2000 4.0 OHV - Missfire Cylinder 2

[cal74]

Picked up a 2000 4.0 OHV with approx 150,xxx on the clock.

Rough idle between 1500-2000 rpm, down on power.

Replaced plugs, affected wires, checked another coil pack. Have a fuel injector on order, but just tested two injectors and they're both similar resistance. Around 16.2 I believe. Did it while they were cold, don't know if that makes a difference? Before I install the new one, I'll probably just swap 3 with 2.

No signs of a blown/leaky head gasket. Cannot hear any broken valve springs.

I realize that neither of the last two mentioned things are fully conclusive as I have not down a compression check.

Any other ideas? Picked this up reasonable enough, that if worst case I ended up replacing the heads I'm into it for about market value. Obviously I would rather keep the change in my wallet vs sticking more money in it.


Thanks for your time....


ps: Don't know if it makes a difference, but the kid who I bought it from had removed the cat and has a glass pack on it. So the O2 sensor behind the cat is gone.

 

[RonD]

Warn engine Idle should be down around 650 manual, 750 auto

And the engine doesn't smooth out at higher RPMs?

Clean MAF sensor, also unplug it and then start and drive truck to see if it runs better without MAF

CEL(check engine light) should be on with no downstream O2 sensor connected?
Does CEL come on when key is turned on?

And no other codes than P0302?

What did #2 spark plug look like?
Steam cleaned is a coolant leak into cylinder
Blackish is Rich running, maybe sticking injector

You can unplug the 4 wire coil pack connector, so no spark, and then crank the engine a few times.
Pull out spark plugs to check that all are wet with fuel, i.e. injectors are working

After cold start squeeze upper rad hose, should be soft and easy to squeeze
After engine runs for 1-2 minutes squeeze it again, if it is hard then you do have a coolant leak into a cylinder, i.e. blown head gasket or cracked head.

 

[cal74]

Ron - Thank you once again for the response

Plugs only have probably no more than an hour run time, but regardless #2 is getting a little carboned up. Doesn't look terrible. I do get another error, but can't recall it at this time. It's an 02 sensor error.

Before reading this today, I swapped #2 with #3 injector.

No difference, double checked spark and that's real good.


Did a compression test with a very cheap gauge. Zero compression in #2, other two I checked were around 100 on a cold engine.


I'll pull the valve cover on that side tomorrow for a look. I know that without getting all the way in there I'm not going to know, but what are the odds this is a lower end problem? Kind of hoping it's a broken spring... What else should I be looking for when I pull the valve cover off?

150,xxx on the motor, everything else is in decent shape but I'm not going to stick a grand into it.

 

[RonD]

If you add a bit of oil, teaspoon, to #2 and repeat compression test it will tell you if rings or valves are the problem.
But 0 psi on #2 would indicate valve issue, most likely burnt exhaust valve since that is most common issue on gasoline engines.

Bad rings would show some compression, gap/hole in exhaust valve 0 compression

You can rotate engine manually until #2 valves are both closed, then use a hose of the right size to blow into the spark plug hole, it should hold pressure, but at 0 compression it won't, have someone listens at the intake and then tail pipe for escaping air while you blow, or they do, lol.

This is called a Leak Down test, usually done with air compressor, not lungs

If exhaust valve is the issue you will hear escaping air at tail pipe

You can do similar if you remove all 6 spark plugs and then put in compression gauge or spark plug in #2, crank engine, it should slow on #2 compression stroke, but probably won't, and then listen at tail pipe for the escaping air.
Do same test but with #1 spark plug in and all the others out, so you will know what compression stroke sounds like when it "hits" while cranking engine, very noticeable

 

[cal74]

Appears to be a burnt valve, following the leak down test.

Started surgery yesterday and following getting the exhaust off the manifolds I'll be ready to take the heads off and have a look.


Appreciate the help



PS: Wondering if it's worth replacing the fuel injectors while I have everything apart. Again the trucks got a 150,xxx on it. I'll clean them and all the electrical resistances are good.

Other than a new thermostat, anything else I should replace at this time while it's easier?