Ok, so I recently bought a 2003 Ram 1500 5.9 4x4. It was throwing a code for a misfire in the 5th cylinder. The dealer looked it all over, found 3 cracks in the head, and installed a new one. Yesterday I picked it up, and I didn't even make it home (37 miles) and the check engine light came back on. So I took it back in today, and it's now apparently misfiring in the 8th cylinder (and occasionally the 4th) while idle. Under load, the misfire goes away. They are attributing this to the computer adjusting to the new heads and told me it should reset itself in the next few days. Is this accurate?

They said they are ordering a new cap and rotor and will replace that just in case, but they don't think that is the problem because it would still present the problem under load if it were. They think it's just not calibrated correctly, and giving too much fuel at idle to cause the misfire, and that it will correct itself once the computer learns to compensate for the new heads.

Also, there is a slight bouncing when stopped, in Drive, with foot off the brake, that they also contribute to the "adjustment period". It doesn't do it in park, and I don't notice it when moving.

Any thoughts on this?

 

I call bull... have them check the timing on both banks, and at the crank...

 

Im with Izero

 

Thanks for the suggestion.

I'll have a third party look into it.

 

Timing both banks? The 5.9 is a single cam engine..

Did they route wires per TSB?
Did they replace the plenum gasket?
Did the intake gasket seat properly? Are there any leaks?
Are you missing a vacuum line somewhere?
Did they clean the fuel rails while the intake was off?
How old is your coil?
Is fuel sync set to dead nuts zero?
Did they reuse valve seals and push rods? If so, were they benched?
Have you checked fuel pressure?
Have you pulled plugs to inspect color?
Have you pulled the dipstick to look for coolant?

 

There you go OP someone that knows what they are talking about, if you/your mech make it to the bottom of that list with no answer i would be talking to the shop owner

 

Don't know much about the 5.9 sorry about the misinformation....

Still think the timing is the problem....

 

I would agree with you, but there is just too many things that can go wrong with a head replacement..

5.9: heads are known crackers.. they crack in the valve seats like it's cool.. if you have one with any miles on it, you have cracks- it's about that simple.. I've not seen them cause misfires, though.. what they are bad for is causing hot spots, which causes pre-ignition.. that's bad enough, and going on long enough is pretty capable of busting wrist pins, burning pretty holes in pistons, tossing rods, or letting loose the dogs of war on cranks..

the plenum gasket blowing is common too.. it WILL happen at some point.. somewhere in 2001 it was 'somewhat' addressed by using shorter bolts from the factory which allowed the plate to maintain torque throughout the temperature range.. but it can still happen.. it leads to:

- excessive burning of oil which ruins cats and o2 sensors..
- cracking of heads/valve seats
- oil fouled plugs, most often in cylinders 7/8/1/3... which causes misfires.

If they had the intake manifold off and didn't swap out the lower manifold gasket (plenum gasket), they need to be beaten repeatedly for a few days straight.. that $3 gasket causes all grades of grief..

if they 'repaired' one head, but not the other, they should be beaten as well.. if one was cracked, the others are as well.. by pulling just one head and not the other, there is a dang good chance the deck heights are different, which cause things to tweak and not align properly on the intake manifold install, which WILL create bad mating of gasket to gasket surface.. which leaks.. which will cause misfires..

I'm trying to dispel huge concerns, and what I just said isn't small- I hope it's not that, but it likely is just that.. in order to avoid stripping the engines top off again, I highly rec he checks every vacuum connection, inspects plugs, and looks for intake gasket leaks.. hopefully that is his issue..

timing on those rigs:

ignition timing- controlled by PCM alone
valve timing- mechanically controlled by relationship of crank to cam (chain)
fuel sync timing- controlled by dizzy position in relationship to cam (valve timing), but has to be monitored by scanner capable of reading fuel sync..

I'd look at fuel sync on a scanner, set it to dead nuts zero.. I'd hope the guys who did the work set dot-to-dot on the timing sprockets, and I'd check the wiring routes.. then I'd look for vacuum lines being installed and seated.. then I'd look for manifold leaks..

do you have a vacuum gauge? what does it read at idle on a warm engine? does the needle hold steady or does it bounce?

 

and we have found the new 5.9L Guru... *highfive*

All of what he said sounds plausible

 

Your not kidding about the 5.9 guru! Good info