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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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 Posted: Thu Sep 07, 2023 9:07 pm Post subject: low mile 924 jerks on throttle lift and application |
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Hi,
My first post in a while. As some of you may remember, late last year I purchased an '84 924 manual with only 9800km. I have been driving it a little here and there over the summer, trying to rectify issues, and now comes one that is bugging me a bit.
When I press or let off the accelerator quite abruptly, the car really jerks. Can be in any gear and any rpm, but naturally more noticeable in the lower gears. From what I have read online, this symptom could be either a failing rubber clutch disc, or engine mounts. I can't imagine the clutch is failing, but maybe time has just degraded the rubber? I also understand that engine mounts can also fail over time rather than distance.
But what do people think? More likely engine mounts or the rubber clutch failing?
Thanks!
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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morghen
Joined: 21 Jan 2005
Posts: 9027
Location: Romania
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| Posted: Thu Sep 07, 2023 9:16 pm Post subject: |
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Define jerks...ro better describe whats happening...i could also understand that the engine hesitates from your description.
You could have bad engine mounts (the one under the exhaust can have a broken spring), you could have bad gearbox mounts...or bad driveshafts..or just a vacuum leak and the engine buckles.
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Fri Sep 08, 2023 1:48 am Post subject: |
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| morghen wrote: | Define jerks...ro better describe whats happening...i could also understand that the engine hesitates from your description.
You could have bad engine mounts (the one under the exhaust can have a broken spring), you could have bad gearbox mounts...or bad driveshafts..or just a vacuum leak and the engine buckles. |
The engine definitely doesn't hesitate. Almost like it is too eager when I step on the accelerator from either coasting or low rpm in low gears. The whole car jerks/jumps around for a little over a second. A bit like a bunny hop when you let the clutch out too fast, but the clutch is not being used, and it is definitely not slipping.
The engine is actually very responsive in all rpm range.
If I am super gentle on and off the accelerator, it is relatively smooth, along with higher speeds when naturally the car's momentum overpowers the lift off the throttle to change say 4-5.
When coming off the accelerator, it can be at low rpm or high, but only if I really lift off fast. Again, if I am very soft, no jerking.
I doubt the driveshaft can be bad with only 10,000 km on it. Maybe a vacuum leak. But I am leaning towards engine mounts considering they are 39yrs old. Gearbox mounts could also be suspect then... hmmm.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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morghen
Joined: 21 Jan 2005
Posts: 9027
Location: Romania
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| Posted: Fri Sep 08, 2023 3:30 am Post subject: |
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A friend’s 924SC does something similar, cant point out why exactly but i think the gearbox mounts are dead on it.
Drop me a line if/when you want a supercharger or efi kit for that 924 
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Cedric
Joined: 27 Aug 2004
Posts: 2730
Location: Sweden
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| Posted: Fri Sep 08, 2023 3:59 am Post subject: |
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My old na did that when ignition timing was out, which happened when the breaker points wore.
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1980 924 Turbo
www.instagram.com/garagecedric/ |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Fri Sep 08, 2023 6:03 pm Post subject: |
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| morghen wrote: | A friend’s 924SC does something similar, cant point out why exactly but i think the gearbox mounts are dead on it.
Drop me a line if/when you want a supercharger or efi kit for that 924 |
Funny man  (re SC)
I really hope it is not gearbox mounts, as they are super expensive from what I can find  Is there an easy way to check these?
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Fri Sep 08, 2023 6:04 pm Post subject: |
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| Cedric wrote: | | My old na did that when ignition timing was out, which happened when the breaker points wore. |
I severely doubt the breaker points are worn with only 10,000 km on them?
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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Cedric
Joined: 27 Aug 2004
Posts: 2730
Location: Sweden
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| Posted: Fri Sep 08, 2023 7:17 pm Post subject: |
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| SecaBlue wrote: | | Cedric wrote: | | My old na did that when ignition timing was out, which happened when the breaker points wore. |
I severely doubt the breaker points are worn with only 10,000 km on them? |
Maybe Double check the timing and do a vacuum leak test to be fully sure.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Wed Sep 13, 2023 2:41 am Post subject: |
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I have bought these engine mounts from Design911 which are supposed to be a direct replacement for both left and right mounts on '84 924. Anyone else used them and can confirm they fit ok?
https://www.design911.co.uk/p/engine-mount-replacement-porsche-924/?source=doofinder
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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Cedric
Joined: 27 Aug 2004
Posts: 2730
Location: Sweden
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| Posted: Wed Sep 13, 2023 3:22 am Post subject: |
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They look similar to the vibratechnics, but not identical, i really hope these are better, because the vibras were quite crap.
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Wed Sep 13, 2023 5:34 am Post subject: |
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| Cedric wrote: |
They look similar to the vibratechnics, but not identical, i really hope these are better, because the vibras were quite crap. |
They were the other brand option on Design911. Rosepassion had no option, and the only other way was a back-order from Utzon here in Sweden for the RS mount like OEM, and just the spring for the LS. Thought maybe it best to try the ones I ordered now.
Just out of interest, how did you measure the 'crap'ness of the other brand?
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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Fifty50Plus
Joined: 28 Feb 2008
Posts: 1401
Location: Washington DC area
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| Posted: Wed Sep 13, 2023 6:37 am Post subject: |
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I've had the VibraTechniques in my race car for 6 years and no problems.
_________________
1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Tue Sep 26, 2023 11:23 pm Post subject: |
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Finally have my car back from Porsche here in Sweden, after many checks and adjustments. Their summary from their veteran mechanic is as follows:
Timing re-checked (new timing belt was installed only a month ago), and all lines up correctly.
Vacuum leak found near TB, fixed.
Mixture off, so adjusted - CO down from 4.5 to 1.5.
Idle lifted slightly.
Engine mounts were not replaced, as visually they appeared like new. Same with the gearbox mounts.
Verdict:
Car still jolts around with harsh throttle application and lift-off in 1st, 2nd and 3rd gear low to meduim revs, but about half as bad as it was. They could not give a solution to make it smoother.
And now car bunny-hops slightly when applying throttle from anything sort of 1500-2000rpm in 1st, 2nd and 3rd. (and no, I am not trying to load up the engine with too lower road speed). This symptom was not there prior to what they did above.
Any clues? I know I have issues with the WUR, as I don't have a high idle at cold starts (if I understand that is causing it). But the engine does start immediately cold or warm. Just when cold and I let the rpm sit lower than 1200rpm, it is not happy. Warm idle is fine.
It revs fine both cold and warm.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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Cedric
Joined: 27 Aug 2004
Posts: 2730
Location: Sweden
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| Posted: Wed Sep 27, 2023 2:18 am Post subject: |
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Co screw doesn't do much outside of idle though. A fuel pressure measurement of both control and system pressure should be important, they should have done it if they know anything about kjet. Hooking up a wideband Sensor in the exhaust and take it for a ride could also be very helpful. I could help with both of those, but i dont think you live close to Stockholm?
_________________
1980 924 Turbo
www.instagram.com/garagecedric/ |
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SecaBlue
Joined: 16 Sep 2022
Posts: 37
Location: Sweden
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| Posted: Wed Sep 27, 2023 2:49 am Post subject: |
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| Cedric wrote: | | Co screw doesn't do much outside of idle though. A fuel pressure measurement of both control and system pressure should be important, they should have done it if they know anything about kjet. Hooking up a wideband Sensor in the exhaust and take it for a ride could also be very helpful. I could help with both of those, but i dont think you live close to Stockholm? |
I'm down in Skåne, so not close to you unfortunately
I think I will just garage the car now for the Winter and review stuff in the Winter or Spring next year... the WUR and AAV need a review/test too. Just didn't have time or means to dive into that yet. And since it does actually start cold or warm with relatively small issues, it was not a priority.
_________________
1984 924 manual.
1993 928GTS Auto.
1990 944S2 manual (sold).
1987 928S4 Auto (sold).
2001 996 Turbo (sold). |
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