LocostBuilders - powered by XMB

Running on 3 Cylinders

lordbenny - 21/4/13 at 09:03 AM

I have brand new leads and I've check the plugs....(they're about 250 mles old) I'm getting a spark but car (zetec 2.0) will only run on 3 cylinders until I get to over 4500rpm then it seems to jumps into life. as soon as I back of the car goes back to three. Could it be the coil and is there an easy way to check it?

loggyboy - 21/4/13 at 09:13 AM

What management?

lordbenny - 21/4/13 at 09:17 AM

MBE

loggyboy - 21/4/13 at 09:27 AM

Does it use an ignition module of some sort? I had similar symptons on a silver top but running standard management. The ign module was at fault but was part of the ECU in that situation.

lordbenny - 21/4/13 at 09:35 AM

By 'ignition module' I presume you mean a little black box...If so then yes it does

britishtrident - 21/4/13 at 09:48 AM

I would start by doing a compression test.

ian locostzx9rc2 - 21/4/13 at 12:54 PM

Swop no 2 and 3 lead on the top of the coil pack and see if it changes which one is losing its spark if it changes its the coil pack... then do the same for 1 and 4 and see if it changes...thats if its a spark issue if its not it could be an injector issue or sticking or very slightly burnt out valve compression test may show it up....

[Edited on 21/4/13 by ian locostzx9rc2]

lordbenny - 21/4/13 at 01:57 PM

Just checked the jets, they seem ok. As I said it picks up after 3/4000 rpm!

lordbenny - 21/4/13 at 03:35 PM

Swapped leads 1 & 4 and its the same!

[Edited on 21/4/13 by lordbenny]

lordbenny - 21/4/13 at 05:11 PM

The plug is sparking but is black and sooty, not oily and wet.

perksy - 21/4/13 at 06:08 PM

If its using MBE, Which model of MBE unit is it using ?

This engine is using Carb's i take it ?

ian locostzx9rc2 - 21/4/13 at 06:21 PM

Are all the plugs sparking if so its not ign issue ,need more info carbs or injection.pics of engine may help?

lordbenny - 21/4/13 at 07:37 PM

quote:
Originally posted by ian locostzx9rc2
Are all the plugs sparking if so its not ign issue ,need more info carbs or injection.pics of engine may help?

2.0 Zetec, 45mm Dellortos. Was running fine when I wen t out this morning although I've had a slight misfire around 2500rpm for a while now (I live with it!) , I kept it under 3000rpm until the car was warm, one warmed up it started to misfire!

I got it recently rolling roaded and changed the HT leads last week. The plugs are under 500 miles old and I have no reason to think the coil pack is faulty especially as I did the lead swap test that was recommended earlier.

ian locostzx9rc2 - 21/4/13 at 07:47 PM

which cylinder is misfiring?

lordbenny - 21/4/13 at 08:01 PM

quote:
Originally posted by ian locostzx9rc2
which cylinder is misfiring?

lordbenny - 26/4/13 at 04:27 PM

Fitted brand new Motorcraft coil today.....problem UN-resolved!

Cant see its a compression problem if it behaves over 3000rpm.

Took it for a spin round the block, same issue....up till 3000rpm the car is running on 3 cylinders above that its ok. When on 3 cylinders its banging and popping from the exhaust and carbs.

britishtrident - 26/4/13 at 04:48 PM

A misfire one that smooths out at higher RPM with DCOE carbs is either going to be a blocked or loose idle jet or a valve sealing problem.

britishtrident - 26/4/13 at 05:07 PM

quote:
Originally posted by ian locostzx9rc2
Are all the plugs sparking if so its not ign issue ,need more info carbs or injection.pics of engine may help?

Sort of but not the whole story, testing for a spark isn't really going to show that if the plug is sparking in the cylinder when under load. At the end of the compression stroke the required plug voltage to make the spark jump increases greatly so any breakdown in the insulation of the coil pack or plug insulator will show up.
A typical coil pack misfire will often show at high throttle opening from around 2,000 rpm.

MikeRJ - 26/4/13 at 07:00 PM

quote:
Originally posted by lordbenny
Cant see its a compression problem if it behaves over 3000rpm.

Low compression caused by e.g. leaking valves gets better the faster the engine runs as there is less time for any compression to leak away. This is why old worn 2 stroke engines can be a sod to start, but run ok once you get them going.

My Fiat Coupe had a melted piston, and would only idle on 4 cylinders, but above about 2500RPM the 5th cylinder would start working.

However, I suspect your problem is more likely to be carb related.

[Edited on 26/4/13 by MikeRJ]

lordbenny - 26/4/13 at 07:37 PM

quote:
Originally posted by MikeRJ

However, I suspect your problem is more likely to be carb related.

I bloody well hope so!

At the moment I've stripped the wire from the ECU to the coil, bought a new connector and am about (when I get it!) re-wire and solder everything!

MikeRJ - 26/4/13 at 10:14 PM

One trick of the trade (from the old days) is to partially choke the carb barrel of the cylinder that isn't running, using e.g. a bit of alloy plate (or your hand if feeling brave). This will richen the mixture, so if the problem is a lean misfire it should start running on four again.

Briefly fully choking the barrel as you open the throttle (don't use your hand for this!) can help to pull out any crap from the idle jets.

[Edited on 26/4/13 by MikeRJ]

britishtrident - 26/4/13 at 11:08 PM

The normal change over point from idle jet to main jet for an engine of this size on twin DCOE's is roughly 2800 to 3000 rpm, hence idle jet is a prime suspect

lordbenny - 28/4/13 at 01:41 PM

quote:
Originally posted by MikeRJ
One trick of the trade (from the old days) is to partially choke the carb barrel of the cylinder that isn't running, using e.g. a bit of alloy plate (or your hand if feeling brave). This will richen the mixture, so if the problem is a lean misfire it should start running on four again.

Working on the car as I write this and tried your hand over the carb barrel technique. The car started running fine on #4 cylinder almost straight away!

So at least we've diagnosed the problem! will keep you updated.....thanks guys.

rusty nuts - 28/4/13 at 02:15 PM

quote:
Originally posted by lordbenny

quote:
Originally posted by MikeRJ
One trick of the trade (from the old days) is to partially choke the carb barrel of the cylinder that isn't running, using e.g. a bit of alloy plate (or your hand if feeling brave). This will richen the mixture, so if the problem is a lean misfire it should start running on four again.

Working on the car as I write this and tried your hand over the carb barrel technique. The car started running fine on #4 cylinder almost straight away!

So at least we've diagnosed the problem! will keep you updated.....thanks guys.

Very good chance that restricting the carb inlet has caused the vacuum on that choke sucking out the blockage in the idle valve, have used that method countless times for cars that will not idle which when you think about it is what your car was suffering from albeit on one cylinder.

lordbenny - 28/4/13 at 03:54 PM

Taken carb off, opened it up after draining the fuel and found loads of little brown lumps of crap inside! So, now going to strip both of them and give them a damned good clean. This had better fix my problem

lordbenny - 5/5/13 at 08:50 AM

So.....the moment of truth....Did my electrical problem turn out to be a blocked idle jet????

YES!

Car is now running sweeter than ever. Its got a new coil pack, leads and a re-wired coil and coil connector too, as well as having shiny carbs to boot!

My carb guru has visited and balanced them up beautifully and Im now a very happy bunny.

Thanks for all your help guys and putting up with my mechanical ignorance...most appreciated.

matt_gsxr - 5/5/13 at 11:50 AM

Can't remember who suggested it first but there is an old adage "90% of ignition problems are fueling problems"

cliftyhanger - 5/5/13 at 03:08 PM

And * hope a fresh fuel filter has been fitted