AEM FIC + O2 Sensors = Stumble City??

Cozmo

Cozmo

Legendary Member
Joined
9 March 2008
Messages
2,016
Location
Seattle WA
Right before I got my turbo put on almost a year ago I replaced my O2 sensors. When I got my car back from the install it had a hesitation problem under light acceleration. I only recently tried unplugging my O2 sensors again and the problem was completely gone (but then my car runs crazy rich). I thought maybe my replacement sensors were bad so I replaced them last week and it turns out that it drives exactly the same as with the other sensors.. so there wasn't anything wrong with them after all. (I reset the ECU at this time)

I can see on my guage that when this is happening my AFR bounces back and forth between 14 or so and 16, and this is what I can feel when I'm driving.

The question is, do other people that have the FIC have this problem? I know there's at least one other person here with this exact same problem because he asked me if my car did this too.
It almost seems like there's too much delay between the o2 sensor voltage going into the FIC, being processed, and being sent back out to the ECU and it is way overcompensating with the fuel due to this.

I also have another problem where cruising at 3k rpms or so with my foot just barely on the throttle to maintain rpms, it will go WAY lean like it is adding almost no fuel. I've tried compensating for this in the FIC fuel map and it doesn't do any good, since it isn't adding the fuel anyway, trying to make it add more 0 fuel has no impact.

If I had a couple thousand dollars sitting around to spend on car parts I'd just throw this shit away and try the EMS.
I don't know if these are FIC specific issues or if something else is wrong with my car, so if you have the FIC and don't have either of these problems please let me know.
 
This may or may not be related, but here's my story.

After pulling my tranny to do a clutch swap, I had a problem that sounds exactly like yours. BUT I do not have a FIC, this was just with the stock ECU.

When the car was cold it ran fine. Full throttle, it ran fine. Under part throttle it stumbled and ran like crap until I would go ~1/2 throttle.

The short term solution was obvious, just drive full throttle all the time:rolleyes:

I realized that the problem was that when running in open loop mode (cold or heavy throttle) the car ran fine, but when the ECU would go into closed loop it was having trouble.

The problem was that I had the o2 sensor plugs mixed up.

Since your problem sounds like it started after they were all unplugged (installing the turbo kit), you should check that they are plugged in correctly.

When swapping them around, make SURE you don't connect 2 plugs from the ECU together (which can be done), as it can fry your ECU (ask me how I know).


My 2 cents.


- Craig
 
I suspected that too, and made sure when I changed the sensors that the sensor on the front side of the engine was plugged into the connector on that same side. Since I have aftermarket headers with o2 extensions it'd be easy to mix them up.
 
Coz,

From what I hear it rains cats and dogs in Seattle. I know here in Florida if I leave my car out of the garage and it rains really hard, I have a similar hesitation that clears up once I get on the throttle. It is possible that your engine is getting a little damp and then arking? Are your coil packs original?
How is your idle when starting? Can your detect a "miss" at idle. Have you cleaned your throttle body? Good luck. Try the simple things first!
 
It idles a bit rough. I've changed my spark plugs in the past 4 months and my coils have never appeared wet and they're not rusty or anything. I don't know if they've ever been replaced though. I did check the resistance on them a while back and they were all the same.

I did clean my throttle body as well as I could with it still on the car (microfiber towels, tb cleaner, and a screwdriver). It was NASTY inside.

I've been thinking about taking it off and making sure it is completely clean, OR just getting the SOS BBTB just so I end up with one that I know is clean and has a recalibrated TPS.
 
This really seems to be an O2 sensor issue, maybe check the connectors (since you have adapter harnesses, this means you have twice the amount of connectors = BAD)

If there is the slightest amount of corrosion in the pins it can cause the signal to be modified, causing the issues you describe, this was found to be the problem on an NSX I just saw.

Since the "limp" mode(caused by unplugging the sensors) fixed your issues, I would also try measuring the o2 voltages at the ECU directly (drive around and record the voltages at different times), then at the boomslang harness, then at the FIC directly (compare these readings to the voltage measured directly at the sensor), if the signal is not correctly reaching the ECU then you need to find out why.
 
angus said:
This really seems to be an O2 sensor issue, maybe check the connectors (since you have adapter harnesses, this means you have twice the amount of connectors = BAD)

If there is the slightest amount of corrosion in the pins it can cause the signal to be modified, causing the issues you describe, this was found to be the problem on an NSX I just saw.

Since the "limp" mode(caused by unplugging the sensors) fixed your issues, I would also try measuring the o2 voltages at the ECU directly (drive around and record the voltages at different times), then at the boomslang harness, then at the FIC directly (compare these readings to the voltage measured directly at the sensor), if the signal is not correctly reaching the ECU then you need to find out why.
Click to expand...

The FIC software tells me what the voltages are. I can check that as a starting place. I'll check my connectors too, they may be dirty. Especially after being disconnected for a few weeks.
 
Coz,

I checked the resistance on all of my coils. They all came out fine. I purchased 3 rear coil packs due to a small amount of rust on two. Installed and problem solved just like night and day. I have no expertise on 02 sensors.
 
I'd check possible for air coming in the from the outside and intermittently throwing off your 02 sensor signals (ie leaking header joints that show carbon deposits). Make sure the wires on the 02 sensors aren't making any contact with anything to possibly briefly short them out.
 
AdvansCPAP.com said:
I'd check possible for air coming in the from the outside and intermittently throwing off your 02 sensor signals (ie leaking header joints that show carbon deposits). Make sure the wires on the 02 sensors aren't making any contact with anything to possibly briefly short them out.
Click to expand...

I don't think there's any leaks. I looked over the area pretty closely when I was trying to find if I had a boost leak or why my turbo was spooling slower than others. I even stuck my head under there with the engine running and didn't see or hear anything.
 
Sounds like it could be a vacuum leak? Check all your vacuum lines and the one that runs to the fic they probably teed in somewhere.Avery slight leak will do exactly what you are describing.It runs good when you unplug the o2 sensor because it will run rich. Good luck.
 
Funny you say that. My boost gauge and FIC are T'd off the FPR. The FPR was installed when I got my turbo put on, and it does leak vacuum just a small bit. The FIC and boost guage don't leak whatsoever.
 
This is why the F/IC is not recommended for OBD1 cars. It becomes very difficult to tune OBD1 cars in closed loop conditions due to the lack of a viewable 02 sensor correction percentage. In other words you have no idea what the factory computer is doing to compensate for AFR conditions.

If you have an OBD1 car, upgrade to the AEM EMS and have a reputable tuner tune the car. You won't regret the results!
 
I'd love to switch to the EMS if I didn't think it was going to take some guy 12 hours on the dyno to make it run worth a damn.

How long do you guys think it should realistically take starting from scratch, or a base configuration for our cars?
 
I changed my car from an FIC to an AEM ems and took it to UMS tuning in Phoenix, it took Tony 6 hours on his dyno to tune the car properly.The car now runs and idles nicely and has 600 hp on race gas.So it should take no more than 6 hours if the tuner knows what he is doing.
 
Cody@LoveFab said:
We average 5 to 6 hours to tune a standard Turbo setup as well.

I should note that we prefer that we have the car for a few days to ensure that cold start and drivability is perfect.
Click to expand...

That's not bad at all. Unfortunately my options around here are pretty limited since I doubt there's anybody within 500 miles that has any substantial amount of experience with turbo NSXs that could do a quality tune in that amount of time.
 
I was looking at the installation manual for the Aeromotive 13105 just now and saw this:

NOTE: Testing the enclosed regulator by applying air pressure or vacuum to the vacuum port with a
hand-held pump will yield poor results, due to the slight air leakage through the adjustment screw
threads. This minute leakage, which is typical of all adjustable fuel pressure regulators, does not, in any
way, affect the performance of the regulator.

hmm so maybe my AEM FPR is just fine.
 
Last edited:
Reply from a local tuner:
"The AEM standalone is a good system and I would think a complete tune would take about 2-4 hours. We charge $125.00 an hour. "

2-4 hours.. there's no damn way haha. My guess would be triple that.
 
Cozmo - told you you should have gotten the standalone on NA1 ;)

..Try better O2 sensors. The OEM can easily get clogged up when you mash on it with turbos.
 
So far I've tried Denso and NGK and they're exactly the same. They are like this when brand new, so age or my turbo has nothing to do with it.
 
Took my TB apart just now and my throttle angle sensor is broken. I'm hoping that explains my problem or at least some of it.
 
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