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Dodge expert
Dodge expert, ASE Cert Technician
Category: Dodge
Satisfied Customers: 10370
Experience:  30 years experience, ase certified,shop owner
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98 dodge dakota: 3.9l..tune up, new injector..swapping

Customer Question

Hi. i have a 98 dodge dakota 3.9l. before my customer brought it to me, he had a cylinder 2 misfire, so after a tune up, new injector, various other parts swapping, still had a cylinder 2 misfire. vehicle was this way when he bought it. it has a rough idle but runs great off of idle and down the road unless the rpms come down like in final drive, in gear at a light you can feel it worse. So he pulled the heads, and replaced both with new (machine shop said both heads in both front and rear banks where cracked between the valves) which i have seen before. so the customer bought the new heads, replaced lower intake pan gasket and all head set gaskets and reassembled. Thinking the cracked heads where the smoking gun. Well, not the case. after numerous attepts by him he still had the cylinder 2 misfire at idle, also causing a CEL. A week ago brought it to me, i started from scratch, cylinder 2 misfire code, on my (snap on versus scanner) at idle can steadily watch cylinder 2 rack up misfires, anything off idle it will stop. so i swaped injectors around, same, took his autolight plugs out and installed champions, same, swapped plugs wires, same, did a compression check on cylinder 2, 130psi, seemed ok. put my versus lab scope on each injector and watched the waveforms, idling and throttle snap, all cylinders showed the same. so then i pulled the fuel rail off and inspected for rust or debris, none found, swapped injectors around again, same. ive sprayed the intake down with spray lube and brake cleaner, same, while i had the fuel rail off, disconnected ignition cranked of and all injectors sprayed well. i even pulled the passenger valve cover off, swapped number 2 and number 4 rockers and push rods, same, watched for full travel, looked good to the eye but i had no dial indicator. what am i missing, or where to go now, im more than happy to start fresh again now that they brought it back today. i only have it for the day of thursday as they use it for a mail route. any advice would be greatly appriciated.
Submitted: 5 years ago.
Category: Dodge
Expert:  Dodge expert replied 5 years ago.
Welcome to just I'm here to help you and your 100% satisfaction is my goal. The next step but I would do is a cylinder differential leakage test see what percentage of leakage you have up on the number two cylinder and compare it to the rest of the cylinders, also using a dial indicator checked to see that the valves on the cylinder number two and have the same list as the rest of the cylinders. We possibly have a faulty camshaft or faulty piston rings
Customer: replied 5 years ago.
ok so my next step is to do a cylinder leak down test, to check the rings,. and get ahold of a dial indicator to check valve lift on all the cylinders. how much leakage and how much measurement is allowed, or what is the out of range.
Expert:  Dodge expert replied 5 years ago.
On an older engine I wouldn't wanna see any more than 10% but realistically it I like to keep them around 5% leakage
Customer: replied 5 years ago.
ive got about 8percent on cylinder 4, with rockers off, no air from exhaust or intake, but i hear a hissing, if i bolt the valve cover on with the rockers off, it will push my finger off of the dipstick tube.
Customer: replied 5 years ago.
and cylinder 2 sorry
Expert:  Dodge expert replied 5 years ago.
Two other things I would like to check, using a vacuum gauge tell me if the intake manifold vacuum is nice and steady or if it fluctuates at the time it misfires also remove the spark plugs one at a time and do a running compression test and compare that cylinder to the other cylinders tell me what the compression reading is while it's running