Grr another Misfire - what else can it be?

Black Beauty · Mar 11, 2009

Ok, in the last few weeks I have replaced the DME relay, the plugs, leads, coil, distributor cap and rotor, air filter and a few other unrelated items.

But yesterday and today she decided to mis-fire on me driving home on the A3.

After she had misfired, it felt as if she was only firing on 3 cylinders and then when I got home, I attempted to restart her but lil ol' Black Beauty was having none of it and just turned over.

This leads me to believe I have a faulty DME relay but could there be something else I am overlooking, or is it the air flow meter?

Cheers
Spence

PS - I think she's pulling a strop because I said I fancied a 4 Turbo.... these women eh!

944 man · Mar 11, 2009

Fuel pressure regulator perhaps or maybe even the fuel pump?

Simon

peanut · Mar 12, 2009

Not likely to be the DME relay or your pump would't work and the car wou'nt run at all .
an intermittant problem like that could be down to a poor connection or earth . It might be worth pulling all the connections and earth straps and cleaning them all with a proper electrical contact cleaner.
Have a look on Clarkes Garage workshop manual section. There some good troubleshooting guides there .

A few things to check maybe .
Check the crank sensor is nice and tight. Wiggle the lead when trying to start next time it refuses.
Check your ignition switch if its original it could be on its way out.
Check all your wiring and connections on your alarm and immobilser.
Check the fuse/relay box maybe pull the relays and fuses and clean contacts .
maybe drain the tank and flush, change fuel filter in case you have water in the fuel.
Clean the contacts to the petrol pump particularly earth.
Clean all the earth points to chassis.
Clean connectors to injectors
I shall be doing the same thing this weekend ...mine won't start.. good luck

Black Beauty · Mar 12, 2009

Peanut

Thanks for your tips

You're right about the DME, as I changed it this morning for a brand new one and 20 miles into the journey she coughed and spluttered more than she had done before and to be honest I thought I was going to be stuck on a section of the A3 without a hard shoulder.

But she kept going but again when I got to work, I turned her off and then back on again and again she wouldn't start. [

] [

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S

peanut · Mar 12, 2009

sounds like it could be a blocked tank vent. It certainly sounds like fuel starvation .
Try removing the fuel cap the next time it conks out and see if you have a vacumm in the tank.
My work Mondeo sucks air like a bellows when I fill her up

PORKA · Mar 13, 2009

Hi,
Had similar trouble with my Turbo but replaced DME, ignition relay, X relay, leads, rotor arm,cap, both sensors, checked all the earth connections,checked the fuel pump and pressure, the ECU plugs and eventually turned out to be the ECU itself!
If you moved or wiggled the unit about the engine would cut out or not start, nothing wrong with the plug.
Put in a second hand unit no more trouble.[

]

zcacogp · Mar 13, 2009

Spence,

Be methodical. To fire, the engine needs air, fuel, a spark and an unblocked exhaust.

First Q - did this problem start all of a sudden? Or did it appear progressively over time?

Check for a spark first. That's the easiest. Plug out, rest it on the block, try and start the car. Do you get a (nice big, fat, juicy white/blue) spark across the plug?

Checking for fuel is a bit harder, but does it smell as if there is petrol around when you take the plug out? Is the plug wet? If possible, take an injector plug off and see if there is a signal going to it. Or take an injector out and see if it is spraying.

Oli.

edh · Mar 13, 2009

have you changed the fuel filter recently? - It's a bit of a pain (you tend to get petrol down your sleeve [

]) but needs to be done regularly

Black Beauty · Mar 13, 2009

It did it again this morning, and most unusually, within a couple of miles of leaving home - usually its about 15miles into the commute.

However, despite that, the bit I don't get is that it won't restart once the car has done the commute, ie it will only restart once its cold. It turns over, but there's no fuel getting in.

In the past, this has been cured by changing the DME relay, which I did on Wednesday morning, so either the new relay is faulty or there's something else, which only wants to work when its cold?

JamesO · Mar 13, 2009

Anybody else near you with an early 944?
If so you could try 'borrowing' an ecu (dme) to eliminate it as a cause

peanut · Mar 13, 2009

ORIGINAL: Black Beauty

It did it again this morning, and most unusually, within a couple of miles of leaving home - usually its about 15miles into the commute.

However, despite that, the bit I don't get is that it won't restart once the car has done the commute, ie it will only restart once its cold. It turns over, but there's no fuel getting in.

In the past, this has been cured by changing the DME relay, which I did on Wednesday morning, so either the new relay is faulty or there's something else, which only wants to work when its cold?

if its a hot start problem then it might suggest a problem with the AFM Clarkes garage has a fantastic article on rectifying the problem.
Basically the AFM is a flap in the inlet like a barn door which sends an electrical signal to the EMU (DME) The flap is attached to a electrical track and wiper arrangement which over time oxidises and wears gving an intermittant contact.

If the DME gets the wrong information about where the flap is then you either get no cold start or when it warms up a bit it won't restart until it has cooled down.
I'd take the AFM apart and check that the flap is not rubbing anywhere .Ease as necessary. I'd then check the wiper track for excessive wear. You can bend the wiper to get it to contact a fresh area of the wiper track.