Maybe an alternator problem?

[paulmurr]

Hiya
My car (2003 Mk2.5) is playing up. I changed the battery last night as I assumed that it was buggered by the cold temps lately. Started it this morning and it ran for a few minutes while I was defrosting the windows then it cut out. I restarted and it ran for a few seconds then died. Then it would turn over but it wouldn't catch.

I can only guess that it isn't charging from the alternator...

Can someone please let me know how I would go about diagnosing this? I've got basic equipment (multimeter, socket set, trolley jack) but nothing that I can plug into a laptop....

Thanks in advance...

[Murdoc]

Does sound like the alternator, can you measure the voltage across the battery when it is running, switch headlights and blowers on too.

If you see a voltage below 13.8V the alternator is gone.

Edited by Murdoc on Thursday 4th March 07:41

[paulmurr]

Thanks mate, I'll check that over the weekend.

[paulmurr]

Just had a quote for the alternator, and I thought that it'd be prudent to do the timing and drive belts, water pump and some bits that were noted as needing done at the service (NSF drop link and rear brake pipes).

£760 + VAT

fk

A

Duck.

[NeoVR]

Murdoc said:

Does sound like the alternator, can you measure the voltage across the battery when it is running, switch headlights and blowers on too.

If you see a voltage below 13.8V the alternator is gone.

Edited by Murdoc on Thursday 4th March 07:41

Just as an aside.. am i right in thinking a healthy alternator should generate around 14.5 volts with engine running? (as measured across battery terminals)

[Oldandslow]

TBH it doesn't sound like the alternator to me. The new battery should be enough to keep it going even if the alternator isn't recharging it (more than a few minutes anyway). I've driven 20 miles with a duff alternator praying that the battery would last out and I had headlights on. The fact that you were turning it over but it's not firing would point to something else. What that might be I'm not sure. Fuel, ignition, AFM, ICV etc.

[NeoVR]

re-reading the top post i dont think its the alternator either.. cranking the car is the most stressful time for a battery with massive current draw (hence big fat cables)
if its turning over the battery/charging system will be fine...

what youve described sounds more like an immobiliser problem.

[Murdoc]

14.5V would be fine.

When you say it turns over but doesn't catch is it turning over slowly or at a normal speed?

[paulmurr]

Hi guys,
It's cranking over at normal speed. I've not had a chance to check the voltage over the battery but I'll do that tomorrow morning.
If there is an immobiliser issue how would I doagnose/resolve this?
Thanks in advance!!

[MX-5 Lazza]

If it's turning over at normal speed then the battery & alternator are fine.

http://www.pistonheads.co.uk/gassing/topic.asp?h=0...

Edited by MX-5 Lazza on Friday 5th March 08:30

[paulmurr]

Thanks Lazza...

I'll have a poke about tomorrow morning and see what I can see.

[NeoVR]

Turning over at normal speed will either mean no spark or no fuel..

Do you know if your car has a immobiliser?.

[paulmurr]

Yep, it has an immobiliser and alarm. I've called an autosparky. I've neither the skills nor the tools to sort this out. I know when I'm beaten

[Murdoc]

I'm going to back pedal sharpish and join those guys, alternator seems fine. My immobiliser did give me similar problems, bad PCB design and the relays had very bad joints that got hot.

[paulmurr]

Just been out for a poke about. Car started on the first turn of the key then died after 30 secs. Restarted, caught and then immediately died again and then cranked but wouldn't catch. Checked all fuses and they're fine. Tried spare key with same results as above. Waiting for autosparky to call

[Jafinkeesaurus]

While you're waiting for him you could take the spark plugs out and clean/dry them. When you put them back if the time it takes to cut out is back up to 30 secs again it would at point towards a fueling/mixture problem.

[paulmurr]

Snotrag in another thread said:

Good point made in that post - does yours run in 'diagnostic' mode?

What is this diagnostic mode of which you speak?

Also, can I get the car to tell me the fault code without having a reader? On my mates Accord Type R he can do some button pushing and a light flashes on the dash corresponding to the fault code.

I've called a few electricians and not one has got back to me...? WTF is going on?

Edited by paulmurr on Monday 8th March 10:34

Edited by paulmurr on Monday 8th March 10:35

[snotrag]

Yes you can do that.

You can run the car in 'diagnostic mode' or whatever its called, which takes the ECU out of the loop - you use it to set the base timing for, or the idle speed example, so the ECU isnt automatically advancing/retarding it.

It also means the fuel pump runs constantly, rather than just on-demand, and various other things.

Look on the PAS side of the engine bay near the light, there'll be a blue power connector and a black box with a flip up lid.

Flip the lid up, and look at the diagram. Use a paperclip to connect the 'GND' and 'TEN' connections.

Then start the engine, see if it runs.

I cant remember the exact process but there is also a way to read the error codes using the flashing ECU light and a table of codes.

All available on miata.net/garage

Edited by snotrag on Monday 8th March 11:36

[paulmurr]

Thanks Snotters, is that the same as this page? It specifically says that it does not work for Mk2.5s...

[snotrag]

Ah right missed that you were on a later model.

I think after the Mk2 the cars are OBD2 compliant in which case you can get generic code-readers for not a huge cost IIRC.