Confidence with Technology or Back to the Basics??
Hey guys hoping to have a discussion about diagnostics and how to bridge the gap between old school methods and new methods of diagnosis. Or maybe there is no gap at all and its about using the most efficient, accurate methods to get to the root as quick as possible. I realize every car is a different situation and diagnostic approach depending on the fault. I was recently called to our sister store to diagnose those 2016 Rogue. It had 38k miles. It had an intermittent cold start misfire on number 4 that only lasted for a few seconds and then cleared up. It had a #4 coil, all the spark plugs, and the negative battery cable replaced with no change in the symptoms before i got to it. I am immediately thinking head gasket, injector leaking or carbon buildup. However this engine is regular port injection so at this mileage an injector or carbon problem is a lot less likely than on say a GDI engine. I did notice the coolant was not full, definitely a pint or 2 low. The first test I did was an RC test, #1 coil trigger, WPS 500 on range 3 in the intake, and Pressure pulse sensor in the radiator.
Wow to me the results speak for themselves . There is a repeatable spike in the radiator immediately after every #4 compression event. Here is another with WPS 500 in #4 cyl. and the FLS in the radiator. The exact same spike repeats itself there.
I was not confident enough in these captures to call a headgasket. The car had already been too 2 dealers because it was still under Powertrain Warranty. But the dealers could not diagnose it. So I was the last resort to nail this thing. I had to be right. I put full shop air in #4 and couldnt get anything out of the radiator. I did a block test with the chemical and it passed with flying colors. I let the car sit overnight with a pressure tester on the radiator and there was no coolant on top of the piston the next morning. The top of #4 piston was much cleaner than all the rest but I really wanted to see coolant on top of the piston. I finally went and drove the car hard, and came back and immediately pulled the plugs hot. I put my borescope in the cylinder and and there was the coolant. Just a little puddle that obviously contributed to the very intermittent nature of the misfire because it could evaporate quickly with the hot piston. This horrible pic of the borescope screen but you get the idea....
Anyway my question is this. How many of you guys would have looked at the RC and Pulse Sensor test and called a headgasket and walked away? I guess confidence is built on experience but I am just curious of your thoughts. Even after all this and me printing and notating my results and sending them with the car it went to 3 different Nissan dealers before we found one who would agree the headgasket was bad. A headgasket did fix this car. As I am typing this I realize a 5 gas would have nailed this quickly but well right now I cant afford one but that will change with time.
I like your persistence. Over the years, I have used a FLS in the cooling system, but have not been satisfied with my results. The waveform you grabbed sure is consistent and shows some pressure spikes in the cooling system. Over the years, I have worked on a lot of compression leaks through head gaskets and cracked heads and there is no one way that will find them all. Oh BTW, what is "old…
Oh BTW, what is "old school"? :) A can of Bar's Leak and a prayer? :0)
No Gary, Old school would be using black pepper to seal up the leak :) Merry Christmas!
And a very Merry Christmas to you and Alice. I miss the both of you very much... :0)
I was showed that by an uncle who wrenched in the 50"s and 60's
Hi Caleb. Given the cold start misfire and symptoms, coolant level etc, there are simple ways without resorting to technology, but the smart technician will use whatever resources work in conjunction with one another to prove the failure as efficiently as possible. Sometimes the use of more technically involved diagnostic tools can lend itself well to learning. One has to keep an open mind about…
How are you connecting the FLS to the radiator? Are you using a pressure tester cap with hose? I'd like to add this test to my arsenal since I've never done this one before. Nice job, BTW. Jim
Thank you Luis. I have all the equipment you mentioned except the adapter that goes into the funnel. I'm sure that won't be too hard to find. Jim
Hey Jim. I really dont have any pictures right now. I use an assortment of rubber fuel line and heater hose attached with brass double male unions that I jam in the neck however I can.
you can use pressure test cooling adapter or I also have a cone is 2 in dimension. just make sure you lower the coolant level to leave a volume of air to be compressed.
You definitely had a good find and I liked your thought process. I think that as long as a diagnostic method is soundly rooted in physics that it is good. In this case, with a pressure spike in the cooling system that was timed with a cylinder the only logical conclusion is that the pressure came from the cylinder. Just to put my mind at ease, I would have pulled the spark plug and run the test…
You know I feel like an idiot for not doing that now lol. That would have been the definitive answer I was looking for!!
Just like so many other things with diagnostics everyone has their own sequence. All that matters is that you found the issue and proved the failure point. Like I said I definitely appreciate your process and determination.
Thanks for posting this, Caleb! So the head has already been resealed... How long have you been sitting on this case study? For what it's worth, no, I would not have been content with just the waveform. The method isn't the problem, IMO, it's convincing others that the waveform tells the story. That's why finding the coolant in the cylinder is so valuable, right? You can't argue with that. Er…
Hey Tyler, yes I have been sitting on this post repair for at least a month. And yes you are correct, convincing service advisors, customers, and other techs at times of the meaning of waveforms can sure be a challenge.
Another great case study Caleb! After reading through all of the responses so far I think the use of "old school" and "new school" are complementary concepts. As technicians who have spent hours analyzing oscilloscope patterns I think we all like to see the hard failure causing the anomalies in a waveform, the worn cam lobe, the carbon on the valves, the coolant in the cylinder. I feel…
This is a great case study. With the advancements of today’s bore scopes I use them quite regularly. Usually if I am going to pull a spark plug to confirm a problem with a pressure transducer I look with a bore scope first. Another thing I have noticed is the last several head gaskets I have diagnosed fail while cooling down. If you have a car that you suspect has a head gasket failure get the…
Caleb excellent job documenting your process. I especially like the fact that you inserted the scope captures at a point in your case that allowed me and others to look at and analyze before the next step. Personally I am working to bridge the gap from the way I used to do things (not a pulse sensor in the radiator that is for sure), to learning new methods and learning how and when to deploy…
What an excellent case study and example. I still have a hard time "trusting" my equipment and usually go by the trust but verify mantra. I also would not have thought of pulling the plug and see if the pulses went away.
youtu.be/D-C34kQqxzY thanks for sharing , good finding this is another method I started using , applying the leak donw test and the inches of water tool that can pick up very low pressure. on coolant system . this vehicle had the same condition than the one you had 629 and something miles after I clear the dtc the first time it returned.
I like that pressure gauge on the reservoir tank.