2000 3.9 Dodge V6 misfire

[WarWagon]

2000 3.9 Dodge V6 Dakota pickup. So it has over 1/4 million miles towing scrap metal to yard for the Boy Scouts. Around 237,000 miles.

Yeah, wrong tool for the job.

Anyway the #5 cylinder is missing. Computer code with light says so, cold exhaust manifold on #5 vs. the others, you can hear the RPM change with altonator noise change, Tach twitches, and you feel it shake.

Spark good, voltage to fuel injector, injector clicks. Didn't check injector ground path. New injectors installed due to miles, but, had issue randomly before this. Computer takes it's time to turn on light after code reset when condition exists.

Can hear slight tick noise from the engine now and then. Also have heard a hollow thump like main bearings are loose from it in the past.

 

[3500GMC]

Time for a compression test.

 

[THEFERMANATOR]

Also check the intake plenum gasket. Those engines are notorious for popping out the plenum gasket, and sucking oil in that in turn fouls the plugs and causes misfires. Look down in the throttle body and see if theres a slick on the plenum pan.

 

[WarWagon]

Plugs are coming out clean. I'll look for a air/oil leak.

 

[79jasper]

Maybe pull the valve cover and take a look.

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[WarWagon]

You assumed correctly that the plugs wires cap and rotor were already done. Owner even replaced the single spark plug at my suggestion.

Shop replaced all 6 plugs and so far so good. I assume plug was being cracked on install.

 

[WarWagon]

Add 10K miles... Compression is 120 PSI on that hole. Plug is coming out fuel wet, manifold still is colder. Verified with LED and resistor that computer IS firing the injector and I hear it click. Other work done was remove and replace intake manifold due to suspected vacuum leak.

Hear snapping noise at back of engine start when it idles down. Likely secondary flashover for #5.

Put spark tester on at that cap - ok. Added a spark plug wire to the tester and then to plug - spark went out.

Put tester on coil and oddly enough engine ran better. Real WTF moment. Color of spark may not matter, but, not happy with it. Purple orange.

Did vacuum leak burn up the wires, cap and rotor? Replace cap and rotor: no change.

Unreal. Marginal ignition system with EPA run it lean and modern oxygenated gas just want to make the high voltage leak out elsewhere instead of firing the plug. TSB is more or less: Route coil wire away from other plug wires.

various single cylinder misfire (1, 3, 7,) ad especially 5
http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v6.htm



So the coil wire moving away from the plug wires with the coil tester made a difference. All the hold downs on the passenger side where the coil wire runs are gone.

Ok, it's over $100 for the ACCEL wire kit. Owner went *CHOKE!!!*... But talked him into ACCEL coil, Cap, rotor, plugs, coil harness adapter, and lots of 8mm Mopar wire standoffs and spacers.

Not ruling out other issues, but, will pull the valve cover just to be sure. The extreme mile chain is suspect, but, would affect all cylinders. Flat exhaust lobe is my next guess as well as broken valve spring.

Work a spark engine? Lets just say I get reminded now and then why I own the expensive diesels...

 

[WarWagon]

Noted #3 and #5 were fuel wet when installing the ACCEL parts kit. Plugs, Ceramic plug boot 8mm wires, Lethal Voltage sticker ACCEL Coil, ACCEL Cap and rotor. Work of art as each wire is separated and the ignition coil wire is a class of it's own.

Made a difference, but, still not 100% IMO. The difference being not surging in town and the AC compressor isn't kicking off at idle - IMO the AC compressor was kicking off to reduce load via the ECM's stall saver.

It isn't idling smoothly and the heat gun on the exhaust manifold is still showing a big IR gun temperature difference on the #3-5 combined port. The backside is 30 degrees colder than the front and about same colder than the other manifold ports. Still got a loud High Voltage snapping noise coming and going at idle from maybe driver's side rear of engine. I would guess it's from the distributor as I don't see any HV leaking. Possible injector as I need to listen to them when that's going on.

Time and owner not willing stopped removal of valve cover. After all it was 106 and 20% humidity. NOT A DRY HEAT!!!

 

[Olddieselguy]

Did you try a running compression test? Bet it has a worn exhaust valve.

 

[WarWagon]

Did you try a running compression test? Bet it has a worn exhaust valve.

Compression test was good in the #5. Should have tested the #3 while I was at it. Again a world of difference in running better with the ignition overhaul. Have to look at it again sometime to see what the code is coming from now.

 

[WarWagon]

Thought I had updated this. This past Spring the owner had a shop check it out and was going to do a new timing chain as the single roller chain used is prone to stretching. The chain went into a completely different engine!

The shop did a compression test and found low compression in #5. The pulled the engine and found cracked heads, shot camshaft, worn valves, cracked block at a head bolthole. The owner says he used Mobil 1 engine oil since new. Again this tows the scrap metal in our extreme heat and had around 250K on the engine. IMO needs to change the oil more, use a thicker oil and add a zinc additive. *cough* Or get a v8 or a diesel for towing... The return trip empty will show a vacuum leak in the system as the doors direct air to the floor from the lack of high throttle vacuum. He is using Amsoil now. I have UOA going on for the truck to see if the oil is failing or just was high miles and too hard work for a V6.



It runs really well with a different rebuilt block, new heads from @RockAutoLLC and a double roller timing chain in addition to the better ignition system.