UEGO WB goes full lean under load -- only in MS, not on gauge! - Miata Turbo Forum - Boost cars, acquire cats.

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Old 03-18-2009, 09:38 PM   #1
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Default UEGO WB goes full lean under load -- only in MS, not on gauge!

I finally got the MS working, Braineack took care of a small issue and it started up as soon as I got it back.

I took the car to a shop and had the uego sensor installed, ran the wiring, etc etc. It took a while to get wired because i had some trouble finding the ground for the MS (thanks harness diagram!).

I did the volts to AFR fix in megatune, and the values match pretty close between the gauge and the MS at idle.

However -- whenever i start driving, the gauge goes to full lean almost immediately, even though the gauge itself is still reading reasonable numbers?!

Has anyone seen this before?

-Tomaj
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Old 03-18-2009, 09:40 PM   #2
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Undo the AFR fix and come back telling me you don't have this issue anymore. Please

(Worth a try to eliminate any variables in the modifications you made.)
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Old 03-19-2009, 06:34 PM   #3
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hey, i undid the modification.. it didnt make a difference so i removed megatune altogether and downloaded the newest versino ffrom diyautotune's site. i re-sent several MSQs starting from the beginning to the latest, i had the same issue..

Under light acceleration for example, i can see on the gauge: 15 (at idle), going up and down around 14, thru lets say 12 or so..At the same time, the laptop gauge will show 15 (at idle), and the go all the way to lean nearly immediately and stay there until i completely let off the gas.

-Tomaj
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Old 03-20-2009, 01:13 PM   #4
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Check the voltage on the MS's input pin.
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Old 03-20-2009, 07:38 PM   #5
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OK so i started out doing what you said, to check the voltage..

I decided to disconnect it from the MS entirely to eliminate any variables.

I found out something pretty crazy.

The UEGO turns off completely once i put the car into gear AND let off the clutch entirely. Clutch off but in neutral, no problem. Clutch in and in gear, no problem..

I was able to locate the exact clutch position that would cause the uego to freak out, and also the exact position going into gear.

It's like some freaky on off switch...

I also noticed that there's some weird high pitched hum when i press on the clutch which varies in volume depending on clutch position, but is silent if clutch is out..

someone please have some ideas !!
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Old 03-20-2009, 08:03 PM   #6
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You sure you got the ground? It sounds like your MS is connected to the cruise control line or something like that. What year is your car?
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Old 03-20-2009, 08:07 PM   #7
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You wideband and megasquirt should both be connected to the stock ECU ground location. You saying your clutch engagement is causing this to short. Sounds like your wiring is messed up.
Where do you get the power and ground for the MS and the Wideband?
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Old 03-20-2009, 08:10 PM   #8
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Hehehe i'm not sure i got the ground

The car's a 1991. I tapped into the green-black wire on the MS side of the harness. My car came with cruise control, but it was removed during the installation of the turbo.

-Tomaj
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Old 03-20-2009, 08:12 PM   #9
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I got the MS with the boomslang harness from Braineack. For the uego, i tapped the red 12v wire on the MS side of the boomslang, and the green-black for hte ground... that was after trying two of the black wires which turned out not to be the ground

You guys can flame me all you want, just tell me how to fix it !!
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Old 03-20-2009, 09:13 PM   #10
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Make sure nothing is connected to the first pin on the bottom of the first connector (brown/white and black/blue). That is the neutral switch that seems to be causing your problem. It's 1V on the ECU pinout diagram.

That line reads 0V when in neutral or clutch in and a voltage (equal to or higher than your AFR voltage it seems) when in gear and clutch out.
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Old 03-20-2009, 09:19 PM   #11
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There should be a group of black wires coming out of the DB37 plug to the connector to the factory harness. All the way at the end of the longer connector. Those are ground. Use em.
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Old 03-20-2009, 09:49 PM   #12
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Hey, thanks for those tips. I'll take a look at how it's wired in the morning.. The neutral switch thing seems like a real possibility.
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Old 03-21-2009, 12:49 PM   #13
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sounds like you grounded the UEGO to the clutch/neutral safety switch.

there are two thick black wires next to each other coming off the MS, those are the grounds. black and black/light green on the oem side.
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Old 03-21-2009, 02:09 PM   #14
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yeah i definitely didn't use the THICK black wires at any point..i thought those wre for the injectors?

When you say they're next to each other, you mean that they're horizontally next to each other, not vertically right?

So in other words

XXabcdefghijk
lmnopqrstuv

as opposed to

Xabcdefghijk
Xlmnopqrstuv

where "X" is one of the black wires.

-Tomaj
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Old 03-21-2009, 02:50 PM   #15
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Use these pinout diagrams.
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UEGO WB goes full lean under load -- only in MS, not on gauge!-90-93_miata_standalone_ms-harness.jpg  
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File Type: pdf ecupinout.pdf (310.0 KB, 72 views)
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Old 03-21-2009, 05:21 PM   #16
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That did it, you guys rule!

I didn't cut the thick wire, just stripped off a small piece of insulation near the middle and temporarily wrapped the ground from the uego around that...

Worked like a charm! Before, even when working, the values were always off a few tenths.. now, it seems 100% accurate.

I went out, drove around, did some tuning, finally! Thanks guys!

So just to clarify in case some other newbie comes along in the future -- I used the THICK BLACK WIRE labeled ground in the diagram above.

The car's already running much better after just 5 minutes of driving / tuning, although when i push it into higher rpms with boost, i think i'm hitting a fuel cutoff or something, i noticed the car will just hiccup and the WB goes full lean for a few seconds. I'm sure i can figure that out though hehe

-Tomaj
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