Hi guys sorry for dragging up an old thread but need to shed some light on a strange problem.
background to this thread. ..bought an rx8..hot start problem no cel lights whatsoever. ..
drove 70 miles..cut it out at a set of lights. .had to wait 20 mins to restart..to be expected. .
leftcar lying for 3 months
engine removed and rebuilt. ..took omp position sensor off pump to prevent it being broken. ..
Marked position of sensor before i removed it.
engine put back in with new clutch radiator spark plugs and coils.also new battery.
omp position sensor replaced...have put 500miles on car without any faults...brake caliper locked up as a result of being left lying..car left for 3 weeks...calliper rebuilt 3 days ago.
this morning drove through torrential rain. .front under pan u
is present. .cover immediately under engine is missing.
After 30 miles left car idiling in my workplace car park. ..cel on in limp mode.
left car..
came back 4 hours later limp mode gone cel stil on
disconnected battery for an hour. ..blanked cel..
drove home..30 kms...no problem. ..again went to park car...cel on limp mode.
read codes half hour ago. P1688
​​​​​​​so its definitely an omp intermittent fault....
so i would like to draw on the knowledge of my fellow rx8 enthusiasts.
i spoke to a specialist today he said if the omp position sensor was improperly set it would have shown up way before 500 miles and that the pumps rarely break.
..i haven't got under the car yet but would like help narrowing the possible problems down..
so
is it
.dirty/wet connection on sensor
broken sensor keeping in mind that the problem is intermittent on stopping after a long drive.
.broken pump.
or going against my spealislist 's advice improperly set.
from what i understand of the positioning sensor its fully clockwise/maximum flow ...this is how it arrived to me

 

Yeah you should have never messed with the position sensor.

 

yeah thats what the specialist said too😂but i did and now i have to fix it...
anything constructive to add

 

You can try adjusting it until it works. But I assume you tried that already.

 

..it worked for 400 miles after i replaced it in exactly the same position it came off..only acting up now...do you think i should try re- adjusting

 

Yep.

 

1688 code seems to point to open circuit on the omp position sensor
1687 ..high flow
1686 ...low flow
If the sensor was improperly set would it not be 1687 or 1686
My dtc is 1688...initial check of control circuit
Ie:is the control system present and correct
​​​​​​​

 

So break out the meter and find out.

 

On further investigation the omp cel 1688 is being triggered only on hot starts?

 

Is this a statement or a question?

 

It doesn't cost anything but the time & effort to try. I'd do that before anything else. Anything else is going to cost a lot of $$$$ because the only other solution is replacement.



.

 

Im going to look at it today. ..The weather has been very bad so couldn't get near it....
yeah if i have to readjust i will...
im going to start by unplugging the sensor and power lead to the pump one by one and starting the car to see if it triggers 1688 i would like to see if i can find a definitive answer to code 1688..i suspect that code 1688 is open circuit on the position sensor..but if not its adjustment time

 

Sitting in the rx8 now...took position sensors of...did reset...it was perfect original position. ..what i did find was a weep from a cooling pipe above the sensor...the sensor stank of coolant...
it was shorting out cos it was wet...connectors wet aswell...
Connector cleaned and dried five hot restarts no problems. ..

 

You can see the red coolant
Coolant pipe directly above omp pump
​​​​​​​Pipe started weeping after half an hour running. ..omp pump wet
cel on again. ..its a leaky pipe shorting out the sensor
​​​​​​​

 

For anyone thats interested. ..engine running with position sensor disconnected produces code p1687 High flow
p1688 is produced by disconnecting the main big square socket. ..power for the pump etc..obviously indicating a problem internally in the pump.

 

Pipe not leaking when cold
​​​​​​​..once heated up its weaping..hence my omp problem when hot

 

Hose isnt even split. ..just one of those stupid spring clips not seated/gone weak...
​​​​​​​ill put a jubilee clip on it tomorrow

 

So I've stopped the leak above the omp pump completely. ..
and after 3 or 4 starts and a good thrashing the cel light is still being triggered. ..it was every start when hot before. ..now its after 3 or 4 starts and only when hot the light is coming on and limp mode.
Is it possible getting drowned in coolant has damaged a microswitch inside the omp pump
ive reset the pump and the sensor so im going to use electrical connection cleaner on the omp pump connection after that i think im looking at a replacement but im open to suggestions . ..i disconnected both the big square connection and the position sensor while the car was running to see what cel was triggered. ..its something internal in the pump because the position sensor triggers a different code on a dead short/disconnection
...the car was a bit down on oil today so im pretty sure that the pump itself is pushing oil

 

check the series I manual - it may take up to 12 cycles to clear the code & limp mode

.

 

thats some very useful schematics...Thanks bro
I've been erasing the cel light with a generic obd2 piece of software. ..
ill clean all the connections with contact cleaner..erase the cel again. ..disconnect the battery for an hour. .
this fault is so annoying. ..
comes on when hot after 4 runs and then dispears when cold leaving the cel recorded...
its definitely heat related. ..
The funny thing is i tried it 9 timesin the driveway...
no light...when hot..but after a long drive and a restart its triggered. ..
Ill have to try the wiggle test...again 😠

and disconnect the battery for an hour. ..

 

Keep us in the look on the "reset".

 

This unit was corroded inside...with the help of a can of electrical connection cleaner I've completely solved this problem. ..due to road water/a coolant leak above the pump the pump sensor sprocket /moving mechanical part was partially locked up. ..not enough to cause a constant cel but enough to be intermittent. ..after a thorough clean of the above mechanism with the elecrical contact cleaner i also drownded the entire position sensor in it...
​​​​​​​

 

After cleaning up the parts i discovered that both the pump flow position unit and the position sensor are spring loaded...the spring mechanism on both units was locked up /stiff.
both units should return to zero position under their own power. ..
its impossible if both units are clean and working properly to install them in the wrong position. ..mazda or whoever manufactured the pump made it so would always return to zero position under a simple spring power..i suspect a lot of these omp problems are a result of partially or fully locked up mechanism. .
i don't know if the north American rx8s have the same spring set up but this European one does.
have started the rx8 today 31 times in a row..used a laptop and software to monitor the temperature. ..31 starts from 90-98.c no cel...
​​​​​​​

 

Apologies for copying the above pic my hands were too covered in contact cleaner to use ny ph

 

OMP failures are rare. But yeah coolant leaking on stuff in generally not good. Glad you got it fixed.