5.9 Misfires on 4 cylinders

[catch_kc]

Hello all, first time post on this forum, so thank you for having me.

Well, as the title says, I have multiple misfire codes on my 2001 5.9 magnum that I just bought. The code scanner reads P0300, P0301, P0302, P0303, P0304, and P0305.

I bought this truck for cheap with 160k miles and the seller told me the head gasket was blown... however, no coolant in the oil and vice versa. Also, no smoke or condensation from the exhaust. The truck does run and idles pretty smooth, but revs and drives rough. It doesnt overheat either or seem to consume coolant (ran it at idle for about 30-40 mins while searching for vacuum leaks and temps stayed aroind 215-ish.).

I pulled the spark plugs and they all looked like it's running rich.... except cylinder 3... that plug was melted. So I replaced all plugs (with Champion Copper plugs) and verified plug wires were going to the correct cylinders from the distrubuter.

I then restarted and still had the misfire codes minus the P0305. So now I only have the front 4 cylinders misfiring (1-4)... I'm kind of at a loss.

I have searched for this issue on this forum and havent found anything thats similar to this. I've also read through the plenum posts... but I'm not sure if this applies or not.

So any input is greatly appreciated. I love the truck, I just want to enjoy it. I'll be testing the compression tomorrow, so I'll post those results.

Thanks for your help in advance.

 

[Yeret]

That's a pretty ugly set of misfires! I had very similar issues a few years back when my plenum gasket was shot. Replacing the plugs temporarily resolved the issue but multiple cylinders would inevitably start misfiring one by one after a month or two. I had the plenum gasket replaced but I also replaced the heads as they each had multiple cracks (common problem).

If a head gasket is blown and coolant isn't mixing with oil, the gasket is likely blown between two (or more) cylinders and this will cause a heavy compression loss which can result in misfiring. A simple compression test will verify pressure loss (although the cause of which can be many things). As a general rule of thumb, you're looking for no more than a 10% difference between the weakest cylinder and the strongest cylinder.

215 is a bit high. OEM operating temperature is 195. Anything beyond that and you're inviting spark knock. Contrary to what some say, 195 is not too hot and isn't going to create spark knock on it's own but 215 may make the fuel/air mix too volatile and could result in knocking. Generally speaking, in our engines if you've got spark knock, it's because of carbon buildup, likely from burning oil, on the pistons and combustion chambers. This buildup holds heat and creates "hot spots" which will cause pockets of fuel/air mixture to combust under compression and result in multiple flame fronts which collide with each other and creates the signature rattling sound and can result in engine damage if you try to push it while it is happening. After doing the plenum gasket and replacing the heads, I've not heard one bit of spark knock even when running 87. I now run 91 with my tune and everything is still good.

In regards to spark plugs, there is some discrepancy between the Champions that our engines use. OEM calls for RC12YC, however the local O'Reilly's down here sells RC12LC4 and there is an RC12LYC that can be used. What the difference is between these, I'm not really sure, other than the LYC having a longer reach than the YC. I know nothing about the LC4. What difference these styles would make I'll leave that to someone with more knowledge on the matter. Me, personally, I'm using NGK BKR6E as recommended by Ryan for my tune. Absolutely DO NOT use platinum or iridium plugs with the factory ignition. These have too much resistance and will almost certainly result in misfiring, which nearly everyone who uses these plugs report. You can use these plugs if you switch to an aftermarket, high-voltage ignition coil but there are apparent issues with using those. But that's a whole different can of worms...

I'm approaching TL;DR territory here so hopefully you got something from all this, LOL.

 

[catch_kc]

Hey Yeret, Thank you for your reply, very informative.

I just drove the truck to a reputable shop on my side of town to do the compression testing and diagnostic for me. Hopefully they can point me in the right direction. I'll be sure to post their findings.

As for the temp being around 215... the middle of the gauge is 210... the needle sits slightly to the right of that at around 215. I would've thought that 215 was normal, but I'll take a look at the cooling system as well if the operating temp is supposed to be closer to 195. Thanks for that info.

As for the spark plugs, the previous owner had some Bosch platinum 4 electrode plugs in there. The Champion Copper Plus spark plugs I replaced them with are the RC12LC4... so is that a no-no or will they be fine? The engine is stock as far as I can tell.

Lastly, I forgot to mention this in my original post, but the engine makes a high pitch whistling noise until it reaches operating temp... then it stops doing it. It's pretty damn loud. Thoughts on that?

Thanks again for your reply, I really appreciate the input and information.

 

[catch_kc]

Welp... its a blown head gasket. I'll be picking the truck up tomorrow and start tearing it apart. The mechanic DID find coolant in the cylinders. He also thinks the heads are warped. I'd really expect to have more codes than just a misfire.

Anyway, with that said, what should I expect? Cracked heads? Possibly decking the heads if warped? Are they even worth decking or just replacing?

 

[Yeret]

Factory heads are notorious for cracking between the valve seats so it's generally not worth spending money on them. Look around eBay for a set of heads that have thicker castings. You can get a pair assembled for $500-600.

 

[catch_kc]

Factory heads are notorious for cracking between the valve seats so it's generally not worth spending money on them. Look around eBay for a set of heads that have thicker castings. You can get a pair assembled for $500-600.

Gotcha. Thanks for the heads up. I'm going to send the heads to a machine shop to have them checked out and replace them if need be.

As of now, I've ordered an entire head gasket kit (with valve cover gaskets, intake/exhaust gaskets, etc...), new head bolts, new plenum bolts, plenum gaskets, aluminum plenum plate, and new fuel injector O-rings. Have I missed anything?

One more thing... Should I swap out the water pump and thermostat while everything is accessible? Or should I wait to see if the head gasket fixes my higher engine temps?

 

[dapepper9]

If you haven't torn anything apart yet, were you upfront with the mechanic about you doing the headgasket job BEFORE he did the test? I would self verify with your own comp test, you can rent the tool from a parts store and get your money back when you return it. If you haven't changed cap rotor and wires it would really suck to do all this work just find out something cheap was the issue.

 

[catch_kc]

If you haven't torn anything apart yet, were you upfront with the mechanic about you doing the headgasket job BEFORE he did the test? I would self verify with your own comp test, you can rent the tool from a parts store and get your money back when you return it. If you haven't changed cap rotor and wires it would really suck to do all this work just find out something cheap was the issue.

That's true. Trust NO ONE! lol. But I've been meaning to pick up a compression gauge anyway...

The mechanic said that he had all plugs pulled and coolant squirted out of a couple of the cylinders while he was testing a different cylinder. It would be easy to duplicate that and see it for myself.

Thanks for the idea.

Any suggestion to the loud ass whistling noise the engine makes prior to getting to operating temp?

 

[catch_kc]

So I pulled the engine apart today to replace the head gaskets and noticed number 3 piston detonation. That was the same cylinder with the burned up spark plugs. Also, the head gaskets looked fine. Leads me to believe that the block may be cracked.

So with 163K miles, my options are this:

Send block/heads to machine shop to see if they're salvageable... and rebuild the original engine. I have no clue how much that could add up to.

Or... buy a used motor with 145k miles and 3 month warranty for $1k.

Thoughts?

 

[SYKRAMMAN]

You can find engines with less mileage then that one for the same or cheaper, just keep searching. If you do end up buying that engine then at least pop off the v covers and oil pan and have a look at the internals before purchase. Trust me, I bought a used 100,000 mile engine and the guy said “she runs great” yeah ok, got it home, set it up on my run stand and it was rappin worse then will Smith. So it went back. Couple weeks later I found one that was in good shape.

 

[catch_kc]

Thanks for the advice Skyramman.

I'm in Las Vegas and finding these Z code 5.9 motors is proving more difficult than I imagined. So hopefully this motor isnt beat to **** when I go take a look at it.

I'll be sure to keep everyone posted. Thanks for all the help guys.

 

[dodge dude94]

I personally would just drop the cash on new heads due to this reasoning: 95% of used magnum engines are going to have head problems. Just a fact of life. SO, $600 for heads on this one wouldn't be an awful loss if you end up having to toss the whole engine out later. Just swap the heads.


I personally think it's a head issue as these bottom ends are fairly stout and rarely wear the rings or anything else out unless it's past 250k mi.

 

[catch_kc]

I personally would just drop the cash on new heads due to this reasoning: 95% of used magnum engines are going to have head problems. Just a fact of life. SO, $600 for heads on this one wouldn't be an awful loss if you end up having to toss the whole engine out later. Just swap the heads.


I personally think it's a head issue as these bottom ends are fairly stout and rarely wear the rings or anything else out unless it's past 250k mi.

It's not just new heads that's needed... Here are some pics of cylinder 3 piston detonation....



Here is the left head... with a close up of cylinder 3.



As you can see, the heads, the piston, and the cylinder itself is wrecked. I MIGHT be able to get the machine shop to machine the block and heads... or just replace the heads... but I'm not sure how cost effective that's going to be vs. buying a used 5.9 with warranty for $1k.

 

[catch_kc]

There's also a little on cylinder 2.... notice the bottom of the piston.



Right head, with close up of cylinder 2....



So I'm not sure that machining these things are even possible... or worth the $$.

 

[Yeret]

Oh boy, that sucks. Fixing the heads is probably going to cost as much as just buying a new set fully assembled with improved castings.

Definitely looking at machining the block as well as new pistons. If you're on a budget, you're probably better off just looking around for a low-mile used engine. Before you even drop the engine in, do the plenum repair as you will never have a better and easier opportunity to do so. Also, a good time to do the cap, rotor and wires as they can be...tricky when the engine is installed. Hell, it's a good time to replace as much stuff as possible because engine parts are 10x easier to install when the engine is out.

 

[catch_kc]

Oh boy, that sucks. Fixing the heads is probably going to cost as much as just buying a new set fully assembled with improved castings.

Definitely looking at machining the block as well as new pistons. If you're on a budget, you're probably better off just looking around for a low-mile used engine. Before you even drop the engine in, do the plenum repair as you will never have a better and easier opportunity to do so. Also, a good time to do the cap, rotor and wires as they can be...tricky when the engine is installed. Hell, it's a good time to replace as much stuff as possible because engine parts are 10x easier to install when the engine is out.

Yeah, that's true. I plan on pulling this motor and buying a low mileage motor to put in its place. Now I just have to source one locally.

I've already ordered the beefy plenum plate and gasket kit, so I'll definitely swap those out on the new motor prior to install... as well as the cap/rotor/wires (good idea, thanks).

As for the beat up motor that's in there now... I figure I'll pull it out, tear it down, and send the block to a shop to see if they can machine it... if not, then I might pick up a new block and start building a badass 360/408 motor as the funds permits. Who knows, when it's all said and done, I might have a kickass fully built motor to throw into a classic mid-40's Dodge Pickup that I've been dreaming about for the last 10 years.

 

[dodge dude94]

OOOOOOOOO THE PLOT THICKENS.

Yeah, she's toast. You could save the bare block, pistons and heads are gone.

Used motor will be you're next plan of attack.

 

[jotin]

Never mind lol

 

[dodge dude94]

Guess you missed the massive chunk out a piston too eh?

 

[jotin]

Guess you missed the massive chunk out a piston too eh?

Lol yup. My bad. I skimmed over


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