Greetings from Alaska,

Surprisingly (at least to me on Kodiak) my 404 is a vapor locking machine.
I had a slight problem with fuel starvation going up long grades so I rebuilt my fuel pump and added a clear filter after the pump. Then it began.
I think that replacing the pump diaphram has increased the
suction enough to vaporize fuel at the same time the truck reaches operating temp (80 C). I can watch the clear filter remain full of fuel during the warm-up, then at that critical temp 80 to 85 c the filter will start to fill with bubbles. I have presurized my fuel system and found no leaks.

So all that to ask, has anyone tried to retrofit the firetruck 24v fuel pumps to standard 404.1 tanks? And if so, what kind of results did you have?

Do you guys out there with firetrucks/electric pumps have less trouble with vapor lock and cheap fuel?

Does super or reg fuel vaporize at a lower temp?

Regards,

Jim in Kodiak
76 Belgian 404.1 (TOP SPEED 15 MPH)

Jim you know my answer but I'll add it here for others searching the topic cause Im sure it will come up again. Also you may want to bring this up in the General 4x4 forum since vapor lock is not just a Mog problem. The higher readership of Gen 4x4 should net you more suggestions.

and of course.... use that little http://www.pirate4x4.com/forum/images/top_search.gif button up yonder. I just did a search on "vapor lock" in all forums out of curiosity and got lot of stuff. I'm sure some of that info will help ya out too.

From Coachgeo at Mogml

Jim,

I think Chrystler cars had a vapor lock issue on a few of their rigs
that they solved by using a prefilter with an air bleed. Another words it has the normal fuel inport and outport but it also has a 3rd port designed to be fed back into the fuel return system that bleeds off vapor. The filters are about 4 buks and can be found at any auto parts stores. I have some of the part #'s but its just as easy to go to the store. You may have to add a one way check valve to keep returning fuel from the carb going the wrong way into the prefilter. I know of two sources for those if you need.

My understanding is you want the prefilter that will fit your set up
according to hose size and the position the filter will sit in. As in
the bleed port (usually smaller in size than the other two) needs to be verticle as best as possible so the vapor will travel up and out of the vapor bleed port.

Thanx Coach,

Good idea about the general board.
But what I need is to get a consensus from the 404.1 fire truck guys on how the pumps work to see if using a stock fire mog fuel pump will fix the problem permanently or not. Apparently the motor is located on top of the tank with the pump in the bottom connected with a drive shaft. If not I will take out the existing fuel system and replace it with rubber lines and NAPA 24V pumps at the tanks to push the fuel under pressure, with a good aftermarket fuel selector valve.


Regards,

Forgot to add,

With a T filter located after the engine fuel pump to recerculate the fuel back into the tank vent line, to help keep the lines cooler.


P.S. It seems that if you don't have a diesel mog or are talking about off topic items you can't get mutch time on the other mog lists. I have gotten more from a few folks "off list" for some reason.

Regards,

Jim with the gasser 404.1

Originally posted by Jim in Kodiak
Thanx Coach,

Good idea about the general board.
But what I need is to get a consensus from the 404.1 fire truck guys on how the pumps work to see if using a stock fire mog fuel pump will fix the problem permanently or not. Apparently the motor is located on top of the tank with the pump in the bottom connected with a drive shaft. If not I will take out the existing fuel system and replace it with rubber lines and NAPA 24V pumps at the tanks to push the fuel under pressure, with a good aftermarket fuel selector valve.


Regards,

hmmmm..... wierd. Mine "was" a fire mog. I'll PM you an email address of a guy that has a few fire mogs. Maybe he can help.

I have been tempted to add a 24volt fuel pump to my truck. You would also have to get a regulator? to keep it down to 2-3psi so you don't fill up your eninge with fuel..hehe

One of my trucks was a firetruck and I see no sign of the fuel pump you're talking about.

Later.

Ken S.

ok...... I read the manuel closer and low and behold I now see the remenants of the aux. fuel pump on my mog. I assume you have a manuel? In mine it did state it's use is for high ambient or engine temps. Not sure why its a problem in Kodiak unless its related to the lower atmospheric pressure. I wonder if the lower atmospheric pressure there makes it easier to reach boiling under pump pressure? hmm. Course that is assuming you have lower atmospheric pressure up their compared to other parts of the Mainland .

From Mogml
1. What is vapor lock?

When fuel boils to a vapour in the carbie or in the fuel lines.

The carbie is designed to recieve LIQUID fuel then measure it as a liquid through the carbjets to where it atomises and THEN becomes a vapour of the correct fuel&air density in the intake of the motor. If fuel comes into the carb ALREADY a vapour, it cant be measured into the motor in the proper air/fuel density and the motor wont run.

2. How do I detect it ?

Firstly the motor runs like crap, then or quits all together
If you have a glass window into the carbie fuelbowl or a transparent fuel line, you will see no liquid fuel or will see alot of bubbles.

3. Under what circumsatnces does it occur?

Usually high atmospheric temperatures or the fuel system lines, hoses, etc are too close to very hot parts of the motor.

4. Where geographically does it occur ( I know the RMM folks talk about it) Its more common at higher altitudes since the temperature to reach boiling of any liquid is lower temperature at higher altitude.

5. How do I "on the spot" cure the problem,

Let things cool off, A quick fix can be as simple as wrapping water soaked rags over the fuel lines and keeping them wet.

6. Does blowing into a hose, which has been forced over the small gas tank breather spout (behind the cab), cure the problem?

Does not really "cure" the problem. What happens is, It places a higher atmospheric pressure on the fuel supply. The higher pressure will slightly increase the boiling point temperature
of the fuel. That slight increase in boiling point temperature, may be all it takes to keep the fuel from boiling under that specific condition, But its not really a "cure". All it takes is the altitude to go a little higher, or the fuel temperature to increase and you are back to boiling fuel and vapourlock. Of course this could be overcome again by blowing even harder into the fuel tank !!

Håkan Andersson