can someone please help? i have 99 dodge ram 1500 with a 5.9. i have had an idling issue for a little while but recently i had a check engine light pop on with a random misfire/misfire cylinder 3. So, i changed the spark plugs and wires. it still ran a little rough so i changed out the cap and rotor. It still runs like crap. I did a compression test and this is what i got cylinder 1- 140psi cylinder 2-140psi cylinder 3-130psi cylinder 4-155psi cylinder 5-150psi cylinder 6-150psi cylinder 7-120psi cylinder 8100psi. i checked for spark in the wires and i have spark what am i missing here?

Asked by Feb 27, 2018 at 06:57 PM about the 1999 Dodge Ram 1500

Question type: Maintenance & Repair

9 Answers


8 Is on the low side. did you also check for a vacuum leak?

I have not checked for a vacuum leak yet. i know i have one but not sure where. vacuum has been leaking for a while now (many years). with cylinder 8 being low on compression it doesn't make sense as to why cylinder three is misfiring. i have also checked to make sure i have fuel pressure and the pressure is there. would block or body grounds cause this issue?


#3 is missing? did you do any fuel injector testing yet?

negative. that is what im wondering is the problem the injectors are original from 1999. what would be the best way to test the injectors?


ohm readings, just need to find specs.

Ok, cool thank you.


check to see if the cat is clogged/pull the front O2 sensor n start 'er up...does she idle better?...the #8 cylinder takes the brunt of a clogging/clogged cat, which could explain the low compression on #8. If the cat's clogged, then the next thing you gotta ask, is the floor of the intake manifold a swimming pool of oil? Take a gander down the throttle body, if it's dark brown or black...wet...blown plenum gasket. Idle problems can be caused by sooooo many things. Do you have access to a scanner with live data capability to monitor fuel trims?

no ticking just a misfire. my vacuum problem has been happening for quit sometime now.... sense about 2007 or so and sense then i have had a engine rebuild. my problem is somewhere in the vacuum lines or possibly behind the dash when i had to replace my heater core. i may have accidentally left a vacuum line partially disconnected.

ok so ive done a fuel injection service to clear out any carbon build up. when i took the truck on a drive to clear out deposits my check engine light came back on with not only a cylinder 3 misfire but also a cylinder 3 misfire, cylinder injector circuit malfunction and the same thing for cylinder 5. i checked the harness side with noid light to see if the injector harness was firing in 3 and in 5 and found that 3 was ok but cylinder 5 was dim but firing rapidly. Then i did a leak down test on cylinder 3 and found that the cylinder is good, i did the same on cylinder 5 and 5 was good. I checked the cat to see if it was clear and not clogged and looked down into the bottom of the plenum. plenum was dry but looked brown.

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