rough idle and miss fire

[ben10]

so my truck if it sits for a day will run really rough for 10-20 seconds before smoothing out, it has gotten progressively worse... If I go to the grocery store or something where its been sitting for less than 5 or 6 hours before restarting it starts fine, but if it sits all day or overnight it starts rough again.

also occasionally driving down the road it will start to miss for a few seconds then smooth out, its an auto and I shifted gears and it continued to do it, I also tried flooring it and it continued to miss for the few seconds. I am not getting any CEL codes. I have cleaned the IAC and MAF the coil pack only has about 10k on it, same with the plugs and about 20k on motorcraft plug wires, where do I go from here? its a 99 4.0 ohv with 130k on it.

 

[ben10]

no one?

 

[Stimpson.06]

my buddy had the same problem thought it was a maf sensor got that fixed it ran alittle better and then we found a vacum leak and it runs fine now

 

[ben10]

hmmm could be a vacuum leak I guess, I think its time for a check up on the hoses and such.

 

[Earl43P]

I have two pieces of advice for you Ben.

First, Prime your fuel system before you start it.

Do that by turning the key to Run (warning lights come on in dash and fuel pump runs for 2 seconds). Then turn the key back to Off, back to Run, wait the 2 seconds for the fuel pump to prime again and crank over the starter. If that works, continue to do that before every cold start.

Loss of fuel pressure after shutoff can be a number of things, which leads me to my second suggestion....

Replace the fuel filter.

Fuel pressure bleed down is pretty common in Fords, many times it is the fuel pump itself, since it has a checkvalve in it. A stuck open injector will also cause bleed down as will a bad fuel pressure regulator. Unfortunately, your FPR is inside the fuel tank, a part of the fuel pump and sender unit. Replacing yours will be expensive, so rule out the fuel filter first.

You can drive that truck for a long time with a bad fuel pump checkvalve (most common cause of bleed down), simply prime the fuel system, as earlier described.

 

[ben10]

good call, I will start doing that and see if it helps, fuel filter has been replaced, no change, I am starting to lean more towards a tranny problem for the miss, the rough idle could still be a pressure regulator tho... damn my luck.

 

[cr_the_machinist]

Have you hooked up a scan tool to see if there are any pending trouble codes stored in the pcm?

 

[stiluv]

i have a good scan tool ben if we go wheelin sunday i will bring it

 

[ben10]

yeah its been scanned no codes or pending codes...

 

[ben10]

Ok so update on the issues, I took the exhaust off to build up a new one, just the cat back. With the louder exhaust I can tell its missing under acceleration, it only does it when its cold once it warms up it starts running fine, what would cause it to miss only when the engine isn't warmed up? And its still not throwing a code.

 

[92dangerrangerCO]

my truck used to have the same issue and used the MAF sensor cleaner from Napa which helped but also repalced the fuel filter and that helped for awhile but the item that set it straight was the PCV fliter. its a $2 part at autozone and its a simple unplg and plug back it but honestly replacing that filter has my 4.0L running dang near perfect and lost all rough idle at start up.

hope this helps you out.

 

[ben10]

hmmm havent changed the pcv Ill do that next.

doubt that will change the miss under acceleration tho...

 

[92dangerrangerCO]

it might like i said my ranger was having the same issues as you mentioned before and that happened to do the trick, best of luck

 

[ben10]

for sure thanks for the input. ill try to get to the parts shop tomorrow and pick one up. damn that would be a nice fix hahaha

 

[staker]

I have a 2000 ranger doing about the same thing. I was wondering if you tried to pcv valve and if it helped. i changed my tranny fluid and that seemed to help with the bucking going down the road but it still happens. My abs light is on so i'm wonding if i have a vacuum leak on the brake booster or something that might also cause it.