1990 RX-7 GXL with stock ECU

Error Code Meanings:
8 AFM
10 AFM Temp. Sensor
12 TPS Full Range
15 O2 Sensor
18 TPS Narrow Range

The engine is running great right now, so I'm a bit confused. Maybe the problem is a loose connection or wire, but having all these go wrong at once seems unlikely.

So far I have reset the TPS sensors using a multimeter to perform the "two light" method for the closed throttle plate state. This fix seems to have cured my slightly pulsating idle problem.

I also have measured the swept resistance of the AFM and TPS. Both the AFM and full range TPS of them have dead spots in them unfortunately.

Another symptom is that while in neutral, I can gently open the throttle and get it to a range where the engine's speed pulsates between 2k and 1k RPMs. Perhaps the AFM hits a dead spot here and does something bad with the fuel (too much or too little). Any ideas here?

I've not recently checked the voltages at the ECU, but I've done that in the past. They always seemed good. I'll do that next. I also have a wideband that I can put in to check the AFR. It seems that I don't get the engine codes unless I'm driving for a while in 5th gear. I reset the codes earlier today and have not had them reappear.

I'll post my progress, and I'm open to suggestions...

 

If you reset the ECU and the codes dont come back you shouldnt have to worry about them.

 

on the s5's the ECU stores the fault codes until you clear it...

I suspect that it picked up the dead spots in the afm and the tps at one point or another and saved the trouble codes... doesn't necessarily mean that the car wont run, just that it picked up a fault at some point...

If you got dead spots the codes will eventually come back

Yes, I would think that the AFM dead spot, if its low in the range, could cause your 1-2k pulsation at partial throttle. If you mash it, the AFM will jump over the dead spot so quickly, that the ECU may not even see it.

If you haven't replaced your O2 sensor in a while.. you might consider it being that gas prices will probably be over 3 bux a gallon by the fall!!!

 

I installed a brand new narrow band O2 sensor only a few weeks ago. I'll have to check its voltage reading to see if it is no good per the FSM.

 

How can you just install just the narrow band side???
Don't you need to swap the double TPS as a complete unit?


-Ted

 

I meant that I have a wideband O2 sensor that I can use to check the Air Fuel Ratio. I was not trying to say that I can swap only the full range TPS. The S5 dual TPS appears to be a single unit.

 

Well..... you CAN just replace on or the other... they are kinda "tabbed" onto the mounting plate.. but you have to be real careful getting htem off.

If you pull the oxygen sensor to stick the wideband in and leave the stock O@ sensor wire dangle.... that will produce a code....

 

I have a PLX O2 sensor & controller with a narrowband output that I have used with complete success in the past. I'll see how it goes...

 

How Is It That U Check Codes On An S5? I Have A 90 Turbo.

 

Check the codes by grounding the green single pin test connector in the engine bay near the battery (behing the driver's side headlight). Then put the key in the ignition and turn it to the second (ON) position without starting the engine.

The check engine light will then flash the codes with long flashes giving the first digit and short flashes giving the second digit with 4 seconds between codes. The codes are output from smallest to largest and continue to repeat. Clear them by disconnecting the negative battery cable for a few seconds then reconnect it.

 

http://fc3spro.com/TECH/HOWTO/ERRORC...KI/kerror.html

For all Zenki 1986 - 1988 FC's, I got it here:
http://fc3spro.com/TECH/HOWTO/ERRORC...KI/zerror.html


-Ted

 

Update!

Found and repaired a mostly broken wire on the back side of the O2 sensor's black connector on the passenger side of the engine. The wire practically fell off when I went to disconnect the sensor. Checked continuity after the fix from the engine bay to the ECU's input (0 Ohms resistance). Everything looks good there, and no more engine codes for the O2 sensor!

Also, I readjusted the TPS's idle state. It seems that it was set to just barely be in the right place, and sometimes letting off the throttle would make it return to the correct position. Other times it would be so close that tapping on the TPS with a screwdriver would get it to be in the right position. I manually opened the throttle plates by rotating the shaft in the front of the throttle body and let it fall back into place for the testing.

Here's another set of instructions for doing the TPS adjustment that I found useful:
http://www.johnr.com/tps.html

I still have a bit of a pulsing RPM during warm up (centered around 1500 RPMs or so), but everything seems fine once the engine warms up. I did not expect such a dramatic difference in the TPS depending on whether or not it was at full operating temperature or not.