Second and Third plug not firing

Asiangunner · Nov 27, 2013

Thanks guys, I will check that tomorrow when i have day light.

Mike_Pollock · Nov 28, 2013

when teting the plugs hold them with some insulated pliers or similar against an earth point (cam cover) as they can give you a nasty jolt

Still have the scar from banging my head on the edge of the underside of a mini bonnet. very careful checking the first two........

Asiangunner · Dec 2, 2013

Morning guys,

I've finally had a chance to get back to the car today.

I tested the leads with the cleanest old plug as directed and I am getting a spark at all four leads. The spark isn't massive but i'm not sure if thats because i am not grounding it properly of because the spark plug design is the four prong style.

I've had a wiggle of all the fuel rail wires, I tried starting the car up to see if it would start up fine like last week and then suddenly start misfiring again but this time it just miss fires straight away and in fact feels and sounds like its only firing on one cylinder now as oppose to two that it went down to last week.

What to do next guys? i could call my local indie but i know he'll only be able to look at it once he's got it back to his shop which is £40 towing+ £40 diagnostic i just can't be paying right now on :-( as tax and mot are due now

JamesO · Dec 2, 2013

Is your car watertight? might be worth checking the ECU (DME) hasn't got wet with all the rain we had the other month. On the early cars it's located on the drivers side near the hatch release button IIRC.

Asiangunner · Dec 2, 2013

Ill have a check now mate, I haven't had any blockages etc and the car has been in regular use lately.

Asiangunner · Dec 2, 2013

Taken a short video of the engine whilst running, the sound isn't great....think i had my hand over the mic ....doh

https://www.youtube.com/watch?v=P30RK3nMq60

tref · Dec 2, 2013

OK... So we believe it has a spark on all four cylinders, 3 out of four plugs look like they are running with varying degrees of richness... ignoring the "firing" noise from the engine, it sounds like it is hunting - as one would expect from a particularly rich-running engine. Have you looked at the state of the air cleaner? I suspect that isn't the problem, but it is the obvious start. After that if you can the next logical thing to do is look at the fuel pressure.

Asiangunner · Dec 2, 2013

update...

I had the car running like in the video and and i've gone through and unplugged each injector one by one.

Result being only when unplugging 1 and 4 it makes a difference. The engine fires no differently when i unplug 2 and 3.

I've not swapped over the injector from 1 to 2 and 3 to 4 to see if the injectors are failing and in makes no difference, car is still only firing on 1 and 4 so that eliminates the injectors.
With the injectors swapped i tried switching over the wires again and it makes no difference.

What to try next?

Asiangunner · Dec 2, 2013

ORIGINAL: tref

OK... So we believe it has a spark on all four cylinders, 3 out of four plugs look like they are running with varying degrees of richness... ignoring the "firing" noise from the engine, it sounds like it is hunting - as one would expect from a particularly rich-running engine. Have you looked at the state of the air cleaner? I suspect that isn't the problem, but it is the obvious start. After that if you can the next logical thing to do is look at the fuel pressure.

I did clean my k&n filter about a month ago when i changed my radiator mate, it was a bit grubby but nothing major, It should be nice and clean now.

Asiangunner · Dec 2, 2013

ORIGINAL: JamesO

Is your car watertight? might be worth checking the ECU (DME) hasn't got wet with all the rain we had the other month. On the early cars it's located on the drivers side near the hatch release button IIRC.

Checked all round my fuses and ecu mate and no sign of dampness or water getting through.

tref · Dec 2, 2013

Hmmm... have you done a compression test? just wondering if it could be blowing by between two and three without showing the usual head gasket failure symptoms? Although that wouldn't explain it running rich/blackened plugs... probably worth doing anyway though just because it is an easy test, and compression is fundamental to an engine running well!

Asiangunner · Dec 2, 2013

ORIGINAL: tref

Hmmm... have you done a compression test? just wondering if it could be blowing by between two and three without showing the usual head gasket failure symptoms? Although that wouldn't explain it running rich/blackened plugs... probably worth doing anyway though just because it is an easy test, and compression is fundamental to an engine running well!

How would be the best way to do a compression test mate?

tref · Dec 2, 2013

You need a compression tester - a few quid from Halfrauds... or they should be!

ChasR · Dec 2, 2013

Do you still have the old leads? I know for me the Magnecors have not been the leads that everyone says they are (Christ, some Bosch leads over those cured a misfire on a car of mine!). It does sound a little like an injector driver issue I admit.

I am happy to post out a compression tester if you wish.

Asiangunner · Dec 3, 2013

Just bought one from halfords mate, thanks for the offer to post. I'll put results up asap

Asiangunner · Dec 3, 2013

Compression test done, all 4 cylinders measuring 14 bar.

I turned it over with foot on the gas and held each check of 7-8 seconds

Asiangunner · Dec 3, 2013

The new plugs i had put in are lightly backened , from over fuelling..

PS... the engine was slightly warm as recommended for the test.

Asiangunner · Dec 3, 2013

Just spoke to my local specialist who's pretty hot on 944's as he used to race them and he is saying it sounds very much like the head gasket has gone.

I did have the head gasket changed under two years ago after having a over heating issue and the head was skimmed then.

As its 2 and 3 misfiring and nothing else has flagged up it looks like it could be the head gasket. The compression test would show good figures like it has because it not under pressure.

This is going to be a very expensive month [

]

tref · Dec 3, 2013

I would expect a variation in compression figures if it were the head gasket - unusual to get all four down, and I haven't converted it, but it sounds a pretty healthy compression figure to me...

I must admit before pulling the head my next step would be to find 4 identical sized jam-jars, pull the injector rail off, and hold it over said jam-jars, and figure out to lie to the ECU and tell it to squirt fuel in, and compare the amount of fuel going into each cylinder. This will also allow you to have a look at the spray pattern. Again, if two cylinders aren't running, this should allow you to see if it is the signal to two of the injectors"¦ even after that, I would be wondering if the barn door track is telling the ECU lies, and trying to figure out how to check that.

Asiangunner · Dec 3, 2013

ORIGINAL: tref

I would expect a variation in compression figures if it were the head gasket - unusual to get all four down, and I haven't converted it, but it sounds a pretty healthy compression figure to me...

I must admit before pulling the head my next step would be to find 4 identical sized jam-jars, pull the injector rail off, and hold it over said jam-jars, and figure out to lie to the ECU and tell it to squirt fuel in, and compare the amount of fuel going into each cylinder. This will also allow you to have a look at the spray pattern. Again, if two cylinders aren't running, this should allow you to see if it is the signal to two of the injectors"¦ even after that, I would be wondering if the barn door track is telling the ECU lies, and trying to figure out how to check that.

I could get 4 water bottles to check that tomorrow morning. If i fired the ignition with the injectors out the fuel pump would still pump out and fuel will come out of the injector right?

From what my local garage said he said there is the potential the head is cracked, he does weld heads and if i remember correctly mine was welded when i had work done two years ago.
Because of the tax and mot running out i'm a bit stuck, I need to get the car off the road asap.

I've been looking at doing the head gasket as a DIY job and it looks very doable for my skill base and tools. As the HG was done just a couple of years ago and any trouble head bolts etc that needing drilling etc have now been done so i won't be battling decades of corrosion. Issue i could have is that if the head needs to come off for welding/repairing it might be difficult for me to diagnose things like that.

Even if it takes me 2 days it will still be worth my while as i'm off work now till sunday. With a house renovation on the go money is tight...