Hey all, I have been looking at a way to advance the timing on my TJ and think I have found it...
From what I can tell the only sensor that solely affects timing is the barometric pressure sensor. It outputs 3.7-4.3V @ sea level, and 3.2-3.8V @ 1200m.
Now I'm presuming should we alter the signal getting to the ECU to read say... 2.5V @ sea level (a resistor?) we could alter the timing about 5deg advanced...
I'm going to experiment with it so ill keep you all posted.
Could even have a switch or rheostat in the cab to allow adjustments from stock to advanced, for when no pulp is available...

I will keep you posted! :D

Oh yeh, meant to say in there, any reasons why this would be a bad idea (do you know something about baro sensor i dont...)?

You're talking about ignition timing? You might find a certain crank angle sensor foiling your plans.

Sounds about as convincing as the $10 "performance chip" you can buy from eBay. :doubt:

Why would the pressure sensor affect timing? Wouldn't it combine with the MAF sensor output to affect fueling? (i.e. less dense air = rich mixtures -> pull fuel out)

I'm with those guys ^^

Don't see what the pressure sensor has to do with ignition timing. The only sensor I can see having an effect on timing is Crank angle.

And without the aid of diagnostic software, I seriously recommend leaving that **** up to the professionals, since the car isn't equipped with a knock sensor. Infact - even with diagnostic software - it's a job better left to professional tuners.

And without the aid of diagnostic software, I seriously recommend leaving that **** up to the professionals, since the car isn't equipped with a knock sensor. Infact - even with diagnostic software - it's a job better left to professional tuners.
Haha I didnt....Now yes my engine is completely differend to the 6g74, I thought I might be able to add 2c.....I made a mark in whiteout line on the main pully, then undid a bolt that holds the crank angle sensor firmly down. Using a timing light, the line *should* line up at the 10' mark. (+ or - a degree)...keep in mind the mazda BP engine runs standard 10' timing. By turning the crank angle sensor, i adjusted it to 14' timing, tightened the fastening bolt, made sure everthing was kool, and disconnected my light. No major difference in power, but a little extra in torque. The main changes are its happier to rev, and fuel consumption (using 98ron fuel) is now a bit better than standard timing on 91ron

First up, i did think about possibly lean mixtures. This is easily solved as i have an adjustable FPR on there. (not that i think i'll need it)
Second up is the barometric pressure sensor function is detailed in the workshop manual (which i have on cd) and is not listed at all on the fueling system diagnostic charts. This led me to beleive that it wouldnt affect fuelling calculations... that is left up to the tps and maf.
As for the lack of knock sensor, well, thats what ears and bp ultimate are for... lol
I could always run a pyrometer and cold plugs just to be sure.
And last of all the crank angle sensor won't foil this idea becuase this modification fools the ecu into adjusting the timing, so it won't try to correct it...

It is very similar to the ebay 20$ "chips" except they use the air temp sensor or coolant sensor, which can result in false air flow readings, and also affects fuelling... not many cars have barometric pressure sensors and i hope this might yeild a better result...

Any more input is still welcome, i hope to get this done on saturday or friday... i havn't gotten my rheostat or timing light yet though so i can't experiment...

Well, all I can say is, make sure you let us know what you learn (and good on you for getting off your @ss and trying something different). To be honest, I didn't even know our cars had a barometric pressure sensor, and if it's not used for fuelling, then I can't imagine what the hell it does (undocumented onboard weather predicting computer maybe :confused: )

Anyway - Good luck!!

Second up is the barometric pressure sensor function is detailed in the workshop manual (which i have on cd) and is not listed at all on the fueling system diagnostic charts.

I just had a squiz through the workshop manual. As far as I can see the barometric pressure sensor is an integrated part of the air flow sensor; indeed its output is on the same harness the rest of the airflow sensor along with an air temp sensor and the mass air flow signal itself.

I'm still not seeing why you think it affects timing? I'm not saying you're wrong here, just that I don't understand your logic. Can you publish the page numbers you're looking at?

I've been reading 13A p.61 #25 and 13A p. 67 for the behaviour of the sensor, and 13A p. 88 for the location.

ok, i hunted about, first ref is (13A Pg 1 Para"Ignition Timing Control") says "The ignition
timing is determined by the Engine-ECU from the engine speed, intake air volume, engine coolant temperature and atmospheric pressure."

I also just noticed if you see 13A pg 3 and 4 input sensors, one of the mentioned sensors is knock sensor....:shock:

In 16 pg 24 we have "When the engine is cold or operated at a high altitude, the ignition timing is slightly advanced to provide optimum performance to the operating condition."

However... I have noticed that the fuel injection system troubleshooting page lists the pressure sensor as a possible culprit of rich fuel mixture...

11A pg 6 states "NOTE 1. Ignition timing is variable within about 8deg, even under
normal operating conditions. 2. And it is automatically further advanced by about
5deg from 15degBTDC <6G72> / 10degBTDC <6G74> at higher altitudes"
thus implying pressure sensor can advance timing...

a rich fuel mixture will at least pose less of a problem than a lean one... i can always just lean it out with the FPR... hmmm will soon know...