turbotrks

Hey guys, I have a bad misfire that I've been chasing on my WS6 with no luck. I have tried to log misfires with hptuners but nothing ever shows up. So I used an infrared laser thermometer to at least try to find which cylinder is the culprit. Sure enough, I checked the headers a few inches from the head at all 8 exh. ports and they all read over 400 degrees Except for cyl #2 which reads around 270. So here are the things I swapped out, one item at a time, with no change in header temperature: plug, plug wire, coil and injector. I also checked compression which was 120psi(low due to cam) just like the other cylinders.

I am out of ideas!
Does anyone know what I should do next? Thanks

2000PewterT/A

Did you test to see of the coil is getting power and the same with the injector. I would check over the wiring next to see if there is a break in the wire somewhere.

turbotrks

Yeah I forgot to mention that I also tested the spark with an inline spark tester and also checked the injector power with a noid light and both appeared to be spot on. I know it's not misfiring 100% of the time because if I unplug the coil or injector, the temp. of the header drops.

I'll go ahead and check the wiring though.

NHRAFORMULA00

iTrader: (2)

It might be sucking oil past the valve guide.

turbotrks

Hey, you could be right, because when I pulled the plug, I noticed oil on the threads! So does that confirm your suspicion? If so, do I just need to replace the valve stem seals?

Marc 85Z28

iTrader: (8)

If a valve guide was worn to the point that it would allow enough oil into the cylinder to create a misfire, you would have a crop duster along with a few other more serious problems.

You probably cracked a ringland. They don't always show up in static compression tests. And 120psi IS LOW. Pull the valve cover and inspect. If you don't see any valvetrain issues, pull the head.

turbotrks

Ok thanks, I'll pull the valve covers and check it out.

jp98

iTrader: (2)

did you check the fuel rail to make sure it is not plugged, and not getting fuel to the injector.

armyinfantry3id

i would try a leakdown test to try and find out how the oil is getting in the cylinder, good luck

t_raven

iTrader: (12)

I once read an article in a magazine at a shop I worked for about a Mustang the tech had a heck of a time finding a misfire on. In the end for what ever reason he had the heads off and realized one of the cylinders wasn't coming as high up in the bore as the rest. The rod was slightly bend from a previous bad head gasket letting coolant in and whoever did the head gasket job didn't catch it. If I remember right, static compression was with in spec, and everything else was working fine, but that cylinder wasn't making enough power.

Not saying that exact thing could be your problem, but if it ever had a bad head gasket it could be. I would definitely check leak down. It's amazing how much static compression you can get out of a cylinder with 90% leak down.

turbotrks

Tomorrow I'll do the leak down and take a look at the valve train.

I really appreciate all the input from you guys!

garygnu

if you do a leak down test ,look for leaking air .if you have a bad intake valve ,you will hear or feel air coming out the TB.if you have a bad exhaust valve ,you will hear or feel air coming out the exhaust pipe .if you have bad rings ,you will hear or feel air coming out the oil fill cap.

RockinWs6

Check for a cracked valve spring

SOHCNightmare

A friend of mine had a similar issue on his c5z, turned out to be a cracked ring land on cylinder 5

CattleAc

iTrader: (7)

Possible vacuum leak...???

Spray a little carb cleaner around that #2 intake port.

SOHCNightmare

^^ Not a bad idea, better to try this before a tear down.

turbotrks

Yeah I tried that, and didn't find any leaks.

If this rain would quit I'll do the comp. test tonight.

2000PewterT/A

I know your probably checked this already but I have had seemingly good spark plugs cause ghost misfires on me before, shoot I had a plug with less than 300 miles on it with no visible cracks or damage cause a misfire. You probably check the plugs already but I would try switching them around to see if the misfire goes away. It’s worth a shot.

turbotrks

I did go ahead and replace the plugs, but the miss is still the same, so I decided to go ahead and replace all the plug wires too, so they should be here tomorrow (MSD 8.5).


I did the leak down test and could not detect any leaking from the valves of cyl #2, but the there was a little bit of blow-by via the pcv. I tested several other cylinders and the results seemed identical to #2.

Is it common to have some blow-by on a leak down?

RockinWs6

Of course it is, 8-10% is about normal...............If they all seem to be about the same good. Are you sure the valves are opening and closing properly NO CRACKED springs or bend push rods...the valves open all the way.