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E24 1983 Staring Issue

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Gareth91971 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gareth91971 Quote  Post ReplyReply Direct Link To This Post Topic: E24 1983 Staring Issue
    Posted: 14 Feb 2021 at 3:54pm
My 1983 635csi is a problem starter. The battery is new and on conditioning charge, but if the car is left for more than a couple of days without starting it turns over but will not fire up. If I come back to it a few hours later or early the next day it usually fires up. It runs well and seems to start no problem if it is used daily in the summer. I am finding through winter though it is harder to get it to start. I have been told it could be the computer, or possibly to do with fuel pressure. Any other owner had this problem? Suggestions and things to try welcome as otherwise it will have to be a recovery to a garage.
Thanks, Gareth
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Mike Fishwick View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike Fishwick Quote  Post ReplyReply Direct Link To This Post Posted: 15 Feb 2021 at 10:13am
My bet would be fuel starvation, caused by depressurisation of the fuel system when the car has been at rest for a while.  This can be easily checked by measuring the fuel pressure at the test point on the fuel rail, using a suitable gauge, which I think is avaiable from Halfords.

The cause of this is probably a leaking fuel pressure regulator, which could be due to either an accumulation of gum produced by prolonged use of UK 95 octane fuel, which is filth - try to use 97 octane fuel, particularly if the car spends a lot of time out of use. This will stop the valve from seating fully, so allowing fuel to return to the tank.

A good check for this problem is to use a small G-clamp to compress the fuel return hose frm the regulator, so stopping any leakage from getting back to the tank.  Leavet his for a few hours, remove it, and see how the engine starts.

It would also be worth putting a can of fuel injection cleaner into the tank, a process which should be regularly repeated with 95 octane fuel.

Another not-unknown problem is a porous diaphragm in the regulator - this has fuel one side, and inlet vacuum on the other, which opens and closes the fuel return valve in response to the pressure of a spring and the level of vacuum in the inlet manifold.  A porous diaphragm will allow fuel to leak into the inlet manifold via the regulator vacuum pipe, which strangely enough dos not give any symptoms of rich mixture, although in small engines such as BMW motorcycles it sometimes causes the oil level to increase.

A defective fuel pump can also allow a return flow to the tank if it has a failed roller - the roller-cell pump uses rollers to squeeze sectios of its liner to force fuel against the pressure if the system - but in this case it makes an unusal noise.



Edited by Mike Fishwick - 17 Feb 2021 at 10:42am
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Gareth91971 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gareth91971 Quote  Post ReplyReply Direct Link To This Post Posted: 13 Mar 2021 at 6:51pm
Thank you Mike for your response.
I will endevour to explore these suggestions. My main problem to start with is not having a workshop manual to point out all these parts and areas on the engine etc. There must be something available as BMW must have had something for their workshop mechanics back in the day as computer downloads weren't around back in the 80's. I have had no help from my local BMW dealer as they are not interested in such an old car.
The fuel rail hasn't got a schrader valve so will have to work out how to check the pressure buy tapping into the pipes. My main fear is creating more problems by breaking something or not carrying out the correct maintenance procedures. I will research the internet for info and try to find a knowledgable sympathetic mechanic near me.
Thanks again Gareth 




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Mike Fishwick View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike Fishwick Quote  Post ReplyReply Direct Link To This Post Posted: 14 Mar 2021 at 9:44am
Your injection system is an L-Jetronic derivative, which is pretty common.  Dealers are only interested in routine servicing on cars they have sold, so try talking to any independant BMW specialist, who should not have any problems.

The system is not much different from the systems used on Golf GTis etc from about 1986, so a VW indie should be capable to a fuel pressure leakage check.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndrewE Quote  Post ReplyReply Direct Link To This Post Posted: 15 Mar 2021 at 4:55pm
635CSi's from 9/80 have 1st generation Bosch Motronic (DME). The first step is to establish whether it has fuel (spark plug wet upon removal) and a spark. ECU's either work or they don't but there is a lot to go wrong on these old pre E32/E34 systems. It could be fuel pressure related but at this age it's worth replacing some bits anyway - cap and rotor if they're less than 100%, the two DME relays next the fusebox as well as the two flywheel sensors (TDC and crank speed) you'll see fitted to the gearbox bell housing. 
These cars also have an in tank fuel lift pump that supplies the main fuel pump.

When it's not starting, establish the fuel/spark first and go from there. 


Edited by AndrewE - 15 Mar 2021 at 4:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndrewE Quote  Post ReplyReply Direct Link To This Post Posted: 17 Apr 2021 at 5:41pm
Why do I bother?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gareth91971 Quote  Post ReplyReply Direct Link To This Post Posted: 29 Apr 2021 at 5:21pm
Hi Andrew
Thank you for your reply about the starting issue. I am sorry it has taken me so long to respond, with my current work situation I haven't spent anytime on the E24 and as you can see checked any replies.
I do appreciate peoples time in responding to questions and fully take on board all your suggestions.
Would you believe that I went to it to try it thinking I would get no response, but it fired up and ran well.
I think possibly the warmer weather has helped, but I still think there is a problem that needs finding.
I will endeavour to try to get time to use it and address on going things.
Thanks again
regards,
Gareth
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Post Options Post Options   Thanks (0) Thanks(0)   Quote AndrewE Quote  Post ReplyReply Direct Link To This Post Posted: 14 May 2021 at 4:23pm
Good stuff! Thumbs Up
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