Maddening Running Issue
Moderators: hot66, impmad2000, Barry, Viv_Surby, Derek, Mike Usiskin
Re: Maddening Running Issue
Thank you! Will order.
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'72 2.4S Targa
Re: Maddening Running Issue
thanks rob. have added to the list of checks!RobFrost wrote: ↑Thu Apr 04, 2024 6:11 pm It'll probably run with this squirted in the intakes if it's a fuelling problem.
https://amzn.eu/d/inJdQQO
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'72 2.4S Targa
Re: Maddening Running Issue
Hello again - to update:
Got the pressure gauge and installed today. Ran pump and it was showing 12psi solid on first try and of course then she fired up without much trouble. See here:
https://youtu.be/YlsVygWm-Xc?si=y9tDeSbuKtyiHGPY
So after checking for any fuel leaks warmed it up and went round the block.
Now pressure has dropped to 9psi and you can see from this second video that it’s doing that weird hunting thing no matter what throttle input I use:
https://youtu.be/hAvmVciCwxo?si=5ybcAlgFoIT8DIrT
So what is the next logical step here? I am thinking it’s the check valve but your thoughts as always are appreciated.
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Got the pressure gauge and installed today. Ran pump and it was showing 12psi solid on first try and of course then she fired up without much trouble. See here:
https://youtu.be/YlsVygWm-Xc?si=y9tDeSbuKtyiHGPY
So after checking for any fuel leaks warmed it up and went round the block.
Now pressure has dropped to 9psi and you can see from this second video that it’s doing that weird hunting thing no matter what throttle input I use:
https://youtu.be/hAvmVciCwxo?si=5ybcAlgFoIT8DIrT
So what is the next logical step here? I am thinking it’s the check valve but your thoughts as always are appreciated.
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'72 2.4S Targa
Re: Maddening Running Issue
Update - let the engine cool for 30 mins then ran fine at about 10psi
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'72 2.4S Targa
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- Nurse, I think I need some assistance
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Re: Maddening Running Issue
.
Fuel pressure for mfi needs to be ~ 14.5psi from memory ...
.
Fuel pressure for mfi needs to be ~ 14.5psi from memory ...
.
Andy
“Adding power makes you faster on the straights;
- subtracting weight makes you faster everywhere”
“Adding power makes you faster on the straights;
- subtracting weight makes you faster everywhere”
Re: Maddening Running Issue
The hunting is probably because the pressure isn’t enough to open the injectors, until the pump builds enough pressure then they open & pressure drops until they shut, then repeat.
Re: Maddening Running Issue
Agreed. The question is therefore whether this is because of a dodgy pressure control valve or dodgy electric fuel pump. I’ll have a look through my notes from when I did this test a few years agoBruce M wrote:The hunting is probably because the pressure isn’t enough to open the injectors, until the pump builds enough pressure then they open & pressure drops until they shut, then repeat.
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Gavin
'73 911E -> 2.7mfi
'94 968 Sport
'73 911E -> 2.7mfi
'94 968 Sport
Re: Maddening Running Issue
Thanks Andy, from what I have read on Pelican it appears the consensus is that 11.8 PSI +/- 3 is spec so 8.8-14.8 is within spec so I would be at the bottom of that range but still should be ok. I haven’t checked flow yet so maybe that’s the best next step?
Or maybe just bite the bullet and get a new $$$ pump. Autoatlanta will do a rebuild for about $400 anyone have any experience of those pumps?
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Or maybe just bite the bullet and get a new $$$ pump. Autoatlanta will do a rebuild for about $400 anyone have any experience of those pumps?
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'72 2.4S Targa
Re: Maddening Running Issue
Thanks both - that seems very logical.gav p wrote:Agreed. The question is therefore whether this is because of a dodgy pressure control valve or dodgy electric fuel pump. I’ll have a look through my notes from when I did this test a few years agoBruce M wrote:The hunting is probably because the pressure isn’t enough to open the injectors, until the pump builds enough pressure then they open & pressure drops until they shut, then repeat.
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GavP is there a way to test the control valve?
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'72 2.4S Targa
Re: Maddening Running Issue
official docs agree with Andy with 1bar ( 14psi)
James
1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster
Its not how fast you go, but how you go fast
1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster
Its not how fast you go, but how you go fast
Re: Maddening Running Issue
That hunting is weird .. so that was at part throttle ? All 6 cylinders effected which does point to something pre the MFI pump if fuel related
James
1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster
Its not how fast you go, but how you go fast
1973 911 2.4S
1993 964 C2
2010 987 Spyder
1973 MGB Roadster
Its not how fast you go, but how you go fast
Re: Maddening Running Issue
Thanks James. Yes, part, half, full, makes no odds.hot66 wrote:That hunting is weird .. so that was at part throttle ? All 6 cylinders effected which does point to something pre the MFI pump if fuel related
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'72 2.4S Targa
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- DDK 1st, 2nd and 3rd for me!
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Re: Maddening Running Issue
You should hook up a timing light during hunting and confirm there's a spark when the revs are falling.willbrown wrote:Thanks James. Yes, part, half, full, makes no odds.hot66 wrote:That hunting is weird .. so that was at part throttle ? All 6 cylinders effected which does point to something pre the MFI pump if fuel related
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Is there a smell of unburnt fuel?
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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
Thanks Rob - I’ll add to the list. No smell of unburned fuel. I’m pretty convinced it’s not spark - all ignition parts new and have tested with a replacement CDIRobFrost wrote:You should hook up a timing light during hunting and confirm there's a spark when the revs are falling.willbrown wrote:Thanks James. Yes, part, half, full, makes no odds.hot66 wrote:That hunting is weird .. so that was at part throttle ? All 6 cylinders effected which does point to something pre the MFI pump if fuel related
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Is there a smell of unburnt fuel?
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'72 2.4S Targa
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- DDK 1st, 2nd and 3rd for me!
- Posts: 2065
- Joined: Thu Jul 08, 2021 8:18 am
- Location: Lichfield
Re: Maddening Running Issue
I asked re unburnt fuel partly in case the mfi timing is off. How about the plugs, what colour are they, and are they wet with unburnt fuel?
If it is fuel I can't be of much help as I don't knownthe mfi system well at all.
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If it is fuel I can't be of much help as I don't knownthe mfi system well at all.
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.