free hit
Fuel starvation - Fuel System/Carbs - The Lotus Forums - Official Lotus Community Partner Jump to content


Fuel starvation


Recommended Posts

I had the car die on me while idling in the driveway.

Traced the fault to the fuel pump not working.

Replaced the pump with the Bosch fuel pump alternative.

I fitted a new fuel filter at the same time.

The car had full fuel tanks at the time.

At about half tank the car left me stranded next to the highway. :blink: Approx. 230 km later.

I checked the fuel pressure at the regulator and found it very low.

I then traced the problem to a blocked banjo at the bottom of the left tank and dirt in the tank. (The fuel pump is fed from here.)

I "washed" the tank as well as I could in place and fitted a strainer on the banjo bolt so that any dirt left would not enter the system.

The car currently does the following:

It idles for as long as I want without fault. (10 Min no problem)

Drive it and it starts missing not 3 blocks from home.

The pump pumps 3 Bar pressure if you restrict the outlet.

The regulator is clean and set to 0.35 bar pressure. (0.4-0.45 psi)

The fuel line to the regulator,and the return, is clean.

When I switch the ignition on I can hear the pump running continiously.

New plugs and leads are fitted.

The pumps volume seems ok, but this must be where the problem lies. I don't think it is pumping enough fuel for higher rpm.

I spoke to a mechanic at the Bosch claim centre. He recons the pump will make a noise or stop completely if it got dirt in it, although he will check the pump for me free of charge. (Amazing. You do still get customer service!)

I will do that tomorrow.

He did however suggest I check the wiring and fuel pump relay. A bad current supply could also affect the pumps efficiency.

Where is the fuel pump relay?

Does anybody have any other ideas or had similar symtoms?



Ps. My girlfriend won't let me come near her because I have been smelling of fuel for 5 days. :rolleyes: Can't even scrub the smell out. It is in my skin. Need to get this sorted out pronto!

Link to comment
Share on other sites

Upgrade today to remove Google ads and support TLF.
  • Replies 17
  • Created
  • Last Reply

Top Posters In This Topic

I had something verry similar on mine which turned out to be something with the tanks.

I never did get to the verry bottom of it but the tanks would flow fuel when i had them out but for what ever reason the would not when they were in the car.

Bear in mind that at idle if the carbs are full it will run for a fair while anyway!

I would suggest to see if you have fuel getting to certain areas either start aftert the pump and work forward or start at the carbs and work back.

If the pump is running and pumping fuel then it should run and i would be tempted to look at carbs. if you follow it through you should hopefully find where the fuel is stopping.

Have you tried running it at high revs while on the drive to see if it eventually runs out of fue?

Sorry thats a bit random but is really just my thought process

Link to comment
Share on other sites









Link to comment
Share on other sites

Has the inertia switch gone off?

Do you have a fuel cut-off solenoid and, if so, is it working? It may not but leaking enough to top up the float chambers so you can idle but when you drive the car they empty quicker than they fill.

Try dissconnecting a fuel line from a carburetter and put the end into a jar. Get someone to turn on the ignition and see if you are getting fuel. If not, do the same as near to the pump as you can but be careful. I don't know if fuel can drain from the tank through the pump when it is off. I think you may smell of petrol for a while yet. Good job you don't smoke.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE


Link to comment
Share on other sites

Check the float chambers, float valves and any integral filters, all the carb. jets - could be the muck got that far......

Scientists investigate that which already is; Engineers create that which has never been." - Albert Einstein

Link to comment
Share on other sites

My S1 did the same when I got it from the PO.

Two things were happening.


The tanks were loaded with rust and clogged up the banjo and lines and filters. He had a nice but overly complex arrangement of braded lines and special filters.

Run a test. Get a small gas can. Fill with high test gas. Run a new fuel hose from the can to the pump. Try running the car. If it runs ok, it the lines, filter or whatever behind the pump which is tge problem. If it still stumbles at high revs, read on. It could be crap in the cards or your coil.

Ultimately I pulled the supply tank (US car-right side), cut it open and sand blasted yje inside. The banjo leading to the fuel filter and pump was almost completly clogged. Welded it back, spot welded some tiny holes that I found, then put her back.

I replaced all the special lines and fittings in the process because I found the path for fuel was so long and complex that the fuel pump could not pull enough pressue. It just kept running. Of course, i replaced it first before this discovery.

So, a nice new line from the tank to the primary filter, then to a small glass one so I can observe the flow. Then to my new solid state pump then straight to anothet glass filter mated to the pressure regulator, then onto the carbs. All regular fuel lines with hose clamps. With the system nice and tight, fuel delivery is no issue.

As in did NOT pull the left tank, I watched for a while ans still saw some debris. So, assuming it was from the left tank, I added a small filter under the car right where the left tank feeds the balance pipe. I also replaced the crossover pipe with larger diameter fuel line. I change that filter evey few months when I start to see debris in the glass filters.


Assuming you checked things like, debris in the carbs (jets, correct float operation, balanced operation) then the high rev stumble may not be fuel. If the coil breaks down you get that symptom. Great idle and bad stumble or loss of power above 2500rpm. $36 and a nex Epoxy coil later, she ran great.


Simplify fuel line arrangemet

Ensure couplings are tight so you get no air leaks.

For old tanks, use filters. I like the glass ones to augment the regular filter and allow me to monitor the fuel quality.

Consider a solid state fuel pump.

Do a flow check (into a bottle at the carb connection)

Ensure the carbs are clean.

Get a new coil


77 S1 Esprit

Dom Giangrasso

1977 S1 Esprit - Lagoon Blue

Link to comment
Share on other sites

Thank you for all the advice.

Taking the fuel pump to Bosch today.

There was a lot of crap in the pump that I washed out this morning. (It was still pumping strong despite that)

Hope Wayne's prediction is wrong. :( (Don't want to buy another pump because of my own stupidity)

Hopefully the pump checks out fine.

I will fit another filter between the tank and the pump to stop crap going into the pump and chase it from there.

DomG thanks for the ideas, think I will end up following the same route.

Feeling much more positive today. :)

Might even get rid of the fuel smell, and get lucky with the girlfriend by the weekend. :)

Will keep you updated with my progress. (on the car ;-))

Thanks again


Link to comment
Share on other sites

A few years ago I had exactly the same symptoms with an Excel. Only got to the bottom of it when I tried to fill up one day and the petrol cap wouldnt undo. After "heavy" persuasion it came off suddenly with a wooshing noise. Turned out the petrol tank was in vacuum. When I investigated there was an air line venting out through the rear valance that allowed air to flow into the top of the filler so that as fuel was run out of the tank, the internal pressure stayed at atmosphere. This air line had become trapped, kinked and therefore blocked. As I drove the car and it used petrol the tanks gradually developed a vacuum which after a time the fuel pump couldn't overcome. At this point it would die. Half an hour later it would restart (as the pressure in the tank gradually equalized). No idea if this helps but maybe worth checking?


Mat Kutub

1979 S2




Link to comment
Share on other sites


Hope everybody had a great Christmas.

Fuel pump turned out to be fine. Was blocked up with dirt which washed out.

I fitted a fuel filter before the pump too.

Now this filter keeps blocking up after about 50 km.

Blow it out (towards the inlet) and a lot of dirty fuel comes out.

Do another 50 km and the same thing happens.

Joke is I had the tanks cleaned and coated (inside and out) when I did the motor. (In the last 6 months)

Is it this coating busy coming off?

I can't get hold of the company that did it to discuss this. They are closed for this week.

Can I get the tanks out without taking the motor out again?

If I end up having to do that I will have stainless tanks manufactured.

I am going to run the car from home to work and back (30 km) and clean the filter daily and see if I can't get the dirt out that way.

Any other ideas?



Link to comment
Share on other sites

When I was going to have one of my S1's tanks coated I was advised against it. A few folk commented on debris from a poorly done job causing havoc.

I opted to cut the tank open, sand blast and repair it then weld it together and swear never to let the tanks sit for any time unless they are full AND are topped with some Stabul to stop the fuel from breaking down.


77 S1 Esprit (Federal)

Dom Giangrasso

1977 S1 Esprit - Lagoon Blue

Link to comment
Share on other sites

Thanks for the advise.

I have decided to take them out and have new tanks made from stainless steel.

Looks like a terrible job. :blink:

So the Lotus is standing in the garage again until I can find the time to do this. Then again: What's new? Starting to get very frustrated. The car has been off the road more often than on. Hope I can get it to a point where I can enjoy her reliably. Would hate to see her go, but so far she has been more trouble than joy.

(If it wasn't for the forum and enthusiasm for the cars displayed here, I would have gotten rid of her long ago)

On a more positive note: HAPPY NEW YEAR!

Wishing everybody a prosperous 2006.

Greetings from sunny South Africa


Link to comment
Share on other sites

Steady on, Duncan. i would think long and hard before selling the car as I think it will be very hard to replace should you later regret the decision. You will probably have to fix the problem before you can sell it for a sensible amount so you may as well as get the benefit of your hard work and drive the thing for a while.

Good luck.

S4 Elan, Elan +2S, Federal-spec, World Championship Edition S2 Esprit #42, S1 Elise, Excel SE


Link to comment
Share on other sites

NOOO Duncan :D

Thought all your issues where sorted.... Look on the bright side, at least you got your car back and new stuff is causing problems, not what you've just had fixed.

If you're going to replace the tanks with stainless, let me know. Got a few connections in the trade and can get you sorted for cost of materials only. (And I'll conveniently have a template to get another set made up for myself :blink: )

Still no sodding car for me. Tried to pick it up on Xmas eve - No clutch. Master cylinder's stuffed and has pissed fluid all over the front trunk. Lets see what this week brings...

Let me know about the tanks - Mark

Link to comment
Share on other sites

Guest teigan

hold out for polyethylene tanks. they'll be lighter and outlast the car. only disadvantage is you won't find an exact fit, so the fuel capacity may be a few litres less.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Create New...

Important Information

We use cookies to enhance your browsing experience, serve personalized ads or content, and analyze our traffic. By clicking " I Accept ", you consent to our use of cookies. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.