Car won't start - occasionally

[SM25T]

From memory, it's the red and white wire into and out of the MFRU

[Gridgway]

To explain my suggestion better .. yes disconnect the wire to the solenoid at the solenoid end.  Pull it off the spade connector.  Then you won't get any noise of cranking so your can hear of there is a relay click or not.

[Neil220]

Many thanks for the link.

I don't have the infamous K series heat related click problem.

So although I shall do this mod it won't solve my problem if it's the MFRU.

As suggested I'll confirm the wire in and out and bypass it.

Thanks all for advice and suggestions. 

[SLR No.77]

Neil, take a look at this page.

In post #1 Andrew has drawn two diagrams relating to an FIA cutout switch being fitted or not ....

If you look carefully at either diagram you'll see the output wire from the MFRU (at 8/5) to the starter motor is labelled "NR", this denotes a brown wire with a red tracer and if you check your MFRU it's a reasonably thick wire. This can be used as the trigger wire for the relay mod, simply cut the wire, the side from the MFRU now goes to your new relay as the trigger wire, the side going to the starter motor is connected to the switched output on your new relay. This wiring method keeps the original MFRU relay in circuit and is how mine is wired, with 100% reliability. Of course you also need a +ve feed to the relay from the battery and an earth connection.

Also looking at either diagram, if you need to bypass the MFRU relay completely you need to use the white wire with a red tracer (WR) that enters the MFRU relay at 6/6 as the trigger wire for your new relay, then take the brown wire (N) that enters at 8/7 and use that as the switched feed through you new relay to supply the starter, effectively your new relay doing the job of teh old MFRU relay.

The first option is much simpler and unless your MFRU is completely shot should work fine.

Stu. 

 

[Alan Bowler]

SM25T said; "The small trigger wire to the solenoid is the one that normally fatigued and fails inside the insulation. Easy to replace"

I would certainly check/replace this first.  Replacing it postponed my need to do the relay mod by a couple of years.

Whilst K click is typically hot start related, if the wiring is original from '96, I would expect some crustiness/issues.

Also, check the wire tab on the solenoid itself, if at all loose.

And if you have an FIA switch (not mentioned that you do), worth checking the small tabs also. I don't think you would get fuel pump priming if it was the fault, but depends how its wired. My failing FIA switch caused electrical mayhem, and its apparently a common weakness.

Not personally had issues with the wiring for ignition barrel, but a bad connection there would seem to explain your symptoms, if there is no definitely no "click" at all.

 

[Neil220]

#29

Stu,

Many thanks indeed for taking the time to send that information. 

First for me is check nothing is amiss with the ignition switch/connections.

If okay then I'll add the extra relay and bypass the MFRU on the basis that if I can't hear the starter solenoid clicking it's because it's not getting a feed from the MFRU.

Visually all the wiring looks good, it's been routed away from the exhaust and wrapped to reduce heat.

Can the micro relay in the MFRU be heard clicking when it operates?

It's very small!

[Neil220]

#30

Alan, 

Thanks for your advice.

No FIA switch. 

Wiring looks good but will investigate more thoroughly. 

[SLR No.77]

If it's starting sometimes the MFRU relay is still working, in which case I'd fit a relay as per my option 1 and see how you get on, it's a very easy solution because you just break into the brown/red wire. The MFRU was designed for a full Rover install, the Caterham install is a Rover engine with a Ford gearbox and starter setup, for whatever reason the small relay in the MFRU struggles with this. It's very quiet so you may not hear it anyway.

Stu.