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Mazda MX-3 surging


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leelaw
Novice

Jul 21, 2017, 4:43 AM

Post #1 of 13 (1087 views)
  post locked   Mazda MX-3 surging  

1994 Mazda MX-3
1.6L 16V DOHC
50,000 miles
Vehicle was parked unused for 9 years under a carport. In 2015, brakes, battery and fuel pump were replaced and vehicle resumed service. Initially, vehicle ran well, but seemed slightly lacking in power. After 6 months, a rough idle was noticed, with the vehicle exhibiting what seemed like an intermittent misfire at idle.
At this point the spark plugs, plug wires and distributor rotor were replaced without a successful resolution to the problem and the misfire grew worse.
Eventually, the Check Engine light started blink codes for the Mass Airflow Sensor and the Throttle Position Sensor. Both were replaced which caused the Check Engine light to stop, but did not have any effect on the idle or lack of power.
Recently the transmission HOLD light began flashing from time to time. This resulted in the Transmission Speed Sensor being replaced, but did not resolve the flashing HOLD light. Transmission fluid was replaced, but still no resolution to the flash of the HOLD light.
Within the last 3 months, an Oxygen Sensor (Inversion) code from the Check Engine light and the engine will not rev past 2400 RPM. At 2400 RPM it will drop RPM’s and then surge back to 2400, drop and surge, drop and surge, until the throttle is released. Sometimes there will be a backfire through the intake. If the throttle is just at 2400, the surge cycle is slow, if the throttle is opened wider, the surge cycle is faster.
O2 sensor replaced, throttle body removed and cleaned, EGR valve tested, checked for vacuum leaks and inspected vacuum hoses, still surging. While the Check Engine light for the Oxygen Sensor (Inversion) has stopped, the codes for the Mass Airflow Sensor (08) and the Throttle Position Sensor (12) have returned.
Lee


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jul 21, 2017, 5:53 AM

Post #2 of 13 (1072 views)
  post locked   Re: Mazda MX-3 surging  

Looks like the parts cannon is being fired at it and no diagnostic is being done.

At the TPS connector what are the voltages on each of the wires with the ignition on? You have to back probe the connector for each wire with your volt meter black lead connected to battery negative.

Write down the color of the wires and the voltages on each.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.


leelaw
Novice

Jul 21, 2017, 12:52 PM

Post #3 of 13 (1038 views)
  post locked   Re: Mazda MX-3 surging  

Thank you.

Green w red stripe: 5.02 volts
Blue w white stripe: .4 volts
Red w white stripe: .45 volts
Black: .02 volts
Voltage measured with engine off, ignition on, TPS connected to connector.


leelaw
Novice

Jul 21, 2017, 5:49 PM

Post #4 of 13 (994 views)
  post locked   Re: Mazda MX-3 surging  

I’ve found that if I rev it immediately upon starting, it will rev beyond 2400. However, once the RPM’s drop below about 2700, it starts the drop and surge process. Ironically, it’s idling great.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jul 21, 2017, 6:14 PM

Post #5 of 13 (989 views)
  post locked   Re: Mazda MX-3 surging  

Have you verified the EGR valve isn't sticking open?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



leelaw
Novice

Jul 21, 2017, 6:25 PM

Post #6 of 13 (985 views)
  post locked   Re: Mazda MX-3 surging  

Thanks for the advice!
I took the EGR valve off and pulled a vacuum on it (it was not a measured vacuum, so I don't know how much it took to operate) and the diaphragm would move the valve.
I made the assumption that it was good.
Should I test it in some other manner?


Hammer Time
Ultimate Carjunky / Moderator
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Jul 21, 2017, 6:28 PM

Post #7 of 13 (983 views)
  post locked   Re: Mazda MX-3 surging  

The question isn't whether it is opening but whether it is closing all the way at idle. If an EGR is open at idle, it will give symptoms as you are describing.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jul 21, 2017, 7:02 PM

Post #8 of 13 (973 views)
  post locked   Re: Mazda MX-3 surging  

If the egr was open during idle, the engine would idle rough or stall. It almost sounds like it is going into fuel cutoff. The Tps sensor has a switch inside called an idle stop switch. The switch tells the ecu when the throttle is closed. It uses that switch for fuel cutoff when you let off the gas while coasting. The ecu sends 5 or 12 volts on the red white wire. With the switch closed the voltage is pulled low. The throttle is pressed the voltage is high. If the ecu doesn't see the voltage high when you open the throttle, it will cut injectors and cause a surging rev limiter.
Monitor the voltage on red white wire with throttle closed and open. See what the voltage is when the problem is occurring. Let us know.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 21, 2017, 7:10 PM)


leelaw
Novice

Jul 23, 2017, 2:10 PM

Post #9 of 13 (903 views)
  post locked   Re: Mazda MX-3 surging  

TPS Voltages - Engine Running

Green\Red - Throttle Closed 4.9V; Open 4.9V
Blue\White - Throttle Closed .4V; Open 3.4V
Red\White - Throttle Closed .3V; Open 6.0V
Black - No Voltage

Voltages do not fluctuate when the problem is occurring.

MAF Voltages - Engine Idling

White\Red (1B PCME Pin) - 13.87V
Green\Black (2O PCME Pin) - 1.39V
Pink\Black (2P PCME Pin) - 1.68V
Blue\Black (2D PCME Pin) - .01V
Blue\LightGreen(2F PCME Pin) - 0V

These appear to be within limits, according to AllData.

I've cleaned the EGR again as well as the IAC and Throttle body.

What are the odds of a problem in the PCME?


Discretesignals
Ultimate Carjunky / Moderator
Discretesignals profile image

Jul 23, 2017, 3:33 PM

Post #10 of 13 (889 views)
  post locked   Re: Mazda MX-3 surging  

That voltage on the red white doesn't seem correct. If you have 12 at the ecu connector, then it should be close to 12 on the Tps connector with the throttle open.
What is the voltage at the Tps connector with it unplugged and ignition on at the red white wire?





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Jul 23, 2017, 3:36 PM)


leelaw
Novice

Jul 29, 2017, 4:12 AM

Post #11 of 13 (838 views)
  post locked   Re: Mazda MX-3 surging  

Thank you to all!
I have replaced the computer with a used one from Ebay, and the issue seems to be resolved. I can now rev past 2400, however, there is still a dead spot around 2400 where it wants to drop a bit, but pressing the accelerator pushes the RPM's on up. I'm going to work on adjusting the TPS today, as I understand, it needs to be fairly precise in its position.

Thanks again!


leelaw
Novice

Jul 29, 2017, 10:07 AM

Post #12 of 13 (820 views)
  post locked   Re: Mazda MX-3 surging  

Adjusted TPS while engine was running at troubled RPM until it smoothed out. Tightened it down, and I'm back on the road. Running great.


Tom Greenleaf
Ultimate Carjunky / Moderator
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Jul 29, 2017, 11:19 AM

Post #13 of 13 (813 views)
  post locked   Re: Mazda MX-3 surging  

OK - I'll consider the "surging" solved and close this out. YOU may ask any moderator to re-open it if you wish,


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