miss on dodge 5.9l gas engine

[Haveblue]

A busy day today, and I was frustrated late this afternoon to diagnose a problem on a 98 Dodge truck with a 5.9 gas engine. The truck came in as a no-start. With a P0320..no signal from crank sensor.. But still showed RPM. The customer said it ran fine...untill it died. I replaced the cap, rotor, and plugs, because they were obviously junk. I had weak spark from the coil,and than no spark. after replacing the coil, It now starts, but the Modis is showing a miss on #6 and intermittent on #4. Its an obvious miss at idle. Im aware of the crossfire issue, and have re-routed the wires.. im also aware of the intake issues. The trottle body and intake were pretty oil contaminated, but I cleaned them, to no avail. IAC count is at 45, and LTF trim is at around -15. I welcome any advice! : MODS feel free to move this, I screwed up, and posted in the wrong thread.

 

[devoncoolman]

Check the injectors ive chased misses on those before. And they are known for intake leaks.

 

[Murphy4570]

You replaced plugs, cap, and rotor, but not plug wires? Why not sell a full tune-up to start? That's what I usually do.

If ignition system is working, start chasing down either intake leaks or fuel issues. Spark, air, fuel. Not much to it, really.

A good way to check injectors leaking is to put a fuel pressure gauge on it, see if it holds pressure when it is not running. Fast leak down? Bad injector(s) or leaking fuel pressure regulator (if return-style system). Easy way to verify if injector or FPR if pressure is leaking down, is swap injectors, see if miss follows the injector.

You can also hook an evap smoke machine to the intake, see if there's a vacuum leak. Or use carb cleaner around intake gaskets and listen for change in RPM at idle.

 

[619DioFan]

sounds like the intake lower plate gasket is leaking ( .ie - oil inside the intake ) common on 2nd gen 5.9. replace with the hughes kit - prob solved

 

[Haveblue]

Fuel pressure is good, with no leakdown. fpr seems fine. Carb cleaner method shows no results. We have a smoke machine I have not tried yet. I threw a good plug wire on #6 with the same results. Its pretty oily in the intake, and a few plugs were oil fouled when I pulled them. I hate it when the customer says, "it was running great till it qiut" I call B.S. I think I have an intake leak on the right bank. Ive seen it before on these, but it has been more obvious, and not quite the same. Ive never seen an intake leak set a P0320..

 

[OHMS LAW]

Have you checked map. If your ltft is that out of whack you are super rich if its taking that much fuel

 

[Haveblue]

Map shows about 19 inches of vacuum at idle,I forget the voltage, This is what puzzles me, why would the pcm be leaning out the mix, if it was a vacuum leak? Btw The miss is at open, and closed loop.

 

[OHMS LAW]

Pull up the live data graph mode and look at o2 map, Iat , tps. I'd also say put the scop on and look at crank pulse and cam just to be sure

 

[diesel research]

Whether the intake leak is the cause of the problem or not, doesnt really matter, since it still exists and needs to be repaired either way.

Looking in the throttle body was the first clue, but if you still dont believe the obvious info in front of you, you can attach a vacuum gauge to the breather hose that leads to air filter box. Disconnect pcv hose from intake. Plug intake and and pcv hose.

Normal blowby gases would build up causing positive pressure readings on vacuum-pressure gauge. A crankcase side intake leak will show a slight vacuum since the floor of the intake would be sucking the crankcase vapors and putting crankcase under vacuum. Vacuum bad, slight positive pressure good. (more than 3psi risks blowing out several weak gaskets)

 

[Murphy4570]

diesel research, that's a really smart way to figure out an internal intake leak! I'm gonna keep that trick in mind from now on.

 

[diesel research]

fortunately, save for an extremely rare crack, most [other non dodge ram/dakota/B-van 92-03 or so] makes/models would not likely have a internal intake leak (unless the bottom side of the intake manifold gasket was leaking)

In the case of this make/model, its not a manifold gasket. It is the plenum floor gasket that is leaking. (exposing all cylinders to false air, but fouled plugs nearest point of vapor entry)

 

[Haveblue]

Ive seen a lot of them that have cracks between the valve seats. Seems like the 5.9l has a few issues.

 

[MattPersman]

I am with diesel research on this check your Pcv system for intake pan leak.

 

[Haveblue]

Thanks for the tips guys! I did what diesel research suggested, and Ive got 8" vacuum in the crankcase.

 

[Alta_Racer]

Everything sounds correct about the intake leak, and it may very well be the problem.

If it is repaired, and still has the miss, be aware the fuel rails on those engines like to flake inside, plugging up the injectors. Most of the **** tends to end up on cylinders 6&8, farthest from the fuel inlet. All cylinders on that bank are prone to collecting this ****. We know that unless it has had a fuel pump recently, the filter is very old, being it is on the bottom of the pump, inside the tank.

 

[diesel research]

In a high production shop, you cant sell the correct fix (new ALUMINUM thick cover pan) so you need to make sure the gasket is an upgraded reinforced style and that the flanges are 100% flat and clean.

The astute reader might figure out the vacuum gauge isnt absolutely mission critical, as a piece of paper over the pcv inlet hose tells the same story (less numerically) as does a thumb over hose. I am a numbers guy myself, and love gauges.

For smaller shops capable of selling unique services, the injector screens can be replaced for $2/pc, and simply remove by inserting sheet metal screw into screen basket and pulling. This is essentially an "injector rebuild" minus the cleaning/flow rate matching/ohm checking. Mean the basket, o ring, and pintle cup are only parts replaced. Would not call it a "rebuild", but some small shops may find a way of selling this rather universal service "while they are in there".

The filter is NOT inside the tank. It is on TOP of the tank, and typically runs about $100.

 

[Haveblue]

I didnt have much time to work on it today other than to run the crankcase vacuum test. (for once the customer is not needing it back right away) I found out today his hired hand normally drives it, and was at the time it died..so his claim "it ran fine untill it died is not believable" I put a clutch in it a couple of years ago, and it ran fine then, but havent worked on it since. Regardless, im glad to at least verify a problem, now I have a place to start, and can prove it. Ive never scoped a ckp, but I will do it as well, just to be sure. Im usually the guy they ask to do injectors..we have this at work. I OHM,flow test, leak test, Clean and re flowtest, and replace all o-rings and baskets. If im gonna fix an intake leak, you can bet your *** im gonna do that too!!

 

[Squankum]

I have uttered the incantations and casted the bones and using my special Squankum powers, I am bringing this thread back from the dead!

Haveblue, whatever happened in this case? I know it was 413 customer cars ago, but..

I’m in a similar pickle.

2000 Durango 5.9L
290K mi – fear not! It is a very happy motor. Starts right up, BAROOM, runs all day, 30K mi/yr, clean inside, Mobil1 for the past 90K mi, regular changes before that.


Symptoms:

1) Very subtle miss at idle. Very.

2) No miss anywhere else. New plugs, C&R, fresh enough plug wires. Smooth power everywhere else.

3) Threw a code, P0420, catalytic converter efficiency. When, I’m not sure, as the light is always on for another, silly problem.

4) A little black soot in the tailpipe

5) But starts like a champ and drives happily, idles steady, too.

6) I opened the throttle plates and got a big whiff of gas. I didn’t see a lake of motor oil, but it wasn’t dry. I put a bit of paper towel on forceps and gave it a wipe, and it just smelled like gas. Dipstick shows oil is darkening and stinky, too. Must fix soon!

7) I put the vacuum gauge on it as the esteemed Herr Doktor Professor Diesel Research prescribed above, and got this: 18” steady vacuum from the intake manifold at idle, 12” vacuum from the breather. Ha! No wonder this engine doesn't leak! Why would it?!

8) Oil consumption? Nothing that bothers me. Some, but not dramatic or anything.

9) Put my new, wacky Waekon injector tester (fancy electronic stethoscope, really) and all the injectors seem to be, well, firing rhythmically, so there’s no total deadness going on there, I guess. (BTW, I’m a Bosch CIS caveman, and your new “electronic” injection frightens me.)

That’s about where I stopped. Before I worry too much about injectors or something, I suspect I should fix this.

Question 1: So, time for the Hughes plenum fix kit, right?

Question 2: I was tempted to remove the injectors from their harness and check for Ohms… and the retention clips look, well, 14 years and 290K mi old and brittle and some look damaged from some other mechanic in the past.

I didn’t take over as high level shadetree crew chief until the 200K mark, but it’s one owner with a decent, if jumbled, paper trail.) So, is there a way to replace the plastic retainer clips without doing a whole harness or something?

Thanks in advance,
Squankum

 

[Haveblue]

The customer in that situation decided to get rid of the truck. With 290k on the clock I'd be very suspect of the heads...the exhaust seats sink to the point they cannot be reground and the heads are prone to cracking. I've personally seen this on three 180k- 200K trucks. Before you tear into it, run a compression test on all cylinders. Do it several times on each cylinder and document the results, because rotation of valves can give you readings that fluctuate. Also do a leakdown test on all cylinders.. I would also bet that if you pull the throttle body you will see a good amount of oil inside the rear of the intake manifold. I forgot to add that most parts stores will probably have "pigtails" and o-rings for the injectors. I like to use picks to get the connectors apart. I think I need someone to show me how to paragraph LOL! I still haven't figured it out!

 

[Haveblue]

Another thought...Get any suspect cylinder at tdc compression stroke and apply air to it with a compression tester hose with the schrader valve removed(90 to 150 psi) If you loosen the rocker arm on the exhaust valve, and the engine turns a bit..you know the seat is toast. The rocker arms are a pedestal mount type, and after that many miles the lifter wont take up the slack.

 

[Squankum]

Oh man... yer bummin' me out...

Would exhaust valve seat recession lead to positive crankcase pressure? If it recedes and the lifter can no longer adjust, isn't that going to cause a loss of power? (Hmmm... and unhappiness for the cat.)

A cylinder head crack, if it let exhaust gas throught it to the rocker/valve cover area?

It's late and my brain hurts.

I can easily do a compression test on this next time the vehicle's back home, and heck, now that I have compressed air, a leakdown test. Hoo boy, another tool to buy!

 

[Haveblue]

Would exhaust valve seat recession lead to positive crankcase pressure? no, the exhaust valve will not seal, and will blow it out the exhaust, could be why the cat is unhappy..incomplete combustion. I just thought of another simple trick... hold a dollar bill, or stiff piece of paper over the end of the exhaust pipe with the engine idling...it should blow somewhat steadily outward. If the pipe intermittently ***** the dollar bill in, you have a valve (valves) That are not sealing.

 

[Haveblue]

how do the plugs look?

 

[Squankum]

Changed plugs a few weeks ago, 25K mi on them, looked normal to me. I didn't break out the magnifying glass or anything, but they were were just somewhat worn.

Cheap Champion coppers.

 

[Squankum]

Brief update, more data later.

Did the flutter test last week with a sheet of thin paper. Oh yeah, it's not just a miss, it's a ****-back. I can't say it happens on every eighth cylinder downstroke, it's more like very two or three seconds.

Also, did a compression test. Great readings! On six cylinders. Two are off. I didn't squirt oil or go any further, I ran out of time and mental focus and I was too bummed.

I'll have numbers later. And will be doing much more testing this weekend.

 

[Squankum]

Also, I've been pondering burnt valves now, thanks to you, HaveBlue.

What's the band aid for such a situation? Does Dorman sell a shorter pushrod in a HELP! blister pack? (Joking... slightly.)

Would an adjustable roller rocker, Qty 1, be a crutch?

I'm looking at some kind of new/new-used motor, eh? Or, heads. The price of reman heads shocked me.

 

[bimmer630]

I am fixing a miss on a dodge Durango, also with a magnum small block, and in reading around the forums about it, I saw some guys discussing worn out distributors, which were causing the rotor to spin in an eccentric motion.

My misfire actually ended up being a stuck lifter (which is also making a noise)

 

[Squankum]

How did the lifter stick? Collapsed? Some other position? Which valve?

Trying to learn here... I've spend decades in a world with a much simpler valvetrain ... not that these aren't simple, but I'm talking SIMPLE... and need to learn how the failures lead to the symptoms.

Have you fixed? Did you install a different plenum pan at the same time?

 

[bimmer630]

I still haven't gotten around to fixing the thing.. but Im just GUESSING that the lifter tick on cylinder #4 has to have something to do with the misfire code on cyl#4. I put an injector, cap, and rotor on it (wires look almost new and I tried swapping that cylinder with another, and the miss stayed on 4)

 

[Squankum]

Here are the compression readings from last weekend, warmed up motor.

<firewall>
#8 185 #7 185
#6 160 #5 160
#4 180 #3 190
#2 180 #1 190
<fan>

I'm guessing for now that 5 & 6 have exhaust valve seat issues and #1 has a li'l carbon.

 

[Haveblue]

Run it again, hold rpms at about 2500 for a couple of minutes.. and then redo the compression test..or it may be a waste of time, if you can do a leakdown test. Those valves and seats will wear in to a point that can be inconclusive with a compression test alone. I may be full of bull, but my theory is the valves find a "comfy" spot they like to settle to on the seat, and don't rotate until higher rpm. That is why the miss can be intermittent. A leakdown test will reveal all!

 

[Squankum]

I wouldn't call the miss intermittent, it's just very subtle. The engine has a very small shake at idle. All other speeds, feels good.

I'll do one more compression test when it gets back home this weekend, since it will have travelled hundreds of miles by that point, then I'll do a leakdown test.

 

[Squankum]

Say, if I loosen a rocker arm nut for a test, is it reusable? Is it a locknut or just a nut?

 

[Haveblue]

The rocker arms are pedestal mount..they use bolts for mounting, and the hydraulic lifters take up the slack. This type of valvetrain is non-adjustable. But yes, you can reuse the bolts.