993 poor high rpm performance

[993G]

gwsinc said:

Also may be worth replacing the fuel pressure regulator if it's original (as a test, remove the furthest left vacuum line from intake manifold and sniff it, if you smell fuel the FPR membrane is probably gone), throttle position sensor (very cheap) and intake temp sensor (also cheap).

Once you've replaced these take the DME out for a few seconds and replace, this will reset ECU 'learning'.

Still think your best bet is to have a look at the injectors, this is what mine were like after 25 years!


Before and after:

Wow your injectors were dirty!

[gwsinc]

993G said:

Wow your injectors were dirty!

Yes that black gunk was horrible, glad cleaning worked as new ones are £250ish each!

[993G]

gwsinc said:

993G said:

Wow your injectors were dirty!

Yes that black gunk was horrible, glad cleaning worked as new ones are £250ish each!

Did you clean them yourself or send them out ?

[gwsinc]

993G said:

Did you clean them yourself or send them out ?

Did them myself. Sprayed carb cleaner through them till the stream of fluid out the other end became a mist, then replaced all the o-rings, pintle cap, filter etc and popped them back in.

[993G]

Hey just wanted to update you all. I changed the fuel filter yesterday and attempted to test the pump. I did a volume report and got almost 2 liters in 30sec with the jumper. I tried to test the pressure and my gauge failed. It looked like 56psi with the jumper but that’s when the leak sprung.... so I put everything back together an took for a quick drive and its runing like new?

My fuel filter was only 1 year old , maybe defective? Or just clogged . I’m puzzled but runs better now.

Thanks for all the help!

[Aircooled_Bug]

Are you running the original cat? When they are knackered they can cause running issues when hot at higher RPMs. If it doesn't do it when cold probably won't be this.

[993G]

Aircooled_Bug said:

Are you running the original cat? When they are knackered they can cause running issues when hot at higher RPMs. If it doesn't do it when cold probably won't be this.

Thanks yes stock cat original. It’s running like new now. I think I was getting some restriction at the fuel filter not sure why as it only had one season on it , possibly defective.

[gwsinc]

993G said:

Thanks yes stock cat original. It’s running like new now. I think I was getting some restriction at the fuel filter not sure why as it only had one season on it , possibly defective.

Great news

[993G]

Ok ... so this problem manifested again

It seems to only happen when the engine is really warm it breaks up under load and runs on low power again?? Slow to rev to red line .

The fact that this has been intermittent I’m leaning toward a sensor but maybe I’m wrong . Possible culprits I was thinking head temp or Flywheel sensor .

Any suggestions

Edited by 993G on Friday 8th May 16:12

[Aircooled_Bug]

993G said:

Ok ... so this problem manifested again

It seems to only happen when the engine is really warm it breaks up under load and runs on low power again?? Slow to rev to red line .

The fact that this has been intermittent I’m leaning toward a sensor but maybe I’m wrong . Possible culprits I was thinking head temp or Flywheel sensor .

Any suggestions

Edited by 993G on Friday 8th May 16:12

I had something similar. Pull the cat and take a look inside.

[993G]

I kinda thought of that first I put a camera in there and thought it looked ok . No build up nice and white honey comb.

What did your cat look like?

[Aircooled_Bug]

One side looked fine, the other was like Pompeii.

[993G]

Any ideas guys?

As soon as the car gets to operation temps like after 20 minutes of driving the car it goes into a low power mode? But still runs smooth ??

[2u2r]

Crank sensor braking down would be my guess.

[Slippydiff]

2u2r said:

Crank sensor braking down would be my guess.

Crank sensor, MAF or Lambda sensor issue.

[porkey]

Ignition leads. My old 964 had a similar problem. Run the engine in the dark with the lid open and see if you get a light show with the leads arcing.

[Mishima]

I suffered a drop in power a few years ago, the cause of which 2 indies couldn't identify. Autofarm quickly found that it was only firing on 6 plugs and traced the fault to an ignition control module which I think is under the l/h seat and sends a low-voltage signal to somewhere or other; it sounds as if you have the knowledge and competence to test it?
It was something that happened suddenly but the car ran smoothly and felt the same all the time; I just knew it wasn't right.

[993G]

Well looks like sometimes its the simple things . I replaced my dme relay last fall because the original was bad. Low and behold something happened to my replacement because it went bad again. I replaced it and back to normal!

What could cause one to go bad so quickly?

Shocking a relay could cause all those problems.

[Orangecurry]

...or, as it's an intermittent fault, changing the relay is a red herring.

[gwsinc]

993G said:

Well looks like sometimes its the simple things . I replaced my dme relay last fall because the original was bad. Low and behold something happened to my replacement because it went bad again. I replaced it and back to normal!

What could cause one to go bad so quickly?

Shocking a relay could cause all those problems.

I suspect it’s not the relay causing the issues, each time you unplug the DME relay it resets ECU learning so it will run off the base map till it gets more info from your sensors.

I think a sensor somewhere is sending duff information to your ECU causing running issues. Given you say it gets worse when the car is up to temperature I would look at everything affected by temperature first. So O2 sensor and intake air temp sensor first (£100 for both and easy diy).