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Ask Dodgerench Your Own Question
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3404
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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2003 hemi ram, the engine is running..running rough..running perfectly

Customer Question

in a 2003 hemi ram, the engine is running rough, scan shows cylinder numbers 1,2,3,4, and 5 misfiring, cylinders 6,7,and 8 running perfectly, what could be isolating 5 out of 8 cylinders and causing them to misfire? plugs and wires have been changed, and a compression check performed showing no defect.
Submitted: 5 years ago.
Category: Dodge
Expert:  Don Knight replied 5 years ago.

Don Knight :

Good morning.There are a few things that can be causing your problem.I would first start by checking the injectors.You could try some injector cleaner but I would also check each injector to make sure that they are firing.You will need a noid light and just unplug each injector (one at a time)and see if they pluse.If the injectors are not firing then your problem is with the computer.If they are firing try the cleaner.Please let me know how it goes,Don

JACUSTOMER-dimmg2t3- :

The injectors are all firing normally, and the fuel pressure checks out @ 48-52lbs. The odd thing is while the engine is running, I can unplug the injectors and coils on the misfiring cylinders and get no response in performance, and it will still continue to run on only cylinders 6,7,&8. I put a vacuum gauge on it, the gauge flutters @ idle,(with all cylinders plugged back in) and reads 20 @ 2000-3000 rpm, which leads me to think its drawing in air somewhere although carb cleaner sprayed around all possible leakage areas reveals nothing. I've since removed the intake because I've found cracks and other damage on the plastic intakes in the past which created these same symptoms, this one appears undamaged although there is evidence of some leakage past the rubber seals and I also noticed a considerable amount of oil standing in the intake ports of the effected cylinders so maybe the pcv system is not functioning properly or there is a large amount of blow-by (the engine does have 150.000 on it). What doesn't make sense is if it is high mileage then why did these symptoms just suddenly appear on a good running engine and why only cylinders 1 thru 5? So far I have yet to come up with anything concrete to explain this misfiring problem. the computer only repeats the same 0300 code, random multiple misfires. I would greatly appreciate any help you can give, and thank you for your time, Jim

Expert:  Dodgerench replied 5 years ago.
From what you've described, I think it's time to pull the valve covers. Hi, my name is Ed.

A broken valve spring will allow an unbroken path between the engine's intake and exhaust manifolds, allowing exhaust to be dragged back through the affected cylinder, connecting to the intake system... where it pollutes other cylinders as they attempt to accept charge.
Exhaust content has very little oxygen available, so this diluted charge will burn very rich in the most-affected cylinders. Blackening of the spark plugs is common in these circumstances.

This effect is most acute at light throttle loads as engine intake vacuum is highest and will reduce in severity as load is increased. You may find that some of the cylinders showing misfire at idle will pick up performance as you pour the coal to the engine. Be wary of running the engine too fast though; you don't want to float the valve far enough that it smacks its piston. At this point the spring can be replaced without pulling the cylinder head, but once the valve is bent, that option is gone.

Most instances of broken springs will result in the sort of compression readings you've found, which is a GOOD thing; it means no valve-to-piston contact has occurred yet. The Hemi uses a beehive-type spring that tends to collapse on itself when snapped, so it can still close the valve and handle low-load situations like cranking compression tests, but things fall apart rapidly as engine speed increases.

You may also find that the injectors will not be firing on the cylinders misfiring occurs. This is because the Hemi fuel management system is designed to prevent catalyst damage during catastrophic misfire situations by cutting fuel to the affected cylinders. With less unburned air and fuel leaving the cylinders, catalyst damage is minimized.

I wish I could tell you which cylinder it will be... or even which side... but it's impossible to say, even with the great info you sent. With two out of four possible cylinders firing on the right bank, your statistical odds are that it will be on the left side, but that's still only a guess. My preference is to pull the easier valve cover first and take my chances (this would be the right side). As luck would have it, my last Hemi-broken-spring customer found his broken spring on the LEFT side... eventually (sigh).

Let me know if you have any questions or problems.

Good luck,