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Alternatives for OBD2 piggyback? (potential issue with my F/IC)

3 July 2013
Northern Virginia
Background: '00 NA2 w/ Comptech supercharger from dealer floor; I purchased in 2014, one head lifted shortly thereafter; rebuilt engine and redid fueling with AEM F/IC, RC 550 injectors, an AEM fuel-pressure regulator, and a DW200 fuel pump; mileage was 40k. Car has run quite well since then and now has nearly 60k miles.

The last few times I drove the car, I noticed a bit of a miss or cut-out when I went over a bump like a freeway expansion joint. Not very significant, but enough that I wondered if perhaps traction control had engaged, but no light appeared on the dash. Then, the last time I drove it, the same thing happened (on the freeway), but the car freaked. CEL and very rough running, with low AFR readings. It resolved itself after a short period (maybe 15 seconds) and I drove home cautiously. There was a P0107 code (MAP sensor low input). I reset the code and have not driven the car since.

There don't appear to be many posts on here regarding that code, but this one shows up. It seems like a notable difference that he was getting a crank sensor error too. I have not dug into my car, but I thought about grounds a bit and the MAP sensor does not use a grounding point—its ground goes directly to the ECU. This morning I realized that the behavior was consistent with the F/IC having a problem. I don't think they are known for being all that reliable. So I figure that maybe I should get a replacement F/IC.

And here I am. The F/IC appears to be discontinued and not available anywhere. I have no love for them, and would happily go in a different direction, including a standalone. But my car needs to pass an OBD2 check for another three years, then I could register it as an antique. I do prefer to maintain normal registration (w/ OBD2 tests) if possible.

As I understand it, to pass an OBD2 test, I could remove my piggyback, but then I'd have to replace the injectors with factory injectors and make sure my fuel pressure is at factory levels; as long as I don't exceed atmospheric MAP, the factory ECU should be okay. I'm okay with that approach, but it will require buying new injectors just for that purpose.

I'd really appreciate any advice on:
  • Things to investigate that may cause the P0107 code
  • Alternative piggyback controllers that would allow OBD2 testing
  • Standalone controllers that might allow OBD2 testing
  • any other way forward

I haven't been on the forum much, mostly because my car has been running well and trouble-free. I'm pretty sad that my car is in its current state, and I know there's nowhere I'll get better advice

I've experienced these random issues over the years and it screams a loose ground connection to me. I've had loose grounds from main chassis grounds, but usually ground loops on harnesses. I've even had a loose ground from a relay mount where the relay chassis was the main grounding point. I forget which one that was on the NSX.

I only have experience with 3 types of piggybacks.
- HKS F-Con iS (not recommended because of proprietary software)
- Split Second - believe it or not this has been reliable on my supercharged Tacoma since 2007

I wish I could help more. I finally uninstalled all the Zeitronix stuff just earlier this year and thought of you. Funny, not funny I know. Glad to hear from you on here!
No experience with a CTSC or F/IC, but it sounds like a wiring issue (loose connection, loose ground) instead of an issue with the f/ic. I imagine the f/ic itself is all solid state components and probably wouldn't show symptoms because of running over an expansion joint. If there was soldering issues or bad caps I think the issue would show up based on temp, not vibration or impact.

The locations of grounds should be in the service manual, and you should be able to poke around the engine bay and check the connections between the f/ic and the ECU.
First off, it would be best practise that the MAP sensor is not externally grounded. Best practise has the sensor grounds running isolated directly back to the ECU to avoid galvanic coupling from currents flowing in the chassis.

P 0107 is low voltage on the MAP sensor output. That could be caused by a short to ground on the +5v supply to the sensor, an open circuit on the +5v supply or a short or open circuit on the sensor output. It could also be caused by an intermittent failure in the MAP sensor itself; but, I think that is a lower probability event. I would be inclined to start with a bad electrical connection somewhere in the MAP sensor circuit mainly because you have reported that the problem occurs when the car receives a physical impact of some sort which I presume may be shaking an electrical connection. The CEL and a low AFR could be consistent with an explicit problem on the MAP signal. The ECU has a fail safe mode for a MAP sensor failure. If the P 0107 error code triggers that fail safe mode it is likely that it would operate with safe AFRs and limit operation. If the short / open circuit cleared, normal operation would resume just leaving you with the stored code.

I am familiar with the concept of the F/IC; but, not the details. I believe the F/IC has provision to intercept the MAP sensor output signal. I personally would start with looking at the integrity of that connection path, probably starting at the connection to the F/IC. I seem to recall that AEM offered a custom harness for interfacing with the NSX ECU wiring so the connectors on that custom harness would be a good place to start. This could ultimately include the inspection of the F/IC board where the interface plugs solder to the board (the dreaded Main EFI relay solder cracks). I consider it unlikely that the actual F/IC electronics are failing. When the actual electronic components fail, they tend to stay respectfully dead.

With an OBD II data logger you could log the MAP sensor voltage or inferred manifold pressure while you drive and then start looking for some rough pavement to try and induce the fault. This might help to confirm that the problem is on the MAP sensor circuit if the voltage / inferred pressure takes a sudden spike when hitting rough pavement.

Intermittent electrical problems are an absolute pain to diagnose. It pretty much involves getting in there with a good electrical tester (digital multimeter with a very fast update time) and measuring circuit continuity while tugging / shaking on stuff. Because wiring checks are such a drag, you may wish to replace the MAP sensor to rule it out as the cause of the problem before you start the wiring checks. That is your choice. If your car was stock, that would be a logical place to start. However, since you have the added non OEM wiring harness, I think that is a more logical place to start.
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Ack, sorry for not responding sooner. I thought I would receive notification of any replies.

I haven't spent any time on this, but I appreciate the advice. I will start by looking at connections and any grounds I can find. I do have all the service manuals.

I have heard the F/IC connectors are not great, so that does seem like a strong candidate for the MAP signal failing. The sensor voltage supply is direct to the factory ECU but the signal runs through the F/IC, using a harness with connectors. So I will look at that too.

First I have to take out the harness bar, to get at the ECU and F/IC...

Thanks again for the thoughts.
Just to follow up, I found two broken grounds near the alternator. Almost for sure because my right-side engine mount had broken both bolts to the engine and had no captive nut on the frame. Super unclear how that could happen but I repaired it all and my car seems happy again. In a few years I won’t have to pass emissions inspection and can change to a standalone engine management.
If you end up wanting to upgrade i do have my aem series 2 stand alone. I upgraded to the Infiniti for a bunch of cash so have been looking to sell off my series 2. I'm in arizona of your going to expo

sold to a future turbo owner last week
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