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Topic: Engine bogs down up at speed - brownish gray smoke (Read 1650 times) previous topic - next topic

Engine bogs down up at speed - brownish gray smoke

I am having trouble with my 95 U280 Cummins C8.3 engine.  It starts quickly, idles perfect, accelerates through the gears easily. The problem arises when reaching approximately 50 mph in 6th gear and the accelerator is depressed to increase speed in high gear. The engine seems to fade and sometimes downshift to 5th gear. It will continue to fade and decrease speed as long as the accelerator is depressed.  There is gray/brownish smoke from the exhaust during this time. The turbo turns free and has no perceptible slack. The charge air system to the turbo appears to be good with no apparent leaks. The fuel distribution pump was replaced new (not refurbished) less than 30,000 miles back. The lift pump mounted on the engine was replaced last year. (new) I notice that the pump in the tank is much louder than it used to be. Both fuel filters are clean and clear, and have been for the last 3 changes. They are both new now.  Has anyone experienced this before, and if so, what was the solution?  I am leaning toward the pump in the tank, but I can find no specifications for the tank fuel pump as far as pressure and volume. The 150 gallon tank is half full.

Re: Engine bogs down up at speed - brownish gray smoke

Reply #1 –
You didn't mention the air filter, have you checked it?

Re: Engine bogs down up at speed - brownish gray smoke

Reply #2 –
You engine is being deprived of fuel. You need to check pressure at several points in the fuel delivery system. Not the easiest to do as the starvation only occurs at full load. So, it's either a restriction somewhere, bad pump(s) or air getting into the fuel system. I would first pull the line from the tank off in a convenient place and then check the output volume and pressure from the tank pump. We frequently had the starvation problem with Mercedes OM617 engines. Was usually the primary filter picking up algae but since you have replaced yours, the problem is somewhere else in the fuel delivery.

Cummins lift pumps are not known for their reliability while the Cummins Bosch inline mechanical injection pump is outstanding. The rotary pumps in the electronic engines leave a lot to be desired in comparison.

Pierce

Re: Engine bogs down up at speed - brownish gray smoke

Reply #3 –
I have a 95 U280 and didn't know I was supposed to have a lift pump inside the tank.
Mine must be battery operated (no wires to the tank) or a PO removed it.

I'll have to research this one.

Re: Engine bogs down up at speed - brownish gray smoke

Reply #4 –
Here is a thread by Gary B. on the 8.3 lift pump. He is a 95 U280 expert!

Lift pump

Re: Engine bogs down up at speed - brownish gray smoke

Reply #5 –
In reading Gary's post on the lift pump, I noticed he replaced the Powertech fuel pump with a Facet electric pump from Aircraft Spruce. Here is the link to Aircraft Spruce.  Avoid the square looking pumps as they have a higher failure rate. We use the 476459E on our Grumman but you should check your existing generator pump for the fitting size, internal or external threads and voltage. These are all the tubular construction with a removable cap to get at the filter on the bottom (5/8" wrench). Prices have gone up a little since his post but not bad and well under $100. Note: these pumps work on both gasoline and diesel.

FACET GOLD-FLO INTERRUPTER TYPE PUMPS from Aircraft Spruce

As I recall, Jerry M replaced his this last year and found a good price.

Pierce

Re: Engine bogs down up at speed - brownish gray smoke

Reply #6 –
The first thing I would do is have the lift pump pressure checked, if that is OK have the check valve in the injector pump checked, if
 either one is not correct it will it will show up as low power.

Re: Engine bogs down up at speed - brownish gray smoke

Reply #7 –
I'm pretty sure you don't have a pump in your fuel tank.  As far as I know, Foretravel never added one and relies completely on the engine mounted mechanical lift pump on the C8.3 to suck the fuel 25+ feet from the tank.

I'd check a couple of things besides the ones mentioned, especially the fuel pump overflow valve that was already mentioned as it is solely responsible for the fuel pressure that your engine gets.

1-Have your fuel lines been replaced?  If not, you may be sucking air in.  Also may be sucking air from somewhere else in the fuel system.
2-Possible issues with your King Controls drive-by-wire system and/or accelerator pedal signal.

Re: Engine bogs down up at speed - brownish gray smoke

Reply #8 –
There is most likely NO fuel pump in the fuel tank.  One thing that can cause your engine balking at full fuel flow is the fuel return spring valve on the back of the injector pump is not keeping enough fuel in the injector pump. 

This is a replacement that we installed:
Cummins Adjustable Overflow Valve by Tork Tek - OFV010

Two years ago, we were running just fine, but decided to preventatively change the mechanical fuel lift pump ourselves.  Well, to our amazement take offs were smoother and we felt more power.  We must have been running lean without knowing it.

After the new lift pump, we added electric fuel pressure gauge and a new fuel return valve.  If we had the pressure gauge before the new pump, we would have had before & after pressure readings, but we are stuck with only knowing we run better and pressures are 15 to 30 psi.

BTW, the clicking sound we may hear in the bays, that some think is fuel pump sound is likely the sound of pulsing fuel being returned to the fuel tank. 

A lot of fuel is cycled into and back out of the injector pump to help cool the injector pump and injectors.  This warm fuel needs to be cooled down by mixing with the fuel in the tank, so when we let our fuel tank get below half or third, there is not much fuel to cool the returning fuel, causing tank fuel to over-heat.  Warm fuel is considered less efficient for combustion.

Re: Engine bogs down up at speed - brownish gray smoke

Reply #9 –
There is no pump in the tank on a 280. What you are hearing as you stand near the tank is pulses that originate at the lift pump/injector pump. These sounds are carried back to tank by fuel return line.  Sounds like a pump but it is not, probably louder when tank is near empty and resonation is louder.
Brownish grey smoke sounds like lack of air to intake, check for restrictions in intake system.  I once found a birds nest in the downpipe on my 280.
Gary B

Re: Engine bogs down up at speed - brownish gray smoke

Reply #10 –
Thanks Gary,
I plan to replace the lift pump next week.  Also going to check the separator that is ahead of the air cleaner for any restrictions. I removed the air filter and ran it with no results, but hadn't inspected the separator. I will keep you posted.
Best regards,
Garlan

Re: Engine bogs down up at speed - brownish gray smoke

Reply #11 –
If concerned about the air filter or what "is ahead of it", what is your air filter minder reading?

Re: Engine bogs down up at speed - brownish gray smoke

Reply #12 –
Quote from: Barry & Cindy –
Two years ago, we were running just fine, but decided to preventatively change the mechanical fuel lift pump ourselves.  Well, to our amazement take offs were smoother and we felt more power.  We must have been running lean without knowing it.
Fortunately, what Barry is talking about is not enough fuel supplied to the injection pump for full performance at the particular throttle opening.

Diesels, fortunately, don't have to worry about a "lean" mixture like gasoline engines do. While a diesel engine may run an air fuel mixture (by weight) of 14 to 1 (absolute maximum) at full throttle, the mixture can be 60 to 1 at idle with just enough diesel injected to overcome internal friction. This is why a European taxi can idle all night and only use a tiny bit of fuel. With a lean burning gasoline the combustion temperature may rise to damaging levels. With a diesel, the less fuel injected means lower temperatures and horsepower. Since most diesels don't have a throttle butterfly, it's the amount of fuel injected that controls the power/rpm.

Our RV diesels are in a relatively low state of tune compared to a boat or emergency vehicle. In a mechanical diesel, the pump can be re-calibrated and larger injectors installed to produce more power. With our electronic engines, the ECU can be "flashed" to keep the injectors on for a longer time. This may be illegal for the street and Cummins, Detroit and CAT may not do it without the proper engine serial number.

For a mechanical diesel engine to produce it's designed horsepower, the injection pump must have it's designed pressure inside the pump's interior reservoir. If the check valve leaks or the lift pump can't keep up with the demand of high throttle requirements, rough running, smoke and a loss of power will be noticed. The mechanical injectors need about 3000+ psi to operate. Less pressure and they operate intermittently.

One of the nice advantages (or not) of the mechanically injected diesels like the 8.3 Cummins is the injection pump can be removed, recalibrated for a more even distribution of fuel between all cylinders giving a much smoother idle. While some coach owners may complain about a rough idle, it's generally the pump giving a little different amounts of fuel to each cylinder.  As good as the inline Bosch pumps are, they only get several minutes on the bench for calibration when new. Fuel can also be added at the same time to increase HP. Adding too much fuel will result in black smoke, more emissions and angry people behind you. Air/fuel ratios lower than about 23 to 1 usually will have undesirable results.

Pierce

Re: Engine bogs down up at speed - brownish gray smoke

Reply #13 –
I would recommend that you NOT run your engine without an air filter, if I understand what you are saying here. Your engine will suck up dust and particulates like nobodies business. Particularly, I would never drive the coach without an air filter. I go so far as to disconnect my start battery while changing the air filter just to make sure I don't have a senior moment and forget that I was in the middle of the process and decide that I need to start it to build air or some such...
Just my two cents.
Don
Quote from: thisldu –
Thanks Gary,
I plan to replace the lift pump next week.  Also going to check the separator that is ahead of the air cleaner for any restrictions. I removed the air filter and ran it with no results, but hadn't inspected the separator. I will keep you posted.
Best regards,
Garlan

Re: Engine bogs down up at speed - brownish gray smoke

Reply #14 –
I want to thank everyone who responded and offered ideas and suggestions.  I just finished a road test that confirms full power again and no smoke.  The culprit was an 8" thick bird nest, probably several that had been built while I was workamping at a birding nature center for 3 years.  Except for trips out, this coach has been garaged since 2008. The nest was located on top of the separator, that is between the air intake grille on the outside of the coach and before the air filter.  It could not be seen by looking down into the intake through the grille.  After that, they were probably packed down by the suction on the intake, until the driveability  problem appeared.  Thanks to all who offered ideas and suggestions.  All were really helpful.
Garlan

Re: Engine bogs down up at speed - brownish gray smoke

Reply #15 –
GOOD that you discovered the problem!  I recommend a fresh new air filter, if not already installed.  No telling how much trash fell down from the nest construction activity.  I had a similar problem, but with RATS...photos in thread linked below.  I was very lucky, and discovered the blockage before I tried to start the engine.  I installed wire mesh on the air intake to prevent this problem recurring.  You might be able to do the same thing - it just needs to keep birds (and rats) out - won't hurt engine performance.

RAT - My First

Re: Engine bogs down up at speed - brownish gray smoke

Reply #16 –
It sure seems that the filter minder should have given a good indication of the problem... but I am sure it feels great to have fixed it!
Don

Re: Engine bogs down up at speed - brownish gray smoke

Reply #17 –
I love finding a fix that is easy and cheap.  Good find.  👍

Re: Engine bogs down up at speed - brownish gray smoke

Reply #18 –
Thanks. I have been a mechanic for 60+ years, but this one almost got me. Sometimes it's hard to see the forest for the trees.
Garlan

Re: Engine bogs down up at speed - brownish gray smoke

Reply #19 –

Glad you found the restriction, weird is sometimes normal.
On old friend taught me that diesels only need two things to run, air and fuel. Then you can add injection timing, fuel management, turbos, air supply etc and then they get more efficient.  I am sure that everyone here knows these things but sometimes we tend to try to look for the worst when simple will solve the problem.
Gary B