intermittant non start?

[SGP]

My '89 320i doesn't always start first time,everything is in good order ie no vacuum leaks, all new leads, cap and rotor.sensors working etc. sometimes it just wont start untill I stop cranking and turn the key again.This happens intermittantly whether hot or cold what could it be ?

[Brianmoooore]

Connect a 12V bulb between the + terminal of the ignition coil and earth, and place it where you can see it. Could be an ignition switch problem.
If this is Ok, suspect a dying fuel pump.

[SGP]

Thanks,I'll try that tomorrow and report back.

[SGP]

I checked the power to the coil as you reccomended Brian,the light came on everytime I switched on the ignition,so far today the car has started everytime on the first crank.Am looking on the partsgateway site for a good single pipe fuel pump to have as a spare just incase mine dies.Thanks.

[SGP]

Went out this evening and the car would not start until the second turnover,cranked it for a good 5 seconds the first time but it wouldn't start.This is very annoying and embarrasing. If theres one thing that pisses me off most this is it !

[E30Mark]

My car broke down this week

Found out the problem was a dodgy connection to the fuel pump, I dismantled the the fuel pump connector and crushed down the sockets slightly to create a tighter fit, and now all is OK! Took me a while to locate the fault, but at least it didn't cost me anything to fix.

[SGP]

Thanks Mark I'll give it a try.The fuel pump is powered by a signal from the ecu (if I'm not mistaken)so I should probably check the interface too.

[Brianmoooore]

Went out this evening and the car would not start until the second turnover,cranked it for a good 5 seconds the first time but it wouldn't start.This is very annoying and embarrasing. If theres one thing that pisses me off most this is it !

So what did the light do?
Don't start trying random things - you'll cause more faults than you'll fix!

[SGP]

The light came on each time I tested (turned the key). I did not leave it in situ, should I leave the bulb connected to the circuit for a while and observe?

[Brianmoooore]

, should I leave the bulb connected to the circuit for a while and observe?

Definitely, until the fault puts in an appearance.

[SGP]

Thanks will do.

[SGP]

Well then,this evening the car didn't start first time.I gave it a good crank and the bulb stayed on but no start until the second crank.I guess that rules out a faulty ignition switch,I've also given the pump connectors a squeeze to tighten them up.BTW this is the second fuel pump I've fitted. late last year the car refused to start despite repeated attempts , the problem was rectified by fitting another pump.Strangely enough however,the original pump is now working in a 316i WTF ! ? ?.I should also point out that the intermittant non start also happenend with the original pump.Could the FPR be a factor?

[Brianmoooore]

Right - ignition supply OK.
Now take the bulb and push the wires into the pins with the green/purple and brown wires on the connector that you will find under the right hand side of the rear seat cushion.
It should light all the time you are cranking the engine and when it is running. See if it fails to light when the car is reluctant to start.

[SGP]

Thanks, will do.

[SGP]

By Jove, I think you've cracked it Brian. I'm delighted to say the test light failed to come on when the engine didn't start , on the next attempt the bulb lit up and the engine started.What next pray tell ?

[Brianmoooore]

Fuel pump relay is under extreme suspicion! Check fuse 11 is making good contact in its holder as well, and try a new fuse just to be on the safe side.

[SGP]

Thanks,will get back.

[SGP]

Ok, have changed the fuse and relay, cleaned all the cotacts with switch cleaner.It all looks ok, so I'll see how it goes tomorrow.Test bulb still in-line.

[SGP]

I have changed the DME relay now aswell but I'm still having non starts.Bulb not lighting.Any suggestions for the next check?

[Brianmoooore]

Move the bulb to terminal 87 (green/purple wire) of the fuel pump relay. This is the same wire as it's connected to now, but at the source of the voltage.
Wonder if there's an old immobiliser connected in the fuel pump wire?

[SGP]

Thanks I'll do that tomorrow,there was an alarm system removed a few years ago.A new ecu has been fitted at the local dealership since.It took them some time to diagnose the ecu .

[SGP]

Right, the light is not lighting when there's no start, where to next?

[Brianmoooore]

Pin 30 of the same relay. Should be lit all the time, so you'll have to take out the bulb or disconnect the earth when you stop.
Do you have a LED and resistor suitable for 12 volts?

[SGP]

No I haven't got the led and resistor but I can make one up.

[Brianmoooore]

If you do, connect it between the brown/green (85, I think) of the fuel pump relay and earth. Should come on with ignition and go out when cranking and running.
We're getting very close! The only trouble is, you may disturb whatever the problem is, and temporarily cure it, only for the problem to come back again later.

[SGP]

Thanks Brian, I will endeaver to make up the test LED, will consult the Bently manual tomorrow for the specs.I have noticed the engine seems to be changing idling character when I'm fiddling in the relay panel.From perfectly smooth to lumpy and rich smelling.

[SGP]

Have not got the LED rigged up yet, but the bulb stayed lit today (on pin 30) when the engine refused to start.It seemed to weaken during cranking and brightened up when the engine started (on the second attempt.)

[Brianmoooore]

It'll go dimmer when cranking because the starter motor pulls the battery voltage down.
Pins 30 and 87 of the fuel pump relay are its switching contacts. We have power at 30 when the fault is present, but not at 87. Therefore the relay isn't switching on.
You've tried a new relay (?), so, under fault conditions, either power isn't present on the red/white wire to the relay coil, or the other side of the coil (brown/green) isn't being earthed by the ECU.
Connect the bulb to the red/white wire.

[Taylor325i]

Faulty crank sensor?


Taylor.

[Brianmoooore]

Faulty crank sensor?Taylor.

Might be, depending on the results of the latest tests.
Actually, I thought we'd already established that sparks were always OK at all times, but looking back at the previous posts in this thread i see we haven't. That's the problem when you've about 20 different threads on the go at the same time!

[SGP]

I have the LED hooked up as outlined above,its performing as you described ie. switching on with the ignition & switching off on cranking and running.So far the engine has started first time every time.will post when she next fails to start. Point : it starts up with the fuel pump fuse removed and runs for a second or two until the fuel rail pressure is depleted - whereon it will cut out.I must presume therefore that we have a no spark scenario co-incident with no power to the pump on non start incidences.It's behaving exactly as if the immoiliser were activated. Much head scratching etc...

[Brianmoooore]

We know that the fuel pump isn't running when it fails to start, but there may be no sparks as well, although we've established that power is present all the time at the + terminal of the ignition coil.
LED test will establish whether the ECU is switching the fuel pump relay, or if the relay isn't getting power.

[SGP]

I think we're getting somewhere with this...The LED stayed lit earlier when she failed to start,on the next attempt it went out and the engine started.Where to next ?

[Brianmoooore]

If the LED stayed lit, then there was power on the red/white wire to the coil, but the ECU wasn't earthing the other side of the coil.
The most usual cause of this is no input to the ECU from the crank position sensor. This will result in no sparks as well, but I can't see how you can test for sparks on such an intermittent fault!
Best way forward would be to try a different crank sensor. They usually start off failing by giving trouble when they warm up, but yours (if it is the problem) seems to be the other way around.
You can run the sensor's cable over the top of the rocker cover for test purposes, rather than fitting it behind the water pump pulley.

[SGP]

Thanks,I have another sensor will see how it goes.