free hit
counters
Power loss at larger throttle opening - Fuel System/Carbs - The Lotus Forums #ForTheOwners Jump to content


Power loss at larger throttle opening


Recommended Posts

I bought my Lotus Esprit Turbo 1984, US specification a few months ago. Some troubles started a few weeks ago. I couldn't solve it, so I'm looking for help on this forum.

The car runs steadily while the engine is running at low speeds and moderate throttle.

1. When I add throttle sharply, the engine loses power and starts bouncing like a kangaroo.

2. When I add the throttle slowly, the engine slowly increases the speed, but after a while I feel some misfirings / loos of power / judder and then the engine stops working for a while. Eventually it recovers a bit, but starts to jerk.

When I release the accelerator pedal for a while, the engine recovers and is able to run at low power and low speed again. I can drive the car in this regime. Anyway, I can use the engine power and enjoy LOTUS driving!

I have asked the specialist for ignition check , but he did not find any trouble there. It looks that it is fuel system trouble. Does anybody have such experience? Any idea what I have to check first?

One more note. I didn't know that it is not recommend to use E10 gasoline with ethanol content and my problems could be caused by that gasoline. It is not easy to find gasoline without ethanol in our region. There is strict law and nobody can sell gasoline without ethanol. Therefore there is minimum of 5% ethanol in premium gasoline in Slovakia. If the trouble is because of the ethanol in the gasoline, then it will not be easy to drive the car.

 

Link to comment
Share on other sites


Upgrade today to remove Google ads and support TLF.
  • Gold FFM

Check whether the airbox to turbo hose is collapsing under load.

British Fart to Florida, Nude to New York, Dunce to Denmark, Numpty to Newfoundland.  And Shitfaced Silly Sod to Sweden.

Link to comment
Share on other sites

Also check fuel pressure under dynamic conditions.   Very simple with a T-Piece between fuel regulator and either carb inlet and a pressure gauge visible from bulkhead vindow.    Pressure should be circa 4.5 at idle.   You then need to add any turbo boost pressure to the base 4.5 psi.   E.G.  to run at 7.5psi of boost pressure, you need 12psi of fuel pressure (4.5 + 7.5).   So its entirely possible a failing pump, or possibly blocked system can seem fine at idle, but fail in higher rev ranges.

NB - If it is running out of fuel at higher revs, I'd generally expect to see the plugs running dry/weak.   If it were an ignition problem, i'd probably expect the plugs to be wet/rich

  • Like 2
Link to comment
Share on other sites

John W - it is with original Dellorto carbs and automatic choke.

Atwell - when I bought it, was running fine. The problem starts later. Therefore I asked about gasoline E10 with high content of ethanol. I used the car approx. one time per two weeks.

I also thought of the fuel pressure regulator. I will check the pressure during engine operation.

One question for sure. The small hose on the top of the regulator is not connected anywhere and I did not find a place to connect it. However, the end of the hose appears to have been plugged in somewhere in the past. I have information that someone has converted a manual choke to an automatic one in the past. Could this be the reason? According to the information I found, the hose should not be connected anywhere.

I will check the cable connectors, because I had trouble with engine speed also and the trouble had been done by bad contact on connector.

FPR.jpg

Link to comment
Share on other sites

42 minutes ago, TRLOTUS said:

John W - it is with original Dellorto carbs and automatic choke.

The carbs never had an auto choke, there should be a choke pull under the dash, the choke cable can be seen in your photo attaching behind the rear banjo.

This diagram shows the hose attaching to the rear carb banjo bur that doesn't look like this '89 model which has two metal pipes (51 & 59 in the diagram) where you have one & a rubber hose.

090902075011_esp3.jpg

Edited by jonwat

Cheers,

John W

http://jonwatkins.co.uk

Link to comment
Share on other sites

John, I have the automatic choke on my Jaguar 3.8S 1966 with two SU carbs also. And I have another one classic car (1949, my new project waiting for a place in the workshop, but i drived it already) with carb, where I don't have the ability to manually control the choke.

I do not know how is the automatic choke done on my LOTUS, but the "choke cable" is fixed and dismonted from the dash. The automatic choke is really working. I never had any trouble with engine start! It doesn't matter if the engine is cold or hot. If the engine is cold, the engine starts, slowly increases the speed and keeps it somewhere between 1000 and 2000. When the engine is hot enough, the speed comes back to standard idle speed. This is really working with fixed choke in closed position.

If anybody know such solution, kindly let me know how it is done and how it operates or where can I find relevant information.

Link to comment
Share on other sites

2 hours ago, TRLOTUS said:

One question for sure. The small hose on the top of the regulator is not connected anywhere and I did not find a place to connect it. However, the end of the hose appears to have been plugged in somewhere in the past. I have information that someone has converted a manual choke to an automatic one in the past. Could this be the reason? According to the information I found, the hose should not be connected anywhere.

 

This is a US spec car with an air pump at the back. The vacuum solenoid seems to operate a flap by the looks of it. Is that solenoid connected and operating? Unsure if that’s is related to your issues. I’d look to the fuel delivery system first, fuel pump, pressure regulator and then carbs. 

526389CA-CC5C-49F0-816D-94301CE56BAF.jpeg

  • Like 1

Ad initium

Link to comment
Share on other sites

It’s easy to check what that flap does. Start the engine, control the throttle from the engine bay, rev it and observe the function of that vacuum solenoid and connected flap. 

Ad initium

Link to comment
Share on other sites

On second look, fully agree with Steve. No connection to the plenum. Stuffs up your pressure regulator. There are typically 2 small connection points on the plenum,. One is right next to the pressure regulator (from below) and the other is at the front of the plenum (cambelt side).

  • Like 1

Ad initium

Link to comment
Share on other sites

Thanks guys!

Fuel pump operation had been my first check. Looks correct.

I did the fuel pressure check today. The regulator had been set for 3.2 psi at engine out of operation, 3.5 psi at idle and the pressure increased in approx. to boost pressure increase. Than I changed the pressure regulator setting. I recognized that somebody changed the setting in the past and original position had been at 4 psi. Therefore I set 4 psi and tried to drive the car. I recognized that the engine operation is  much more better, but the problem persists. Next step had been regulator change to 4.5 psi. The engine operation had been better again, but the problem persists. But I recognized that the low speed engine operation is a little unstable now.

From my point of view somebody has had trouble with engine operation in the past. He did not find the correct failure and tried to repair the engine by decreasing the fuel pressure. Maybe the engine operation had been close to correct. But the real failre persists. Probably there is not one trouble only. My idea is to replace fuel pressure regulator, to do deep carbs check and electric system check.

Link to comment
Share on other sites

19 hours ago, TRLOTUS said:

Thanks guys!

Fuel pump operation had been my first check. Looks correct.

I did the fuel pressure check today. The regulator had been set for 3.2 psi at engine out of operation, 3.5 psi at idle and the pressure increased in approx. to boost pressure increase. Than I changed the pressure regulator setting. I recognized that somebody changed the setting in the past and original position had been at 4 psi. Therefore I set 4 psi and tried to drive the car. I recognized that the engine operation is  much more better, but the problem persists. Next step had been regulator change to 4.5 psi. The engine operation had been better again, but the problem persists. But I recognized that the low speed engine operation is a little unstable now.

From my point of view somebody has had trouble with engine operation in the past. He did not find the correct failure and tried to repair the engine by decreasing the fuel pressure. Maybe the engine operation had been close to correct. But the real failre persists. Probably there is not one trouble only. My idea is to replace fuel pressure regulator, to do deep carbs check and electric system check.

with the fuel pressure regulator boost pressure sensor disconnected fuel  pressure will increase with boost due to the increased back pressure but it will not stay the required amount ABOVE the boost pressure leading to problems.  if this is wrong there may be other major things wrong with the pressurized carb set up that cant easily be seen from your photos.  if you dont understand how pressurised carbs with blow through turbo works then find someone who does, as lots of little issues of not properly sealing the carbs and all their connections can give you a problem.

 

cheers

Rohan

Link to comment
Share on other sites

I understand how the regulator adjustment works to hold the fuel pressure above the carb pressure and that the regulator will "try" to hold a constant fuel discharge pressure relative to atmospheric pressure if the sensor hose is disconnected.  

As the throttle opening increases and the boost increases the pressure in the carb bowl increases.  This means less fuel will be delivered as the back pressure on the float valve increases and the float has to drop to deliver the required fuel. The lower fuel level will lean out the engine leading to loss of power.

The fuel regulator is a simple proportional controller and its delivery pressure will increase with increasing fuel back pressure due to increasing carb pressure if the reference pressure line is disconnected

There are multiple influences fighting each other  here but the end result is a lower fuel level in the carbs and the engine running lean and loosing power.  Connect the sensor tube to the plenum and assuming everything else is correct it will work. Unfortunately the odds of everything else being correct are not that great

 

cheers

Rohan

 

  • Like 1
Link to comment
Share on other sites

  • 2 weeks later...

Welcome to TLF @TRLOTUS. :welcome:

Have you been able to correct the engine issues yet?

You should duck over to the Introductions area and say hi in there as well. :) 

Any questions or issues with using the forums, feel free to ask one of us mods. We're here to help. :) 

All we know is that when they stop making this, we will be properly, properly sad.Jeremy Clarkson on the Esprit.

Opinions are like armpits. Everyone has them, some just stink more than others.

For forum issues, please contact one of us Moderators.

Link to comment
Share on other sites

Hi Michael,

I've been busy lately and haven't had room to do a thorough inspection. So far, I know that it will be necessary to thoroughly find out what has been neglected and changed on the engine. My goal is to restore the engine to its original condition.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...