I have a 99 F-250SD with 5.4 automatic that just all of a sudden started running unevenly at random times, but frequently. There is a pending code P0300 Random/multiple cylinder misfire. I have had the truck for 12 years and it has run perfectly for the last 10+ years and just started this problem, it did not come on slowly but all of a sudden. I have seen on here that some people say that 90% of the time a PO300 is a bad cop. I replaced the plugs 60k miles ago when I had a bad coil on plug 10 years ago that did not set any codes, but this seems very different that more than one cylinder seems affected, like maybe 2 or more cylinders are not firing momentarily. There is a big power loss momentarily while it happens, but doesn't happen for long. The fuel pressure stays pretty constant (30 psi at rail) even while it happens, and it can affect the idle as well as while accelerating or cruising at speed. I cant imagine more than one coil on plug would be skipping at the same times or fail at the exact same time, but maybe having only one bad cop could cause this much hesitation? Does the code that indicates random/multiple cylinder misfire rule out only one bad cop? It just seems like running on 7 cylinders wouldn't be so noticeable. Could a sticking egr valve cause unevenness at idle and higher rpms and set a P0300 code? Would checking manifold vacuum be they way to see if egr valve is not working correctly. Thanks for any advice from anyone who has had a similar problem or anyone knowledgeable in this area.

 

if you’re getting a P0300 Random/Multiple Cylinder Misfire Detected code, that would indicate a universal problem that applies to all cylinders. In that case, start by checking fuel supply issues like poor fuel pressure caused by a bad pump, restricted fuel filter, or a defective fuel pressure regulator. If all those check out, look for a major vacuum leak or EGR valve leak. EGR is recalculating exhaust gas back into the intake manifold. If it isn’t operating properly and letting too much exhaust in, it will lean out the air fuel mixture to all cylinders. So check those things first. Good luck.

 

Thank you for your advice. I removed and checked the egr valve which functioned perfectly, then removed the PCV and found that the insides were mostly missing allowing constant vacuum to be applied to crankcase. I hope the PCV parts did not damage anything in the combustion chambers when they were sucked in. Three dollars or so and all seems well again. I am posting this because so many times I do a search for the problem that I am having and it seems very few people post their solution.

 

Thanks for checking back and letting us know the fix....

 

Well I thought all was well, but the problem has come back and worse. This time it set code p0302 first, so I replaced the COP on number 2 and checked the plug which looked perfect. Am I right that #2 is drivers side second back? I erased codes and drove again and there was no change, but PO300 came back along with P0302 again. Fuel pressure stays pretty constant at around 30psi at the rail. It runs perfectly then it randomly stumbles seemingly running on four cylinders or so, kind of put-putting. The ignition advance seems weird that it can be 30 degrees at idle then go down to 10 degrees or so when accelerating (that seems the opposite of how it should work). Any experienced advice would be appreciated.

 

Maybe bad fuel injectors? Did you say how many miles?

And yes 302 is #2 cylinder, just replaced that COP today!

 

cly. 2 is passengers side second back, not drivers side.

 

When you experience power loss, does the exhaust note change?

I've seen failing catalytic converters and bad mufflers act like this. Picture the internals of the cat failing (or a rusted baffle in the muffler). Some of the ceramic matrix is moving around in large chunks. Every once and a while the chunks line up to block your exhaust, which kills power. Then, the piece moves out of the way and everything is normal.

You could try whacking the cat and muffler with a mallet, see if they sound solid or they rattle when struck.

 

Hey I just wanted to drop another note because maybe your issue related to mine. I replaced my boots and coil wires last year, and just recently my #2 started to miss. I am up at school so I do not have a shop or time, so I bought a new ford coil. Ran better, but was still slightly missing, and no longer showing the bank 1 lean code or 302.

The old coil tested good! I think my issue is water in the coil boot. Going to replace all 8 again and use more dielectric grease this time. I was recommended to use foaming battery terminal cleaner to clean the inside of the coil contact, mine have corroded!

I dont think the other 7 coils were consistently missing or as bad, hence the rougher running and no codes.

 

So I realized my mistake and was working on #6 instead of #2. I replaced that COP and it seems to be running fine, of course that is what I thought the last time when I found the bad PCV valve. It is amazing how much power loss can be contributed to one bad COP. It must make the ECM do some weird adjustments to try to compensate, because like I said, the ignition advance would go backwards when engine was accelerated(less advanced) the opposite of what it should do, now back to normal. I know if on an older non ECM controlled 8 cylinder engine, if one spark plug wire were removed it would not make nearly as much power loss as this one bad COP. I've driven several trips and all seems fine now. Thanks for your replies.

 

Cool glad it was just a mistake, I had to look the cylinder diagram up myself. And it really freaked me out too! Curious, how many miles does your truck have, and has anything major ever failed on it?

 

It has 145k miles. I bought it in 2003 with 75k and apparently the AT had been replaced with a Ford reman. unit. I had to replace the front pump, input shaft and torque converter early on as apparently the pump hadn't been correctly aligned, and it would sometimes dump fluid out the front seal when hot. A couple of COPs, alternator, power door lock fix, and routine maintenance are all I have had to do. It has been very reliable and a nice driving truck, but the gas mileage has never been above 13mpg, now it gets around 10mpg, which I consider atrocious. I do use it for work hauling small equipment and ladders around.