Acceptable map voltage with engine off (also strange pics that need explaining)

[Dct5289]

Ok so i have a 93 civic with a B18c1 in it. I also have a Vafc in the car for tuning which i have not done because i need to get a wide band first so i just use it to change my vtec point atm. But anyway heres my problem/annoyance. when i turn my ignition switch on and let the vafc boot up the pressure shows -.5psi when the engine isnt even on. So I used the vafc to check the sensor voltage and it reads 2.810 on the map sensor. I know that it should be 3v and i was wondering if this is an acceptable voltage or if it could be causing a my engine to bog a little when I just tap the throttle under idle. also other things like if I try to rev it up real slow it seems to bounce and struggle to get up to where it should be RPM wise. I already posted this on honda-tech forums and they were no help so i came here to see if there are any actual intelligent civic owners.


Also, just for fun, in case anyone might know why. My car (93 civic hatch) has a vin number that starts EH2 instead of the hatches EG. just wondering if anyone knew why.

I tried to get pics of this but my POS camera put a glare over it every time and it was too dark to not use flash, i dont think it needs pics to explain anyway.

 

[AHHVTEC]

thats normal i think the si comes eg and eh both ways like that even if yours is not a si thats normal

 

[Dct5289]

yes but what about my map sensor? also its not an si, its a CX. Also if it isnt my MAP sensor what would cause my car to do those things described in the earlier post?

 

[welfare]

Manifold pressure ------------Voltage specifications*
5in HG (125mm HG) -----------------2.5v
10in HG (250mm HG) ---------------2.0v
15 (375) -------------------------------1.5v
20 (500) -----------------------------1.0v
25 (625)------------------------------ 0.5v

*measured at ECM terminals: D17(+) and D21(-)

 

[welfare]

engine off map sensor should read Approx 3 volts
engine running sensor should read Approx 1 volt

2.810 is approx 3 in my book, I don't think that there is a problem with your map sensor.

 

[welfare]

if you really feel that there is a problem with your map sensor, swap it out for a different map sensor and see what readings you get.

 

[Dct5289]

ok, but what about the symptoms described? any ideas? (also, i don't just have these things sitting around, what do you think i have money or something?)

 

[welfare]

Im assuming you have a cx engine in the car?? you never said otherwise.
That engine is a little boggy to begin with, but if you think it is being tempermental maybe you should do a tune up, how many miles are on the engine, when was the last time you had it checked out??

 

[Dct5289]

It has a B18c1 in it as said in post 1. the engine has around 75000 miles on it and the oil has been changed regularly.

 

[welfare]

so the engine has 75,000 on it,
scheduled maintenance for a b18c1
every 35K replace trans fluid (AT or MT)
every 30 K valve adjustment
at 60 K replace plugs cap, wires rotor
75k change coolant, replace fuel filter
90K replace timing belt

 

[Dct5289]

Its got a new timing belt, new coolant, valves were adjusted at about 57000 (when I bought the engine), i may need to check the fuel filter, i plan on changing the tranny fluid soon, but i thinks its probably fine, plugs cap etc are all fairly new still.

Its a good engine and it runs smooth as butter, but it just feels like theres some power missing somewhere. it will break the tires loose in first but only when its cold. Im not sure if it will bark 2nd or 3rd because i dont drive like that, I want this engine to last. My brother drove it and it ran a 9.7 in the 8th mile. he went easy on it though. The exhaust is 2.5 all the way back, and the intake is a 3'' cold air kit. it has a msd on it but i don't think that could cause a problem.

 

[welfare]

if the msd is not properly tuned it can give you a problem.
you should def be able to break the tires loose when the engine is warm, how many miles are on the chassis of the car? it may be time for a fuel pump
do the filter and get back to me.
my gsr was a little slow when I bought it, I did new plugs and a fuel filter and it perked right up. I used some engine leaner (the kind you put through the intake manifold with the engine running, expensive stuff)
that helped even more.
I put JRSC on it about 6 months ago, she hauls ass now, I can spin the tires in 3rd if I'm hard on it.

 

[welfare]

Oh yah, if you know how to check your codes do so, some p72 ecu's don't turn the cel on if the o2 sensor is bad, but will store a code (dont ask me why, I had 2 diff p72 ecus that didn't throw a cel even with the o2 unhooked). Check that out too.

 

[Dct5289]

I know its not the fuel pump, that was changed before we even put the engine in, and a high flow one was installed too, not stock. As far as the MSD goes im not sure there is a way to tune it. ive got a 8000 rpm rev limiter chip in it and thats it, there are no ports to hook up a computer or anything.(the only reason i have it on the car is because my brother bought it and decided he didn't need it when he put a 3sgte in his celica). I will replace the fuel filter as well very soon, next time i get the chance probably.

Thanks for all the help so far, i can see that this forum is much much better than honda tech.