Hello all,

I'm working on my brother's truck (07' F-250 Super Duty, 5.4, 2wd) and trying to diagnose surging/no power under load. It works good up till about half throttle then falls on it's face and misses/shakes and generally is very doggish until you get near full throttle. I read some codes at the auto part store and the counter salesman told me that it looks like there are a couple of issues. The speed sensor was one of them, and another issue with a lean fuel problem. He read off about 7 codes but I didn't get a chance to write them down. Something about misfire on #3 and #8 and a lean error. After doing some research on the forum, I have a few questions as I haven't messed with something this new very much. Does anyone know what the fuel pressure is supposed to be? Key on engine off, running at idle and under load at say 3k RPM's if you know. Also, I didn't see a fuel pressure regulator for sale at RockAuto.com, just a fuel pressure sensor. Is this something that goes out often and causes the injectors not to fire for a long enough duration? I've also read about the cat's becoming plugged and plan on getting a vacuum gauge to see what the vacuum is under load. Does this sound like it could be an issue also? If so, is it hard to gut a cat on these trucks and will it cause any issues (like a CEL constantly) if it is gutted? Can the muffler be plugged? He has around 110,000 miles on the original plugs and we are going to start there to see if we have any improvement. I'm just looking for some ideas since this has been going on for a while and is getting worse. Thanks to all in advance!

 

Well the fuel pressure I do not know. But number 3 and 8 sounds to me like bad COP on cylinder's #3 & #8. So I would replace the COP's. One for each cylinder. I would replace the fuel filter. I would clean the MAF, and see how that works. I would think that the CAT would be ok and not an issue. I think that bad COP's would cause misfire and would also cause a lean error code

 

Thanks for your reply. Sorry for not posting earlier but I already changed the fuel filter and cleaned the MAF and it didn't change a thing. I also changed the TPS thinking that it was getting a funny reading the fly by wire throttle. Wouldn't a misfire on a cylinder cause the unburnt fuel to be passed through causing a rich condition? Is there any way to check the COP's when I change the spark plugs? Thanks!

 

Well you could switch the COP's to another cylinder. If the code follows to the new cylinder you have narrowed it down to a bad COP. If you moved the COP and the code did not follow the switch. I would look at the injectors. If your brothers ride has 100K or near 100K in milage. I would think of replacing the COPs and plugs anyway. But switching the COPs first to see if the code follows is a start.

I just re-read your first post. so with 110K miles I would definitley replace the plugs and COPS anyway. If that does not fix it then look at the injectors for each cylinder. If they are good I would start to think at a stuck valve BUT you got codes for 2 cylinders so I am leaning towards plugs and COPs, then maybe injectors.

 

Thank you for all the good info V10ZILLA! I'll switch the coil packs around to see if the code follows. To be sure, cylinder number 1 is on the drivers side at the front of the vehicle and it goes back from 1 to 4 correct? 5-8 is on the passenger side from front to rear also correct? I'm not sure if he wants to spend the money on all new COP's yet but if he has to, well then I guess he has to.

Could the VSS have anything to do with the stumble issue? I know he said that the tow/haul light was flashing at him but yesterday but when I drove it later, the speedo stayed steady and I couldn't repeat the issue. Were going to change it anyways to see if it helps. Could the ABS wheel sensors cause the VSS code or cause the tow/haul light to flash, or would it be the ABS light?

Has anyone experienced the CAT's clogging up? I'm still going to get a vac gauge and see what the vac level is under load. Are they easy to gut if need be and would this throw a code from the downstream HEGO sensor? Thanks!

 

Look up the plug numbers but i thought that 1,2,3,4 were in front to rear passenger side and 5,6,7,8 were in front to rear drivers side. I could be wrong. Please check first. DO NOT FORGET TO WRITE DOWN WHICH CYLINDER PLUG YOU TOOK OFF AND TO WHICH CYLINDER YOU PLACED IT. Its easier to write it down then to try to remember it later.

Remember you might not get a code for a few days. So write it down. Drive it around for a couple of days.

As far as the VSS is concerned. From time to time they do make a weird noise and the tow/haul will come on (blink) when this happens. It has someting to do with the vehicle
braking system and ABS, VSS, tow haul working together. What your brother experienced is normal. I would not attempt to fix anything unless the lights stay on permently. I had this happen to me on a 2wd truck before. I took it to the dealer, they told me that was normal. They were all trying to work together as I was driving on some slippery road. It made sense to me at the time. I do not know how to explain it to you so it would make sense, sorry.


I do not have any experience with the CATS.

 

Also, if you switch the COPS and the code does not follow. The code remains on the same cylinder, I would think plugs, if you change the plugs and still have the codes, I would look at injectors.

 

Alright, i'll try to take a look at it this weekend and let everyone know what I find. Thanks for all your help. Rep sent!

 

I can't help much on specifics either but I will warn you on the plugs. With 110,000 miles on the plugs you need to be VERY careful taking them out, don't just put a socket on them and twist like you might be used to. Ford had a lapse in judgement and used 2 piece spark plugs in those engines, that coupled with any carbon build-up and they like to sieze and you only get half the plug out. There's a TSB on the proper method, but to summarize, first start of w/ the engine at room temperature, then take off the COP and boot and blow out the well to get any dust or crap out and then spray carb cleaner down there (1/2-3/4 tsp), and let it sit 15min - that is supposed to wick down and loosen the carbon buildup. Then start to loosen the plugs as gently as you can, go back and forth a few times and a bit of praying wouldn't hurt either. Lisle sells a tool that's reported to work very well in extracting any broken ones but I've never used it. It might not be a bad idea to invest in one though. Then on the new plugs (new ones should be 1pc design) coat the ground shield (round shaft area below the threads) w/ light layer of high temp antisieze to prevent the problem next time. Do a search on here for plug removal on 2005-07 trucks, you'll read some horror stories.

Also, on the tow/haul flashing, that means the transmission has stored a code but a cheap home scanner or the ones at an auto parts store aren't capable of reading those codes so you'll either have to go to the dealer or find someone w/ a high end scanner to find out what's going on there.

Btw, I had miss and lean codes on one cylinder and it ended up being an injector. That was a known problem for 2005 5.4's though.

 

Thanks for the info. I've heard the horror stories about the plugs breaking off in those engines and the thought has put me a little on edge. I'll try to be extra careful and I believe that he has a fresh can of seafoam, which I heard works well at loosening the carbon. I'll look into the transmission a little more before I tell him to order the sensor. Thanks!

 

Tagging for outcome.

Dads 06 has some of the same symptoms.

 

Well, I changed the plugs this weekend and it was a bear of a job. I think it's the longest amount of time i've ever spent on a spark plug job. lol. That being said, I didn't break any but the old ones were worn way to hell. I didn't measure the gap but it appeared to be around .080" to .090" from gauging it with my eye. Replaced them all and moved the two suspect coil packs (#3 and #8) to the front (assuming that cylinder 1 is at the front of the vehicle on the passenger side) of the engine to see if they misfire and throw a code again. The truck runs better than it has in the past few years now but still has the hesitation at 50% to 90% throttle under heavy load. Does anyone know what the engine vacuum is supposed to be under load at around 3,000 rpm's? I was taking it for a test drive and put the engine under medium acceleration and I was able to tap the brakes untill I lost vacuum to the booster. It took about 8 times but it lost it. I know that the engine doesn't build much vacuum under acceleration but didn't think that the booster should of lost all vacuum. Anyone have any ideas? Thanks!