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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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 Posted: Sat Sep 26, 2015 10:38 pm Post subject: Cool down starting issue! |
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Hey guys. 924 NA starts cold no problems starts when fully warmed up no problem, after about 30 mins still okay, but leave the beast for at least an hour and it struggles to fire! Full throttle then turn her and she fires a bit after a couple of turns but splutters and you have to rev a little to get her to idle, after that it okay until the next cycle time!
I read somewhere about either the accumulator or check valve in fuel pump, causing vapour lock!
Any advice would be GR8 
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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Fasteddie313
Joined: 29 Sep 2013
Posts: 2595
Location: MI
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| Posted: Sat Sep 26, 2015 11:14 pm Post subject: Re: Cool down starting issue! |
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| RobertN wrote: |
I read somewhere about either the accumulator or check valve in fuel pump, causing vapour lock! |
I'm not sure about them causing vapour lock but the are responsible for holding residual fuel pressure to aid in hot starting conditions.. The check valve keeps your pressure from going back to the tank and the accumulator maintains pressure while allowing for some loss of fuel volume like a sprung reservoir.
The system pressure regulator plunger in the fuel distributor also is responsible for holding residual pressure as it shuts the main fuel return line and the WUR return line when it closes..
When you get to your condition where it doesn't like to start try jumping the fuel pump to get some fuel pressure going on before you try to start it like that and see if it helps.
If you have a CIS tester hook it up when it's still cold and run it until hot, then keep an eye on your residual pressure as your car cools off into your problem area..
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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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| Posted: Sun Sep 27, 2015 4:57 am Post subject: |
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Good point Eddie. Just looking at the diagram which shows the flow of fuel from the regulating valve to tank and WUR. If that's opening too soon would that cause a vacuum in the system, and how can I test it? Silly question but how can I "jump" the fuel pump?
Don't have cis tester, but I will invest in one now.
At one time I thought it was the WUR, but she starts on the button when fully warmed, it's just that period of about 1 hour that causes problems, so I thought system pressure and possible accumulator or check valve problem, simply because I read about that, and not my amateur mechanic brain. 
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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Fasteddie313
Joined: 29 Sep 2013
Posts: 2595
Location: MI
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| Posted: Sun Sep 27, 2015 1:15 pm Post subject: |
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| RobertN wrote: | | Just looking at the diagram which shows the flow of fuel from the regulating valve to tank and WUR. If that's opening too soon would that cause a vacuum in the system, and how can I test it? |
What its main job is is to regulate your system pressure, it drops the high fuel pump pressure down to whatever system pressure it is supposed to give by returning just enough unused fuel to the tank to get down to the spec system pressure.
It opening too soon would lead to low system pressure, easily adjustable with shims on its spring, but I don't think ever a vacuum.. It not closing all the way would make it not hold residual pressure though. You can take it apart to clean it but be extremely careful with the piston as it is super duper precision and just a scratch can render your entire fuel distributor scrap metal, so don't drop it..
| RobertN wrote: | | Silly question but how can I "jump" the fuel pump? |
Take your fuel pump relay out, make a jumper wire between its pins 30 and 87, put the relay back in with the jumper wire on it.
That's the way I do it, actually I have a switch under the hood now but that's another story.
You could also make yourself a wire with a male spade connector on each end and just stick that into your fuse panel where the relay's pins 30 and 87 go in, that works too..
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gerben1986
Joined: 13 Mar 2008
Posts: 232
Location: The Netherlands
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| Posted: Sun Sep 27, 2015 11:08 pm Post subject: |
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First: get a pressure meter, otherwise you will keep replacing parts.
I also had this problem and there were a couple of reasons, which together made the problem:
- WUR
- Accumulator
- Temprature switch in the rear part of the engine
- Adjustment
So, when you don't know exactly what's the problem, you don't know what's the cuse of the prolem.
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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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| Posted: Mon Sep 28, 2015 2:53 am Post subject: Cool down start problems. |
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Thanks Eddie. Should I keep the wire in permanently? Also if I clean out the WUR also, is there anything special needed to do when re-installing?
Thanks.
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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| Posted: Mon Sep 28, 2015 2:58 am Post subject: Cool down start problem |
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Thanks gerben for your help. Can you test the accumulator and WUR. The only thing I have done us test the resistance of the WUR and its 18.1 ohm.
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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sheepdog924
Joined: 03 Dec 2013
Posts: 20
Location: United Kingdom
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| Posted: Mon Sep 28, 2015 3:29 am Post subject: |
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| There is a screw in the base of the accumulator, if you loosen it and fuel dribbles out then the diaphragm inside is knackered and you have to replace the whole thing. Be careful it reseals when you tighten it up again. You really have to do the pressure test, step by step to diagnose where your problem is. |
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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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| Posted: Mon Sep 28, 2015 3:40 am Post subject: |
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Nice one sheepdog. I'll try that also. Looking for a CIS tester kit I seen one in Amazon, for around $155 approx £118 do you know anywhere else cheaper in UK? I usually buy my parts from Frazer or Euro car parts here in Belfast.
Thanks.
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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Fasteddie313
Joined: 29 Sep 2013
Posts: 2595
Location: MI
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| Posted: Mon Sep 28, 2015 3:40 am Post subject: Re: Cool down start problem |
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| RobertN wrote: | | Should I keep the wire in permanently? Also if I clean out the WUR also, is there anything special needed to do when re-installing? |
No you should not leave the wire in as the wire will turn your fuel pump on and it will stay on as long as the wire is there. It's just for running the pump without running the engine, you do not want to run like that because it bypasses all the safety features that are good for you and your engine..
| RobertN wrote: | | Can you test the accumulator and WUR. The only thing I have done us test the resistance of the WUR and its 18.1 ohm. |
The accumulator is tested in your residual pressure reading, and also the screw on the bottom as he mentoned.
The WUR test is control pressure, you can also test it's bimetallic strip as you have but just because the strip works doesn't mean the rest of the WUR works.
If you want to pull and clean the WUR read this thoroughly first..
http://www.ferrari400parts.com/Warmupregulatorrepair.php
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gerben1986
Joined: 13 Mar 2008
Posts: 232
Location: The Netherlands
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| Posted: Mon Sep 28, 2015 6:14 am Post subject: |
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| RobertN wrote: | Nice one sheepdog. I'll try that also. Looking for a CIS tester kit I seen one in Amazon, for around $155 approx £118 do you know anywhere else cheaper in UK? I usually buy my parts from Frazer or Euro car parts here in Belfast.
Thanks. |
I think this one will work: http://www.ebay.co.uk/itm/121678956048
EAN: 8718475826798
And by using this tool you can see how the pressure drops after turning of the engine, based on that you can identify the problem.
There's a lot of information about that on this board, like this one: http://www.924board.org/viewtopic.php?t=35734
Once you have the pressure meter, send me a PM with your mailadress and I'll mail you some documents with a step-by-step checklist how to detect the problem.
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RobertN
Joined: 19 Apr 2015
Posts: 142
Location: Lisburn Co Antrim
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| Posted: Mon Sep 28, 2015 6:28 am Post subject: |
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Thanks Gerben. The eBay one has ended but I'll hunt one out no doubt soon.
Great write up from your link to the post here for the cis test, seems like a mine field of info, but I'm sure step by step I'll be able to get some result! I'll PM once I've sourced the tester, as ire ally need the help. Thanks a lot.
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Robert.
Porsche 924 N/A 1984.
Electrical Engineering Sales to Control panel builders. |
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