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Glutton For Punishment
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Discussion Starter · #1 ·
I may have diagnosed my running issue. My air bypass valve seems to be flowing air at all times. I hooked up vacuum to the small port, and applied voltage to the pins. The unit releases the vacuum when powered but doesn't open the valve. The valve is leaking air and not sealing completely when not powered and no vacuum applied. Also leaks air when vacuum is applied but no power.

Bosch p/n 0 280 142 020

The question is, does the bypass valve seal with no vacuum applied, no power applied? When there is vacuum and power applied the valve opens?

Thanks
 

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Wingless Wonder
1988 Esprit Turbo
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6,369 Posts
Can you troubleshoot by blocking the hose(s) to the valve?

Sorry, I don't know the answer...maybe Autocross7 does (he cleaned his).

If the valve is as gummy as the other components on your car, you may as well take it off and have a look.
 

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Glutton For Punishment
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251 Posts
Discussion Starter · #3 ·
Just to clarify, this is the valve that opens to bypass the air metering plate on decel, aka "econ" light unit. It plugs into the side of the airbox and routes down to below the metering plate.

I took it off, and it is very clean. Bench tested it and it doesn't act as I would expect.

I am going to block it off and tune the car that way until I can get a replacement.
 

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Wingless Wonder
1988 Esprit Turbo
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6,369 Posts
Stop! I thought you were referring to the Aux Air Valve (Item 45, parts list 45.05A)

You mean Item 69 on 45.05A? Fuel Bypass Valve.

Yes by all means block off any flow at the hose going to the MCU (mixture control unit) to see if the engine runs better. (Just as a diagnostic)


Be advised that with that hose blocked, spirited driving will result in flames shooting out the exhaust on decel! No Joke...

That circuit can be troublesome, I've spent a few hours work on mine...let me know if your ECON light works (in the right bank of idiot lights, in the binnacle). It should come on at Key On, Engine Off, and at decel over 1500 RPM. It's a dim indicator (Lotus used a 24 volt bulb in a 12V circuit) so evaluate it at night...

:popcorn:
 

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Unfortunately, the fuel bypass valve is a part originally made from 'unobtainium' and thus it can no longer be sourced as far as I know...

However, I offer the following... pull it off the car. Unhook everything and hold the part. Now, it should be difficult to get air through. Just blow through it... either direction.

This is assuming that the issue is as noted and it is not closing properly. Then you will know it is leaking... If you cannot blow through it it may be okay.

In a resting state the internal spring holds the diaphragm closed. The vacuum serves to pull the diaphragm open. The vacuum is constant provided the motor is running. The opening occurs as the electrical pulse from the relay powered by the TPS "tells" the vacuum solenoid internal to the part to open... and thus vacuum is applied and the diaphragm opens. The relay contacts and the solenoid closes and the diaphragm spring again shuts off the air passage.

If you cannot easily blow air through the by pass valve then your issues could easily be a stuck relay causing the solenoid internal to the part to be in an open state. Just swap the fuel by pass control relay with another...

If you have not eliminated them, the hose that runs from the bottom of the mixture control unit base housing up to the oil separator from the crank case is worth a look.

Also, the hose that runs back to the charcoal canister may be leaking...

However, if you can easily blow air through the fuel by pass valve whilst holding it in your hand, it may have a bad spring. Now, laugh if you want to... but in this case it is worth using your finger to 'bounce' the diaphragm spring. Carefully and slowly push the diaphragm in and let it out. This can have the effect of re-seating the spring and you may be good to go for a while longer. Bounce the diaphragm and then try to blow through the valve...


Cameron
 

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When my fuel bypass circuit was not working the culprit was the speed sensing relay that operates the fuel bypass valve. It is actually adjustable to where it will turn on the ECON light and open this valve. There is an adjusting pot inside the cover on the board. Mine however would adjust no where near where it should of turned on the ECON light. I replaced it with one from JAE, I was surprised it was only like $69. I imagined $300 plus.

When the system works the car does not backfire nearly as bad on deceleration I found.
 

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Wingless Wonder
1988 Esprit Turbo
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6,369 Posts
Just swap the fuel by pass control relay with another...
Whoops, You can't do that.



The FBC relay (left-most one in the top row of adjacent relays, gray plastic case) is a unique dual-contact relay and cannot be swapped with any of the others in the car.

I tried to get a replacement locally (even at a old-time Bosch repair shop) and failed. The Usual Lotus Parts Suspects can get the factory part, however.

A082M6182F

And yes they DO fail (but the ECON light won't illuminate, which is why I asked). But, you can also have continuity problems because of loose connections in the relay SOCKET.
 

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Glutton For Punishment
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251 Posts
Discussion Starter · #8 ·
My ECON light works intermittently. The valve though is definitely toast. Vacuum wont open the diaphram when 12v is applied, and it is bypassing air all the time. I poked at it and it just doesn't seal all the way closed. Bypassing lots of air.

I blocked off the line and the car certainly idles better, and I was able to lean out the mixture a bit. I have pinched off other vacuum lines and listened for engine changes, and haven't found any other leaks. Also sprayed all possible vacuum leak points with carb clean and haven't heard a rev.

How do you eliminate the oil seperator, and is that a good idea? Why does it run a line to the MCU? Mine is still intact and I checked that out.

All my vacuum lines are new, and went through the whole charcoal canister system with new lines. I am curious if the canister is connected correctly though, as my vacuum diagram and canister look different and there are no marks on the canister. Pinching off the vacuum to the canister did change the engine sound ever so slightly.

I guess I should still hunt vacuum leaks, as the frequency valve is still operating way out of spec. Car runs better with the new oxygen sensor disconnected than with it connected. However, with the O2 sensor disconnected i am under the impression the frequency valve should operate at 50% duty cycle. Readings still show it operating at 10% duty cycle in open loop. I have even measured it at the valve itself. Hot or cold doesn't matter, 10% duty cycle, and that is on two different multimeters and on the dwell meter.
 

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Wingless Wonder
1988 Esprit Turbo
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6,369 Posts
I just sent an inquiry in your behalf to see if some friends have that unobtanium fuel bypass valve.


But, if you have blocked it off that's not your idle problem.


++++++++++++++++++


The oil separator functions like a PCV valve, that is, it vents the sump into the intake (at the MCU) so that all the 'boogers' don't go into the atmosphere of the planet. :p

Mark (Amanda) had an issue with the AMOUNT of vacuum, he installed a restrictor (roll pin) in the vac line that comes from the #4 cylinder IIRC. When I replaced my own vacuum lines I looked for a restrictor in that vacuum circuit and didn't find one. :shrug: My car runs really great.


+++++++++++++

It's possible that the fuel delivery ports in the MCU itself are gummy. You might want to PM jtrealty, he has experience taking those things apart and could advise if this is a worthwhile endeavor for your problem.
 

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Glutton For Punishment
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Discussion Starter · #10 ·
Be advised that with that hose blocked, spirited driving will result in flames shooting out the exhaust on decel! No Joke...

:popcorn:
Maybe I'll leave it blocked off! Sounds exciting! Connect a spark plug at the tailpipe and re-route the decel wiring to fire a coil connected to that sparkplug. BIG FIREBALLS!

Wait, getting side tracked...
 

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Whoops, You can't do that.



The FBC relay (left-most one in the top row of adjacent relays, gray plastic case) is a unique dual-contact relay and cannot be swapped with any of the others in the car.

I tried to get a replacement locally (even at a old-time Bosch repair shop) and failed. The Usual Lotus Parts Suspects can get the factory part, however.

A082M6182F

And yes they DO fail (but the ECON light won't illuminate, which is why I asked). But, you can also have continuity problems because of loose connections in the relay SOCKET.

Yep, I was not clear. I meant swap it out with another... one off the shelf. a new one. I just keep these things in a drawer in the garage...

However, O'Riley's and/or Advanced always has them here. I have had to take the old one in and pull the book myself, but i have never not been able to get one out of the back. Just do not expect the kid behind the counter to be able to find it for you right off... they run me about $25 or so. Comes from an AC Compressor...

BWD R33021
http://shop.advanceautoparts.com/wc...ge//597/large/3996301_bwd_r3021_alt1_larg.jpg

NAPA and GP Sorenson also produce this relay, but I do not have those numbers right off...
 

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I removed the hose running up from the bottom of the mixture control unit base housing and blocked the openings at the base and on the bottom of the air oil separator. Serevs no function other than to bring oil vapor back into the engine via the combustion chamber.

I also put a hose on the pipe inside the air box, drilled a hole in the bottom of the air box, installed a grommet, and then ran that hose down and out the back of the car. Could have routed differently, but without putting the car up in the air and looking you cannot tell anything was done. The oil vapor goes out the back and not into my engine...

Benefits? Can't really speak to how much oil vapor might mess with combustion, but my intake is not all oily when I remove it now :)
 

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Wingless Wonder
1988 Esprit Turbo
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6,369 Posts
O'Riley's and/or Advanced always has them here. I have had to take the old one in and pull the book myself, but i have never not been able to get one out of the back. Just do not expect the kid behind the counter to be able to find it for you right off... they run me about $25 or so. Comes from an AC Compressor...

BWD R33021
http://shop.advanceautoparts.com/wc...ge//597/large/3996301_bwd_r3021_alt1_larg.jpg

That's nice to know,

and BTW: RD Enterprises (one of the ULPS) charged $28. So, SUPPORT OUR VENDORS!

I too, keep one on hand just to play with.
 

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Usually get my stuff form R and D or JAE... great guys all the way around. I actually hit up O'Riley's for this relay at one point at Jeff Robinson's suggestion as shipping was going to be more than the part. Jeff is so straight up he will talk you out of buying stuff! LOL :bow:
 

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Actually Carbuff, I must have never posted a follow-up to that post with the restrictor in the ignition advance vacuum line. But I thought I did.

I learned that after buying the car, removing all the old hard lines and installed new flexible vacuum lines at the same time, is when this problem started, however with me just buying the car I didnt really know its initial problems yet back then. It would miss about the same time the car would warm up. It was driving me INSANE, I then found a post on some forum where someone said their Esprit CIS would start to miss due to a missing restrictor in the vacuum advance line once it switched over to vacuum advance after warm up. AH, that explains it, I threw the restrictor out with the old line when I replaced it. So I put one in the new line and the problem went away for a few days, however it came right back in a few days (the weather must have been cooler here or something LOL). I finally one day happened to have my timing light in the trunk when the car started missing, I put it on every cylinder as soon as it happened and turns out, off and on the cylinders wouldnt make consistant spark. Because the plugs were overheating (I knew this because I had already replaced every other ignition component), I then bought those fancy E3 plugs (that a guy at Advance auto talked me into), they would overheat also. I then switched from BPR7ES NGK that was in it originally, to BPR8ES, and its ran like a champ since. The next coldest running plug solved my issue. I heard BPR7ES is the plug for the car, dont know why mine cant use it.

It actually turned out to be an education on spark plugs, and how a hotter or colder plug will dissapate heat to the head differently and run at its own designed temperature, I first thought "WHAT the cars not overheating!" But I learned alot anyways.
 

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Glutton For Punishment
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Discussion Starter · #16 ·
I bought one off ebay for a Saab 900 turbo. Apparently it is a slightly different size but can be adapted to work. I'll let y'all know how it goes. Car is now running great. I dialed the mixture in by ear in open loop, then reconnected the o2 sensor. Pops on decel, as expected, so I am looking forward to getting this valve. Thanks for everyone's input on this.
 
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