Ongoing issue for a week and a half now. Always the same thing, loss of power, cutting in and out, when I pull the codes, it's always cylinder misfire #6 cylinder. I put a brand new spark plug in. I replaced the coil. I pulled the injector, hooked it up to a spare fuel pump with some rubber hose and gave them both the juice, it was spraying just fine. Still got the same code. So I put the #5 cylinder's coil and injector on #6, and still getting the same code. So I ran a compression test. 170psi. I inspected the wiring going to both the coil and injector, no cuts, the pigtails are in good condition, the wires aren't loose inside them, they still have the rubber insulators. So I set a screwdriver across the coil while I cranked it, and it was sparking like crazy, so I have spark for sure. Then I started the truck and listened to the injector with a screwdriver, I could hear it opening and closing just fine. So I have spark, I have fuel, I have compression, and I have air. But STILL it runs rough, and I get the CEL with the cylinder misfire code. Dudes I am completely stumped on this. All I know is I do NOT want to have to take it to Ford. ANY ideas what else I should check? Thanks!

 

Do you have a simple hand held scanner or something with more features?

I've used autotap, but there should be others that can offer: if any injector shorts, miss count, cumulative cylinder miss fire, O2, MAF and EGR. Everything is testing fine out of the vehicle, but when together there is something wrong with that cylinder. Did you check any other cylinders for compression? Was that a leak down or just compression test?

 

No I don't have a scanner for my truck. My friend has a pretty extensive diagnostic system that he runs from his laptop. I think we're gonna try and hook it up to that and run an injector test among other things.

It was just a regular compression test. I know you're supposed to test several cylinders, but when I saw it was 170, I knew the compression was fine.

 

A compression test of one cylinder will only tell you if you have compression on that particular cylinder. All cylinders should be checked and compaired against each other. I haven't done a compression check lately, but 170 sounds a little high. You might have a broken valve spring.

 

150-200 psi is normal for a stock modular.
JL

 

slc10844, thanks, actually I know that compression tests have to be done on several cylinders for comparison, but I also figured 170 was about on par, so I didn't see the need to run more.

 

You mentioned nothing about actually replacing the wire to teh plug in question. A cam position sensor might also cause a misfire code, though I would replace the wires (with Motorcraft) first.

 

Bear, these motors don't have actual plug wires, they use a coil over plug system. I did check the wiring harness running to that cylinder, and it looks in good shape.

 

Ok, learn something new everyday, I thought they still had regular wires. A leak in the intake manifold is known to cause a miss on other Ford models. Is that a possibility?

 

Actually some of the early Tritons did have plug wires..
Your best bet would be to hook your truck up to your friends laptop to see what it says.

 

Bear, I'm sure an intake leak would cause a miss. But I'm stumped cus it's ONLY on number 6. If it were a vacuum leak, intake leak, fuel problem, I would think that it would show up across the board ya know? Not just number 6. I had a 5.0 Mustang for several years that I had to track down a vacuum leak that caused it to run poorly, but it was all cylinders ya know?

Bobby, yea I'm gonna get together with my friend this week and see what the computer tells us. It'll pulse each injector individually while the motor is running to see if one is not working right. So hopefully I'll find something.

 

Being an easier cylinder to get to I might pull the valve cover and see what both valves look like from above. Off the top of my head one of the valves acting up is all I can think of with everything else already covered. What did the old spark plug look like?

 

The old spark plug looked alright. When I pulled this new one the other day, it still looked brand spanking new. It had been in there for 4 or 5 days, long enough to at least turn colors, but it looked like it had just been pulled outta the box.

 

Went to a mechanic buddy that worked at a Ford dealership a while back. He looked it over and said that if it's not drinking coolant (meaning the intake gasket or head gasket), then it's probably a fatigued valve spring. He suggested pulling the schrader valve outta my compression gauge then leaving the gauge in the head while running the motor to see what kind of actual numbers I'm running. At higher rpms the spring might not have enough tension to get the valve all the way closed in time. Makes sense I suppose. Although if you ask me, this seems kind of ridiculous for a truck with only 120k miles on it.

Out of curiosity, what does a valve spring replacement cost at fomoco? I don't have the tools to do it myself (nor the time).

 

I'm still betting against it. I've never,ever seen a modular with a valvepsring problem(other than a broken spring). 120K miles is just a baby-it's got 2-3X that much life still left in it.
You don't wanna even know how much the dealer will charge to R&R valvesprings.
JL