Engine/Transmission (1998.5 - 2002) Modifying fuel system so temperature input to VP44, 80* - 100*, your inputs.

[Mundgyver]

There are allot of different ways to skin the cat so to speak with keeping the temp of the fuel down. I think it all comes down to comfort level of what is being done and does it work the way one intended for it to work.



On the flip side I have read that if one could increase the injected fuel temp to 185* that you get about a 30% gain in power and economey. This information was observed in an industrial puplication for mining equipment. I had checked on the viability of doing this for the economey, but Bosh came back and said not to do it. At the time the would not give me an answer to why, but we all know why now. Heat kills the VP. So I am keeping the VP cool, but if I knew how the get the temp of the fuel up to 185* after the VP, I would be trying it to see what the effect would be.



That is the nice thing about this forum, lots of ideas and good discussion on what works, what might work, and what sometimes comes out as a dismal failure.

 

[keimmmo]

Mundgyver,



I will SWEAR that my truck has better part throttle responce and is DEFINITELY getting better fuel economy since installing the fuel cooler! Someone told me that there is a temp sensor in the VP that is advancing the timing due to the cooler fuel. Can anyone verify that comment?



Bob,



I have been dreaming about that chassis mounted cooler all day. I can see it now!!! Eight INCHES high and eight FEET long!!!!! Hey! When you put it into production to sell to other TDR members, what kind of a box will you put it in???



Steve Keim

 

[Mundgyver]

This comming summer will be interesting to see how the temps work out on the VP. The one thing I have noticed is that on the really cold mornings here, 36*, Yea I know it is not cold to some, but on those cool mornings that the VP seems just a little noisier to me. I have about a 4 1/2 mile drive out to I-5 which I take slow to alow everything to warm up. When I roll onto the freeway, my water temp is around 160* and climbing and my fuel temp is in the high 40's and will settle out about the mid 50's. The VP seems to quiet down once I get above 52* on the temp sensor I have in place on the cover.



I know that adding the cooler earlier (late summer - early fall) seemed to have made a small increase in fuel economy. Nothing outragous, maybe . 01 to . 05 overall. So overall I am very happy with the results. My main goal was to protect the VP from heat and I think I have done that.



I had thought about cooling the return line to the tank but then decided not to. For me the cooler provides what I wanted and I think I want the hot fuel going into the tank anyway for when I take to couple of trips over the Idaho up to McCall and Salmon or up to Spokane, Wa. That warm fuel getting back to the tank in the winter is a good thing I think.

 

[rweis]

On the rail fuel cooler,



Bypass it in the winter time, run it in the summer time. Something like multiple lines running back to the tank vent line. For the northern members one of the lines could be just a rubber fuel line with a ball valve on the other lines to shutoff in the winter.



Mundgyver, I would bet your actual input fuel temps are just like mine. Take the VP EBC temp and subtract about 5 - 7 degrees. Generally I can see OAT on the overhead computer, add 10 and that is the fuel temp sensor reading, add another 5 - 7 and that is the VP EBC temp. All that is running empty. If running with the 5er, add another 10 to the EBC or a total of 15 for the EBC + 10 for the fuel sensor for a total of + 25 - 30 to the OAT (110 OAT = 140 EBC).



One reason my EBC is higher when pulling is I pull at 2400 rpm instead of the 1400 rpm I run down the road to work. The additional rpm adds about 3 - 5 degrees to the EBC because of higher rpm. I think another thing that adds heat when pulling is the slightly higher engine compartment temperatures (about 10 degrees I think, because I see about 10 degrees higher on the engine cooling temperatures). And that about accounts for the additional 15 degrees when towing. Gary saw about 10 degrees higher in underhood temps when towing also.



Try going to work in one gear lower that you normally do (ie run at a higher rpm). About the same OAT day to day, same speed, same distance, change the rpm and see what you get for a difference in the VP temp. I think it is about 5 degrees / 1,000 rpms. The VP gearing is 1/2 of engine rpms so the VP pump is turning 500 rpm faster and generating 5 degrees more heat measured at the EBC. Really not too much additional temp for the work being done.



Now we know the VP EBC temp what do you think the internal temp of the VP actually is? I have no idea. To be safe I guess another 20 degrees. Some have said only a few degrees. No one knows for sure. Any input here for the actual internal VP temp if you know the temp of the frame at the EBC? The VP44 is made out of aluminum I think. Heat transfer of aluminum?



Bob Weis

 

[keimmmo]

Mundgyver,



Yea, I have noticed the exact same thing. The VP is noisier when cold, but makes much less noise from about 50* up. My guess is that it is due to an internal timing advance for a cold motor... and with the cooler we are making it think the motor is colder than it really is.



This brings me back to the same two questions I have asked several times, but I have never gotten a good reply. First, can some one verify the existence of a temperature sensitive sensor in the VP? And, in cool conditions, is cooling the fuel possibly harmful?



Steve Keim

 

[Mundgyver]

Good food for thought for the internal temp sensor if one is there and what it would tell the VP to do for fuel. Do we know any Bosh VP Electronics Experts out there I would suspect that they would know something

 

[Texas Diesel]

I'm not aware of a fuel temp sensor but I know that injection timing is based on the coolant temp sensor on the block.

 

[rivercat]

Off topic I know, but has anyone seen a trend in failing VPs that were overrun often? Meaning any time the throttle position is 0 the vp only passes enough fuel for idle and when engine braking with or without an exhaust brake, The rotor is turning as fast as the engine and may not see enough fuel COOL or hot to properly lubricate it. There for it seems that the worst case would be towing down a long continuous grade with no throttle input and rpms over 2000 for a sustained period. Just wondering if this mode of failure is as common as the hot board/heat soak falure you guys are trying to prevent.


Back when I was a logger I noticed it was bad to overrun any equipment. Had one skidder that would never burn oil till you coasted down a steep hill on the brake and off the fuel petal with a good pull of wood to build speed.

 

[Marco]

The VP has an internal fuel temp sensor. In fact the VP has to adjust the closing of the fuel metering valve based upon that input. Hot fuel = less BTU per volume. Thus the fuel metering valve has to be held closed slightly longer in order to deliver the demanded fuel. The VP's computer adjusts the fuel metering valve based upon the input from the fuel temp and the voltage supply.



Marco

P. S. on edit. Obviously the MAIN input for the VP is the ECM. Fuel temp and supply voltage are used for "fine tuning" the fuel output.

 

[Texas Diesel]

Off topic I know, but has anyone seen a trend in failing VPs that were overrun often? Meaning any time the throttle position is 0 the vp only passes enough fuel for idle and when engine braking with or without an exhaust brake, The rotor is turning as fast as the engine and may not see enough fuel COOL or hot to properly lubricate it. There for it seems that the worst case would be towing down a long continuous grade with no throttle input and rpms over 2000 for a sustained period. Just wondering if this mode of failure is as common as the hot board/heat soak falure you guys are trying to prevent.





Back when I was a logger I noticed it was bad to overrun any equipment. Had one skidder that would never burn oil till you coasted down a steep hill on the brake and off the fuel petal with a good pull of wood to build speed.

Interesting you bring this up. I was talking to a DC man who had just come back from a training class on the VP-44 equipped trucks. One thing they talked about was VP operation in "over run" conditions. He explained that when you let off the fuel (down hill coasting or after a run to pass a lower vehicle) the VP rolls off the fuel injection in a programmed manner. And that some of the VP failures were lubrication based becuase (some of) the after market fueling boxes cause a max fuel to zero fuel in one step and that "shocks" the rotor head. Bosch designed the system to throttle back the fuel but the aftermarket devices defeat that.



Cant prove a word of it but the source is 100% reliable.



----------------------------------



Marco, so what is the effect of us cooling the fuel? Less fuel because it is more dense?

 

[Marco]

Marco, so what is the effect of us cooling the fuel? Less fuel because it is more dense?

Less volume delivered.



Marco

 

[Texas Diesel]

Thats what I thougt but probably a good trade off (keeping the VP as cool as possible)besides, I can add more volume with the right side pedal :-laf

 

[Marco]

The DRB III shows the fuel temp read by the VP... .



Marco

 

[Mundgyver]

So do we know which after market fueling boxes cut the fuel to 0 in one step. This is getting interesting now.

 

[Texas Diesel]

So do we know which after market fueling boxes cut the fuel to 0 in one step. This is getting interesting now.

I asked that same question but for liability reasons DC wouldnt say. :{ :-{}

 

[rweis]

I bet a MAD Catcher (I think that is what Marco's ECM is called) would follow the Bosch protocol!



Bob Weis

 

[rweis]

Can we sum up the last couple of post?



ECM is primary timing and uses engine water(?) temp for that,

VP has a fuel temp sensor and uses it to fine tune timing,

Some boxes do NOT follow Bosch protocol on fuel reduction (ie lubrication) and abruptly stop fuel with abrupt APPS / TPS movement to minimum fuel request. (I probably did not write that correctly)



Cool fuel is good (I am sure to a point 50*?) Does cool fuel lubricate better than hot fuel? Additives for lubricity come into play here I would think.



Anything else?



Bob Weis

 

[rweis]

Oh, one other thing



I had put my fuel feed coolers BEFORE the RASP / LP. BAD IDEA!



The RASP / LP (FASS, ... ) are trying to SUCK fuel and more fittings = more chances of air leaks.



I am going to move my fuel feed coolers to AFTER the RASP / LP (FASS, ... ) where there is PRESSURE and I can get a better handle on the integrity of the lines and fittings.



Just bad design on my part, concept of cooler fuel is good I am pretty sure. Just put the coolers AFTER the RASP / LP (FASS,... ) presurization section and avoid my design errors.



Ah well,



Bob Weis

 

[RAJohnson]

Thanks guys



I have been watching rweis's post as well as all others for months now, and I really have been enjoying it. Keep up the good work. And thanks for your time, in this endeavor.



FWIW The last couple of post concerning the ECM and the defueling mode as been really interesting.



Thanks again, Rob

 

[Marco]

ECM is primary timing and uses engine water(?) temp for that,

Water temp is only one of the parameters the ECM uses for the timing.

Boost, intake air temp, load just to mention a few are the others.

VP has a fuel temp sensor and uses it to fine tune timing,

Nope, not timing. Fuel delivery. ( How much )

Some boxes do NOT follow Bosch protocol on fuel reduction (ie lubrication) and abruptly stop fuel

Who cares what the box does? The ECM will still cut of three cylinders and deliver minimum fuel while coasting in order to keep the VP lubed. Doesn't matter what "the box" does.



Marco