peter_964rs

In my RS lightweight, as I was driving off from home, perhaps a quarter of a mile away, engine cold and with barely 2000rpm in 2nd gear, I flexed my right foot slightly and suffered a sudden loss of power. Sort of like hitting a giant elastic band for a second or so.

Then, power returned and I carried on. Worried that this might be a repeat of an embarrassing incident at the Nurbergring two years ago when something in the boot flew across on a corner and hit the battery isolating togle switch (D'oh!), I tiptoed back home and left the engine running in front to get nice and warm whilst I checked the switch, oil level, dials, etc.

There was nothing obviously wrong. So, engine nice and warmed up, I set off again. Everything fine until about ten miles down the road - once again in 2nd or 3rd gear, from fairly low revs, a sudden loss of power that was just as suddenly restored. This was quite a shocking and sudden power loss - no quite like hitting a brick wall, but close.

So I kept fairly calm and controlled, did my driving and visited a few people, and it happened two more times.

Now, I suspect either fuel supply or lack of spark. Specifically, last time I filled up the tank, I used super unleaded and topped up with STP injector cleaner for the first time ever - a friend's recommendation. I then drove in a big journey up the motorway (up to the PCGB event at Bramham Park if anyone else was there) and back again, around 700km all told.

I allowed the tank (it's the 60 litre version) to get almost empty before filling up again with super at a petrol station around two miles from my home, then parked up and didn't use the car again until last weekend.

Soooo.... what's the likely cause? Crud in a fuel line? The car starts OK and turns over healthily enough, so I think the battery has plenty of charge (I isolate it if I don't plan to drive for some time, and I ditched the lightweight RS battery for a higher-spec one a couple of years ago)

I'm about to book the car into my local Porsche centre to have new rear brake pads fitted, what can I ask them to (quickly - labour rates are high) check for me? I plan to ask them to check the fuel filter and fuel pressure or fuel lines for blockage (if that's a logical step?) and also the distributor to see if the belt's broken, or something.

What else? Hopefully not terminal......

Cheers

Thomas Linser

Dear Peter!
You mentionned that you used a injector cleaner and that you went all down the tank before reffilling with fresh gas.

First thing, Adrian warned a few times ago about those injector and or valve cleaner fluids you can add to the fuel. In summ what Adrian stated was that the fuel injectors gum up, and thus are no longer spraying the fuel by the amount ordered via the DME.

Second thing, I was warned by my mechanic not to drive my fuel tank empty, as he said that there are always a few debris and residues at the bottom of the tank, this can lead to fill up the fuel filter with those residues, which then isn't able anymore to supply the needed fuel.

I'm sure as soon as Adrian will read your post he will give you some more good advices.

Hope thus that it's nothing serious to worry about. Regards THOMAS <img src="graemlins/wave.gif" border="0" alt="[byebye]" />

peter_964rs

Thanks Thomas

This is more or less what I expected. I was dubious about the injector cleaner but thought I'd give it a go on someone else's advice..... "can't do any harm" I thought.

The fuel filter is supposed to be very large and "bound to" filter out any debris, so I'm inclined to think the injectors are gummed as you describe. Are they easy to clean?

If I need new injectors then this is all pushing me towards 930 motorsport's MOTEC ECU and power upgrade, which includes new injectors, and which I'm really lusting after!

Thomas Linser

Dear Peter!

The gum up thing dont look to expensive, Adrian says he clenas them once a year if I remember correctly, so it does not seem to be a dramatic job! I never did it 'till now but it's on my list of to do's. I think he uses clean and freshly filtered fuel to clean them, he explained the procedere on the subject I started a few weeks ago, search the forum for "gum up" and you'll get the response to your question

Er... concerning the fact that you have a RS, please don't tuch it, it's an icon a piece of mobile art. Any change will depreciate it. I know that in one or two years I will change from my C2 toward an RS, and by God I swear that I'll never buy a RS wit 3.8 cyl. increase or super dooper something, I just want it stock fullstop. If Porsche built it as it was, they had their reason. If I really want a 3.8 engine I'll have to save a lot more monney and buy myself a RSR or for less a 993 RS. Just my humble opinion, you mustn't agree but think about it.

Ragards Thomas <img src="graemlins/wave.gif" border="0" alt="[byebye]" />

DaveS

Peter:

These same set of symptoms have happened to me over the past 2 months, but the bad news is that I don't have an RS, lightweight flywheel or use injector cleaners. It happened occasionally when I was either in 2nd or 3rd at around 2800 RPMs, sometimes going up a slight incline. RPMs drop to 2000 suddenly and then kick back in. Kinda like a cruise control run amok.

I swapped out the aftermarket DME with the original but it didn't help. Some have suggested looking at distributor belt, but I don't think that's it. Others have said look at flywheel sensor, which could match your situation. I swapped out my DME relay with the 993 upgrade today. I'll let you know if that helps. For now, I have taken to making sure that I keep thr RRMs at or above 3000, especially when heading up a hill.

Good luck.

DaveK

Hi,
Flywheel sensor certainly can cause a similar effect. Mine died (actually the bolt holding the bracket on dropped out and the sensor then got smashed to pieces). For a few miles before it died completely I would be driving along perfectly happily and then would get a brief "hiccup" - everything died for a split second and then returned to normal.

Dave
90 C4

Adrian

Dear Peter,
Loss of power like this could be a number of things. Most likely an interruption in the fuel supply. My first culprit would be relay R41. The DME relay. I also point out that this relay provides the power to the O2 sensor heater. If this fails you will get dumped into limp home mode. Fuel filter. Certainly, I would have this changed if you cannot find when it was last changed.
I never recommend the use of injector cleaner in pulsed injectors. Remove and clean and have the spray pattern checked.
The fuel pump itself could be stalling. These are brush motors which do wear out.
I would certainly advise you check the secondary distributor belt. It may not be broken just yet but they shred and slip before they break. I have seen some that makes you wonder how they stayed together but they did but they slipped like crazy. Worth an inspection.
I would remove the airbox cover and the airfilter. Check for condition and check the inside of the airbox for any form on contamination. Anything from overfilling the oil to engine degreaser, even anti-corrosion spray that some people use. If you have a K&N set up check you have not used too much of that filter oil stuff.
Once you are past these basics then it is time to look harder.
Ciao,
Adrian
911C4

Kevin Ross

Peter

I second Adrian's first option. My C4 had the same issue, and eventually one day simply lost power altogether, and stopped in the middle of the road! I was in second at the time.

It turned out to be the DME.

I was told that these should be replaced as a matter of course at around 100000 kms anyway.

Have it checked.

jonfkaminsky

I had a similar problem a while back. My mechanic traced it to the ignition coils- which apparently get flaky when going bad.

peter_964rs

Thanks guys. My car is booked in with an OPC next week and I'll compile a list of potential problems for them to look at. Just as a prompt - they should know what they're doing, but you can never be too careful......