So this case study proceeded to almost kick my butt . I made a lot of mistakes and it took way longer than it should have but in the end we won. Got called to a shop I do diagnostics for on the side, Im wanting to start my own diag business and this shop is a great training ground. I learn a lot and he is happy I come to him and I get paid a little. I diagnosed this vehicle Sept 2018 so I only have 2 saved captures but I think it will be good none the less. Anyway 2006 Dodge Durango dead miss all the time P0304. This vehicle originally came to this shop because they wanted him to program a used PCM for a p0301 and p0304. He installs and programs the PCM . P0301 is gone but p0304 remains. I plug in the Modis and verify a current P0304 and dead miss on #4. I want to make sure the scanner is telling me the truth. I unplug coil #4 and no change in engine rpm. Ok cool this is our problem child. I do a quick coil ramp an injector ramp with my amp clamp. They both look good. I dont have anyway to check secondary ignition and Im not really good at analyzing the waveforms yet so I do a little swaptronics with the #4 coil and plug. No change. Im worried of a restricted injector and the rail is easy to pull up on bank 2. I pull up the rail and the injector sprays good just like the rest. Okay i do a relative compression test with my amp clamp, looks great. Hmmm what the heck am i missing here?? I dont have my pressure transducer with me so I do a quick manual compression test an compare to another cylinder they match perfect. At this point shop owner tells me head gaskets have recently been done an p0304 occured after this. Ok cool Im thinking maybe they forgot a lifter or pushrod. I quickly pull the valve cover an everything looks great. They crank it and the intake and exhaust valves open and close beautiful. Wow i feel like an idiot. I think maybe there is something stuck in the exhaust port or intake runner for #4. I put shop air in the cylinder with exhaust valve open, air pours out the tailpipe. Same result with intake valve open, air pours out throttle body. Wow Im stumped. I go to the shop an get my pressure transducer. I stick it in a known good cylinder engine running for a reference.
Ok so now with a known good I put the transducer in cylinder #4. Wow, I think to myself " Ive never seen anything like this before. It looks like I have a compression event every 360 degrees or during the exhaust stroke!
At this point I sit down and think. The pattern is way too uniform. Then a little thought creeps in the back of my head. This engine just might have cylinder deactivation. I jump on Identifix real quick and sure enough it does! Okay sweet now I have an idea. The deactivation cylinders are 1,4,6,7. I put the transducer back in #1 and command on the # 1 MDS solenoid while the car is running. Instantly i get the same waveform as the cylinder #4 capture!
Sweet now we are on to something, but I dont understand why the PCM is not setting an MDS solenoid code and why there is no engine or lifter noise??!! I current ramp the #1 and #4 MDS solenoids and command them with the scan tool. They both pull the same 1 amps. Ok so thats why the PCM isnt setting a code, it sees nothing wrong with the circuit. However when I command #4 there is no click heard as opposed to a loud click on #1. Now Im excited , I tell the shop owner" We need to remove the intake an inspect the #4 MDS solenoid, its mechanically stuck open"! We pull the intake and find new Dorman solenoids installed that appear to have been beat in with a hammer. We have to pick an easy out the #4 solenoid to get it out it is thoroughly stuck. A new Mopar #4 MDS solenoid fixed this vehicle. The valve in the solenoid was stuck open allowing oil to collapse the lifters at all times. So I got the runaround but in the end we gave it the smackdown lol.
Good diagnosis. The rounded pockets are a classic symptom of the valves not opening. Once you see it you'll recognize it easy in the future.
Great case study Caleb! We've all gotten our butts kicked more than a few times but those are the jobs you learn the most from. Not to mention the lessons you never forget. The important thing is you stuck in there and figured it out. Thanks so much for sharing!
It's the Snap On 500psi. It used to work well like in these captures. But recently it's been giving me junk waveforms. Think I'll be getting something else soon.
Hi, i've got a question. I'm from Europe and never work on these engines. I'm proberbly missing something because I'm not familiar with this system. You told us you pulled the valve cover and see the valves opening and closing. But did they?
Danny I thought the same thing at first when I read the post but I think I have the answer to your question. This system uses oil pressure to deactivate the cylinders by internally collapsing the special lifters when it wants to run in 4 cylinder mode. Since the solenoid for cylinder number 4 was stuck open always allowing oil pressure to collapse the lifters, this caused the dead misfire he was
Great logical approach. Thanks for sharing this. Would've loved to see those injector current ramps. Might've seen pintle movement on known good, and lack of movement on the number 4. Nonetheless a great example of a step by step diagnostic process!
Mario the injector would have looked good, it was the MDS solenoid that was stuck.
😂😂😂 oops totally mis-worded that! Current to the solenoid, i meant!
Never would have thought to current-ramp those Mario. Great idea! MDS/AFM hasn't reached our Time Warp out here yet.
Thanks Mario. I know, I'm kicking myself now for that. But at that point I think just stuck the leads in the amp jacks on my multimeter. Can't remember if my amp clamp had died ??!!
Caleb good logical diagnostic approach. A little off topic, you should start charging more than “ I get paid a little”. When you do start doing your own thing you will need to charge more. Get your customers used to it now. Don’t under value your skills. Good luck. Once you get started working for yourself you’ll love it.
Lol yea I know. This was 6 months ago. I make a very good living at my current job. This is one of the only shops I go too right now because I haven't done any advertising. Like I said it's very good training for me. I'm not ASE certified or anything like that. Yes I'm planning on starting here this summer /early fall. Just need to build a customer base first. My area has no mobile guys for at