Diagnosis Challenge
 

I'm running out of ideas here, so any intelligent suggestions would be appreciated. Here is the story.

When the temperature drops, to 40 and below for instance, the check engine light comes on whenever the engine is under load. It also lacks power, according to my ass dyno. The malfunction code is for the pressure sensor, but the sensor passes the tests described in the factory service manual. Note that the error light does not turn on at idle or low load.

When the temperature warms up the check engine light no longer comes on, but at lower temperatures the engine seems to lack power, specifically from six to eight thousand rpms. When the temperature starts nearing 80 or so the car seems to do just fine. Note that engine temperature seems to have no impact, as these conditions do not change when the engine goes from cold to hot.

I first thought it must be an intake leak, but smoke testing showed no leaks (which is good, 'cause I spent time and money to get them all plugged). I next thought that it must be the intake air thermosensor, but replacing it (I broke off one of the connector tabs while attemping to test it) did not fix the problem. I also checked the the air-flow meter, and it passed as well. I intend to check the water temp sensors, but I do not believe they are the cause.

So what else can I do? Unfortunately the error light was the only good way I had to tell if the problem was fixed, as ass dynos are rather unreliable. Maybe a standalone a/f monitor would be able to tell me when a/f ratio significantly deviates from stoch, but it wouldn't help me narrow down the cause.

I have the exact same problem...

Suggestions anybody ???

Have you tested a different pressure sensor?

Yep... I'm looking for an AFM and an intake air thermosensor(engine) to see if it makes a difference. So far no response here in the RX7 forum in quebec :(

unplug the thermosensor on the back of the water fill neck. do this both when its cold, and when its warm. see if you get any changes.

i would check the wiring in between the ecu and the pressure sensor.

actually, which sensor are you checking? code 14 is the sensor IN the ecu, in which case you need to replace ecu and recheck.

the other one is the one on the shock tower (code 13 afik?), check the wiring, and then try a different sensor.

also have a good look at the vacuum line, is it good? does it go to the right nipple? does it have the restrictor in it?

unfortunately the CEL is your best clue, so you need to chase that.

It'the code 13, the pressure senror. I doubt it's the wiring cause it only happens when the weather is cool/cold (the colder the temp, the more sensitive the CEL)...

Checked the vacuum by adding pressure in the system (found a leak :)) but didnt solve my problem...

Changed the vacuum that goes to the pressur sensor and bought the restrictor... nothing changed !

check the 5 volt ref signal to the AFM and pressure sensor. next up would be to reground that passenger side wiring circuit through the AFM, pressure sensor and TPS and cleaning the grounds on the battery, driver side strut tower and at the starter. then last but not least, clean the main injector ground at the rear rotor housing.


25 year old wiring can be a bitch and wires need attention too, usually last on people's list of things to check/clean.

Interresting... but I need more precision !

All my grounds were cleaned when I changed my shortblock...

Changed my AFM and everything seems to be working perfectly so far :nod:

Thanks everyone !