fuel pump

Author
Discussion

noble4862

Original Poster:

78 posts

169 months

Saturday 13th September 2014
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car wouldn't start earlier but after a while fired up ok , went for a drive and engine completely died can't hear the pump priming now when i switch on ignition its has an upgraded pump and wiring , could someone please tell me where the relay is situated and any other problem it could be the car is a 2.5 and what part no i may need to get thanks

noble4862

Original Poster:

78 posts

169 months

Sunday 14th September 2014
quotequote all
More info on my fuel pump problem:

I have an upgraded fuel pump (Bosch 056 254 044) which has been wired with an extra relay by the pump. This relay appears to have been wired in series with the original fuel pump relay as when I remove the original then the new relay doesn't switch. Both relays only stay on for less than 0.5 second !!! I have checked each relay (connected 12v between 86 and 86) and measure the resistance between 30 and 87 on each relay and got 0 ohms or short circuit so each relay is good.

This has had a new ECU installed (MBE9A5).

My understanding of how the system works is this:

1) The ECU should control the relay(s) coil(s) to enable the 12v to the pump to prime it for approx 2 seconds.
2) After this the ECU turns off the relay until it sees revs from the engine via the CAM timing or RPM. (Is this correct?).
3) As stated above both relays only stay on for less than 1/2 a second so the pump never starts up.
4) I have wired 12v to the pump separately and the pump works and car starts okay.

Is there a current sense circuit on the ECU for the return from the relay that the ECU detects that the relay has switched on or is it a dumb circuit and just runs of a 2 second timer?

Has anyone any ideas on this ECU? The car did drive okay from Leicester to Bristol ok after I had the ECU fitted but has now packed up due to this fuel pump issue? Is it recommended to have the original fuel pump relay and the extra relay (by the pump) in series?

Does anyone have any ideas why the ECU is only holding the relay coil voltage for less than 1/2 a second.

Many Thanks in advance

J

Evo2aGTO

37 posts

163 months

Sunday 14th September 2014
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Sound more like an alarm/immobiliser issue. Have you tried alarm reset on the key fob when this occurs?

noble4862

Original Poster:

78 posts

169 months

Sunday 14th September 2014
quotequote all
yes have tried resetting with the alarm fob but still no joy ,have wired the pump to a separate power source and starts fine would the alarm just immobilise the ignition ?

ajf

428 posts

205 months

Monday 15th September 2014
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Have you checked the relays on the bulkhead above the battery. I ended up getting jetstream to move all the fuses and relays to inside the car and check over the wiring to sort mine

noble4862

Original Poster:

78 posts

169 months

Monday 15th September 2014
quotequote all
Yes if i remove the far right relay above battery it kills the power to the relay adjacent to the fuel pump have tested both relays and there working fine.

Adrian W

13,848 posts

227 months

Monday 15th September 2014
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Reading your earlier post, (2) I thought that if the ECU does not see pulses from the cam sensor it then cuts the pump output.

I would start going back with a 12v feed until it wont start, pump relay then the next relay etc

Edited by Adrian W on Monday 15th September 11:48

Hairsy16

135 posts

137 months

Monday 15th September 2014
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I have an uprated fuel pump and it has an extra direct positive feed from the battery. This feed has a fuse close to the battery and recently the fuse holder melted, causing the same symptoms.

Regards

Dave

TitaniumBoy

2 posts

114 months

Monday 15th September 2014
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I was the person that posted (2) as I was assisting J in isolating the fault. The ECU runs the pump (via the relay) old or new for a couple of seconds to prime the injectors.. then stops it... that's the normal operation **IF** the ECU doesn't see the engine start either via REVS or CAM timing then it won't start the pump again. This isn't even getting as far as starting the pump.. The supply volts are on one side of the new relay and the relay very quickly tries to energise and switch the 12v over to the pump but only for less than half a second.. this is with the ignition in enabled mode.. not turning the engine..

Either the ECU is shutting it down quickly or there's resistance from the battery positive that's preventing enough current from flowing to the motor.. maybe a loose connection.

If there's and inline fuse we'll look there first if that gives a similar fault.. The cabling runs under the chassis to the battery... is the fuse near the battery or near the new relay? Can't see it there

P

TitaniumBoy

2 posts

114 months

Monday 15th September 2014
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Sorry just re read your post Dave and the fuse holder is near to the battery..we'll check that

thanks

Paul

Hairsy16

135 posts

137 months

Monday 15th September 2014
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It was an aftermarket addition so no guarantee that yours will be in the same place (or even exist!) but hopefully it will help.

Dave

noble4862

Original Poster:

78 posts

169 months

Tuesday 16th September 2014
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problem solved !!! thanks for the replies and you were spot on Dave the fuse holder and wiring close to it had melted .