4.6L, 02 Screw, 83,000 miles. Had a miss develop under load a few months back. Replaced the plugs, checked the COPS with an ohmeter put back together, threw a code and replaced the DPFE sensor. Ran great for a few weeks, started missing again. Ran it for a month or so trying to get a code to throw. Took it to Auto zone, nothing showed up. I recently (two days ago) examined the plugs, replaced the boots and used dielectric grease. Couldn't find anything suspicious about the plugs, all looked ok. The truck runs worse now than ever. Misses even under heavy load. Starts and idles fine. Any ideas? Thanks

 

You have to get further into it...

Have someone check the misfire counters - Autozone I don't think will be able to with a cheapo scanner... it might cost you the $60 or so at the dealer to find out which cylinder is missing...

When you find out which cylinder is missing, change the COP on that cylinder and see if it goes away.

If it doesn't, do a compression check to see if the cylinder has a bad valve or rings (or even a bad head gasket leaking to another cylinder). Or, do the compression check first if you can do it yourself and save the cost of the COP until you know you need it.

 

I did find a plug on #2 that had some black around the ceramic portion of the plug. Do think this could be an indicator of the bad COP?

 

To go along with what art said .
also look at the following

Tell us what the code # was that you got when replacing dpfe sensor?
also the egr might be sticking or
Try cleaning the maf sensor. it may not reading properly and causing the fuel trims on the rich side. causing a rich stumble.


Black on the plug is usually a blow by.
did you use ford plugs when changed?

Rich

 

Code - I believe it was P303???? Anyway, it said insufficient airflow. I changed it out and ran great for a while.

Plugs, Autolite double platinum. I've read in here that many were using these.

I'm believing the problem is still a COP. The way of checking them with an ohmeter is not very feasable due to the COP needing to be hot before it starts acting up. I've got an extra one that I bought during the first change. I will start changing these out one by one and maybe find the problem.

MAF - never been cleaned, will do this this evening. Everything I've read about the MAF being dirty seems to effect the engine after 2000 RPMs. Mine is missing anytime under light load and during increased accelleration.

Thanks guys, Keep it coming.

 

A dirty MAF will be noticed at any rpm.

 

Will a dirty MAF have the same symptoms as a bad COP? I've checked all the COPS again last night and the truck is running worse each day. I'm very surprised it hasn't thrown a code yet. It's bucking and jerking steadly throughout the RPM range. Thanks

 

A dirty MAF will affect ALL cylinders, but it's possible that it's on the hairy edge and one or more are misfiring because of it.

A MAF will effect the motor from idle all the way up the RPM range.

 

I just reset the computer and will see if this makes a difference on the drive home tonight. Thanks, will keep you posted.

 

NO luck. The truck ran great for about 10-15 minutes after resetting the computer then started gradually getting worse and by time I got home it was missing horribly again. I cleaned the MAF again last night. I didn't take it out of the housing, coudn't get those "special" screws out. The wires looked clean, couldn't see no residue or gunk on them. Reset the computer, drive to work this a.m. and the same result - did great initially and by time I got to work (30 minutes later), it was missing badly again. Any thoughts? I'm thinking it's still a coil gone bad that needs to get good and hot before it starts breaking down. I did the ohmeter check and all were within the specs. Thank

 

Jarret,you need to get this vehicle scanned with a good scanner looking for misfiring cylinders.you can approach these things in many ways.But without tools to do the job its difficult.
You could have other problems also
I'm going to list them you choose
bad fuel
Fuel filter
fuel pump
fuel injectors
fuel regulator
maf
IAC
o2 sensors
Cop( buy 1 and start switching it out with others)
plugs
other electrical problems pcm,loose connections
vacum leaks
but since your not getting codes right away,
I'd start with scanned for misfires


Rich

 

my 87 f150 is having the exact same problems! exactly! and I havent taken it to a dealer yet waiting on cash

 

I'm finding it hard to believe this truck will not throw a code as bad as it's running. Anyway, I'm working this whole weekend and I'll take it and have it scanned Monday or Tuesday.

 

ns. I cant believe it either! Thats what I dont understand!also I was messing around with the gas the other day and disco the inertia switch for the gas, I never changed anything, but when i was done i plugged it back in and now the damn thing dies when im stopped at a light or something

 

have you tested the tps yet? Buddy at autozone says my symptoms sound like it may be bad or have "dead spots". If you take it off they can test it. Will prob do mine in a few or tomorrow.