charging system problem

[nosfera2]

I hate to post a problem, they're far less interesting than a V8 build, but what the hell, i could do with advice.

I seem to have a changeable charging system problem

Firstly for info. the car is basically stood, no driving due to busyness and lack of confidence that it won't let me down (when I'm busy!). Also it's a 20V.

First symptom - sometimes it seems fine, no problems.

2nd - sometimes the battery will discharge completely (literally) within a small number of hours (stood not running).

3rd - with full charge starts but runs rough and warning lights (all) come on with higher engine speed.

4th - Battery will fully hold charge for weeks no problems, starts fine, but after running for a while, all dash warning lights come on bright and won't go off. Engine sounds a bit 'putt putt putt' but runs OK

For info. the belt is not slipping.

Thoughts please

Thanks

[MartG]

Is it stored outdoors ? If so it could just be damp connectors in various places

[nosfera2]

It is and you may be correct, although I've never seen such a variable and dramatic problem before and I would think that the fact that recently ran cold with no warning lights, then the lights came on as it came up to operating temperature would suggest otherwise.

Could be wrong of course.

Thanks for you suggestion, i will attempt to dry it out and see how it goes.

[PW@Woodsport]

What is the actual charging rate? Have you put a meter on the battery terminals?

[nosfera2]

No, I haven't, but if you're willing to post instructions, then I will

[PW@Woodsport]

Set a multimeter to volts, put the probes on both battery terminals, read the screen, should be reading 13.5v- 14.5v with the engine running.

[nosfera2]

Arrrgh, not pouring down today so was going to check the charging voltage, but the battery is dead as a door nail, so no chance to start the engine.

Very weird, it holds charge perfect for weeks, then just dies very fast, won't even light the door open indicator on the dash. It's like there is a battery discharge switch that just gets switched on. Anyway charging the batt again now.

[JMR_AW11]

It could be your alternator and/or Vreg breaking down or it could be another component in the car breaking down or it could be a poor connection somewhere (eg a dodgy short circuit?)

I think you should be very wary of a car that discharges a battery erratically and quickly for no reason.

Therefore I'd recommend you don't leave the car unattended with a freshly charged battery until you fix the problem. It's unlikely, but there could be a fire risk associated with your problem.

BTW what does the voltmeter display on the dash do when it is in good mode and bad mode as you drive it?

[MartG]

If it's discharged the battery very quickly, it sounds like a short circuit somewhere. With the battery disconnected, use a multimeter to check the resistance between the +ve battery lead and the -ve lead. With everything off it should be a very high resistance, but if there's a short the resistance will be quite low.

If you see a low resistance, try removing fuses one by one to try and identify what circuit the short is associated with.

[nosfera2]

Thanks for the advice so far. The answers to everyones questions are as follows:

- The car v.meter shows voltage in normal range.
- Battery removed and resistance check does indeed show v.low resistance, but removing every fuse makes no difference.
- Battery back in and running, volt meter reads 14.7, dash lights off. I was walking away when I heard the idle drop and looking back, the dash lights were back on. So I took another reading expecting low voltage, but I guess that would be too easy, the voltage reading was 16.7

[PW@Woodsport]

Your regulator is faulty.

[nosfera2]

Thanks Paul, i guess it is alternator off time I don't suppose you know if it is the same part on the 20v as stock?

[toxo]

According to my parts catalogue, the regulator in the 20v alternator is the same part as some MK2 MR2s (and a shed load more Toyotas), part number T27700-74030. I am using a 92 AE101 catalogue.

Replacement is a very straight forward process, but you might as well do the brushes while you're in there.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... 0281490394

[nosfera2]

Thanks Toxo, i think I will see what price I can find for a recon alternator, which does appear to be different (at least in code) to the std AW11. Just removed the bu88er and have the scars to prove it.

I was overjoyed to find it at the back of the engine (changed one on the opposite side of a 4agze SC years ago), was less pleased to find that it couldn't be removed without removing exhaust, driveshaft or intake plenum first

[toxo]

Ah, in the same place as the MK2 then You're right, after I'd posted above I checked part numbers for the AW11 alternator and they are different. They're both 70A units though so I imagine in usual Toyota style the mounting points will be a few mm different.

Due to this you may find sourcing a recon alternator difficult. They're not too complicated to rebuild yourself though if you fancy the challenge. You'd need a new regulator and brushes, and to replace the bearings which will be off-the-shelf sealed for life units. The only tricky part is getting the pulley off without mashing the 10mm head on the end of the alternator shaft

[jimi]

Most of the MK2 alts are interchangeable with the MK1 alts as long as the plugs are the same, even then you can change the plug

and to replace the bearings which will be off-the-shelf sealed for life units

errr no they aren't. They are sealed but are non standard and are pretty hard to find, I've haven't managed to find them yet
Post up the part number of the alt you've taken off and I'll see if it cross references with any of the other MR2 numbers I have

[nosfera2]

Well, I replaced the alternator a couple of weeks ago and it started and ran OK, but today was the first chance I have had to take it for a run.

Sadly it seems the problem is not solved, I took it for an approx. 10 min run, towards the end of which the dash warning lights were flickering on and off and I was left limping for home (made it thankfully). It was the first trip into the higher rev range that initiated the lights, say 6500-7000.

To be honest it didn't feel like it was running right anyway, felt quite sluggish but without any obvious problem. It's a hard comparison for me to make, as I normally drive a 3.2 Audi, but I remember 16v MR2s of my past being much quicker and revvier and would expect a 20v to be even more so.

Thoughts please

[cartledge_uk]

There could be an issue with the wiring (as in the initial wiring of the 20v to the aw11 16v loom).

Who did the conversion?

[nosfera2]

I bought the car already converted and the previous owner also was not the convertor, so I don't know. Seemed to run OK at the time, but perhaps that was pure chance and the weather was UK standard, which always makes an inspection more difficult (not that I'm a 20v expert anyway).

[Jim-SR]

youre still running the same battery right? might be worth changing the battery as well, especially if its been sat a lot. ultimately it sounds like its probably an issue elsewhere, but ruling the battery out is going to be a lot easier than finding wiring issues.