Swapping injectors will tell you right away if the injector is the problem.....

 

I did a quick ohm test and all injectors are reading 12.3 ohms. All make the tick tick noise too so I know they're not dead. Ran some fuel injector cleaner through, and so far after 40 or so miles I have not seen any improvement. Further results TBD...

I did a fuel pressure test today and it held at 48 psi at idle. Specs call for anywhere between 44.2 and 54.2 psi, so I know I'm getting good fuel pressure. I will probably swap fuel injectors around like HeyYou suggested (is that a Pink Floyd reference??) to see if the misfire truly is a result of the bad injector or not.

Here's what's interesting - The intake manifold was swapped for a Hughes model HUG 5409 (links below) sometime in the indefinite past. Apparently these really helped increase power, mileage (as a by-product), and even addressed the plenum plate crack issue that seems to be prevalent on these engines. I decided to take a look down below the throttle body, and low and behold the driver side opening had a little bit of oil sitting down there. My engine has always lost oil but I never knew to where... Is that a sign that my plenum gasket has failed? I'm unfamiliar with this Hughes product, but do they utilize the same stock/OEM replacement gaskets? The spark plugs also are running too hot since the air/fuel mixture appears to be running lean. More signs seem to be pointing to plenum and/or intake manifold gasket issues. Anyone else had these symptoms?

https://www.manciniracing.com/huenmaaiefii.html
https://www.hughesengines.com/Index/...p?partid=24773

 

The Hughes intake manifold doesn't have a plenum plate like the factory kegger style intake. I would replace your PCV valve with a Mopar PCV valve, as it may be allowing oil to get into your intake. The aftermarket PCV valves have a different metering rate than OEM. Lastly, are you running copper style spark plugs?

 

Yes, I'm running copper plugs and will replace them all again with copper once the misfire issue is resolved.

If the PCV valve is bad, wouldn't all cylinders be affected? Or just #6 is getting the worst of it so far? If oil is leaking, doesn't that mean a gasket has busted from the unvented blow-by pressure? Or can the oil leak through the PCV valve? Should I look into replacing my intake manifold gaskets as well? Any suggestions as to why else I'd be running lean?

 

PCV stands for "Positive Crankcase Ventilation". The idea is to pull combustion gases that get past the piston rings back into the intake, to be re-burned, thus, reducing emissions. A side benefit of this is that the slight vacuum on the crankcase also helps with piston ring seal, reducing emissions even more. (and increasing engine efficiency.) For the valve, its all about flow rate... too high of a flow rate, and it sucks in oil as well. Finding some in the bottom of the intake isn't unusual.... an excessive amount though.... yeah, need to address that, and the MOPAR pcv valves are dirt cheap, even from the dealer.

What does the number 6 plug look like? Is it fouling out??

 

I wouldn't say the amount of oil in there is excessive, but take a look at the picture below and weigh in on that. The Mopar PCV valve on RockAuto is like 10 bucks so I'll pick one up and replace it.

Below are also images of spark plugs #6 and #4.They were replaced back around March of '23. Copper plugs. To my untrained eye they seem to show signs of excessive heat, and my guess was that it came from the engine running lean and getting too much air since all plugs show the same wear. Is there a good way to get that little bit of oil out of the intake, or do I just let it eventually burn through the engine?


Oil in driver side intake.

Spark plug #6 - first photo

Spark plug #6 - second photo

Spark plug #4

 

Those do look like they were runnin' hot...... Did you fix the lean running condition?

I would be real tempted to throw some new plugs in there, and see what happens.

 

To my knowledge I have not fixed the lean running condition...I was hoping to maybe get an idea or answer on this chat. I know I'm getting adequate fuel pressure (48 psi), so we'll see if the fuel injector cleaner does anything. My initial thought was a plenum gasket leak, but now that I know I have a Hughes I know that's not the issue. Maybe an intake manifold gasket issue? Is there a leak test I can do to test those?

New plugs are also on the list... looks like OEM ran copper champions.

 

Copper plugs please, brand of your choice. I don't really care for Champions, but, some folks like 'em.....

Should be able to spray something around the various gasket surfaces, and see if the idle changes..That would indicate a leak.

Also, how old are your O2 sensors, and do you know what brand they are? These trucks really don't seem to like the Bosch O2 sensors, and you get some odd and strange running issues with 'em.

 

So I think I've found the culprit.... corroded distributor cap and rotor. It's got alot of that white dust buildup (aluminum oxide?). The rotor also looks worn down. Both rotor and cap look original to the truck, so I'm going to be replacing them. Any luck with aftermarket distributor caps and rotors? I feel like OEM is the way to go on this. RockAuto has rotor and cap for around $26 each, which is fine.

I also checked the O2 sensors, which are also original to the truck (Mopar #56030111AA). I have not inspected their condition but they are probably due for a change. If they were causing a misfire I'd assume there'd be a specific O2 sensor code (like P0139)...

Looks like the spark plugs that came original to the truck are Champion RC12YC...I've been running NGK ZFR6F. The Champion have a 12 heat range while the NGK have a 6. That may explain why it's been running hot. Curious what brand you like to run in your engine HeyYou and why.


Corroded distributor cap