Possible Faulty DME - Diagnosis advice please

[charlieb]

Hi guys,

I have just got the car back from having some new front wings fitted. It drove fine when I picked it up and for the first week was
not a problem. I took it out last week for a run and it cut out after about 15 mins when it was warmed up and I had been sitting in traffic.

It was really struggling to keep alive, kept stalling and was running very rough, hesitating and not burning fuel.

It was a little low on fuel (light not on FYI) but I thought it might have picked up some crud from bottom of the tank - so I topped it with super plus and crossed the fingers. Drove fairly spiritedly and it seemed to clear. No problems after that.

So fast forward a week - Car starts fine, then runs fine but after about ten-fifteen minutes in traffic it stalls again! I pulled over and popped the bonnet - left it running and it would run for about 30 seconds, then cut out. I managed to limp it home at high ish revs so it wouldnt stall, but i was having to fight it.

At a total loss because it was sat fine for at least 5 mins outside my house while I looked in the engine bay in confusion when I got back.

I drove 2k miles to France and it did not miss a beat (had new plugs and leads before the trip etc) - I have just had some bodywork done (not mechanical) and now its died twice in two weeks! Feels like it must be down to the fuelling system (not head gasket, not burning oil, not spitting out of the exhaust while idling) just running like a dog.

So could this be down to the DME? Forgive me for sounding thick but is that the chipset?

Any help appreciated

Cheers

Charlie

 

[chrisg]

Charlie

I'm no expert on this, but my understanding is that if the DME relay (in the fuse/ relay box passenger side under the bonnet) fails the car won't start or run. To my mind this is more likely to be a mixture or tickover/idle issue. The Idle Control Valve or ICV under the inlet manifold could be your culprit. I'd also check all the boost (large) hoses and the various small vacuum pipes as well. If a boost pipe is leaking or come loose the engine will run very rough.

Yours

Chris

 

[charlieb]

Hi Chris,

Cheers for that! OK so DME is out of the equation. Last time I thought it was that I had actually blown the head gasket!

Did go around and check all the vacuum hoses/jubilee clips etc and I completely forgot to mention (in my haste to blame the DME) there was one thing that was not attached at all! It was one of the small black lines that comes from somewhere on the bulkhead in front of the driver and runs about 2ft worth then has a little blue/black bobbiny type thing, then a little more line, then attaches to a small 4 way connector of more vacuum lines under the air intake manifold. Could that be the ICV? Just wondering why it was off now!

I would take a picture but my under bonnet light is on the blink and its dark now.

Cheers

Charlie

 

[robwright]

That sounds like the vacuum feed to the heater unit. The ISV is burried under the intake manifold but I am not sure that would cause these symptoms. My first bet would be fuel. Is the fuel filter old? I would take a look at the Fuel Pressure Regulator (FPR) and it's associated vacuum feed.

 

[charlieb]

OK, the heater was not working properly and I had some work done a few months back to fix it so thats probably why that was off then!

The fuel filter is probably 2 years old. Ill change it anyway as its due a service (fresh oil/filter,air,fuel etc) Will I need to whip off the intake manifold to look at the FPR? I have worked on engines before (rebuilt my alfa 33 16v quad cam when I was younger) but am a little scared to go near it for some reason!

Can see myself needing a workshop manual for this one. If it is the FPR/vacuum feed is that a major fix?

Any other thoughts guys?

Thanks for the help

Charlie

 

[robwright]

On the fuel injector rail on top of the engine there is a gizmo at either end with a small hose attached to it. The one at the front is the damper and the back one is the regulator. Doddle of a job to swap. Not saying that is what it is but it is an easy try if you can get or borrow one to swap out.

 

[charlieb]

OK cheers Rob.

Will pop out today and have a look. I have just read elsewhere about the symptoms and they match mine. Incidentally when I changed the plugs
(denzo iridiums) the ones I pulled out (bosch) were black and fouled up, and I did have poor running before the swap but put it down to the plugs/leads/ignition circuit rather than fuel so I swapped all of that and it remedied the problem.

The fresh plugs must have dealt with the dodgy fuel loading on france trip but may have become fouled themselves now and hence the same problem has reared its head.

It seems that it might have been this little FPR all along!

http://www.buzzle.com/articles/symptoms-of-a-bad-fuel-pressure-regulator.html

ill order one from berlyn/exeter and see if that remedies the problem.

Thanks
Charlie

 

[peanut]

this is quite common on a car that has had infrequent use and the tank has been allowed to get near empty.
It effected my S2 twice last year .
In the end I concluded that it was primarily down to the injectors not passing sufficient fuel as a result of some water or muck picked up by the pump blocking the fine filters in the injectors. Additionally some of the ignition components needed some attention like filing and cleaning sparkplugs, distributor terminals, rotor arm and key earthing points around the car.

Whatever you do don't be tempted to use a fuel additive in the tank because all the crud that gets removed from the fuel lines on the far side of the fuel filter will simply block the tiny injector filters even more.

First thing i would do is to make sure the tank is at least 1/4 full to ensure the pump can create sufficient fuel pressure to for the injectors

Next thing i would do is to remove the DME relay and replace it with a 3x way bypass cable (as per Clarkes garage workshop guide.)
This will remove the DME relay from the equation therebye completly eliniminating the DME relay as being the source of the problem .

You will now have the fuel pump constantly running and hopefully have fuel pressure.
You will also have a supply to the ECU and ignition system. If the pump doesn't run continuously check that you have 12v+ on terminal 30 on the base of the DME relay socket where your bypass cable is fed from

Crank the engine for a least 30 seconds and check
1. you have tach needle bounce
2. you have a strong spark at both plugs and coil
3. check plugs for fuel to make sure your injectors are passing fuel to the inlet.

If the car doesn't start one or more of these 3x things will not be working . We can then look in more detail when we know which it is .

Alternatively you could have a few people 'fiddle' with it and then buy a load of new parts like fuel pump, fuel filter ,distributor , rotor, plug leads etc in the hope that it will miraculously spring to life before your bank is empty []