Impossible electrical problem

[Lee H]

Right, been chasing this fault for a year on and off now, it has existed since I stripped and rebuilt my car and its driving me mad now, made me close to breaking the car in fact. The car is a Nova fitted with a C20LET.

I seem to have some sort of wiring problem. The car has blown one digidash, one rear wiper motor and the leds in the electric window switches so far and these are not commonly things that fail.

Also the main strange problem is the oil pressure on the digidash. When you start the car it goes up to four blocks and then goes to full (5 blocks) a couple of seconds later. When driving at 2k it can be reading full and then when you get up to 4k it will drop one block off full and then if you back off it goes back full again within a few seconds of normal cruising. Then randomly on the motorway it will drop a bar off full and not come back for about 15 mins.

I have ran a new wire to the dash straight from the sender, no difference. I have also fitted a new sender, again no difference. I have ran the oil pressure sensor to my mates digidash (still wired into his car) and it reads full straight away when I start my car. Tried it the other way and his engine won't even register full pressure when wired into my car loom and digidash.

Makes me feel my engine is fine and the readout must be wrong?

I have then swapped the alternator as it didn't appear to be charging very well and renewed the earth strap on the alternator and the one to the chassis leg. I have also swapped the engine loom in case there was a problem in that. Have checked the earth in the back of the car and the one behind the clocks. Have also tried unplugging the front wiper motor as the bracket was powdercoated and i've had this causing earthing problems before but still no joy.

Have also tried a different battery with jump leads to the power and earth strap to rule out the battery earth and am all out of ideas now.

Anyone think of anything else I can try short of changing the whole car loom (don't fancy doing this as cage has to come out to remove dash plus I have a Clifford alarm wired into this loom)?

Cheers

[dan16v]

Not that it will help Lee but my digi dash reads all bars on the oil pressure all the time! i just use the spa oil pressure gauge

[Lee H]

It used to work so would like it working again plus the car keeps blowing random other electrical components so I can't really ignore it anymore as my spares pile is rapidly decreasing!!

[AlexW]

By what you say i presume its blown the digidash, rear wiper and the electric window switchs a couple of times?

if not that dont sound too bad, ive known off all the above to go on a perfect car.

And i dont quite understand the fault with the digi oil read out. Have you tried another digi dash?

[bmw156]

is it blowing the fuses or the items, because if its blowing the items then there is probably a problem with your fuse box/fuses maybe check they are all right and in the right slots? this might stop them blowing the components

and also maybe if your battery is over powered? just another idea

also some things do just go at once, might be bad luck

[AlexW]

The battery wont be "Over powered", if its putting a higher amp it shouldnt matter, but i doubt it.

If it is blowing the items then its more then likly just chance like i said, or a earth fault. Blowing fuses would be bad wiring usualy.

[Lee H]

Its blowing the items, wiper motor won't work on my other Nova and window switches no longer light up.

First digidash, half went out and then it started smoking so thats no use now. Tried two other dashes and all three have had the same problem with the oil pressure.

Fuses are all correct and in the right places, not touched the fuse box although it does have a fair amount of bodyshop dust in it I noticed?

[AlexW]

Do any of the other gauges move in similar ways?

and have you tried another motor? could have just been that one went, they do go from time to time.

Dust in the fuse wont make much differance really, blow it out if you can but otherwise dont worry about it.

[Lee H]

All other gauges are fine.

Fitted spare motor and its working for now but things seem to go randomly. Also remember the central locking solonoid for the alarm blew as well. All seems too much of a coincidence?

[AlexW]

Could be, do you know the specs of the battery? I presume its not a standard vauxhall one or is it?

If its a standard vauxhall one you can rule that out. The one thing i would check is that each fuse in the fusebox is the correct amp, rather than a 30amp fuse in what should be a 10.

As for the oil pressure that seems very funny, if your sure the acual engine pressure is fine, my thinking was it could be a voltage change causing the gauge to move slighty (a bit like when you turn on things like fans the lights might go a bit dim for a sec or two)

[Welsh Dan]

Have you double checked all of the earths?

[Lee H]

Could be, do you know the specs of the battery? I presume its not a standard vauxhall one or is it?

If its a standard vauxhall one you can rule that out. The one thing i would check is that each fuse in the fusebox is the correct amp, rather than a 30amp fuse in what should be a 10.

As for the oil pressure that seems very funny, if your sure the acual engine pressure is fine, my thinking was it could be a voltage change causing the gauge to move slighty (a bit like when you turn on things like fans the lights might go a bit dim for a sec or two)

Standard Vauxhall battery. All fuses are the ampage recommended.

Checked all the earths I can find, one behind dash, one in boot, two in engine bay, one to battery, alternator one.

[AlexW]

Hmm strange.

[jimbob-mcgrew]

i was gonna say swap the loom and fusebox lol but its a bit extreme

[Lee H]

Especially when you have to remove the cage to remove the dash and the alarm loom is probably as big as the car loom and would need rewiring in.

[jimbob-mcgrew]

oh my god

[mowgli]

I actually think that what you have is a bucket of red herrings.
the oil sender thing is simply that the dash turns an analogue signal into a limited digital signal. so (as a wild guess) 3.9v makes it read one bar & 4v makes it read 2 bars, so if you are driving along, the slightest alteration in the feed makes the number of bars change for apparently no reason...

the wiper motor failing is what you can expect in such an old car, as it the whole LEDs not working. none of this stuff was designed for 20 years of use. it had maybe 10 years designed into it, any more is a bonus.

[Mark Sparks]

my digi dash used to stop working all together i found the prob only happened when it rained. then realised it was when de misting front windscreen turned out to be the duct had come away and was blowing hot air onto the dash making it over heat.

try to work out when the pobs happen as the could be linked. if it was a wiring fault it would blow fuses first. good luck.

[novasaloon1984]

i think a may be a electrical pigme that has been sent to p*ss you and your car off

[GRUNT 16V]

i had a prob years ago where the bonnet lamp wires came loose and they were earthing out behind the lamp had me going for days give it a look !

[Lee H]

Mine doesn't have a bonnet lamp so I am guessing it won't have the loom for one either?

Good idea though as I have removed the lamp in the boot and I know its the same as the under bonnet and interior one. Can't remember if I taped the wires up.

[joff-turbo-nova]

Lee,

Try and put some extra earth wires in on both the body loom and the engine loom .

Earthing problems are normally the source of strange electrical goings on - won't cost much plus it makes things more reliable longer term.

I put some extra cables direct from the battery to the fuel rail on both my nova and vectra LET / XE engines just to be on the safe side of things!

Joff