evodave

My '93 WRX is running on 3 cylinders and we cant seem to find the problem. We fitted a set of new plugs but it is still doing it.

We then fitted the plug lead / coil pack from a 94 WRX (which runs fine) but this made no difference, still on 3 cylinders. When we fitted the lead / coil pack from 93 WRX to 94 WRX it also ran on three cylinders, therefore we thought the lead / coil pack was dodgy, this turned out to be true as it was cracked and a piece actually broke off it.

We tried fitting the 94 lead / coil pack on the 93 car with the plug fitted and earthed to find that the plug sparked fine but once fitted back into the engine it STILL ran on 3 cylinders !!!

What I did notice was that when we removed the plug after trying this I expected to find a wet or at least damp plug but it seems to be dry.

Can anyone come up with anything else to try and solve this problem ?

We have a complete 94 WRX to use to swap parts with to try and get the 93 one to run properly. I also done a compression check on it when cold and all cylinders are around 150psi cold.

Any help greatly appreciated !!!

David_Wallis

stuck injector..

ive got loads of spare injectors if you need one.

David

evodave

Is this quite common ?

It must be bad luck if both the injector & lead / coil goes at the same time on the same cylinder then !!! You dont happen to have a spare coil pack / lead as well do you ?

Cheers !
David

David_Wallis

I dont have a coil pack, sorry.

coincidence I guess about the same cylinder.

David

David_Wallis

did you get the injector (well injectors, I sent two)

jonny gav

iTrader: (1)

if its not that it could be the signal from the ecu to the injector is not getting through, had this problem on a fiesta the other day.

evodave

Yes, got them today, much, much, much appreciated !!!

I will let you know how I get on !!

Thanks again !
David

David_Wallis

No probs,

As jonny says could also be an injector driver or cable, if you want info on how to test then let me know.

David

Jolly Green Monster

iTrader: (4)

The coil pack was probably fine on the car and the bit broke off when you removed it?!

Hope the injector switch solved it.

They are a bitch to get out.. mole grips!

evodave

Still no joy Im afraid !

I tried it with a new injector in and plenty fuel now. Also had plug out, fitted to lead and earthed to body and it sparked fine. Once it was fitted to the engine it still ran on 3 cylinders.

Any ideas ?

I had a similar problem a few years back with a Cosworth and it turned out to be that when I had used jump leads to start the car it caused a surge of power and damaged the ECU. Could this be a similar problem ?

Thanks for all the info from everyone so far, hopefully will get it sorted soon !!!

Cheers !
David

P20SPD

iTrader: (1)

compression test just to be sure

David_Wallis

read the thread u *****

he has..

So is the plug wet now?

Your getting a spark on this cylinder?

No disrespect (assuming the above is correct.. ) have you got the right cylinder..

David

evodave

The plug is wet, the plug sparks but when fitted it doesnt run on this cylinder. All other plugs are getting dirty but the one I am talking about is aleays clean and now wet.

Driving me nuts now !!!

Eprom

The only other suggestion I can see, from what you have tried already, is the possibility of the new plug breaking down under compression, it may provide a spark when earthed to the engine, but may track over when under compression.
Proved by swapping over.

Hope you get it sorted

crusher

Could be doggy plug lead or plug as suggested by eprom...have seen this before where insulation is breaking down...Can you see any tracking marks on the plug exterior?...Try a different lead/plug and see what happens...

evodave

Plug lead is temporarily borrowed from another car where it works fine, also tried in different plugs too just in case it was a dodgy plug.

What do you mean by "but may track over when under compression.
Proved by swapping over."

Cheers everyone !
David

crusher

I'll answer this in Eproms abcense..The plugs insulating properties may not be up working adequately when in place with the engine working. The effect of the engines compression means that the insulation needs to be better if you like...so that the plug may work ok out of the engine...no compression,but will fail in the engine..compression more insulation needed...The eht current from the coil /ht lead will always try to find the easiest path,so if theres any fault in the plug or leads insulation,the "spark"..may happen there..instead of at the electrodes at the tip of the plug...
If this happens the you obviously get no fuel ignition in that cylinder...
If the plug lead (say) is faulty, the spark may try to find a way to earth...the engine block..via a different path,if thats on the outside of the plug because of faulty manufacture( have seen this with new plugs..the white insulator section was slightly flawed)..then the spark occurs there and after some little time leaves a tell tale black mark..caused by the arcing of the spark...Have you looked for this?....
You can also sometimes see arcing when looking at the engine in the dark...but thats not so easy on a Scooby at the spark plug end!
I'd try to eliminate things. Use leads and plugs that you know are ok...they work in another car,or in your own cars other cylinders...
If it's not the eht system,and cylinder compressions are ok,then it points to the fuel..ie injector control as mentioned by Jonny and David...
When you checked compression,did the cylinder match the other 3 in terms of it's initial first pulse reading...?
Hope this makes some sense....

Eprom

Thanks crusher could'nt have put it better myself, Dave_Wallis has made a point not to over look, man made faults are the worst to trace,
ie no disrespect is it the correct cylinder, or is it firing on the compression stroke.

crusher

Have you solved the problem yet Evodave?

evodave

The problem is not totally solved yet but getting closer.

The plug that goes onto the injector usually has two wires coming out of the loom and going into it. On closer inspection of my car there is only one wire going into the loom and the other one has been Scotch locked to a single black wire which I managed to trace back to the ECU (it is the wire at the top of the ECU closest to you when looking in the footwell if that helps !). I cannot trace where the original wire should be at the injector end but back at the ECU end there is the original wire (brown w/ silver spots) coming out of the ECU which has been cut and this single black wire added by use of a Scotchlock. The other part of the original wire (brown / silver) disappears into the loom going from the footwell over the gearbox tunnel.

I have removed the Scotchlocks (or maybe we should call them Japlocks !) and I am planning to properly solder the wires together to ensure a good connection followed by using heatshrink to finish it off. Hopefully (fingers crossed) that it has just been a bad connection with the Scochlocks that has been causing it to run on 3 cylinders.

Has anyone anyideas as to why the wire would have been replaced all the way back to the ECU ?

Also, any other suggestions as to what to do ?

Cheers !
David

Jolly Green Monster

iTrader: (4)

Perhaps there was damage to the wire in the loom somewhere and this temp fix became permenant?

Do any add on gadgets need injector pulse inputs? could have been wired to something which was removed and just scotchlocked in?

JGM

crusher

Before you solder it can you check continuity from the ecu to the injector with a meter?...If your right and this wire is the problem you should get an open circuit...

evodave

Thats what I'll do, a continuity check on this replacement wire prior to soldering it then if that is ok then the circuit should work ok.

What I did think what was happening was that once up the revs the engine sounded fine but seemed to drop onto 3 cylinders at idle. Would it be possible that with these scotch locks in place causing a bad connection that it would cause the injector to stick open or closed causing it to go off on that cylinder on idle ?

Hopefully I will get a bit more done to it tonight and maybe even get it running !!

crusher

Unless the signal strength is increased as the revs rise to maintain a clean signal I'm guessing that the problem could be intermitent..the worst kind!....so that you might have periods when the car is actually running on 4 cylinders...and then 3..then 4 etc... If the signal strength is increased by the ecu ( I don't know if it is or not)..then it could be a possibility that the signal could jump a small break in a wire...but I think this is unlikely...

In another thread there has been mention of cars running on 3 cylinders due to other problems (say valve burnt out..) where it's not been imediately obvious...so it wouldn't be a complete surprise if you had had this problem for a while before you spotted it...
Hope you've found the problem!!!

David_Wallis

the compression test would have shown valve problems

crusher

Post wasn't meant to mean that he had burnt valve, just that he might have been running on 3 cylinders because of the wire fault and not noticed...especially if it was intermittent...I appreciate that a compression test would show up valve/ring/piston problems....

evodave

Didnt get much done last night.

Managed to solder the wires together at the injector end and get it heat shrinked too, looks a lot tidier already and hopefully should work better too. Planning to do the same at the other end tonight and then check the wire for continuity, hopefulloy this should solve the problem.

Then it just leaves the rest of it to re-assemble and see if it will run on all 4, fingers crossed !!!

Has anyone got or know of a plug lead / coil for sale or where to get ?

Thanks everyone for their input and I'll let you know how it goes !!

CustomScoobyIOM

Could be a number of things mate really.