dookie454

This should work exactly the same for OBDII.

2 Bar MAP from the older Sunbird Turbo from mid 1985-90 is what I have.

Running unboosted shouldnt matter, just get on the boost slowly/limit rpm as you tune it.

Eric Bazan

Is there an easy way to identify a 2 bar map sensor? I got a sensor here that was sent with an old T-trim set up I bought a while back. I believe its a 2 bar. The sensor is made by wells and has a orange/red insert at the wiring connection. I tried looking up the number printed on the sensor on wells site, but it comes up with nothing.

Thanks,

Eric

97s10ondubs

I see you have 83lb injectors, who makes them, and what converter box are you running?

cjmatt

fyi, I believe racetronics nw sells 83 lb injectors that u dont need a converter box for. The Grand National guys are starting to run them with good results

97s10ondubs

They are 79lb and I'm seriously considering them, but dont see anyone running them yet.

dookie454

I run the AEM box, it was the cheapest I could find. Seems to work perfect so far.

Found this a while ago:
2 Bar:
GM part # 16009886
Wells part # SU-129
standard part # AS-4
91-93 GMC Syclone & Typhoon 4.3 turbo
87-90 Pontiac Sunbird Turbo 2.0
84-86 Sunbird (actually any J-car) turbo 1.8
886, 012, 539, 609, 701

97s10ondubs

Just came up with another question, what happens if you want to run more than 15psi, should you get a 3bar sensor?

engineermike

I'm finding that the lost resolution with a 2 bar does in fact slightly hurt the tuning ability. With a 3 bar, I think too much resolution will be lost.

You have to consider that most of you cruising is done in 3 columns normally (I think 50, 55, and 60 kPa). With a 2 bar, it becomes only 2 columns (25 and 30 kPa). With a 3 bar, it would probably become 20 only and there are no columns below 20.

Mike

Highlander

I guess.. that being in stock form the best computer would be the ls1 computer with the added tables....

engineermike

I had always assumed the stock ECM uses linear interpolation for values between cells. Based on some stuff I've seen, I'm starting to think it just rounds the value up or down to the nearest cell.

Mike

Highlander

They have always said interpolation... and it might be true. I guess the problem lies in the MAPS own accuracy. Remember that they still use 0-5v range... so the more "maps" you ahve to fit in 5v the less resolution you get via the sensor ONLY. Add to that, the interpolation and you can have a huge discrepancy...

Even still.. i have tuned a few boosted engines with the ls1 computer having 0 issues at all.

One way to find out if its the computer or the sensor is to use an older type 2bar sensor like the ls1. (there is a 2 bar with the shape of the regular ls1 map sensor)...

In the end, I am sure its the lt1 pcm.. why? simple.. its too slow, proof??? do a speed density tuning with an ls1 computer vs an lt1 computer and you'll be amazed at the differences in both...

What i will do is use a Pro-M maf with yet another converter to patch up the stock pcm....

I wish the bs3 controlled the cluster well...

dookie454

Once again Im not seeing one issue at all with the 2 bar on the LT1 PCM (no issues = no problems = nothing worth improving). Specifically what would I be amazed at when comparing to LS1 pcm? I have instant crisp throttle response at any rpm/load level (even with 83lb injectors), no lean/rich spots and no timing problems, even running closed loop.

Dont know how switching to LS1 PCM would fix improve on that. I guess a better example would be good here (I dont understand how the LT1 PCM being slower than LS1 could affect anything??). If your running a larger cam than myself maybe that could uncover something with the reduced resolution however I wouldnt benefit from more resolution at this point.

I did hear the LS1 PCM could be modified to allow 2-3 bar tunes, that's nice for obvious reasons however has nothing to do with speed of the PCM.

I think it comes down to proper tuning/cam profile since my 2 bar LT1 PCM is better than my 1 bar tune ever was and couldnt expect it to be any better since there's nothing I would improve on (unless I switch to 3 bar sensor then I'd have to do something).

BTW, im not trying to act like im puposely ignoring something just trying to figure all this out... so far I havent found a problem and trying to figure out where all the bad rap originally came from. From what I was reading alot of the negative experiences were from people who never tried it or put much time into tuning it. I do think there's less room for error with this setup.

STSturboLT1

I overcame the lost resolution with my setup (not that it would have likely been a problem anyway) by adding an op-amp circuit to the MAP sensor to scale the output voltage to maximize the use of the 0-5V range. I'm only running 7 pounds of boost but using a 3 bar sensor + circuit makes it effectively 1.5 bar. So if you were running something like 18 psi, you could add a similar circuit to scale a 3 bar sensor to ~2.5 bar to get some resolution back.

engineermike

It's a good idea, but I want a 3 bar but am having some minor resolution problems at 2 bar.

I would need a circuit that adds resolution in the 0 - 1 bar range, but reduces it in the 1 - 3 bar range. My 0 - 1 bar output would need to be 0 - 3 volts, while 3 - 4 volts would be 1 - 2 bar, and 4 - 5 volts would be 2 - 3 bar. I think that would work. Too bad we can't reformulate the lookup function in the ECM. . .

Seems to me that the VE changes very rapidly around 50 - 60 kPa in the 1500 - 3000 rpm range. But, once you get over about 80 kPa on up toe 300 kPa, the changes aren't much, so you dont' need much resolution there. I could probably just stick one number in the table from 100 kPa on up and it run just fine.

Mike

STSturboLT1

It should be possible to come up with a non-linear amp circuit that works similar to what you're describing. I'll let you know if I come up with a way to do that. Like you said, it would be nice if the PCM functions could be modified instead, it would be a lot easier.