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ECU knob adjustment

Does anyone know how I can set the mixture by ear or feel or whatever, until I can get it into a shop to be adjusted correctly? I think I remember somthing that was posted but my search comes up negative. I know I am running rich on idle and seem to bog down a bit upon acceleration. Maybe my TPS is not adjusted correctly Hmmmmm... any suggestions. Oh, 74 2.0 FI. Thanks to all.
Old 08-29-2003, 11:54 AM
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You can do it by ear. Just mark where you start and turn it counterclockwise. If that makes it worse go back to original and turn clockwise. Make sure it is warmed up and at standard running temperature when you start adjusting. You may try adjusting the idle screw also. Take it for test spins after adjustments to check performance.
Old 08-29-2003, 02:31 PM
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The ECU knob ONLY affects idle mixture...which is controlled by the ECU when 2 of the contacts in the TPS are engaged. Off idle, the engine sensors take over.

Has the MPS been adjusted? Ever? My guess is that it is off.

Teh A/F mix cannot be adjusted by ear reliably like a carbed car. It needs a sniffer to know exactly what to adjust and how.

Seen Brad Anders D-Jet site?

http://members.rennlist.com/pbanders/DJetParts.htm
Old 08-29-2003, 04:29 PM
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If you look at the adjustment knob from directly above it you should be able to see a (very) small pointer protruding from it. There is a ring around the knob that should be stationary. It has a small space or indentation which represents the middle or where the factory setting is. (at least that is how it was explained to me!) Try puting the pointer to that space and see how it idles. As Bowlsby said, it is only for idle. You will need to adjust the idle mixture and get it to 8 or 9K.
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Old 08-29-2003, 10:37 PM
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Regarding the factory mark that Bruce mentions, it isn't always present. ECU's that have been rebuilt may lack the mark, or it may have no correlation to the "factory" setting.

What the mark signifies is the adjustment point where the idle mixture setting is solely determined by the engine speed mixture correction circuit in the ECU. On early ECU's, there was no knob, and the idle mixture was unadjustable and set by the engine speed mixture correction circuit. I would guess that over time the factory found that there was enough variation in volumetric efficiency to warrant some degree of adjustment to get the best idle performance.

Clockwise is richer, counter-clockwise is leaner. I've found that when everything is right on a stock motor, that when the idle mixture is set to the factory specification, the knob is within a few clicks of the mark. Note that as Jeff says, setting the idle mixture "by ear" (i.e. smoothest or highest idle speed at a fixed air bleed screw adjustment) does not usually result in the mixture being set to the factory specification. You need to have the car FULLY warmed up (drive it fairly hard for at least 30 minutes in warm conditions) and use a shop quality CO meter to set it properly.

I've seen several cars with idle problems, almost always, they were set to very rich mixtures, as much as 8%! Do it the right way and you'll get much better idle performance. Make certain before you start that the valves are properly adjusted (makes a big difference on idle performance), the ignition is perfect (plug gap, timing, dwell, and vacuum retard operation), and that the FI system is in good working order (right parts for your engine, all paramters in spec - see my web page, MPS not leaking and adjusted to factory specs).
Old 08-30-2003, 06:54 AM
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Knob with pointer at 'factory setting'. (Damn...close-ups really show the grim)



I wish my car would idle there, but it sure won't. I'm about 6-8 clicks rich. Need to get it to a shop with the right equipment and know-how.
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Old 08-30-2003, 08:32 AM
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Quote:
Originally posted by Bruce Allert
You will need to adjust the idle mixture and get it to 8 or 9K.
bruce
After reading Brads post I realized I mentioned the Idle RPM's at the thousands rateinstead of the hundreds!
Thanks, Brad, for coming in on this. I got mine running pretty good after going thru your page. I even traced all the leads from the ECU to their components & measured the ohms to be sure they were all complete (unbroken) wires. The ring around the adjustment knob of the ECU was loose on mine and I had to find the correct position of it & tighten it.
I must say, this car has been the greatest learning experience I've had. Never knew so much about cars until I got the teener
bruce
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Old 08-30-2003, 08:33 AM
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So with all this you should be able to get it to run ok to get it to the shop eh?

Good shot Rusty. For a 25+year old component, it's bound to look a bit ......used
Old 08-30-2003, 10:58 AM
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Thanks for the replies. I set the knob to various positions to see which one was best off idle to part load and it was pretty close to what the factory one was. I know I will have to bring it to a shop to get it properly adjusted but for now it is interesting tinkering. My idle now surges on start-up and if I dont feather it for awile she will die, does that indicate a vacume leak or do I just have everything out of whack. Also, does anyone know of a shop in the Seattle area that I could bring it to to get things dialed in? The DJET article by pbanders is what has taken my car from a setting for 10 years piece of junk to my daily driver and I thank you so much.
Old 09-02-2003, 08:34 AM
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Glad my pages were helpful. Surging during warm-up usually indicates a lean mixture. If you're happy with your idle when the car is fully warmed-up, you can try adding a SMALL amount of series resistance (50 to 100 ohms max, 1/4 W rated resistor) to the head temperature sensor. This will enrichen the mixture ONLY during warm-up and will not affect the fully warmed-up mixture. If you want to experiment with what value to add, try using a 100 ohm linear potentiometer instead of the resistor. Once you get the setting that works best, measure the resistance of the potentiometer and substitute it with a fixed resistor.
Old 09-02-2003, 11:12 AM
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Do not leave the potentiometer in there permanently! After a while (a few months in at least one case), they get "flakey". Sometimes they'll be the resistance you've dialed in, sometimes they'll go open-circuit, every once in a while they'll even short directly across. (Guess how I know that???)

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Old 09-02-2003, 01:45 PM
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I am in Seattle and can take a look at it.

Geoff
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Old 09-02-2003, 03:30 PM
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Quote:
Originally posted by Bleyseng
I am in Seattle and can take a look at it.

Geoff
Take Geoff up on his offer, he knows his stuff.
Old 09-02-2003, 04:09 PM
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Guru Brad,
What effect will adjusting the idle screw only have other than raising or lowering the idle presuming that all other factors are set as they should be?
Old 09-03-2003, 09:37 AM
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Quote:
Originally posted by p914
Guru Brad,
What effect will adjusting the idle screw only have other than raising or lowering the idle presuming that all other factors are set as they should be?
When it comes to setting the idle, here are the things that I'd be looking at:

1. Make certain the engine is in good shape. Good and even compression, valves properly adjusted, and good idle vacuum (at least 12 in. Hg, fully warmed-up). If you have a non-stock cam, even the Webcam "stock" or "FI performance" cam, you may have some problems with achieving a smooth idle with low emissions, due to the increased overlap.
2. Ignition system in good working order. Timing set properly (with a light and to factory spec), advance (73 2.0 only) and retard cells on the dizzy working, points plate rotates smoothly, points plate copper strap in good shape, plugs correct type and properly gapped, dwell correct and not varying more than 1 degree over engine speed range, etc.
3. Fuel pressure set to spec (29.4 psig), clean fuel filter.
4. All FI components in place, correct part number for application, all measurable parameters (see my web page) from the ECU plug in spec, MPS in non-molested condition and holding vacuum. Throttle position sensor correctly adjusted so that the idle contact is actuated when the throttle is fully closed.

Once all that is assured, then setting the idle speed and mixture is straightfoward:

1. Warm engine to operating temperature (30 minutes of driving, fairly hard)
2. Using a shop-quality CO meter (e.g. Sun infrared analyzer), set the CO to factory specs (see spec for your engine from the workshop manual) using the CO adjustment knob on the ECU.
3. Adjust the air bleed screw on the throttle body to set the idle speed (usually 950 rpm).
4. Drive car down a slight grade, lift off the throttle completely. If you get any intake "popping" (sounds like a very light backfire), the idle mixture is too lean. Click the CO adjustment knob one click clockwise and try again. Measure CO again to make sure you are within emissions limits for your state.
Old 09-03-2003, 09:59 AM
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You sure you can't just turn the knob full to clockwise and call it good?

Well said...it takes a few small steps to get a good idle, that's it.

Geoff
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Old 09-03-2003, 11:24 AM
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Thank you for the quik response. What are neg effects of too rich a mix? long term and short term.
Old 09-03-2003, 11:28 AM
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too rich = less mileage = more $$$ for gas
long term = lots more $$$ for more gas
sorry, just couldn't help myself!
bruce
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Old 09-03-2003, 12:01 PM
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That's what happens when you live in a Boring Oregon city!
You should live in Zig Zag where driving is fun and the roads are like the name of the town.
Old 09-03-2003, 12:07 PM
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There are other effects. Your idle can "bog down" under some circumstances. It will drop more than it should when you put an electrical load on the charging system. A very rich mixture can accelerate cylinder wall wear. And so on.

Minor stuff, but it does add up!

--DD
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Old 09-03-2003, 02:41 PM
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