Running Rough on Cylinder 3.....Help Please

OK.....I would appreciate your views and comments on this problem. I have posted this on the Engines section as well, but there are more veiwing this section...

My car has been running a little 'rough' for a while now on both LPG & Unleaded. I took it to a garage who put it on their test book and said that it was a 'misfire on cylinder 3'. When I questioned him on this , he said that it could be:-

1) Faulty Spark Plug
2) Faulty HT Lead
3) Faulty Coil
4) Faulty Fuel Injector
5) Sticky Valve.

Anyway....I now have a Faultmate Extreme and have started to diagnose this myself.....I replaced the spark plugs last night and run the diagnostics and it states that it is 'running rough on cylinder 3'. The values on the other cylinders are either 0 or 0.1 where as cylinder 3 is between 4 & 7.... What does this mean?

The HT leads were replaced early last year with Magnecore so although it is unlikley to be these ( I will swap the leads around tonight to see if the problem moves) I will check anyway.

The coil packs were replaced at the same time, however is it likely that only 1 cylinder would be affected, and how could I check this....

If it was a Fuel Injector, surely this would not affcet the running on LPG and visa versa, unless both types of fuel injectors are faulty on cylinder 3.....

I have recently been using red-ex in the petrol and had a flash lube kit fitted to the LPG while I had it serviced to help with injectors and valves......



Does anyone have any ideas or comments that would point me in the right direction....?? I have not had a proper play with the faultmate as yet, so is there any functionality on there that may be able to help me further.... :doh:

Warm it up, clear the fault and then start on gas and run her around for a while, then read the codes again. This will tell you if it's fuel related. Next I would do a compression test.

rewmer said:

Warm it up, clear the fault and then start on gas and run her around for a while, then read the codes again. This will tell you if it's fuel related. Next I would do a compression test.

Click to expand...

Thanks....I Reset the fault codes and took it for a run, still running rough on cylinder 3 and also showing mis fires on cylinder 3..... tried both times on LPG and Petrol.

I have now ordered myself a pressure tester, so will follow that advice next.....

If it is the exhaust valve would I need to replace them all ( probably would anyway while the head was off.....)or just the duff one and would I need the head re-skimmed or is this only of the head gasket has blown?

cheers

Chris

Its fair to assume if you have one bad valve, the rest wont be all that good. It would be a false econonmy not to do the rest of the valves.If it was mine I would skim the heads and have all the valves re-seated.The skim may not be totally necessary but for peace of mind..... Just had the head on my shooting discovery done and that was £58 for the skim and all valves re-cut and seated.

Ok, It would be safe to assume that I would get both sides done then, while I am at it?

obviously dependant on the work shop, but ball park, how long does it take to reskim and reseat the valves?

rewmer said:

Warm it up, clear the fault and then start on gas and run her around for a while, then read the codes again. This will tell you if it's fuel related. Next I would do a compression test.

Click to expand...

Ok finally got a working pressure tester and the results are:-

Cylinder 1 - 90 psi
Cylinder 3 - 90
Cylinder 5 - 180
Cylinder 7 - 90

Cylinder 2 - 180
Cylinder 4 - 180
Cylinder 6 - 180
Cylinder 8 - 180
So what do you think the issue is? head gasket or burnt valves?

head gasket at a guess

hoarec said:

Ok finally got a working pressure tester and the results are:-

Cylinder 1 - 90 psi
Cylinder 3 - 90
Cylinder 5 - 180
Cylinder 7 - 90

Cylinder 2 - 180
Cylinder 4 - 180
Cylinder 6 - 180
Cylinder 8 - 180
So what do you think the issue is? head gasket or burnt valves?

Click to expand...

Sorry crystal ball away at cleaners. Get the head off you know it makes sense. Unlikely to be valves unless the heads have fallen off them.

Yep, head off time.

Cheers....

Ok...Finally worked up the courage to do this, (picked the F**ing worst weekend in history to work on the car ( I have no garage).

Very long story short, The cylinder head gasket was complety blown between the first and second cylinder, so the compression stroke on cylinder 1 was pushing the fuel mixture into cylinder 3 on the exhaust stroke, causing a mis fire on cylinder 3......Looking at the gasket it was starting to happen on 5 & 7 as well.....

Anyway, completly changed the head as well while I had it off........well chuffed, started first time, drives like a dream.......( fingers crossed, as I am towing with it this weekend....)

hoarec said:

Ok...Finally worked up the courage to do this, (picked the F**ing worst weekend in history to work on the car ( I have no garage).

Very long story short, The cylinder head gasket was complety blown between the first and second cylinder, so the compression stroke on cylinder 1 was pushing the fuel mixture into cylinder 3 on the exhaust stroke, causing a mis fire on cylinder 3......Looking at the gasket it was starting to happen on 5 & 7 as well.....

Anyway, completly changed the head as well while I had it off........well chuffed, started first time, drives like a dream.......( fingers crossed, as I am towing with it this weekend....)

Click to expand...

Good job; take for a drive to warm up everything to operating temp and then let cool down and re torque your head, and they carry a jug of coolant with you and check coolant level after 100 miles for proper level
and have fun on holiday

I was informed that Stretch bolts do not need re-torque'ing....if so it it a hell of a job to re-do it, I woulkd have to practically strip the engine again.....