Wiring Question

[gruffalo]

Does the wiring for the speedo go through the ECU?

I have an interesting issue, coughs and splutters some times on wide throttle opening, almost cuts out till I lift off the throttle, does this a few times then a big backfire and all fine for a while. A bit later she starts to feel slightly hesitant I look does and the speedo and tachograph doing weird things and jumping around a bit.

[gruffalo]

As the app is fed from the ECU that answers my question, thanks.

I either have a wiring loom fault or an ECU fault.

[gruffalo]

CerbWill said:

Aides app uses GPS for speed. The signal from the speed sensor at the diff goes to a splice joint to tell the door ecu that the car is moving so it will disable the door opening function. The other half of the splice goes to the dash connector through multiway 1 that joins the front and rear wiring looms.

Do you know where this connector is, my first plan of attack it a good spray of contact cleaner on everything, it that doesn't work try a new engine loom, it is 20 years old and could do with a refresh anyway.

[gruffalo]

No faults logged in the ECU and non show up when it is misbehaving.

If I do go down the loom replacement I will probably take it to STR8SIX first for proper diagnosis before spending on the loom, I will let them then sort the issue out.

The issue has been coming on since the winter when it spent many months under a tarp while the chassis was away for a refurb, this is what leads me to think it may be damp/corrosion in the connectors some where and it is strange that it affects the speedo so I don't believe it is mechanical or something like fuel pressure but electrical.

Not the big fuse of that I am fairly sure, I have the upgraded one, it was changed recently and that normally makes the Tacho bounce with the indictors but this is it starts spluttering and the speedo and tacho start bouncing around and mis reading.

Also may be over fuelling as some big bangs out of the exhaust last night, injectors are quite new green tops that have done about 14,000 miles, coil packs are new and have a nice clean trace on the software readout, leads are new.

Symptoms worse when you suddenly apply throttle and the car starts doing a kangaroo impersonation.

[gruffalo]

tofts said:

The erratic tacho etc, sounds like an ECU earthing issue, your running a 4.7? Is it the standard ECU, in which case there is a large braided cable coming from the ecu for grounding. This goes to a lug underneath the dash on the LHS of the centre console, common for it to be heavily corroded and would cause issues as you describe as all of the major electronics in the car are grounded here. If not this, it could also be the main grounding for the entire fuseboard behind the fuel tank, or alternativly the main grounding for battery on the LHS from suspension. I would bet good money on this being your issues.

Edited by tofts on Thursday 23 June 12:17

Yes standard ECU obviously different map.

I have just been out for a spin over lunch and thinking about it while driving and come to the same conclusion, will check the earths inside the car and the battery earths first, the car was better just now but not 100%, wipers decided to stop so killed the ignition and restated while driving up the M40 and the wipers came back to life.

It has to be an earth and I think the one under the dash will be my first point of call and then the battery earth point.

[gruffalo]

Ok the earth behind the dash, I know where it is but how do I get to it?

[gruffalo]

Thanks you are a gent.

[gruffalo]

Issue found, the nice shinny new powder coat is doing what powder coat does and is contracting slightly.

The bolts holding the top part on the chassis were not very tight at all even though they were nice and tight 2 months ago.

Going over the car with some spanners last night has resolved the issues.

Tofts you are a star, thank you.

[gruffalo]

I am sorting out access to a ramp so I can get underneath and go over the whole car with spanners, just to make sure, I will do the dash pod at the same time, probably next weekend.

I will let you know how it goes.

[gruffalo]

tofts said:

My instructions made sense then? Did you manage to sneak the tray out without removing the whole dash?

Jody

Perfect spence thank you Jody.

I must have a Friday car as the centre console was held in using gravity and no sign of ever having been held down by anything more substantial.

Earths tightened, chassis bolts tightened and all is now well, runs smoother delivers much more power, amazing now that the ECU is getting a proper 12volt supply.

Thanks again for your help!

Gruff

[gruffalo]

Could be, does it effect anything else, on mine it was the speedo playing up the same time as the bad running that made me put two and two together and look for what was common to both and the earth point is about the only thing.