Please help with my misfire issue!

[macd7919]

Hi Guys, you may have seen my other thread regarding the lean codes I was getting. Well unfortunately as of last Saturday I now have worse issues.

A bit of background:

Truck is a 1997 Ranger 4.0L with manual transmission and 160k on the clock.

I've had a P0171/P1443 light on for awhile now but the truck has been running fine outside of the light being on and annoying, maybe slightly low mpg. Occasionally it would go off on it's own but is generally on 98% of the time. I have had a cracked filler neck on the fuel tank for awhile which needs to be fixed but in the meantime I had started to look into some of the EVAP components and found that the EVAP solenoid wasn't working. Replaced that and checked voltage range on the EVAP sensor and it was good. So I was driving the truck here and there to get some drive cycles in and this is how I got to my current issue as described below.

So it all started as I was accelerating to get on the highway, I noticed a couple hiccups that weren't normal but nothing too terrible. I kept on going just cruising along and truck seemed to be running a little rough but was able to keep highway speed without much issue. I got off on my exit, stopped at light and immediately noticed the truck was misfiring at low speed/rpm. Now the truck misfires and bucks pretty bad below roughly 3000rpm. For instance, if I put the truck in 2nd gear and accelerate (slowly or quickly) from say 1000rpm the whole truck bucks and hiccups until about 3000rpm. Once it hits 3000 rpm it seems to clear up quite a bit. It doesn't completely go away above 3000rpm but maybe 75% better or so.

So long story short: Basically any type of load below 3000 rpm and the truck bucks and misfires. I have also noticed the smell of fuel from the exhaust after driving around the block. Ironically the check engine light HAS GONE OFF since all of this started happening

PRIOR to this misfire problem, say in the last 6 months, I have replaced:

MAF
Autolite Double Platinum Plugs gapped to approx .050 (With what looks like recent 8mm plug wires by previous owner) have approx 5k on them now if even that much.
DPFE Sensor
PCV Valve
Numerous vacuum lines
Cleaned throttle plate
Checked Intake manifold bolts
Replaced EVAP Purge Solenoid and all related vacuum lines
Tested EVAP sensor, tested good

SINCE THIS ISSUE STARTED in the last few days I have replaced/checked:

New Fuel Filter (old one didn't seem to be ancient and wasn't the original so it's been changed at some point).
Tested Coil Pack (Came out within range on primary and secondary and very close to resistance I tested on a brand new one at the auto parts store)
Cleaned MAF
Checked all the outputs on the coil for spark
Pulled plug wires one at a time while truck was running to see if there was a change, seemed about the same across the board no matter which plug I pulled)
Tested for intake manifold leaks with damn near a full bottle of brake clean (no idle changes)
Pulled a couple plugs to see what they looked like. Gap was fine, slight reddish hue to electrode (not porcelain).

From here I guess pulling the injectors? Truck has been running great (even though the check engine was on) then BAM! Running like crap and misfiring (especially at low rpm and load). On top of it all ironically the day after it started this misfiring stuff the check engine went off and hasn't come back on, WTH! So anyways, there has to be someone out there who's experienced this issue. I've googled and read a million different threads but they either never get resolved with the answer posted or they are something I've already tried. Hoping someone here at TRS can help me out before I go nuts messing with this thing. Thanks in advance for any help!

 

[RonD]

Reads like you are chasing a ghost in the system.

Maybe the computer is the issue.
I would pull it out and look at the connectors and pins.
Then open it up and look for burned parts.

 

[macd7919]

I'll take a look at the ecu, anyone else have any suggestions? Seen lots of views but no one has had similar issues?

Fwiw I crawled up under and found the crack in the filler neck hose. It's about 1/2-3/4" long stemming out from the clamp on the fuel tank. Doesn't seem like a very large crack but def leaks fuel. Started the truck up today and was missing at idle, had a funny smell in the exhaust, almost a plastic-y rich smell. Anyways, hopefully someone can identify with these symptoms and chime in.

 

[RonD]

I think that is because you have checked or replace most of the externals that can cause your symptoms.

Sensors only report data to the ECU, ECU is the ultimate end point that uses that data, a bad sensor would report bad data so swapping it out or cleaning it would correct the problem.
But if the MAF, for example, is reporting good data but ECU is misreading it then bad MAF would be the symptom but not the cause.
An O2 sensor doesn't control lean or rich, the ECU controls that, based on O2 sensor data.
The IAC valve doesn't set the idle the ECU doesn't that.

Wiring between a sensor and the ECU could also be the issue.

 

[HAPPY+RANGER+GUY]

check grounds

Wiring between a sensor and the ECU could also be the issue.

Take the grounds off the grounding studs and clean them all up, especially ones related to the ECU.

You could pull the ECU out and slam it on the deck a couple of times....hehe (worked for us on Navy aircraft!)

 

[HAPPY+RANGER+GUY]

Egr?

What about an issue with the EGR valve? I saw the DPFE was changed but the other parts of that system are okay?

 

[HAPPY+RANGER+GUY]

Ironically the check engine light HAS GONE OFF since all of this started happening...

Are you sure the bulb didn't give up the ghost and burn out?

 

[HAPPY+RANGER+GUY]

Tested Coil Pack (Came out within range on primary and secondary and very close to resistance I tested on a brand new one at the auto parts store)

Keep in mind also...just because a part tests good, doesn't mean it can't be the source of the problem under actual operating conditions. Many times when we test components we're only testing a portion of the device for a few desired parameters. In other words, our testing many times is lacking either due to lack of knowledge or lack of more complex (and more expensive) testing equipment.

I'm not saying the coil pack is bad.

 

[Earl43P]

I'm also going to recommend looking at EGR.

Simply remove the vacuum hose from the EGR valve itself and go for a drive / couple days.

I have personally seen DPFE go bad with no CEL and steady speed bucking. Look also into the the two silicone hoses TO the DPFE. They can develop cracks. They could also have been attached to the wrong ports, one is Signal, the other is Reference. The nipples are different sizes.

I've also seen EGR valves stick partway open / never fully close. On Fords, you can exercize the valve full throw by attaching vacuum straight to it and start the engine (or use a MightyVac). When its open, spray carb/choke cleaner onto the shaft in an effort to clean off the crud that can build up.

http://www.tomco-inc.com/Tech_Tips/ttt36.pdf
http://www.tomco-inc.com/Tech_Tips/ttt33.pdf

 

[macd7919]

Update:

Problem solved, though there were no check engine lights from the misfire I pulled the plugs again and took a close look at them (originally I had just pulled a couple as I had time before dark). Apparently the plug in cylinder 3 was defective and showing markings in a few spots on the porcelain around the electrode, replaced that single plug and truck ran perfect. Since then all plugs have been replaced with Motorcraft Platinum.

FWIW the plugs used originally (4k ago) were Autolite Double Platinums gapped to .052. From the way the truck runs now it makes me wonder if there wasn't an issue from the get-go but hard to say as at that point in time the truck was new to me (purchased with roughly 155k on it) and had an intermittent check engine light so I had begun by replacing the basics just as a tune up and also so I would know for myself when the "consumables" had last been done. It's fully possible that the truck had been running slightly rough since that point but as it was "new to me" I didn't realize it was this way until there was a noticeable misfire under load. In the meantime I had replaced a considerable amount of parts for maintenance as listed in the original post chasing down the check engine light which has also seem to have been solved (Plugged EVAP Solenoid).

Either way, I'm happy to say the truck is running better and smoother than it ever has (knock on wood).

 

[HAPPY+RANGER+GUY]

Those darn new parts aren't suppose to be the problem!!! LOL.

Good detective work to double back and take another look.

Kudos.