Well thanks in advance for reading. I have got a 2003 Ram 1500 with a 3.7L with a p0303 code. I have done a tune up, swapped coils,and even changed the injector. The misfire only happens at idle, under a load there is no misfire. (I have a scan tool thats why I know.) I did a compression test I had 90 on cylinder #1, 120 on cylinder#3,and 170 on cylinder#5. Which is weird no problems on cylinder#1 at all. I also did a vacuum test which showed 20HGm and the needle stayed still. The question is does this sound like an internal engine problem, a computer issue, or what? Again thanks in advance,if there is anything else I should check please feel free and ask or tell me to do. I am kinda lost right now with this.

 

I'm thinking maybe plugs. I didn't see anything about changinh them, but if you did what type did you use? If oems was the gap set to the right value? If you didn't change the plugs what did the plug from that cylinder look like?

 

That much compression differential between cylinders, yeah you have an internal problem. Be sure to do compression on all 6 cylinders and do them twice. I've done many valves and heads on 3.7L for this same problem. If the seats are Ok you may be able to get away with new valves.

Google TSB 09-007-06 ....It will clear some things up for you about the misfires.

 

Thanks for the posts. Tafet yeah I changed plugs, I put oem NGK's in.#3 plug was black and sooty basically looks like it is running rich misfiring.
Tntech I was thinking the same with that much difference however wouldnt you think there would be a problem on #1 cylinder just as much as #3 though? I did have a lifter rocker arm issue on cylinder3,that was 25,000 or so miles ago. I had the lifter and rocker arm changed and everything was fine til about 2 weeks or so ago I had a new muffler put on,now I know that sounds stupid but could that cause more back pressure to cause a problem like this?

 

Have you disconnected the battery during all this? If you did, then you reset the misfire monitor and it won't show anything on the scan tool other than electrical DTCs until it is enabled again.

 

Actually I have disconnected the battery and your right it doesnt show any misfire on any of the cylinders for a couple of drive cycles if that makes sence? It then starts it's misfiring all over. What would that mean exactly? The other thing to, when I am watching the scan tool it will start misfiring at idle but when I start to drive it stops and will actually reset the misfire count until I come down to idle or there about.

 

I think it's probably time to do the cylinder leak-down tests to be very sure about what's going on. Keep in mind that you now may have a fouled plug or two in addition to the valve issue. Possibly even a coil damaged due to being overworked for a long period.

When there are mulitple misfires, the more cylinders acting up the less reliable that monitor info is. I've seen the 3.7 and 4.7 throw misfire codes for cylinders that have no issues and no codes for the bad ones. That's usually when there is a "catstrophic" failure on a cylinder or a severe and erratic misfire. One can make a whole bank go crazy and even opposite banks show misfires. The crank sensor is monitoring and PCM is seeing erratic crank speed so it just does what it's programmed to do. The best way to hone in is which one has the higher misfire count, but that doesnt always work.

Here's a piece from that TSB I referenced

 

That TSB and this problem has been driving me up a wall LOL. I do get a fouled up plug (black and kinda sooty looking) meaning it's misfiring. Now what's funny is when the one time I did the compression test I flopped cylinder 3 spark plug with 5 and that miss moved to 5 like I thought but I didnt start misfiring on cylinder 3 for like 2 or 3 minutes, then 5 was fine after that plug cleaned up I guess and started misfiring on 3. So by doing that TSB procedure, if it is still misfiring like it does right now then it could be something other than an internal problem or it still could be? I'm kinda lost LOL.

 

Short version is you're probably going to be pulling the heads off for valve issues. I've seen about half repairable with valves and a grind, and half not. The way it sounds is that you're beyond the TSB now. I just posted it so you would be a little more clear of why the random misfires on good cylinders and so that you would be aware that valve issues with 3.7 are not rare.

 

Thanks TN and Tafet for your input on this issue. One last thing TN I know you said you have seen a valve issue with these 3.7 engines. Did those engines still have good vacuum reads as well? I think I posted before mine is at 20 and the needle is steady.