Hey guys,

I been chasin this one 3 weekends now and its caused me to stop drivin the truck to work. She's got 265k miles on her, with a five speed. Everything been replace and rebuilt at this point save for the transfer case and the engine itself. I live in California, but the truck came from Nevada and doesn't have an EGR.

Symptoms: when its hot, not warmed up, but hot like getting off the freeway or driving over a mountain. PO306, cylinder 6 misfire. I watch the total misfire count on my scanner app and determined it only happens at idle. In fact it'll stop when I throw the AC on and it loads the engine a little. If I let it idle and cool down it improves and idles better. You can smell it saturate the cat when its missin. Doesn't use dino squeezins or ice cube juice. No overheating. no smokey exhaust. No bad noises. Has plenty of power going down the road, just wants to roast my cat when I stop.

No other codes, just cylinder 6 misfire.

Fired the parts cannon at 'er:
Plugs, old ones were worn but came out clean, gapped new ones to .054
Wires,
coil pack,
New Injectors as they were a bit goopy lookin,
O2 sensor on that side (I did actually see the voltage flatline on this one at one point so I think it was on its way out)
while I was at the injectors I replaced the two sets of gaskets on either side of that crazy fuel rail they got in there
Cleaned the MAF
Ran seafoam down the intake, twice, didn't do anything.

When none of this worked I started runnin some other tests:
Don't see anything weird in fuel trims, always within 5%
smoke tested the intake system while hot, expected to find leaks everywhere, didn't find a single one.
23 on the ol' vacuum gauge, nice and steady. Builds a little when revved so I don't think the exhaust is plugged
Compression test reads around 130 psi, though when hot it takes a couple extra pumps to get there. Was the same for the other 2 cylinders on that side.
Leak down test was <10%
So what I'm gettin at is I don't think there's anything wrong with the cylinder, head, or valves.

So, basically somethin is gettin hot and gets unhappy. Question is what?

If it has a PCV valve, I don't know where it is. The hose that comes off the underside of the throttle body heads on down and over to an electric/vacuum operated plastic valve mounted below and behind the battery that I think is for the evap system maybe.

I haven't checked the crank or cam sensors, as that doesn't really make sense to me, but I could be wrong. I thought maybe this one has the camshaft synchronizer that can wear out, but when I had the upper intake off it I didn't see it stuck in the heads like I've seen in photos. Am I missing something?

Any other suggestions?

 

Do you FEEL the misfire?

I would swap #2 and #6 wires at coil pack to see if misfire changes to P0302
3/4
2/6
1/5
These 3 pairs fire at the same time on coil pack
But long shot since coil and wires are new

Only thing I can think of is #6 intake valve's Guide seal is leaking
At idle and higher vacuum, or when hot and thinner oil, #6 is sucking in a bit of oil fouling the firing every now and then
Not really any test for that
But should have been signs of that from old spark plug tip, a darker color

 

Hey Ron,

Thanks for the reply.
I can feel/hear/smell the misfire. It is most definitely misfiring. Idles like absolute garbage when its doing it. No surging like when they've got a bad vacuum leak, more like "chugging".
I have not tried swapping wires, at least not long enough to toss a code. But now that I think about it, if its got a timing thing going on maybe it'll follow the wire even with that waste spark system its got. I might give it a try tomorrow, will take a bit of time to get it to at least throw a pending code, gotta miss 500+ times I guess? I wish I could get cylinder specific misfire counts to work in the Torque app but I can only get a total...

no oil is getting into these cylinders, like at all. The plugs came out clean, albeit a bit worn not gonna lie. I even put a dual cam boroscope down it at one point, pretty much just saw some carbon buildup around the valves and on the head, this is why I was messin round with the seafoam. Nice cross hatching on the cylinders still though!

Do you know if this engine does or does not have a cam shaft synchronizer? Seems like it should, but I found a note somewhere else that mentioned they were really only on the California trucks with EGR. Not sure how true that is.

 

1995 to 2000 4.0l OHVs have a cam sensor on top of the synchronizer
Top rear of the engine
1999 should have a 2 wire cam sensor, earlier were 3 wire
Also have EGR system

1990-1994 4.0l OHV didn't have cam sensor or EGR system, unless Calif. Emissions required it

130psi is quite low, but probably just the gauge
150-160psi is expected
Since 3 cylinders tested at 130psi and only one misfire then it was the gauge reading low

 

It's on the block, not the heads.
https://www.therangerstation.com/tec...-synchronizer/

 

Ron,

Yes I agree it is probably my gauge, its not exactly new. In fact I've had it 25+ years so yeah. I was a mechanic way back, enginerd now. That's why I compared it across cylinders and made sure to include at least one that wasn't adjacent in case of head gasket issue between 5 and 6. Other side of the engine a little hard to access and work on, so too lazy to do all 6. Regarding the EGR valve, I'm 90% positive it doesn't have one, this is because not only have I looked and its not there, but I also had a reputable mechanic tell me it didn't have one when I was getting it smog tested. There's no tube for it or anything.

Mr Supercab, thanks for that. While that engine looks a bit older than mine (I see an aluminum plenum, mine is composite) I'll have a deeper look at it tomorrow.

 

Hey Guys,

Found that synchronizer, was buried under the intake more than I expected but its there.

So I swapped 6/2 and couldn't get it to throw a code pending or otherwise in time I had today. I think I'll try driving it to work tomorrow, sitting through traffic etc to try to get it to throw a code.

Three new observations today:
1) when we got to the top of my test hill, the wife who was with me noted she could smell burning oil. I didn't pick up on it but will take her word for it.
2) It ran like absolute garbage for about 5 minutes, like it had a dead cylinder, then it cleaned up and the miss became more intermittent.
3) after it cleaned up I discovered I could hold it at 3k, let it drop to idle and cause the cylinder to go dead again for 30s-1min. Here's a vid:


I noticed something a little funny with timing advance while I was doing this.

Bring RPM up, advance comes up to 23 degrees ish:
https://drive.google.com/file/d/1V2A...ew?usp=sharing
Let it drop to idle, advance drops but then comes back up around 20 ish while misfire is happening.
https://drive.google.com/file/d/1V5g...ew?usp=sharing
As idle cleans up, advance drops from 20ish to 10ish
https://drive.google.com/file/d/1V9D...ew?usp=sharing
Final idle with intermittent miss:
https://drive.google.com/file/d/1V9w...ew?usp=sharing

I suspect this isn't an issue but rather the confuser reacting to the miss and trying to bump up the idle.

Doesn't this kinda seem like a vacuum leak that's not showing with my smoke test or somethin?

 

I still like the leaking valve stem seal

Try this since you have a hill nearby
Go to top of the hill and when going down the other side shift into lower gear to use the engine as a "brake", this sends the vacuum in the intake sky high close to 30" +

At the bottom of the hill give it some gas and watch the tail pipe for a puff of smoke, meaning the cylinders had sucked in some oil from somewhere

Holding the engine at 3,000 then letting it drop to idle does the same thing in that when the throttle plate closes intake vacuum goes high until RPMs drop, so could explain the rough running after that for a short time

 

Ron,

Thanks for the reply. Lets think about the valve stem seals a bit. In my experience you tend to see smoking at cold startup when the vehicle has been sitting overnight or longer because the bad seal shrinks and lets oil down the stem. This is not something I'm seeing and believe me I've looked because I'm constantly checking for blown head gasket. I would also notice oil smoke at stop lights or after stop lights, haven't seen this. I do engine break down that hill in 3rd and haven't noticed any smoke, but I wasn't looking in particular since the road is rather curvy. Next time I'll have the wife look out for it.

Lets not forget I've not had any oil fouling on the plugs.

 

I think I have a theory.

So the intake manifold becomes part of the sealing surface of the valve covers yeah? Whose to say I don't have a vacuum leak right to the valve cover from the lower intake gasket? Being at the top of the head and away from oil passages, its not gonna get flooded with oil AND I WOULD NEVER SEE IT WITH A SMOKE TEST!

 

Just working on that in another thread, here: https://www.ranger-forums.com/2-9l-3...w-what-168652/
He has high negative pressure in the crankcase/valve covers with PCV system disconnected

He pulled the Breather hose off the air filter tube and sprayed ether in the hose(into the valve cover on that side), engine REVed instantly so not from getting it through PCV Valve on the other side of engine
Conclusion is lower intake gasket has a vacuum leak into the valve cover on that side, so wouldn't show up on a smoke test and wouldn't show up using propane or ?? on a running engine

 

I'm gonna drive it tomorrow, see if I can't finish off the 6/2 wire swap code test, cuz that'd disprove the theory. But if its still cylinder 6, or I don't get a code, its comin apart on saturday.

 

All,

The ECM this morning so graciously treated me to a pending code for P0306. Therefore it did not follow the wire swap. Turns out it needs to count 1500 misfires in one session to pop a code.

Also, I know my account says I'm in San Jose but I'm really in Boulder Creek now, need to update that. What this means is I cross over a mountain to get to work. I have blind spot mirrors that allow me to see my tires and by extension my tailpipe. If I had blue smoke after engine braking down the mountain it wasnt enough to see in my mirror. Therefore I don't expect there to be enough oil to foul combustion.

I feel like I've done a decent job at eliminating ignition, fuel, and compression issues from the equation, just leaving air. The more I think about it the more an undetected vacuum leak right at the head makes sense.

Not to mention when I did the injectors I noticed the studs through the fuel rail were finger tight. that's when I decided to do the smoke test after the injector replacement didn't solve the issue,, as I thought maybe the lower intake bolts might have rattled loose or something..

Will report back after lower intake and valve cover gaskets.

 

hi, im the one with the high neg crank case pressure. try this to see if you have any change, remove the oil fill cap and go for a drive, that kills the PCV system. I have a misfire on cyl 1 at low rpm and it goes away at about 2000rpm. basicly the intake port on cyl1 is leaking, sucking into the crank case. I'll be changing lower intake manifold gaskets soon hoping to fix my problem .
I'll be following your link, interesting hope you solve it.
doc

 

Hey guys,

So first I pulled the upper intake and valve covers. I then tried to smoke test by jamming my tester pipe and some shop towels in the #6 intake runner. Was pretty fruitless, couldn't see anything. I then proceeded to remove the lower intake. I wouldn't say the bolts were super tight, I was able to crack them loose with 1 hand using a 3/8 ratchet with an extension on it. They did crack though, and all seemed even.

Only thing I'm seeing so far is the #6 intake port seems to gave extra goop on it underneath the gasket towards the valley. Maybe that's my problem? Can't say there's anything obvious going on with the gasket. Pics included

Intake off overview

5-6 port comparison

#6 a little closer

 

I guess that could create a vacuum leak to the valley/crankcase/valve covers

 

I've been cleaning stuff up and another observation stood out to me. The lower and upper intakes are quite oily which I thought was blow by, but there's hardly any at all in the breather or PCV hoses. I think it's been pulling oil past that gasket thus collecting that gunk there in the photos, then the vacuum from the other cylinders distributing it through the rest of the intake. Getting spread between all cylinder might explain why I never saw any smoke. Drivers side valve cover is quite a bit dirtier on the underside than the passenger's side as well. Might be pulling gunk from around the pcv valve.

I had a good long look at the cam lobes as best I could and they all look about the same. So it's not like I've got one that's all scrubbed down from a bad roller or anything. If I had a dial indicator I might be inclined to measure the valve lift at the rockers. But I don't.

this isn't getting finished today since I decided to freshen up some other things as well and a couple of those other things needed to be ordered. But hopefully by the end of my 3 day weekend I'll be able to test drive it.

Happy Easter if that's your thing!

 

Sad to report, all this work did not fix it. Code still comes back.

I think I need a picoscope or something to rule out electrical issues at this point. I pulled the pcv out and plugged the port, sprayed carb clean into the valve cover and no change. So it doesn't seem to be pulling anything past the valve guide.

I will say it took more driving to get it to act up this time. But that might be a factor of having the battery disconnected for 3 days. And it might be arguably less severe in that at its worst today it didn't sound like a completely dead cylinder like it did before. But this wasn't wasn't brand new truck I was looking for. Too bad cuz it scoots down the road now with all this tune up work. Wants to run, it's spunky

The hotter it is under the hood the worse it idles. I can leave it running and just open the hood and let the heat out, within 5 minutes it'll get significantly better. Leads me to beleive maybe I have an electrical issue somewhere under the hood.

Also noticed this while I was changing the oil post intake reinstall, not sure if related... if I'm not mistaken that's part of the crank position sensor rubbing one side of the crank?

 

Yes, those are rubbing marks from the crank sensor holder, shouldn't do that but wouldn't effect operation, you can see the two plastic "teeth" that were rubbing in the picture, probably are not rubbing any more

The harmonic balancer rubber looks like its on its last leg

 

Good eye, didn't see that when I was in the moment. you don't suppose that's softening up when things are getting hot and letting the crank vibrate/move enough to contact that crank sensor do you? I'll probably pull the sensor off and see if its rubbed through anywhere.

I forgot to mention, and this may or may not be related, I noticed when I get in and out enough, opening and closing the door, I'll get a trouble code flashing for the airbags. 27. Interweb seems to indicate that means the passenger side "off" lamp is burned out, but it works. Some weeks ago I was working in that general area making an adjustment to my hurst shifter to eliminate vibration noises. The ECM is in there too. Maybe I'll pull the console off and have a poke about and see if I see anything, who knows maybe I caused a couple wires to rube through or knocked a connector loose. I doubt that's where my misfire issue is but...

I keep finding little things everywhere that remind me this is an old truck. My fan is on its last leg too with the plastic being pretty badly cracked. Add it to the list...

Edit: what I mean by "working in that area" I mean that I was struggling to get the console off without disassembling the shifter and undoing all the loctite I put on it to keep it from coming loose. So I was lifting the rear and pushing the front into that area a lot, until I added a little "clearance" on the console with a dremel to get it out.

Stew on things for a bit, I still have a loner vehicle for the week. Let me know if anything might come to mind. I'll go on a waiting list for a local shop renowned for diagnostics, but they're weeks out. If I have some harness issue or weird sensor issue they might be able to find it with their scope.

 

Hi, I would also replace PCV and remove the oil fill cap and spray carb cleaner on that side valve cover, doubt if there would be a change verify that, that side has no leaks either. Just an idea. Good Luck

 

Hey Guys, I'm back at it. Keeping the May 9 appointment but also still just gonna keep investigating. All a guy can do.

Docm, I did actually do that at the same time I was sprayin the driver's side, just didn't note it because nothin happened. PCV was replaced along with most rubber as I replaced lower intake gaskets. Basically gave it an intake "tuneup"

Ron, I pulled the driver's side valve cover and rockers. I expected to be able to grab the valve/spring and move them all around due to worn valve guides. That didn't really happen, I could feel a little "click" but its not visible movement. I did, however, put a straight edge across them where things got a little more interesting. So first I have to ask, where can I find information on the acceptable tolerances of the installed valve stem height (not spring height) and how that affects valve train geometry?

I ask this because, obviously, I found the height of my valve stems are rather all over the place. If I try to put my straight edge across all 6, I find it only touches the exhaust valve stems on 4 and 6. 5 is maybe .03" lower (I'm estimating, I couldn't find my feeler gauges), and all 3 intakes are easily 1/8" lower being no where near the straight edge. I imagine lifters can accommodate variations in installed valve stem height, or valve stem length, but how much? Could I be seeing worn valves or seats, raising the valves up to the point where when everything is hot and expanded that I'm starting to bottom a lifter before they close completely? Or maybe I've burned one...this wouldn't surprise me given how I've used the truck in the past year. I remember a particular hot day pulling my little RV trailer (1750lbs) across central valley it got hot enough that heat coming off the trans tunnel was painful on my throttle foot. Gauge said I wasn't overheating though... I did climb up the mountains towards Tahoe that day to visit someone up that way as well and it wasn't happy about it. Its also been known to ping on the steeper parts of highway 17 on my way home even running empty, which is why I usually put midgrade or premium in it.

What I'm trying to prove to myself is do I have an issue that may result in intermittent compression issues, such as a worn valve guide or worn valve seats, hence what I did above. Basically can I prove the heads need to come off without actually taking them off?

 

Interesting, so you checked by turning the motor over? what did the intakes read? I guess you could check what the stock cam lobe hight is? its hard for me the think this could make a misfire?
good observation !

 

docm,

This test was not to check the lift from the cam. I removed the rocker arms, thereby unloading the valves so they were all seated/sealed, and I put a straight edge across the top of all the valve stems (where the rockers push down on the valve). No turning of the engine etc was required. The estimated measurements I spoke of are top of one valve stem to the top of another valve stem, to try and understand how far the valves are receding into the head, which helps understand the wear of the valve at its sealing surface (edit: relative valve to valve, to try and find any that are different, which they all are in my case but I do not know how much difference is acceptable). Hope this helps.

 

yeah, ok got it, good idea. but you are looking for a misfire in #6, did you find odd or off in cyl 6?