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

Aaarrghh · August 12, 2016, 11:57 AM

After all the excellent advice given here on this topic, this may sound a little simple-minded, but please indulge me. I was having similar problems, bogging on hills and stalling after stops. My Warrior has a clear plastic fuel filter halfway between the tank and the pump. The filter is fresh, but the short lengths of rubber hose connecting it were old, and soft. I suspected they were collapsing under a strong vacuum, so I changed them. The new hose was a lot stiffer. It's been just a little while, but I haven't experienced the stalling and bogging since. Also the motor starts a lot quicker. Odd, really.

Just my 2 cents

Rickf1985 · August 12, 2016, 04:14 PM

That is entirely possible but if you are getting that much suction from the tank you may also have a clogged pick up sock. A filter before the pump is really not needed on a mechanical pump since anything that makes it up the line will generally pass through the pump and be caught in a filter upstream. This lessons the suction load on the pump but I can tell you that a mechanical pump in good condition will pull quite a vacuum.

EldoradoBill · August 12, 2016, 08:33 PM

have you changed the tiny-and-easily-plugged filter that sits in the carburetor inlet fitting?

Bill

legomybago · August 15, 2016, 10:39 AM

I have a Thermoquad, their is no filter in the carb. I have been out of town, haven't had a chance to run it yet....

Aaarrghh · August 15, 2016, 10:46 AM

Quote from: EldoradoBill on August 12, 2016, 08:33 PM
have you changed the tiny-and-easily-plugged filter that sits in the carburetor inlet fitting?

Bill

Yes, last year, but when I went to change it again, the fitting was stuck and the tubing started to twist, so I tightened it back up. Replacing that tube is going to be a headache, but it's not leaking, so it can wait. Since I have an inline filter ahead of it, the filter is probably not going to clog anytime soon.

Aaarrghh · August 15, 2016, 10:48 AM

Quote from: Rickf1985 on August 12, 2016, 04:14 PM
That is entirely possible but if you are getting that much suction from the tank you may also have a clogged pick up sock. A filter before the pump is really not needed on a mechanical pump since anything that makes it up the line will generally pass through the pump and be caught in a filter upstream. This lessons the suction load on the pump but I can tell you that a mechanical pump in good condition will pull quite a vacuum.

How much trouble is it to check/clean that sock? It's very likely to be dirty, at least, after all these years

Rickf1985 · August 15, 2016, 11:30 AM

To do it right means dropping the tank and pulling out the sending unit to get to it to clean it. The down and dirty way of doing it, and this is ONLY if you do not have an in tank pump, is to blow a little air back through the line. I do not mean put your air nozzle on there and blast away!!! That method will remove the dirt, and the sock! You just want to gently blow some air into the line to push the fuel in the line back out and some air with it to dislodge some of the crap some the filter sock. Keep in mind that this stuff is still in the tank and will eventually end up back on the sock so you are just buying yourself some time this way.

DaveVA78Chieftain · August 15, 2016, 06:02 PM

Careful guys. Your mixing Dodge and GM products together which have 2 different fuel system designs. This will confuse people.
N:(

legomybago · August 15, 2016, 06:21 PM

Yeah! Stay on topic!! Patiently wait for my lazy butt to drive mine and see if I fixed it!!

Rickf1985 · August 15, 2016, 06:26 PM

I added the pump disclaimer so that anyone reading this from another forum would know not to blow back through a pump.

Aaarrghh · August 16, 2016, 12:29 PM

Quote from: Rickf1985 on August 15, 2016, 11:30 AM
To do it right means dropping the tank and pulling out the sending unit to get to it to clean it. The down and dirty way of doing it, and this is ONLY if you do not have an in tank pump, is to blow a little air back through the line. I do not mean put your air nozzle on there and blast away!!! That method will remove the dirt, and the sock! You just want to gently blow some air into the line to push the fuel in the line back out and some air with it to dislodge some of the crap some the filter sock. Keep in mind that this stuff is still in the tank and will eventually end up back on the sock so you are just buying yourself some time this way.

Thanks, Rick. Very helpful. I didn't want to start a new topic just for this question!

legomybago · August 22, 2016, 02:50 PM

Yesterday was the perfect 100 degree day to take it for a drive.....

. Ran great from stop light to stop light, Ran great on the 40 mph four lane hwy hammering the throttle down, then it ran great on the 50 mph four lane hwy hammering the throttle down from time to time picking up speed. I'm now about 7-8 miles away from home where I decided to take Interstate I-5 back to the house. It ran like $hit as soon as I merged into traffic on the Interstate!!! Same scenario as described earlier in this thread (pulls hard until about 50 mph). It seems as though when the ambient or "under hood" temps get to a certain temp, It starts vapor locking...So I took it easy and drove it home, runs great at slow speeds! These rear engine FMC's pack some serious heat in the engine compartment. I couldn't even touch the rear bumper it was so hot! I opened the rear access hatch to the engine, and touched the fuel supply line before the pump, and it was smoking hot, even with the fuel tank in front of the engine behind the fire wall, the fuel supply line was hotter than hell, that doesn't help with vapor lock issues....So I'm going to check the supply line for any resistance (like the fuel tank pick up assembly, which was mentioned earlier in this thread), and if all is good there, I will order a Carter 4070 electric pump and install and then get rid of the mechanical pump....

Rickf1985 · August 22, 2016, 08:58 PM

I was never aware this was a rear engine, not that it would have made a difference in my diagnosis. What does the fuel line runs past that is hot? Exhaust? I would think something is wrong since they made more of these than just yours and they all apparently ran just fine as did yours up to this point. Is the fuel line and exhaust all in their original configuration? Does the engine mounted pump run a bypass back to the tank? Older Dodge Power wagons and WC's used a bypass fuel filter as did the V8 AMC Jeeps. It is mounted close to the carburetor with the bypass line on top so gases can go back to the tank and also keeps fluid circulating.

legomybago · August 23, 2016, 12:41 AM

The fuel line is no closer to anything then any other 440 out there i suppose It used to have an electric pump in it, but was removed long ago I guess? Some of the wiring is still intact and a Carter style fuel pump mount still in the rig. The fuel supply line blows through clean, I checked that tonight. I just need to install an electric pump and more then likely put this to bed. I may still pull the Thermoquad and inspect (I rebuilt it close to 3 years ago). I put low style exhaust manifolds on it that came in some of the late 70's class c dodges. so it's not stock configuration. No fuel return to the tank. I already tried that, and it killed my fuel pressure!! I think the crap fuel we have now is the main culprit.

Rickf1985 · August 23, 2016, 08:06 PM

How close to the fuel line are the manifolds? A simple metal shield between the manifold and the line will deflect a LOT of heat. And you did the return line with a bad fuel pump. Got to remember that. The fuel return line has to have a restriction that is why I was thinking that filter I mentioned.

legomybago · August 24, 2016, 11:59 AM

Remember when I did the return line, My pressure went from 7 to 1 pound with the old pump, so it wasn't the old pumps problem. The flow volume with the old pump was bad.
My supply line runs about 6" away from the exhaust manifold

legomybago · August 24, 2016, 12:01 PM

Here's the old Carter elec pump mount still in the rig....Both the fuel filter and new pump will be located on the firewall instead of the side of the radiator.

legomybago · August 24, 2016, 12:03 PM

And to finish drawing the picture Rick, here is the supply line running out of the firewall to the filter to the pump. The 3/8" rubber line comes out of the firewall, down to steel and runs along the outside frame rail, then does a 180* next to the genny oil filter and over to the filter etc...

legomybago · August 24, 2016, 12:15 PM

I also took the thermoquad off last night and found no restrictions or anything weird with it other than I was able to snug up the bowl cover screws a little...I was able to blow freely through the needle and seat.

Rickf1985 · August 24, 2016, 12:22 PM

Ok, the pictures help a lot. The radiated heat on the pump may cause issues mainly because you do not have airflow over it like you would in a front mounted setup. The other thing I see is I follow the fuel line past the generator and down and don't I see the exhaust and muffler right there? Or is that the fuel line to the right of that red thing on the fire wall?

And by the way, Yes, your old pump had a volume problem, remember how you get pressure? Volume has to have a restriction, if you have low volume then even a small restriction will not give any pressure where as high volume through a small hole will be a lot of restriction, hence more pressure. And you can get vapor lock even with an electric pump if the gas boils faster than it can flow through the line. That is the idea behind return line plumbing, keep the gas flowing so it does not have time to boil.

legomybago · August 24, 2016, 12:44 PM

The red thing you see up on the firewall is the genny in-line fuel shut off valve I put on it. The line to the right is the 440 fuel supply. Both mufflers are mounted directly under the genny, so yes the duel exhaust pipes are under the fuel line as it runs along the frame.

Rickf1985 · August 24, 2016, 04:25 PM

That could be a source of heat related fuel problems too. All you need is a flat metal shield with an inch of space between the shield and the lines between the heat source and the fuel line, The metal deflects the radiated heat and the air gap takes care of what the shield absorbs. And if the shield is painted silver or chrome even better.

legomybago · September 10, 2016, 08:44 PM

Well.....I installed the electric pump and relocated the fuel supply lines further away from the exhaust. The pump puts out 6.5 pounds pressure. The spark plugs i looked at are showing lean burn vs rich. Took it for a drive and as soon as I hit the highway!!!! BAM still have the same issues! It actually runs worse with the new pump. I had to nurse her home around 25 mph's. I pulled the coil and it checks out good on the specs (I even compared it to three other coils at the part store), I also checked the resistance specs for the pick-up coil in the dizzy = good. So I am going to tear into the Thermoquad I guess...

Rickf1985 · September 10, 2016, 08:51 PM

I was looking through a Jegs catalog I got and I saw insulated fuel line covering. I usually deal with Summit but I am sure it is available across the board. Are you checking the pressure at the carb with it running or are you checking the deadhead pressure? Deadhead means nothing, that just tells you what the pump is capable of with 0 flow. If anything on the carb be sure the float drop is set right, a lot of people concentrate so much on the height setting they do not set the drop and the float does not drop enough to let fuel in at a fast enough rate.

legomybago · September 11, 2016, 12:03 AM

Today I just did a "deadhead" test like you mentioned. I'll maybe hook the gauge back up and run it, I was thinking about taking the air filter assembly off also. It's a bit of a pain working/trouble shooting an engine thats 29' behind ya! I buy from Summit also Rick, and I do have some heat wrap and part of the fuel lines. I did notice that the fuel lines were cooler today after a quick stop to get out and look at the engine, they and everything else gets hot fairly quick at idle in the 90 plus degree day we had today though.