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NO START

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Rob Perry:
Have a 2001 Marquis with a C12 425 Cat that seems to have a air leak of some kind. When the coach sets for a week and I attempt to start it, it's a no start. I installed a manual pump on the fuel filter so I don't have to pay the Cat dealer the $100 per hr + travel.
The coach sits for about four day and won't start unless I pump up the pressure. Filters are tight, it has to be somewhere else.
Any ideas????

Thanks

Gerald Farris:
The O-rings on the cylindrical sight glass on the Raycor water separator are the most common cause for an air leak in that fuel system. The next likely cause for an air leak would be the hand pump that you installed.

Gerald

Ron Johnson:
I did not have this problem but had the o-rings on the sight glass replaced last year after I noticed constant fuel leakage. My Coach has a little 'purge' panel in the rear 'cockpit' [aft passenger side compartment] allowing one to purge either water or air by pushing a button. I am guessing you do not have this feature 'cuz you installed the manual pump. It's strange what they included or did not include from the factory. Maybe this little panel was an option.

If I remember correctly from a post on rv.net the fuel goes from the primary filter to the lift pump then back to the secondary filter. Could the fuel leak\air in be occuring at the lift pump? I know Cat lift pump seals are not supposed to be bothered by ULSD however it would not hurt to check.

I really feel for you. One of the greatest joys of having one of these is to hear that big Cat start up like a switch was thrown. Hope whatever it is you find it.

Ron

Edward Buker:
This is not an easy thing to do but it was what a Cat mechanic did on my 89 Contessa  that had lost prime on a mechanical injection pump due to an air leak. (Died on an on ramp in Denver, had to be towed, bad scene) He installed an inline sight glass coming from the fuel tank prior to the water seperator and observed no air stream in the fuel with the engine running. It required different fittings to adapt the sight glass to different locations. He then installed it on the line going to the engine injection system just after the final filter and hand pump. We could easily see a bubble train in the fuel with the engine running at that location. Shut down and with fitting changes installed it between the pre and final filters and there were no bubbles in the fuel stream there. My leak point was sourced to the fittings, handpump,filter of the final filter/pump assembly. We replaced the final filter and reinstalled the sight glass on the outlet side going to the engine injection pump and it was now bubble free. The cat final filter was a new version and it had been redesigned with a compromise placement of the o-ring in order to replace several different filter PNs with one for cost savings. That compromise design caused an air leak.

Because it is relatively easy I would change the pre and final filters and the Oring set in the water seperator as Gerald mentioned. An O-ring is the most likely source of an air leak and I believe that would eliminate all of those as a possible sources. One thing I noticed is that the Cat mechanic really tightened things well beyond what I would consider safe without breaking fittings or filters but when he was done it was trouble free. He had many years of experience. If you do get to the point of frustration where you have a mechanic temporarily install a sight glass and find no air in the fuel stream then I believe there is a check valve in the return line that is intended to keep fuel from returning after the engine is shut down to prevent hard starting. If nothing else this lets you know how Cat diagnoses the fuel stream for air leak points. Without some diagnostic method to source the leak it is all guesswork.....Hope this helps.

Edward Buker:
To clarify....My last post regarding using a sight glass applies to all of the fuel system that is behind the first fuel pump where a vacuum pull would suck air into the system at a leak point. After the pump there should be pressure in the line and a visible leak would be more likely. I do not know where the fuel pumps are in the C12 fuel delivery system and the transition from vacuum to pressure is made. Hope this helps...

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