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Old 13-07-20, 08:37 AM   #1
BackintheFold
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Default Won't Start

Long story, short version :
car in front drive, won't start.
All lights come on dash, engine turns. There is PROBABLY no spark (hard to tell yesterday in the time i had to check), the fuel pump doesn't energise when the key is first turned to get the dash lights on-and probably not during turnover either although that is harder to hear!.

My first question, is what exactly is needed to make the pump energise?
I'm thinking, its a signal from the ECU (and if spark isn't working) then the power to the ECU has been interrupted.
Fuse is OK for pump (13), if i press the relay contacts shut with the cover removed, the pump does run. MOTEUR fuses both OK.

I'll be looking at the circuit diagrams later, and might even try to read the ECU codes!
But if there's anyone who could suggest things to try, that would be helpful.

Thanks!
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Old 13-07-20, 09:03 AM   #2
Hanuman
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A reminder about which car?

On a WR, we had a problem with the ECU signal to the relay being lost due a weak contact in the fuse/relay box. The relay was fine, the car would start most times, but would lose power during a turn. Just enough to break contact, the relay de-energises, the car slowed down, the strain on the relay eases off as a consequence, and the fuel pump runs again. We found that we could reproduce the problem with simple sideways pressure on the relay while installed in the relay Position.

Other electrical issues that associate with age-

Tarnished contacts- high resistance
Broken solder joints, intermittent contact/dry joint. Iíve had many relays with problems like that.
Relay bases/fuse contacts- weakened over years, not making good contact. Along with tarnishing, this leads to high resistance.

3 sensors that have interrupted the WR previously.
Hall sensor on the distributor
Pin/teeth sensors on the bellhousing.

In the vast majority of cases over the years, most similar problems have been resolved by simply going through all the electrical connections, unplugging and plugging in.
Relays&Sensors.

As a starting point.
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Old 13-07-20, 09:19 AM   #3
BackintheFold
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Sorry, MB ur quattro.
Maybe we could put this info in our profile, so it shows next to our name in posts? I've updated my location to show the car now...

I am tending towards an electrical fault-but don't want to say why in case it influences other suggestions!
But the Hall sensor and the pin/teeth sensors wouldn't affect the energising on "ignition lights on only", so I would not start there. (or would they?? I can say that the info they provide is not necessary, but does the ECU check for those signals anyway?)

0th call-try to read ECU blink codes (not done that before!) I do have the engine management light showing.
First call-check power to ECU
2nd-check signal from ECU towards pump relay.
3rd call-check signal being received at relay pin.

sound good?
If anyone knows what the ECU looks for before energising the pump relay on "ignition lights on only" that would be very much appreciated!
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Old 13-07-20, 10:02 AM   #4
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Check the connection under the rear seat to the fuel pump Gets hot and then fails

I think you can bypass the fuel pump relay with a piece of wire to test the fuel pump
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Old 13-07-20, 10:19 AM   #5
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Fuel pump is working, I have taken cover off relay and pressed contact shut to test.

I’ve previously put a relay under the seat for the pump, but haven’t done that here (yet!)
So there is no signal reaching the relay to energise the pump.
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Old 13-07-20, 03:05 PM   #6
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I'd suggest an attempted start and check codes.

Your fuel pump doesn't prime with ignition on the MB but will start to run when the engine turns on the starter, providing everything else is in order.

no spark is often the hall sender or pin issue but see my first line.
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Old 13-07-20, 07:52 PM   #7
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The mystery deepens
Used the blink codes. Marvellous things.
Told me problem is hall sensor.
So I did all the checks on Phil Payne’s site.
All is working fine, so I got to the point where I’m supposed to retime the engine.

With number 1 cylinder at TDC (plug 1 out, wooden dowel maximum straight up) and with camshaft lobes also pointing up, (so valves are closed) and with cam timing mark spot on position, and with crank at 0 position, the distributor is now roughly 100 degrees out. Instead of pointing at plug lead 1, it is just after 3.

Now, I’ve been turning the engine to move the cam etc, and there’s been no contact so I am hopeful the (1000 mile old) timing belt hasn’t slipped, and the crank is in the right position BUT the dizzy rotor seems to have slipped 100degrees.
Is that even possible? I’ve not had any car do that before (always a first!)

Before I slacken the dizzy and twist it into a new position, anyone got any comments as to wtf has happened?

I suppose if the gear on the bottom of the dizzy rotor is worn, a slip is possible, and perhaps it’s been slipping a tooth at a time until it’s just gone too far for the ECU to cope!

Extra info-the car was running and then the engine cut out.

Last edited by BackintheFold; 13-07-20 at 09:27 PM.
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Old 13-07-20, 09:37 PM   #8
Colin Aitchison
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Don't no much abut MB engine management Mike is you man for that but the mechanics of MB and WR engines are very similar, in your post you say "CAMSHAFT LOBES ARE POINTING STRAIGHT UP" That just sounds wrong, you need to set TDC from the window in gearbox bell housing, it is quite hard to see but that is the place to set the timing, do not use the cam shaft pulley or the crankshaft pulley marks

Their is a key on the timing belt drive on the crankshaft that can be damaged when refitting but that is not the place to look first.

Is the timing belt tensioned correctly? if so it the belt will not have jumped.
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Old 13-07-20, 10:53 PM   #9
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I wouldnít do anything until youíve confirmed the timing belt hasnít skipped. Thatís ground zero.
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Old 13-07-20, 11:23 PM   #10
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Quote:
Originally Posted by Colin Aitchison View Post
Don't no much abut MB engine management Mike is you man for that but the mechanics of MB and WR engines are very similar, in your post you say "CAMSHAFT LOBES ARE POINTING STRAIGHT UP" That just sounds wrong, you need to set TDC from the window in gearbox bell housing, it is quite hard to see but that is the place to set the timing, do not use the cam shaft pulley or the crankshaft pulley marks

Their is a key on the timing belt drive on the crankshaft that can be damaged when refitting but that is not the place to look first.

Is the timing belt tensioned correctly? if so it the belt will not have jumped.
Re:lobes. Yes sorry, very hastily and badly written-I did correct it later.
I also managed to find the O in the bell housing.
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