fullsize guys werent much help

[91rangerxlt]

Sorry didn't kno were to post this but I didn't get much help from tge fullsize forumn. I have a 1999 f150 with the 4.6 it has 253xxx miles, and when I'm cruising under acceleration my check engine light flashes. Tge ownersnanual says its a misfire. I put new coil paxks on hoping to fix it, but that didn't help at all. When autozone plugged it in to there scannee, nothing came up about a misfire. It said I had bad o2 sensors which I new when I got the truck, and it said bad cats, but it don't do iy all tge time which leads me to beleave its not tge cats, I had a bad cat in my ranger and it had no power wat so ever. Should I clean tge MAF sensor? If to what do I clean it with?. Any ideas? The few people tgat replied said it gad to be coil packs, but like I said, new ones are on and same problem. Aby help will be appreciated. Sorry for the long post and sorry if its in the wrong spot, didn't know were else to put it.

 

[85_Ranger4x4]

First off the "H" key is usually hit with the right pointer finger as opposed to the left.

When you changed coilpacks, did you change spark plugs and boots too?

There are o2 sensers in front of the cats that tell the engine how rich/lean it is running and there is another pair after the cats to monitor their effeciency. It might be that they are bad.

 

[BRUTUS_T_HOG]

this would be hard to diagnose over the internet.

low fuel pressure under load.

dirty MAF causing lean misfire, clean with MAF sensor cleaner or brake cleaner

who knows. does the engine run smoothly when not under load or does it shake like a constant misfire?

 

[91rangerxlt]

First off the "H" key is usually hit with the right pointer finger as opposed to the left.

When you changed coilpacks, did you change spark plugs and boots too?

There are o2 sensers in front of the cats that tell the engine how rich/lean it is running and there is another pair after the cats to monitor their effeciency. It might be that they are bad.

Sorry bout the spellin I'm on my phone. No I didn't replace plugs or wires yet, they are next in line. I was gonna do the coil packs first and go from there. It has a rough idle. Ilk clean the maf sensor tmrow. Also plan on changing the fuel filter.

 

[85_Ranger4x4]

'99 is coil over plug isn't it?

You are going to kick yourself for not changing the boots and plugs while you had the coils off...

 

[91rangerxlt]

'99 is coil over plug isn't it?

You are going to kick yourself for not changing the boots and plugs while you had the coils off...

No it still had 2 coil packs. Not over eachvplug.

 

[BRUTUS_T_HOG]

sounds like it has a constant miss. you are on the right track.

checking/replacing the spark plugs will give you a clue