Intermittent cut out - traced to burnt power pin on fuel pump loom plug

[vertew]

Hi all - I've traced a cutting out issue to a burnt loom connector plug, but don't think that's the end of the story.  Any advice welcome …

Over the last couple of weeks I've had a few momentary cut-outs in my 2006 CSR 260, which has got steadily worse.  I used easimap to check running data and a cheap portable scope to monitor power supply to the fuel pump at the point the engine cut out, which all pointed to fuel pump electrics.  I checked the fuel pump plug (under boot floor) and sure enough, there was a burnt power pin.  I did a rough clean up on the plug and ran the car around again and no more cutting out.  Intermittent cutting issues out can be in a needle in haystack, so pretty pleased that I've found a key part of the problem.

Should say that there's a bit of previous here - I've had issues in the past with the fuel pump circuit seeming to carry a lot of current, which has scorched power pins in the inertia switch plug, causing cutting out. 

The question is: why is the fuel circuit burning out loom plugs?  It's not blowing the fuel pump fuse.  Is it happening slowly over months / years?  Or was this the result of a one-off incident?

Could be:

(1) Fuel pump has an internal problem which is causing it to draw too much current?

I've taken out the fuel pump to have a look.  It's part # WFX100631, which is fitted to various Rovers, so nothing particularly fancy for the CSR!  The pick-up gauze filter had a small amount of clogging, but nothing that looked like it would cause a restriction and perhaps high current draw.  Don’t think there's an easy way to check whether the FP is marginal, so replacing it probably the only way to be sure.

This fuel pump part doesn't look like it appears on the CC parts site.  Has this been superseded?  Can a different fuel pump be fitted to the CSR?  The part is on rimmer's site here.  There are also other cheaper parts on ebay.

(2) Caterham loom not quite up to the job of supplying the fuel pump?

The pins on the cable connector plug near the fuel pump do look worrying small and possibly too small for carrying a continuous load of 10 to 15A.  Same as the pins on the inertia switch connector which also take the full load of the fuel pump.  Contrast this with the output pins on the MFU which are huge in comparison.

Is this a widespread issue though?  There are lot of different fuel pumps fitted to caterhams, all using the same or similar loom wiring.  The various different pumps fitted will also all have different current draws.  Lots of combinations which will have different impacts on the wiring.

Perhaps it was all down to an old plug with dirty pins and the new plug will fix the issue.  Seem to remember checking an cleaning the plug before though ...

Next steps …

For now, I'll replace male and female sides of the fuel pump loom connector (which is type Sumitomo HM 6 way sealed).  I'll also use a silicone grease to help resist any corrosion.  I'll probably replace the fuel pump too, which is annoyingly expensive.

Still don't feel I've got to the bottom of this though.  Though, if the new fuel pump has a lower current draw, then that'll be the fix.  Those power pins in the fuel circuit loom plugs do look stupidly small though …

Any thoughts on this, please let me know…

Tks, Andrew.

[7 wonders of the world]

You could convert your tank to accept a Bosch 044 with a pre filter this will then plumb into your existing filter and pressure reg -all now externally mounted.

Your problem might just be down to to a slack contact between the male and female pins in the plug, arcing etc. which is a high resistance so therefore the fuse wont pop, were it a short this would allow an easier path and therefore draw sufficient current to pop the fuse - thus protecting the circuit.

Consider just replacing the pins / plug crimped with the correct pliers.

 

 

[vertew]

Thanks for that.  The corner of the plug is sufficiently scorched that it'll need replacing and new connector should be arriving today + I'll solder with wires in.

Thinking you could be right and it's just a problem with 14 year old connector building up resistance.  I'm erring on putting the old pump back for now and monitoring the loom connectors ... eg. go for a run, then see whether there's any heat building up in the connector.  If there is, I'll need to look at other things, like replacement fuel pump / upgrading to a better pump.

tks, Andrew.

[Tony Whitley]

Thanks, that's something I can look into on my car which started dying occasionally after a track day - maybe the extra load on the fuel pump was the last straw.

[vertew]

Definitely worth checking.

I've had a few intermittent cut-out and misfire issues over the years and they've all involved earths / connectors in the critical fuel pump circuit.  On the main fuel pump circuit connection points, I suggest checking, cleaning (replacing if needed) and protecting with silicone grease.  Here are the key connections to check, which will vary depending on which flavour of 7 you've got ...

1. MFRU output plug (pin 1 and 4 are FP supply)
2. Main engine to vehicle loom plug - large 14 pin plug
3. Immobiliser earths - various reports of poor earth connections.  The immobiliser includes two relays inside, one of which is a switch for the fuel pump.  Ensure earth tabs are not bolted to plastic casings and painted metal (!)
4. FP fuse - though mine has never been an issue.
5. Inertia switch plug
6. Fuel pump loom connector - under boot floor

I use the circuit diagram here (by revilla) which isn't a perfect match for my Duratec car, but is close enough for fueling (if not ECU).

 

[7 wonders of the world]

If your buying pumps use a reputable seller I fell foul of a fake Walbro in tank (Rover type) 

There's plenty on how to distinguish genuine from fake in the web.

The impeller parted company on mine....

[vertew]

Been a year since I had this fault, but remembered I didn't follow up with what happened.

I bought a new FP (WFX100631) from a reputable supplier on ebay and set about fitting it.  The new part was a direct replacement, with the exception of the fuel level float which did look different.  I reused the float from the original FP, which was a simple clip fixing.

The new fuel pump worked as expected and the tank level sensor gave the correct reading.  The fuel pump power connector is obviously new and I also replaced the plug on the loom side and packed the joint with electricians silicone grease, to help prevent future oxidisation.

I'm still suspicious that various parts of the fuel pump circuit are somewhat marginal for the current needed, but all has been fine for a year and counting ...

[anthonym]

a familiar tale. Spoiled several years for me. Turned out to be all the connectors in the pump circuit. Seems like you found the most obscure one first. Also check for heat soak damage to the yellow green and the purple (both rear of engine) and the purple wire connector..  with hindsight I'd just replace all the connectors in the circuit, including the inertia switch.

my pump works fine and still does, but it does like a good feed.

Anthony

[vertew]

Hi Anthony, yes, I think I read about your fuel circuit issues and got some pointers on what to check.  I cleaned / replaced most of the FP circuit connectors, inc the inertia switch and loom-side wire leading up to it, which looked a bit overheated.  Probably still issues lurking somewhere, but has been fine for some time now.  I'll add another detailed check to the to-do list though.