Ground problems?

1slow95 · Jun 3, 2009

I've been having problems tuning, and I'm almost positive my wideband isn't reading right which is why I'm having so many problems. I'm using an external AEM UEGO WB controller and AEM EMS. For the WB, I have my +12V wired to the +12V pin on the MAF connector(switched to MAP), and the the ground going direct to the battery. I was checking the voltage directly out of the UEGO controller with my voltmeter when I noticed something very strange...When I check voltage using the UEGO ground that goes direct to the battery, the O2 voltage reading in the AEM software would jump up by almost a half volt. When I used a chassis ground(cig lighter) there was no change in the AEM and the Fluke meter read about .3V lower. When I touch the ground lead to the AEM EMS itself, the voltage reading is an additional .1V lower.

UEGO O2 Output; AEM matched to read 4.70V, O2 Gain setting at 1.06
Battery ground: 4.70V (AEM jumps to 5.00V)
Chassis ground: 4.35V (AEM no change)
AEM ground: 4.20V (AEM no change)

What I don't get is why the voltage reading in the AEM changes when I use the battery ground to test the UEGO O2 output. The only thing I can think of is that the voltmeter is causing me to ground the ECU directly to the battery. If that's the case, then I need to fix some ground problems...

Thoughts? Opinions? Advice?

Where is the ECU ground on these cars? I have my battery in the trunk with the ground running directly to the starter. The block is grounded to the chassis in the stock location. If I know where the ECU ground is I can run an additional ground wire directly to it.

donkey_punch · Jun 3, 2009

i noticed you didn't say anything about grounding the battery to the chassis?

battery to chassis, chassis to engine, engine to battery, seems like your missing a one

i thought the ECU was grounding by the mounting hardware, but i could be wrong.

and i've read of guy grounding the wide band to the same ground for the EMS. i don't recall why at the momment. i've just been reading up on post about AEM every where cause i want to install mine this winter.

1slow95 · Jun 3, 2009

The ECU mounting hardware is a piece of plastic. Can't do much grounding through that!

I think I'm going to try a jumper wire from the UEGO ground (battery) to the case of the EMS to see I get the same voltage fluctuations. If I do, then that should confirm that I need some better battery-to-chassis grounds.

I'm getting very frustrated with my AEM, and I think this ground issue is what's been throwing me off though. My WB shows 10.5:1 to 11:1 most of the time, and if I lean it out to 11.5:1 the car acts like it's too lean. I've been going in circles, adding fuel to get the car running decent at 10.5:1 AFR or lower, then taking fuel out and it barely runs. If everything was working correctly and I knew what I was doing, the AEM would be awesome. Even with my half-assed tune I've noticed a nice improvement in driveability.

toyman · Jun 4, 2009

QUOTE=Low-5.0;7925512]I've been having problems tuning, and I'm almost positive my wideband isn't reading right which is why I'm having so many problems. I'm using an external AEM UEGO WB controller and AEM EMS. For the WB, I have my +12V wired to the +12V pin on the MAF connector(switched to MAP), and the the ground going direct to the battery.

You don't want to ground that way. You want the same ground as the EMS located behind the passenger kick panel. I would also suggest that you create a more positive ground by running a 10 or 12 ga wire directly from the battery. You want this location to minimize battery volt offsets. Is the 12v source on the MAF connector on all the time or is it switched on with the ignition key?

I was checking the voltage directly out of the UEGO controller with my voltmeter when I noticed something very strange...When I check voltage using the UEGO ground that goes direct to the battery, the O2 voltage reading in the AEM software would jump up by almost a half volt. When I used a chassis ground(cig lighter) there was no change in the AEM and the Fluke meter read about .3V lower. When I touch the ground lead to the AEM EMS itself, the voltage reading is an additional .1V lower.

UEGO O2 Output; AEM matched to read 4.70V, O2 Gain setting at 1.06
Battery ground: 4.70V (AEM jumps to 5.00V)
Chassis ground: 4.35V (AEM no change)
AEM ground: 4.20V (AEM no change)

The AEMPro wizard should set this up correctly. As stated above change the ground as described and I'm almost certain your problem will vanish.

What I don't get is why the voltage reading in the AEM changes when I use the battery ground to test the UEGO O2 output. The only thing I can think of is that the voltmeter is causing me to ground the ECU directly to the battery. If that's the case, then I need to fix some ground problems...

Yes

Thoughts? Opinions? Advice?

Where is the ECU ground on these cars? I have my battery in the trunk with the ground running directly to the starter. The block is grounded to the chassis in the stock location. If I know where the ECU ground is I can run an additional ground wire directly to it.

Is the AEM-EMS not located where the original ECU was located? The ground is to the chassis at that location behind the passenger kick panel.

BlownFiveLiter · Jun 4, 2009

The AEM plugs directly into the factory harness, correct? The EEC ground is under the hood on the driver's side of the core support.

This isn't a good pic, but it's all I can find, while sitting at work. It's one of the two wires bolted to the core support, behind the hood adjustment on the driver's side:

millhouse · Jun 4, 2009

Unless you are using the 02's for use as a simulated narrowband for the stock ECU, use the back of the heads or somewhere on the engine as your grounding location.

EDIT: I just re-read your post and you MUST ground it the same location where the ECU is grounded if you plan on seeing a coorilation between what the wideband sees and what the AEM sees. What you are noticing is the effect of a ground offset.

1slow95 · Jun 4, 2009

I installed it per AEM's instructions...

The black wire is to be connected to battery negative (do not use the chassis as the power
ground). The red wire is for switched +12 volts. This wire should be powered only when the
ignition switch is “on”.

The AEM will be installed in the factory location, right now it's laying on the passenger floorboard. I'll look for a ground wire around there tonight after work.

1slow95 · Jun 7, 2009

Something strange is going on here....when I run a wire from my battery/engine ground the chassis, my O2 voltage jumps up by 2 volts. I was reading 6.5V on my voltmeter and the AEM maxed at 5V. If I ground the wideband to the chassis it works fine, if I ground it to the battery it works fine. When the two ground points connect together I have problems. Also, when I disconnect the ground completely from the wideband it outputs 12V.

Install Instructions said:
Orange Sensor #1 0-5 Volt Output
White Sensor #1 0-1 Volt Output
Brown Signal Ground (use only on systems with a differential input, not the AEM EMS)
Red Switched +10 to +18 Volts (10 Amp Fuse Required)
Black Battery Ground

Here's how I wired it:
Orange = plugged into the factory O2#1 connector
White = not connected
Brown = not connected
Red = MAF +12V (switched)
Black = Battery/Engine ground

I drove about 50 miles yesterday and the car drove great, but my AFR showed 10.7:1 while cruising at 55mph. I used almost a half tank of gas on 50-60 miles, so I know it's running rich.

I think the highest AFR I've seen with the engine running is just over 13:1, and that was engine braking in 2nd or 3rd gear from 4000-ish RPM down to 2000. The injectors were shut off and they come back on around 1900 rpm. I would think it should read higher in that situation.

toyman · Jun 7, 2009

Low-5.0 said:
Something strange is going on here....when I run a wire from my battery/engine ground the chassis, my O2 voltage jumps up by 2 volts. I was reading 6.5V on my voltmeter and the AEM maxed at 5V. If I ground the wideband to the chassis it works fine, if I ground it to the battery it works fine. When the two ground points connect together I have problems. Also, when I disconnect the ground completely from the wideband it outputs 12V.

Here's how I wired it:
Orange = plugged into the factory O2#1 connector
White = not connected
Brown = not connected
Red = MAF +12V (switched)
Black = Battery/Engine ground

I drove about 50 miles yesterday and the car drove great, but my AFR showed 10.7:1 while cruising at 55mph. I used almost a half tank of gas on 50-60 miles, so I know it's running rich.

I think the highest AFR I've seen with the engine running is just over 13:1, and that was engine braking in 2nd or 3rd gear from 4000-ish RPM down to 2000. The injectors were shut off and they come back on around 1900 rpm. I would think it should read higher in that situation.

The AEM appears to be reading something different than AFR Gasoline. It will default to AFR Methanol. So, go to Configure-Units-AFR Units-AFR Gasoline-Apply-OK. Also after you have done that check Setup-Sensors-Oxygen Sensor- O2 Sensor #1-O2 Sensor #1 Cal Table. Check the volts vs AFR values. The AEM WB calibration is v*2+10. At 2.35v the AFR value should be 14.7. To set the gain (if needed) unplug the WB, the gauge should read 14.7. In AEMPro click on any of the parameters that shows O2 and adjust the gain (+/-) as needed to have the AEM showing 14.7 AFR.

See if that fixes the problem.

millhouse · Jun 8, 2009

I can only speculate as to why AEM recommends using a battery as a ground (perhaps they are assuming it’s in the stock location or you are using a floating electrical ground). Regardless, your entire vehicles grounding is done via the engine block and chassis (not the battery). All major electrical components are grounded either to the engine…or in close proximity. By tapping different grounding locations you are seeing the effect of ground offsets. A good example of this would be to take a voltage reading from your alternator at the source using the case as the ground. Leaving the + on the alternator, stretch the ground to read from the battery…and you’ll quickly see what I’m talking about.

Use the stock ECU grounding point and make sure the grounding strap from the engine to the firewall is up to snuff.

1slow95 · Jun 8, 2009

toyman said:
The AEM appears to be reading something different than AFR Gasoline. It will default to AFR Methanol. So, go to Configure-Units-AFR Units-AFR Gasoline-Apply-OK. Also after you have done that check Setup-Sensors-Oxygen Sensor- O2 Sensor #1-O2 Sensor #1 Cal Table. Check the volts vs AFR values. The AEM WB calibration is v*2+10. At 2.35v the AFR value should be 14.7. To set the gain (if needed) unplug the WB, the gauge should read 14.7. In AEMPro click on any of the parameters that shows O2 and adjust the gain (+/-) as needed to have the AEM showing 14.7 AFR.

See if that fixes the problem.

I switched from AFR Methanol to AFR Gasoline when I first started tuning a couple months ago. I just checked and it's still on AFR Gasoline. However, my O2 cal table shows 2.35V as 11:1 AFR....According to the manual 4V is 14.7 AFR. I'm using the external UEGO 30-2301.

toyman · Jun 8, 2009

QUOTE=Low-5.0;7929163]I switched from AFR Methanol to AFR Gasoline when I first started tuning a couple months ago. I just checked and it's still on AFR Gasoline. However, my O2 cal table shows 2.35V as 11:1 AFR....According to the manual 4V is 14.7 AFR. I'm using the external UEGO 30-2301.[/QUOTE]

That doesn't look right. 4v should be off the scale 21+ AFR. I would give AEM a call. I'm using a Zeitronix Zt-2 controller with a Bosch LSU4.2 WB sensor and 2.5v is the reading for 14.7 AFR. The sensor is off the scale at 3.27v on the analog WB curve. I just checked the manual forthe AEM 30-2301 and I can see where the table shows 14.7 @ 4.06v. Since we both have the same O2 sensor I can only guess that the AEM controller translates the volts differently. See this link for the Bosch sensor voltage curve.
http://www.zeitronix.com/installation/ZT2instructions.pdf

1slow95 · Jun 14, 2009

I messed with it some more today and got some interesting results. First, I tried to test the voltage output with the sensor unplugged...0.13V The manual says it should be putting out 4v with the sensor unplugged....

I then followed this video to test the sensor, YouTube - O2 Sensor Test - How to check to see if your aftermarket O2 sensor is bad
It tested fine, but full lean was only 4.40V, or around 16:1 AFR. Full rich was at .17V, 8.5:1 AFR.

I tried different grounds and that didn't make a difference. I then disconnected the battery from the car and wired the WB directly to the battery. Same thing, full lean at 4.40V. It actually jumps up to almost 4.5V, then falls off to between 4.35V and 4.40V after a minute.

What if I adjust the gain so that it reads 5V in the AEM at 4.5V from the sensor? That would put the AFR reading closer to where I think it should be at, but I still don't know how accurate it would be...

Ground problems?

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