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Canucker
Dodge Dakota
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9/12/2002
14:39:06
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 Subject: MAP Sensor ... Bernd? Anyone?
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Does anyone know exacly what the PCM uses MAP sensor info for in terms of
fuel and spark adjusting? (not in terms of deciding whether to operate in
closed loop or not).
The reason I ask, is it is one of the only sensors that is still read during
WOT, open loop operation. Wouldn't it be possible to trick the PCM,
similar to the IAT adjuster concept, by offsetting the voltage value that
goes into the PCM one way or another?
From what I could guess, with a decreased pressure reading, the PCM would
a)retard the timing and b)increase fuel right? ... if you tricked it into
reading a higher pressure (i.e. less vacuum and less load), wouldn't it
increase timing and decrease fuel? ... if you did this, you'd have to get
around the decreased fuel somehow ... maybe just increase the fuel pressure
to offset? or use a hypertec AFR controller? and tune the A/F ratio on the
dyno to get optimum ...
without the AFR controller, this would be way cheaper than a PCM flash, and
in conjunction with the IAT, it might be effectively the same thing w.r.t.
timing and fuel at least.
Any thoughts, or am I just blowing smoke outta you know where?
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Canucker
Dodge Dakota
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9/12/2002
17:25:27
| RE: MAP Sensor ... Bernd? Anyone?
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Anyone??
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Chipster
Dodge Dakota
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9/12/2002
17:41:08
| RE: MAP Sensor ... Bernd? Anyone?
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The MAP sensor compares the pressure in
the intake manifold to the internal pressure of
the MAP sensor (usually near a perfect
vacuum). The difference of these to pressures
is the manifold absolute pressure. It is
expressed as an electrical signal to the PCM.
By using the MAP, TPS and intake air temp
sensors, the PCM comes up with a calculated
value for the amount of air entering the
engine.This is called a speed density fuel
injection system.
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Duner
Dodge Dakota
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9/12/2002
18:00:04
| RE: MAP Sensor ... Bernd? Anyone?
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When you get to WOT, the MAP sensor is reading zero vacuum. That among other things is the PCM's cue that you are in fact at WOT which sends it into open loop. I don't know this for fact (I could be wrong) - but changing the MAP sensor signal (voltage) going to the PCM would probably just keep it in closed loop longer. The problem with that is it will be using the inputs from the O2 sensors.... which will trim back the fuel and probably cause the truck to ping if the timing is still advanced. Upping the fuel pressure wouldn't cure this because the PCM would keep trimming the fuel until it was closer to stoich.
Good idea though.... the system is just too constricted to allow much playing.
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Canucker
Dodge Dakota
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9/12/2002
18:23:15
| RE: MAP Sensor ... Bernd? Anyone?
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hmmm .. I see your point Duner...
wouldn't the TPS be the #1 indicator that its at WOT .. that alone _should_ be enough to throw it into open loop. ??
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CW
GenIII
9/12/2002
18:34:22
|  RE: MAP Sensor ... Bernd? Anyone?
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My thoughts would be to have fuel pressure that only went up when vacuume went down.
2001 4.7 5sp 3.92 LSD
Ported 68mm TB, IAT adjuster, 3" flowmaster cat back, TPS @ .76V, 4" Z-tube, Roadmaster active suspention, Removed Third cat, Electric fan Convertion, HO cams, Robert shaw 180 therm, HO intake manifold.
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Canucker
Dodge Dakota
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9/12/2002
18:51:27
| RE: MAP Sensor ... Bernd? Anyone?
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Yeah you could be right too ...
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Duner
Dodge Dakota
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9/12/2002
19:50:48
| RE: MAP Sensor ... Bernd? Anyone?
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My understanding of the system is that the PCM looks at the MAP and the TPS to decide whether to go to open loop.
If the MAP gets to zero vacuum and the TPS is still showing part throttle - the PCM gets confused and the engine will actually chug or buck. The supercharger guys have had to deal with this fairly often. I can make it do it with the turbo also - but I almost have to work at it.
If the TPS tells the PCM it's at WOT and the MAP says it still has vacuum then it throws a code and says the TPS is out of range. People that have over adjusted their TPS have gotten this code.
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sicminds
GenIII
9/12/2002
20:08:21
| RE: MAP Sensor ... Bernd? Anyone?
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this could be a dumb question.....
So when you are WOT there is no vacum.
What exactly is the Vacum? I have been
having my 98 dak throwin the tps code
a couple times and then it goes away.
Could it be somthing with the vacum?
now you know thats..................
sic
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kota on 20s
GenIII
9/13/2002
00:16:35
| RE: MAP Sensor ... Bernd? Anyone?
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duner, how did you cure your problem of it chugging? or did it never chug bad?
also, do you run rich with the 24# injectors when not in boost? or does the pcm trim it enough?
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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Duner
Dodge Dakota
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9/13/2002
00:38:00
| NO CHUGGING!
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It never really chugged bad, mainly because the boost came on so quickly. With the S-3 compressor and wheel it would go into boost too easily. You would end up hitting boost at part throttle accidently unless you really paid attention. That would freak the PCM because the MAP said "no vacuum" which meant go to open loop, but the TPS was still at part throttle. That caused it to "chug" if you tried to back off the throttle to control the boost. If you just kept leaning into the throttle from that point it would just rocket away! That was lots of fun but sometimes smoking the tires is a bad thing! hahaha I would have hated to try and explain to some officer that I was just trying to keep it from chugging! hahaha
Now that I went to the 60-1 compressor and housing, it spools slightly slower but is MUCH more controllable. No more accidental boost, which means no more accidental chugging or tire smoke. That makes this combo about 10 times more "trailer towing friendly" also. The compressor change also increased the airflow/boost capacity by 50% more.... which SHOULD show up on the timeslips. (I hope)
The 24# injectors are no problem for the PCM in closed loop. It trims the fuel just fine. Perfect starting, perfect idle, perfect cruise. Way smoother than the stock injectors were. I'm still playing with the A/F mixture when in boost. It's still on the rich side, but not nearly as bad as it was in Tucson. The difference in altitude helps that also.
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kota on 20s
GenIII
9/13/2002
01:42:02
| RE: MAP Sensor ... Bernd? Anyone?
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the symptoms you are decribing are happining to mine. if i hit boost at anything less than WOT it chuggs like a bitch! REALLY BAD!! like hitting a rev limeter. if i can get into WOT before boost, it is fine, but then when i shift, it starts chugging again.
is there anything that i can do? i have not heard of anyone else haveing these problems. atleast not as bad as i am having.
did your gas milege suffer with the 24#'ders?
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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Duner
Dodge Dakota
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9/13/2002
02:00:40
| RE: MAP Sensor ... Bernd? Anyone?
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Have you tried relocating your MAP sensor? I have no idea if it's even effective for that - I just read about it on Bernd's website. The MAP sensor on the 4.7 isn't in the same place so it wasn't an option for me.
Do you have a blowoff or boost bypass valve? That might vent some of the boost until you are farther into the throttle. With mine - I can actually hear the boost being blown out when the turbo spools but the engine isn't using much of it. I'm sure that without the blowoff valve in place it would be chugging like mad at that point.
My gas mileage actually improved with the 24#ers! I'm sure it's because they work so much better at atomizing the fuel. It might also be partially because they are a balanced set. Either way I'm VERY happy with them.
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kota on 20s
GenIII
9/13/2002
02:11:24
| RE: MAP Sensor ... Bernd? Anyone?
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i have moved the vaccume line from the map sensor from the TB to the manifold.
i dont have a bypass valve yet (im working on that) and im SHOULD be getting some 24# injectors soon.
i guess we'll see what happends.
thanks
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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Canucker
Dodge Dakota
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9/13/2002
12:04:55
| RE: MAP Sensor ... Bernd? Anyone?
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Interesting ... so when you tow Duner, you can't get part throttle boost (well you can get it, but you can't utilize it)? That woulda been one of the reasons I got forced induction was to get some part throttle help when towing in 5th gear ... but if you need WOT so you don't freak out the PCM, that's not very good.
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Duner
Dodge Dakota
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9/13/2002
12:26:45
| RE: MAP Sensor ... Bernd? Anyone?
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You can get part throttle boost - but you have to continue accelerating. If you try and modulate the throttle to stay at the same speed with boost it's impossible. That's where it will start to chug, or if you let off the throttle enough the blowoff valve will dump the boost. The biggest problem is that the boost is an all or nothing kind of deal (with my setup). You get all the boost at once. So when you come to an incline with the trailer - you have to either downshift and keep the revs up and pull the hill making sure you stay in vacuum, or you go ahead and nail the throttle and fly up the hill! Since the trans is only rated at 350 ft-lbs torque with a full load - putting 500 ft-lbs torque to it with a full load would be the end of it. I would be stuck on the side of the road with a broken transmission.
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Canucker
Dodge Dakota
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9/13/2002
13:54:05
| RE: MAP Sensor ... Bernd? Anyone?
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So when you hit a hill towing, you can't just keep cruise control on, say and let it get you up a hill? cause cruise will still depress the pedal on your behalf, but only enough to overcome the hill, not to speed you up.
How do stock turbos get around that problem (i.e. a diesel, say)?
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Duner
Dodge Dakota
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9/13/2002
14:18:19
| 1 BAR isn't enough
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I tried that! hahaha It was a neck-jerking experience. The cruise wasn't gentle enough in it's application of "pedal" pressure and it would send the thing into boost in nothing flat. Your neck would snap back and then it would let off almost as quickly because you passed the speed threshold. It only took me a couple of times to figure out that using the cruise wasn't very smart if there were many hills around.
When turbo systems are built from the factory - they don't use a speed density fuel injection system that's based on just a 1 bar MAP sensor.
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Canucker
Dodge Dakota
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9/13/2002
16:06:33
| RE: MAP Sensor ... Bernd? Anyone?
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LMAO! that's funny. I bet the guys in the lane beside you were thinking you're nuts ... or you wanted to race or something!
You haven't found any mass air conversions for the Dakota have you?
I wonder if relocating the MAP sensore to before your turbo would still generate enough vacuum under load... that would solve the going into open loop problem. But that would also take into account the vacuum created by the turbo even when you're not using boost (i.e. its venting out your blowoff valve). And it probably wouldn't be enough vacuum to trigger open loop - you'd need a signal conditioner to scale the pressure fluctuations back to the same as they were near stock. Or, you could make a restrictor in front of the sensor to get the right amount of vacuum, but then you're robbing power doing that. Man .. this stuff gets pretty tricky eh?
..oh well, I'm still laughing about your neck-jerking experience .. ha ha, how's your neck feelin' these days.
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Canucker
Dodge Dakota
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9/23/2002
10:33:35
| RE: MAP Sensor ... Bernd? Anyone?
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Bump ...
Duner, have you read my last post? The more I think about it, the more logical it seems to me to relocate the MAP sensor upstream of the turbo... what do you think?
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dr0p0ff
GenIII
9/23/2002
14:37:32
| RE: MAP Sensor ... Bernd? Anyone?
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hey duner, eric.. or anyone else for that matter. what does a "chug" feel/sound like?
Keep On Truckin!
Sgt G
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KRC Tech
Dodge Dakota
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9/23/2002
20:58:40
| RE: MAP Sensor ... Bernd? Anyone?
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Eric, the 1 bar map is the issue, that's why the 2 bar PSC controllers cure this. The part throttle hiccup is caused by a partial boost/ lean condition. Usually around 2800-3100 rpm. This is because mother mopar writes a lean condition at the 5 volt line to pull fuel when shifting, so the truck won't backfire through the exhaust. You are just stepping on that line of code when part transitioning to boost near that point due to the 1 bar spread of voltages. Spread the 0-5 volts over a range of 20 vac to 10psi and it will be a smooth transition. Right now with a 1 bar MAP, you reach 5 volts at zero boost and supply the same till max boost. That's why running a blowoff check valve, sometimes two on the MAP vac line buffers this condition. The MAP is also used at WOT open loop, I do that with the Roe Controller or the ARC 1/ PSC 1 on the dyno all the time to fatten up WOT fuel.
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Canucker
Dodge Dakota
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9/25/2002
13:53:52
| RE: MAP Sensor ... Bernd? Anyone?
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KRC, does the factory PCM know what to do with voltages greater than 5V? or would that have to be a custom PCM flash?
Would a 2 BAR sensor output 0-20V for a 0-2BAR range? or 0-10V or 0-5V (0-10 seems most logical)? or can you get sensors that do either one of those? (or does the PSC do it all).
Does that combination allow for part throttle boost that is easily controlled (for towing up a hill for example)?
thanks!
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Canucker
Dodge Dakota
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9/27/2002
16:18:00
| RE: MAP Sensor ... Bernd? Anyone?
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I hate replying to my own posts but ... bump.
Does anyone wanna answer this question for me? Or do my questions just not make sense? :)
(my single biggest goal is finding a setup that allows for easily regulated part throttle boost)
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Jon
Dodge Dakota
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9/27/2002
18:02:26
| RE: MAP Sensor ... Bernd? Anyone?
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You can't really mess with any sensors without screwing things up. If you wanted to increase fuel you can just mess with the fuel pressures, the ecu will shorten the injector pulses to keep everything at stoic at part throttle then a wot you can tune it to run rich. This will give you a good amount more power but will fry your cats.
-Jon
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conig
Dodge Dakota
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9/27/2002
18:24:47
| RE: MAP Sensor ... Bernd? Anyone?
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I have a fuel modifier I want to install on my 4.7l and have posted this before but which wire is the signal wire on the map sensor?
I have a afr-d so I can just hook it up and let ya'll know if it works.
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kota on 20s
GenIII
9/27/2002
19:26:24
| RE: MAP Sensor ... Bernd? Anyone?
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try this little trick.
http://www.speedtweaks.net/Boost_Bypass.htm
it seems to work pretty good so far
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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Bernd
*GenIII*
9/27/2002
23:49:16
| RE: MAP Sensor ... Bernd? Anyone?
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There is also another way to "fake" the MAP without any expensive electronics. A simple logic circuit does the trick (we did this over a year ago with a test case - "MAP Charger" box).
The "Chugging" (lean-out condition) happens at the 2.3x-2.5xV TPS and 4.2x-4.5xV MAP readings (MAP never hits the total 5V range). Control them with a voltage check system...problem goes away.
Kota: On the MAP/Boost Bypass, make sure you run the NAPA/Echlin valve...those little Black/Whitish valves from PepBoys don't last long at all. You can also play around with the various Ford (1988-1994 era) check valves as they have different release points (time delay for a simpler explanation).
1997 Dodge Dakota SLT - V6
Supercharged/Intercooled @ 10# w/Nitrous
14.55 @ 96.01mph
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kota on 20s
GenIII
9/28/2002
01:29:39
| RE: MAP Sensor ... Bernd? Anyone?
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cool. i got the napa one.
bernd a question for ya. i had a magnum performance TB on the truck. it chugged BAD under boost. then i put the stock TB on, and it ran bitchen. now i have a 51.75mm fastman, and it started to chug again WTF? i put the check valve in, and it runs good again
my question is, why does it run good with the stock TB, but not a ported one? i have never heard this before.. does the 5 speed have anytihg to do with it?
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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Bernd
*GenIII*
9/28/2002
08:56:51
| RE: MAP Sensor ... Bernd? Anyone?
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I also had a Magnum Performance TB (long time ago) and it did the same thing. The other modified TB will do the same thing as well but not as bad. Jules (Mr. Magnum Performance) uses small cuts in the bores as a method of dropping the MAP signal to richen up the fuel. If the MAP signal drops too quickly, you'll get the "chugging" sensation pretty bad under part throttle due to the modified MAP signal. It's not quite as bad as on the Fastman, APS, or Flometrics TB's...but they also drop the MAP signal a bit quicker than stock. (Bruce - Flometrics - did play around with the 48mm TB and a restrictor in the MAP port when I was testing the 48mm TB's out on my V6 - Still supercharged back then - and it helped out a little bit as well.)
Yes...the 5spd has a lot to do with it as the boost comes in a little bit quicker than on an automatic (again...same problem on my V6...it's a 5spd as well). The automatics also "absorb" some of the shock.
1997 Dodge Dakota SLT - V6
Supercharged/Intercooled @ 10# w/Nitrous
14.55 @ 96.01mph
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kota on 20s
GenIII
9/28/2002
12:15:48
| RE: MAP Sensor ... Bernd? Anyone?
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thanks for the info bernd!!
-Eric
Injection is nice, but i'd rather be blown.
5.2L, 5speed. Powerdyne SC, 50mm TB, 2bbl M-1, 1.7RR's, MSD 6BTM, ciramic JBA headers, carsound cat, dumped gibson
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