MAP and fuel tables

Anyone happen to know what the minimum value the MAP sensor needs to read in order for the PCM to deliver max fuel?

Not sure what you're asking.

To my knowledge the PCM will fuel fully up to 23psi, then defuel if it doesn't have a map fooler.

A regulator, BRV, or resistor all do the same thing, only let the MAP sensor "see" less than 23psi, so no defuel.

Well what I'm wanting to know is that if the PCM sees low boost, will it also cut back on the fuel?

The reason I'm asking is during live tuning Jody discovered that my MAP sensor was only reporting 13 lbs of boost to the PCM at WOT, when the gauge was reading much more. I've got that fixed now so the MAP is reporting 23.7 lbs of boost at WOT (and no overboost code), but I don't know if there is going to be any noticeable difference because of it. It'll be a few weeks before I make it to the track again.

Yes, boost does control fuel. Talk to Jody and see if he addressed those tables after he found your MAP sensor problem.

Curtis so what was the problem bad map sensor?

Tom

Yes, boost does control fuel. Talk to Jody and see if he addressed those tables after he found you MAP sensor problem.
Well he told me to fix it and I would probably see a bit more fuel, so I'm sure he set the fuel tables so I would see max fuel with a fixed MAP. Guess I'll find out next time I'm at the track. So far my truck won't break past 15.4's, so if I'm under that time then I'll know it made a difference.

Also he was mentioning that even the exhaust backpressure sensor can have an effect on the fuel tables. Right now my sensor is capped off so it doesn't actually read anything but normal air pressure. I know that extremely high exhaust backpressure can set a code and possibly cause a defueling situation, but what can it do for fueling?

Maybe next time I'm at the track I'll make a few passes with it capped and not reading exhaust backpressure, then reconnect it and make a few more passes to see if there is any difference. Good or bad results, I can post them up for everyone.

Curtis so what was the problem bad map sensor?

Tom
No it was actually the overboost annihlator. I have no idea how it was misadjusted. I must have accidently knocked it or something. It's been on my truck since I first chipped it, and up until recently I was always reading normal boost from the MAP on AE. In fact about 3 months ago I had AE hooked up and reading boost and it was hitting 22 lbs. That was right before I installed the Terminator setup, so maybe I knocked it loose during the install of the HPOS. :shrug:

Well at least it was a cheap fix. I was under the assumption that the EBP sensor might start pulling out fuel if it got too high of a reading. Is my assumption right or wrong?

Tom

Well at least it was a cheap fix. I was under the assumption that the EBP sensor might start pulling out fuel if it got too high of a reading. Is my assumption right or wrong?

Tom
Yeah I believe it will defuel a bit if it's too high. I started having that problem a while back when the sensor tube was getting plugged with soot. MIL came on and truck started to wheeze out at WOT. My fix was to pull the sensor off the tube, plug the tube, and cap the sensor. It's been that way ever since and never given me issues. However Jody noticed that my backpressure sensor was always reading normal air pressure during tuning, and mentioned that it might have a very small effect on my fueling. So I may play around with that a bit next time I'm at Bandimere and see if it does anything. At least I'll have some kind of numbers to back up these tests.

There's two things that will happen. Either it will have a slight effect, and if you want to squeeze every bit of performance out of your truck you'll keep that sensor tube clean.

The other is that it won't have any noticeable effect, and we'll have a nice cheap new mod where you never have to clean the exhaust backpressure sensor tube again.

I put a EBP sensor eliminator on my truck after live tuning. DIdn't really notice anything in SOTP but it could have been a slight improvement.

Mine was really wack anyway. Read 30lbs of back pressure at idle, and went to 50 under any throttle and just stayed there...

I think that the map sensor has to see 17 lbs. boost to deliver full fuel.

Deleted due to ...uhhh I didnt read all the posts.:bow: