misfire

[rustys_rocco]

having some troubles with my gt2. have changed the coil, leads, dizzy cap, rotor arm and plugs but still have a constant misfire on cylinder 4. any advice on what else it could be really starting to wind me up now. checked the compression and its reading 200psi seems high but musnt be a problem with compression....

[james butler]

had similer prob on cyl 1 turned out to be headgasket.

[rustys_rocco]

compression test would suggest the head gasket is fine though?

[bensspares]

my 2 penny's worth is a sticking inlet valve (shut).it has to be mecanical.

[bensspares]

is it regular or speradic ???

[rustys_rocco]

regular when i pull the lead off no.4 no change to the engine note. still revs up and ticks over fine but with a massive misfire lol.

[bensspares]

without being a doom merchant, your going to have to remove the head and look at the valves on that cylinder,maybe its a good time to recon the head/valvestem seals and the headgasket will be changed in the process.the compression is about right for the cylinder so if its not ignition then it has to be the valve sticking,sorry for the bad news diagnosis but unless anyone else has alternative suggestions my prognosis has to be true.

the other alternative is to remove the cam and phsicaly press on the valves for no4 to check for the correct opperation.

ben

[rustys_rocco]

surely there could be other causes. the problems started with an electrical fault and i've had a few carb problems (not sure how this would cause problems with 1 cylinder). plugs are getting wet which suggests fuel is getting into the cylinder.

[bensspares]

are you sure the plug is sparking ??????????????.if it was a carb fault it would effect all cylinders ???????? not just 1..... you have to bear in mind that the car isnt infront of me lol

[rustys_rocco]

yep deffo got a spark as i succesfully electrocuted myself earlier on. lol. could the tcih (i think thats what it is under the scuttle tray) cause this or the hall sender?

[bensspares]

have you checked the symptoms with mr haynes ???????????....i have never heard of the thc unit packing up or causing problems,i have 1 if you want to buy it lol.

if you have a spark lol and feul then mr haynes says its valve or head gasket issues..............which i confess i agree with.

[rustys_rocco]

yeah had a flich through the haynes but its a bit awkward when nothing states about missing on just one cylinder just general misfires.

though i'd add that the problem started when a ht lead came loose and the rotor arm fried (possibly due to the ht coming loose?) corrosion had got into the lead and contact ontop of the dizzy (if that makes sense). did have it running briefly on 4 cylinders (30 secs or so before it cut out) a few weeks ago before i realised the rotor arm had fried?

[bensspares]

now you tell me lol............its possible that some how someting has done some damage to the thc or the hall sender in the dizzy but again just 1 cylinder being effected is a head scratcher......if you give me the part number on the thc then i can let you know if i have 1 for a carb engine (i have many).

[rustys_rocco]

nice one i'll have a butchers at some point and get back to you.

[GT Matt]

Before you start ripping your engine to bits

I've seen this exact problem a couple of times now and both were caused by split/missing vacuum pipe on the one-way valve on the pipe between the inlet manifold and brake servo.

As the inlet manifold is open to atmosphere, it affects the mixture but mainly just to cylinder 4 and causes a light misfire. Both cars I had seen were weber carb'd where the rubber blanking plug that comes in the kit had failed or was missing but any split/missing vac pipe will obviously have the same effect.

Hope this helps