Air in injection pump

[simon]

Hi there fellows

I have that 6.2 I have installed in that wheel loader i talked about a couple of postings further down { 1800 rpm }.

Now here a couple of month's ago I put a rebuild I P on it , after bleeding it it started up just fine. but lately it seems like it takes a lot of cranking to get it going, matter of fact the only thing to get it started is to use starting fluid. yes it scares me too!. Glowplugs are manually controlled.and even then it takes a couple of tries before it fires up ,I desided to look into matters yesterday

Glowplugs are ok as are the injectors ,I have a electric industrial liftpump on it and it supplies 20 psi of pressure, taken between the filter and the IP but it takes a couple of seconds to build up, as soon as i turn the ignition of the pressure leeks back to zero. probably the checkvalve in the liftpump kaput.

the funny thing is that the bleed off line on the top of the IP does not pass any fuel back trough that checkvalve there back to the tank with 20 psi pushing fuel? After taking the valve out there was no fuel in sight inside the pump.

Questions
1: Is that checkvalve only operating with the engine running? I did not check that out. I thought it was there to mantain about 10 to 13 psi in the pump.
2: how come there was no fuel present when i took the checkvalve out of the IP.
3: is the fuel pressure normally maintained with the engine shut off, or not?

The fuel filter is mounted higher then the engine.
When i took the fuelline of the filter to put a gauge in the line there was no fuel running out there either, so it seems like there is an airlock there , unless all fuel is running back to the tank when the engine is shut of. But that still does not explain the checkvalve on the IP. I checked that one and it seems OK

Any suggestions??

[john8662]

1: Is that checkvalve only operating with the engine running? I did not check that out. I thought it was there to mantain about 10 to 13 psi in the pump.
2: how come there was no fuel present when i took the checkvalve out of the IP.
3: is the fuel pressure normally maintained with the engine shut off, or not?



1. The pumps with the checkvalve are rumored to be '87+ lift pumps, I have not found any supporting evidence of this, but still specify one for an '87.

2. No fuel at the return line of the IP? You got's a leak somewhere, and it can be a few places.

3. No fuel pressure is maintained when the engine is turned off, that I have witnessed in taking things apart.


Fuel system leaks are frustrating but very common on these older trucks, primarily due to aging rubber lines and hose connections, and some poor hose clamps in certain areas.

Something that's over-looked usually in regards to the fuel system is the fuel return system.

I have found that leaks on the fuel return system, render problems starting. Usually right on top of the injection pump itself. You'll find a small spring-clamp as the only hose clamp. I simply replace this with the appropriate sized screw-type hose clamp. Fuel return lines injector to injector cause problems too (slight) the usual suspect is the end caps on the back cylinders.

Anyways, your fuel filter being dry is concerning. Makes me think that perhaps it wasn't bled fully.

Re-install everything and bleed the fuel filter fully.

Disable the fuel solenoid on the Injection pump (red/pink wire on top, just unplug it). Install new filter and open bleed screw on top of the filter housing. Attach hose to nipple on housing, and crank engine over till you get fuel out of the hose completly.

Then prime the rest of the system, just crank on it in intervals until it fires is easiest.

J

[dkburgess]

john??? with an electric lift pump shouldn't you be able to just leave the pump on and get fuel out of the top of the housing??? at 20 psi, i'd think it would force the air out of the system, but i'm having issues of my own, and still can't figure them out!!! btw how do you "bleed" the rest of the system!!! i hear it alot, but need help with the step by step!!! my truck runs, but i have issues with acceleration...that's another story!!! just keep coming up the the good advice!!! thanx
dburgess

[simon]

I still do not know if the I pump fuel returnline is supposed to bleed fuel trough with the lift pump operating. I believe it should, how else can the air in the pump be purged.
there is no leak in the system anywhere . the air bleedoff in the filter has a good stream of fuel as soon as i turn the liftpump on, but nothing out the IP return ?. The engine will start that way but it takes a while.
the liftpump and the shutoff solenoid are both energized with ignition on as is the cold advance solenoid.
this is a new IP, engine is believed to be an 86.

I AM STUMPED

[simon]

Update.

I found out that the return nipple on the IP is not a checkvalve but a flow restrictor so as the engine is shut of it will in my case siphon all fuel back to the tank and empty the IP and filter . The liftpump has no checkvalve either.
But will maintain 24 psi with engine running.The IP return line will only pass fuel with the engine running.
I put a clear plastic hose from the pump to the return line and observed fuel bypassing the pump after apr 5 min idling and after shutdown it drained back slowly.
So my solution will be installing a checkvalve in the supplyline right at the tank.
problem solved