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intermittent starting problem


Redstokie999

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Hi ive recently purchased a vauxhall 2.0 powered caterham had a few problems last one was resolved by the feed back i received from this site so thank you, next problem is occasionaly the car wont start, sometimes its in the morning (today late for work) sometimes after a run the symptoms are buzzing noise coming from the left hand relay (hopefully see picture) on the bulk head, after leaving it for a while it starts then runs fine, ive tapped all around it to make sure nothing sounds loose checked all the earth leads, replaced relays and done a visual check on the wires has anyone got any ideas, thanks in advance caterham
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no picture yet! Can you give a bit more info about your car, e.g. carbs or injection or throttle bodies, ecu type etc. When you say not starting does it crank but just not fire?

 

Edited to add its helpful if you can keep it all in one thread as it saves having to dart around to see how far the enquiries got and suggestions received 😬

 

Edited by - Paul Deslandes on 26 Apr 2011 11:01:51

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Hi Paul, thanks for your swift reply the car has gor jenvey throttle boddies, an MBE management system, the car spins over but doesnt start, the relays are situated just behind the battery on the right hand side if you are standing in front of the car, the noise from the relay is quite loud.
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Do you know which MBE ECU you have, an earlier 956, 967 or the current 9A4. If, as is likely, its one of the earlier two and is on an SBD supplied loom, one of the two relays controls the ECU +12V supply and, the other, either the fuel pump or shift light.

 

The supply relay is switched 'on' when the ignition is switched on and supplies +12V to the ECU. So one of the relay coil contacts is grounded and the other has +12V if ignition is 'on'. The second relay has +12V to one of the coil connections and the other is grounded by the ECU, either to switch on the fuel pump or to light the shift light, depending on which option was setup when the system was installed in the car.

 

You've done the obvious things - changed the relays and checked the connections. When it eventually starts has the relay already stopped buzzing and/or does it stop when the engine starts? Under either condition (buzz/quiet) can you hear the fuel pump running?

 

Normal operation, if the ECU is controlling the pump via one of the two relays, is for the pump to run for about 2 seconds after switch on and then cut out. It comes on again once you start cranking the engine and stays on until you switch off. This is a safety feature so, if you have an accident and the engine stalls, the pump stops after a couple of seconds to prevent fuel from being sprayed around if a fuel line is ruptured.

 

Its not unknown for one of the relay socket female connectors to get pushed back into the moulding and to make intermittent contact. I had this once and it had me going for days 😳. Pull the relays and inspect the socket to make sure that all the connectors are fully home.

 

If one of the relays is buzzing it sounds as though its not getting enough volts to control it properly. So either the ECU is not getting power or the fuel pump isn't being powered up, depending on which relay has the problem. It could be an ECU fault but I would put more money on a poor connection somewhere.

 

Keep us posted.

 

Paul

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Hi Dale

they sound like separate shift lights and not controlled by the ECU although they will be triggered from its rev counter output. Some of them do hunt up and down on cranking until the engine's running. This makes it likely that the second relay is controlling the fuel pump.

 

Can you identify whether the relay that's clicking is the one controlling the fuel pump or the +12V supply to the ECU? That might help getting to the nub of the problem. If you can see the wires going into the relay socket and it is an SBD loom, we should be able to identify which one it is from the colours. If you can supply both sets of colours (no need to identify the relay pin numbers) it would help.

 

Paul

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Okay. The left hand relay with orange, yellow, grey and 2 x purple is the fuel pump relay. The other one controls the power to the ECU.

Ignore my comments about the choice of either fuel pump or shift light for the relay. That was only on the earlier 956 ECU. The 967 can have both and I would guess that yours is connected up so that the relay in the loom controls the fuel pump. The way to check would be to see if the grey wire goes to ECU connector pin 16 (shift light) or 17 (fuel pump).

 

So, the likelihood is that its a fuel pump electrical circuit problem and I would guess a poor connection somewhere as described before. If you have a voltmeter you could try and measure the voltages of each of the socket connectors with the relay removed. With the ignition on I would expect the mauve and the yellow both to be +12V and the grey (which goes to ECU pin 17) to be 0V for about 2 seconds after switching on the ignition and then going back up to roughly 12V. For the last grey wire test the relay will need to be in situ otherwise you will only see 0V. Have you tried wiggling the ECU connector in your efforts to find the problem? Make sure its pushed fully home and has the red locking clip in place.

 

Too bad you're up in Stoke as I'd be very happy to have a look at it for you.down here.

 

Paul

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Do you have a FIA cut out switch? If so also worth checking the connections on the rear of the FIA switch as this also provides a feed to the ECU. Worth bi-passing the FIA switch so you can to eliminate.

 

I know about FIA switches causing ECU / non-starting issue. I spent many hours finding out mine way faulty.

 

Cheers,

Andy

 

 

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Paul, will have to check them wires, will let you know how ive got on, just tried it again at work and it did it again, someone wiggled the wires and it started wether that was coincidence or not im not sure, the only trouble is the guy just grabbed a bunch of them so i as yet cant work out which one it may be.
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well that's beginning to make sense. If the relay is intermittent due a dodgy connection the fuel pump will play up. When you switch on the ignition without the engine running, you should hear (and feel if you're touching it) that relay click and then click again as it goes off after a couple of seconds. Check the socket connectors to see that they're fully home into the moulding. Try wiggling the relay rather than the wiring as it could be that one of the connectors has opened up and loose on one of the relay's flat 'pins'. If the latter you'll need to do a bit of judicious work with a small screwdriver type blade to close it up a bit. Or you could try bending the relay contacts so that they touch more easily. Only a short term fix though.

 

Paul

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Hi Paul, im still on the problem, ive taken out the left hand relay, got my volt meter on the yellow, disconnected the plug from the ecu and put the other lead on the yellow and i cant get a reading,put the relay back and tried the grey and no reading there !! when i build everything back again the car starts and has done on numerous occasions today (typical) what am i doing wrong ?????? *confused*
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Hi Dale

With or without the relay and ECU connected, if I have the wiring colours right, you should see +12V between yellow and chassis, i.e. meter set to a range to read 12 Volts dc, probably 25VDC, and black wire (-ve) to chassis and red (+ve) to the yellow relay wire. I would expect this to be the case with or without the ignition switched on but I can't be sure how its been connected. Similarly I would expect the mauve wire to be +12V with respect to chassis with ignition ON. With both the ECU and relay connected, the grey wire should read 0V for about two seconds and then go high (+12V 'ish but might be a bit lower) until you start cranking the engine when it should go back to 0 Volts.

 

Have you checked that the relay socket connectors are okay? The symptoms really do sound like an intermittent connection and I would guess that its one of the relay sockets or the wires connected to them that's causing the problem. Even though its the left hand (fuel pump) relay that's buzzing, it could very well be the other, power control relay, socket that's intermittent as this controls the supply to the ECU and will affect the other relay too.

I'm hoping that the wiring loom colours are as I'm expecting them to be, and they do sound right. I'm pretty sure you're in the right area and you'll get there in the end. It will be obvious when you find it but they can be a right b* to locate.

 

Paul

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Hi Paul, checked all the wires and they seemed ok, a friend called in (lot better at electrics than me) and rechecked the relays as you said on your previous posts he noticed on some of the spade terminals on the relays that although they were new they were slightly discoloured which he said could of been where they had been tracking across, he's gone through all the connections so hopefully all will be ok................. fingers crossed, many thanks for all your advice, regards Dale. *wavey*
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