Help with pulse waveform
I built a pressure pulse sensor to try and learn a little about using it.
Would someone look and see if this is a usable waveform or do I need to buy a sensor made for automotive use?
The file attached is from a 2011 5.3 that I think may have a cam and/or lifter problem. This is from the intake while cranking.
Thanks for any help
Hello James, I only have PICO 6 (32 BIT) downloaded and it will not let me view this. Are you using PICO 7 (64 BIT)? Just curious. I will say about transducers, you will need a good one to read vacuum pulses, it needs to be a true vacuum transducer and not a generic that claims it can read vacuum and pressure. Aftermarket ones often give a very dirty signal (even with a filter applied) but…
It looks a little noisy. Your in cylinder isnt going to 0 or pulling a vacuum. Do you have the correct range set for all your stuff. I know the homemade is tricky. Looks like the waveform is in the exhaust? And this is running or cranking?
Hi Erik The in cylinder sensor is not scaled my good sensor quit working so just used an old sensor for a reference. It is in the intake cranking. Thanks
James, My first suggestion is to ALWAYS try out a new tool or test technique on a known good vehicle. That way you can determine if you have a tool that provides a usable signal. But taking a look at this and applying some rulers and cursors you do see a pattern in the intake waveform. I'll post a screencap for all to see. I'm not the pressure waveform expert that some on here are, AND we don't…
Hi Richard The sensor is set up for vacuum on the downward spike. Thanks
Your pattern sure looks like vacuum on the up spike. I've gotten several buzzers to build transducers that were wired reverse polarity. I'd apply vacuum (suck on it) and actually see which way it goes.
Hi Tom That is what I did to check the polarity . I reversed the wires to the scope so vacuum would pull down but did not check the other way to see if pattern was better. Thanks
Looks retarded timing at the EVO 49 degrees and the IVO is at approximately 86 degrees opening. The towers are even but it isnt even pulling a good vacuum. The pull only gets to 25 psi not negative pressure. Id have to do some research unless your equipment is off of range but it shows you on range 1 so thats weird.
Which sensor is yours? Channel A? What sensor are you using for the in cylinder capture, channel B? It is best to practice a lot on known good vehicles, save your captures and then you can use them to compare to the problem vehicle to determine what is wrong.
Hi Eric The pulse is channel A and the in cylinder is B. I did try it on other cars but it still looked noisy that is why I was not sure the homemade sensor will work or I just don't know what i'm doing. Thanks
Hi James, Using firing order 1,8,4,3,6,5,7,2, from left to right. #1 has a pressure transducer so I could see that one being off a little possibly, but #4 appears to have a problem. This pulse pattern is hard for me to distinguish. I might suspect a broken valve spring before a cam or lifter.
Hi Glenn I have checked the valve springs, cannot visually see a worn cam just by looking while cranking, leak down check, fuel and just about every test I can think of. I know something is going on in the motor because the scanner is showing a lot of knock but I cannot hear anything, That is why I was thinking maybe bad lifters or something. What this truck does is, idle good and run fairly…
Just a thought: when looking at the cranking event, it is very helpful to have the starter current trace – sometimes it is so much easier to analyze the rest of the waveform when you can link it to each of the compressions.
I guess I needed to phrase my question better. Which of the two sensors in use is the one you made? Did you make the in cylinder pressure tester, channel B in red? Did you make the vacuum sensor unit, channel A in blue? Upload a couple more files that were from a known good vehicle so we can see those too please.
Hi Eric On the files I first uploaded the channel A blue is the homemade pulse sensor and the channel B is an old A/C pressure transducer I was using as a sync and to see if it would work any at all for in cylinder as my good sensor quit working. Here are some more files, the 2011 is the truck I'm working on and the 2015 is a known good running truck. The channel A blue is my homemade sensor…
Your signal on Channel A (Blue) is consistent and seems to be good enough to use. I think having a sync signal is important and using a second matching sensor in the exhaust at the same time would be helpful. The signal on Channel B (Red) is lacking vacuum. I good sensor should show the vacuum as well as the compression. Here is a known good from a 2001 Toyota Corolla. Everything below the…
Hi James, This might be a long shot, but try holding the throttle partially while sucking a little tranny fluid into a vacuum hose (about a pint should give good results, it will smoke, but that will clear up with running. Comparing the two patterns to me appears to be “sticky valves” on the 2011. Try the tranny fluid then take it out and run it under various loads for a few miles, then…
Hi Glenn I will give that a try. I'm one of the older techs and have used water and fluid in the past. This engine has almost 200,000 miles and has a very young driver so I'm sure it gets run. They are willing to take it somewhere and get a motor put in so I think that may be best. This truck has been to 4 shops with one installing a transmission, I guess thinking it was the problem. I was…
Hi James, Ah, the memories of my first car as a young ambitious man of the world… LOL. My dad made it clear that if I broke it, I fixed it or I didn't drive. After a couple of salvage engines, a tranny and a few frustrating weekends of not being able to go out, I learned to slow way down and appreciate what I had. Not to mention the money I would have if I didn't run it like a bat out of hell…
Hi Glenn I agree with you 100%. I retired and closed my shop about 3 years ago and now do a little side work for the body shop here doing a little adas, programming and a lot of wiring problems. The cost of the tooling and programming and all the other things that go along with it has gotten to be more than it is worth for the volume of this type of work in a small town. Thanks James
Hi James, I am semi retired, but still working like you. I get called quite a bit for big tractor AG these days. One because I can understand the CAN bus systems on them. Two, I can read and comprehend the service information and Three, I can carry a logical conversation with technical support if I need to contact them online for in depth diagnostic assistance.