Please help with MAP sensor (data inside)
08-18-2005, 09:21 AM
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Car: 85 Berlinetta
Engine: sort of working
Transmission: B&M 700R4
Please help with MAP sensor (data inside)
Within the past week I've gotten WinALDL working with my ZZ4 computer/chip & my 350. The MAP sensor data is not making sense. In fact it looks almost (but not quite) the inverse of what it should be doing at idle versus acceleration.
Here's data during idle (Park):
Here's data during steady cruise:
and Here's data during heavy acceleration and decel after:
If my calcs are correct, at idle the MAP says I'm running about 6.8 inHg. My mechanical gauge plugged into the manifold port shows a steady 17-17.5 inHg, which would be about 42kPa.
The acceleration also looks suspect since @ WOT there should be almost no vauum (ie. MAP near BARO). It's reading just the opposite!
This is a new MAP sensor from Advance Auto, GP Sorensen #77911509 for my '85. What I'm thinking of trying now is hooking up a vacuum hand pump to sensor and seeing what computer reads at various known vacuums. If that still doesn't make sense, I'm at a loss. I'm also wondering what effect these bad readings would have on my computer's performance.
Here's data during idle (Park):
Code:
Time RAW:MAP RAW:BARO SENSOR:MAP SENSOR:TPS SENSOR:O2AVG SENSOR:MC Solenoid DC SENSOR:RPM SENSOR:BARO 0.6 177 232 75.7 1.4 0.071 51.4 1100 99.91 1.9 184 232 78.3 1.4 0.473 56.1 1100 99.91 3 180 232 76.8 1.4 0.062 50.6 1125 99.91 4.2 179 232 76.4 1.4 0.367 56.1 1100 99.91 5.4 180 232 76.8 1.4 0.066 51.4 1100 99.91 6.6 177 232 75.7 1.4 0.597 49 1150 99.91 7.8 187 232 79.4 1.4 0.601 53.7 1075 99.91 8.9 181 232 77.1 1.4 0.513 53.7 1100 99.91 10.1 182 232 77.5 1.4 0.424 53.3 1125 99.91 11.3 186 232 79 1.4 0.583 56.1 1100 99.91 12.5 179 232 76.4 1.4 0.057 50.2 1075 99.91 13.6 181 232 77.1 1.4 0.296 49 1100 99.91 14.9 182 232 77.5 1.4 0.906 51.4 1075 99.91 16 180 232 76.8 1.4 0.685 52.5 1100 99.91 17.2 180 232 76.8 1.4 0.062 49.4 1150 99.91 18.3 179 232 76.4 1.4 0.327 47.8 1025 99.91 19.6 174 232 74.6 1.4 0.049 43.1 1075 99.91 20.7 177 232 75.7 1.4 0.455 40 1150 99.91 21.9 186 232 79 1.4 0.888 46.3 1075 99.91 23 179 232 76.4 1.4 0.256 42.4 1075 99.91 24.2 181 232 77.1 1.4 0.323 45.5 1125 99.91
Code:
Time RAW:MAP RAW:BARO SENSOR:SPEED SENSOR:MAP SENSOR:TPS SENSOR:O2AVG SENSOR:MC Solenoid DC SENSOR:RPM SENSOR:BARO 61.3 187 232 31 79.4 11 0.853 75.3 1700 99.91 62.5 184 232 31 78.3 11 0.871 75.3 1700 99.91 63.7 184 232 31 78.3 11 0.888 75.3 1675 99.91 64.8 185 232 31 78.6 11 0.884 75.3 1725 99.91 66 185 232 31 78.6 11 0.902 75.3 1675 99.91 67.2 186 232 31 79 11 0.884 75.3 1700 99.91 68.4 187 232 32 79.4 11 0.897 75.3 1750 99.91 69.5 189 232 32 80.1 11 0.897 75.3 1775 99.91 70.8 190 232 33 80.5 11 0.871 75.3 1775 99.91 71.9 195 232 33 82.3 8.7 0.906 75.3 1600 99.91 73.1 219 232 33 91.2 2 0.857 75.3 1525 99.91 74.2 216 232 32 90.1 1.4 0.88 75.3 1625 99.91 75.5 200 232 32 84.2 7 0.911 75.3 1650 99.91 76.6 200 232 32 84.2 7 0.84 75.3 1650 99.91 77.8 200 232 32 84.2 7 0.893 75.3 1625 99.91 79 199 232 31 83.8 7.6 0.809 75.3 1650 99.91 80.2 195 232 31 82.3 8.7 0.813 75.3 1700 99.91 81.3 182 232 31 77.5 13.8 0.871 74.5 1775 99.91
Code:
Time RAW:MAP RAW:BARO SENSOR:SPEED SENSOR:MAP SENSOR:TPS SENSOR:O2AVG SENSOR:MC Solenoid DC SENSOR:RPM SENSOR:BARO 323.9 64 232 37 34 95.4 0.95 39.2 2625 99.91 325 37 232 41 24 102.2 0.99 39.2 2925 99.91 326.2 38 232 47 24.4 102.2 0.977 39.2 2875 99.91 327.4 37 232 53 24 101.6 0.968 39.2 3050 99.91 328.6 36 232 59 23.6 101.6 0.964 39.2 3350 99.91 329.7 35 232 65 23.3 101.6 0.941 39.2 3650 99.91 331 34 232 70 22.9 101.6 0.933 39.2 3925 99.91 332.1 35 232 76 23.3 101.6 0.928 39.2 4100 99.91 333.3 35 232 80 23.3 101.6 0.897 39.2 4225 99.91 334.5 35 232 84 23.3 101.6 0.897 39.2 4400 99.91 335.7 36 232 88 23.6 101.6 0.88 39.2 4675 99.91 336.8 38 232 91 24.4 80.2 0.906 69.8 4425 99.91 337.9 252 232 91 103.3 1.4 0.804 74.9 4100 99.91 339.2 252 232 88 103.3 1.4 0.716 75.3 4000 99.91 340.3 252 232 84 103.3 1.4 0.636 75.3 3950 99.91 341.5 252 232 80 103.3 1.4 0.743 75.3 3775 99.91 342.7 252 232 77 103.3 1.4 0.76 75.3 3600 99.91 343.9 252 232 74 103.3 1.4 0.499 71.4 3500 99.91 345.1 252 232 71 103.3 1.4 0.738 75.3 3350 99.91 346.2 252 232 69 103.3 1.4 0.791 75.3 3275 99.91 347.4 252 232 66 103.3 1.4 0.707 75.3 3150 99.91 348.6 252 232 64 103.3 1.4 0.911 75.3 3050 99.91 349.8 251 232 62 103 1.4 0.813 75.3 2925 99.91 350.9 250 232 60 102.6 2 0.844 75.3 2825 99.91 352.1 228 232 58 94.5 11 0.941 75.3 2750 99.91 353.3 248 232 56 101.9 1.4 0.88 75.3 2500 99.91 354.5 246 232 53 101.1 1.4 0.933 75.3 2150 99.91 355.6 238 232 47 98.2 1.4 0.95 75.3 1750 99.91 356.9 222 232 39 92.3 1.4 0.964 75.3 1475 99.91 358 205 232 32 86 1.4 0.968 75.3 1200 99.91 359.2 182 232 24 77.5 1.4 0.972 75.3 975 99.91 360.3 161 232 18 69.8 1.4 0.964 75.3 1075 99.91
The acceleration also looks suspect since @ WOT there should be almost no vauum (ie. MAP near BARO). It's reading just the opposite!
This is a new MAP sensor from Advance Auto, GP Sorensen #77911509 for my '85. What I'm thinking of trying now is hooking up a vacuum hand pump to sensor and seeing what computer reads at various known vacuums. If that still doesn't make sense, I'm at a loss. I'm also wondering what effect these bad readings would have on my computer's performance.
08-18-2005, 11:32 AM
#2
Supreme Member
Wait a minute. I see one of the columns is labeled "MC Solenoid". Is this a computer controlled carburetor induction system?
If so, you should know it doesn't have a MAP sensor, it has a VAC (vacuum) sensor which reads exactly the opposite way of a MAP sensor. This would certainly make everything make more sense, wouldn't it?
If so, you should know it doesn't have a MAP sensor, it has a VAC (vacuum) sensor which reads exactly the opposite way of a MAP sensor. This would certainly make everything make more sense, wouldn't it?
08-18-2005, 12:50 PM
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Car: 85 Berlinetta
Engine: sort of working
Transmission: B&M 700R4
Well, that's certainly news to me. My car ('85 Berl. LG4 originally, CCC yes) has both a BARO and MAP sensor, which from what I gather was not too common on 85's let alone those with carbs. I'll have to double-check my shop manual and make sure it really is MAP not vacuum. Even so, the 77 kPa sensor reading, if direct vacuum would correspond to about 22-23 inHg, still not even close to reality.
Like I mentioned before, I'm going to put some known vacuum on it tonight and post my results later. Maybe that will help figure things out more.
edit:
I searched the Advance Auto website again. Originally I requested parts for the 87 since that's what the ZZ4 computer is from. For 85's there is another sensor listed, but doesn't have the same hookup as mine. The new one I got just plugged right in. One's called a MAP the other is Manifold Differential Pressure. Now I'm wondering which one I need for the ZZ4 computer. Is it expecting MAP or vacuum or differential? Anyone have any experience with this?
Like I mentioned before, I'm going to put some known vacuum on it tonight and post my results later. Maybe that will help figure things out more.
edit:
I searched the Advance Auto website again. Originally I requested parts for the 87 since that's what the ZZ4 computer is from. For 85's there is another sensor listed, but doesn't have the same hookup as mine. The new one I got just plugged right in. One's called a MAP the other is Manifold Differential Pressure. Now I'm wondering which one I need for the ZZ4 computer. Is it expecting MAP or vacuum or differential? Anyone have any experience with this?
Last edited by Dirty Dave; 08-18-2005 at 12:58 PM.
08-19-2005, 06:20 AM
#4
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Well, I know for sure that computer controlled carburetor setups from the factory definitely read the OPPOSITE of a MAP sensor. I'm beyond question about that. Whether it's called a VAC sensor or a Pressure DIfferential Sensor, I couldn't say without doing some research, but I recall it being called a VAC sensor off the top of my head. Might want to post up in the Carburetor section of this board instead of the general tech section. There's a few guys running around who know the computer systems for computer controlled carbs pretty well,
Of course, you're playing mix-n-match with the computer and sensor which complicates things considerably.
Of course, you're playing mix-n-match with the computer and sensor which complicates things considerably.
08-19-2005, 10:23 AM
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Car: 91 Formula WS6 (Black, T-Tops)
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Transmission: Built '97 T56, Pro 5.0, CF-DF
Axle/Gears: 4.11 posi Ford 9"
Try subtracting your calculated kPa values from 100kPa and then see if they make more sense to you....
08-24-2005, 12:24 PM
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Car: 85 Berlinetta
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I appreciate all the ideas, guys. Damon definitely put me on the right track.
What I did was measure what the computer was reading vs. actual input vacuum with a hand pump and gauge. Here's what I came up with:
Indeed this seems to be a direct vacuum sensor! The curve fit of this data is extrememly close to the following equation which allows for exact conversion of the "MAP" reading in kPa to "Hg so you can have real-time manifold vacuum data like any other true MAP sensor:
Manifold Vacuum ("Hg)= (29.92/101.3)*kPa - (29.92/101.3)*20
or in simpler terms:
Man Vac "Hg = 0.295*kPa - 5.91
This actually matches my data well at idle of 76 kPa which converts to 16.5 "Hg!
I just hope this is the type of sensor the ZZ4 computer needs to see data from. I compared 2 "MAP" sensors from CCC quad cars and the output is virtually identical to what I found, so I'm taking that as a good sign.
Also, even though my car has a BARO sensor and all the proper wiring for it going to the computer, the computer either ignores it or only takes 1 reading right at key on because with the power on I varied the input vacuum on it too but the output didn't change.
I hope this is useful info to someone besides me
What I did was measure what the computer was reading vs. actual input vacuum with a hand pump and gauge. Here's what I came up with:
Code:
Input Vacuum ("Hg) MAP reading (kPa)
------------------------ ----------------------
0 21.4
5 36
10 53
15 70.2
20 87.4
25 103.2 Manifold Vacuum ("Hg)= (29.92/101.3)*kPa - (29.92/101.3)*20
or in simpler terms:
Man Vac "Hg = 0.295*kPa - 5.91
This actually matches my data well at idle of 76 kPa which converts to 16.5 "Hg!
I just hope this is the type of sensor the ZZ4 computer needs to see data from. I compared 2 "MAP" sensors from CCC quad cars and the output is virtually identical to what I found, so I'm taking that as a good sign.
Also, even though my car has a BARO sensor and all the proper wiring for it going to the computer, the computer either ignores it or only takes 1 reading right at key on because with the power on I varied the input vacuum on it too but the output didn't change.
I hope this is useful info to someone besides me
Last edited by Dirty Dave; 08-24-2005 at 12:27 PM.
08-26-2005, 11:04 AM
#7
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If that's the ZZ4 computer/chip that GM put out when they were selling a complete kit to replace old 305 computer controlled carburetor engines in 3rd gen f-bodys then it should work just fine. It was designed as a direct replacement for older 305s and was designed to work with all the original 305 sensors and such that were used on computer controlled carburetor engines- including the stock VAC sensor.
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