Anyone know where I can get a custom MAP sensor
calibrated to operate from 10-14 instead of the factory 14-18 inches vacuum

 

It's Manifold Absolute Pressure, so it's 0-30.

I've played that game, and you want to just use the stock one, and get the prom right. There are too many places in the code for things to get screwy, or need adjusting after doing something like that.

 

Yea Grumpy, we all know what MAP stands for. But the absolute pressure isn't pressure at all. It's vacuum. And a factory MAP sensor is calibrated to operate at 0 atmosphere which is 1 bar which is 14.7.As no engine operates at exactly 14.7 the base range is 14-18 inches of water (vacuum) at idle speed which is normal for most engines with standard cams. When a larger cam is installed which causes the vacuum to drop below 14, then you can use a custom MAP sensor to give the ECM the info it needs. Ben Riggs TPIMAN1@aol.com can supply them. Phone 503-784-0587

 

I get MAP readings from 100 Kpa to as low as 15 Kpa (on deceleration). It makes more sense to recalibrate the eprom so the engine operates properly ALL the time.

"Mechanical fixes" tend to correct one aspect but skew others. Using an adjustable MAP to fix an idle problem will require either the eprom to be recalibrated to give the proper VE tables for normal driving or for you to constantly "adjust it" between "idle and driving". Sounds like a real hassle in stop n' go traffic.

Fix it right, do it once.

 

Just wondering, where did you hear of Ben? I live about 10 miles from him.........he built my 406................that's all I'll say.

 

Some of the stuff you are saying is right, except that you are obviously very confused.

Yes, the MAP sensor is calibrated to show PSIA (pressure, absolute), meaning that if you were to get a perfect vacuum on it, it would read 0. At 14.7 PSIA (standard atmospheric pressure) it will read full swing (~5V)
Your first big area of confusion is in your understanding of the various units involved. 14.7 psia is a standard english pressure in pounds per square inch, relative to a perfect vacuum. Vacuum is measured in inches of mercury, 30" is a perfect vacuum (or is it 31?) Thus, an engine idling at 18" of vacuum has (30-18)/30 psia pressure in the manifold, or 5.88psia. A rough idling race engine may idle at 8" of vacuum, which is 10.78 psia. At WOT, vacuum is 0, so MAP is 14.7psia.

Now that you understand the units, you can see why your notion that the factory MAP is calibrated to work at a certain pressure is silly. The factory MAP simply send a voltage based on the pressure at it's input. It covers the full range from 0 pressure (perfect vacuum) to standard atmospheric (no vacuum). The ECM has a look up table that knows that 3.8V is equal to X psi, etc.

I think what you were trying to say is that the factory MAP ECM is calibrated to work with a stock engine that idles at 18-20" of vacuum.
As glenn and grump have said above. The idea of fooling with the output of the MAP sensor is not a new one. It provides a mechanical kludge to trick the ECM into thinking you're idling when your cam doesn't pull enough idle vacuum, etc. This is a very flawed way to go about things however. If you're serious about making your car run right, you have to get into the chip. If you can afford to mod an EFI car, you can afford to burn chips for it. Just like you wouldn't tune a carb by sticking boogies in the idle air bleeds to play with the mixture, likewise you can't lie to the ecm to fix one thing w/ screwing something else up.

Example: So you have a racy cam that pulls let's say 12" of vacuum at idle, and the stock engine that the chip is for pulled 18" of vacuum at idle. So you use a MAP fooler to boost (actually cut) the MAP signal so that the ECM thinks you have 18" of vacuum at 12" and now your idle fuel curve kinda lines up better, and with some FP tuning it mayb be close. However, what happens when you're lightly cruising down the highway at 2500 rpms in your racy engine and you're getting 18" of vaccum. Well, since you've screwed up the integrity of the MAP reading, now the ECM might think you have 24" of vacuum or so. So now you're running WAY WAY WAY lean. Also, your timing will likely be on the too high side as well when set like this. So you're running lean, with too much timing, gee, i wonder how far you'll get before you cook your valves or crack a piston from the detonation?

And thats one small example of how fudged sensor readings just screw you over. Virtually every calcualtion the ECM makes will have a similar error factor in it just cuz you had to kludge the idle in. And if you start trying to band aid all of them, you're just gonna be chasing your tail. In the end you'll realize that a few simple PROM tweaks would have had you 100% instantly, and for a lot less money and hassle...

 

Alright, alright I've had enough. I'll just wait till I get the LT1 intake installed then do the tuning on the chip.
By the way Ed, it is not the moderators concern to the financial ability or inability to spend money on whatever vehicle mods they may do. BUT TO GIVE TECHNICAL ADVICE, NOT CRITICISM!

 

Alright, alright I've had enough. I'll just wait till I get the LT1 intake installed then do the tuning on the chip.
By the way Ed, it is not the moderators concern to the financial ability or inability to spend money on whatever vehicle mods they may do. BUT TO GIVE TECHNICAL ADVICE, NOT CRITICISM!

 

Thanks GlennL98, your advice makes good sense without all the BS

 

(Ben Riggs TPIMAN1@aol.com can supply them. Phone 503-784-0587)

If you already know who can supply them why did you ask the question in the first place?

 

Didn't know when I made the post. Found out afterwards.

 

I was giving technical advice. Fooled MAP sensors are a bad idea w/ flawed logic, by design. I think it's important for people to know that and understand why, which i explained. Sorry if you took it the wrong way.

 

Thanks Ed, I apologize also, I have never doubted your your technical knowledge. As I stated above I'm in the process of converting an LT1 intake to install now. I may be getting in touch with you for some particulars in the programming when I'm ready to give it a go. Thanks again, Wayne Scott

 

Wayne, where did you hear about Ben? Wondering if he advertises..............or how you heard about him?

 

Heard of him from some guy that had a chip for sale on Ebay. I ask him about getting a chip burned and he gave me Ben's number. Said Ben was his boss.