Fuel Starvation

[kmcrofton]

Standard 1st Post for a long time lurker...

My '72 Series III Petrol is having issues with pumping fuel to the engine. It will run great for about 15 minutes (20 miles) and then when I try to start it again after leaving it sitting for a few minutes it will not start. The in-line fuel filter is nearly dry, and the fuel pump does not pump enough fuel to the engine to keep the motor running from what I can tell looking at the process.

When I start it cold and it runs, the fuel filter looks like it barely has fuel in it, only about 1/4 inch deep in the filter. From what I've read, this should be nearly full of fuel.

I've replaced the fuel pump with a Proline one, and no change really. My next step is going to be to give the tank a good rinse. There was not a screen on the end of the fuel line into the tank, but I don't think this would be restricting fuel. My other thought is that the tank is not vented properly and it is becoming a vacuum in there to restrict the fuel flow. When I've taken off the gas cap there is no change to the fuel flow.

Any help is appreciated. I have a new fuel line from the pump to the tank on backorder, but will check to see if this line is fully clean tonight.

Kevin

[Tim Smith]

You could have a collapse in the fuel line. Probably a good time to replace it while you are rinsing the tank.

[jp-]

Also it might not be a bad idea to take out the fill tube and blow it out with compressed air, as well as the fuel line itself.

[Leslie]

Also it might not be a bad idea to take out the fill tube and blow it out with compressed air, as well as the fuel line itself.


Triple-check the pick-up tube! Years of varnish, rust flakes, etc., can clog it up and keep decent flow from passing on....

[kmcrofton]

I'll give that a try tomorrow. No access to an air hose until the weekend, but I've heard people clean it our with a gun cleaning brush, so I'll try that.

[BellaCoola]

I have a late model s3 and thought I too was not getting enough fuel to the card. Looking at the inline filter I could barely see any fuel running through? Thought like yourself that there must have been a plug up somewhere.

Went through the entire fuel system, disconnecting and blowing through to ensure no blockage...this all in the bush btw.

Turns out according to my "mechanic mentor" that this is very common and not a cause for alarm...He said that this is flow rate is normal. I just got back from a 2100km run in Northern BC and had no problems...my problem turned out to be a loose ignition wire. Car would start...then stall...start then stall....Your problem is obviously different.

What type of carb are you running?

Under load I've heard of people putting in an electric fuel pump, that would guarantee flow.

I would first check all your lines as previously mentioned, and check the pickup from the tank itself.

Good Luck

www.freewebs.com/83s3109

[kmcrofton]

I'm running a Weber carb. I took the line apart from the tank to the pump and blew air through it, and it seemed clear, but I"m still going to clean it this weekend.

When I try to start the car after it has run for about 20 minutes, it will start and then cut out after the fuel in the carb is burned.

I've only had the car for 3 months, and the PO said he did not see this issue. I am in Las Vegas, so the 100+ degree hear can't be helping.

[daveb]

you said you blew out the line. did you blow out the pickup tube too?

does your fuel line run over top of the valve cover? That's a vapor lock special there, run it in front the thermostat housing clipped to one of the 3 bolts there.

also on the carb under the fuel inlet there is a big 5/8" or so brass nut. undo that and you'll find a filter, make sure it is clean.

last but not least, pull the line off the carb and have a friend crank the engine while you hold the end of the line in a glass jar. you should see regular strong spurts of gas. if you do and the carb jets aren't blocked and the carb float is ok, then everything is fine and you should be looking at the ignition system.



I'm running a Weber carb. I took the line apart from the tank to the pump and blew air through it, and it seemed clear, but I"m still going to clean it this weekend.

When I try to start the car after it has run for about 20 minutes, it will start and then cut out after the fuel in the carb is burned.

I've only had the car for 3 months, and the PO said he did not see this issue. I am in Las Vegas, so the 100+ degree hear can't be helping.

[KSMTAW]

I had a similar problem. Turned out to be dirt/ rust/ flakes that would get sucked up into the screen in the fuel pump bowl. When it was shut off, the flakes/ rust/ dirt would settle to the bottom of the fuel bowl making it an intermitent problem.

Check your fuel bowl. You will spill a little gas, but it is good to do once in a while if you have an older tank. When the glass bowl is out, you can pull the screen down off of the fuel pump. In other words, don't just clean the glass bowl, but make sure the screen is not obstructed.

Good Luck.
Todd

[kmcrofton]

Update.... Blew out the pickup tube as well. The fuel line was routed over the top of the valve cover. I reouted the line in a gap above the water pump.

As far as testing the flow of fuel to the carb in a bottle, I have done this in the past when it won't start, and the fuel flow is very minimal, maybe indicating blockage? When the engine is cold and I check the flow it is regular spurts of fuel.

Thanks for the help so far, still thinking it is a blockage issue in the tank from old rust and particles.

Kevin

[jp-]

Could be vapor lock.

Definitely check the glass bowl filter screen as Todd suggests.

[Tim Smith]

Could be vapor lock.
2x. Routing the fuel line away from the hot engine block does help avoid vapor lock.

Don't ask how I know this.

[kmcrofton]

I just changed out the fuel pump last weekend and it came with a new glass bowl. Vapor lock sounds like it could be the issue after some reading. Over at LRO there are a couple good posts on it from a 109 in Dubai.

Has anyone that lives in a hot climate insulated their fuel lines? I would think this would help. Any suggestions on a brand of tubing insulation?

[jp-]

I have insulated a metal fuel line before by taking a piece of flex hose, slitting it and sliding it over the metal tube. Not the prettiest thing in the world, but it worked.

[greenmeanie]

Living in Phoenix and being too lazy to reroute the fuel lines as Daveb describes I ocasionally vapour lock. This usually only happens on a hot day (105°F+) with a high speed run on the freeway and then stopping giving it time to heat soak. I then make it a few hundred meters down the road and she dies.

I usually carry a gallon jug of water in the truck as part of the emergency kit anyway and pouring this over the carb and fuel line usually has me running within a minute or two.

I am running a 'lecky fuel pump which helps but it just doesn't happen with normal day to day driving.

Cheers
Gregor

[Tim Smith]

I'd be too afraid of cracking the exhaust header to run water over a hot motor. Guess I shouldn't be...

[greenmeanie]

It's pretty much the same as hitting a deep puddle so I don't worry.

[gudjeon]

I was frustrated with the mechanical system and diagnosed it down to fuel starvation. A new faulty replacement pump only added to this. I opted for an electrical pump and used a recirculating fuel system. Added one extra line to the system but no vapour lock and no more difficult hot start up. It's not pretty, but it works. Late 80's Chrysler spec fuel filter and fabrication of return fitting onto tank. (note) the air intake elbow is fabricated because is needs low clearance for the 2.25L in my ser1.

http://i35.photobucket.com/albums/d187/gudjeon/fuelpump1.jpg

This is what I used the old pump for once I got to the bottom of the problem.

http://i35.photobucket.com/albums/d187/gudjeon/roverfeb08004.jpg

[Leslie]

Have you verified that your pump is up-to-snuff? Checked its rate of flow into a bucket?

If your fuel pump checks out, and your lines are clean, along w/ the pickup tube, and you're sure you don't have crud in the tank getting pulled over to block off the flow, then in that case, vapor lock is the suspect, IMO.... FWIW.....

[daveb]

*total* long shot but is the sediment bowl perhaps a bit on the loose side of things and when she warms up it allows air in?

oh and did this happen before changing the fuel pump or did it start after?

and gudjeon there were a few LRO's a number of years ago that had some sediment bowl shot glasses engraved with LR club logos. Wish I had one...



I just changed out the fuel pump last weekend and it came with a new glass bowl. Vapor lock sounds like it could be the issue after some reading. Over at LRO there are a couple good posts on it from a 109 in Dubai.

Has anyone that lives in a hot climate insulated their fuel lines? I would think this would help. Any suggestions on a brand of tubing insulation?

[jp-]

Gudjeon,

If you use a low psi generic electric pump (3 to 7 psi) there is no need at all for a complex return system, as the carb needle valve can easily handle the pressure. Fuel return systems are generally used only in high power carb applications where the carb may need a great deal more fuel at high rpm, or in EFI applications.

[gudjeon]

Howdy jp,

That is what I first thought when I went to the electric pump and I hooked it up inline. I purchased a low pressure pump from NAPA that was set up for carburator systems. It turns out that it flooded my engine silly when it was shut off hot. The fuel pump did not release pressure once shut off. This paired with the elastic nature of the fuel line, enabled an unwanted amount of fuel to feed the carb when shut off hot. I went to a return system and no more problems. Vapour lock disappeared altogether and now my fuel is constantly filtered as a bonus.

[jp-]

Either the pump has just a little too much pressure, the needle valve has problems, or the float may not be working as well as it should, because I have had no such trouble on vehicles that I have put electric pumps on.

The fuel being filtered is nice though.

EDIT: It's also possible that the fuel pump has an anti-drainback mechanism on shutoff.

[gudjeon]

I suspect the drain back was the issue in my case. I installed those little universal pumps in the past and never had an issue either. The main thing is it works:thumb-up: