Checking rail pressure while cranking

[Lonestar10]

If the check valve is is the small one I replace it's on the back of the fuel module the module the actuators/elec fuel pump/gear pump/fuel shutoff has to come off it comes off with everything attached to it. Believe it was 5 bolts maybe 6 and 3 fuel line connections.

[Konstantin]

(11-10-2019 )Lonestar10 Wrote:  If the check valve is is the small one I replace it's on the back of the fuel module the module the actuators/elec fuel pump/gear pump/fuel shutoff has to come off it comes off with everything attached to it. Believe it was 5 bolts maybe 6 and 3 fuel line connections.

I find in quickserve that it is located above lift pump. But it also says that my truck has one more check valve above fuel filter

[Waterloo]

Just hearing your symptoms, are you sure it is fuel related? Could be the starter, or the ECM is a bit long in the tooth and in need of replacement. Have you gotten under the truck and inspected the wiring to the starter? How old is the starter? Then the ECM, run the truck, get her warmed up and smack the ECM with a screw driver handle or rubber mallet... Something I would do before tearing apart the fuel system... Is there a Davco unit on the truck, may want to inspect the o rings, change out the filter and clean the bowl... Something else to look at.

[Lonestar10]

i show in a quickserve parts diagram for a cm-870 IFSM numbered part 42 - check valve 4010078 the only one it shows is above the electric fuel pump. although i did put a cm870 IFSM on my CM871 and it did have the small little check valve on the backside of the IFSM against the engine as my CM871 IFSM did in the CM871 parts diagram the part number is 4076594 Check Valve for the small one on back side. the only thing i see on my cm870 diagram is a pressure regulator above the fuel filter.

[Konstantin]

(11-10-2019 )Waterloo Wrote:  Just hearing your symptoms, are you sure it is fuel related? Could be the starter, or the ECM is a bit long in the tooth and in need of replacement. Have you gotten under the truck and inspected the wiring to the starter? How old is the starter? Then the ECM, run the truck, get her warmed up and smack the ECM with a screw driver handle or rubber mallet... Something I would do before tearing apart the fuel system... Is there a Davco unit on the truck, may want to inspect the o rings, change out the filter and clean the bowl... Something else to look at.

i would hit ecm and see what will happen. starter is 1 year old and cranking like crazy. not davco, just regular pre-filter.

[Konstantin]

(11-10-2019 )Lonestar10 Wrote:  i show in a quickserve parts diagram for a cm-870 IFSM numbered part 42 - check valve 4010078 the only one it shows is above the electric fuel pump. although i did put a cm870 IFSM on my CM871 and it did have the small little check valve on the backside of the IFSM against the engine as my CM871 IFSM did in the CM871 parts diagram the part number is 4076594 Check Valve for the small one on back side. the only thing i see on my cm870 diagram is a pressure regulator above the fuel filter.

I see the same thing, thanks. when i was reading description it mentioned that it is one more valve at fuel filter, but nothing on diagram. so cm 870 and cm871 are interchangeable . wau

[Konstantin]

Ok, I changed lift pump and removed and cleaned anti drain back valve. I installed used lift pump from another truck with dead engine. Now my problem disappeared. I know Rawze told to wait 10-15 seconds and that is what I will do , but for the sake of experiment I tried to start truck right up and it starts every time. So i guess my problem is solved. But I run into another one. I connected a gauge to check what pressure lift pump gives. When I first turn ignition gauge reads around 13 psi. What happens next is kind of weird, after some time like 30-50 seconds pressure suddenly changes to 0 and stays there. Pump is working 2 minutes. If i disconnect it and connect it pumps 12 psi, but after some time drops to 0 once again. The noise is also changing when pump pumps 12 psi and pumps 0. Is it normal? Or I did something wrong? Quickserve says I need to install new gasket, but mine looked pretty good, so I reused old one.

[Lonestar10]

could be a deadspot in the sensor that it moves into and goes limp. biggest thing is that the elec is pumping fuel and that fuel pressure skyrockets above 200PSI as soon as you hit the key which means the gear pump is good. the pressure sensor is on bottom of the IFSM looks just like the exhaust back pressure sensor. its on the bottom left side just to left of fuel filter.

[Chamberpains]

Could also be a junk lift pump. You did scavenge a used one off another unit... Used parts are always a gamble.