Cavalier running on 3 cylinders

If you have a spark, then the next possible causes are no fuel or no compression. As the engine has single point injection, then no fuel getting to the intake valve can be discounted - as all other cylinders would be starved of fuel also. If the intake valve is not opening, then no fuel will enter the cylinder, as well as no air, giving no combustion. Conversely, an exhaust valve not opening will prevent burnt gas escaping which in turn pollutes the fresh mixture and prevents combustion.

I would suggest that a compression test is carried out, then a check for the correct operation of the intake and exhaust valves (also checking cam lobes for wear, broken rockers etc).

Can't give an idea of cost, as there are so many possibilities as to what is wrong.

Anthony Remove eight from email to reply.

I think it's extremely unlikely that this is anything other than a spark problem, and I would do some more checks / swaps before attempting anything more drastic and expensive. Can you swap the plug and its lead for another cylinder (i.e. for something you can be 100% sure is working ok)?

You say you're getting power to the plug - is that a strong spark at the gap (when resting plug on earthed engine) or just a feeble spark at end of HT lead?

If the ignition / spark all tests out ok, I guess it's going to be a major or complete loss of compression on that cylinder, which sounds expensive if you don't DIY it. I guess that might be consistent with a dry plug, but my money's on a spark problem - especially as you say it runs ok at high revs.

Have you had it ticking over in the dark, to see if a spark is "escaping" elsewhere?

You've probably just answered your own question.

Depending on how bad the pitting is, you might get away with giving them a clean up with some emery cloth - this is not something people recommend, as it scratches the surfaces concerned, but it should prove whether or not these are at fault, and you then know to whether to waste some money on new ones or not - if it turns out to be something else, sounds like they need replacing anyway if you're going to continue using the car reliably.

Also, these tend to suffer with the plug leads failing, especially if it has the metal caps, plug end.

Try swapping a couple of these over, and see if you still get the misfire on the same cylinder.

HTH

You may have a point.... I was a bit wary of testing for spark strength as I've heard it can cause problems(ECU?) ... so I just pulled off HT lead cap by with insulated pliers... I could hear, rather than see, the crack of a spark discharging against something ... so assumed it was producing enough power... I also didn't check the real spark @ the sparkplug... just replaced plug with a new one and assumed it was sparking...

I've tested sparkplugs on earlier cars (non electronic ignition like VW polo and old minis) - resting plug on earthed engine part ... but wasn't sure it this was safe (to me and the car) to do with this system... what do you think?

I was also though that the plug ought to have been wet when I did remove it, if it was just not sparking...?

AJ

You've got to be careful with modern high power systems. I learnt the hard way when I pulled a lead off with my bare hands. A trick we used to do with the older systems which was fun was to pull off a plug lead with the engine running, it would then go on to 3 cyls, then, holding the end of the lead in the hand, you could point a finger at the plug, the spark would jump out of your finger and the cylinder would cut back in again! Great fun in the dark. I once made a bird scream and cower when I did that to her moggy :-))

That will happpen if it's not starting and the engine is cold, but with a hot engine, by the time you've stopped the engine and removed the plug, it's evaporated away. The plug might be suspiciously clean though......

All in all, with the cylinder cutting in at higher revs, my money is on a burnt out valve. As someone else posted, a compression test is the next step.

HTH

Steve

Ditto

.. but

I can't answer this one - sorry. Cars I've had are mostly too old to worry about this new fangled thing called "electronics" :-(

So play safe - and certainly keep hands and arms clear of HT etc.

Sounds like you're getting two messages here - (1) first check ignition / spark more thoroughly if possible; (2) get a compression check before dismantling head etc. A small "village" type garage should be able to do this in minutes, and therefore may not charge very much.

One other thought - have you got a mate with the same car, and could try his dis.cap and leads? Cost about £2.05 for a pint !!

Please let us know what you find...

Ok thanks for the advice ... I've booked it in to the local garage for end of next week ... In the meantime I'll check out the spark side a bit more.... in the hope that I can save a big bill (which the alternatives sound like)

thanks again to all AJ

Suggest you also check that there is no vac leak on the inlet manifold

Graham

or remove the plug from the suspect cylinder run it for a moment or two and pass a lighted spill across the plug hole (for gods sake wear thick gloves and dont look down the hole do it from the side) that will tell you if theres fuel getting through and increase your heart rate if there is Derek

Check for a vacuum leak, particularly if the vacuum pipe for the brakes is there, they can split. If it has individual injectors (can't remember) then check that one is plugged in.

mrcheerful

I agree with those that say its more likely to be ignition than anything else, having had similar problems.with an identical car (or at least a 1995 model)

Does it mainly happen in damp weather? - or even, has it just started happening now the hot dry weather is leaving us? Is it alleviated by spraying with wd40?

Try spraying the plug end of the lead and see if it works.

if it does not try spraying the dizzy cap - I found this sometimes indicated which bit to replace next!

Or simply just replace stuff working backwards - plug, lead then dizzy cap. If you are in a hurry then replace all 3 - but that way you won't know what the cause was.

If the dizzy cap/rotor do look gobby, replace them first and see what happens.

Pour a few (3 or 4) teaspoons of engine oil into the cylinder, this will temporarly increase compression (by making a better seal between the piston rings), if you hear the engine run ok and see smoke out the back (blueish) this is burnet oil so the cylinder if firing.

What is the car like when starting from hot after about 20 mins? I had a Mk2 fiesta that had done 180k on a 950cc engine and has bad problems starting hot due to low compression. Cold starting was great.

Peter

Well the verdict is in .... Everyone gave good advice...

Results from local garage ...

- The plugs were sparking fine (even with a grotty dist cap).... (actually I did work that out myself ... in the end I clamped the spark plug to the engine block and attached the ht leads one at a time to see that they all sparked equally well)

- The compression in all cylinders was fine (175+ psi in each ... presume this is good for an engine of this age?)...

- but poster "graham" wins the top banana... the inlet manifold gasket had blown ...

apparently too much air was getting in to fire the cylinder ... but it was probably firing at higher revs...

anyway better result than I feared... =A395 :-) later (only =A35 for gasket :-( ) ... all seems well ... the cavalier lives on for a while longer.

thanks to everyone for their good advice AJ

Well the verdict is in .... Everyone gave good advice...

Results from local garage ...

- The plugs were sparking fine (even with a grotty dist cap).... (actually I did work that out myself ... in the end I clamped the spark plug to the engine block and attached the ht leads one at a time to see that they all sparked equally well)

- The compression in all cylinders was fine (175+ psi in each ... presume this is good for an engine of this age?)...

- but poster "graham" wins the top banana... the inlet manifold gasket had blown ...

apparently too much air was getting in to fire the cylinder ... but it was probably firing at higher revs...

anyway better result than I feared... £95 :-) later (only £5 for gasket :-( ) ... all seems well ... the cavalier lives on for a while longer.

thanks to everyone for their good advice AJ

Thanks for updating us - and I endorse your congrats to graham...

Thanks for the feedback and the mention. :-))

Actually your original post was good and gave the necessary facts to aid diagnostic. 3 cylinders at idle, not bad at cruise and dry plug.

If it had been spark or lack of fuel (injector problem) then it would still have been off on a cylinder at higher revs. If low compression your plug would have been wet.

The false air at idle was enough to create a very weak mixture on that cylinder, burn but no power released. The same amount of false air at higher revs was then much lower % wise, so its bad effect on the burn was much less.

Graham