993 poor high rpm performance

[993G]

Hello.
I’m new here I have a 1995 993 3.6 manual gearbox. It was a bit neglected when I got it. So I did the full 60k service all new parts. However still I get poor top end almost like my timing is off or it’s slow to rev to red line. No warning lights present. I checked the distributor belt first all is well there. Tested vacuum entire system is holding good. New dme relay also replaced ignition module,coils, maf, gas filter, air filter, and cleaned isv .

Motor runs really smooth just feels like I’m down on power.

Any suggestions where to look next.

[993G]

Yes still same problem I’m going to test fuel pressure and volume test tomorrow. Maybe weak pump?

[993G]

Orangecurry said:

1995... is is Varioram or pre-?

Pre-vario

[993G]

Slippydiff said:

Check the resonance flap actuator diaphragm isn't split.

I did it’s holding vacuum.

[993G]

How does cam timing slip? Cam chain itself slipped?

Leads and coils are new and are both working

[993G]

trantorman said:

Worth checking both Rotor arms are turning they can run fairly well with a broken distributor belt.

I did both are working and car will run on either distributor .

[993G]

ras62 said:

The 993 use 2 methods to set cams, some have the older 964 holed sprocket and pin arrangement while others use the later clamp friction method which can slip. This would effect performance across the range. I would check the wide open throttle first then air leaks then cam slip as a last resort.

Ok thanks

[993G]

Slippydiff said:

993G said:

I did it’s holding vacuum.

When you apply a vacuum to it, does the actuator actually move ? It may be holding vacuum in the closed position ...

Yes the arm moves on he actuator

[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!

[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 ?

[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!

[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.

[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

[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?

[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 ??

[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.

[993G]

gwsinc said:

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).

Thank you I’ll run it some more and see if it reverts back to it’s bad running condition. I replaced both the air temp and the oxygen sensor already.

I was going to pick up a head temp sensor but I noticed they changed the plug I have to buy a 996 part.

[993G]

Well still having issues , I’m leaning towards flywheel sensor /head temp sensor/ distributor/ fuel pump.

My distributor belt is intact. I have been putting off the sensors in the back as I have to update the wire harness to 996 plugs.
Pictures attached of my cat converter both sides , I thought they looked ok?
[url]

[993G]

Car runs awesome low to mid range and on part throttle. When I floor it or try and push past 5k when the problem starts. It does not want to rev higher.

[993G]

gwsinc said:

993G said:

Car runs awesome low to mid range and on part throttle. When I floor it or try and push past 5k when the problem starts. It does not want to rev higher.

Throttle Position Sensor perhaps? Around £20, so worth a shot.

Also how’s your throttle pedal adjustment, does foot to the floor open the throttle fully?



Boom !! My man , TPS sensor fixed it. I have full throttle now amazing.

My cable has some slack too, I need to snug it up but not sure how. I had someone else push the gas pedal and it moves about 1/4 before throttle is actually opening.