Everything was Replaced?
This is a case study that was originally written by my friend and one of our peers Pete Rudloff with the information collected on a vehicle I diagnosed and repaired. Not sure how this post is going to turn out but wanted to contribute something rather than just be a spectator, an observer and just comment on other post.
The late great Dave DeCoursey taught me years ago at a TST Big Event during a misfire diagnostic class to have a systematic approach and stay with the system that works for you. Thanks Dave, that class changed my career for ever.
This truck was towed to me from another shop about 30 miles away, I'll save you the conversation I had with the shop owner over the phone, it was humorous and unprofessional on my part.
Back story on this everyday typical Ford pickup is that the truck came to the shop with a misfire on cylinder #3. The shop performs a complete ignition tune-up, plugs, boot kits and a new coil for cyinder #3. When that didn't correct the problem they swapped injectors around to try to move the problem I assume. Next they figured to call in a favor to a Ford master tech from another shop, his suggestion was the PCM, so the truck was taken to a local Ford dealership to have a PCM installed and programmed. Problem still present. Now this truck is taken to another reputable shop in their area and they diagnose the engine to be a valve issue of some sort, so with about 150k on the odometer the original shop sells and brand spanking new Ford engine, possibly re-manufactured. Again, no change in the running condition. What was left the shop figured was the engine harness, needless to say after replacing with one from a parts recycling plant, aka junk yard, no change. This next part is when I lost my professionalism with the shop owner. They decide to take the truck to a 3rd shop, this shop is totally convinced this new engine has a valve issue and the cylinder head needs to be removed. Wait for it............The original shop removes the cylinder head and installed another head.
After 2 years of tinkering and having to purchase the truck from the owner my name gets dropped and that's when I got involved.
Parts replaced: Spark plugs and boots, #3 coil, PCM, Engine, engine harness and Bank 1 cylinder head.
My approach to any conventional, non-hybrid, internal combustion engine misfire is 1, some sort of relative compression test 2, test ignition 3, test fuel delivery and 4, go in-cylinder to look at breathing and valve events. That works for me and has not let me down since learning how to narrow problems down by eliminating funnels.
My relative compression test was performed with my high current amp clamp around the starter cable.
Primary testing and current ramping the #3 ignition coil gave me no reason to suspect an ignition problem.
Primary testing and current ramping gave me no indication of an injector issue, if this truck didn't already have injectors moved around I may have hit it with propane as another quick fuel test.
Finally, I get to play with the pressure transducer. Bam, there it is, pressure building on the exhaust stroke. Valve openings are pretty obvious, even for a Snap-on scope. Maybe a Cat converter?
Drop the transducer in another cylinder on the same bank. No pressure on the exhaust stroke tells me the clog is isolated to just cylinder #3.
After 35 minutes of quick basic testing and 15 minutes to remove the manifold that was already removed a couple times when the engine work was done, there it was, a bad casting in the manifold.
Turns out that the shop put that manifold on the truck a year or two before the customer started complaining about the slight misfire.
I wanted to teach the shop how I came to the diagnosis but he didn't want to learn, I suppose a little embarrassed.
Nice find ! Testing not guessing . With hard facts to back it up
Good job and approach David. Yes, having a proven logical organized approach is absolutely key to successful diagnostics for any issue. The simple fact that it must be understood is that all engines are essentially just air pumps and any irregularities in the ability of the engine to move air into and out of the cylinders will be reflected in a variety of ways. How we interpret the clues, is
Dave it looks like you had a good diagnostic game plan. When a drivability problem rolls in it important to have that plan. If you don't have a plan you either won't find the problem or it will take forever finding it. Glad our buddy Dave DeCoursey (may he rest in peace) was able to put you as he did with many on the right track at one of our … Big Events. Hey Dave... you the Joe's , Ron
Dave, This was a fun exercise , thanks for sharing
Brandon was just talking about this case study this past Saturday at Super Saturday Event. In pressure waveform acquisition and analysis Class he was teaching. Which by the way was so an awesome class To sit in all day. Thanks to everyone for all that you‘s do for this industry
Yep, Brandon shared this and it was great. Great approach. I saw the TST video on YouTube of Dave Decourcey's misfire strategies, that video alone drove me to grab a transducer. Amazing instructor. Thanks for sharing David, it made for great class material!
Good morning Dave , thanks for remembering and mentioning Dave in your post Dave had a great way of making the complex look easy when I’m stuck with a tough one I alway stop and say “ what would Dave do “ what would be his next move his guidance still keeps me focused when getting lost in the automotive forest Great post and awesome find thanks for sharing
Just when we think we have seen all the possible causes of a fault we find something like this. I find this to be great detective work. Without the in cylinder pressure testing this would have required blind luck to find. Great job in diagnostic approach. Finding something to effect your fault is normally a good way to find a related cause, but being able to measure and analyze is key.
AWESOME example of checking all of the BASICS first, which put you in the correct FUNNEL ( "G" General Test ) then driving down the FUNNEL with ("P" Pinpoint Test). Nice Diagnostics, My Friend.
I told you this the other day, completely impressed! The whole time Brandon was giving this presentation on Saturday in the back of my head I kept thinking... no way! John Thornton did a case study on something so close to this a few years back on a Jeep 4.0. I never in a million years thought I would see a fault like this again. I love how systematically done your approach was to this
Thanks Andrew, that was my thought when the truck came into the shop. As soon as the problem was narrowed down into the correct funnel I could see where the problem had to be. Honestly I was thinking a rag or something was stuck originally. I remember John's case study and had trouble thinking that was possible.