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PostPosted: Wed Jun 07, 2017 9:46 am 
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Recently bought an import 1994 GT4 St205 WRC, it's been off the road 5 years and I've been carrying out work on it, everything sorted apart from a battery which wasn't charging, so carried out the voltage checks on the alternator and found that seemed to be the issue.

Installed a new alternator of the same part number from the old unit removed.
When starting up the car will run for around 20 seconds, the revs will climb slightly and then the fuel pump will cut out turning off the car.
If the alternator is unplugged, the car can be jump started and will run fine and not cut out.
I have also changed the battery and checked the voltages output from the alternator and they are correct.

Any ideas as to what could be causing this would be greatly appreciated.



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PostPosted: Wed Jun 07, 2017 8:48 pm 
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Location: Camberley, Surrey
Car Model: ST205
Very basic but have you checked for any error codes?

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PostPosted: Thu Jun 08, 2017 9:11 pm 
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Hi and welcome.

If it runs ok with alternator unplugged, then it does sound like a power problem.
Can you confirm a few things:
When jump starting and it runs ok - do you leave the jump leads connected, or disconnect ? This implies the battery is flat and/or duff. This could be the issue. Bear in mind that running a lead acid battery flat will damage it.
Have you tried jump starting and running with jump leads connected and alternator connected ?

It is important there is a battery in good condition wired in to the car properly. A very flat / damaged battery or jump leads to another battery present too high a resistance and won't cope with the short period current pulses needed to drive injectors and other devices correctly.

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PostPosted: Thu Jun 08, 2017 11:39 pm 
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Thank you for the replies.

I shall check the error codes first thing tomorrow.

When jump starting with the alternator disconnected, I removed the jump leads once started and it ran fine, that was with the old battery.

I've put a new battery in it now but haven't used jump leads on the new battery to start it yet as there's still plenty of charge but with the new battery I'm getting the same results.

Had a suggestion made to me that it could maybe be the fuel pump resistor?

Thanks




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PostPosted: Fri Jun 09, 2017 12:15 am 
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It is possible the fuel pump is left on full power (resistor not switched in) if the voltage is low. Normally the resistor is swiched in series during idle & cruising, presumably to reduce noise.

You can prove a point by linking B+ anf FP in the diagnostic connector which runs the pump flat out all the time the ignition is on.

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PostPosted: Fri Jun 09, 2017 12:18 am 
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p.s. - with the alternator connected and engine running, measure the voltage between the big output terminal on the alternator and engine ground (e.g. alternator body). Should be about 14 - 14.5V.

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PostPosted: Thu Jul 13, 2017 12:00 am 
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Thanks for all the replies, the problems seemed to disappear, and the car is through the MOT and is now on the road...

However... after a spirited drive the other night, once back down and driving around town at 30mph the car decided to cut out just like it was doing previously. The car started up fine today and again drove great at higher speeds and under acceleration but once driving at slow speeds it cut out.

The power seems to just disappear, the revs slowly drop off and the car needs to be restarted. Once restarted the car runs for around 20 seconds before cutting out again.

Would this likely be a fuel issue or an intermittent electrical fault?

Just purchased a fuel filter today, as I read it could be blockage in the old filter.

I have also checked coolant level and filled whilst running.

Any help would be greatly appreciated!


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PostPosted: Thu Jul 13, 2017 10:18 pm 
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If the problem is on light throttle, it's unlikely to be fuel filter blocked.

The 2 that seem most likely to me:

1. - problem with power feed to fuel pump via resistor which is switched by 'fuel pump relay'. Check for this by linking FP to B+ in diagnostic connector as above.

2. Knowing the car has been stood (presumably unpowered) for 5 years, have a look at the following thread about capacitor failure in ECU's. The thread covers gen 5, but I have heard of a couple of gen 6 ECU's with problems with capacitors leaking. The ECU is located under the dash, behind the centre console, bolted to the transmission tunnel. Access by pulling back the footwell carpet on both sides (connectors on passenger side, fixing bolts on both).

viewtopic.php?f=2&t=5617

It is also worth checking fault codes. No special equipment needed, follow the guide on the following link.

http://www.gt4dc.co.uk/info/howto/ecu/e ... _codes.htm

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PostPosted: Fri Jul 21, 2017 8:06 pm 
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Thanks for the reply.

Started the car, ran then cut out.
So I bridged the FP and B+. Started fine and didn't cut out.

Does that indicate that the resistor is faulty?




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PostPosted: Sat Jul 22, 2017 9:53 pm 
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Resistors don't normally go wrong unless it's physical damage. I have heard of a resistor which hadn't been bolted on wear through from the vibration / rubbing, but it's the only failure I've heard of.

Most likely failure of the relay or it's holder, or a wiring issue. On the relay pins and the socket check for signs of overheating - melted plastic, discolouration of metal, corrosion. If that all looks ok, then try another relay.

In the meantime, I have heard of plenty of these cars being driven around with the B+/FP link without issue. I would just avoid leaving the ignition on without the engine running.

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PostPosted: Sun Jul 23, 2017 2:24 pm 
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Ok thanks I shall check that.

I've been having a look and read about the mod that bypasses the relay and resistor, would you recommend doing this or would I be better to try keep the system like it was originally designed?




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PostPosted: Sun Jul 23, 2017 8:42 pm 
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I see no benefit in bypassing the resistor as it is only switched in during idle and cruising.
On the other hand, by running the pump flat out all the time, wear is increased plus the slight increase in fuel pressure will affect mapping.

As a short term fix to keep the car mobile while the fault is found and corrected then no problem.

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