Our Foretravel is now back in comfortable heated storage, but (once in preparation for our Christmas trip south and twice after returning home) we had interesting starting issues. (There were no issues when starting in warmer weather.) Everything ran perfectly on the trip (~2000 miles).
Once (temperature in mid 30s; no engine pre-heating), once in the mid teens (limited engine pre-heating) and once in the mid-teens (3+ hours Aqua-Hot engine pre-heating) the engine would fire normally, run for 2-3 minutes and then die. It would re-crank properly but wouldn't fire for several minutes and then would re-start and run well. No codes appear to have been thrown.
Any ideas on the root cause and what could-be done to correct the issues? (Yes--I already know we should "winterize" the coach by moving to a warmer climate. Seriously considering that when the opportunity presents itself!)
David,
Sounds like air is getting into the system to me. I take it that it dies while idling? Can be hard to find the entry point as there are quite a few between the tank and injection pump. To make sure, you could put the fuel return line under the surface of a container with diesel in it. Bubbles are a sure sign of air in the system. Before doing that, I would check the gaskets/O rings on the sight glass on the bottom of the primary filter if you have one. They are frequent sources of air leaks. Check all clamps for seepage and cracks in the hoses. The supply/lift fuel pump or associated fittings may also allow air in. Leak is probably between the lift pump and fuel tank.
Once it starts and gets oil pressure, you can try bringing the engine up to a fast idle of 1000 RPM or so. This will purge air from the system much faster.
It takes a little effort for the fuel pump to bring fuel from the tank. When the engine has been running for a while, the fuel is warmer and it's viscosity is less so easier for the fuel pump to supply to the engine and less likely to introduce enough air to stall the engine. Some air still may getting into the system but not enough to stop it. Air can also result in less power and may effect the lubrication in a mechanical high pressure injection pump.
Pierce
You could/should look for air leaks, but if it ran well and started well in a warmer environment, I'd be looking at a fuel problem. Did you take on fuel during the trip? Maybe you got some contaminated fuel. Warm it up good with heaters and try it again. If it acts the same, I'd sample the fuel tank. Have a great day ---- Fritz
My first thought was that the thickened fuel from the lower temps was showing fuel line leaks?
I regularly bring the idle up to 1000 RPM as soon as the oil pressure is acceptable.
This issue has occurred only on the three occasions I cited, and those were all under cold/very cold conditions. No problems at any other time, and even on those three occasions the engine started normally and then died after 2-3 minutes at high idle, and then after it finally restarted it ran perfectly--both at high idle and then on the highway. Something unique is happening only under these quite cold conditions and then it happens only once.
I will change the fuel filters and carefully examine the system once Spring arrives, but until then it would be very interesting to find out if anyone else has experienced this unique, temporary fuel-starvation phenomenon.
Yes. The Winn system leaked air even after multiple repairs. Seperate from the cracked fuel lines.
I assume the thickened cold fuel had something to do with it, but I'm not sure how the thicker fuel would show a fuel leak. Moreover, the same cold thicker fuel worked quite well after each single, temporary, apparent-fuel-starvation event.
The first event was with different fuel than that used in the second and third events. In all cases except for these three one-time-start-run-die-then-restart-later events the fuel seemed to perform properly and the fuel mileage has remained quite consistent. In addition, the Aqua-Hot has appeared to perform normally throughout this entire time period.
Clogged fuel filters will usually rear their ugly head at higher power settings like going up hills or on ramps. A partially clogged filter will lose some of the algae/dirt/etc to the bottom while stopped and generally won't affect starting or idling.
Heading up a steep incline before shutting down with a partial fuel load can also introduce air into the system. If you park after such a climb, it's best to run the engine at a fast idle for a minute or two. Example would be a driveway or road with a pretty good angle and or slant to it just before you park and shut down.
Pierce
I agree with your statements, but none of those conditions are applicable to the events I described.
David,
A full fuel tank will require less suction from the lift pump. When this starting/stopping problem occurred, how full was the tank?
Pierce
I am just throwing this out there as a suggestion but what about a weak lift pump? Could it have problems pulling thicker more dense fuel?
Mark
Mark,
Sure could! Weak and or air leaking. This has been a problem with a lot of Cummins. Replacement has been a simple fix to cure several problems like above and also low power/boost, injection pump wear, etc.
Ford/Navistar 6.9 and 7.3 mechanical pump diesels had frequent air problems in the fuel and were mostly related to the large combination of fuel filter, fuel heater, multiple sensors in one unit. The best fix was to completely remove the whole assembly and replace it with a simple single remote filter. Once this was done, they started and ran well. The rotary injection pump was also not the best design and not even in the same league as the inline Bosch pumps.
Pierce
I have a different thought on why it happens only in cold weather: differences in thermal expansion between different materials in the fuel system. Specifically threaded joints and O-ring joints. Example: a brass male fitting threaded into a steel female fitting. Brass will shrink about 1.5 times as much as the steel. Normally the preload (or tightness) is enough to handle it, but if the connection is marginal it can show up only in cold weather. Similar thing can happen with O-rings: marginal at room temperature cold mean a small leak at cold temperatures. I know my air brake system looses air about 3x faster in cold weather.
I would consider this a warning that it might get worse and start occurring in warm temperatures or after long periods (weeks) of being parked. I think the advice is the same: check all the fuel line connections, O-rings on filters and fittings. You might just find the culprit when it turns easier than you expect it to.
Do you still have the original electric fuel priming system? My understanding (from a buddy with a '95 U320) is they are full of O-rings, seals and potential leaks areas as they age. Cummins advised him to get ride of the system which he did.
Thanks! Excellent thinking!
I haven't made any detailed inspection of the fuel system in the two-plus years we have owned the coach. I planned to replace the fuel filters this past summer, but didn't--primarily because we are now generally using fuel from Love's (participating in the Prevost fuel discount program) and Love's diesel tends to be roughly B10 (biodiesel blend) fuel. (I keep a set of fuel filters with us just in case of any clogging issues.) So far I haven't noticed any issues that can be traced back to the biodiesel blend.
This Spring I will fully inspect the fuel system and replace the filters, keeping in mind all of the points you mentioned.
Definitely something to keep in mind. Thanks!
MAZ,
I don't know the precise reason, but that was my exact issue with our '98 8.3 mechanical, at one point. In cold weather, in the fall, engine starting became slower and engine stumbled a bit on start, took a few seconds to run smoothly. Get out of New England to FL and all would be well until running into cold weather headed north, in early April. Fuel lines and fittings all remained good throughout ownership (no cracks, no seep indication, weakness of any sort, fittings and hoses completely dry). Before the second Fall season turned to cold weather, I rounded up fittings and installed a lift pump output pressure indicator. Sure enough, pressure low. How great the temperature change and how much the tank level was low also affected output pressure. Dissassembled and used a Cummins Lift Pump rebuild kit. Only increased pressure a few pounds (I had all of the numbers written down somewhere but they escape me now). Talked w/Cummins and they sold me on replacing the fuel lift pump ($$$$). The lift pumps themselves and the seals are severely attacked by today's fuels. The design and the material compositions are constantly tweaked by Cummins to improve longevity. Cummins had little good to say about the aftermarket miracle pumps and the adjustable outlet pressure devices. They cited several negative examples, no positives.
So, new lift pump, lift pump output pressure more than doubled, set idle up 25 RPM and everything was like new again! Instant starts, smooth running, regardless temperature. +1
Neal
More excellent information. Thanks!
if this this sounds too simple I hope it is as I ran across a variation of a problem that might be related to yours. maybe.
I replaced my fuel tank caps with locking ones a while ago and experienced fuel pouring out of the ground or fuel smells after a extreme climb.
finally the light bulb came on a few days ago. hmmmm
so versus embarrass myself here in front of my peers and more expert owners I called mike grimes today to ask about other parts for my coach and finally remembered to ask if the coach used vented or non vented fuel caps.....
bingo. needs vented. I bought non vented. coach had non vented when I got it.
as the tank and fuel cools you may have a vacuum in the tank.
several easy tests to verify this. I also had cold starting issues for the last three years. duh.
I don't disagree that you should have vented fill caps, at least our '98 and '02 both had vented caps.
But you should never experience a vacuum on your fuel tank as there is a fitting on the fuel tank top suface connected to a length of fuel hose that runs down to a point near the front bottom surface of the fuel tank, usually held in place by a grommetted clip near the hose's termination. All FT's should have either that vent hose or a"caved in" fuel tank. Vacuum is not forgiving. 😬
Neal
while I agree my overflow tube released a qty of fuel in a 1/3 full tank after a banzai run up a long steep grade. so the pressure side overflowed. hence my cold suggestion.
fuel jelled in the vent hose? maybe does not drain completely. water in vent hose?
David,
Have you replaced all the fuel hoses in your coach. You don't mention them and your coach is certainly in the suspect model years. My fuel lines caused engine dying after starting, but at warmer temps. Did you try priming after each of your episodes?
I also had to reprime mine. sometimes more than once in cold weather.
Metal contracts when cold. Sure doesn't hurt to retighten clamps and filters. In a perfect world, diesel engines would run on air, but all I have worked on like a clean "un-aireated" supply of diesel.
Thanks! I definitely plan to go through the fuel system in the after the coach is out of storage. I will change all of the filters and inspect the hoses and clamps. Any specific recommendations on things to check on an M11, or just a thorough end-to-end check?
If air is entering the fuel system, it will be on the suction side of the system-- i.e. before the lift pump. If there was a leaking connection after that, it would be leaking fuel OUT, not air in.
Got it. I guess I just assumed we were all thinking of the fuel lines, fittings and filters between the tank and the pump, and possibly the pump itself, and not the pressurized side
after the pump.
Does anyone have a good description/graphic/schematic of the 1995 U320 M11 fuel system (ahead of the pump)? I have all of the replacement filters, and I think I have a good idea of the system, but I don't recall seeing details of the overall system.
With your engine serial number in hand, Cummins QuickServe Online (https://quickserve.cummins.com/info/index.html) will serve you better than any person here can with regards to fuel system drawings.
Just another comment on the original Winn system. My coach would run fine but occasionally die at idle. I replaced the Winn and no problems since. Good luck.
jor
Yes, I believe it is common knowledge that Parker/Racor has a complete replacement for the Winn system because of all the failures.
The Winn system has a lot more leak-prone areas. Yes, one can keep them working, but for most, replacement with a more reliable system is indicated.
I have a QuickServe account, and it's a most valuable resource for the engine, and the
M11 fuel system. However, I've found nothing there regarding the
overall fuel system on my 1995 U320. Therefore, I'm wondering if anyone has that information available.
Use a ViceGrip, welding clamp or other clamp on the feed hose at the tank or other convenient spot and then use a MityVac ( Mityvac Vacuum Pump - Save on Mityvac Pumps at Harbor Freight! (http://www.harborfreight.com/mityvac-vacuum-pump-39522.html) ) starting at the first connection closest to the tank and work toward the discharge side of the engine lift pump. As soon as you start to lose vacuum, you have found the leak. About an hour of work should find any leak. Don't go crazy with the teflon tape putting the fittings back together. I like a little teflon compound on the male side, never on the female side. Rule is that if it's pipe threads on both sides, you can use teflon compound to seal it but just a little. Some fittings are designed to seal themselves and don't use anything.
Pierce
I am (almost) positive that you have a fuel return check valve and a fuel strainer.
The fuel check valve is forward on the ECM fuel cooler plate (fastened to the block) and is in the 90 degree fitting that connects to the primary fuel filter hose behind the ECM wiring bundle (all forward of the ECM.)
(Be ginger moving the ECM wire bundle out of the way when removing the 90 degree fitting.)
The fuel strainer is at the forward end of the fuel pump, under the (large) button style +screw. pc
How do you think this could be related to the cold-weather starting issues I described? Does that strainer filter the fuel returned to the tank?
The check valve stops fuel from syphoning back to the tank and the little strainer keeps debris from going through the pump.
If the check valve is stuck open, fuel will drain back to the tank. pc