Possible bad MAP sensor. Your opinion please.
07-08-2015, 05:10 AM
#1
Possible bad MAP sensor. Your opinion please. I don't know much of tuning so I'd like your help. I've been dealing with this issue for over a month now and have cleaned, checked and or replaced all of the pre intake sensors.
It's an 02 Formula. Auto with stock manifolds and cats. The rear O2's have been tuned out.
Symptoms:
Rough/low idle when warm. Will stumble when coming to a stop and if in gear still act as if it's going to die. It has before, but now I'll put it in neutral when stoping to prevent it.
Under throttle there is no noticeable loss of power. However, the trans will randomly act as if it wants to downshift, but go right back into gear. It's like it doesn't know what it's supposed to do.
Also, every time I start the car my gas gauge drops to E setting of my gauge light. Then when I put it in gear, it jumps right back where it was, but will slightly float back and forth.
No back fires at all. No easily detectable vacuum leaks though I've only checked what I can see or feel. I don't hear any hissing, even if I push on the TB cable to rev it I can't hear anything unusual.
I borrowed HPT from a buddy to see what's going on with the scanner. I got no codes ever, after several starts, and maybe an hour of letting it run and checking every few mins.
The only reading that seemed odd was my MAP sensor. It was set to read PSI, and I was at 4-6 psi at idle, but giving it throttle the MAP reading dropped to 0. Is that normal, or should it increase?
I need to check fuel pressure I know. But given the symptoms, does the MAP seem likely? What could cause this without setting off any code at all?
It's an 02 Formula. Auto with stock manifolds and cats. The rear O2's have been tuned out.
Symptoms:
Rough/low idle when warm. Will stumble when coming to a stop and if in gear still act as if it's going to die. It has before, but now I'll put it in neutral when stoping to prevent it.
Under throttle there is no noticeable loss of power. However, the trans will randomly act as if it wants to downshift, but go right back into gear. It's like it doesn't know what it's supposed to do.
Also, every time I start the car my gas gauge drops to E setting of my gauge light. Then when I put it in gear, it jumps right back where it was, but will slightly float back and forth.
No back fires at all. No easily detectable vacuum leaks though I've only checked what I can see or feel. I don't hear any hissing, even if I push on the TB cable to rev it I can't hear anything unusual.
I borrowed HPT from a buddy to see what's going on with the scanner. I got no codes ever, after several starts, and maybe an hour of letting it run and checking every few mins.
The only reading that seemed odd was my MAP sensor. It was set to read PSI, and I was at 4-6 psi at idle, but giving it throttle the MAP reading dropped to 0. Is that normal, or should it increase?
I need to check fuel pressure I know. But given the symptoms, does the MAP seem likely? What could cause this without setting off any code at all?
That will 
07-09-2015, 09:25 AM
#5
Most people look at MAP values in kpa but 4 to 6 psi of vac is about 30 to 40 kpa so that looks normal and 0 psi vac at sea level is about 14.7 psi absolute pressure which would be about 100 kpa so you're good there. Your map is reading like it should. Is this a new tune or was it fine and this happened out of the clear blue?
07-10-2015, 01:52 AM
#7
Most people look at MAP values in kpa but 4 to 6 psi of vac is about 30 to 40 kpa so that looks normal and 0 psi vac at sea level is about 14.7 psi absolute pressure which would be about 100 kpa so you're good there. Your map is reading like it should. Is this a new tune or was it fine and this happened out of the clear blue?
The only thing that was new was a kg3 alt swap. But that was done about 2 weeks before this started and voltage is fine. I have a video of it I'll upload shortly.
Yes, it's a problem when it's hot. Cold start it seems fine, or at least close to what I remember being normal. When I put it in gear to pull out of the driveway, I mainly just cost in gear and it's fine. But once i drive it, letting off the throttle and costing to a stop in gear and it will drop low. Even in neutral it still does but not so badly.
The other day while getting on the highway, I was at wot from about 40-80mph and I smelled, not really gas but something. I couldn't really tell what it was. Not electrical burning, not pure gas, kind of a smoky smell, but I didn't see any.
***Added video
The ABS and Brake lights are due to having a 4 channel rear in a 3 channel car. Low oil is new, oil was changed the day before.
Last edited by Mongoose350; 07-10-2015 at 02:09 AM.
