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Join Date: Sep 2020
Posts: 49
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89 3.2 AEM 4110 AFR Problems
About 2 months ago my car started running crappy at part throttle, backfiring on run over, etc. I first did the AFM track adjustment but it didn’t seem to help.
So, I figured I needed some diagnostics. I bought and setup the AEM 4110 gauge and connected the white wire to the old green o2 sensor wire to send a simulated o2 signal. I put the gauge into position 4 as specified in this thread https://forums.pelicanparts.com/porsche-911-technical-forum/895323-aem-wideband-o2-gauges-4.html It didn’t run any better, maybe worse. I also noticed the plug wires were old and arcing, so I replaced plugs & wires. Then I noticed the reference sensor connector was totally crumbling apart, so I put new speed, reference, and cylinder head temp sensors in. I also fixed a few small vacuum leaks. Still - it would start fine, idle fine cold, AFR read 14.5 or so. Then while sitting and idling and warming up, the AFR would drop to around 13, then rise up to 15-16, the engine would start sputtering. But would keep idling, just seemed to be misfiring a bit. I took it for a spin, same symptoms, if not worse than before I put in the AFR gauge. Pretty severe bucking at part throttle, AFR reading 17+ to off the charts. Wide open throttle it seemed to clear up. I suspected the o2 signal, so I unplugged the gauge while the engine was running. Immediately it smoothed out and I drove it for 20 minutes, ran great. The original problems I was having are fixed - probably due to a combination of the components I replaced. Or maybe the original o2 sensor was going bad. So now it seems something is wrong either with the AEM gauge, either the values it’s reading the simulated o2 signal that it outputs. My car has a custom chip and I think it was probably intended to be run with an o2 sensor. I could go back to a regular o2, would have to splice the old connector back to the green wire since I cut it. Still, would like to have AFR feedback though. Does anyone who runs this AEM 4110 AFR have any tips for me? Appreciate the help. Here's a video with it idling warm with the AEM plugged in. It's a little hard to hear but it's rough. When I unplug it it smooths out immediately. https://imgur.com/a/aem-unplugged-9S6FmPZ Last edited by JohnOfTheJungle; 10-05-2025 at 01:28 PM.. |
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10-05-2025, 12:29 PM
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This is my understanding.... Experts feel free to correct me.
The Uego outputs 0 to 5 volts (windband). See the pict from the Uego manual. The DME needs a narrow band signal which is 0 to 1 volts. So, if the AFR is 14.7, The Uego is sending about 3 volts to the DME. The DME sees this as a very rich AFR and leans the engine. I think the Innovate Wideband has a narroband wire that can be send to the DME, but not the Uego. I got the Uego and run without sending anything to the DME. the 
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84 911 Targa 3.4L |
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10-05-2025, 05:04 PM
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Quote:
If it's still running bad with the o2 sensor plugged in - well I did read more threads about disconnected o2 sensor making the engine run better. It would be likely that I still have a vacuum leak (or leaks) and running open loop is just covering them up. Also when I unscrew the oil fill cap nothing changes with the idle. I'm gonna do another smoke test and also going to shoot the exhaust headers with an IR thermo to see if any one particular cylinder is being affected. I already bought intake manifold gaskets in anticipation, but I want to drive the car this weekend so not going to dive into that task yet unless I see for certain that's the cause. |
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10-06-2025, 05:13 AM
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I did another smoke test with better methodology. Connected it by using a nitrile glove with the tip of the finger cut and with the other end of the glove over the throttle body snorkel.
The hose clamp securing the throttle body to the engine was loose, so that was one vacuum leak. The oil filler cap also was leaking like crazy. So I fixed both of those up. Since I cut the o2 wire to install the AEM, I had to crimp a bullet connector onto the green wire of the o2 sensor to hook the original sensor connector back up. There’s hardly any slack in the wire, little room to work. So I *think* the crimp worked fine, but not I’m not 100%. It ran well, I also tried disconnecting the bullet connector while the engine was running and really couldn’t tell a difference between open loop and closed loop. So assuming my o2 sensor is connected with my bullet connector splice, then all is well. Likely the AEM was fine, it was probably just my vacuum leaks. But I will try hooking the AEM back up to see if it works. Last edited by JohnOfTheJungle; 10-07-2025 at 04:25 PM.. |
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10-07-2025, 04:23 PM
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Sorry for the bad advice. Glad it worked out. I had a hard time with lean AFRs and vacuum leaks a while back, so i understand your frustrations. Thus, I was trying to help.
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84 911 Targa 3.4L |
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10-07-2025, 07:39 PM
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As I’ve been trying to diagnose and fix things on my own car I’ve used this forum as a great resource, and a lot of knowledge comes out of discussions on the threads. |
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10-08-2025, 09:38 AM
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Location: wisconsin
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Odd... I have a PLX AFR, and installed their wideband o2 sensor. I split the output wire to feed both the PLX and the cars ECU.
Works with no issues... Pretty sure you can use just one o2 sensor to feed both with no issues... You arent using the stock porsche o2 sensor are you? That isn't wide band... Addendum... sorry, just saw that the PLX does have a low voltage output, and I used that, not a Y connection... Last edited by bpu699; 10-15-2025 at 05:29 AM.. |
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10-15-2025, 05:19 AM
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Targa
