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3.0 Cylinder 4 Slight Miss / Rough Idle Diagnosis


OneSlowVulcan

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Hello all, I had a few quick questions for those more experienced with this 3.0L motor.
I just bought the truck with around 120k miles on it, and it had a little issue. If given enough time, I am talking like 10-15 minutes of idling, to the point where it was warm, it would to start to sputter, and then miss badly on cylinder 4, the CEL did come on and flash. If you just restarted the engine, you would be good for another 5 minutes or so. Since the truck was pretty old and the wires/coil looked OEM, I first replaced the coil, wires, and plugs to their OEM Motorcraft components. This helped drastically and I have not seen the code yet while idling, and the truck does idle smoother. However, now every so often the rpms will drop (normal 750, then drops down to around 500 or so), and it will feel like it is missing again just for a brief moment, but there is no CEL. So my questions are,
- Is this "rough idle" just a normal thing for the 3.0L?
- Any other things I should look at replacing on such a high mile truck?
- I hear a tick that increases with rpm until it fades, but then returns as soon as the gas is let off. With a stethoscope, it sounds like its coming from an injector, should I look into replacing those as well?
- Apparently, some exhaust valves didn't seat properly in a few 3.0L motors, causing cylinder 3 and 4 misfires due to a loss of compression, is a compression check in order then? or should I not worry about that with such a small miss
 


rusty ol ranger

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Hello all, I had a few quick questions for those more experienced with this 3.0L motor.
I just bought the truck with around 120k miles on it, and it had a little issue. If given enough time, I am talking like 10-15 minutes of idling, to the point where it was warm, it would to start to sputter, and then miss badly on cylinder 4, the CEL did come on and flash. If you just restarted the engine, you would be good for another 5 minutes or so. Since the truck was pretty old and the wires/coil looked OEM, I first replaced the coil, wires, and plugs to their OEM Motorcraft components. This helped drastically and I have not seen the code yet while idling, and the truck does idle smoother. However, now every so often the rpms will drop (normal 750, then drops down to around 500 or so), and it will feel like it is missing again just for a brief moment. Eventually, it will get worse and the CEL comes back. So my questions are,
- Is this "rough idle" just a normal thing for the 3.0L?
- Any other things I should look at replacing on such a high mile truck?
- I hear a tick that increases with rpm until it fades, but then returns as soon as the gas is let off. With a stethoscope, it sounds like its coming from an injector, should I look into replacing those as well?
- Apparently, some exhaust valves didn't seat properly in a few 3.0L motors, causing cylinder 3 and 4 misfires due to a loss of compression, is a compression check in order then? or should I not worry about that with such a small miss
Pull the plug on the cylinder the tick is coming from...see if its blacker then the other plugs...you could have an injector sticking open.

Could also be lifter valvetrain related.

Try pulling codes again on it when it does it
 

sgtsandman

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Since it seems to be an injector, try running some fuel system cleaner through it first. It could be that deposits are just clogging it up and causing the issue.

Pick the cleaner you like and dump it into the fuel tank before you fill it up. I like Chevron Techron but there are others out there. Doing this will mix the cleaner with the fuel for more even distribution throughout the gas tank.

Run the truck until the fuel light comes on if you have one or until the tank is darn near empty.

Some advocate driving the vehicle like you stole during this process and they may be right or they might not be. I’m not sure it makes a difference and I run a fuel system cleaner every Spring and Fall. So I doubt it makes much of a difference in my case.

Anyway, it might fix your issue. Of not, it will help the rest of the injectors run more efficiently.

From there, if you still have a problem, troubleshoot it before throwing and injector at it. It could be a connector or wire issue. So, throwing an injector at it will only be money spent needlessly if it turns out there is a wiring problem.
 

OneSlowVulcan

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Pull the plug on the cylinder the tick is coming from...see if its blacker then the other plugs...you could have an injector sticking open.

Could also be lifter valvetrain related.

Try pulling codes again on it when it does it
Thank you for the advice! When I did pull the cylinder 4 plug to replace all the plugs it didnt seem any blacker than the others, but was rusted and the electrode seemed to be in bad shape. As for the lifters, that would just be causing a tick right, not a miss? Also, I have pulled the codes, its simply a P0304 (Cylinder 4 Misfire)
 

OneSlowVulcan

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Thanks for the helpful tip! I believe I actually do have some injector cleaner already I could put in on the next fill up, hopefully thats it.
It could be a connector or wire issue. So, throwing an injector at it will only be money spent needlessly if it turns out there is a wiring problem.
How would I diagnose something like this? It only happens at idle in a closed loop situation after the engine is both warm and idling for a while… is there any specific circuits that run then?
 

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Thanks for the helpful tip! I believe I actually do have some injector cleaner already I could put in on the next fill up, hopefully thats it.

How would I diagnose something like this? It only happens at idle in a closed loop situation after the engine is both warm and idling for a while… is there any specific circuits that run then?
I only know the basic theory. Enough to get me in trouble without a troubleshooting guide. I would look at the connector and the wires first. Make sure they are in good condition and that the terminals and wires going into the connectors aren’t corroded.

Anything beyond that, you need one a of the resident walking encyclopedias or a troubleshooting guide to move you along any further.
 

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"Tick" can be a bad or loose spark plug wire arcing, sounds just like a lifter tick, and will cause misfire

If possible, anytime you get a P030x code you should do a compression test just to take that off the table because you can chase your tail on spark and fuel if its a compression issue
And compression is black and white
Cold engine
Remove all 6 spark plugs
Test each cylinder and write down results, 3.0l 160-170psi is expected, but depends on gauge and battery condition(cranking speed)
Point of a compression test is to get the average and see if any cylinders are 10-15% away from that average

i.e. if 5 cylinders are 150-160psi and 1 cylinder is 135psi(or less) then there is a problem with that 1 cylinder
Usually a burnt exhaust valve, which can't be fixed with spark or fuel changes :)
 

OneSlowVulcan

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"Tick" can be a bad or loose spark plug wire arcing, sounds just like a lifter tick, and will cause misfire

If possible, anytime you get a P030x code you should do a compression test just to take that off the table because you can chase your tail on spark and fuel if its a compression issue
And compression is black and white
Cold engine
Remove all 6 spark plugs
Test each cylinder and write down results, 3.0l 160-170psi is expected, but depends on gauge and battery condition(cranking speed)
Point of a compression test is to get the average and see if any cylinders are 10-15% away from that average

i.e. if 5 cylinders are 150-160psi and 1 cylinder is 135psi(or less) then there is a problem with that 1 cylinder
Usually a burnt exhaust valve, which can't be fixed with spark or fuel changes :)
Wow, thanks for all the info! Okay, I will do a compression test just to rule that out (hopefully). The tick has been there since before I replaced the plugs and wires, so I dont think its a loose plug/wire. But I guess its possible it was loose before and when I installed the new ones I installed them loose. I just tightened by hand, then down with a ratchet, as I saw there is lots of different torque specs and generally tight is good. That should be fine right? And the new wires I pressed on real tight. The truck is coming up on an oil change, could that be the reason the lifter tick is now apparent?
 

Plasso

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I just went through very similar symptoms with my 2002 3.0 engine (140K miles). It misfired when idling, but only after warming up. After replacing plugs, wires, etc. I then ran a lot of injector cleaner through the engine.

After some research, I finally did a compression test and had compression as low as 30 in the bad cylinder and compression below 90 on the other side of the engine.

Now I'm weighing the options of trying to replace/repair the cylinder heads after replacing the valves, or just buying another engine. Hope you had better luck than I did.
 

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