Maddening Running Issue
Moderators: hot66, impmad2000, Barry, Viv_Surby, Derek, Mike Usiskin
-
- DDK 1st, 2nd and 3rd for me!
- Posts: 2066
- Joined: Thu Jul 08, 2021 8:18 am
- Location: Lichfield
Re: Maddening Running Issue
Will it hold at 3k revs, given sufficient throttle?
1970 911T, Signal orange (Restoration thread)
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
-
- DDK addict
- Posts: 118
- Joined: Fri Jan 06, 2012 4:55 pm
- Location: Buckinghamshire, United Kingdom
Re: Maddening Running Issue
I know this is a different car ('72 T, running on Webers), but I had similar symptoms with what turned out to be a largely blocked fuel filter. I am not saying your filter is blocked, but more just echoing your hunch that it is fuel and not sparks. It is easy to forget the old rule, but check the really obvious things first. Good luck with this. I know how annoying a small thing can be when it stands in the way of enjoying your car!
Best wishes,
Sam.
'72 911T - '72 3.0csl - 1990 Z1 - Austin 7 Ulster Replica - Derelict 1925 Rolls Royce
Sam.
'72 911T - '72 3.0csl - 1990 Z1 - Austin 7 Ulster Replica - Derelict 1925 Rolls Royce
Re: Maddening Running Issue
JB, not resolved yet as have been away - looking to do the 30 sec fuel pump test next week.
Sam, it's a good point re. fuel filter - will check that too.
Rob, no it wont hold revs at all. It just carries on as per the video.
Sam, it's a good point re. fuel filter - will check that too.
Rob, no it wont hold revs at all. It just carries on as per the video.
'72 2.4S Targa
-
- DDK 1st, 2nd and 3rd for me!
- Posts: 2066
- Joined: Thu Jul 08, 2021 8:18 am
- Location: Lichfield
Re: Maddening Running Issue
It appears to be a problem which accumulates over a period of two to three seconds while the engine's running, and resolves itself over a similar period when the engine's not running.
That points to a "insufficient rate of flow" problem, which is most likely fuel.
Most likely some crap in the system. That's made more likely if the problem started abruptly.
I'd be curious if you turn the key fully off in-between starts - so the fuel pump's not running - does it fail to recover between starts?
There's a theoretical possibility the cdi has a bad earth. If so, I could imagine charge building up on the supposedly earthed plate of the capacitor, which might take a few seconds. But I think that's less likely than fuel. Ignition is testable by spraying carb cleaner into the intakes as you crank. If it runs better with that, you have ignition and your problem is fuel.
Sent from my SM-G988B using Tapatalk
That points to a "insufficient rate of flow" problem, which is most likely fuel.
Most likely some crap in the system. That's made more likely if the problem started abruptly.
I'd be curious if you turn the key fully off in-between starts - so the fuel pump's not running - does it fail to recover between starts?
There's a theoretical possibility the cdi has a bad earth. If so, I could imagine charge building up on the supposedly earthed plate of the capacitor, which might take a few seconds. But I think that's less likely than fuel. Ignition is testable by spraying carb cleaner into the intakes as you crank. If it runs better with that, you have ignition and your problem is fuel.
Sent from my SM-G988B using Tapatalk
1970 911T, Signal orange (Restoration thread)
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
Re: Maddening Running Issue
Rob, thanks.
Re "turning fully off between starts" - it doesn't fully start - i'm having to crank it over in the video.
It hasn't been an abrupt fault - seems intermittent. When the car was running fine after re-built it did exactly as per the video one night after a fairmile meet, although it did start and eventually it cleared after a lot of revving and then ran fine.
Bad earth is still a possibility I guess, but all connections are good.
Re "turning fully off between starts" - it doesn't fully start - i'm having to crank it over in the video.
It hasn't been an abrupt fault - seems intermittent. When the car was running fine after re-built it did exactly as per the video one night after a fairmile meet, although it did start and eventually it cleared after a lot of revving and then ran fine.
Bad earth is still a possibility I guess, but all connections are good.
'72 2.4S Targa
Re: Maddening Running Issue
I had issues like this that I traced to fuel delivery on my MFI, for me the issue was variable fuel pressure caused by sticking pressure control valve in the return fitting of the fuel filter assembly, pressure would stick high and low randomly when driving around. I found this by fitting an inline analogue pressure gauge in the fuel line in the engine bay. I think this is a great addition to have as I can see the fuel pressure is good an consistent now whenever I want, this would also help diagnose blockage problems from crud etc mine runs around 11psi and is consistant now, the car was instantly improved. Theres more details in my resto thread showing how i checked the valve operation and how I fixed it without replacing it
Re: Maddening Running Issue
knapmann - thank you - i will definitely check that out. i think the control valve was mentioned earlier as a potential problem. very interested to see how you fixed without replacing!
'72 2.4S Targa
Re: Maddening Running Issue
here's a link to knapmann's resto post with in-line gauge etc for those following: viewtopic.php?t=66841&start=465
'72 2.4S Targa
Re: Maddening Running Issue
my comments around the pressure release valve are here posted 14th & 15/03/2021, pages 24 and 25 of the thread.
viewtopic.php?t=66841&hilit=square&start=345
viewtopic.php?t=66841&hilit=square&start=345
Re: Maddening Running Issue
it might be totally different issue, but if the OP suspects fuel delivery is part of the problem for me the best way to check is to get a pressure gauge then if that shows a problem it can only be a blockage at the intake in the tank, a blocked filter canister (unlikely), a problem with the pressure release valve, or a failing electric pump.
This assumes it is piped up correctly. There are/were issues with incorrect fuel line diagrams from the factory depicting incorrect routings of the filter canister to & from the MFI pump and tank return etc If it has been piped up incorrectly then who knows!
The error is shown by Grady on post #19 here
https://forums.pelicanparts.com/porsche ... blems.html
This assumes it is piped up correctly. There are/were issues with incorrect fuel line diagrams from the factory depicting incorrect routings of the filter canister to & from the MFI pump and tank return etc If it has been piped up incorrectly then who knows!
The error is shown by Grady on post #19 here
https://forums.pelicanparts.com/porsche ... blems.html
Re: Maddening Running Issue
knapmann, this sounds like a good first option. do you have a link to the gauge you installed please?
have checked the line plumbing - it's all correct.
have checked the line plumbing - it's all correct.
'72 2.4S Targa
-
- DDK 1st, 2nd and 3rd for me!
- Posts: 2066
- Joined: Thu Jul 08, 2021 8:18 am
- Location: Lichfield
Re: Maddening Running Issue
It'll probably run with this squirted in the intakes if it's a fuelling problem.
https://amzn.eu/d/inJdQQO
Sent from my SM-G988B using Tapatalk
https://amzn.eu/d/inJdQQO
Sent from my SM-G988B using Tapatalk
1970 911T, Signal orange (Restoration thread)
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
1988 3.2 Carrera backdate, Black
2001 996 Turbo, Lapis blue (am I allowed to put that here?)
I'm looking for a pre-impact bumper 911S or other high-revving 911 to restore - please let me know if you see one.
Re: Maddening Running Issue
i bought this one... it was only £50 back then!
https://www.ebay.co.uk/itm/111704283762
this looks much the same and cheaper
https://www.ebay.co.uk/itm/284123850859