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Troubleshooting P0303 on 4.0 OHV

swetrid

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Got one in the shop right now with same problem, has cracked cylinder heads.
 



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Dono

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Ok, so the dead sensor was the DPFE. It just so happened that the exhaust gas line came off (The nipple was pretty short from a previous hose going bad) and burnt a hole thru it.

The mechanic looking at it has ran out of time for now. In a week or so, he is going to set it up on the scope at hiw work and see what he can make of it.

He says the cylinder feels like it has good compression, although he hasn't screwed a tester in to it yet.

So, while I have the truck, what do I do next? Do I get an led test light, and poke a couple of needles in the harness at the #3 injector and start the motor? (Brown/yellow stripe) and red wire. The flashing would tell me if signal is consistant.

Think is, there is no percievable miss over about 1000 rpm. I know............I still think injector, but that has been changed out.
 






Dono

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Did a compression test:
1st Bank
Cyl 1: 90, 115, 130 Mult cranks max 140
Cyl 2: 100, 120, 140 Mult cranks max 140
Cyl 3: 80, 100, 120 Multiple cranks max at 120

2nd bank
Cyl 4: 95, 120, 145 didnt take max's
Cyl 5: 100, 125, 145
Cyl 6: 100, 125, 150

Cyl 3 doesnt look good.

On to vaccum test:
pretty stable around 19
I then snapped the throttle to 2500rpm, and released.
-vaccum dropped, then slowly came back to 19. Indicates worn rings?

I'm thinking leak down test on #3. Might give a bit more info.

Not looking good for my motor.
 






Dono

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Ok, New gaskets and head on the way.
Clearwater Cylinder heads is excellent to deal with. They are sending me another head with a pre-paid return label.

I just want to make sure I have covered all bases when I get my motor apart. I dont want to get stuck needing another part. Now, as long as it isn't a piston ring/piston/cylinder issue I'll be fine.

I just can't see the lifters being an issue. Famous last words. Hopefully in a week I'll have the head and be able to do the job over the weekend.
 






Dono

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Final update to close this off. Pulled both heads, Took the valves out of the one good head, and the new replacement head.
I did a minor port and polish. I left intake ports alone. I took the sharp edges off the valve bowls, polished the exhaust ports, and polished combustion chambers.

Then the machine shop shaved off .020 and installed new si stainless steel swirl polished valves. The heads were vacuum tested. The valves needed to be 'trued' to seal properly.

Heads are back on, and my motor is running good and strong with better gas mileage.

Machine shop: $350.00, Valves:$150.00, gaskets:$150.00 Head Bolts: $50.00: Total about $700.00 with about 10 hrs labour.
 












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