No Codes, No DLC, & Driveability Concerns - A Thought Experiment In Diagnostics
Every one of us approaches our diagnoses in a unique way. Challenges arise when our normal go to tests are not viable. I personally like to gather information from the customer, perform a quick walk around to get a mental evaluation of the vehicle and potential operating conditions, then hop in the seat and look at data (usually the first 15 minutes of my diagnosis). Others may have different processes which they prefer to follow, even down to make/model/year. Either way, in my opinion, it is impossible to dismiss the usefulness of a scan tool when dealing with computer-controlled engines.
What does one do when one of the core tenets of our modern diagnostic strategies, live data, is not available? I am not speaking of no network communications or modules being down, nor am I talking about an inability to access the proper tooling, but quite literally not even having scan data as an option. There are those of you who are thinking that there was a time when scan data wasn’t the answer to everything, and you would be correct. There are people here who I'm sure have worked on the early electronic fuel injection systems, from … (Bendix Electrojector) up until OBD-I/OBD-II, and are familiar with this situation and probably have a load of great tricks as a result. Once a month or so I run into diagnosing electronic engine controls with no data and find it a great way to brush up on logical thought process and a clear diagnostic strategy.
The vehicle, though not especially important for this exercise, in question is a John Deere 620i/625i Gator and utilizes a Kawasaki FD620D 2-cylinder EFI engine.
This machine does come equipped with “blink codes” for various faults, but having actively induced ignition coil, injector, and crank sensor faults of varying types I have found the blink codes to be of minimum use at best. No blink codes are present for this experiment.
Key Points Of Engine Operation:
- Engine is equipped with only a MAP sensor, no MAF
- IAT, ECT, TPS1, TPS2, MAP sensors all work off 5V reference, ECU will flag a fault above 4V or below 1V
- EOP (engine oil pressure) is a NC switch but it’s state has no effect on engine operation other than illuminating a light
- Equipped with VR (variable reluctance) CKP sensor which is triggered from 22 protrusions cast into the flywheel with a 2 tooth gap for #1 TDC
- No CMP sensor
- The 2 fuel injectors are fired simultaneously (not mentioned in service information)
- They share a common power source and have separate control wires leading to the ECU but are tied together internally. They share a fuel rail
- The 2 ignition coils also fire simultaneously (not mentioned in service information)
- Common power supply with the fuel injectors with separate control wires leading to ECU which are also tied together internally
- Throttle body contains 2 throttle plates and therefore 2 TPS
- TPS1 is cable actuated by the throttle cable
- TPS2 is operated by an ECU controlled stepper motor. TPS2 position is used to smooth out rapid fluctuations in TPS1 throttle plate as a result of off-road use.
- Utilizes an electronic fuel pump, ECU controlled (on or off, no PWM)
- Has a vacuum operated fuel pressure regulator at the end of the fuel rail
- It is an open loop system, and has no O2 sensor for feedback nor does it have a catalytic converter (added 8 minutes after original post)
- Added 3/2 @ 5:00pm: Per service information "Ignition and injection timing is controlled by the ECU". That is the full description.
Hopefully that is enough background information for everyone.
The engine is hard to start regardless of temperature with additional symptoms of smoking at high RPM, rough/choppy idle, and low power though out the RPM range. All these symptoms are present with or without a load. Machine is used on flat ground and within 1,000 ft of sea level (not relevant here but I figured someone may ask).
There are two main questions I have here, and I will answer them after some discussion.
- What would your diagnostic strategy be for this engine, assuming you didn't have the scope captures I added? Remember no scan data and no codes available. Just a rough outline of the thought process.
- Upon evaluation of the waveforms seen below, what would you believe to be wrong with the engine? Again no scan data, and only the waveforms (I will attach the Shop Stream files as well).
The point of this exercise is not to try to trick anyone, nor is it to correctly diagnose the problem, but to explain your strategy and thinking. It is equally easy to get to any component on the engine for testing, from ECU to fuel rail for pressure testing. I know I have been guilty of finding myself somewhat lost after my standard strategy didn't work and I had to adapt to figure out the problem.
All attached screenshots are from during engine malfunction (these are old captures and I didn't have them clearly labeled as to which cylinder was which). I have also attached the full files, for those who want to play with it on ShopStream Connect. To those viewing the full files, I apologize for the poor scaling of the CKP sensor in that file, these captures were originally taken 3 or 4 years ago when I was just starting to learn scope usage. Updated: For the final capture Pressure Waveform Is Cylinder #2 - CKP Indicates Cylinder #1 TDC - This is an old capture, not sure why I don't have one with cylinder #1 waveform. I will tell you that CKP is in fact indicating #1 TDC & this engine does not have CKP issue.
- Trace 1 (Yellow) - Secondary Ignition Probe [clip on] (remember both fired simultaneously)
- Trace 2 (Green) - Injector Current Ramp (remember both fired simultaneously)
- Trace 3 (Blue) - In-Cylinder Pressure Transducer (0-500 psi, and it was zeroed before use)
- Trace 4 (Red) - CKP sensor
2nd Update For Clarification:
Another Capture With CKP Overlayed Over Cylinder 2 - Pressure Waveform Is Cylinder #2 - CKP Indicates Cylinder #1 TDC - This is an old capture, not sure why I don't have one with cylinder #1 waveform. I will tell you that CKP is in fact indicating #1 TDC.
3rd Update Based Off Of Proposed Tests So Far: Some additional data points for everyone based of their desired testing direction.
ECT, MAP, EOP, and IAT are within specification and not skewed. Service information gives voltage and resistances ranges for sensors, and they check out.
Fuel PSI is at 26 PSI at idle and increase at wide open throttle - Within specs
Spark is good, as evidenced in the scope captures.
Edit: As I just replied to Dmitiry: When I first ran into one of these engines, the thing that stuck out most to me is that the only thing that seemed to vary was fuel injection timing and duration. Ignition is consistent but the fuel injector pattern is all over the place and so that is where I focused my thoughts. I had to determine what would cause the injection timing to change as there was no service information explaining actual operation or input/output relationships.
Final Edit W/ Updated Scope Captures:
The root cause of the problem with this engine, besides a pretty lame engine management system, was that the throttle bore had heavy oil buildup where the plate rests, causing the TPS1 to report accordingly. Due to the engine design, fuel dilution of the oil is a common result of short tripping the engines and not getting it hot enough to burn off the excess fuel. This causes oil level to rise and get forced through the crankcase breather hose into the intake manifold and gum up the throttle bore as well as dumping oil/fuel fix directly into the intake.
Here are the updated scope captures I just grabbed off a known good machine I had at work. It's a newer model by 1 year, but it appears that it still utilizes the same engine strategy. I'll leave it here for discussion as it seems to have raised some more questions in my mind.
To answer the point raised by Albin/Dmitriy (thanks again to both of you), here is a diagram of the crankshaft.
All captures are while cranking. I apologize as I have one 0-500 PSI transducer, and one 0-100 PSI, so the scaling is off for Cylinder 2. It's all I have to work with right now.
- Trace 1 - CKP
- Trace 2 - Cyl 1 Ignition, except last capture which is Cyl. 2 PSI
- Trace 3 - Cyl. 1 PSI
- Trace 4 - Cyl. 2 PSI (or Inj depending on capture)
And The Fancy Throttle Body courtesy of Mikuni
Without data and codes, it goes back to to basics. What does a gasoline engine need to run properly? Air, spark, fuel injected into the cylinder, and it has to happen at the right time. As far as the scope captures, I have learning to do but I look for inconsistencies. What's changing? What is not like the others? In this case the in cylinder looks ok to me, (again, I'm not a pro) but it has a
Martin, That's definitely part of where I'm heading with this. I'm going to add this update to the main text: Service information tells you, and I quote, "Ignition and injection timing is controlled by the ECU." It does not mention that both coils and injectors are fired simultaneously nor what sensors it prioritizes over others, therefore your left up to using your brain and experience to try
I would be checking my inputs to the ecu. Map, Iat, Ect, tps1, and 2. Inputs and outputs right? The basics again. The ecu can only control the outputs correctly if the inputs are correct. Garbage in, garbage out as they say. Because of the scope captures, we know what direction to go. We know something is affecting fuel delivery. Goes back to inputs, checking our signals at the ecu. Now if
After seeing the overlayed capture, I would agree it looks to be out of time. Maybe a loose trigger wheel?
Martin, This is the confusion I was trying to avoid, but reason it out this way, it is a 2 cylinder engine, so #1 TDC should occur when in relation to #2 cylinder. In the description the pressure waveform is cylinder #2, with the CKP indicating #1 TDC when expected. My apologies, not trying to trip anyone up. I think we may be better off if I remove the last capture, and just leave it at the
It is a 2 cylinder. How are the pistons/crankshaft positioned. Are both pistons at the TDC at the same time, thus firing on cylinder every 360 degrees, or is the crank built so only one piston is at TDC at a time?
Excellent question! I did not know this about 2 cylinder engines. Here's a link to some info... And based off of that, and the fact that Chris explained that the missing teeth are TDC #1, I think this image shows where the compression towers should be, if cylinder one were included.
Thank you Albin. I was not aware of that fact. I will do some research on the parts side and see if I can't get some captures of dual cylinder waveforms. It does make sense based off the data. Steve, thank you as well. The least I can do for you guys sticking through the mess is to get some known good and properly labeled scope captures to confirm with.
Pic 1 and 2: The injectors and coils are not firing at the same time. I would want to get a capture of the CKP in relation to TDC compression. I'd gather the "missing tooth" is TDC. Something is moving things around where they shouldn't be.
It is the 2nd shopstream file, attachment 8 out of 11 in the list. Has the CKP on there as well. I had the scaling wrong and it made a screenshot too confusing. Just added to bottom of main post. Here is a copy
Hi Chris: Your OP captures had me believing that while it may be out of time, you had a loose crank sensor or the crank was walking. (CKP capture had no context.) I have no idea of how the sensor is attached. Do these engines use a thrust bearing? This update, with the new capture, shows that it appears to be out of time. How much, I don't know but each tooth appears to be 15 degrees. Guido
Guido, Unfortunately I took these captures quite some time ago, and the CKP is overlaid on Cylinder #2 (rear cylinder). Confusing I know, that's why I hadn't posted it originally. I'm hunting around for another one done on cylinder #1, I can't seem to find it. The CKP sensor only indicates #1 TDC, which it is indicating, and it's not walking. As far as anchored. It is mounted to a boss coming
I guess thinking back, realistically, before I got the scope out, the first thing I would've done is check fuel pressure. Then checked spark output at the wire.
Need to check fuel pressure , map and ect next.
Lots of data here, Chris! Running 1 and Running 2 graphs are captured at different rpms. And slower rpms seem to give higher compression peak. How can this happen? The compression event starts from manifold pressure. What are the exact values here (with the scale of the graph they are too close to 0), and do they indicate restriction in the intake?
Dmitriy, Compression starts from -7.3 PSI (so approximately -14.86 in/Hg, but double check my math). I'll update the case with the resolution in a bit. I'm just trying to stir up some thought processes, although I fear I may have been way too vague in this post to accomplish the overall goal. I got the idea from your solenoid quiz. Perhaps I can fire up Ubuntu and run that plot digitizer for
Oh, sorry, I thought you have the ShopStream fired up for those captures where you can place cursors and look up the values. I‘m on iPad, so “just browsing”. But my eyes tell me that for Running 2 (higher rpm) manifold pressure is lower than for Running 1. Or may be it is a mirage...
That may be true Dmitriy, it would make sense. With the throttle closed more one would imagine that the peak compression should be lower, but there are 2 throttle plates within the throttle body. As I mentioned in the OP, the second throttle plate is ECU actuated to smooth out the throttle actuation. I wonder if that is affecting overall airflow or reacting more slowly and skewing the
The first picture is cranking (not running) I think, since the scope files are labeled as such. The second picture should be running compression. Cranking compression is always higher pressure than running.
Thanks Steve, I believe you are correct and I appreciate you pointing it out. Old captures/screenshots and my record keeping was pretty poor back then. I should have gone over them more closely, but compression variations weren't my main concern during the original diagnosis. I'll change the label up top. Sorry to everyone trying to participate here, I'm really butchering this; this is an
I also notice in the file names is Front and Rear. Does this mean Front or Rear Cylinder, as in Cylinder 1 or 2?
Correct, I know for a fact the one with CKP sensor is definitely cylinder 2 [rear]. I'm starting to really doubt my early labeling. These were captures from the first time I ever used a scope for an actual diag. Sorry to spread the pain.
Oh, that explains it. Nevertheles, we are making progress — relabeling the graphs correctly (though graph #4 looks like Running to me). I think it’s important because the ECU may be using different injector timing strategies for cranking and running.
Ok, some additional data points for everyone based of their desired testing direction. ECT, MAP, EOP, and IAT are within specification and not skewed. Service information gives voltage and resistances ranges for sensors, and they check out. Fuel PSI is at 26 PSI at idle and increase at wide open throttle - Within specs Spark is good, as evidenced in the scope captures. Edit: As I just
It looks like you are guiding us to a fuel injection timing problem, and it definitely looks like it is all over the place. But, before you added that update, I was confused about something else. This may be off the path, but maybe you can clear this up. You said the missing tooth section of the ckp pattern is TDC #1. If so, then it seems as though cylinder 2's pressure peak should be there as
Steven, I honestly never looked that far into, SI says that indicates #1 TDC. I see exactly what your saying but I can't explain it, least not yet. Not the direction I had gone in. I saw good spark, I saw compression and some valve movement, and fixated on fueling. Looking at it, and knowing the fix, i cant explain it. I'll have to head to the shop tomorrow and take some captures off another
You might be able to answer that without scope... Just recall: does it sound like a Harley-Davidson?
Yes it does. I'll have to ask you to explain a bit further on that.
Hmm, is it really Kawasaki then? auto.howstuffworks.com/question325.ht…
Albin Moore helped to clear this up with his question above. See my reply to him above as well.
If we focus on the injection timing and see it floating around, we could say that the system is not in a steady state. In a steady state all system parameters (temps, pressures, throttle plate angles, rpms) would be the same and so would the injector timing. If the sensors are all OK, may be it’s time to look into that fancy throttle plate #2 subsystem and see if the ECU loses control of the
Dmitriy, I've tortured everyone enough with the mislabeled information. I'm giving up on this failed experiment. What I found out, completely by accident, was that the fuel injection timing varied with TPS1 position (the mechanical throttle). It made sense to me because it was easiest to base a fuel map off throttle position, assume certain air flow in the programming, and vary within
I know you were going for a discussion on diagnosis approaches, but with the scope captures and all the data you provided, it's hard not to jump straight into trying to figure out the problem. Like when a dog sees a squirrel, we want to go straight for the kill!😁
Yeah, it's a disease. I've heard there is medication to address some of the symptoms. Guido
I hear you Steve. I just got frustrated with myself for not making everything clearer. I actually gave more information that I originally had. Either way, the stuff everyone pointed out definitely taught me some things, especially Albin/Dmitriy. I believe we will find that those waveforms will look like the set up you had. I'll be at the shop later today and get those captures.
Hi Chris: A few comments, if you don't mind. 1: A little more information would possibly have been helpful. Not knowing much about that engine, I attempted to look for some basic information; spark timing, etc. NFG. But there are a bazillion iterations of that engine. Even looking up a parts diagram was an exercise in futility. I wanted to know how the CKP [or CPS , as I saw it denoted] was
Guido, I was just quite frustrated with myself. I must have been in engineer mode, thinking I had everything that everyone would need. I provided more information than I had originally, but many good points were brought up. I won't say 100% that it is an odd fired engine until I take the dual cylinder waveforms and confirm. The data seems to point that way though. Information on these engines
And The Fancy Throttle Body courtesy of Mikuni TB1 TB2 TB3 TB4
Quote: "Customer complaint: The engine is hard to start regardless of temperature with additional symptoms of smoking at high RPM, rough/choppy idle, and low power though out the RPM range. All these symptoms are present with or without a load. Machine is used on flat ground and within 1,000 ft of sea level (not relevant here but I figured someone may ask)." With this complaint on this engine…
Bob, Very valid point. These things run in dirt. I will be posting the resolution (though it is buried within the comments here) and some new scope captures in the main post at some point today. This didn't go quite as smoothly as hoped, but we did bring up some valuable points which I will try to illustrate with some fresh captures.
And next I would be checking spark plugs and oil.
Hi Chris I was wondering why you chose to use number 2 cylinder for your in-cylinder pressure transducer. Was it because the engine wouldn’t run with the transducer in cylinder number 1 ? If this engine does have an offset stroke, and I believe it does based on the compression peaks compared to the CKP signal. ( I think if you place the transducer in cylinder number 1 the compression peaks will
Allan, This was very early scope usage for me and so I had performed the same tests in cylinder 1 and cylinder 2. In the shuffle of time, crashed laptops, and poor data management early on I have lost alot of the data. The root cause of the problem was the throttle plate angle, which is the only input the ECU uses for injection timing, was off at idle and so skewed the fueling map at idle…
Ok, here are some scope captures I just grabbed off a known good machine I had at work. It's a newer model by 1 year, but it appears that it still utilizes the same engine strategy. I'll leave it here for discussion as it seems to have raised some more questions in my mind. To answer the point raised by Albin/Dmitriy (thanks again to both of you), here is a diagram of the crankshaft. All
So the pistons are not at tdc at the same time then. And from the illustration, it looks like both connecting rods ride on the same crank journal. So that all makes sense right? Does cylinder 1 on the latest captures have an intake valve sealing issue?
If it does have a leak, it's slight. It runs as good as any I've come across. My pressure transducer waveform reading is weak. I'm self educated when it comes to most of this stuff, meaning lots of reading, research, and experimentation. First formal training class I've ever been to for automotive was just last week with ATG, no excuse for it I know. Lots of JD factory training, but that's
These 2 cylinder engine designs are new to me, but Wikipedia has this to say: "Most V-twin engines have a single crankpin, which is shared by both connecting rods...the 90 degree layout will produce an uneven firing interval, with the second cylinder firing 270 degrees of crankshaft rotation after the first cylinder, followed by 450 degrees of rotation before the first cylinder again
Steven, That's awesome. I appreciate that. I'm still a bit off on the crank signal and what exactly it's measuring, but I haven't really had time to examine it today. May I ask where you got the pressure waveform overlay program from? Edit: I see it's your app and you have it on the Microsoft store. Thank you.
I think the service info that said the missing teeth represents TDC #1 is incorrect, or is just poorly worded. I'm sure the missing teeth are used to find TDC #1, but not that they are exactly where TDC is. That's how it is for every single car engine I've ever seen. The missing teeth have never represented TDC on automobile engines, they are used to find TDC by a certain number of degrees (ckp
I'm with you on the service information, it is so vague but then clearly lists "notch signifies #1 TDC". I figured if they took the time to write it, that it's probably true. Then again we know how translation of SI from one language to another can get dicey. Thanks again for the contributions Steven, it's much appreciated. I'm going to play with your program a bit and see if I can't educate
Steve, Where have you been all my life?! Seriously, that is a fantastic app and it's exactly what I have been looking for to make marking up waveforms easier. Thank you Sir - If we ever cross paths somewhere, the beer is on me.
Well, I'm glad you find it useful. I made it because I was also looking for something that was easier to use. Have a good one 🙂
Oh you made that? Wow! Thanks! I also downloaded it. Was playing around earlier. Seems very user friendly. That's my biggest complaint with my modis, no cursors. I'm really excited to play with it. Thanks again.
Hi Chris: That's a foreign looking setup. It looks like it is still commanding he injector open after the spark has ended. I have 2 questions and a statement. Is 36-38.4ms injector duration normal on them? If so then I assume the injectors can plug real easily. Also, is the difference in the combustion chamber pressure graphs due to the transducers or is there a difference in each hole? (I'm
Guido, It is quite a strange setup and confuses me the more I think about it. This is the type of problem I deal with frequently, no known goods (unless i have them), SI that is more fit to use to teach a 5th grade class about basics, no support network (factory or otherwise), and lack of time. Its definitely forced me to develop a diagnostic routine and overall thought processes that probably
Chris, thanks for getting more captures! How does the second capture (IGN1, PSI1, PSI2) mesh with the original ignition description ”The 2 ignition coils also fire simultaneously (not mentioned in service information) - Common power supply with the fuel injectors with separate control wires leading to ECU which are also tied together internally” ?
Dmitriy, I fear this engine has created more questions than it has answered, at least for myself. I will tell you that, per my interpretation of the waveforms, the ignition coils and injectors fire every 360⁰ which is standard for small utility engines that utilize a magnet cast into the flywheel which induces voltage into the coils every 360⁰ (for lack of a better description). This does
hello Chris Can you tell me how old the engine is in any year it was produced What are the engine working hours . Diesel engine problems are often caused by low diesel pressure. Have you checked fuel pressure and injection method thank you
Chris, it is quite amusing how such a simple engine can be so quirky at the same time. And I think you have already listed a reason for that: - No CMP sensor The ECU has no way to know exactly which strokes the cylinders go through, so it should do something that works either way. The result looks funny on the oscilloscope when compared to modern car engines. But, with the engine designed by