Cammed, long tubes. Low MAP readings
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Joined: Sep 2022
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Cammed, long tubes. Low MAP readings
BTr stage 3 cam. MAP reading is about 9 inhg at idle, and doesn’t appear to ever go above 20 inhg no matter load and RPM. When key is in ON position, it reads 29.63inhg. Shouldn’t I be seeing that reading at WOT?
Melting Slicks
Joined: Nov 2013
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From: USA
This 9 inHG at idle... is this 9 inHG of absolute pressure or 9 inHG or vacuum?
It's my assumption these are absolute readings... 9 inHG is about 30 kPa which is lots of vacuum, definitely not right for a cammed motor. My 226/230 113 cam is around 50 kPa at idle.
What kind of gauge is this or are you reading the factory MAP? Aka how reliable do we think this is.
It's my assumption these are absolute readings... 9 inHG is about 30 kPa which is lots of vacuum, definitely not right for a cammed motor. My 226/230 113 cam is around 50 kPa at idle.
What kind of gauge is this or are you reading the factory MAP? Aka how reliable do we think this is.
Thread Starter
Advanced
Joined: Sep 2022
Posts: 82
Likes: 12
This 9 inHG at idle... is this 9 inHG of absolute pressure or 9 inHG or vacuum?
It's my assumption these are absolute readings... 9 inHG is about 30 kPa which is lots of vacuum, definitely not right for a cammed motor. My 226/230 113 cam is around 50 kPa at idle.
What kind of gauge is this or are you reading the factory MAP? Aka how reliable do we think this is.
It's my assumption these are absolute readings... 9 inHG is about 30 kPa which is lots of vacuum, definitely not right for a cammed motor. My 226/230 113 cam is around 50 kPa at idle.
What kind of gauge is this or are you reading the factory MAP? Aka how reliable do we think this is.
Melting Slicks
Joined: Nov 2013
Posts: 2,049
Likes: 316
From: USA
What RPM is it idling at? If you had a big vacuum leak + high idle, it could read pretty low vacuum. Doesn't explain the issue at high load though.
Not sure what kind of scanner it is, but a quick data capture might help ID if anything looks amiss.
Not sure what kind of scanner it is, but a quick data capture might help ID if anything looks amiss.
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Michael S. Palmer
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KOEO at sea level your BARO should read around 29.9 inHg or about 101 kPa…at idle to read manifold vacuum subtract MAP from BARO…29.63-9.00 equals 20.63 inHg manifold vacuum…as idle increases your MAP inHg should decrease…you will need to check the wiring on your MAP sensor…a 5 volt reference, signal, and a Low Reference (ground)…if your MAP inHg does not change you may have a bad MAP or bad ground…to check MAP you will need to disconnect the MAP and with KOEO you should see 5 volts on the reference wire…you can jumper the 5 volt reference to SIGNAL and you should see 5 volts on your scan tool reading MAP voltage…connect test light to B+ and probe the low reference…test light should illuminate.
Last edited by C5 Diag; Jun 23, 2024 at 07:24 PM.
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KOEO at sea level your BARO should read around 29.9 inHg or about 101 kPa…at idle to read manifold vacuum subtract MAP from BARO…29.63-9.00 equals 20.63 inHg manifold vacuum…as idle increases your MAP inHg should decrease…you will need to check the wiring on your MAP sensor…a 5 volt reference, signal, and a Low Reference (ground)…if your MAP inHg does not change you may have a bad MAP or bad ground…to check MAP you will need to disconnect the MAP and with KOEO you should see 5 volts on the reference wire…you can jumper the 5 volt reference to SIGNAL and you should see 5 volts on your scan tool reading MAP voltage…connect test light to B+ and probe the low reference…test light should illuminate.
Racer
Joined: Mar 2015
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From: Indianapolis
Unless when it was tuned it was set to run on MAF only. Not a great choice, but one I've seen lazy tuners do.
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little update. I switched the units of measurement to KPA for the MAP. I believe I had an issue with the scanner I was using. MAP Reading gets up to 97 under heavy acceleration, however I noticed as soon as I let off the gas, the readings drop all the way into the 20s for a second before jumping back up to 50-55. I’m assuming this is from a vacuum leak?
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From: Cape Coral, Florida
High fuel trims only on one bank would not indicate a vacuum leak like an intake leak downstream of the MAF sensor which would be both banks…if the fuel trims decrease at 3000 RPM you may have an exhaust leak upstream on that bank of the front O2 sensor or an intake runner leak.