Bad Injector Ramps (Red Trace In This Image)

Jeff from Memphis Owner/Technician Posted   Latest   Edited  
Case Study
Driveability
2007 Dodge Nitro SXT 3.7L (K) 4-spd (42RLE)
After Running A Few Seconds Sets All 6 Injector Circuit Codes. Pcm Has Been Replaced Twice
Tipm Has Been Replaced

Cylinders 2&3 have no Injector Pulse. I have unplugged the throttle body, Alternator and all injectors. Ramps start out better than this but not as I would expect to see them and then get worse after approx. 6 seconds till they look like the attached picture and follow video link. 

Injector supply voltage stays level and clean. The #1 injector scope pattern voltage looks normal. The circuits shown on the picture are Channel 1 is injector 1 voltage. Channel 2 is red trace and is injector current ramps. channel 3 is voltage feed to all injectors and PCM measured at fuse panel. Channel 4 is coil current ramps. I even switched current probes to see if one of my probes was damaged. They were identical patterns. Any Help on this vehicle will be most appreciated...

youtube​.​com/watch?v=h16NEe…

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Bruce from Spring Hill

 

Technician
 

Where do you have your current probe? 

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Jeff from Memphis

 

Owner/Technician
 

All connections were at TIPM except 31 injector was at injector connector.

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Geoff from Lahaina

 

Diagnostician
 

read a few cases of RFI from a coil doing crazy-azz juju on Chyrsler/Jeep. Try running it with one coil at a time disconnected.

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Eric from Edgerton

 

Owner/Technician
 

That is noise on the wire, and it appears that other hardware is powered by that circuit. Those spikes appear to be there KOEO. I took a quick look at the wiring diagram and found a capacitor on that circuit, I will guess it has failed or is disconnected or damaged. Locate and test it, or just replace it. There could also be a component on that circuit that is extra noisy and the capacitor has been put there to help with the issue. If that component has problems that are causing it to be even more noisy than usual it could be overpowering the capacitor. If the capacitor tests faulty then I would install a new one, if it tests good I would install a new one. I would also disconnect items that are on that circuit one at a time to determine the cause of the noise.

Are there any codes stored?

Chrysler PCMs love to turn off the injectors when there are miss fire codes. 

I doubt the extra current spikes on the injector wave forms are causing a problem with the lack of injector pulses on cylinders #2 & 3. I would think it is more likely that the PCM has turned off those injectors for some reason. Unless you can prove otherwise. If you clear the codes and connect your test equipment to the #2 & 3 injectors do you see activity during the first cranking event after the codes were cleared? Maybe even for a few seconds of running? Until the codes set? 

When you post pictures try to get both sides of the scope so we can see the scales, I can't tell how much current the injectors are drawing, it doesn't look abnormal. It would also be nice to know where you have attached your test leads/amp clamps. I try to connect my leads/clamps as close to the component I'm testing as possible, unless I want to see everything on the wire. If you are going to include one injector battery feed you might as well include them all. Please include the trace color in the description of the scope capture, it makes it quicker and easier to see what each one is for.

In this type of situation, if you can't disconnect something and run the engine, I would isolate each component with the scope and try connecting the amp clamp to each one at a time on both the power and ground circuits looking for the problem part. I would even try the fuel injectors just to see what they look like. You would only have 4 left to test after checking #2 & 3 for activity during cranking as I mentioned previously.

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Robert from Ballston

   

Diagnostician
   

It appears you need to current ramp the injectors at the injector. There is noise from other circuits whre you are tapped in. Also power should be voltage drop tested at the injectors that are setting the codes. Also should scope for he ground switch at the injectors to see if it is switching correctly from the engine module. 

At first glance without being able too see your complete scope setup my thoughts are you are on a bad time base, and you may also have a failing amp clamp and there is noise from other actuators on the circuit where you are connected

If you scope the ground side of the injector at the injector connector and there is no voltage then the power to the injector is open or the injector is open. If the ground wire shows near system voltage but never pulls to ground then the module or harness is at fault. At that point one would scope the injector voltage control at the module. Again there should be near system voltage there until it is pulled to ground by the module. If there is no voltage at the module driver circuit but there is voltage on the ground side of the injector connnector the harness is open between the module and the injector. 

If there is voltage at the injector switch wire at the module but it never pulls to ground then the module is in question. Then try operating the injector with an actuator test to see if the module can pull the injector driver low. 

Also be sure to verify correct number of pulses to be sure some injector wires are not shorted to each other If an injector actuator test is performed with a scanner and more than one injector operates while commanding them on individually then likely there is a shorted harness

If there is a problem with this third module then I would manually ground all of the injectors one at a time at the module connector with it unplugged and monitor current to determine if there is a short damaging the module. The injectors will need to be powered up by jumping the ASD relay in order for that test to work with the module unplugged. 

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Jeff from Memphis

 

Owner/Technician
 

The pcm is setting all 6 injector circuit codes after it runs a few seconds. I will do the tests that you suggest tomorrow and let everyone know my results. I tried to upload the pico file, but it will not accept it. If you want a copy please send me an e-mail address.

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Cuba from Phila

   

Mobile Technician
   

How about setting up a google drive or Dropbox file, and posting the link here? It would make it easier for anyone to see it, either now or in the future. Make sure you make the link "visible to anyone who has it" setting.

FIle you're trying to upload may be too big to post here. 

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Bob from East Longmeadow

 

Owner/Technician
 

That mess is not being mirrored in the voltage waveform so I would say that you are getting noise and/or other signals in your current waveform.

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Jeff from Memphis

 

Owner/Technician
 

Unfortunately this job is on hold due to Head gasket leak found during additional testing by tech on site. I will let everyone know when and if this job resumes.

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