Fuel Pump Relay gets very hot - 2.8

[RCK974X]

My 2.8 has sat for a little while, and after firing her up to check stuff (especially things like the pods going up and down properly) I noticed a burning plastic smell ....

I traced it to the fuel pump relay, which is the 'standard square' style with a fuse on top, and the fuse holder was VERY hot.

Checked fuel pump wasn't seized, it draws 7.5 amps when engine stopped, which apparently is well within tolerance. Engine runs fine , so pressure is OK.

All seems clean, so not dodgy connection, but still gets very hot, not much voltage drop so don't think it's a burned contact.

Anyone else had this kind of problem with relays ? (especially fuel pump one)

[mrzigazaga]

Hi mate..Never had that happen..Have tried it with another relay?...Ziga

[RCK974X]

Yeah, tried another one with a fuse on top and it gets hot as well - I reckon it might be a design issue with those relays ??

Anyway - I'm not putting in a standard relay in without a fuse, so I am doing a little bit of rewiring via a fuse in the fusbox and will then retest...

perhaps the fuel pump IS drawing more power than it should ....

[ElvisWedgely]

Maybe the fuel pump is struggling to work after standing for so long and hence drawing more current. A relay shouldn't heat to the point of smelling burnt plastic. Investigation needed.

Tony. TCB.

[mrzigazaga]

I think the only issue i ever had with a fuel pump relay was that the pump would not operate on crank or with the green metering head plug removed...It was taking an age to try to find the fault and in the end the garage by-passed the other 4 relays that it was connected to which incidentally worked and so it would ONLY work with the metering head plug removed, However...When i got it back from power engineering the green plug was connected and running ok...A bit strange as they didnt do anything except plug it back in???....Cheers..Ziga

[jeff m2]

Acquaint yourself with the way the fuel pump operates.
Via yellow wire on cranking, and on the same run as the AAD and WUR while running.
Check all spade contacts, clean and dielectric grease all connections. These cars aint young.

When the car doesn't need fuel it circulates within the pump. It is possible it is churning some crap in the pump. Churning crap requires more ergs than churning fuel.

Do not run the pump with outuput side disconnected as the pump may arc with only fuel vapour.

This is one of those times you really do need to disconnect the battery.

[superwedge]

i think that all the earths on the car need to be clean ,and maybe some more put on ,sounds like its not getting a very good earth,

[RCK974X]

Thanks Guys,

I've done all the obvious 'leccy checks, spade/ relay base cleans, checked pump current draw, etc etc.

7.5 Amps draw is well within allowed tolerance according to all websites I can find. Pump itself is stone cold when engine running.

Yeah I am a bit concerned that there's muck in the system, but engine runs perfectly, and tanks half full so I'll have to wait a bit before taking the pump out to check it.

I notice the 'bullet' type fuses only have a very small contact area on each side - even more so on these relays - made me wonder if they typically run hot anyway (not hot enough to melt plastic, but still...)

Second relay tried out runs warm (after I cleaned and bent holders so fuse is tight), rather than red hot, so probably original relay is burned contact - can't see those contacts, even with case taken off ...

as I said I'm doing a minor rewire so that I will go to a standard type cube relay, and will be checking very carefully !!

whilst I'm here do you guys all have a 'standard' type cube relay for the pump ?
perhaps mine was changed over some time ago ?

Edited by RCK974X on Monday 30th September 21:02

[mrzigazaga]

RCK974X said:

whilst I'm here do you guys all have a 'standard' type cube relay for the pump ?

Hi Mate..I have on mine...Ziga

[RCK974X]

Thanks Zig.

good luck on finding an engine for Delilah !

[adam quantrill]

Is it the fuse itself getting hot? If it's dropping half a volt (say) then that's 3 watts which will warm it up quite nicely.

Try measuring the voltage drop across the fuse terminals.

[RCK974X]

adam quantrill said:

Is it the fuse itself getting hot? If it's dropping half a volt (say) then that's 3 watts which will warm it up quite nicely.

Try measuring the voltage drop across the fuse terminals.

Yeah, I measured voltage drop across the fuse, then across the entire relay and even the wire between pump and fusebox. I noticed the original relay did have a bit of a voltage drop 0.35v, so at 8 amps or so it is indeed about 3 watts. BUT...

UPDATE - guess what ?

I have been visited by that guy that lurks in the corners and in the shadows... yeah HIM, the guy known as Murphy, and also as Sod, famailiar to all engineers and hobbyists of all types.

Turns out the original relay did have burned contacts, and the second relay I tried ALSO had dodgy looking contacts ! (I took them apart to find out for sure, result =one cleaned, one scrapped)

I have now done a small rewire so I have a standard cube relay (a good quality Bosch one) powered via a 16A fuse in the main fusebox, by moving horn & clock to share with a window motor to get a spare fuse point. Fuse gets just detectably warm and relay is cold. SOLVED !!

So there we have it - both the relays I had with fuses on the top were dodgy....

so can add this to the index marked "Experience" or possibly "Bad Luck"

Edited by RCK974X on Tuesday 1st October 23:39