I have a 1998 Ranger with approximately 130,000 miles on it with the 4.0 in it backed by the automatic transmission. I've had rough running problems with the truck for a couple years now and have been throwing money at it trying to keep it on the road and one thing after another has fixed the surging/ bucking problem for a couple months at a time. Recently the problem has gotten quite bad. At steady throttle and low RPM's the truck surges violently, if I get it to downshift it is not as violent but still very rough running. I've tried bringing it to my local Ford dealer a couple months ago and they couldn't find anything wrong with it. I'm out of ideas on what could be causing this problem any help would be GREATLY appreciated! The truck threw a CEL two days ago. I read it today and all it told me was cylinder 6 misfire which tells me nothing. Below is a list of new parts I have done to try and correct this problem.

Idle Air Controller

DPFE Sensor & hoses going to the sensor

Fuel Filter

Plugs (Almost two years ago)

Wires

Injectors on cylinders 4 and 6

Upper intake plenum gaskets

Bench tested the coil

Pulled vacume on the EGR valve and the engine responded by almost stalling

I disconnected the vacume hose on top of the EGR valve today and it didn't help anything.

I've also unplugged the MAF sensor while it was running and again the truck responds with rough running symptoms also the MAF responds on a scan tool when the truck is running which tells me it's not MAF.

Again any help at all on this subject would be very appreciated
Thanks

 

When the upper was done was it just the o ring type gaskets replaced? Or was it the leaky lower manifold to head gaskets?

 

Sounds like you got DTC P0306. Was that the only one?

Things that I would do:

*The very next time it does it, I'd stop, pull the #6 plug wire and check for spark. By doing this you will rule out one of two systems, fuel system or ignition system. This will greatly help with troubleshooting. I'll assume that there is no danger of a crack in the plug insulator and no damage to the boot on the plug wire, as well as no damage of any kind on this wire between the plug and coil pack.

Depending on the outcome of the above, a few things I'd consider looking into:

* Carefully inspect the coil pack for hairline cracks which may result in leakage/arcing. Be uber **** in the inspection, the crack, if it exists, need not be wide and long. Usually when this is happening and for a prolonged period of time, there will be visible carbon tracking. Also, moisture often encourages arcing/leakage along the crack.

* Scrutinize the quality of all electrical connections leaving no stone unturned, including the grounding, for injector #6.

On edit:

*Keep in mind that sometimes a brand new part is a bad part, it's not often but it really does happen. Just keep this idea in your back pocket.

 

I have only replaced the o-ring type gaskets when I replaced the two injectors the Ford dealer told me to replace (which didn't help anything). I have however, sprayed starting fluid all around the top of the engine in search for a vacume leak without a single jump in RPM

The cylinder 6 misfire is the only code I've gotten recently. The truck rarely throws codes and when it does they are usually misfires on different cylinders. A couple months ago it threw a random EGR/ Vacume leak code (sorry for not knowing the DTC numbers) that was cleared on accident and never returned. I will inspect the coil once more and also check for spark next time I drive it and post what I find out.
Thanks for the replys!

 

Hang on, did you last discover P0306 or are you/have you sometimes getting/got P0300? The answer to this may affect which direction to take to fix the problem. P0306 will direct attention to #6 and possible causes for this specific cyl to mis; P0300, the random misfire brings up other things. P0300 has been associated with vac leaks, including lower intake and the PCV system, like, hoses.

Back in 94, the scheduled PCV valve replacement was at 60K, then down the road it got uped to 100K; I can't remember what year. Have you ever replaced the PCV valve?

 

The last code I read yesterday was P0306. "Cylinder 6 misfire" which I have gotten before along with codes such as P0304 but I dont remember exactly which cylinders as the truck has had problems for a couple years now.I have not however, gotten the P0300 code. It has always been a specified cylinder misfire.I have checked all the hoses that I know of but I have never replaced the PCV valve but I will asap.

 

It just threw the same P0306 code so I'm thinkin theres something going on with that cylinder. I pulled the hose that runs from the PCV valve to the intake manifold and plugged the hole and it didn't seem to make a difference so I dont think it has a bad PCV valve

 

To test the PCV, shake it. It should rattle.

NOTE:
This Pinpoint Test Step is for engines that have damper-mounted pulse rings. Remove the front cover if necessary to observe the crank pulley.

l Observe the crank pulley for wobble.

l Examine the EI pulse ring fastened to the harmonic fastener.

l Does the crank pulley wobble or is the pulse ring loose or damaged?

 

Well I checked the PCV valve and it rattles like it should. I looked at the harmonic balancer and there was no wobble at all. And the pulse ring was solid also. I pulled the spark plug on cylinder 6 and it has great spark but the plug was very dry and a little white, so my guess is its running lean on that cylinder if it getting any fuel at all.
Any thoughts?

 

Injector?


FWIW, my ohv blew the lower intake gasket puking coolant about as fast as you could pour water out of a bottle. The gasket is weak at the water passage from the heads to the lower. After doing the gasket my truck idled better, even though i did not believe I had a vacuum leak. I also did the same on my moms expo last summer. Although it did not fix her no hot start issue.

 

Implement what I suggested in post #3, and ponder the rationale behind each bullet item.

On edit: I specifically brought up the notion of the PCV system in response to the possible random misfire DTC #P0300. I would not replace it if the misfire was isolated to one and only one cyl.