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Fuel pump initial operation


Fridybrydy

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Good evening all,

My 2003 K series R300 won't start. Looked like an immobilser fault so had it replaced with a new item. On immobiliser unit replacement car started fine, however next morning back to exactly the same problem. Now from running the car for 6 years I know once the immobiliser has disarmed when I switch the ignition on, I hear the fuel pump run for a second or two and then when I hit the starter button she fires up.

The problem is now, when the immobiliser is disarmed and I switch the ignition on, I no longer hear the fuel pump briefly run and when I press the starter button I only hear a relay click in the MFRU. I say that but on one occasion since the immobiliser replacement, the fuel pump did briefly run and she fired up.

Anyone got any idea's? Thanks in anticipation David

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Fuel pump is supplied from the main "ECU" 30A fuse, no other fuses in the line. Immobiliser doesn't usually cut the fuel pump on a K in a Caterham (unless the wiring has been modified to be more like a Rover), just stops the ECU firing the injectors. Check the inertia switch as Ian says (push down on too to reset), otherwise could be a wiring fault.
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My car wouldn't start when I built it in '98. Hot wiring the fuel pump and it fired up.

It proved to be a connector in the loom just downstream of the inertia switch in one of the yellow / green wires. It was fixed by Classic Carriage. This year I found the soldered joint which replaced the crimped connector. 
 

I think AnthonyM had a similar issue on his R500. 
 

Perhaps put the ignition on and wriggle the inertia switch loom as it enters the main loom and see if the pump fires into life?

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No point guessing.  I'd start by checking for power and earth at the fuel pump when the ignition is switched on (as you know it should prime then).  If no earth, fix that.  If no power, work your way back up the system until you find where it's stopping.  Ideally use a test lamp that draws a decent current (headlamp bulb in holder is my choice).  2nd best option is a test light.  Multimeter is poor choice.  No idea what you've already been told by PM so please say if this is just repeating what's already been said.

edit:  I would also suggest you don't start wriggling connections.  If the fault goes away you won't know what fixed it and it will leave you stranded at a later date.

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Thanks for all the reply’s. Had her going yesterday after bypassing the main engine loom to main loom grey connector as this had very intermittent continuity. Then this morning re-taped and re-tywrapped all disturbed wiring in engine bay and behind dash wiring Went to pull her out of the garage and back to exactly same problem with the fuel pump not initially running on ignition on. So frustrating. Basically my car is wired as such. Small connecter at MFRU has green/pink wire that comes from ignition. Checked for 12v when ignition on ok. Black/purple wire is switched to earth via ECU. This operates a relay in the MFRU which switches 12v from a brown/slate wire confirmed at 12v to a green/yellow cable which then goes down to the main/engine loom connected, mentioned above, then back to the cockpit fuse box, through a 10 amp fuse, back out of the cockpit to the inertia switch, though the inertia switch and off t’ fuel pump. Had the MFRU off applied 12v and earth to green/pink and black/purple terminals and the relay operates with continuity observed across brown/slate and green/yellow terminals. Re-fitted and connected MFRU. Broke into wiring, connected 10amp inline fuse and wired from green/yellow wire coming out of MFTU to green/yellow wire going to inertia switch, no joy. Pulled large connector off MFRU and shorted between brown/slate wire and green/yellow wire and fuel pump ran proving wiring though inertia switch to fuel pump ok. Re-connected MTFU, and then monitered for 12v and temporarily fitted in-line fuse. Dis-armed immobiliser, switched ignition on no 12v monitored at inline fuse. To summarise, I’ve had a new immobiliser fitted and the car fired up. Next morning, she wouldn’t start. Just a click. Then bypassed grey connector and she started. Then this morning, as soon as I put the ignition on I knew she wouldn’t start as I didn’t hear the initial running of the fuel pump. I’m now going back out to the garage to try and figure out why the fuel pump relay is no longer energising from the ECU. Any divine inspiration?

Thanks David.  

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Update, just plugged everything back in, disarmed immobiliser, ignition on fuel pump had the initial few seconds run, great. Ignition and immobiliser cycled many times all satisfactory with the fuel pump initial run happening. Went and had a sandwich, came back without disturbing anything, disarmed immobiliser, ignition on, fuel pump did not run Aahhhhh. Disconnected and reconnected MFRU both connectors and now back at square one. It is so intermittent. Does anyone know where I can purchase a new MFRU please. Got to swap it out afore I go insane. 

David

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An EU2 MFRU YWB10022 will work in either an EU2 or EU3 loom. An EU3 MFRU YWB100970 will only work in an EU3 loom, it won't work in an EU2 loom. It requires an extra 12V feed to the fuel pump relay, so the symptom would be that the fuel pump wouldn't run ... which would really confuse the ssue in this case!
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Evening all. Thanks for the responses. It sounds like mine will be a EU2 as my distributor is on the back of the head. I’ve had to knock the fault diagnosis on the head for the rest of the bank holiday. Will let you know how I get on when I resume the fault finding.

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  • Area Representative

medium_D603B8AA-D2EB-44F0-A957-963719FE97F3.jpeg.b31a7c309aefcb2cd9686d2a8a0b8fa7.jpegI too have an R300 with EU2. I had a starting problem that took 2 and a half years to find. It’s a long read on here in the archives (A Reluctant Starter) but the problem turned out to be a bad earth on the ECU. It would crank but not fire as the injectors were not working. The multi pin socket under the throttle bodies was also corroded and cleaning that with contact cleaner helped. It’s not easy to get apart by the way. I also have a spare MFRU that I could lend you if in East Kent. I changed that thinking it was the problem.

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Evening all,

Thanks very much for raft of info and offer of assistance. I had another go at the car this morning/afternoon and managed to get her fired up. I'll give you the story from start and hopefully finish of the problem.

Initial problem, Laserline immobiliser disarmed with touch fob and ignition switched on. On pressing the starter button only a click from the MFRU. (Didn't know much about the MFRU in the begining). A local lad from the West Yorkshire and Pennines group kindly gave me a hand and he bypassed the immobiliser. The car then started. He then replaced the immobiliser the following week and the car started.

Next morning, Laserline immobiliser disarmed with touch fob and ignition switched on. Initial run of the fuel pump was not heard, the car would crank but not fire. Placed a spark plug against the block while turning her over an had a really strong spark. With the plug being dry on removal I assumed no fuel was being pumped (Also not hearing the initial run of the fuel pump). Being we had disturbed the wiring up behind the dash in the area near the fuse block, I assumed we may have disturbed some wiring there. Having received some wiring drawings kindly linked from Jonathan Kay I investigated further.

During my investigation I have found the following issues. Badly made connection where a 12v cigarette socket had been previously been spliced in causing the 12v to the brown/slate wire at the MFRU large connector to fail. (Removed 12v cigarette socket wiring and re-made original wiring). Bad connection at engine loom to main loom connector causing high resistance/intermittent continuity. (Re-wired to bypass connector.) Loss of continuity between the main loom connector and the fuel pump fuse in the cockpit. (Unable to find the cause of this, so re-wired from green/yellow wire coming out off MFRU large connector through an inline 10 amp fuse and onto the yellow/green wire into the inertia switch.) Bad connection between the large MFRU connector and the MFRU itself. Resolved using electrical contact cleaner. Several times after curing each of the issues she would start fooling me I had cured the problem only to fail again at a later date. Now I feel reasonably confident she'll start everytime. I am aware however, that the use of contact cleaner to fix the last issue is still a little disconcerting. The only way to more confidently fix this issue is pull the yellow/green wire out of the MFRU large connector and fit a new female termination and I don't have a tool for this. The male connector as part of the MFRU looks ok

MOT in the morning. Thanks again for your assistance. Kind regards David

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Ive wondered during my phases of wiring tidying, whether it wouldn't be best to remove all the wiring loom from the car and attach it to a large board and completely strip and inspect it all.  The best I could do was a full strip, clean, inspection & rewrap on the engine side in-situ, and then to the rear from the around the fuel filter.    

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