Sprinter rough running CMP/CKP and Injector Waveform
This Sprinter idles and accelerates roughly. Low power. Feels almost like severely retarded injection timing. Condition is always present. Blueish smoke is also present.
No codes present.
Relative compression test passes.
Actual and desired rail pressures match.
No cure of symptoms with MAF disconnected. Actually worse with MAF disconnected. Accelerates better with MAF connected. Can barely accelerate with it unhooked due to all the misfiring/dieseling. With MAF connected it still stutters on acceleration but can reach high RPM.
Verified EGR valve does open and close with scan tool and affect MAF . Did not remove EGR valve to be sure it is completely closed.
All temp sensors in scan tool data show correctly.
Fuel filter has been replaced.
Rail pressure actual matches desired.
I visually inspected CKP reluctor tabs on flexplate and could not find any issues. I scoped CKP and CMP signals and was not sure the CKP signal should be allowed to have such a variation in amplitude. I did find a known good waveform from Dodge Service Manual in Identifix Service Information that verified my CKP and CMP signals are in sync with each other. However that waveform did not have the variation in amplitude that this CKP signal does. I verified the CKP sensor has similar fluctuations during cranking or idling conditions.
I then scoped all 5 injectors along with CMP and CKP signals to see if there were any timing issues. I am supposing the double firing on the injectors is pre and post injection? Why the extra injector actuations between actual cylinder firing?
Does someone have a known good waveform capture of what the real world CKP and CMP signals should look like? Also any known good waveforms with injector firing included to indicate whether the injecting timing is correct?
I am leaning towards calling for a set of new injectors but just wanted to check on the CKP and CMP waveforms and injector timing.
Not wishing to overdiagnose this problem but also don't want to miss something obvious or obscure.
All of your scope readings look typical/normal. Our drive in shop works on a ton of Sprinters. If you want to be sure about the injector(s), you can send them in for testing. We are a Bosch authorized fuel injection shop in North Central Florida. We test and rebuild a lot of OM612 and OM647 Sprinter injectors. Let me know if we can help - …
I suspect the CKP signal variation to be an effect of the erratic, instantaneous, speed fluctuations of the crank. The CKP waveform in the top of the injector capture looks more normal. Since there are not extra pulses nor very short pulses I think the signal will read OK. Also the injector pattern is in lock step so, I don’t think the CKP is being misread. The injector capture is interesting…
I agree with your conclusions. I am also confused about the injection strategy. I checked service information and found some information on the strategy but not very detailed. Was hoping to get some insite or scope capture from someone that has scoped injectors on these engines. Thanks for the ideas.
Oddball thought: Is it possible that someone previously messed up the wiring and spliced together control wires for injectors 1,3,4, and for injectors 2,5? An ohmmeter with all injectors unplugged would confirm or rule that out.
I wondered about the injectors being inter connected but seemed unlikely for all 5 to short in such a combination. I didn’t consider human intervention. But that’s sure what it looks like. I wonder if the injector wires are in close proximity in the ECM connector. The high voltage, with a little moisture could make some leakage paths.
The PCM controls both the power and ground side of the injector. This is normal on the positive side. A 5.9L Cummins is split 1-2-3 and 4-5-6 and early Duramax engines are also split into 1-4-6-7 and 2-3-5-8.
Thanks for setting us straight, Ryan. The waveform screenshot looks like it shows voltage on the Common Injector Drivers, not on Control wires… but may be this is because traces are zoomed out too much… diag.net/file/f1dngcg1t…
Being a five cylinder engine, the PCM has two capacitors to drive the injectors. They are split 3 cylinder on one and 2 cylinders on the other. You will see the voltage of the other injectors on that are on the same circuit. I would zoom in on each injection event and measure the main injection duration. Just like a Duramax this PCM will attempt to compensate for an imbalance in the engine by…
Would you say the main injection event would be the second tower of each injectors firing cycle?
Yes, first is the pilot injection and then the main injection. The main injection should be longer than the pilot on this vehicle.
I zoomed into the last attached waveform (TDMS file), and took a look at a few injector events, one is group of 3, and the other is group of 2. As Ryan explained above, the group of 3 has a Common Driver, and the group of 2 has another Common Driver. Expectation is that the Control goes LOW for one injector in the group. But here is what is happening: Group of…
You had me for a moment. It appears that Timothy is connected to the low side on two injectors and the high side on the other three. The two connected to the low side will still show the positive voltage when they are not grounded.
That is quite an unexpected twist, hope Timothy would be able to double-check.
I wish I could say of a surety that I was connected to the same side on each injector. I did it out of state at my Uncles shop who doesn't have an oscilloscope. So I am no longer at the vehicle unfortunately to redo the capture. Although I was pretty sure I was on the same side of each injector connector. As was pointed out there are two injectors that appear to be showing connected to the low…
Obviously, I cannot verify this either as I was not there. Having said that, it does appear to be the most likely reason. If you have a circuit issue with the low or high side driver, the PCM will shut down that ‘bank’, either 2-5 or 1-4-3. If this happens, both sides are disabled to all injectors in that bank. I had an intermittent short on the 1-4-3 circuit and the engine would stall. I image…
Well,,that answered a question and left me wondering why there is a voltage spike, on release, equal to the positive voltage supply. Thanks to Ryan, I see it that yellow is #1 of the 1,4,3 grp and white is #5 of the 2,5 grp. Your zoomed in shots of the two groups agree with yellow being the ground side 1 and white being the ground side of 5. Why the spike, only on the ground side? I recalled…
These early Sprinter engines have coil actuated injectors and not piezo. This is just the normal spike after the magnetic field collapses around a coil of wire. This spike is actually stored in a capacitor in the PCM to drive the next injector in the group.