So I got this 2010 3500 at copart had a small engine fire melted some injectors near firewall. Changed out injectors with used ones got it to run but would only make it down the block then engine dies. Did that a few times then wouldn't start at all not getting more than 450 psi rail pressure. Rechecked all the fuel tubes are tight etc no change. Put in a used CP3 same issue. Also bought new injector set off eBay bosch but prob counterfeit still no fuel pressure. Changed the fuel pressure sensor on fuel manifold and also the relief valve on it and cleaned it well took it off twice. I am getting plenty of fuel to the Cp3 with line off key on floods out from filter. I have cranked truck with a fuel line off no 1 and fuel does shoot straight up out of manifold but it may be low pressure just from the gear pump. I have since capped off all the fuel line plugs on manifold and plugged the return line on it with a fine thread bolt in place of the banjo Still no fuel pressure via Witech with everything capped off fuel manifold have disconnected the fuel pressure regulator on cp3 and the fuel control pressure valve on it as well was getting some fuel out the return port before I did that. Seems to point to the old cp3 was bad and same with used one I tried another used cp3 same issue. That's 2 used CP3s of unknown condition I tried no fuel pressure and the original one. Just throwing this out there if anyone else experienced this. Driving me nuts spent a lot of time on this.
On the Witech pic shows command from ECM 5799 psi but getting negative 10 psi at manifold. That's with everything capped off all 6 with JIC caps and a bolt into the return port on manifold where banjo bolt was.
It's just strange 3 CP3 used pumps could be bad including the original. The other 2 questionable used off eBay but one was supposedly from a crashed 6.7 and the other from a 6.7 with a broken crank.
And the low pressure pump is ok?
Yes it's getting fuel from the intank pump. Lots of fuel going to the CP3
Just something to get out of the way.
That's the manifold with pressure sensor on the back have new one. The return line is plugged and all the outlet ports for 6 injector lines capped off with JIC caps.
Yes plenty of fuel flows out a lot with line off cp3 key on
Only line that's going to that manifold is the high pressure line from CP3. Can read pressure from sensor on back number 5 with Witech. Not building any pressure.
Yes it's strange 3 used would all have a issue, but imo--I've never had good luck with used fuel system main pieces. I had a 12.7L Series 60 that just up and quit, never seen one do that, replaced with known good used, lasted a little less than three days. Replaced with oem new unit end of problem. Yours I can't say that spending on a new or reman unit would fix the issue--it's not my money.
Ok I think you right. Need to get a reman prob just junk eBay. I have 2 other 6.7 Cummins 2008 CC 5500 and 3500 never had issues with the cp3 they not like the cp4s so thought used prob be ok.
Aside from trying to get a pressure gauge right off port on CP3 that's all that left to test in case something weird going on in fuel manifold. But these pumps make 26,000 psi my hydraulic test gauges go to 10k need some special high pressure fuel gauge kit. Just easy to check actual fuel pressure with clone Witech.
I'm assuming #8 is feed line, I think I would remove manifold and run compressed air through it first just to make sure.
Ok I have done that I'll check again. It's not that difficult to remove the manifold 4 10 mm fasteners and unplug pressure sensor. At the opposite end of the manifold of the pressure sensor is a relief valve I replaced that with new. Some guys will put a solid race type plug there when they mod the fuel system increasing pressure. There is no number on that part but u can see the hex plug on parts diagram There looking inside at each port is like some kind of filter stone or something you can't just look in each port and see inside manifold tube, kinda like an exhaust port on a equipment small air system dryer filter with the clear plastic oil cup.
Local injection pump rebuilders don't touch these cp3s, he said tiny orafices and requires a clean room lots of small parts. Said get new, used ones sitting around dust can cause problems
Just wanted to update after getting an almost new CP3 still have negative -18 psi manifold pressure. It's all that's left is the manifold I plugged all ten outlets left sensor and relief valve on shot some air into intake high pressure fuel port put in a bucket of water huge leak in manifold. So I am guessing why it never leaked fuel from it because the cp3 is drawing negative pressure in the crack creating negative pressure in the manifold so I never assumed it was bad. Gonna order a new manifold. That's where it's leaking air big time in bucket of water fuel manifold and Witech showing negative fuel pressure.
@Roadoil I have a 2019 6.7 same problems no pressure at rail replacement lift pump cp4 conversion to cp3 got the truck from Iaai with damage at front when you referred to manifold it’s the fuel rail? I would have to take mine to see if it’s cracked hope mine hasn’t a leak last thing to check
Yeah manifold. I was doing this test all wrong using JIC caps on the fuel manifold. You need the bullet type plugs can get a set of 6 off Amazon $30 to properly plug and test for pressure. I didn't believe the clone Witech fuel pressure settings negative 15 so bought a 2500 bar gauge fuel pressure tester off AliExpress $120 verified no pressure. When I used the proper bullet type plug caps I showed no pressure on the used CP4 I bought looked new put old CP4 on instantly built pressure 20,000 psi with it unplugged FCV. I had a combination of fuel pipe to injector issue on one cylinder and a bad new injector leaking once I fixed that truck instantly started. But my problems have just started there instantly over heated gasses pressure in coolant have a bad head gasket or cracked head in process of removing head now.
You can connect the fuel pressure gauge 40,000 psi direct off CP4 crank to verify it's building pressure. When you stop cranking the pressure instantly drops back to 0. But yoi can also plug all the outlet lines 6 on fuel manifold with the proper caps as long as your relief valve is not bypassing on fuel manifold you should instantly build pressure up to 20k with FCV unplugged and check Witech for actual pressure.
Mines is little bit newer 2019 which tool you think i should buy bullet type plugs? When you did your test it was in a bucket of water right with the plug in? So your high pressure pump it was bad I have a brand new from the dealer
Yeah used a bucket of water but the JIC caps don't seal the manifold as the threaded ends are not welded all the way around.
You need a scan tool that can let you see the fuel pressure live with the plugs in. I have a Witech clone works great but it's offline only.
Thank you so much my Brother I really appreciate your help and support gonna try to buy that one you just told me