with the motor hot (you need a different resistance if the motor is cold or warm) and then driving it is a better test I think. If the problem goes away you'll know it's the sensor.
-Chris

[brit911]

Thnaks for all the tipa, I will go get a 270-300 ohm resister today and test on monday, I have read on this forum that if you disconnect the o2 sensor when warm and drive, it will tell you if the sensor is faulty?? any help on 02 sensor testing would be appreicated.

Thanks for all the posts, this forum is wicked!!!

[toolman]

Clogged cat?