5.9 cummins no start
Seen this truck few months back crank no start, at that time I got fuel sample looked ok but filter was dirty lack maintenance, so just capped fuel rail one at time, and when capped cyl#2, it started. I tried sell guy set injectors, he just went with the one injector and fuel filter.
Now its back doing same problem, and his other mechanic changed 5 others sometime after I worked on it. I checked fuel and it's cloudy, and filter is black looks like algae. It's a farm truck so I think we have see where he is getting fuel.
Scan tool hasn't showed codes I am sure it had a rail psi code but other guy erased it. Wont start as only builds 2000psi. I decided to hook up the wps500 to the fuel return line, and I isolated the cp3 return, also verified the relief valve wasn't leaking. I amp clamped cyl1 and got this capture. I had to start the truck with just small amount gas on rag, I had read on iatn a guy experimenting with this setup. Anyways, I am just trying to learn if its possible to tell what is going on with the return line trace. And would like some ideas on how prove what is going on (what is the higher hump? what is the lower hump?).
I will probably block one cyl on fuel rail off and get another capture. And I will have another truck about same yr with new injectors to get known good in day or so. Shoot me some ideas.
If needed I can get truck hot and do injector volume test on each injector which I may do just get more information. Just trying figure a better way.
To clarify here where exactly did you take the reading with your wps? Also could you post the scope files? If I could look at it on my lap top it would help.
I hooked wps on return line coming out rear of engine. I get a picture of the setup tomorrow. I will also try to post up scope files if I can figure that out.
I am on pins and needles. I would like to regulate the return a bit (very slightly, maybe even just a fuel loop)for what I assume may give more clarity. I have wanted to do this for a while as well. I think its a great idea. I assume 5 6 and 1 have excessive return for the reason that there is a steep decline in pressure after the injection event that you don't see on the others. Is that pattern repeatable? Very interesting. Thanks for posting!
I restricted the return a little bit with a ball valve will post pics of the rigging. Also some scope captures. Hoping all you great minded techs can help me understand what is going on. And perhaps after that make life a bit easier in the shop for us diesel techs.
I will be watching your progress and I am hoping for something solid to hang your diagnostic hat on comes as a result.
I am trying to imagine what effect an injector that is leaking all the time into the return side would have on the pressure waveform. This is often what causes the symptom you described. Also don't overlook the fact that loose transfer tubes end up bleeding around the injector and into the return flow. It's not just excessive dumping into the return during the injection event that you will be measuring.
Well I apologize on this post, I got carried away and thought I had a excessive return on the injectors, since it wouldn't start cold or hot. 50ml/min Injector Return Isolated hot this really surprised me (spec 177ml/min). I also had over 750ml of fuel supply from the lift pump to the fuel filter in less 30 seconds. Next I checked cp3 return @ idle and had 750ml/min which (I understand over 1000ml\min replace pump) I then checked Hi Psi Output from cp3 while cranking 3x for 10 seconds each time. 30secs I had 325ml which should be ok. Well I tossed known good psi regulator on cp3 and it made no difference. So based on no excessive return from fuel injectors, and good volume from lift pump, I sold a new fuel filter, clean tank lines, and cp3 pump. She starts and runs well.
I had another truck that needed injectors, and got some scope captures of it. I thought this would be ez to do. ButI will still have to do more testing when time allows. I have not used the wps500 much at all first time. I had scale on 3 then zoomed 3x. The trigger is on cyl1 and I have the wps500 on return line, there is a shut off valve between wps500 and fuel tank, I would close the valve some till I got 3 to 5 psi on wps500. I then would hit zoom3x and try see what was showing up. Got see how to attach my scope captures.
The two pics below are on diff truck with new injectors, one with cp3 reg unplugged. Kind feel like I wasted all dang morning.
No apologies needed. I can't wait to see excessive return in a capture. If I have some play time I will grab one on a Duramax at some point. It may not end up being a conclusive enough test at any point to confirm injector replacement, but it is a very interesting idea. Its always interesting to me just to discuss ideas. Thank you for your efforts.
Yea I think the higher the upward pulse the more return but I could be wrong. I did manage to use scan tool at times and kill an injector, and at times I could see the scope loose an upward pulse. But more time will be needed and of coarse one with excessive returns.