While on vacation I decided to do some maintenance on my 98 F 150 4x4 5.4 w/ 170k. I started with the throttle body and went as far as pulling the upper intake, cleaning all the emission/vacume ports and all carboned up areas in both. Changed the plugs with the oem motorcrafts - gapped and used anti-sieze on the threads with dielectric grease on both ends of the boot. I spent the good part of three days doing all this. Now I have a problem that I cannot figure out!! It's misfiring bad - Engine light is not illuminated, made sure everything is hooked up properly about 3 or 4 times. This 5.4 has cops one per cylinder, I pulled each one out and pulled the plugs as well. New plugs so I could tell right away which were firing. No. 4 looked as tho it wasn't. At one time one of the lines leaked by the heater core - I fixed that some time ago but the coil below was dry but it has been wet before. I replaced it without checking it thinking that it might of been weak, I replaced the plug as well. That wasn't the problem. My vacations up now and I'm on personal days from work trying to fix this!! At this time I'm testing all the coils because I don't know what else could have went wrong - so far I tested 5 thru 8 which have passed the ohm test . 55 resistance and I even grounded each coil after removing and made sure it sparked by starting the truck just to be sure it was good. So far - so good on the coils tested. Testing 1 thru 4 now. The truck ran great before I attempted to do it some good, so anybody have any ideas ?? I also blew out the injectors with compressed air - could I have screwed them up somehow? Any help would be appreciated.
Thanx jbrew - 98 F 150 4x4 5.4 w/170k

 

What model plugs did you get and what did you gap them at?

Did you put new gaskets on?

 

Me in same boat, replaced plugs with new oem plugs, new boots and front 2 o2 sensors. Now missing only when going up a hill and starting to downshift??????

 

Motorcraft (SP-479) - AGSF22WM Gapped @ 0.054 inch.

Sad to say, no, I re-used the old intake gaskets. They didn't look that bad and with this being the only vehicle I own It would have been difficult to retrieve new ones. I didn't plan on removing the intake until a couple of the fuel injector hats remained inside the manifold upon removal. As for the throttle body and EGR gaskets I used permatex high heat black as a substitute. I have tested all coils and plugs except # 3 and 4 doing those two now, all other pass the ohm test and generate a healthy spark with engine running. You think it could be the intake gaskets? I can drive it, but it runs like only 7 of the 8 cylinders are firing throughout the rpm range and the check engine light is not on.
Thanx for your reply

 

I asked about the gaskets because the gas mixture has to be correct for combustion and a misfire could be no spark, no fuel or marginal air/gas mixture. I have forgotton to connect a vacuum line sometimes and wonder why I got a check engine light or why the engine runs rough. I usually go back an check all vacuum hoses, COP harnesses and fuel injector harnesses when that happens.

Have your vacuum hoses ever been replaced on your vehicle.

When you say only 7 spark plugs are firing, do you feel shudder from the engine or it feels like the engine is running a bit rough?

I would think that you would get a engine check light sooner or later.

Here is a thread with a post by PKRWUD (#54) about misfires that can occur because of the harness next to the accumulator. I posted a picture of the accumulator (#58) a few posts down in the thread. Maybe you knocked the harness closer to the accumulator?

https://www.f150online.com/forums/sh...change+misfire

 

I ruled out the vacuum hoses, that was was my initial thought as to the problem and they are fairly new - about 20k on them. It sounds more like a shudder I would have to say, it never varies and is constant from idle on up. I've only drove it to the parts store to pick up a coil for it when I thought that might be the fix it needed, so that was about 5 miles. I had this truck for a long time and love it , it's been very good to me and has never ran like this. 170k on original head gaskets that don't leak. I've read that people have allot of problems with cops on this V8. I guess I'll test the remaining coils and plugs (3 and 4) and then the fuel injector portion of the harness, from there I'll check the pressure on the fuel pump and maybe new injectors unless I get an engine light before then.
Thanx for your input, these forums are great!!

 

Good luck!

It never hurts to spray electrical contact cleaner on the harness plugs and connectors either.

I also disconnect my battery for a few minutes to reset the computer and let it learn all over again.

http://www.obdii.com/drivecycleford.html

 

I had the same "uphill/downshift" problem when I had my truck serviced and the tech reinstalled my MAF incorrectly so that the sensor was horizontal instead of vertical. Did you reinstall youre MAF correctly? Good luck.

 

That's something I would have never thought of. I will check that out for sure tomorrow. Thanks........

 

Note that even though a coil checks out okay resistance wise, that doesn't mean that it won't flake out under load.

You need to isolate definitely which cylinder ain't pulling it's weight and start from there. Even though the CEL ain't on, that doesn't mean that there isn't a pending misfire code. If you've got access to a scan tool that'll display Mode 6 results, see which cylinder has the highest misfire counts and go from there. Verify fuel pressure and spark, check cylinder compression.

 

try spraying carb spray around the gaskets you reused to see if they are leaking. the engine should stumble when there is a leak. also try unplugging fuel injectors while running,(it will set code) to see if you can isolate which cylinder is misfiring. if you find the dead hole try swaping injectors with a good one and see if the missfire moves to the cylinder you swapped it with. you may have gotten dirt inside the injector when you aired it off and plugged it up. good luck.

 

Wow!! So many good replies and very good ideas, I will try them all, so far temp1 informed me of a thread in the archives to check out having to do with the accumulator and wiring harness. As it turns out when I reinstalled the harness after cleaning and re-tapeing I re-routed the end of the harness were it plugs into the AC and CPS I believe around the accumulator. I don't believe this is how it was routed before now that I thought about it, any way I rerouted my wires so that they were not contacting the accumulator and finished checking the coils (resistance and spark with motor running) I did not preform the secondary on the coils, just the primary and live test if that makes a difference. Moving the wires away from the accumulator made a big difference!! ( : That's puzzling.. However there's still a problem, the miss is still there but allot less apparent. The idles sounds rough but the tach is steady and doesn't flinch (thought that was strange), from idle it revs pretty good and can barley tell there's a miss, but you could if it was your truck if you know what I mean. Going into the last two gears through the drive cycle is were you can tell there's a definite problem!! It shudders and vibrates, I can get it to smooth out enough to stop shuddering eventually - I think I screwed up the injectors blowing them out with compressed air - I also cleaned the throttle body and all the ports , I read that it is possible to screw up the TPS that way. I thank you all for the help and this gives me plenty to check out - I'll gitter .. Question - if I unplug an injector while the motor is running it will signal the check engine light to come on, correct? If thats the case then I can run up to auto zone and get some codes to see what's been happening here? I have had the battery disconnected for about an hour prior to starting it before running it this time. Thanx allot

Jbrew - 98 F 150 SC 4x4 5.4L w/170k

 

Update - The Check Engine light came on this morning, heading up to Auto Zone to get it scanned, I'll make sure to write everything down and post it when I get back. Going to pick up some carb spray as well to check for leaks around the intake. There's a set of Boch injectors (new) on eBay I'm contemplating. Will 24's work? as long as it's more than stock It seams like it should , not totally sure on that yet.

 

the only code that would probably show up is the one you created by unplugging the injectors. i would be leaning towards a vacuum leak

 

jbrew,

Stock injectors flow 19 lbs per minute. The 24s flow 24 lbs per minute. All that will happen is the PCM will shorten the pulse width becasue the 24s flow too much fuel. It will not add any power. It may even casue an overly rich condition if the PCM cannot shorten the pulse width enough to compensate the extra fuel that they flow. Nothing gained by adding 24s.


JMC