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Topic: fast cranking, slow to to fire up, no lift pump?  (Read 1056 times) previous topic - next topic

fast cranking, slow to to fire up, no lift pump?

My start batteries are fresh, individually load-tested fine. The diesel supply line and return line were replaced 2 years ago, no leaks apparent.

M11 cranks fast but it only starts after approx. 10 seconds of cranking. This happens even if the engine was shut down for only a moment.

Diesel psi = 130psi while engine is running. As soon as the engine is turned off, diesel psi immediately drops to 0 ( I expected it to s-l-o-w-l-y drop to near zero). There is 3.4" Hg vacuum (as tested on a fuel port on curb side of the engine, at the cam-driven fuel pump) when M11 is shut down. 

The mechanic found the plastic pre-filter leaking and the 12v 'primer pump' next to the old WINN system dead so he removed it, awaiting a replacement pre-filter/primer pump.
 
Is there a lift pump on the M11? If so, where is it? If not, diesel appears to be draining back from the diesel pump when engine is turned off, causing the delay in firing the engine? Is there a drain-back valve in the system?  If so, where?

Steven

Re: fast cranking, slow to to fire up, no lift pump?

Reply #1 –
Quote from: StevenOrlando –
Is there a lift pump on the M11? If so, where is it? If not, diesel appears to be draining back from the diesel pump when engine is turned off, causing the delay in firing the engine? Is there a drain-back valve in the system?  If so, where?
CAUTION!  I know nothing about your M11 engine.  I just read stuff online and try to figure out answers to Forum member questions.

I don't know the answer to your "lift pump" question.

That said, I'm reading various online reports of problems similar to yours.  Some of them mention the fact that fuel flows through a "cooling plate" which is mounted under the engine ECM.  I also found the video below that talks about a check valve that is supposed to be installed at one of the plate fuel ports.  Perhaps watching the video will provide a clue to what is causing your hard start issues.

https://www.youtube.com/watch?v=xY3ac0_-0LE

Re: fast cranking, slow to to fire up, no lift pump?

Reply #2 –
I know a little. No lift pump that operates during normal operation. There is a bleed pump that powers up during start buy quickly shuts off. Your air leak at your secondary filter is causing your issue. Mine runs at like 14 inches of vacuum on the fuel system. This is why any air drawn in will produce poor starting do to low fuel pump output pressure. Air compresses, fuel does not so it will reach much higher pressures. I personally would prefer a positive pressure on the fuel pump but the designing engineers felt the system would function correctly. The screen and four orings to install it are available. Yes I said FOUR o-rings. Steve I plan to eventually replace my secondary filter assembly with a FASS fuel system. Will also keep head pressure on pump and polish fuel.
Scott
U320 fuel screen
Fass fuel filter system

Re: fast cranking, slow to to fire up, no lift pump?

Reply #3 –
Quote from: Chuck & Jeannie –
CAUTION!  I know nothing about your M11 engine.  I just read stuff online and try to figure out answers to Forum member questions.

I don't know the answer to your "lift pump" question.  If it does have one it would be electric, not mechanical.

That said, I'm reading various online reports of problems similar to yours.  Some of them mention the fact that fuel flows through a "cooling plate" which is mounted under the engine ECU.  I also found the video below that talks about a check valve that is supposed to be installed at one of the plate fuel ports.  Perhaps watching the video will provide a clue to what is causing your hard start issues.

https://www.youtube.com/watch?v=xY3ac0_-0LE


ECM fuel cooling plate uses return fuel that is unused and returned to the fuel cooler than fuel tank.
Scott

Re: fast cranking, slow to to fire up, no lift pump?

Reply #4 –
As Chuck says,, I'm not a M11 geru but most diesels have a spring loaded restriction to keep fuel in the system after turning off the engine. If it's a mechanical engine with a Bosch P pump, there is a return valve on the back side of the injection pump. The spring loaded ball developes tiny channels over time and may not keep specified pressure in the pump plus it may also allow pressure to drop after the engine is turned off. The electronic engines will have one if a different place.

Any kind of air leak will also allow the diesel to drain back into the tank with the fuel being replaced by air. So, the engine has to go through a mini prime each time it's started. A leaking injector can also cause the pressure to drop when the engine is stopped but since your does that immediately, I would suspect an air leak in a filter housing, bad return valve bad fuel hose clamp, etc.. If you can't get any suggestions here, try a forum that addresses the M11 engine.

What is the pressure from the outlet of the lift pump just before you crank the engine? Lift pumps can also leak air or fuel into the crankcase also letting air in. Cummins lift pumps do occasionally fail.

Pierce

Re: fast cranking, slow to to fire up, no lift pump?

Reply #5 –
Quote from: dsd –
ECM fuel cooling plate uses return fuel that is unused and returned to the fuel cooler than fuel tank.
Scott,

Like I said, I don't know anything about the M11 engine, but using the return fuel to cool the ECM wouldn't make any sense.  The fuel returning from the engine is the hottest fuel in the whole system.

The video I linked above says the fuel comes from the fuel tank, goes through the cooling plate, then through a fuel filter, and finally into the injection pump.  That routing would make more sense (to me).

I don't know if the diagrams below are the same setup as the M11 engine in Steven's coach, but they do match the engine fuel line routing in the video.

Re: fast cranking, slow to to fire up, no lift pump?

Reply #6 –
When I replaced all the factory rubber lines the fuel entered the secondary filter followed by entering the primary filter to fuel pump. Unused fuel exits pump to fuel cooling plate via hard lines then exits cooling plate for ECM by flex hose to fuel cooling radiator if equipped then returns to fuel tank. Just saying that's what my 2001 was set up. Fuel tank still hets quite hi during summer and lower fuel levels also makes the fuel tank hotter. This is why they added the fuel cooler and earlier coaches didnt have it but many have added them. Heat is coming from the ECM during operation. Im confident that the injection pump also produces heat but the primary concern was the heat generated by the ECM. 2001 ISM 450HP. Not the caps system. In viewing the diagrams you posted my engine has a much longer ECM with three plugs facing outward. Curious about the differences?
Scott

Re: fast cranking, slow to to fire up, no lift pump?

Reply #7 –
Our '97 the cooling plate gets fuel from the tank first then to the 2nd filter then own to the engine. Like Scott stated those Orings are ,most likely your problem as just a little air can cause a big problem. The thing that does bring a question to me is that it happens so fast in that if you turn off the engine it will be hard cranking instantly. It should take at least a few minutes to be hard starting.

Mike

Re: fast cranking, slow to to fire up, no lift pump?

Reply #8 –
Quote from: dsd –
When I replaced all the factory rubber lines the fuel entered the secondary filter followed by entering the primary filter to fuel pump. Unused fuel exits pump to fuel cooling plate via hard lines then exits cooling plate for ECM by flex hose to fuel cooling radiator if equipped then returns to fuel tank. 2001 ISM 450HP. Not the caps system. In viewing the diagrams you posted my engine has a much longer ECM with three plugs facing outward. Curious about the differences?
Scott,

I kept poking around wondering about the "fuel system differences" subject and found the diagram below.  It matches your description of your system pretty close, but not exactly.  So, anyway, now I understand that there are different fuel routing variations on different model/year big block Cummins engines.  Live and learn!

Re: fast cranking, slow to to fire up, no lift pump?

Reply #9 –
Chuck I just went and looked at my coach. Right or wrong is goes into the secondary filter at the engine and into the pump o the fuel rails inside the head. Comes out to the ECM cooling pad. Exits to the fuel cooler outside of the intercooler/radiator then returns to the fuel tanks. The most calories of heat can be removed at higher temperatures so since the cooler is after the ECM plate then returns to the fuel tank. The tank does get hot during the summer especially if you're running hard and adds to the heat inside the coach but there is no additional cooling prior to the primary filter as it leaves the tank. The fuel ECM lines are quite small compared to the rest of the return system and fuel cooler outside the radiators. So yes it's different than the second print. I did make a mistake on the secondary and primary filter by reversing them. Primary is larger sized filtration and secondary on the engine is finer.
Scott. 

Re: fast cranking, slow to to fire up, no lift pump?

Reply #10 –
My coach the ECM is in between the fuel filters.

Re: fast cranking, slow to to fire up, no lift pump?

Reply #11 –
On our 1995 U320 M11 engine the fuel flows from the tank to the Parker Racor 790R30 pre-filter, through the ECM cold plate, through the engine-mounted filter and then on to the engine-mounted main fuel pump.