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Discussion Starter #1
L tronic is baffling me. In an effort to get my GTV6 running well at all speeds, I decided to mess with the air/fuel adjustment on the AFM only to find out that it was turned all the way in (I believe this to be the richest setting?) So, naturally I backed it out a few turns only to find that the idle speed is no longer adjustable from the idle adjustment nut? Does anyone want to take a stab at what is going on? By backing the screw out a few turns it has also changed my throttle response so that there is a delay in fueling. I don't mind messing with it as it is the only way I am going to learn how all of this works together but it would be nice if someone could shed some insight because I am puzzled. Thanks!
 

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That screw was to fine tune idle emissions at the factory, which is why they came sealed. If I were you, I'd just screw it all the way in (since it just lets in unmetered air), and then figure out your running problems. Since you're in CA, you may ultimately have to pay someone to properly calibrate it in order to pass emissions.
 

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gmjohns…sounds like we're traveling similar roads. I am also fiddling with L-Jet for the first time trying to get my 85 to pass smog. I assume you know about the tuning guide below. Within it, it mentions that sometimes the rubber o-ring that essentially acts like a sphincter valve for air entering the system at the idle adjustment nuts wears out and becomes ineffective for making idle adjustments. Were you able to change the idle speed there before you started playing the air/fuel mix? Might be a good double-check for ensuring the o-ring is in decent shape.

L-jetronic Fuel Injection Technical Troubleshooting Article
 

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Discussion Starter #4
yep, checked that today. In response, I have screwed the idle air/fuel screw all the way down as I found it. I can now successfully adjust the idle at the nut but it just doesn't seem right? Anyway, I will keep screwing with it and report back if I resolve/understand the relationship between the 2. The farther out I back the screw (lean) the more pause I have in throttle over 4000rpm's. It lurches at about 3/4 pedal whereas with the screw closed, the throttle response is pretty linear through rpm's. It's the car I love to hate these days
 

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Is there any evidence the cover on the AFM has been removed? The factory glue would have been neat & even. If a PO removed it the glue line is likely to be less neat.

It was common 'back in the day' to pry that cover off and reduce the AFM's spring tension in a misguided attempt to enrichen the FI. It never really helped and only usually messed up the calibration.

If you find that the cover has benn removed you next hope is to find that the PO marked the original position of the spring. Otherwise you may need to do a lot of trial & error to find a better position for the spring. You can drive the car with the cover off while you try different settings.

Finally, are you sure the O2 sensor is functioning? If it has failed the car will run fine but the computer will not have the ability to use the O2 sensor's inputs to adjust the running mixture and will remain in it's default (slightly rich) fuel map.
 

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I'm going through the exact same thing. I've been messing with the mixture for months, after a Porsche guy told me I was "waaaaay too frickin' rich" for an L-Jet system. I screwed the AFM adjuster all the way down (It was about 12 turns out) and found the car ran better at idle and cruising. Better fuel economy. Less soot. All that jazz. Improvement.

Except now sometimes when I get on the throttle I get a stumble if it's at relatively low RPM, as though it's not able to get enough gas. It doesn't happen if I downshift before slamming the music pedal. So I figured I was running too lean I backed the screw out about 6 turns. The idle jumped up to about 1500 and when I tried to bring it back down (I have a digital tach from Harbor Freight) it became uneven and wobbly.

Back to Square 1.

I've never been able to adjust the system using Greg Gordon's technique of measuring impedance at the O2 sensor either. I'm basically playing by ear, and it ain't working to well.
 

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But Mad North-Northwest
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I've never been able to adjust the system using Greg Gordon's technique of measuring impedance at the O2 sensor either.
You measure voltage output of the O2 sensor, not impedance (or resistance). If you're doing the latter that's your problem. Sensor needs to be plugged in to the L-Jet harness when following the procedure.

To properly adjust the bypass screw on the AFM, the Alfa procedure is to measure CO percentage upstream of the cat converter with the O2 sensor disconnected. Generally you shouldn't ever mess with that screw, though if the PO screwed it up all bets are off.

If you've already farked up the setting, Gregg's instructions should work to get it close. With the sensor plugged in to the L-Jet, voltage should oscillate between 0.2-0.9V at hot idle. With the sensor unplugged, I believe it should be just slightly on the rich side (greater than 0.45V, and right around where the voltage swings from <0.45V to >0.45V as you adjust the screw).
 

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Voltage is what I meant. Been messing with ohms for so long I just forgot the procedure. Maybe it's my cheap HF multimeter, but I just consistently get a big fat nuthin when I try to measure anything from the O2 sensor.

My AFM came borked, so I spent a good year trying to balance out the mixture. I had a local import guy look at it and say it was fine, that I must've stumbled into correct mix, but I was never convinced.
 

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The Idle CO adjustment is a very fine orifice. I doubt that even backed-out all the way you'd get more than a couple hundred RPM's or so. If you can't adjust the Idle RPM, using the idle adjustment fitting at the plenum, then your O-ring is deformed, hardened, or ineffective. When these wear-out there is usually no problem in setting RPM high, the problem is squeezing it down to get your 900-950 RPM idle.

@Chairman - The Idle CO screw is "lefty-loosey, righty-tighty" e.g. Clockwise to close the valve (richen) and counter-clockwise to open (let more air in).

These cars are old and many time the issue is as Greg's tuning guide says unmetered air getting in. Lots of places where this can happen including at the Injector O-rings. Unfortunately, there is no ODBII to tell you which sensors have gone bad (and in some case, the continuity of the wiring from the sensor to the ECU). You have to troubleshoot yourself. You just need to know what you're doing. And if you don't, it helps to get a shop manual (not to place under your knees so you pants don't get dirty, for reading). This is not black magic. It does help to have another set of hands/eyes handy to do this though. Also, O2 sensors don't last forever.

Now these motors are pretty tough and can run fairly well even with various issues. If replacing the Idle O-ring doesn't resolve the idle issue (which I suspect it may fix the RPM value but may still have rough running or too rich). Two things I'd recommend. 1) Replace the O2 sensor 2) Take it to an emissions shop and have a UV smoke detection performed to find any vacuum leaks.
 

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The Idle CO adjustment is a very fine orifice. I doubt that even backed-out all the way you'd get more than a couple hundred RPM's or so.
Well, I wouldn't say very fine. The external orifice is about .25"x.5", and I've flow tested it with water with it full open and there's no internal restriction in the channel (i.e. water comes out as fast as it goes in), so it's easily large enough to overwhelm the tiny o-ring adjustment at the idle-air adjuster. For each half turn open the stream of water increases by roughly 1/16th" in diameter. Full open the stream is over 1/4" wide. That's a lot of unmetered air. It seems to reach max flow about 4-5 turns. Mine came about 3 turns open and always had a very uneven cold idle, really struggled, but was just ok waned up. I changed mine to 1.25 turns open, and now the idle is always smooth, plus the idle air adjuster now has an effect.
 

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Voltage is what I meant. Been messing with ohms for so long I just forgot the procedure. Maybe it's my cheap HF multimeter, but I just consistently get a big fat nuthin when I try to measure anything from the O2 sensor.
If you can remove the sensor it is easy to see if it is working. Hold it in a vise with a voltmeter connected to the output wire and the vise. Now put a propane flame on the end of the sensor and it should start reading up to 1 volt, depending on where you play the flame.
 

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Discussion Starter #12
Just a follow up to the original post and for anyone else struggling with this type of issue. I have been chasing my fueling problems for a while and I should have prefaced my initial post with: I have a 3.0 liter transplant running with the early type distributor and ignition. The car has run lean since I purchased from P.O about 3 years ago. I have played with every possible combination of AFM spring tension/idle adjustment possible and I was able to get the mix a tad rich with a fairly smooth idle but, I didn't do it alone. An air/fuel meter is a must (and it should be a good one) to have any chance of understanding the relationship of spring tension/air adjustment. Even though I got everything working well, at high RPM I was still getting predetonation at higher rpms and I have always suspected the advance in the distributor as it worked well to a point. I bought a brand new early type of distributor here on the BB and installed last week and it has solved the problem. It seems the spring tension for the mechanical advance in the old distributor was tired and, not being very handy, I decided not to F with the old one although the v-6 performance manual goes into great detail on how to modify/change the advance in the older mechanical advance distributor. What I am not clear about is wether or not I need to change the ECU to a 3.0 or anything else so as not to leave performance on the table. I have read about Pandoras box and I am not convinced there is anything to gain there? Any insight or experience would be appreciated as I see the goal and feel I'm really close to scoring. Thanks
 

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Can't help you with the computer, but if you have access to the distributor and ignition system from the 3.0 I'd go with that: it's going to work better.

If you're going to mix and match V6 engines and distributors, you need to be careful with the vacuum advance. The 3.0 would've come with a vacuum advance distributor pulling ported vacuum. The earlier distributor (if it has a vacuum module) is likely a vacuum retard that was designed for plenum vacuum. If you hook that up to the vacuum port on the throttle body of the 3.0, Bad Things will probably happen with regards to your advance curve.
 

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If you're going to mix and match V6 engines and distributors, you need to be careful with the vacuum advance. The 3.0 would've come with a vacuum advance distributor pulling ported vacuum. The earlier distributor (if it has a vacuum module) is likely a vacuum retard that was designed for plenum vacuum. If you hook that up to the vacuum port on the throttle body of the 3.0, Bad Things will probably happen with regards to your advance curve.
I mistakenly mixed an early GTV6 distributor with an ignition advance computer from a late GTV6 and it would hardly run.

There is a difference between the 2.5 and 3.0 CPU's. My 3L motor ran a little better with the 3.0. A friend ran Pandora's box on a race car many years ago and it did not make a big improvement.
 

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Discussion Starter #15
So, That makes sense. Do you think the vacuum advance/retard on the older distributor could have caused a problem? (Never thought of that) Should I cap that to see or is that a bad thing? Honestly, I can probably live with it as is. i'm not that keen on changing the harness/ECU etc. as I am in california and I think it would make it harder to smog. It's already hard but changing the vacuum ports is cake
Can't help you with the computer, but if you have access to the distributor and ignition system from the 3.0 I'd go with that: it's going to work better.

If you're going to mix and match V6 engines and distributors, you need to be careful with the vacuum advance. The 3.0 would've come with a vacuum advance distributor pulling ported vacuum. The earlier distributor (if it has a vacuum module) is likely a vacuum retard that was designed for plenum vacuum. If you hook that up to the vacuum port on the throttle body of the 3.0, Bad Things will probably happen with regards to your advance curve.
 

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Discussion Starter #16
What are the smog test implications with that exchange? I've heard it could get ugly?
Can't help you with the computer, but if you have access to the distributor and ignition system from the 3.0 I'd go with that: it's going to work better.

If you're going to mix and match V6 engines and distributors, you need to be careful with the vacuum advance. The 3.0 would've come with a vacuum advance distributor pulling ported vacuum. The earlier distributor (if it has a vacuum module) is likely a vacuum retard that was designed for plenum vacuum. If you hook that up to the vacuum port on the throttle body of the 3.0, Bad Things will probably happen with regards to your advance curve.
 

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Discussion Starter #17
Is that going to be a smog check problem? I worry about this state....in so many ways
Can't help you with the computer, but if you have access to the distributor and ignition system from the 3.0 I'd go with that: it's going to work better.

If you're going to mix and match V6 engines and distributors, you need to be careful with the vacuum advance. The 3.0 would've come with a vacuum advance distributor pulling ported vacuum. The earlier distributor (if it has a vacuum module) is likely a vacuum retard that was designed for plenum vacuum. If you hook that up to the vacuum port on the throttle body of the 3.0, Bad Things will probably happen with regards to your advance curve.
 

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But Mad North-Northwest
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With any sort of mods to the intake system it's going to be tricky to pass the visual inspection. They also check static timing when smogging so that needs to be set to spec, at least when you have it tested. So I'm not sure what to tell you as I've never tried to get an engine swap past smog.

With your current setup (and ignoring smog) what to do depends what you have. If you're mating a distributor with vacuum retard to a 3.0, I think your best bet is to disconnect the vacuum line, plug the port on the throttle body, and then static time to whatever your spec is. You won't get vacuum advance which'll hurt economy and emissions at cruise, but the car should run okay.
 
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