98 F250 5.4L 4x4 - ~120k miles

Recent tune-up work - within last couple of years replaced MAF, Starter, Alternator. Within last few months replaced all spark plugs, all injectors, all coil packs, fuel filter and HD battery. Mostly stock truck otherwise. I'm a novice mechanic but I pay attention and thru forums/YouTube I have been able to do this all myself with limited help from mechanic friends.

I've been chasing a single misfire code for a few months now. A few times the code flashed while driving and was hard to make it home. I changed the plugs and it went away for a bit. Jumped to another cylinder so replaced the injectors. Went away for a bit then appeared, so changed the coil packs. I'm not trying to throw money round, I just knew it was that time anyway for these smaller consumables.

Each time I do something the truck drives great for a couple months, then randomly has a harder start for about 15 secs then smooths out. Eventually this turns into a single misfire code (p030X).

My latest research turned me onto vacuum leaks. I tried testing that with a water bottle spray and didn't notice any dips in idle, but it was my first try ever at this, so I may not have found enough hoses to try. Another suggestion was getting a vacuum pump tester and check out the EGR's condition. Also to clean the EGR ports.

Thanks in advance for any thoughts!

Matt

 

The truck doesn't always stumble at the moment. It seems to come on randomly. Sometimes a slightly tough rumble after ignition, then smooths out once rpms drop to operating (10 or so secs) and fine for awhile. Smooth accelerating and uphill at any speed, engine is purring. Then randomly it starts rumbling some at speeds. In the past it eventually caused the blinking cel with one misfire code. Recently it's just been doing the intermittent hesitating, but no codes yet. I'm confused how it comes and goes...

 

I would look at fuel trims and fuel pressure which should be 30-45 psi. Verify a lean miss condition before going in another uncharted direction.

 

Thanks for the fuel line advice, that was probably the last part of the fuel system my brother and I thought to check. When I changed the fuel filter a little gas bled out both sides of the line so I hoped that helped to clear the line in case of large debris. Hoping it's not the pump, might have to drop tank or lift bed for that, but looking at test kits from auto store I can check a few things with that (including pressure regulator).

As for the trim data I only have a basic code reader at the moment, but that sounds like it'll help tell me more specifically where the affected region is (would that tell me fuel line data as well or just engine data?). Any thoughts on the mini scan plug-in that you can read the data with an app on phone? It seems the cheapest for the features gained.

Funds are tight but I'll try and get some data from either of those two ideas soon and let you know. Thanks for your time!

 

Maybe the parts store can loan a fuel pressure gauge to check fuel pressure. If the fuel pressure regulator is bad, fuel will leak out its vacuum port even with minimal fuel pressure. The engine will run very rich. You can confirm that by examining the spark plugs.Don't replace it if it doesn't leak. You will waste your money. The regulator actually helps keep the fuel pressure from going too high.

 

If possible ,you might try to see what code (s) are in the computer. Is it always the same cyl or does it misfire on different cyls. Depending on which it is will determine where you go next.

 

Hey guys,

Today driving, the truck started with no issues and drove normal for awhile, 10-15 miles around town. Then started to feel a slight vibration, almost as if the transmission was slipping before shifting gears, but generally normal power for 5 or so miles. Then started to vibrate very noticeably and blinking cel came on. Pulled over off highway and checked it was p0301 - #1 misfire. Sat for a few minutes and limped it home about 20 mph on shoulder (5 or so miles to go at this point). Cel came back on but light was steady. Checked code while driving and this time it included p0171 - bank #1 too lean. Only a couple miles later we noticed the vibrating went away and it seemed to have full power again, like it completely went away (although in 25mph zone didn't fully step on it).

Overall the first misfire was one code, p0307. Then it migrated to p0301. I think there was also p0303, but at this point I'm not entirely sure, I've replaced nearly everything and things are melding in my mind. For sure it went from one bank to the other once.

Still working on getting a fuel pressure kit and/or a live data device. Any other thoughts again is appreciated.

Matt

 

Maybe this might help you some,

A fuel issue would affect all cyls ,EXCEPT ,an injector system problem.
Do you have any plans where to go if the fuel pressure is good?

How does the injector know when to inject? It gets it's signal from the PCM. Where does the PCM get it's info as to when to inject. If it is getting bad /incorrect or intermittent info the result will be a random misfire. If this is what your codes are telling you , you might consider looking for a loose connection , or what might be the possible cause for the bad info. The idea is to work back from the results and try pinning down the possible causes. You need to approach the problem from the conditions you find and go from there. That is what makes finding and solving problems like this interesting and fun to solve.

 

Ok, lots happened in short time.

I decided to check the EGR valve because of various suggestions and since it was accessible and cheap to replace if needed. One of the double-ended bolts broke, and I tried every extractor set with no avail. Disconnected very top of intake manifold (part that EGR was attached to) and found the port from EGR leading down into housing was full of sand/small rock chunk size carbon deposits. We took manifold section to my brothers work to drill press out busted bolt and use his solvent brush machine, lots of gunk came out.

Upon inspecting the engine's naked section of intake I could see where the PCV valve hose ties into the far back of the upper intake assembly. A different misfire thread on here mentioned some kind of vacuum hose like that but I couldn't see it until it was exposed like that. Figured I'd replace all vacuum hoses I could find since it was available and a cheap consumable. The elbow boot from PCV valve into the intake had a gnarly hole on the underside (opposite elbow). Other people's suggestions also mentioned PCV valve so I changed that out too since I was there (it rattled when I shook it, but was pretty dirty looking, I think original too, ha!).

Driving it around today it had about three seconds of rough idle upon ignition, but then started to smooth out. I drove it around town about 25mph to let it get to temp and where I could pull over if necessary. Ran great. Drove on freeway about 20 miles roundtrip and it felt like a new engine. Usually w/in that time I'd notice something. Should anything change I'll update again.

Doing all this I have a lot more confidence to keep replacing the appropriate parts as they age. Thanks for your suggestions. I'm going to check the fuel pressure system soon too to rule out any faulty/tiring components there too.. Any other suggestions for proactive upkeep would be appreciated. Thanks for looking!

Matt

 

If you have the $$$ and time to keep replacing parts, you should --have a fairly new vehicle when you get done,,,,,,,,,,,OR,, BE BROKE lol.

Most folks don't have much of either to spare, so you are pretty lucky. The best suggestion I could offer would be to stick with the schedule in your owner's manual.
Carefully , working and learning will pay later up the road.. If you give it some thought, what you save doing a lot of your own work, allows you to purchase quality parts , and that can make a big difference . Most times we try to stick with OEM quality parts. If you can purchase them cheaper on line , great.There are good aftermarket parts out there , but you need to know which are made here and those not.
Thank you for sharing your good results and fixes.