To Vapor lock or not to, that is the question....Electric fuel pump?

[legomybago]

So I took FMC #850 out for a family cruise last weekend over to the in-laws house for a bbq, maybe an 8 mile round trip is all, 75-80 degree Spring day. It was my girlfriend and my daughters first time riding in it (I've been working on 850 in the driveway for the last two years!) They both loved sitting in the front seat looking out at the world. It's a completely different experience driving and riding in an FMC coach then a standard class A motorhome. We stopped at the gas station and I put 25.00 of non-ethanol fuel in it for kicks. Everything was working great, the only issue I was feeling was a mild flat/dead spot on acceleration from a stop, and at times it would not build rpms real fast with the throttle hammered. Like the 440 was a little loaded up?, OR was it running too lean?? (These were thoughts that were running through my head at the time). It could be caused by multiple things, I will dive into that after I fix my vapor lock issue. Anyway, upon leaving the In-laws bbq, after showing off the rig, and getting ohh's and ahh's. We loaded back up. As I was getting in and about to start 850 up, I happily said to Kt, "I'm really feeling good and confident about the old FMC", (After all, I just got done with ALL the mechanical maintenance you can almost do to a motorhome's running gear!!!) So we headed out, got about two miles down the road, then bam! 850 starts obviously starving for fuel, luckily I was able to nurse the throttle through a few lonnngggg stale green stop lights that we got lucky on, and didn't have to stop before turning onto the old back streets of neighborhood that we live in. So as I still nurse the throttle, I see my house is in sight! Going to make it to the driveway! Nope! Died flat on her a$$ one block from the house. I put on the four ways, ran to the back and opened her up (rear engine Chrysler 440), first thing I did was unscrew the fuel filter canister and found only a table spoon on the bottom (should of been full of fuel), and the filter looked like new still. I put the filter back together quickly, took the air filter housing loose on top of the carb (Thermoquad) and pumped the throttle by hand to listen for fuel. I didn't hear any fuel spraying, so I pumped it maybe ten times then I heard fuel spraying!! yay! Closed the rear doors, run to the front and she fired right up! Kt looked at me and said, "Damn, you are good?" I laughed hahaha.
In my history with a manual fuel pump motor vapor locking, I've never been able to get them started back up and running "on there own" until they cool off, like 30 minutes. 850 was only shut down/out of service/capput for 1-2 minutes in the middle of the road. So by me opening the fuel filter before the manual pump release pressure? Or? Why would the carb start pumping fuel again? Where did the fuel come from? Kinda weird.
What I did different with the fuel system before this "Sunday Drive", was I installed a 3-port fuel filter "after" the manual pump, 5/16" in and out, 1/4" vapor port to return to tank (I read that this style of system prevents vapor lock) I didn't have my new vented fuel cap arrive in the mail yet, so I left the old factory gas cap loose so the tank would vent. Even with the original straight fuel line from the pump to the carb, I think it would have still vapor locked, but who knows, this was the warmest temp day I've driven it so far.
The fuel pump that is on the 440 is old, I don't know what pressure it's pushing either, I need to go pick up an inline gauge and check. But in my history trying to stop vapor lock situations, replacing the manual pump never solved it. So I need to just go electric. I want to run the best pump available, should I buy the Red Holley and regulator? Or?? We have a Red Holley on our 1986 P30 rig, it's been working well, but kinda loud, the P30 also has a built in fuel return system in the manual pump. The 440 does not, that pump will have to go, and put a fuel pump block off plate on.
Which electric fuel pumps and regulators do you run? And at what pressure is your Thermoquad happy at?
Thank you

[Rickf1985]

You have a rear engine, where is the gas tank? I would question the fuel pump before condemning the entire fuel system. An old pump is bound to be weak so it could very well be lack of fuel from a bad pump. The fact that you had no vapor pressure when you opened up the system makes me believe that you did not have vapor lock.Vapor lock is caused by gas boiling in the lines and with the rear engine I don't see the lines getting much preheat from the engine heat and exhaust going back towards the tank like a front engine system where the tank and lines are all downstream of the heat source.

[legomybago]

The gas tank is in front of the engine on the other side of the firewall.  I am picking up a new in line fuel pressure gauge and seeing what I have for fuel pressure first before spending any money on parts etc...It could very well be that old pump. Im sure the pump was new when the engine was rebuilt in the early 90's, but it sat for 17 years before I purchased it!!  W% I will know more info in a couple days.

[M & J]

I'm with Rick on this one.

[legomybago]

Fixed! For starters, don't believe everything you read on the internet! I read that putting this 3-port filter on after the fuel pump would keep fuel moving enough to help with vapor lock issues....well it killed my fuel pressure. I put a gauge on it, and I was getting 0-to barely 3pounds, when I crimped the 1/4" vapor line coming out of the filter, I have a solid 7 pounds going to the carb.  W% So I was starving the engine of fuel, resorting in my sluggish acceleration and slow rpm build under load. AND it mildly vapor locked due to not enough pressure and volume. So yes Rick and MJ, it was definitely a pump issue caused by my own dumb doing. I am going to leave the mechanical pump on, and go back to the stock single 5/16" line straight to the carb, and I will carry a spare pump in the rig. Not going to redesign the fuel system anytime soon. Thanks

[Froggy1936]

As you had not been driving the rig steadily, This is not really applicable, But when any problem arises , Go to the last thing you did to that system , And that is usually where you will find your problem  D:oH!  Frank

[legomybago]

I know that Frank. Don't make me feel any dumber for my mistakes. N:( Hey! If it weren't for trial and error, we wouldn't have this great panel of "experts" here at CWVRV!! 

[Rickf1985]

Did anyone mention to go back to the last thing you did? :)rotflmao :)rotflmao :)rotflmao

[legomybago]

Even if the panel of experts did write that Rick, It wouldn't of mattered? Who listens to advise anymore? hahaahahaha

[Froggy1936]

Or Advice  :)rotflmao  :)rotflmao  :)rotflmao Frank

[legomybago]

So here's a bump/update on this thread....
Rick, I tested my fuel pump for volume today, I get a 1/2 pint at 30 seconds of engine run time at idle. That's half of what I should be getting? Correct? All my fuel system before the pump is in great condition. Now for my reasoning for checking fuel pump volume. So today was a great cruise day, with my fresh tires and a bunch of other stuff done, I wanted to get her out for some shake down runs.  She runs great all over town, stop light to stop light, outside temp was in the 80's. BUT, when you hammer down on the throttle to get up to say 55mph like on a highway on ramp, the engine would just fall flat about 3/4's of the way up to highway speed, I could back off the throttle and it would hold a 40 mph line, then smooth up and be fine, until I wanted to try and get back up to 55. I know it was running out of fuel, but I also had NO vapor lock issues in town. So I think I need another pump. This pump puts out just shy of 7 pounds (good),but weak volume.

[Rickf1985]

Well, here is your answer, short and sweet, you need a new pump.
Now the long explanation of why. Pressure is a product of volume against resistance. Your pump puts out a measured volume and it is produced with a diaphragm being pushed by a spring. The camshaft in the engine forces the diaphragm up which draws gas from the tank and the spring forces the diaphragm down which forces the gas to the carburetor. It is that spring that determines your fuel pressure. In order for that pressure to be met there has to be resistance in the line. An open fuel line from the pump to a can for instance will have no measurable resistance therefor no pressure. In actual use you have the needle and seat in the carburetor and the inlet is sized to be a restriction. Now you have the restriction you need to hold back the full flow of gas so now it is the pressure of the spring that is the determining force for the pressure. In your case it is 7 lbs. when you are not using more gas than the carburetor can use. Here is where the volume equation comes in. In order to maintain the pressure you have to be able to supply more gas than the engine is using, if not pressure drops. And as you said, basically you are running out of gas.

Now, the reason why.
There can be several reasons why, this really needs more testing to be sure but you said you tested the pump and got very little volume out of it. I would do one more test to cover all the bases and to make sure you are not replacing another pump for nothing. You already have the pump pressure tester so I am guessing it is a pressure/vacuum gauge?  Hook it into the gas line before the fuel pump between the pump and the tank and see if it is drawing any significant vacuum. A very little is normal. If it is then you have a restriction in the line somewhere that needs to be addressed and it may not be the pumps fault. This would be indicated by 7-10 inches of vacuum on the inlet line. A engine driven fuel pump can draw a lot of vacuum, I just recently sucked a boat gas tank I was using to move a motor home around in on itself because I forgot to open the vent!
If the gauge shows vacuum/pressure,  vacuum/pressure as you are idling then you have a bad valve in the pump and the pump is bad.
The most common cause of inlet line restriction is a clogged filter sock on the tank inlet, assuming you have changed any filters in the line.

[legomybago]

Thanks for the advice/knowledge Rick! I just have a stand alone gauge for checking pressure. My vacuum gauge has an 1/8" line, might be a pain to adapt. I could probably buy a tee to do the job. When I pull the fuel lines, I'll do a restriction test with my mouth  and see how well fuel pulls from the tank, if any dought to too much restriction, I'll dig deeper

[Rickf1985]

You will never be able to tell anything that way! It will feel like there is a lot of restriction just trying to suck gas and then you get a mouth full of toxic gasoline! This stuff is not the same as the gas we used to ste...... er... borrow from tanks at night with the garden hose. That stuff just tasted bad, this stuff will kill you!

[legomybago]

Too late Rick, I got a small taste of it yesterday, the fuel pulls right out with very little effort I found out ....haha. I'm no stranger to gas/diesel syphoning. My Grandpa once told me that he was happy to have lived a full life, even after having his hands in gasoline his entire life! He was surprised....

[Rickf1985]

An old time mechanic I studied under always had a bucket of gas outside and that was the parts washer bucket. It was also where you washed off cuts and scrapes. Just think of the chemicals you are introducing into the body nowadays if you do that! And back then if you got gas on your hands the smell went away in an hour or so, not today, you are stuck with it for days.

Of coarse back then it was lead you were introducing. that does pretty much destroy brain cells. Of coarse back then it was lead...................... uh, wait a minute.

[legomybago]

haha! yes lead, I was thinking the same thing. And yes on the parts wash bucket, grandpa used to clean all his tools in the gas bucket too (like after an engine build).

[EldoradoBill]

It's a $15 part! Just replace it already  W%

[PwrWgnWalt]

Went through the fuel pump debate myself last year. Found out the ethanol in recent years is terribly bad for old fuel pumps, not being nice to the diaphragm.  So, even if not leaking fuel into crankcase of my 440, it was not producing enough flow.
Then I found out there are a lot of various pumps out there for the 440!  Many are too high pressure for my Edelbrock carb, while others are too low volume for the thirsty demands of the 440.  I wanted to stay mechanical, for constant duty and remote area serviceability. I ended up installing an Edelbrock manual pump, and it has worked perfectly!  I also replaced the hard lines with new 3/8", larger line.
I posted the results of my research on pumps here: http://www.classicwinnebagos.com/forum/index.php/topic,10687.msg64475.html#msg64475

-Walt

[legomybago]

Went through the fuel pump debate myself last year. Found out the ethanol in recent years is terribly bad for old fuel pumps, not being nice to the diaphragm.  So, even if not leaking fuel into crankcase of my 440, it was not producing enough flow.
Then I found out there are a lot of various pumps out there for the 440!  Many are too high pressure for my Edelbrock carb, while others are too low volume for the thirsty demands of the 440.  I wanted to stay mechanical, for constant duty and remote area serviceability. I ended up installing an Edelbrock manual pump, and it has worked perfectly!  I also replaced the hard lines with new 3/8", larger line.
I posted the results of my research on pumps here: http://www.classicwinnebagos.com/forum/index.php/topic,10687.msg64475.html#msg64475

-Walt

I found that most factory 440 pumps were all 30 gallons an hour. You can buy a "high performance" pump that was for dual four barrel set ups and there pressure was between 7.5-9 pounds, or the stock replacement is between 5.5-7 (which is what I ordered). They were both/all 30 gallon flow. Ok, wow, I just read your thread Walt on the different pump ratings, I had no idea there where so many.... I only talked with parts nerds over the phone and asked them specs on the pumps they could get here locally....When I order parts, or talk to a parts person over the phone, I always use 1976 Chrysler New Yorker for my vehicle. I'm not sure how to break down that math for an idle run test, I just googled mechanical fuel pump volume test, and read 1 pint at 30 seconds idle is sufficient for a v8, I never knew this #, nor have I tested for this in the past, I would have just thrown on a new pump and crossed my fingers..... When I tested output, I had half that volume.  I learned something new that day. Today I get the new pump. I would like to do a vacuum test pre pump like Rick mentioned, but I don't think I will unless I have output volume issues with the new pump. Then I will dig deeper.

It's a $15 part! Just replace it already  W%

25 dollars here...I had to save up.

[legomybago]

I picked the new pump up, and the first obvious good sign was the inlet size on the new pump is 3/8. My old pump is 5/16. I installed the pump, but had to go buy a new fitting for the outbound side of the fuel filter and a few feet of 3/8 hose to finish the plumbing. I will now have a complete 3/8 fuel line from the tank to the pump. This will help with volume for sure.

[legomybago]

New pump has 7-8 pounds pressure, and 1 pint of fuel at 30 seconds idle. Still need to drive.

[Rickf1985]

That pressure may or may not give you problems. Have to try it and see. If the pressure gets too high it can push the needle off of the seat and flood the carb or it can force too much gas in too quickly when the float drop and the needle opens and also flood it that way. The second scenario is a tough one because it is almost impossible to catch it happening, all you notice is really bad gas mileage so if your gas mileage drops drastically then that is something to think about.

[BrianB]

I don't know anything about the Dodge engines, but the Chevy motors have the return line on the mech pump that should limit the fuel pressure to some degree.

You could always add a Holley fuel pressure regulator between your pump and the engine.

[Rickf1985]

The regulator might work but not likely, they need more pressure differential to work off of. Example, it would want to see like 20lbs. in so it could regulate to 5lbs. out.