[mlneville]

Hey everyone, I'm fairly new to this site but i've owned my 92 968 cab for a couple of years now. I'm not sure when it actually happenend but here is the situation. My car is running hotter than normal and I cant rev the motor over 4100 RPM under a load. i.e. while in gear.



I'm pretty sure the reason its running at the upper limits of heat is because there isn't enough fuel getting to the cylinders. I also assume that the same reason the car falls on its face at 4100 RPM. I was hoping to find someone on this site who has seen this problem before and tell me or give me some advice on tracking down the source of the problem.



In my opinion, I think it could be a week fuel pump, clogged fuel filter, MAF sensor, DME possibly? or a combination of all of these components.



Other than runing hot and no power after 4100rpm, the car is in great shape. I hope to have some pics available soon. I really enjoy the car.. even without the power but I definitley want to get it back up to par.



HELP!!! I'm sure someone has had to have seen this problem before.



Thanks,

Mike

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[SILVY968]

the varicam comes in at about 4100. You should get a boost in power after that, not a drop.

I would change the fuel filter and the DME relay.

Heat may be the thermo switch fault or a failure/sluggish water pump.

The MAF can be cleaned with MAF cleaner in 5 minutes, I would invest the time and the $5.

If you are being rev limited I would guess a bad computer.

Try the fast cheap stuff first, but do not let the engine overheat or you will be in big trouble with and aluminum engine.

Brian

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[PorscheDude]

Variocam works at 1500 and 5200 or there abouts. The 4100 kick is from the intake manifold.



Try cleaning the MAF, changing fuel filter.

When was ignition system last checked? Plugs, wires, cap and rotor.

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[SILVY968]

[quote name='smokiemon968' post='50501' date='Apr 7 2008, 05:22 AM']Variocam works at 1500 and 5200 or there abouts. The 4100 kick is from the intake manifold.



Try cleaning the MAF, changing fuel filter.

When was ignition system last checked? Plugs, wires, cap and rotor.[/quote]



I stand corrected. It is quite a kick. thanks for the info. What would stop his engine from pulling @ 4100?

Brian

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[flash]

there is a LONG list of things that could cause this - it could be anything from a clogged fuel filter to a leaky head gasket



shooting in the dark is ill-advised



back to basics - 3 things to make an engine run - compression, fuel and spark



pull the plugs and look there first



then, while they are out, do a compression check



if those are fine, then start looking at the fuel pressure and flow, and then the control mechanisms

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[mlneville]

Thanks guys for your input... I'll begin troubleshooting this weekend. I'll keep you posted on how it goes.



Thanks,

Mike

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[Cloud9...68]

How hot is it running? And what happens at 4100 rpm? Does the engine just give out, and not want to rev above 4100? Or does it start bucking/hesistating? Is it worse when the engine/ambient are hot, cold, or doesn't it matter?



Yes, look at the plugs, do a compression test while you have them out, and then I would do a blink test, because it's free, and it may save you a lot of trouble and point something out that will lead you to a solution. Good luck; I went through something similar a few years ago, and know how frustrating it can be. As dramatic as your symptom is, hopefully the problem will be fairly easy to find.

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[banditsc]

I think possibly a bad coil could do that also. It would show spark, but it might be weak.

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[mlneville]

The car temperature gets somewhat close to upper white line of the gauge. It never goes over it. It fluctuates between there and normal termperature. At 4100, it sounds like its starving for fuel and you get motor ping... it wont rev beyond that most of time but sometimes it will. It will rev normal when its not under a load. I'll be checking the compression later today and some other basic stuff as well.

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[mlneville]

OK.. So I did a compression test both wet and dry. Cylinder 2 is a little weak but not bad for the miles on the car. I did determine that I don't have a blown headgasket though. I also took a look at the plugs and they are much whiter than I would like. This confirms my suspicion that it is a fuel starvation issue. I changed the fuel filter and the car runs a little bit better. It doesn't seem to run as hot. Its been running in the normal temperature range and I can get about 4500 rpm's before it starts to cut out. So now i need to test the rest of the fuel delivery system. I need to find a shop that can clean the injectors off the car.. I have a sneaky feeling that i'm going to find my problem with the injectors being clogged or defective. Anyway i'll keep you guys posted as I continue my search.



Mike

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[Cloud9...68]

I used these guys to clean my injectors a few years ago:



http://www.injector.com/injectorservice.ph...cf1fc4d8243216a



Several other on this site have also used them. They produce a nice before & after report on the flow through each injector. Good luck.

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[Cloud9...68]

Yes, adequate fuel delivery is critical. There's a spec for fuel flow rate that should be in the manual - if you can't find it, I could look it up for you. Testing the flow rate is simple - you just disconnect the fuel line at the rail, have a helper turn the key to engage the pump, and measure how much fuel flows into a measuring cup or graduated cylinder in a period of time.

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[mlneville]

Hey guys, great idea on the fuel flow... I will test the fuel flow and pressure to see where that leads. It could very well before the injectors.. I'll let you know the results.



Mike

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[doster]

In an earlier post you said you were getting pinging, You might want to check the timing belt and pull the valve cover and do an inspection. Just a thaught <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



good luck

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[crazyz007]

Did you ever get your issue resolved? One possibility is a plugged up exhaust system. The catalytic converter could be plugged up.

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[luis77]

I had a clogged exhaust and had the same symptoms sometimes at 5k and 6k, wouldnt go above it. Replaced exhaust. Problem gone.

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