CEL 8 - MAF - Any Solution for this?
 

So I was getting a CEL when I first installed the MS. It was for EGR. Traced this to a bent pin that wasn't making contact. Solved, right? No, still get the CEL. Hooked up the jumper to check codes and there is no more EGR code (#28) but now I have a #8 for the MAF.

Car is OBD1, 95.5. Anybody else have this issue? Solutions?

Are you running the MS in parallel or stand alone? Is your MAF hooked up?

Parallel, no MAF.

The stock ECU still controls the CEL and will throw a code if it doesn't see a good signal from the MAF.

I'm getting a wicked case of deja vu, like I've already answered this question once this month. Oh yeah: https://www.miataturbo.net/showpost....9&postcount=17

Even if you wired the IAT straight to the MS, I think it's now paralleling that wire between MS and the stock ECU which I'm pretty sure is going to screw up the values that the stock ECU expects to see from a MAF. Not exactly sure of the basis for it and it's been a long time since I've looked at MS1 stuff, but the solution(s) are the same.
1. In your parallel boomslang/adapter harness, cut the wire to the CEL so the stock ECU can't trigger it.
2. Jumper the two pins in the glovebox connector per the instructions in FM's Link tuning manual pdf, so the light will come on only at ignition then go off when the motor is running, so you don't arouse the suspicion of state inspectors.

IMO the CEL doesn't give a whole lot of useful info when it works anyway. I don't miss it.

I don't see how the IAT sensor is relevant to a MAF CEL. Yes, I understand that the IAT sensor is physically located inside the MAF housing on 1.8 NAs, however MAF and IAT are still separate signal lines.

Regardless of what he's done with the IAT sensor and its signal line, if he has no MAF sensor (and is not externally simulating a MAF signal) then the stock ECU is going to throw a code about it.

An extremely simplistic fix might be to parallel the TPS signal into the MAF input. I honestly have no idea whether this would work or not, it's just the only thing I can think of at the moment that would feed something vaguely resembling a MAF signal into the stock ECU in the absence of an actual MAF sensor and without having to build an external circuit to do the job. The lack of general-purpose analog outputs is one thing that I do miss on the MS as compared to the old EMU.


soloracer, do you actually need a working CEL? I thought Ohio had gotten rid of the smog check system?

What I'm sayin. Cut it, but do the mod so it comes on briefly when the key is turned just in case an inspector cares. It takes 5 minutes.

BTW, these are the fault codes a properly functioning CEL can give on a 94-95:

01 IGF signal
03 SGT signal
04 SGC signal
08 Mass Airflow sensor
09 Engine coolant temperature sensor
10 Intake air temperature sensor (mass airflow sensor)
12 Throttle position sensor
14 Barometric absolute pressure sensor
15 Heated oxygen sensor (inactivation)
16 EGR function sensor
17 Heated oxygen sensor (inversion)
25 PRC solenoid valve
26 Purge solenoid valve
28 EGR solenoid valve (vacuum)
29 EGR solenoid valve (vent)
34 ISC valve

Take away the functions controlled or monitored in a more easily visible fashion by MS and a WBO2 and what are you left with? EGR (which will still work on a parallel install)? A few non-critical solenoids? Nothing of any great importance, certainly nothing about which I feel deprived of critical info due to modifying the CEL.

Well, yeah. And to elaborate, since he lives in Ohio, I don't even think that he needs to do the mod to light up the CEL at key-on, as I'm pretty sure that they did away with the inspection process altogether a few years ago.


Not without a MAF signal.

Yeah, I don't need it here and don't really care if it functions. I just keep throwing around leaving this crappy state and don't want to do something short-sighted that might affect my ability to register the car elsewhere. Austin, TX. is my #1 choice for relo right now and they DO inspect. I think a few counties here still do it. I know they did in southern Ohio until a couple years ago; but not in central, where I live.
I'm thinking the key-on mod might be the way to go. Though the nerd in me wants to test Joe's TPS trick - just to see. Unfortunately I have too much on my "to-do list" (like tune this car and repair 3 motorcycles), so I'll probably take the easy way out.

Seriously? So the EGR system that I left in place is worthless without that signal? Depressing. The engine bay could be a lot cleaner without that and the charcoal canister.

Thanks for all the help.

Heh...oops. Missed that.

Is this true for all the 1.8 cars? I thought I remembered reading (way back in '07-'08) that it wasn't a problem for some folks.

Should be true for all 94-95 (OBDI) parallel installs. The people who didn't have the problem most likely had standalone installs (no stock ECU to trigger the CEL). Later 1.8s were OBDII and have a different set of issues with which I am, thankfully, not familiar.