Air bubbles in the fuel line and stalling on the road trip

[Desert Rat]

Ok, moving this over from a road trip review in the Lounge http://coloradok5.com/forums/showthread.php?t=181238) since I'd hate to endure the wrath of tech in there. Went on a road trip this week with the nearly finished rig. As soon as I started up the Sonora Pass, which is very steep, the rig started stuttering and stalling. I could feather the gas for a while but eventually it would die. Now, here is the background on the rig:

Installed a 45 gallon aftermarket metal tank a while back (write up in the Tech Articles forum). All new parts in the tank including pickup, sender, etc. About a month or two ago I take the rig out on its maiden voyage (http://coloradok5.com/forums/showthread.php?t=178278) After that trip I found out that I had reversed the vapor canister vent line and the fuel return line. The result was that I sent a bunch of charcoal and filter materials into my tank. I drained it as much as I could (there is a drain plug in the tank) and then replaced all the hoses on the fuel line, fuel return line, and vapor line and cleaned the metal lines blowing them out with compressed air. I have three filters actually running, one on the frame rail where the PO had installed some kind of funky electric pump, one outside of the carb, and the internal Q-jet filter. I replaced all three. Now, another interesting thing is the PO had put fiberglass insulation all the way down the fuel line frame rail previously held in by some kind of asbestos cardboard looking pieces tied in with wire. Clearly he had vapor lock issues in the past. It seems that was also the impetus for putting in the electric fuel pump in conjunction with the manual pump. Recently I had removed the electric setup, the insulation, and installed a new AC Delco manual fuel pump.

Fast forward to the trip. When I first crawled under the rig at the first stall, I noticed a lot of crap in the rear filter on the frame rail. I've been replacing this filter over and over and obviously I never got all the crap out of the tank. So, I swap in a new filter (I brought several with me) and let it cool off for a while. I fire it up and away we go. It goes fine for about 5 miles then starts stalling again. It is the worst on steep grades and doesn't do it much on the downhill. Twice more I have to pull over. The first time I check the filter and it doesn't look clogged. But, I see it has air bubbles swirling all around the rear frame rail filter. Now I'm thinking vapor lock. I had put some heat reflective wrap on the fuel lines farther up by the TC but nothing in the back as it seemed far enough from the exhaust that it wouldn't make that much of a difference. I get some cold water from the cooler and throw it on the gas lines and let it sit a while. Back on the road and we finally make it to the summit and down the other side. It runs fine on the downhill and straightaways unless I try and push the speeds up beyond 65 mph, then it starts stuttering again. I'm thinking fuel starvation from either plugged lines, or the gas boiling.

To make a long story short, I swap filters about 4 more times on the trip, barely make it home, and was ****ting eggrolls the entire time. So, I plan on doing a couple of things. First, I am going to insulate the entire fuel line along the frame rail from the exhaust heat. Second, I will remove my tank, pull the fuel takeup setup and check it out, and then have the tank thoroughly cleaned. I'm wondering though if it is going to be one of these two things? What say you? Something else entirely? I'm thinking a combo of vapor lock and something plugging the tank intake? Something else?

 

[dyeager535]

With a return line, you shouldn't be having vapor lock issues.

It does happen, people do get it, but from what I've seen on automotive boards, (and in person) its more commonly something else.

On a carb, bubbles aren't going to matter. It feeds from a well, the bubbles should work themselves out. The pump can't pump air though, with enough air in the fuel, it won't pump obviously.

The PO may have thought he had vapor lock issues as well, but what hasn't been changed since he owned it?

Perhaps you've got a leaky connection somewhere, that's where your bubbles are coming from, and you are actually starving for fuel because the pump can't pull with a leak.

 

[darenofears]

i have heard that too many filters can also cause problems

 

[dyeager535]

As low restriction as most filters are, I doubt that's likely either for a typical application. Even the small plastic clear filters are what, 4 times the diameter of the fuel line. (or more) If a clear filter is a restriction, you *should* be able to see that in how the fuel attempts to flow through it. If the filter is mounted horizontally gravity should keep the fuel towards the bottom of the filter.

I wouldn't run more filters than necessary though, it will add some sort of restriction, not to mention more connections in the fuel system, never a good thing. You've already got the sock filter in the tank, if you want to run one external, fine, but I'd take the one in the carb out if so. It will bypass if there is too much restriction, but more than one filter is excessive if you ask me.

Between the pump and the carb is where you want the filters.

You would be able to measure the pressure after the pump though for a real indication, and is what I'd do if you suspect it's something "downstream" of the carb.

Sticky float, crud in the float bowl, etc, can all cause problems described, as can overfueling, but overfueling (again, stuck float, or bad needle/seat) is usually pretty evident because it's spewing out of the carb somewhere, and on shutdown, you can smell it. Not to mention reading the plugs.

 

[Desert Rat]

I'm beginning to think that perhaps the tank intake is plugged up to the point where it isn't pulling enough gas. But, where would the air come from? I'll find out I guess when I drop the tank and pull the sender. If that is clear though, then I'm not sure where I'll go from there. The PO had this funky setup with the manual pump, but another electric pump on the frame rail with some kind of weird setup with a line running back to the tank. I pulled all that and now it is in stock setup. I replaced the Q-jet filter and it has been checked by a shop who said the carb was clean and working well. That was a couple of months ago and perhaps something has gotten into the carb after all. You would think though that with two G12 Fram filters in line, and the new filter in the Q-jet that the gas would be pretty clean by the time it gets in the carb.

 

[dyeager535]

If the pump is trying to suck fuel through a restriction, it wouldn't be surprising for air to be pulled in through connections, especially on a low pressure carb system where the connections are typically just a clamp of some type, with a flare on the tube. Depending on if it was done "right" or not, there might be fuel line conenctions without a flare on them, such as where filters or pumps were spliced into the existing hard line. That's going to make it even easier to get air in there.

You say stock setup, does that mean it's all back to solid lines (where original) with no more connections than stock, and all connections are done exactly as stock? Just another thing to look at.

 

[4X4HIGH]

Do yourself a big favor and remove the filter from the carb and throw it as far as you can. Install 1 good filter in the system and be done with it. Make sure that the rubber splice in the hard line half way down the frame rail isn't cracked and sucking air. If you need any help just PM me and i'm sure i could come help you out with it. If i remember correctly you aren't too far from me.

 

[Desert Rat]

By stock setup, I mean I removed that electrical pump. The location where it is at though has new hoses clamped in. They are clamped in good and I wouldn't think that would be an issue. After all, you have hoses from the front hard lines to the pump. Hoses from the pump to the carb, and hoses from the tank to the hard lines. I replaced all the hoses with brand new ones so none should be cracked. Originally I was using some cheap VW fuel filters just because I was going through so many due to the crap in the tank. I started using larger Fram G12 filters which have the proper size tube with flair. Now, why would I chuck the Q-jet filter? If it is clean, then what would it hurt? I will say this, when I was swapping in a new one, I did start to cross thread the filter intake piece. I had to put it back in a couple of times to get it to thread right. But, there was a slight gas leak so I pulled it, put some teflon tape on it, and screwed it back in. No more gas leak but I wonder if it could be sucking air? If I am seeing bubbles way back on the frame rail filter, then I wouldn't think this would be an issue, but I'll check it further.

 

[4X4HIGH]

The first good reason to get rid of the filter in the carb is because of what happened to you while you were trying to install the fitting. Too many times in and out and new carb will be needed. Second reason is that those filters clog fairly easy and are junk.

 

[Desert Rat]

Hmmm, I suppose I could yank it, then I have to deal with the thread issue again though. I wondered what I would do if I couldn't get the fitting threaded back in properly. Seems a silly design to have to toss the whole carb.

 

[4X4HIGH]

There is actually a repair fitting that you can buy that will make new threads if the threads are screwed up. You have one shot at that before you throw the carb. With 20 years professionally dealing with car/truck stuff i know what i'm talking about and like i said, willing to help you if you need help.

 

[diesel4me]

yep--toss the carb filter..

The GM original "in carb" filters are a joke--as Dyegear said,when they clog,the spring behind them allow dirty fuel to bypass the filter!!-so why even have it??--plus ruining the threads in the carb sucks....also,I've had issues with a vehicle that had additional in-line filters installed on the suction side of the system..

I had patched the gas tank,and got all but about 1/2 pint of water out of the tank(I filled it with water so I could braze up some rust pinholes)..so I added a big in-line filter,to hopefully trap the water..the car started bucking at high speeds,and would sometimes bog out and nearly stall out!..not fun at all on the freeway--I feel your pain as you were driving in your post--been there,done that!..

I figured it was the water causing the stalling and bucking--but it persisted for several weeks and after many full tanks of gas with dry gas added..in frustration I removed all but the one inline filter between the pump and carb..it never acted up again!..I think I remember reading something in a WIX filter catolog about using filters on the "suction" side years ago..I'll see if I can find the catolog,and post back about it..they didn't reccomend it..

One truck my brother had (66 GMC Suburban) drove us nuts--it would die on a long upgrade on a highway every day,nearly getting us killed--we figured the fuel pump was bad,since it looked as old as the truck--but replacing it only got us up the hill ONCE without doing its bog and die routine--on the second day,it did it again!..we pulled out the tank,and ripped the sock filter out--it looked to be gunked up,so we got a new one--no difference!

Then we decided to inspect the metal fuel lines for rust ,kinks,flattened spots,etc..no damage!..then we saw a rubber hose joining 2 sections of the metal line not far from the right rear wheel--it looked like an inchworm,only 8" long or so--why GM decided to use 2 peices of line and not one solid one is a mystery--we thought someone probably put it there,but looking under my 79 C10,I saw the same setup!..we took that peice off,and the inside was like chewing gum!--the outside looked perfect,even had no cracks,and the lettering was still readable!..after we changed that hose,it ran like a bear,better than it ever had..

I'd opt for a "spin on" water separator filter that has a base you can bolt to the firewall--it'll stop anything from getting in the carb,and they have a drain cock to empty any accumulated water..(goes on the pressure side of pump,between the pump and carb...one guy I know runs the gas from junk cars at the junkyard with it,and he swears by it--hasn't had any problems,just changes the filter every couple of months,and drains any water out every few days..can't beat FREE gas!..

 

[ntsqd]

snippage.....
I'd opt for a "spin on" water separator filter that has a base you can bolt to the firewall--it'll stop anything from getting in the carb,and they have a drain cock to empty any accumulated water..(goes on the pressure side of pump,between the pump and carb...one guy I know runs the gas from junk cars at the junkyard with it,and he swears by it--hasn't had any problems,just changes the filter every couple of months,and drains any water out every few days..can't beat FREE gas!..

FWIW I have about 10k trouble free miles on one of these:

from West Marine. It is mounted to the passenger frame rail of my '79 Sub just above the rear axle, on the suction side of the stock mechanical pump. I used "Push-loc" or "Barb-tite" fittings on the filter base. It is a water seperating filter, but the elements do not have a drain. I also have one on my Dune Buggy. It's been on there over 12 years with the same element.

 

[Desert Rat]

I like those ideas. If I pull the tank and don't find anything wrong with the intake, I'm definitely going that route. Even if I do find gunk in the tank, I think I'll try that anyway. Should I look to put the gas filter after the pump then or before?

 

[4X4HIGH]

I did a little research for you this afternoon. I discovered that the fuel hose that is inside your tank cannot be regular fuel hose, it must be submersible fuel hose otherwise the outside of regular fuel hose will start to break down and cause a rubber mess ijn the tank. You told me about a curved rubber hose in the tank so i would be checking that out first. This submersible fuel hose is costly at about $20.00 ft.

 

[Desert Rat]

Crap, well I will see what it looks like when I pull it. When I did the install, it looked like regular fuel line but since I bought the aftermarket tank from a company that just makes tanks, you would assume that it is the right one. You can see it in this pic:

 

[4X4HIGH]

If that is all that is on the end of that pick-up it looks pretty shady to me. I'll bet it isn't the submersible hose. Furthermore, there should be a sock on the end of the pick-up.

 

[dyeager535]

With that setup you could very easily be sucking air in through the tank if it's below that rubber hose joint.

I'd *seriously* consider having a piece welded to the pickup so that it hits very near the bottom of the tank, and would consider adapting the bottom of a GM sender to that as well, so you can run the "stock" filter in there that keeps water and crud from reaching the engine.

 

[ntsqd]

As to the rubber hose in the tank, somehow I missed that. Had I known of it I'd have pointed there first. Look up "Purosil" hose. It is silicone rubber hose and will work submerged. A better plan is to use a Swage-Lok fitting and eliminate the hose altogether. Use only metal tube and the fitting inside the tank.

 

[diesel4me]

ALCOHOL= hose failure!

The new 10% Ethanol gas is eating up boat gas tanks and old rubber fuel hoses at an alarming rate here--many boats have burned and a lot more car fires since it changed over..