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Old 08-10-2021, 07:09 AM   #1
Mini-Skoolie
 
Join Date: Mar 2020
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6BTa5.9 smokes when pedal is pushed down

I have a strange problem when pushing down my gas pedal to the floor. The engine does not rev up but sputters and smoked. When I push it slowly and only about 80-90% of the travel way everything is fine. I was playing around with the linkage and it made it a bit better.
Is this an adjustment issue with the Bosch pump or a mechanical problem? Looks like I also have a lot of play in the pump linkage.

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Old 08-10-2021, 12:53 PM   #2
Bus Crazy
 
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Not one answer

Smoke. Like black smoke?

Would indicate too much fuel for the amount of air.

Slow gentle throttle application would keep boost low. Stomping on the pedal or 100% pedal would allow maximum boost.

Theater are many possibilities. You description implies too much fuel, or not enough air, or both.

I suggest you learn about stuff that can leak boost. A boost pressure gage on the dash may help in correct diagnosis.

Look to see if symptoms occur at same rpm and or same manifold pressures.

This will the start of the investigation.

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Old 08-10-2021, 02:46 PM   #3
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What color of smoke?


Black smoke indicates excess fuel or lack of air. Could be an intake restriction, leaking/blown charge pipe boot, failing turbo, pump turned up, etc.


White/gray smoke typically indicates air in the system or lack of fuel/fuel pressure.


When is the last time you serviced the bus with new fuel and air filters? How much fuel is in the tank?
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Old 08-11-2021, 12:23 AM   #4
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I have checked the turbo and pipes. That all seems fine. No cracks in the pipes and no play in the turbo.

The filters were changed last week and the tank flushed as well. At the moment its 1/4 full of fresh diesel.

The engines starts fine and revs up fine. ALso I can drive at a good speed on the highwas. Only if I push down the pedal the last 10% its starts coughing.

It is smoking grey not black.

So I am leaning towards the pump.

I have no experience with diesel pumps but my understanding so far is that its either running or not.

I hoped it to be the turbo because in my area there is no one who can check the pump and say if its working correctly or not
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Old 08-11-2021, 08:26 AM   #5
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Quote:
Originally Posted by Flitzeflap View Post
I have checked the turbo and pipes. That all seems fine. No cracks in the pipes and no play in the turbo.

The filters were changed last week and the tank flushed as well. At the moment its 1/4 full of fresh diesel.

The engines starts fine and revs up fine. ALso I can drive at a good speed on the highwas. Only if I push down the pedal the last 10% its starts coughing.

It is smoking grey not black.

So I am leaning towards the pump.

I have no experience with diesel pumps but my understanding so far is that its either running or not.

I hoped it to be the turbo because in my area there is no one who can check the pump and say if its working correctly or not

I'd start with checking fuel pressure at the injection pump (supply line pressure) while under load. Since you've cleaned the tank and such, I'd assume there was a reason for it. Might have a line that is getting plugged or the lift pump getting weak. Otherwise, it could be a calibration issue with the injection pump.


The pumps on these are easy to time and such. If fuel pressure is good, I'd pull the pump and take it to a pump shop and have them bench it to make sure everything is in spec. Might be good to pull the injectors and have them cleaned at the same time. (I'm assuming by Bosch pump you mean the mechanical p-pump and not the VP44 or similar.)
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Old 08-11-2021, 01:48 PM   #6
Mini-Skoolie
 
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I have attached pictures of the Bosch pump. It looks like a mechanical.

On the net I have read that the lift pump is often bad on these buses. Is there an alternative which I can instal? I would like to check all the little bits first because to me it feels as if is not much that is causing the problem.

I have never installes a pump on a diesel and I rather do not do it.
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Old 08-11-2021, 01:56 PM   #7
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Quote:
Originally Posted by Flitzeflap View Post
I have attached pictures of the Bosch pump. It looks like a mechanical.

On the net I have read that the lift pump is often bad on these buses. Is there an alternative which I can instal? I would like to check all the little bits first because to me it feels as if is not much that is causing the problem.

I have never installes a pump on a diesel and I rather do not do it.

That would be a bosch p-pump.


The engine should have a mechanical lift pump... just like an old school small block chevy. If it is mechanical, it'll be near the back of the block on the same side as the injection pump under the fuel filter mount. It may be electronic.. but check for the mechanical pump first. They are easy to change and relatively cheap.


I would do some testing first before buying/replacing anything.
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Old 08-11-2021, 03:04 PM   #8
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O.k. I will do that once I am back in the workshop. I just checked about the p-pump. So there are some threads about increasing fuel flow by turning the star nut? could it be that the problem is solved by turning the nut?
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Old 08-11-2021, 03:23 PM   #9
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yes and no

if you turned it and it caused your problem, then turning back will fix your problem.

but, i suspect, something else is over fuelling you. once you got that fixed, then start playing with the adjustments of the afc.

since the tamper marks on your afc look unmolested, your problem is probably somewhere else.
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Old 08-11-2021, 03:24 PM   #10
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Quote:
Originally Posted by Flitzeflap View Post
O.k. I will do that once I am back in the workshop. I just checked about the p-pump. So there are some threads about increasing fuel flow by turning the star nut? could it be that the problem is solved by turning the nut?

Is this problem new or has it been an issue since day one? From the picture, it doesn't look like the pump has been tinkered with. It could be an injector issue.. could be a low fuel pressure issue... could be an injector crush washer issue (leak under load)..



Start with testing fuel pressure into the pump under load. Then move on to having the injectors cleaned/tested as that is the next cheapest option and since I'm assuming the fuel system was nasty, might be part of your issue. Its typically ~$20/each or so to have injectors cleaned at an injection shop and they are easy to pull on the Cummins.
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Old 08-12-2021, 12:23 AM   #11
Mini-Skoolie
 
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When I bought it it sat for a long time. There were several issues I had to fix and that is the last of them.

I did not touch the injector pump nor the injectors. But I will check them.

Thank you for your help so far.
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Old 08-12-2021, 08:25 AM   #12
Bus Nut
 
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Quote:
Originally Posted by Flitzeflap View Post
When I bought it it sat for a long time. There were several issues I had to fix and that is the last of them.

I did not touch the injector pump nor the injectors. But I will check them.

Thank you for your help so far.

I'm going to guess that the pump or injectors are on the dirty side. Can you pull the supply and return fuel lines at the tank? If so, get a 2 gallon fuel can.. add a quart of ATF and a full bottle of diesel klean (silver bottle).. then fill with diesel fuel. Put the supply and return lines in the can... prime the system and start it. Let it run through this mixture until it's gone (rev the engine hard from time to time).


Then reconnect your tank and prime the system. See if the problem persists.



You can also try Liqui Moly Diesel Purge. It would take 2 cans and it has to be ran straight.. no mixing with fuel or anything else.



Either should clean up the pump and injectors. If the problem persists, pull the injectors and have them tested/cleaned. Replace the copper crush washers when re-installing.
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Old 08-12-2021, 09:28 AM   #13
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I found a shop which can clean the injectors and take it to them. They can hopefully shed some light. I keep you posted. Thanks for the help so far!
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Old 08-13-2021, 09:39 AM   #14
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Check the fuel shut off valve I have seen the rod rust and break and the boot will pull the fuel lever just enough to start and run but you will be down on power.
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Old 08-13-2021, 09:40 AM   #15
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I highly doubt you have inj issues.
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Old 08-15-2021, 12:39 AM   #16
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Check the fuel shut off valve I have seen the rod rust and break and the boot will pull the fuel lever just enough to start and run but you will be down on power.
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