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Troubleshooting P0303 on 4.0 OHV

Dono

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Im looking for help here as all threeads pertaining to this kind of trail off without any real answers.

I was sitting at a stop light, and my motor started shaking. Higher rpm's seem to be fine. Check ingine pops up. My reader gave me P0303, Cyl 3 misfire. Ok, thats the cylinder on the passenger side closest to the fire wall.

I popped the plug, and it looked fine. So, I replaced the plug anyway, and swapped plug wires with the cylinder next to #3.

Next day, same issue. #3 cylinder. I blocked the tires, pushed parking brake, and unplugged one spark plug wire at a time. I'd plug the one I unplugged back in after confirming how badly the motor would shake. No question, #3 is not firing very well.

There was lots of arcing when unpluggung each plug wire, including #3. That rules out the coil pack. Not the plug wires, as I swapped it out. Not the plug, I installed a new one.

So what next? Valves opening and closing (Compression test) or Fuel injector?
Ideas? Heads are new this summer. Heads, rockers, etc. are new this summer. Shoot me now.
 



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Dono

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Thanks Turdle!
As I lay awake last night thinking about it, I thought I'd pull the motor apart and switch injector locations. Sure would be nice if I had a spare fuel injector.

Sad part is, I changed them about 2 years ago, and threw the old ones out about 6 months ago. Figures.
 






Dono

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Turdle

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Those are listed kinda goofy--from what I understand 98 and 2000 take different injectors--return fuel system injectors have a different connector then your returnless fuel system injectors have. Just be sure to get the correct ones.

Edit, I may be mistaken on this but it is worth checking out
 






Dono

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Thanks for the tip.
I was able to get some information off of what I have, and I emailed it to them. It wasn't exactly easy with my ageing eyes.

Here is the info I have on them:
Cream in colour
B280435021/7
0280155846

I offered to send them a picture if it helps.

More research brought me alternate part numbers. I have clearly ordered the wrong ones from ebay.

Other part number that are the same as what I have are:
CM-4895
F87E-H1A
98TF-AA
 






Dono

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And up comes another code. P0301. So add that to P0303. 2 cylinders misfiring

Fuel pressure? Vaccum leak??Finally changed the fuel filter lying in the garage. also dumped fuel system cleaner in to the tank.

I guess I'll need a vaccum guage and a fuel preasure guage. Anyone know the vac specs on a 4.0 ohv? 18-20psi? Fuel should come in at 64psi.

Im so not happy about this. Im tempted to take it to a shop. Problem is, there arent many(none that I know of) competent shops around.
 






Dono

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ok, so I think the P0301 was me pulling plug wires, confirming my issue.

Now, I just changed all injectors and guess what? P0303. Im thinking a lot of not very nice words here. Is it possible that fuel preasure could cause just 1 cylinder to read misfires at low idle?

I have a very bad feeling here.
 






BIGTREAD

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The thing about these codes is that they can be so misleading. The P030 indicates mis-fire, but the book even includes a clogged cat in the list of possibilities. Anything at all that causes the mis will throw the code. My #3 behaved this way for two years. Turned out to be failed head or head gasket or both. You just replaced all that. Comp test isn't hard and could rule out some of the worst issues.
 






Dono

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Yup, next step................Pick up compression tester.
It really never pays to rush. Vaccum leaks now. P1132, and 1152.
 






Turdle

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Just another thought--check the injector harness well. You might also pull the pcm, look for bad solder connections. Each injector has it's own circuit.

Usually a misfire code is induced by a faulty fuel spray. I have never seen an ignition induced misfire code, even when there was a clear ignition mis fire.
 






Dono

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Maybe I'll see if I can match wire colours on the injector against a wire on the pcm and check for continuity.

I doubt I'd be able to see any kind of a electrical pulse with a digital meter (Im guessing a scope would be required) at the connector if the injector. If I could see a electrical pulse happening at the injector, I'd know the the wiring was good.
 






ranger7ltr

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Fuel pressure? Vacuum leaking?

ok, so I think the P0301 was me pulling plug wires, confirming my issue.

Now, I just changed all injectors and guess what? P0303. Im thinking a lot of not very nice words here. Is it possible that fuel preasure could cause just 1 cylinder to read misfires at low idle?

I have a very bad feeling here.

Sure fuel pressure can cause just one cylinder to misfire...What was the fuel pressure on your truck? The spec is 65-72 psi for the returnless system...And vacuum level should be 20 in. or higher especially at idle on a stock engine...

And what did the fuel out of the old filter look like? Was it clear or was the inlet side brown and murky like mud?
 






yavapaires

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Go to your LPH and get a Noid light to check your injector wiring.
 






cobra0357

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I am having the same problem as you on my 2001 explorer with the 4.0 6cyl . My code keeps coming up number 6 misfire. New plugs ,wires, coil and the compression check was 165 to 175 on all cylinders. Same code pops up. Runs crappy at low idle. If I can come up with something ill let you know.
 






Dono

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I am having the same problem as you on my 2001 explorer with the 4.0 6cyl . My code keeps coming up number 6 misfire. New plugs ,wires, coil and the compression check was 165 to 175 on all cylinders. Same code pops up. Runs crappy at low idle. If I can come up with something ill let you know.

It becomes tough to know what the issue is. I don't seem to be seeing te 0304 anymore. No more codes at all. It does sound like we both have exactly the same issue.

The fuel in the old filter was murky. I do need to check fuel pressure and vac pressure. It looks like a fuel pressur guage is about 80.00 locally.

Im starting to move away from the bad injector. The rough engine goes away at anything over 1000 rpm. This is what makes it hard for me to believe the issue is wiring to the injector. Where my injectors sit now is this: 1 rebuilt injector at cyl 3, and the others are the originals.

could the MAF cause this? I've never cleaned mine. Also, I am wondering if anyone has looked at the factory Main board (PCM on the passenger side, by glove box) for electrolytic capacitors that are probably drying out by now. I did see some posts on this for first gen's.
 






joe doe

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if the same plug keeps fouling check the insulator on the plug for cracks ,see the crack on mine below? this happens when you got a cracked cyl head .
if you replace the plug with new and this happens again ,its a pretty safe bet you got a cracked head .
check your antifreeze levels .

dsc00717fx.jpg

Shot at 2010-07-13

and stay away from these platinum plugs ,i think they are junk .
 






Dono

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hahaha, yup, been there, done that. Both heads sucking coolant. Everytime I stepped hard on the gas for more than a few seconds I knew I was going to have to change at least 1 spark plug.

The difference this time is that when I changed the spark plug, my truck still would not idle well when warm. The issue is deffinately getting worse. I am hoping to spend more time with it this weekend.

Thanks for the reply. I'm hoping to get this sorted out soon, and post the results. I may just shoot myself if its my own shoddy work and I need to pull a head again.
 






joe doe

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so you replaced your heads with reman or new ones??
i found out after i had all my gaskets replaced that my head was cracked .:mad:
i used some head sealer in the antifreeze and it must be working ,coolant loss is down ,plug stopped fouling .
but its only a bandaid.
 



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Dono

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So, I took my exploder in to a licensed mechanic. He's a friend of a friend, and is doing the work on the side, He has been struggling with it.

This morning he called me and says I have a dead sensor, and is picking one up. The sensor is about $100.00. I sure hope it fixes the issue. When I see him I'll find out exactly which sensor he replaced.

Crank sensor would cause a no-start, so I'm guessing he's replacing the cam sensor. More to come.
 






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