A friend just called me. They have had a misfire in their 2001 Ram 3500 van and they have it at a mechanics shop. The shop told them it's the computer. SERIOUSLY?

I told them about 2 months ago it would be a cracked head. I've seen this issue before in this era Dodge. I suppose it could be the intake plenum gasket and I think checking the IAC cycling during misfire at idle can narrow that down.

What can you guys share on the issue. I know it will end up being a head. I told him he could swap the injector in the suspect cylinder and recheck the code. I don't think he did. Mainly I am just wanting to see if others have had the issue and found an easier fix.

I tend to think along the same lines you are. Assuming that he's ruled out a bad plug/wire/cap, etc, the next thing I'd look at is the intake and injectors/injector seals, and lastly, the head. All the things that you've already mentioned...

Could be as simple as carbon tracking in a plug wire boot. Happened to me!

R.

I've seen 3ea 3.9's misfires in the last year, all ended up being cracked heads (These are basically the same Magnum head). I think he's done the cap rotor and plugs already. I told them from jump it'd probably be the head.

Napa can't keep the heads in stock and neither can Dodge. Rock auto has them.

I'd like to hear what others may have had cause a misfire. I'm afraid I know what the end result will be here.

I think at some point Chrysler issued a TSB about plug wire routing and crossfire on Magnum engines...

the odd looking wire re-route
to solve ignition wire crossfore,
particularly cylinders 5 and 7,
is here:

http://dodgeram.info/tsb/1998/18-48-98/18-48-98.htm

along with checking the o-ring seals of the injectors,
check the catch screens at the top of the injectors,
particularly cylinders 7 and 8 at the back
which are "first in line" to receive any gunk coming from the fuel line.

cylinders 7 and 8 deserve a bit of extra attention:

the plenum gasket usually blows inside the intake back near the inner inlets to 7 and 8

the headgasket usually blows at 7 or 8

these two cylinders seem to run leaner and hotter,
perhaps because the design of the exhaust manifold gives these two cylinders less backpressure and therefore less internal EGR, more fresh air in the cylinder intake charge

it may also be there is not enough coolant flow to those back cylinders.
When Evans Cooling tested their NPG coolant in Police service 5.2v8 Magnums in MI years ago,
their research report said they had to remove the heads and enlarge the coolant hole in the head gasket for the rear two cylinders.

doing an individual cylinder RPM drop comparison
power balance test
on the might show the weak ones

How does a cracked head cause a misfire? I don't think that is the problem.

I stopped by and hooked up to the Dodge and could not communicate. Something may be shorted killing comm. I think it's a CAN type system.

Funny thing is the guy has a cheaper scan tool thats registering a misfire code, then after I could not read it he picked up p0300 p0305 and p0306 so Im leaning away from it being the head.

I know a computer issue is a long shot but it's only a few months old and it's been a problem more than once (I've repaired this van before). He'll take it to where I bought it for him and have it reflashed. Starting from scratch

The gentleman's wife called to relay a message. He took it to have them read it and they found 4 codes, but no misfire codes. I'm not sure if he was unplugging things or what the shop that had it did if anything.
The van has been sitting and not driven. It had a P0113, P0118, P0123, and P1492. He did not however ask them to flash it. I'm really starting to wonder about this PCM

Computer was flashed, it only repeats the p0306. The other codes must have been set by the shop probing and unplugging things.

Since there's apparently a short, killing communication, the computer was fried twice and there's a misfire on 6. With the warning on the new computers (to check for shorted injectors they'd fry the computer) There might be an easy fix ahead

I need to make time to look at it

Is it constant misfire on cyl # 6?
or does it do random?
Have you put a heat gun on the cyl brought the rpms up see what the heat reading is on that cyl compaired to others?
Have you done a compression check on all cyl ,leak down?
changed cap / rotor wires,plugs?
Just for grins , check the valve springs for breakage??
If it is an actual firng issue, change out the dist?

It's consistently recording that code on every drive. Wires were an issue but not the cause, it runs better, still sets code.

Nope, all I've done is what I've told here. It's on my way home, if I go of course a bit so I just made a few minutes the other night.

Since it seems that an injector short could...
cause a misfire...
kill a computer... (gone trough 2)
Negate communication....
that's where I'll start
check to see if I can read it, unplug the suspect injector and re-read if communication is restored that would be quick and easy.

Computers get the blame for a lot of issue that may not be a computer issue? Just saying.
Most pcms will not keep throwing the same codes, so lead to believe the issue is ,(wiring issues) or mechanical controled!
Misfire could comein the form of injector, easy to see , just remove one from another cyl and put in that hole, if it stays on 6, then not the inj! move to next item
switch wires to the plug, etc,
change plug the same way , time consuming, but xcheaper than throwing money on items not needed!!

If you can not move the issue around by doing the switch method, then it is most likely mechanical! start checking cyl pressures, valve springs, valve lift!

Exactly what I'm thinking guys

I told him to swap the injector from that hole 2 months ago but I guess that's outside his comfort zone. When I didn't hear back, I figured he fixed it

THANKS TO ALL who have offered their thoughts and info