Misfire When Warm

[JeremyS]

2002 3.0L Ranger Edge, 145k miles.

The problem is once the truck is warmed up there is a misfire at idle and eventually it will throw a code and the CEL will flash. The code is P0305, Cylinder 5 Misfire Detected. I checked the plug and swapped with an adjacent cylinder, as well as the plug wire and the problem stayed with cyl 5. Also swapped the wire for cyl 1 with cyl 5 on the coil pack and the misfire stayed at cyl 5, ruling out a spark issue.

My next suspicion would be an injector, but the fuel rail and injector for that side of the motor are buried under the air plenum. Is there any good way to check the fuel injector for #5 without taking the air plenum off? I also noticed a leaking valve cover on that side of the engine so if I end up tearing it apart I'm going to change that while I am in there.

Any other things to check for this misfire on cyl 5?

 

[RonD]

Any pinging/knocking on acceleration?
Indicates Lean

Does misfire go away at WOT(wide open throttle)
WOT is the same as when engine is cold, Rich fuel mix and no O2 sensors used

 

[JeremyS]

I don't notice the misfire when giving it gas. No pinging/knocking either.

 

[Bird76Mojo]

Sounds like a head gasket issue to me. Does it use any coolant, slowly over time?



Time will tell..




GB

 

[JeremyS]

Sounds like a head gasket issue to me. Does it use any coolant, slowly over time?



Time will tell..

GB

It doesn't use any coolant. I suppose my next step will be a compression check this weekend, and then going after the injector if the compression looks good.

 

[RonD]

Cold engine, all 6 spark plugs removed, hold gas pedal down to the floor when cranking engine(this also shut off fuel injectors, FYI)

3.0l Vulcan engine ran 9.3:1 compression ratio
So expected PSI in each cylinder would be 160-165

But this depends on cranking speed(battery) and compression gauge itself

Compression test is more about the comparison of all 6 cylinders than the PSI in each cylinder

 

[JeremyS]

Cold engine, all 6 spark plugs removed, hold gas pedal down to the floor when cranking engine(this also shut off fuel injectors, FYI)

3.0l Vulcan engine ran 9.3:1 compression ratio
So expected PSI in each cylinder would be 160-165

But this depends on cranking speed(battery) and compression gauge itself

Compression test is more about the comparison of all 6 cylinders than the PSI in each cylinder

Thanks for the info. I'm going to check compression this weekend and then go from there.

 

[JeremyS]

Did a compression test this evening.

1:150
2:150
3:140
4:135
5:80
6:150


Looks like I may have a bad valve or valve seat on #5.

 

[RonD]

Yes, you could do a WET test and see how much #5 comes up, if just a little then that would confirm valve issue, if it comes to 140 area then rings are the issue

 

[JeremyS]

Yes, you could do a WET test and see how much #5 comes up, if just a little then that would confirm valve issue, if it comes to 140 area then rings are the issue

I was planning on doing a wet test on #4 and 5 this week.

Since it is looking like I'll probably need a new head I had a couple of questions. Can anyone recommend a good place to buy a reman head?

The last time I did a head replacement was on a 4 cyl Toyota (many years ago). This will be my first V6 Ford but I do have a Haynes manual for a guide.

 

[JeremyS]

Did a wet compression test this afternoon. The good cylinders came up to around 200-210. #5 was still much lower at 125, so definitely a valve problem.

Been shopping around for a pair of heads and will be tearing into it after the holidays.

 

[Fordblue213]

Look at your plugs really close. Mine was cracking the porcelain on the plugs on the cylinders where the head gasket was letting coolant in.

When you shut the truck off fully warmed up, the coolant system still has pressure in it. The coolant weeps into the cylinder, hits the still very hot plug and cracks the insulator. Then you get a misfire from the spark jumping to the wrong part of the plug.

 

[JeremyS]

I wanted to post an update to my thread.

This video on youtube was super helpful to use as a reference on this project.

I ended up ordering two re-manufactured heads from The Cylinder head Shop on eBay. I picked up the head bolts and Fel-Pro head gasket kit from Rock Auto and also bought a new Motorcraft cam syncho and sensor since I was going to have the engine torn down anyways.

There were no big surprises tearing everything apart. Both valve cover gaskets and the lower intake manifold gaskets had been seeping oil. I also discovered that one exhaust stud was completely gone and another had broken off, so the exhaust had been leaking between the manifold and the head. I ended up breaking two more studs on the exhaust trying to take it apart so I decided at that point to use all brand new exhaust hardware. I picked up the bolts at Napa and found the studs and nuts at a local hardware store that had a vast selection of automotive hardware (Napa's selection sucked!).

I was surprised on how clean the inside of the valve covers and the tops of the heads/rocker arms were. I have owned this truck since it had 30k miles and always change the oil every 3k miles. The interior of the motor definitely shows it!

The old camshaft syncho had just just a slight amount of play compared to the new one. The gear showed no wear at all. I at least have the peace of mind that I no longer have a ticking time bomb there.

The post re-built compression test (truck had not been started yet) showed 135-140 across all cylinders. A vacuum test shows the vacuum back in the normal range and stable (before the vacuum would bounce around). I did a leakdown test on the old heads using brake parts cleaner and the exhaust valves for cylinders 4 and 5 both leaked but all of the others looked ok.

Initial test drives show a very noticeable increase in power on acceleration. The idle is also MUCH smoother. Before the new heads when I would come to a stop at an intersection the motor would hiccup, it no longer does that.

Thanks for all of the help!

 

[Fordblue213]

Glad to hear it went back together well and running normally. After mine having issues for so long, I am still amazed how nice it runs with the new heads and gaskets.

 

[JeremyS]

Glad to hear it went back together well and running normally. After mine having issues for so long, I am still amazed how nice it runs with the new heads and gaskets.

Thank you for sharing the great information in your rebuild thread!

The misfire and loss of power wasn't a sudden thing but is slowly crept up. Small things like slight inclines on the interstate would just bog my truck down. Now it doesn't even phase it.