15a engine run sensor,fan & primary relay fuse.

[SteveOS3]

Broke down today en-route to get fuel and found that the 15a engine run sensor,fan & primary relay fuse had blown.

Never happened before.

The only thing of note recently has been a drop of about 8 mpg in consumption.

I have a separate fan so it would only be the 'run sensor' (whatever that is) or the primary relay.

Does anyone have any ideas as to why the fuse blew or what to check?

Thanks,

Steve

[phillpot]

Good old TVR wiring diagrams!

Only the 2.8 engine has a "engine run sensor"

trying to follow the wiring diagram and the 2.9 addition it looks like that fuse now feeds the coil of the "fuel injection relay" so if that blew you'd come to a stand still.

cannot see anything referred to a a "primary relay" on the diagrams?

[SteveOS3]

I did indeed come to a standstill - just past the entrance to the local crematorium.......

Changed the fuse and all is ok now but would like to try and figure out why it went as I have a few big trips planned over the next couple of weekends.

[SteveOS3]

Managed to get the car back this morning and it looks like the fuse controls the fan and 'fuel injection' relay.

The fan isn't part of the equations any more so I'm down to the 'fuel injection' relay.

The fuse layout diagram from the 'bible' is here, showing the blown fuse and relay with melted connector.

|https://thumbsnap.com/Tnhp4gpQ[/url]

The relay is below. The top connector, number 3, has started to melt.

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The wiring diagram in the 'bible', below shows 'fuel injection' and a 'fuel pump' relays but that doesn't seem to match the fuse diagram above...




Anyway, I'm guessing a new relay and fuel pump are in order. But, 81AG 14N089CA is the number in the parts list for the 'Yellow' relay but it's 4 pin and mine is 5.

Thanks for the help.

Steve

Edited by SteveOS3 on Tuesday 24th May 09:14

[GreenV8S]

I'm not sure how you're reading that diagram but in any case it isn't especially reliable.

If the relay is overheating you probably have loose and/or corroded connectors in the relay socket and/or corroded contacts within the relay.

You need to fix whatever is wrong with the relay socket and replace the relay.

It's a standard automative relay. Just make sure you get one withe the same pin arrangement (there are two different arrangements which look physically similar but are not electrically compatible) and current rating.

[phillpot]

Some confusion here, the Lucas relay you're showing, is that the fan relay? If you have your fan wired independently just bin it, it's not doing anything.

As I'm reading the wiring diagram the fuse that blew only does the fan relay coil not the main fan power feed?

The burnt relay connection, 30, is main power, 25A fuse. Only needs a 4 pin relay but you can use a 5 where only a 4 is needed but not a 4 where a 5 pin is required.

Looking at the 2.9 wiring supplement the Fuel Injection relay (a little brown relay on my car) contacts are fed from fuse M, which, if I've got it right, is the fuse that blew?

Inj. relay and pump relay are not on the main fuse board but hanging free in the tangle of wiring by the ECU.


Had a similar issue a while back, 15A ignition system fuse blew, checked everything I could think of, that circuit should pull nothing like 15 amps, found no fault, been okay since
Carry a couple of spare fuses and cross your fingers!

[SteveOS3]

Thanks -the local motor factors say they have the relays but not the sockets do you know where I can get the relay socket from?

To confirm, my relay has this layout:




Pin5 87

Pin1 86 Pin4 87a Pin2 85

Pin3 30





and the schematic is:



As long as the pins are in the correct place with the same numbers and the schematic shows the same connections(even if drawn slightly differently) it should be ok?

Steve

[Blue 30]

Mike is right, it's all about current flow. Which should not be approaching or exceeding the fuse rating. One thing I have done in the past, is to remove the offending fuse, and temporary replace with an old style car ammeter gauge. This will show you the standing current flow, and if it's in your eyeline you will see the excess current or see it flick, when that over current occurs.
At least then you'll have something to go on, in investigation terms.
T.

[SteveOS3]

Thank all - let's scrub everything as I don't have the 2.9 wiring supplement and the 'bible' pages 304/305 don't match what I have in the fuse compartment.

Here's a couple of pictures of my footwell:







I am guessing the brown and yellow relays in pic 1 are standard and are what are mentioned on other posts.

As for the fuse box:

Bottom left is what blew, the two burnt out ones on the same row were for the fan and fuel pump - both have been replaced with in-line fuses a number of years ago.

I started the car without the 'burnt' relay and absolutely everything worked, lights, heater fan, horn, wipers, boot lock, the lot, so Mike is right - it's not needed.

Mike, can you confirm that the fuel injection system is the one monitored by the fuse that blew? If so, then I'll just stock up on the 15 amp fuses and keep my fingers crossed - going to the Laon Classique with a mate in his Jensen Healey(only three fuses, lucky fella).

Thanks for the help everyone - much easier than Facebook

Steve

[phillpot]

SteveOS3 said:

Mike, can you confirm that the fuel injection system is the one monitored by the fuse that blew?

No guarantees but as far as I can make out from wiring diagrams, yes. But I'm not going to pull my car apart to check!

If you have the Steve Heath book you should have the 2.9 injection supplement?

Your duff relay is a "standard" 5 pin relay but for a simple switch something on operation you only need four pin (no 87a). Relays and holders on Ebay aplenty

Blue 30 said:

One thing I have done in the past, is to remove the offending fuse, and temporary replace with an old style car ammeter gauge. This will show you the standing current flow, and if it's in your eyeline you will see the excess current or see it flick, when that over current occurs.
At least then you'll have something to go on, in investigation terms.

You can now get clamp on ammeters that will read DC amps, treated myself to one recently

The one I bought wasn't this much . . . . . . https://www.test-meter.co.uk/kewtech-kt203-400-amp...

Edited by phillpot on Tuesday 24th May 13:47

[SteveOS3]

Thanks, Mike.

That shot looks like page 305 - trip to Specsavers coming up !!!