Misfire On One Cylinder

[stimpysaurus 0]

hi everyone,

I'm having some trouble with my saxo, I've done a few checks and internet research and I think the problem is only on one cylinder not firing. 3 of the plugs look normal but one is sooty, I also noticed that one of the leads and the end of the plug is a little brown (not sure if that's normal?)

I've fitted all new plugs and the problem is still there. The leads have also been checked with the multimeter and the needle moves to 0 on every lead, though it does take a bit of wiggling to get it there.

 

what would be the next thing to check?

My dad said I could get a compression test at the local garage but it would be cheaper to get a new set of leads and try that first. Does this sound like a good idea or does it sound like something other than the leads to you guys?

 

thanks

Lianne

[DamirGTI 342]

Could be few things try mixing up the leads a bit i.e. unplug the 1-st one and connect it on the cylinder No.2 , and so on .. in order to check if the problem will move onto another cylinder which will pin point affected lead , also , wait until it's dark outside pop up the bonnet switch the lights OFF start the engine and take a good look at and around the engine in case you can spot current leaking/arcing which will manifest as a bright blue spark jumping from the lead or the coil (or both) onto the engine metal parts , usually coped with clicking sound as well ..

 

Worth checking the injectors too , can do the same as with the leads , mark them and mix them up and you'll see if the problem "moves" .. providing that the connectors are sound in the first place ..

 

And the compression test will be must yes , in case of the blown HG or burnt valves/seats etc.

 

Damir

[DrSarty 90 1 Cars]

As Damir says, it's either a process of elimination or straight in for a compression test.

 

Good comp test results will mean the engine itself is likely to be physically fine.

 

But of course for that test you need a comp tester, whereas your fault could be purely a buggered plug, injector or HT lead.

 

Swapping over one pair of HT leads, and seeing what happens when you remove one of those will help chase down either a lead or a particular cylinder being the problem.

 

You just need to go down the list ruling things out.

[stimpysaurus 0]

Swapping over one pair of HT leads, and seeing what happens when you remove one of those will help chase down either a lead or a particular cylinder being the problem.

sorry I'm pretty bad at visualising what you mean and understanding the process of elimination too . Do I take the lead off one plug and stick it onto another? or take the whole lead off both ends and put it in a different place?

 

sorry, I feel really stupid for not understanding

[DamirGTI 342]

Just the plug end of the lead , they should be long enough allowing to re-connect them inbetween the two adjacent cylinders ..

So -> unplug the lead on the cylinder No.1 and connect it on the cylinder No.2 , and connect the lead which was on the cylinder No.2 on the cylinder No.1 .. do the same with the cylinders No.3 and No.4 (but each pair at a time ! not all in one go).. as well as injectors , mark them first , then remove them out and mix them up in between cylinders ..

 

Damir

Edited January 17, 2010 by DamirGTI

[stimpysaurus 0]

Just the plug end of the lead , they should be long enough allowing to re-connect them inbetween the two adjacent cylinders ..

So -> unplug the lead on the cylinder No.1 and connect it on the cylinder No.2 , and connect the lead which was on the cylinder No.2 on the cylinder No.1 .. do the same with the cylinders No.3 and No.4 (but each pair at a time ! not all in one go).. as well as injectors , mark them first , then remove them out and mix them up in between cylinders ..

 

Damir

thanks for that

one more thing, is the swapping done when the engine is off or do I swap them all about with the engine idling? I don't wanna get myself electrocuted!

[stevem099 0]

id turn engine off, right off n take the key out , i disconnect neg on battery as well but im a whimp.

get a shock off ht lead youll know about it

[lagonda 42]

Definitely with engine switched off.

 

Not sure I understand Damir's description...I think he means, or should mean, that you unplug BOTH ends of 2 adjacent plug leads, & literally swap them over. So for example, unplug leads 1 & 2. Plug the lead that was no. 1 onto no2 plug, & the other end into no2 socket on the distributor cap. The no2 lead you then connect to no1 plug & distributor socket. Just swapping one end over will just give you incorrect ignition timing...probably wouldn't start, certainly would run badly....unless of course, the leads have been incorrectly fitted in the first place!

 

Compression testers aren't expensive & are pretty easy to use...worth buying one rather than paying garage to use theirs.

[lagonda 42]

Just to add, yes, shock from the HT side of ignition would certainly be something you'd notice, especially with the higher power systems used today.

 

Many years ago I was working on my V12 (1939) & I'd read a pre-war car maintenance guide that stated to check the ignition to one cylinder, just grasp a plug terminal (exposed on many pre-war cars). So I thought I'd give it a try...should have taken note of the fact the coils had been replaced by Lucas sports coils from the '60s. Next thing I know, I'm flying through the air, & hit the garage wall with some force! Some things you just don't try a second time. Mind you, when I was a kid, I did connect all 3 rails of the Southern Electric together with a bit of wire....still don't know how I got away with that one....probably lucky that a train was actually taking the current right then!

[DrSarty 90 1 Cars]

OK, I'll explain the process of elimination bit.

 

It's likely that one thing is causing your problem; you need to find that one thing. But it could be one of several things as stated earlier, such as a dodgy HT lead, a bad injector or spark plug to name a couple.

 

You can do a process of really simple steps to find out what IS at fault, by finding out what ISN'T, i.e. ruling possibilities out one by one, i.e. eliminating them.

 

So here's what I would do:

First: you need to find out which cylinder is misfiring, which means it's not providing a (decent) power stroke.

 

I would do this by starting at cylinder 1 (gearbox end), and disconnecting a fuel injector. If the revs drop even further, and it runs even lumpier and nearly or actually stalls, then you know that cylinder was doing what it should. It means nothing in that cylinder's system is incorrectly working. You know it's providing a decent power stroke which means the comp's OK, the HT lead works, the spark plug works and so does the injector.

 

Then just move along 2, 3 to 4. If the misfire is as you say, so it's running on 3, one test on one cylinder as above will make no change at all. Disconnecting the injector won't change a thing. So now by a process of elimination we now know which cylinder to concentrate on; we have removed 75% of where we have to look.

 

BTW: At this stage if all of the above tests yield no change in tickover, then something else is wrong in a general fashion higher up the chain, e.g. main fuelling or ignition/management.

 

So now you can concentrate on one cylinder, and find out if the misfire is fuel or ignition related. Also remember that the problem may be compression related, in which fuel or spark will make no difference, e.g. when the head gasket has failed.

 

So to check for a simple HT fault for example, if you simply swap HT lead 1 COMPLETELY over for HT lead 2, and the problem is still on that same cylinder, you'll know it wasn't the HT lead on that cylinder that was causing the misfire. Again, you've eliminated a possibility.

 

If the misfire has shifted to the cylinder where the first lead was swapped to, then you know it was that HT lead.

 

I'm not going to explain any more, but you have to think of it very simply and logicially. Your car's engine needs a sealed combustion chamber to be filled with the right amount of fuel and air mix, which then gets the right amount of spark at the right time. It's nothing more complicated than that. If any one of those elements is missing or an incorrect value, it won't work correctly. It's like a fire triangle, remove one of the 3 parts and the fire goes out.

 

I hope that helps and enables you to track down your problem, or at least eliminate what it isn't.

 

Edited January 18, 2010 by DrSarty

[DamirGTI 342]

unplug BOTH ends of 2 adjacent plug leads, & literally swap them over.

 

Righto ! was thinking right but misswrite this wrong .. confused myself , sorry boys ..

 

Damir