Quick background: Engine replaced 3000 miles ago with Pineapple inspected reman. Only mods are DP and CB (RB dual tip). I've repalced alternator and air pump, and all hoses were redone with silicone. Runs VERY nicely, smooth and fast, but...

The problem: I'm getting a check engine light occaisonally when I boost. It's not every time. It will come on, sometimes for only a few seconds, sometimes until I shut off the engine. When the light comes on, I experience NO change in driving characteristics, no stumble, smoke, hesitation, or loss of boost. Just an annoying yellow glow. Here's the wierd part: no codes are being stored to the ECU. I shut it off, ground the TEN connector, click the key over to "run" position, get the normal all lights lighting up and seatbelt beep, then the CEL and a couple other lights go off and stay off (as they normally do, in other words)! The check engine light stays off when I restart the engine, and it restarts just fine.

I would think O2 sensor, except it shouldn't care what the O2 is under boost (open loop) and "should" go back under regular driving (closed loop). Sometimes the light does go out under regular driving, sometimes not. It would also store a code, no?

Last data point: I replaced the O2 sensor about Feb or so (in the cold rain, that sucked) with one from O2 sensors dot com place in the forum. It WASN'T the walker unit, but one for the 92 probe that seems more similar to stock. Might this be my problem?

This behavior just started before the engine re-pop, and the air pump/alternator replacement point me away from those related circuits.

Lastly, does anyone have any experience with the real time monitoring tools thay talk about in the manual? I think this is my only real hope of diagnosing, other than blind parts replacement.

Or just shut up and be happy it boosts at all?

And 'cause I love to type, I haven't yet tried to throw a code to make sure the ECU is storing them. Is the best to pull the MAP sensor while idleing? I assume if I do this, the usual bucking idle and smoke will commense. To clear, I shut it off, reconnect the MAP, unplug the battery and step on the brake (discharges the memory voltage supply capacitor?), reconnect the neg cable, and start it up, right? Will this flood the engine, and maybe I ought try a different artificial code throw, like pull the O2 sensor plug?

 

the o2 check engine light will come on under throttle. i had the same problem a few cars ago. you can order them online cheap.

 

Just go to the local auto parts store and buy the universal O2 sensor, it will save you so much money since Mazda wants a large sum of money for the exact spec O2 sensor. The cheaper one is just as good. Mine has caused me no trouble at all.

 

I don't understand why you guys think it has something to do with the O2 sensor? The only error code related to that is for the feedback system, and it only comes on (and sets an error code) if you've been at cruise for some period of time and the feedback system (i.e. O2 sensor most of the time) isn't working. It should ALWAYS set an error code..right? And I see no reason for an O2 sensor to cause a check engine light under boost, ever...the ECU is completely ignoring the O2 sensor under boost.

I get a semi-random check engine light when I give medium to heavy throttle, but it sets the speedometer sensor code...I think I have a problem with that sensor. Now, some check engine lights are persistant, i.e. once you get it it never goes away until you reset it, and some are not (light goes away once you shut down the car and restart it) but even then the code persists. What am I missing?

jds

 

See, that's my question. If the code isn't stored, I have no clue what the problem might be. I'm not all devastated about it, as the car operates normally with it on or off. I'm hoping someone can come along, read this, and say, "Oh, well, the headlight fluid level sensor, wind buffeting sensor, and pucker factor sensor all light the CEL, but don't store to the ECU", or something even mor useful!

 

The OIL LEVEL sensor will light the CEL but should Light the Low Oil Light in the Oil Press gauge also. I don't think it stores a code b/k the ECU is not involved in this process as it is part of the logic built into the instrument cluster flex circuit (at least my intense study of the flex circuit for my custom guage install [ https://www.rx7club.com/forum/showth...hreadid=199144 ] leads me to this conclusion).

 

I didn't say it WAS the O2 sensor, a person said it might be and I gave him an answer on the best way to do an o2 sensor. Tiss all.

 

DON'T DO THAT !!! (Don't shut it off.)

Pull over. Open the hood. Ground the TEN connector. Then watch the light.

 

Ah-HA! I knew I was being an idiot!

 

That's not usually true. Error codes do not get erased ever unless I erase them, at least not on my car. Are there particular error codes that do not get saved?

jds

 

Check page F-23 of the shop manual.
The "Memorized" column indicates which codes are stored or not stored.

 

OK, so for the ones that are not stored, I stop the car with the CEL still on, jump out and jumper the TEN to ground, hop back in and watch the blinking show?

And if the CEL goes out before I can stop, then go again until it comes on again?

Just checking to be clear. I had forgotten that F-22 and the next few pages listed whether they are memorized, and hadn't really though about how you would check them.

 

I guess I must have misinterpreted that. I thought that was referring to whether or not the Check Engine light would persist after the car is restarted, but clearly that's not the case as it lists Speedometer Sensor as memorized, and the light clearly does not stay on after you restart the car. I guess you learn something new every day!

jds

 

Dragging it up from the dead...

FINALLY got the thing to stay lighted until I could stop and check the light while the car was still running (thanks jwhite ) I get six short pulses, and long pause, then six pulses again. The manual says this is a faulty speedometer sensing connection. My speedo works just fine, thanks. Looking a little further, I see the signal for the speedo is taken from the tranny, and goes directly to the speedo ecu. There is then a wire going from the speedo to the ECU (main control), so I'm guessing my problem lies there. I notice the wire runs through connector X-07, which I've had problems with before, when I was getting no speedo or turn signals or hazard.

Anyway, the thing I was noticing from the manual is this is supposed to be a stored to memory problem, yet as I describe above, it's not getting stored. To further make it weird, the problem ONLY occurs when I boost, but not every time I boost, and there seems to be no regular type of throttle action that give rise to the CEL. Maybe the ECU is just looking for this signal when it sees positive pressure and gets freaked out? Have any of you guys had codes that are supposed to be memorized but weren't?

Thanks for all your help so far, and I'll update this if I figure anythig else out. I theeenk I can tap into the connecto at the ECU and read the voltages to see if they are correct, and I'll inspect X-07 again...

 

For what it's worth I found this on Steve Cirian's web site:

Date: Sat, 11 Oct 97 20:15:00 EST
From: "Houseman, Carl W. x1323" (CHOUSEMAN@genicom.com)

The diagnostic trouble code table, pages F-22 to F-25 in my 95 manual, has a column marked "Memorized" with yes/no indications for each code. Codes which are not memorized go away immediately upon battery disconnect. Codes which are memorized require you to step on the brake pedal with the battery disconnected, to clear them (procedure on page F-64).