L-jet running rich Options

[Ctrout]

I know that everyone here has D-jet but does anyone know of any L-jet gurus anywhere? My car has smelled like it runs rich since I got it. While doing some exhaust work this morning, it was confirmed by the black soot everywhere. I thought I read somewhere that these cars ran rich from the showroom floor. I have backed the idle adjust all the way out with no apparent change in the richness of the mixture. It did change the RPM to a point though. I read in one thread something about coming in from working on the car and smelling like I had been standing next to a diesel campfire. That's me!

[scotty914]

well i know a fair amount about the ljet drove one daily for more than 18 months.

the screw for the mixture is on the air flow meter, you turn it out to lean it out. the idle screw is just that. do not i repeat DO NOT open the cover.

i would bet someone richened it up due to a vac leak, i would turn the screw out 1/4 turn then take it for a sprited 15 min drive then check the plugs, dont use the exhaust soot to tell ya, either the plugs or a o2 sensor. you might even to be sure take it to a shop that has a o2 meter and set it. but if useing the plugs do not turn the screw more than a 1/4 at a time

now i can still tell you what traces on the double relay do what, because that was my biggest headache

[Brando]

If you've ever adjusted the mixture/richness on a 944 you'd see that they are in fact the same design Air Flow Meter. (Not the exact same unit).

Removing the cover and moving the wiper while it is running you can see exactly how it adjusts the fuel mixture. It will increase or decrease the idle speed a small amount, you will hear knocking or pinging or hear it smooth out.

Do not be afraid of opening the cover. Do take caution, because if you unspring the wiper from the mechanism (you'll see the two-points holding a large sprocket in place) you will have essentialy ruined the unit. The IDEAL way to adjust this is to adjust the wiper with the spring retainers in place, see where it runs best, then remove the spring retainer that holds the sprocket, and move it to the next gears over either direction.

You stated that adjusting the idle mixture screw does nothing. The screw you are turing is an air bypass. Unscrew it, it let's more air pass at idle. To properly adjust the mixture you must adjust the wiper/resistor.

If you have qualms about doing this yourself, take the car to a local Porsche mechanic and ask them to help adjust your mixture. It may cost a few pennies but they should be able to do it within a few moments. If their adjustments have no effect they can at least give you a run-down on what else may be causing it to run too rich. They may or may not have the equipment to test your emissions and let you know if it is running too rich or lean.

Just to ease some fears, the adjustment with the wiper and circuit board I mentioned is the same adjustment made on all 944s to adjust for smog purposes.

Addendum:

Do make sure you have no vacuum leaks. Usually the little elbow point between the AFM, plenum and Auxilary Air Valve go bad (intake leak), the oil cap is on and sealed well (another big intake leak possibility) and that your vacuum advance and retard lines are good (other possibles). If you have an intake leak you will never be able to get the mixture correct (as scott said).

[scotty914]

brando i will disagree with you on this dont open the cover there is a screw to adjust the mixture, and a screw for idle. the idle screw is on the throttle body. the mixture screw is on the air flow meter is is what you want to adjust, if you change the spring rate you will mess up the mixture rate at different throttle settings.

if you tighten the spring you will lean out the motor at higher rpms but not really affect the idle, if you loosen the spring you will run righer at high rpms but idle will be screwy.

I REPEAT DONT NOT OPEN THE COVER THE SETTING IN THERE IS SET FOR YOU MOTOR ACROSS ALL RPMS TO AIRFLOW, THE SCREW ADJUSTS THE MIXTURE ... sorry about that i just want to express you can affect the way the mixture runs across the whole range in a bad way the screw is there for mixture adjustment.

disclaimer if you have the ability to get on a dyno with o2 reading you can open the meter but then you need to see what the mixture is at all rpms, the spring is set to the amount of air the motor draws at all rpms, if you change that the brain sees the wrong amount of air at different rpms, since the brain is set for specific airflow at specific rpms, you can mess that up because the air flow is not linear.

[Brando]

I will disagree with us both, Scott, if it makes you feel better.

TAKE IT TO A THIRD PARTY PORSCHE SPECIALIST. THEY WILL KNOW FOR CERTAIN WHAT THE CRAP THEY ARE DOING.

[scotty914]

sorry brando but porsche put the screw there for a reason. i just wanted to make a point, that there are 2 screws one for idle one for mixture. and changing the flap setting can not be predicted with out a dyno.

[scotty914]

okay here is the page from the l jet trouble shooting manual that explains the adjustment proceedure

[Brando]

Yes Scott, I understand. The point I was trying to make is that if neither adjustment screws are having any effect, the spring tension for his AFS may be set too loose, thus giving too much fuel at all ranges of the flapper being open (throttle open). The two screws are for small incremental changes. The spring tension adjustment is for major and minor incremental changes. Both options are the same adjustments used for all cars with an L-Jet system for obtaining proper mixture for emissions reasons.

[scotty914]

i would say if he is rich on every cylinder i would do things like check the cold start injector for leakage first, as well as check every injector. it may be something very simple and messing with a setting that is not designed to be changed is not the way to go.

and ctrout this is not an attack on you: but Brando obviously he is not too sure about what to adjust and inside the airflow meter is too easy to mess up for a beginer to mess with. its better to go back to basics like injector leaking vac leaks ( lean running ) and other sensor stuff before going that far

[Reiche]

Did you check fuel pressure?

Unlike D-jet, the fuel pressure on L-jet varies with vacuum. If the regulator is stuck or the vacuum isn't hooked up, it will run rich at idle.

[Ctrout]

Thanks for all the replies. I'll go through the basics as you have suggested. Reiche, what vacuum are you refering to being hooked up? To the regulator? I have gone through all of the lines on the engine several times in the past 9 months and have found nothing out of place. Also, I wasn't aware that there were two adjustment screws. I have only used the one that was obvious to me when I poked around looking for it. I'll give another look around. It seems to be something simple because the car runs very well it just smells bad.

[scotty914]

okay the two screws are as follows:

idle screw is on the throttle body its about 1/2 inch in dia with a nice wide slot for a screw driver. what i recommend it that you pull the screw all the way out and use some carb cleaner to blast out the hole. it is not uncommon for oil to clog the passageway. what this screw does is allows air around the throttle plate.

the mixture screw in on the airflow meter on the top near the rear side right next to the air filter part. what it does is allows air to bypass the flapper in the meter. the l jet "knows" how much air in being pulled in by how far the flapper moves, but it is setup to run rich if the mixture screw is closed all the way. so basicly by letting some air by the flapper you can lean it out do to the brain not "seeing" that air. the screw is basicly a controlled vacumn leak, if you back it out ti will lean out the motor, if you screw it in you richen the motor. but the best thing you can to is check the plugs to find out which way you need to go.

if the car is running really rich you can check the cold start injector for leaks ( spraying when the motor is running but not cranking ) . it is located on the front of the plenum, and it is a pia to get out. the way it works is if it is cold out ( below 32 IIRC ) when you crank the motor it squirts gas in to the plenum to rich all the cylinders to help it start. it only squirts when the motor is very cold and the starter is cranking.

hope this helps

[Reiche]

QUOTE (Ctrout @ Mar 26 2005, 09:27 PM)

what vacuum are you refering to being hooked up?  To the regulator?  I have gone through all of the lines on the engine several times in the past 9 months and have found nothing out of place.

Yes, the vacuum to the fule pressure regulator. It should be drawing vacuum from the plenum. I think the decel valve is hooked to the same vac line.

Even if it's hooked up, it may not be working properly. Check the pressure at idle and at higher rpm. I don't remember exactly, but it should be about 28 psi at idle and around 35 psi otherwise? If it is only running rich at idle, it might be the FPR.

I don't know how common it is for the FPR to be bad, but if idle air bypass adjustments aren't having any effect, it could be this.

Or as Scott pointed out, it could be the cold start injector. If it's the cold start injector, it will run rich all the time.

[ClayPerrine]

I agree with the statement .... DO NOT OPEN THE AIR FLOW METER!


I have worked on L-Jet cars for 20 years. The spring tension is calibrated to the displacement and Volumetric Effeciency of the motor. Opening it and adjusting the tenision can cause your car to go to full fuel enrichment way too soon or way too late. Both can be VERY bad for the motor. And the only way to get them back to proper calibration is with a special calibration tool and meter.


I have seen most of the replacement AFM units for the L-Jet 914s are the wrong unit. They substitute or supercede the part number for the 914 with the one for the Beetle with L-Jet. It's not calibrated right, and it won't run right. Because the Beetle is a 1800 type-1 and the 914 is a 1800 type 4 does not make them interchangable. The Beetle AFM on a 914 will run, and it will run rich because the spring tension for the Beetle AFM is lighter than the 914.



The design of the L-jet system will cause it to go lean if there are any vacuum leaks, so that isn't it. Check all the injectors for leaks, especially the cold start injectior. Then check the fuel pressure with an accurate gauge. If the pressure is too high from a restriction in the return line or a bad regulator, it will run rich. Also, if the pressure regulator blows the internal diaphram, it will feed raw gas into the intake via the vacuum line. Pull the line from the regulator and see if there is gas inside.

[rhodyguy]

all the yelling aside, this is a great L-jet thread. if the seal on base of the oil fill tower was shot, could this fool you after you had replaced the oil cap seal? just wondering.

k

[scotty914]

QUOTE (rhodyguy @ Mar 27 2005, 08:43 AM)

all the yelling aside, this is a great L-jet thread. if the seal on base of the oil fill tower was shot, could this fool you after you had replaced the oil cap seal? just wondering. k

that would drive it lean, not rich. the oil cap and filler are vac leaks. on my 1.8 the tower was rtved down, so i disconnected the line to the intake, it ran much better.

[rhodyguy]

but it could contribute to a lean condition? the seal is a commonly overlooked item. messy when it goet bad. i've seen them sealed with rtv, which rarely works. (IMG:http://www.914world.com/bbs2/html/emoticons/icon8.gif)

k

[Cap'n Krusty]

A rich condition, beyond the scope of the idle mixture adjustment is ALMOST ALWAYS a bad airbox. Vacuum leaks may make it fail to run, but they won't make it rich. "Fallse air" going past the valve cover gaskets, the rectangular gasket on the filler box, the o-rings in the cap, all will prevent the car from starting, as the AFM isn't reading the air. A messed with airbox is usually a bad airbox. A reman airbox is usually a bad airbox someone has attempted to fix. Generally, what goes wrong with them, a sticking flap, doesn't get properly addressed in the reman process. Belly up to the bar and buy a new one! AFTER you've tested everything else, that is. In general, L-jet/Digijet FPRs go bad a lot, although the ones on 914s are an exception. Check for a good, even voltage supply to the ECU, check ALL THE GROUNDS, the valves, the dwell and timing, and the filters. The double relay won't affect the mixture, only the ability to run at all.

Hmm. Digijet ........... Anyone here ever given any thought to running Wasserboxer Dijijet on a 914? Seems to me it would be a drop-in ...................... The Cap'n

[rhodyguy]

the CIS-E from a jetta, golf, etc? i think ed morrow ran it on the turbo car. i have 246k on my 85' jetta with CIS-E. it's been flawless, as in never have had any problem at all. complete systems are a dime a dozen in the wrecking yards. if it was an easy swap i'd do it on the 75' in a heart beat.

k

[Mark Henry]

QUOTE (ClayPerrine @ Mar 27 2005, 12:30 PM)

Because the Beetle is a 1800 type-1 and the 914 is a 1800 type 4 does not make them interchangable. .

All late and FI beetles are 1600's (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)