99 Dodge Ram 5.2 misfire 1 and 8 only

[ottomatic]

I have a 99 dodge ram 5.2 and its misfiring on cylinders 1 and 8 only. I have done a complete tune up on it, plugs wires cap rotor. Still missing on those 2 cylinders. Moved the injectors around to different cylinders, no change. anyone had this problem before ? I was thinking maybe internally leaking intake gasket?? thanks for the help

[ottomatic]

I have changed the intake gasket and the plate gasket under the intake, changed absolutely nothing in the way the engine runs. still missing on 1 and 8. Any ideas?

[Chris Stewart]

I've been watching this a coupla days and my 1st thought is #1 & #8 wires are swapped since they're next to each other on the distributor cap.

[ottomatic]

Rechecked the wires and they were routed right. Checked compression again, all cylinders are about equal , well over 100 psi. Could it be a computer problem, or possible wore gear on distributor ??

[bigj-dog]

How about dumping fuel? Have you checked fuel pressure and leakdown? I'm not a real expert on Mopars, but I know the GMs I've worked on will misfire the cylinders next to the vacuum port to the fuel pressure regulator is the regulator is bad and the cylinders at the end of the rail (nearest the return line) will also misfire if the pressure is too low.

[ottomatic]

Fuel pressure is 48 - 52 lbs , no leak down, and have switched the injectors around , and of course nothing changes. It has to be something I have looked over several times and missed because I have done everything to this truck atleast twice, except the intake. I was told to check the gear on the distributor and the bushing. But that looks good as well..

[Chris Stewart]

Is #1 & #8 actually getting fire?
An induction timing light should light off on any plug wire when the engine is running.

[bigj-dog]

I'm stumped too. It almost has to be something insanely simple. The only other thing I can think of to try is a leakdown test on the missing cylinders. That'll tell you if the intake is cracked or leaking, or if the valves are burnt or carboned up, or anything else that's allowing your cylinder charge to escape. One other question (or 2 I guess), can you hear the miss? Is it consistent at idle and throughout the rpm range?

[ottomatic]

The miss is obvious..chugs at idle in park, and terrible in gear. Down the interstate is not that noticable. Even at higher rpms its not that noticable. I was thinking that maybe the cap was was misfiring between the 2 cylinders, seeing as how they are next to each other, even though I have already changed the cap once. Im going to try the leak down test on those 2 cylinders today and hope something shows up that way.

[ottomatic]

Originally Posted by Chris Stewart

Is #1 & #8 actually getting fire?
An induction timing light should light off on any plug wire when the engine is running.

Yes 1 and 8 are firing at the plug.

[ottomatic]

Well the compression test held, no leakdown. Im about ready to take this thing to the dealer. Im lost.

[Chris Stewart]

Check the starwheel (reluctor) that signals the ignition pickup inside the distributor for cracks, broken "fins" or slippage on the shaft.
I opened the Haynes #30041 manual and saw the EGR valve....you might check that too.

[Chris Stewart]

How's it going?

[ottomatic]

Believe it or not, one of the injector seals was tore, a new one, on #8. I just put them on to try and fix the problem, and I guess tore it in the process of putting it back together. For some reason #1 stopped missing when I changed the seal on #8. Just to make sure I changed all the seals again and it seems to run good now. no check engine light nor missing. the whole job still does not make sense to me. but if its fixed , Im leaving it alone lol.. Thanks for the help

[Chris Stewart]

Good work. Thanks for the update.
We'll put your finding in the Bag of Tricks for the next guy.