Mike K Posted January 24, 2016 Report Share Posted January 24, 2016 Hi all, I am a new boy having bought my first TR6 last summer and have next to no experience of any car maintenance. But I am very keen to learn - so I’m hoping to tap into the expertise this forum attracts but please excuse the stupidity of the questions I will be asking! I noticed recently the humming sound from the fuel pump (slung under the N/S/R wheel arch) has disappeared and sure enough the engine won’t fire. Whilst checking the non-functioning car horn I noticed one of the wires leading to the horn was loose and with a little jiggling was able to get a better connection and, lo and behold, the humming resumes, the car fires and off we go for a spin (albeit interrupted by more stopping / jiggling / starting again). Despite not being able to maintain a good connection, ie the pump is not working again today now despite much jiggling, I deduce that the loose connection at the horn is interrupting the power to the fuel pump. Is that at all feasible?? Or is it just a weird coincidence? Any thoughts, much appreciated. Thanks. Mike. Quote Link to post Share on other sites
aardvark Posted January 24, 2016 Report Share Posted January 24, 2016 Hello Mike and welcome. Looking at the wiring diagram it looks like a coincidence. It sounds like the fuel pump doesn't have a dedicated feed with relay. I'd get this done asap and the pump will thank you for it. You can get new pump wiring and relay from TRGB. I did mine on boxing day and it was easy to do. Cheers Dave Quote Link to post Share on other sites
barkerwilliams Posted January 24, 2016 Report Share Posted January 24, 2016 (edited) Mike, When you are fitting the pump feed spend some time looking at the earth return from the pump. Indeed whilst you are running a new power line to the pump, why not run an additional earth wire as well? Probably only cost an extra £5 and will guarantee a good circuit. Alan Edited January 24, 2016 by barkerwilliams Quote Link to post Share on other sites
Peter Cobbold Posted January 24, 2016 Report Share Posted January 24, 2016 Mike, Welcome to the forum and TR ownership. A common interruption to the pump power is the impact cut-off switch failing to 'make' internally. Its a grey plastic cylinder next to the wiper motor. Connect the two wires under it together,making certain to wrap them in insulating tape so they cannot touch metal. If the pump is then reliable, replace the switch. If it fails to cure, refit the wires to the switch. Peter Quote Link to post Share on other sites
TRTerry Posted January 25, 2016 Report Share Posted January 25, 2016 I would also fit a relay to the impact cut-off switch to take the pump load as it sounds like you have Bosch pump and the switch cannot handle high currents (starts to melt). Quote Link to post Share on other sites
matttnz Posted January 26, 2016 Report Share Posted January 26, 2016 I would also fit a relay to the impact cut-off switch to take the pump load as it sounds like you have Bosch pump and the switch cannot handle high currents (starts to melt). +1 on this and above. My inertia switch was completely b*993*d through the high current draw of the Bosch. Fitted a new feed off the battery, switched by the existing feed (with a new Rover interia switch as the old one is NLA). You can get a kit or for 1/2 the price do it better with a relay from your local auto store and beefier wiring. Quote Link to post Share on other sites
Mike K Posted January 29, 2016 Author Report Share Posted January 29, 2016 Thanks all for the very helpful comments. Peters comments led me to the fuel cut-off inertia switch where a bit of fiddling may just have been enough to clean the connection sufficiently get power to the pump - anyway it seems to be happily humming again, so thank you! I'm a bit lost as to how to run new wiring/relays to and from the fuel pump but I will get there and, now the pressure is off, I will be looking to do so in the not too distant future. Is there any difference between the wiring used in TR6's -v- electrical cable available from diy stores? Just need to make sure it can cope with the required amps, right? I understand the wiring system is all about balancing the weight/bulk of cable against the capability of handling the amps demanded by the item to be powered. I don't know how many watts the fuel pump demands so I'm guessing 17.5 amp cable will be plenty. Cheers. Mike. Quote Link to post Share on other sites
kcsun Posted January 29, 2016 Report Share Posted January 29, 2016 DO NOT use household wiring in your car. Even if it is rated at the correct amperage most household cabling is "solid" strand and not multi strand. It will also give your insurance company good reason to invalidate any claim you may make. There are lots of auto-electrical websites you can buy the correct cable from or even Halfrauds will sell you something correct. kc Quote Link to post Share on other sites
Peter Cobbold Posted January 29, 2016 Report Share Posted January 29, 2016 (edited) Mike, From my exeperience that switch can still cut the fuel off completely leaving you with a dead engine, possibly at a critical time. eg overtaking, outer lane on motorway. It may well be knackered - there have been horror-show photos of dead/melted contacts posted on here. Until you have replaced it it would, I suggest, be safer to bypass it, if you plan driving soon. Peter Edited January 29, 2016 by Peter Cobbold Quote Link to post Share on other sites
matttnz Posted February 1, 2016 Report Share Posted February 1, 2016 I ran a relatively chunky multistrand obtained from a car stereo shop (potentially overkill but I was getting another feed for an amplifier so it seemed sensible to run them both at the same time). You also need a good ground/ground wire. By using the inertia switch feed (the original) to switch the relay it reduces the current through that circuit and should limit further damage to the switch. As the Bosch pumps are said to have a high current draw, I suspect the original inertia switch just isn't up to the task. Get a bit of muck or corrosion in there and the current goes through steadily smaller areas of contact-increased resistance-increased heat...until it all gives up the ghost with a melted, twisted mess. Then you must bypass it (the CPs don't have them) but that leaves you with the joyful consideration of high pressure fuel pumping over a hot engine if you're in a crash. If the switch is stuffed, I agree with Peter. It's not original, but it's simple to get a new switch from a Rover or from a parts yard. The main issue is that the fitting differs so I got an adapter 3D printed up. If you want the template PM me. I put the relay in the boot where I could separate the loom in a reversible fashion in case I ever sell to a details fanatic. There's contention whether this is a good idea-concerns about sparking close to the fuel tank-but to my mind: the relay is sealed and probably a lot safer than the existing Lucas switches & light fittings in the boot so I'm ok with it. The wiring circuit is fairly simple to find, but once again-feel free to pm me and I'll suss one out for you. MT Quote Link to post Share on other sites
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