V6 Engine Problem
Discussion
I remember a thread on here a while ago about how the alternator on some S2/S3's doesn't excite and put out a charge until the throttle is blipped to 2000+ revs, so I think you are on the right track checking out the field excitation circuit.
Possibly a failed diode in the alternator reg pack?
And is the engine earth strap sound and making good contact?
A separate consideration, have you altered anything since the faultless drive from Devon to Oxford? E.g. Have you plugged or unplugged anything into / out of the 12v cig lighter socket? This is fed from the same circuit that feeds the alternator charging warning light, and can do strange things. Many other things are fed from this circuit, indicators, instruments, handbrake w/l etc. It's the light green wires. Check out the relevant wiring diagram in The Steve Heath Bible.
Check all your fuses are intact, then start isolating each bit in turn, starting with the cig lighter, easily unplugged from behind, until the fault goes.
Good luck,
Glen
Possibly a failed diode in the alternator reg pack?
And is the engine earth strap sound and making good contact?
A separate consideration, have you altered anything since the faultless drive from Devon to Oxford? E.g. Have you plugged or unplugged anything into / out of the 12v cig lighter socket? This is fed from the same circuit that feeds the alternator charging warning light, and can do strange things. Many other things are fed from this circuit, indicators, instruments, handbrake w/l etc. It's the light green wires. Check out the relevant wiring diagram in The Steve Heath Bible.
Check all your fuses are intact, then start isolating each bit in turn, starting with the cig lighter, easily unplugged from behind, until the fault goes.
Good luck,
Glen
Edited by glenrobbo on Wednesday 15th April 21:33
I confirm that on my s3 like most the battery light will stay on after starting until revs initially get up to around 2000 reeves or so..that's normal...
...but on the vid it looks like that is the trigger point...
....however, Sod's law says that although it is obviously something in that circuit...you will probably find out that it is due to something completely different, like low pressure in a rear tyre!
Good luck
...but on the vid it looks like that is the trigger point...
....however, Sod's law says that although it is obviously something in that circuit...you will probably find out that it is due to something completely different, like low pressure in a rear tyre!
Good luck
Just watched the video and the engine definately cuts out when the alternator cuts in so it could be the sudden rise in voltage that's breaking down a bad connection. Most issues of this type with TVRs are down to bad connections, so its the most likely cause. What about the dreaded "yellow" connector, I'm sure that's not still on the car is it??
Rob.
Rob.
Wierd!
Watched that a few times and it seems that as soon as the voltage regulator in the alternator switches on it dies. As soon as the revs drop low enough for the regulator to switch off (~<500rpm) the battery light is back on again.
Also there is no variation in light intensity during all this so voltages are not jumping around.
I'd swap the alternator.
Watched that a few times and it seems that as soon as the voltage regulator in the alternator switches on it dies. As soon as the revs drop low enough for the regulator to switch off (~<500rpm) the battery light is back on again.
Also there is no variation in light intensity during all this so voltages are not jumping around.
I'd swap the alternator.
You could also connect a 5 watt bulb between the battery live and the little exite terminal on the alternator after first disconnecting the existing little wire. This will bring the alternator in without affecting the ignition circuit. If the car runs ok then you know that the fault is probably in the ignition circuit wiring.
Rob.
Rob.
Thanks for the replies folks, feeling pretty positive that we are heading in the right direction and will check all things alternator related over the weekend, removing it completely if necessary to isolate the problem. Sod's law says it wont be something as easy as a dodgy earth, but fingers crossed!
I'll let you know how I get on sometime over the weekend.
I'll let you know how I get on sometime over the weekend.
From left field... Have you disconnected the real lighs at all?
On my car if these are not straight sometime the I light feeds run to earth and that has odd effects unlocking doors firing fuel pump it's 'possible' this could have blown a totally unrelated fuse..?
Start with alternator wiring first though I like glens diode idea..
Cheers
Damian s3
On my car if these are not straight sometime the I light feeds run to earth and that has odd effects unlocking doors firing fuel pump it's 'possible' this could have blown a totally unrelated fuse..?
Start with alternator wiring first though I like glens diode idea..
Cheers
Damian s3
Well it only took me 45 minutes after work to have the alternator off and everything tied safely out of the way for a very quick diagnostic test run in the garage and it fired up and went past 3000 rpm no problems; looks like with all your help we may have found the guilty barsteward! The voltage regulator bushes look quite worn but rather than just replace that and hope for the best I'll probably take the whole unit into a pro that the guy at work highly recommends and have it tested.
Fingers crossed I'll be back up and running again in no time!
Fingers crossed I'll be back up and running again in no time!
Bugger, back to the drawing board... the alternator guy in Burghfield just called back and said that he has tested it and it seems to working ok. Bearings are a little noisy and voltage regulator a bit worn so I'm going to get it rebuilt while it is off, but looks like I'll have to do a bit more digging when I have it back later in the week!
ukflyboy said:
Bugger, back to the drawing board... the alternator guy in Burghfield just called back and said that he has tested it and it seems to working ok. Bearings are a little noisy and voltage regulator a bit worn so I'm going to get it rebuilt while it is off, but looks like I'll have to do a bit more digging when I have it back later in the week!
Suspected that, but still be interesting to see what happens when it goes back on. Looks like it might be the jump in voltage at cut in that is finding a weakness somewhere. Some interesting diagnostics and head scratching in store.Just a suggestion or 2.
If disconnecting the alternator cures the problem (seems to) and if it isn't the alternator itself (yet to be proved) then doesn't this point to the alternator wiring somewhere???
I would put the alternator back on after refurb and see if the problem comes back. If it does then start looking through the wiring.
Bob
If disconnecting the alternator cures the problem (seems to) and if it isn't the alternator itself (yet to be proved) then doesn't this point to the alternator wiring somewhere???
I would put the alternator back on after refurb and see if the problem comes back. If it does then start looking through the wiring.
Bob
Don't know about the V6 but on the V8 there are really only 3 connections - one of which is the engine earth.
SO - Have you got a good engine earth - a poor earth and the alternator firing up and using the same earth as the ignition could create havoc (electrical noise) I'd guess.
Similarly the high current output to the battery - definitely worth a look - law of sod says this could be more likely than the earth in my head - there must be some kind of electrical earth on the engine otherwise the starter wouldn't work.
The small 'ignition light' output I think must be working.
Don't rule out a duff battery.
SO - Have you got a good engine earth - a poor earth and the alternator firing up and using the same earth as the ignition could create havoc (electrical noise) I'd guess.
Similarly the high current output to the battery - definitely worth a look - law of sod says this could be more likely than the earth in my head - there must be some kind of electrical earth on the engine otherwise the starter wouldn't work.
The small 'ignition light' output I think must be working.
Don't rule out a duff battery.
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