Bought a car tuned on AEM FI/C, need help (misfire). Could it be related? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 04-01-2011, 03:02 PM   #1
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Default Bought a car tuned on AEM FI/C, need help (misfire). Could it be related?

Warning, this is long. Sorry in advance.

I took out the seats, center console, part of the dash and the carpet last week. I was not happy with the wiring I saw underneath and behind. I pulled out the radio and it was a rats nest, with two different radio's harness's wired in back there. So I cleaned it up and ran to Buy Best and bought an adapter harness. Put that it and wired the radio up to it, and it worked. I was happy, but had to tap into a factory harness I believe for power.

The next thing was to follow two relays that were wired and tucked behind that. Turns out they were tapped into factory harnesses as well and ran to each door, then found a black box. Realized it was some sort of alarm system. So I hacked that out of there since it didn't work anyway, and wires had fallen off the relays anyway. After taking the whole thing out, including the locking system, the car still worked. I even fixed the problem I was having with the passenger door not locking, turns out it was the alarm system contraption in there.

After that, I wanted to rewire the switch for the boost and wideband gauges, as well as the random blue LED's the previous owner scattered around the car. So I ripped out the blue LED's and snipped the wires from the gauges to the switch. I put in some new wire and wired those back up, grounded them out, and they worked again.

I now felt a lot better about the wiring in this car. I probably removed a good amount of weight after taking out all that wiring. The radio was now properly wired up and working. I got rid of the alarm system that hadn't worked anyway. And lastly I rewired the gauges on my A-pillar.

Then I went to start the car up to drive her around, it was misfiring. Wasn't terrible, but I quickly turned around and parked her back in the garage. There is a ticking noise coming from the front of the motor.

I was tired and didn't want to deal with it. So I unhooked the battery and let it sit overnight. The next day I went out and tried again, and she fired up and drove the whole day. I wasn't going to complain. Then the day after that, she started misfiring again right away in the morning. After doing some tests, I found out it was the 1st cylinder. I changed the plugs and plug wires, no help. I was told if it was the coilpack, both the 1st and 4th cylinder would be misfiring because they're on the same coil.

I was told to look at the crank angle sensor, and check some grounds. I cleaned off the sensor and looked around, but didn't fix anything. Injectors have also been mentioned, but I'm not sure how to check those.

Did I mess something up with the wiring? I'm not sure how the AEM FI/C was wired into all of this, but do you think if I snipped a bad wire here or a different wire there, it could cause this? Or is it unrelated? I already didn't like the way the wiring was in the beginning, tapped into the factory harnesses and all, but now I'm just sick of this. Could I have messed up a wire going to the sensors, or the ground, or the injectors? I'll be doing a compression test today just to make sure it's nothing internal to the motor.

Once I get this fixed (if I do, that is), I'd like to change my tune up. Right now it's running super rich, but I'm totally unfamiliar with the software and tuning in general. At WOT in boost, the A/F ratio sits right around 10. I guess that's my next project, but I really need help getting this up and running again.

If this is in the wrong section, please advise me where I can move it. I am a bit of a noob, but I'm trying my best and it's always a learning experience. I appreciate any responses, and again, I'm sorry for this being so long.
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Old 04-02-2011, 12:08 AM   #2
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I don't think it is f/ic related, but the F/iC comes with a little by-pass harness adapter. Basically you unplug the f/ic, plug this adapter in, and it puts it back to factory connections. This would be a great way to test if it's the f/ic or not. I'm guessing though you didn't get this adapter, and would probably want to contact AEM to get one.

But as I said, I don't think it's f/ic related.
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Old 04-02-2011, 04:18 AM   #3
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Sounds good, I wasn't aware of this adapter but I will definitely look into getting one to test things out. Thanks for the tip!
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Old 04-11-2011, 12:17 AM   #4
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Bumping this thread from a few days ago.

Could the tune on the FI/C be reset at all? I was messing with the wiring and I'm not sure if I could've shorted something out. How hard is this to tune? I have no experience, but I'm thinking about hooking it up to my laptop and see how things go.

Also, I think the previous owner might have used that adapter, how bad would it be to plug the stock ECU back in? If it ran the same as it is now, would the FI/C be the problem?
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Old 04-11-2011, 12:33 AM   #5
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Resetting the F/iC is very easy. It's just a couple of tables, just zero'ing the tables out would reset it. You will also have to tell it what injectors you are running, etc. And the stock ECU is still in the car with the f/ic, this is just a piggy back assembly. You would really need that patch cable (which btw I have one from my old f/ic) to eliminate the F/ic altogether from the system, or resolder a bunch of wires.
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Old 04-11-2011, 12:54 AM   #6
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Quote:
Originally Posted by dustinb View Post
Resetting the F/iC is very easy. It's just a couple of tables, just zero'ing the tables out would reset it. You will also have to tell it what injectors you are running, etc. And the stock ECU is still in the car with the f/ic, this is just a piggy back assembly. You would really need that patch cable (which btw I have one from my old f/ic) to eliminate the F/ic altogether from the system, or resolder a bunch of wires.
I'm asking if you think the F/IC could've reset itself after the electrical work I performed. The stock ECU is still in the car, so it is a piggyback system. I'll see if I can go out and take a pic of the wiring for you. If you I don't have the cable you're talking about, maybe I could buy/borrow yours. If it would be easier and more efficient to switch to a Megasquirt, I'd like to know. I know you can unplug the stock ECU and put a Megasquirt in, but I'm not sure how easy that will be for me because I've got the F/IC.
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Old 04-11-2011, 01:10 AM   #7
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(Ignore the stereo wires)

It seems like the green wires are connected to a harness that connects to the factory harness. The F/IC wires are connected to some of the wires in the green part. The other end comes from the white box with black electrical tape all the way to the left (I'm assuming this is the factory harness). So if I unplugged the green part and plugged the other part in to the ECU, would this be back to stock?
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Old 04-11-2011, 11:43 AM   #8
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OK well first off I don't think your f/ic could reset itself. And secondly, whoever did that installation saved you a lot of headache because it appears they used a boomslang harness. You should be able to just unplug the boomslang and plug directly into the ecu. But as per previous warning, if you have larger injectors in the car the car probably won't idle.
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Old 04-11-2011, 02:21 PM   #9
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That's what I figured, I'm glad the previous owner had it done this way. And yes I do have bigger injectors, so I probably won't put it back to the stock ECU.

I just don't know why it runs rough sometimes, and then runs smoothly other times but either way it runs super lean. It used to always run smooth and very rich in boost (low 10 AFRs). Anything you know that could cause this? It all came above after rewiring stuff inside the car, but could it be just a coincidence?

I've already replaced the plugs and wires. Maybe O2 sensor? I'm not sure if anything internal in the engine could be doing this.

If I hooked it up to my computer and took some screen shots of whatever you want, would you be able to tell if the tuning looks good?
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Old 04-11-2011, 03:51 PM   #10
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It could be many things. The first thing I would do is plug the f/ic into your computer and see what it's reading. But it could also be a bad fuel pump, something with your CAS, perhaps your Air flow meter... tough to say, but I doubt what you did with the wiring had any effect.
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Old 04-11-2011, 04:02 PM   #11
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Quote:
Originally Posted by dustinb View Post
It could be many things. The first thing I would do is plug the f/ic into your computer and see what it's reading. But it could also be a bad fuel pump, something with your CAS, perhaps your Air flow meter... tough to say, but I doubt what you did with the wiring had any effect.
I'll see what happens when I connect the F/IC to my laptop. Is there a way to test the fuel pump? I'll look at the CAS and MAF. I was also told to look at the primary O2 sensor, so I can look at that too.
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Old 07-12-2011, 04:12 AM   #12
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Issue has been solved. Turns out the vacuum line running to the F/IC was pinched, therefore the F/IC wasn't getting a vacuum signal to do it's thing. Fixed it and the car is back to running great. It's even better with the recirculated BOV too, I'm pumped!
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