K click relay mod to bypass MFRU

16 posts / 0 new
Last post
Jonathan Kay
Jonathan Kay's picture
Online
Last seen: 2 min 48 sec ago
Joined: 17/04/2014

"last time I spoke with Tim Brise, which was ages ago, he was saying he can't fix the problem without being sent devices that exhibit the problem. 

If it ain't broke he can't fix it - so I sympathise.

There was more to the conversation about competitors."

The fndings have been shared with Brise, and their proposed solution has been tested.

Jonathan

anthonym
anthonym's picture
Offline
Last seen: 19 hours 12 min ago
Joined: 17/04/2014

sure, just not when I spoke with him, but pleased to hear it.

thanks for that link: more specifically here

#5 https://www.lotus7.club/comment/2359688#comment-2359688

SLR No.77
SLR No.77's picture
Online
Last seen: 1 min 22 sec ago
Joined: 17/04/2014

Re. Post #5

"What makes all if the various "relay mods" work (and they usually do) is the fact that they usually involve a short length of stout new wire from the battery to the relay and from the relay to the solenoid."

Nope. I had the "short cable relay mod" and yes it fixed it. However, when sorting out the badly bodged wiring in my car I decided that the extra relay located next to the battery was pretty crass and I'd rework the solution. Based on the theory that the loading caused by the Caterham starter motor is too high for the MFRU to be reliable, I reworked the recognised relay mod but did so by adding an addition relay to the relay stack above the passenger footwell, i.e. I now have 6 relays rather than the original 5, correct relay base sourced etc. 

I broke into the starter output from the MFRU (IIRC brown/red?) and linked the MFRU back through the loom to switch the new relay, probably around 1m in length. I've then taken the feed that already exists within the relay/fuse stack (2.5mm brown IIRC) to be switched by the new relay, then back through the loom to be reconnected where I broke into the original starter feed, again possibly another 1m of additional cable over the original setup, so the runs are now substantially longer than standard. I made this change around 10 years ago and it's been totally reliable. Locating the relay where it should be also meant I could add a blade type fuse at the same time, more o/e style than tagging it onto the battery.

Even though my car suffered from K-click, my mod still has the MFRU in circuit and has been 100% reliable, although with a second really it doesn't really matter whether the feed to the new relay is pre or post MFRU. I did suspect the MFRU relay would eventually fail completely but it hasn't, its working perfectly with the reduced load.

Stu.

Lotus Seven Club Leadership Team Member

The register for all numbered limited-edition Caterhams ....... www.thecaterhamregister.net ...... www.instagram.com/thecaterhamregister

revilla
Online
Last seen: 8 min 9 sec ago
Joined: 17/04/2014
Hi Stu, I'm sure the wiring you added and the various joints were of a much higher quality that some of the joints and splices I've found in Caterham and Rover looms! Did you ever find any direct evidence of the MFRU being faulty, other than the fact that the issue went away when you made the changes? I've measured voltage drops across the relays on a couple of cars that were actually experiencing the K-Click at the time and there was nothing significant, suggesting that at least on those cars the relays in the MFRU had nothing to do with it. I also replaced the MFRU on one of them with one that worked fine on my car and it made no difference; I then stripped the MFRU down for inspection and found no evidence of any issues. The relays look like fairly sturdily constructed automotive relays which should be able to handle the solenoid current, which is think is about 20A continuous and 30A transiently. I think the whole system is so marginal that additional resistance anywhere can lead to problems, so the causes in different cases are probably often quite different.

SV VVC 170 - 170.4 bhp @ 7100 rpm - 142.4 ft.lb. @ 4900 rpm

SLR No.77
SLR No.77's picture
Online
Last seen: 1 min 22 sec ago
Joined: 17/04/2014

Hi Andrew, my fault was the standard click issue, same as on my previous K-Series Caterham, I've not taken any measurements though.

My car had been badly messed with so during 2010/11, following a blown engine I reconstructed the Rover engine loom to return the car to standard, thereby agreeing with the wiring diagram for my age of car (1999). Any modifications I then "added" into the loom rather than making changes to the loom itself.

In this case I have simply cut into the feed (brown/red?) from the MFRU to the starter motor and added 6mm male/female spade connectors, the loom can therefore be returned to original by simply re-making this connection. With my relay modification in place it is effectively a new sub-loom that connects into the loom at this point, all the existing wiring is therefore still in place, but with the current diverted via the new sub-loom to include the additional relay.

The starter motor connections are original Caterham, as are the connections at the MFRU, the addition now being a couple of meters of additional cable making up the additional sub-loom, connected into the car loom at a point that was originally a continuous cable length.

Hope this helps!

Stu.

Lotus Seven Club Leadership Team Member

The register for all numbered limited-edition Caterhams ....... www.thecaterhamregister.net ...... www.instagram.com/thecaterhamregister