993 poor high rpm performance

993 poor high rpm performance

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993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
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.

Welshbeef

49,633 posts

197 months

Saturday 2nd May 2020
quotequote all
Have you run a few tanks of super unleaded through it?



Orangecurry

7,399 posts

205 months

Saturday 2nd May 2020
quotequote all
1995... is is Varioram or pre-?

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
Yes still same problem I’m going to test fuel pressure and volume test tomorrow. Maybe weak pump?

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
Orangecurry said:
1995... is is Varioram or pre-?
Pre-vario

Orangecurry

7,399 posts

205 months

Saturday 2nd May 2020
quotequote all
...and you say 'ISV' instead of ICV and 'gas' instead of petrol - are you in America-land?

Welshbeef

49,633 posts

197 months

Saturday 2nd May 2020
quotequote all
Could it be that the car has spent a lot of time doing short trips so it’s coked up - once Virus is over you can take it on long trips really get that motor hot and use plenty of the low gears and high rpm.

There are fuel additives wynns that can help remove the carbon without taking the head off. Costs a few quid worth a try.
Similar option wynns for the injectors they might not be putting in the fuel as a fine mist rather more dripping - but you’d also see sooty exhaust/on revs from the rear.


Slippydiff

14,742 posts

222 months

Saturday 2nd May 2020
quotequote all
Check the resonance flap actuator diaphragm isn't split.

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
Slippydiff said:
Check the resonance flap actuator diaphragm isn't split.
I did it’s holding vacuum.

ras62

1,086 posts

155 months

Saturday 2nd May 2020
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Is full throttle at the pedal giving full open at the throttle body? Other checks... HT leads seated ok and both coils are operating. Air leaks at the inlet stacks/rubbers (spray carb cleaner or similar near them and see if the engine revs change). Could even be cam timing has slipped which does happen on some 993s.

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
How does cam timing slip? Cam chain itself slipped?

Leads and coils are new and are both working

trantorman

88 posts

206 months

Saturday 2nd May 2020
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Worth checking both Rotor arms are turning they can run fairly well with a broken distributor belt.

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
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 .

ras62

1,086 posts

155 months

Saturday 2nd May 2020
quotequote all
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.

993G

Original Poster:

21 posts

46 months

Saturday 2nd May 2020
quotequote all
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

Slippydiff

14,742 posts

222 months

Saturday 2nd May 2020
quotequote all
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 ...


gwsinc

317 posts

79 months

Saturday 2nd May 2020
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My car was in a similar state. Try a bottle of Chevron Techron, and that will clear the fuel system out. If this sorts it out I’d recommend a more permanent fix would be to refurbish the injectors. An fairly easy DIY with a £25 parts kit you can get from eBay and a few basic tools and sprays.

Difference was night and day!

gwsinc

317 posts

79 months

Sunday 3rd May 2020
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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:

BertBert

18,953 posts

210 months

Sunday 3rd May 2020
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My thoughts would be to get an objective measurement on a rolling road. Not to try to specifically get a torque/bhp measurement, but to see what the torque is doing if it is down on power.

Trying to diagnose based one feel, feels quite hard to me.

Bert


993G

Original Poster:

21 posts

46 months

Sunday 3rd May 2020
quotequote all
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