Savoelh

So about 3 months ago I dropped my car off at Mazda because of loss of compression at about 6k RPM, and on top of that it would stall on me once it got to a warm engine.

So far Mazda has replaced the:
-Engine
-MAF
-Fuel pump
-PCM
-Coils
-Coolant temp sensor

The loss of compression at 6k RPM is fixed. However the car still stalls after sitting on a warm engine. I could be mid-throttle sitting at 3k RPM and it will decide to stall. It only happens on a warm engine. The car doesn't have any problems starting back up again, but it soon stalls again after driving a few yards.

Mazda told me that when they hook-up my car to their scanning tool that it reads that my car is always -35 degrees. Even when it is running and fully warmed up. So now they are suggesting that I need to replaced the engine harness due to a possible short. But I dont see how that has anything to do with the engine not idling properly. So I am asking you guys, what do you all think?

RX8Soldier

iTrader: (24)

could be a lot of things.
Compression
MAF sensor
fuel pump
eccentric shaft position sensor
etc.

wcs

iTrader: (2)

What year is your car.
Are they telling you the coolant temp sensor is reading -35 or the IAT sensor?

The temperature the ECU thinks the engine is operating at has a HUGE ... f'n HUGE impact on how the engine will idle
Both with coolant and or IAT

Savoelh

The car is an 05. And I am not sure if its the IAT sensor or not. But they did say that the coolant temp sensor was working fine.

wcs

iTrader: (2)

Check Cat
Check Plugs
Clean ESS
Listen for Vacuum leaks

Doesn't sound serious just annoying

Savoelh

Plugs have already been replaced, The cat has been checked but as for the ESS I have no clue as to what it is or if it has been checked. I will look into the ESS and check for vacuum leaks.

Thanks for the suggestions.

RX8Soldier

iTrader: (24)

ess = eccentric shaft (position) sensor.
https://www.rx8club.com/series-i-tech-garage-22/tired-searching-ess-cleaning-206687/

dannobre

iTrader: (3)

They should check the wiring harness between the sensor and the PCM...would take all of 5 minutes to rule out the wiring for one sensor

If it is open they could run new wires for that sensor without replacing the whole harness that they will want a fortune for....Engine harnesses are easily screwed up when replacing the engines if you aren't very careful

The car will not run for **** if it always thinks it is that cold....

fish1

strange, I have an 05' and had the same problem with the engine temp sensor saying the engine was constantly at -35....
I'll have to go through my bills to see what they did to remedy the problem?
keep in mind this problem was occuring on an engine that was eventually replaced under warranty due to low compression.

Savoelh

I would like that fish1. Maybe you can help me with a cheaper way how of this :P

dynamho

Hmmm. Interesting... the same -35 deg temp reading after engine replacement? Subscribing...

Savoelh

Here is a link about Coolant temp sensors.
http://www.aa1car.com/library/coolant_sensors.htm

Here is a small section in the link about how the coolant temp sensor affects the engine.

* Open/closed loop feedback control of the air/fuel mixture. The PCM may ignore the oxygen sensor rich/lean feedback signal until the coolant reaches a certain temperature. While the engine is cold, the PCM will remain in "open loop" and keep the fuel mixture rich to improve idle quality and cold driveability. If the PCM fails to go into "closed loop" once the engine is warm, the fuel mixture will be too rich causing the engine to pollute and waste gas. This condition may also lead to spark plug fouling.

There is also a section about diagnosing the coolant temp sensor. It says:

* On vehicle systems that provide direct access to sensor data with a scan tool, the coolant sensor's output can usually be displayed in degrees Centigrade (C) or Fahrenheit (F). The coolant sensor should read low (or ambient temperature) when the engine is cold, and high (around 200 degrees) when the engine is hot. No change in the reading or a reading that obviously does not match engine temperature would indicate a faulty sensor or a wiring problem.

Maybe one of these things are happening to me. I also took a look at:
http://foxed.ca/rx7manual/2003mazdarx8/
To be honest I do not understand 1/2 of the procedures that the site is asking me BUT I eventually found myself looking at:
http://foxed.ca/rx7manual/2003mazdar...html#wp1025486
So I think I have a short. Does anyone know of there is a way to detect a short within the engine harness? Could an obd2 do it?

dannobre

iTrader: (3)

Multimeter....