Car won't start intermittently ['87 200 Quattro Turbo]

[John Clayton]

More and more often it has an intermittent fault where the battery is fine but it won’t start. Eventually it sometimes starts running on 1 cylinder (after a few minutes of cranking it in bursts) and then struggles slowly into life. Other times it flattens the battery before this occurs -it’s a close run thing!

I thought that it may be that the mixture screw needs adjusting again, or it may be that this is unrelated to the problem. The screw is “by the frying pan for air filter & half a turn of the allen bolt is enough -even this will make a big difference”.

Checked exhaust gas and it is OK for MoT. It has a burble at idle (sounds like it's running a bit rough) + sometimes needs cranking for several seconds before it fires (and on 1 occasion it wouldn't start at all). Roy adjusted the mixture screw in the injection system by ear again (it was done a few months ago -not sure why it has drifted off again). Roy: “this may help but then it may drift off again”). Roy agrees that putting it on a 4WD rolling-road would be a good idea.

Angus -a skilled car engineer with electro-mechanical expertise -has been driving the car recently and it did it once to him too. He got it going again with part throttle, but he thinks that it must be an electrical problem (and even he said he doesn't know where to start).

Anyone got any ideas?

[ian20v]

Have a wee look on here may be helpful.

http://www.sjmautotechnik.com/troubl...cuf.html#fault

[John Clayton]

Thanks, I will check it out. I forgot to say that the Check Engine light [as designated on your above webpage of Fault Code reading] flashes on intermittently for a second or so (usually when car is under power e.g. going up a hil).

[ian20v]

I'd check over everything ,plugs, distributor,crank sensor,vaccum pipes ,fuel filter,injectors,try some redex cleaner.

[mikes2]

Fault codes should be checked straight after getting the check engine light flashing.

The only codes which have triggered a check engine light while driving my MB were the inlet air temp sender wiring and also a hall sender fault in the distributor

[leggy]

Hi

I'm probably way off the mark here, don't really know about turbos, but your symptoms sound very similar to the ones I was having with my B4 a year or so ago, turned out to be the coil pack; sparks were going in but not always going out, resulting in the engine not always running as it should, sometimes not firing up when battery was okay, firing on only 3/4 cylinders, etc etc...to the point of breaking down one day and not starting at all...might be worth checking yours if it has one.

[John Clayton]

Good call.

The other thing that I forgot to say is that (when it won't start in the above manner) it always then seems to fire up OK when you jump it off another vehicle.

[Groundhog]

If indeed it starts with a jump from another vehicle, and assuming you are connecting jump leads to the battery, then the only thing you are by-passing is your own battery so unless we are missing another piece of info are you sure your battery is 100%? Cars like these,especially as they get older, need a good battery that can spin the engine over with conviction. Try disconecting your battery and clamping the jump leads directly to the disconnected terminals, does it start fine then?

Other than that your original post shouted 'air leak' to me particularly if the engine light comes on on full chatter.

Half a turn on the mixture screw is one hell of a lot by the way.

Another outside possibility is that the meter head is leaking into the air box. When the idle is set it is with the engine using some of the fuel from the leak which then is not available on start up only a weak mixture from the injectors. This invariably creates issues with trying to set the engine at idle.

I can't possibly see that a rolling road would be of any significant help but it's your call

[leggy]

Originally Posted by John Clayton

Good call.

The other thing that I forgot to say is that (when it won't start in the above manner) it always then seems to fire up OK when you jump it off another vehicle.

Originally Posted by Groundhog

If indeed it starts with a jump from another vehicle, and assuming you are connecting jump leads to the battery, then the only thing you are by-passing is your own battery so unless we are missing another piece of info are you sure your battery is 100%? Cars like these,especially as they get older, need a good battery that can spin the engine over with conviction.

Same as John Clayton, mine would jump start no problem, well, up until the day I broke down anyway. As Groundhog states, you do need a good battery to be able to turn the older cars over.

FWIW, back then my boy was eating batteries, at a rate of one/year, all cheap makes, and with the coil pack fault to boot, well, it's hardly surprising that the battery didn't have enough oompf left to start my boy on the day I broke down, it/they barely had the oompf to start my car.
(NOTE: I have since invested in a decent battery! )

[Hanuman]

Originally Posted by Groundhog

Other than that your original post shouted 'air leak' to me particularly if the engine light comes on on full chatter.

Half a turn on the mixture screw is one hell of a lot by the way.

I can't possibly see that a rolling road would be of any significant help but it's your call

Agreed. Mostly. A rolling road session seems an extravagant effort, especially if the knowledge of how it's meant to work is missing.
Nothing in the discussion so far has suggested that the car isn't performing otherwise. What you are experiencing is some form of fault when the car is on load. Knock regulation? Loss of knock regulation? Failure of a sensor?

An air leak compensated for with a little extra fuel at idle will only adjust the mixture correctly in the low Rev, no load state. To be making frequent uncontrolled adjustments points to other issues.

It's time to start at the beginning, with a controlled approach.

Drive the car, read the codes.
What is reported? Do all of the sensors work? Likewise, the switches- idle and WOT.
Is it getting enough fuel?
Is it getting consistent, even fuel to all cylinders?