synesthete

Ok, so i borrowed a multimeter cause i apparently lost mine and i have been checking out stuff on both my 7s. Looking through the manual i discovered something odd...

My GXL has a n327 pressure sensor which is the same sensor i have in my turbo.
According to my manual i should have a boost sensor there. I thought at first that my manual was wrong cause my gxl doesnt have boost, well not really, but i searched and from what ive read it sounds like i have the wrong sensor.

So I unplug it from its harness, not having a vacuum pump i cant really test its voltage reading so i just want to see if it does anything different. My car starts up and i imediately notice a small difference in exhaust tone, sounds a little louder or something.

I drive it around and the motor seems to be running very strong, and responds to throttle at low rpm much better, and the exhaust tone is quite different too. It sounds more like a chainsaw and less like a airplane, which leads me to believe that it is running leaner. Standing outside the car at idle i can tell it is definately running leaner. The engine still starts/idles/runs very smooth.

So I have 2 questions...
1. Do i really have the wrong sensor? (I don't know how this could have happened)
2. Is leaving the sensor unplugged dangerous?

Edit: My turbo actually has a n318 but still reads pressure sensor.

synesthete

ok, so i searched some more and i guess n327 is the right sensor for an NA. But i also read that it should make my car run rich to unplug it...

Thats contradictory to my senses, sounds like its running leaner and doesnt smell as bad. Guess i'll just have to get a vacuum pump and test the stupid thing.

Icemark

A 87.5-88 non turbo would use the N327 pressure sensor.

Your Turbo should not be using that sensor. It should be using a N318 if it is a S4, which your edit says you have.

And yes, the pressure sensor needs to be connected to run right. The ECU uses its input to determine load

jgrts20

my car runs better too, without it connected. Runs like crap with it connected, but I probly have a bad sensor. Oh well puts me closer with installing my new motor.

synesthete

Could icemark or anyone explain load for me? Since im not sure I know what that really means.

According to the training manual the failsafe on the ecu for the boost sensor is -96mmHg (-3.78 inHG) Is that high or low load? How would that then effect AFR?

I plugged it back in, and it seems to be richer again just judging from sound and smell. It seemed much louder when it was unplugged and this is my dd so i didnt really like that, it had much more roar to it, but it was noticably quicker to respond to throttle at least... wierd.

HAILERS

Syn....what your missing is this. THe n/a sensor puts out a given voltage at atmospheric pressure. The Turbo sensor puts out a different voltage at atmospheric pressure.

If I go to my turbo car and install a non turbo sensor on it and just turn the key to ON, NOT START, the boost gauge will almost peg out, whereas if I install the turbo sensor the needle when just turning the key to ON, will make the needle go to just under zero.

Get it???? The n/a sensor is giving the ECU a signal that the car is in BOOST when in fact the engine isn't even running. That messes up timing and idle and ???? stuff.

synesthete

OK, that makes sense. I'm not swapping them around or anything and i confirmed that the sensors were different and both were the correct model for the cars. I thought they were the same at first but looked a little closer.

I'm wondering what it is your refering too when you say low or high load. I'm assuming it has something to do with vacuume strength, or the amount of air being pulled into the manifold.... but i honestly have no clue.

I'm just looking for someone to explain the concept of load, maybe thats a simple question so people are mis-understanding me. Just wondering why we are seeing better performance with the boost/pressure sensor unplugged on our NAs.... is it because of the change in timing like you were talking about, or is it AFR? Maybe it only feels faster but really is just responding faster... i don't know i'm just trying to understand how it works.

Thanks for any info, i am a newbie when talking about the physics of car tuning.
I don't know a lot of the terms like load and im just searching for a general definition and anybodys experience with how the ECU uses this reading.

I'll try another question... Under high load how does the operation of the car change vs under low load?

Like i said I'm just curious, i dont have any real problem just trying to understand.

HAILERS

Well, you can reach over a hundred mph using a light pedal and never getting into BOOST.

That would be a lack of LOAD.

But if you floor the pedal at say 2500 in fourth gear and go up to over 100 mph, you'll be boosting over atmospheric pressure for sure. More like sever plus psi boost pressure. THAT would be under LOAD.

Your secondarys open only under LOAD and being over 3500rpm. I know not the exact figure that is required on the boost gauge but I'd reckon over 2psi for sure, on a turbo car.

So the LOAD would be somewhere over 2psi. Anything under zero boost would certainly be a case of not under load. The afm might also play a function of what LOAD constitutes.

A case in point is a n/a car I have. IF I remove the vacuum hose from it's pressure/boost sensor and plug it, then go for a drive, the secondarys come on line each and every time I reach 3500rpm. Been there, seen that. It's even been given honorable mention in the 87 fsm.

I'm pretty sure I've done this with my turbo cars also (which would mean my 2psi figure above is bs and the real figure is zero boost or atmospheric pressure)

In other words the pressure/boost sensor plays an important part as to when the secondarys come into play AND the timing.

Someday buy a RTEK2-0 and watch the Lead and Trail timing figures for different throttle settings. It'll surprise you how much the timing goes advanced/retard/inbetween on a normal everyday driver car.

synesthete

Thanks for explaining that.

So let me see if I understand...
The pressure sensor is reading the vac strength from the manifold.
So the pressure sensor and the afm are used by the ecu to judge if its getting enough air for your throttle setting?

So the failsafe default of -96mmHg (-3.78 inHG) is probably telling the ecu that its constantly under load. I wonder if that value is just the minimum needed to trigger secondary injection.

HAILERS

Download the Series five FSM section for FUEL. Go to page F2-74 where there is a Relationship Chart. That might be of some help.

Phantomkid

hmm. a while back i was really into the whole pressure sensor thing trying to unlock the secrets of the n318 ecu. The na map will send more voltage at atmospheric pressure so if your running the na map sensor with the turbo it should run rich. the reason you see better perfomance with the map sensor unplugged is it changes the fuel map to a richer map. If your running the n318 ecu many people run the turbo map sensor with the n318 vert ecu. And it works fine thats why im confused i believe the vert na map sensor reads like the turbo, and the maps are very similar. yea ive been trying to figure that out but i gots me a t2 motor to put in my vert. im gonna try both the na map and the n318 turbo map.