MAF Help
Thread Starter
Instructor
Joined: Apr 2002
Posts: 249
Likes: 0
From: Broken Arrow Oklahoma
MAF Help
I'm dealing with an 86 vette. With the engine off and the ignition switch in the run position my scanner shows 15 grams of air. After the car is started and warmed up you can turn the engine off and watch the scanner go from 15 to 23 grams of air again with the key on and the engine off. The car will not start at this point unless you step into the throttle. Sometimes when it starts it runs great after you clear out the extra fuel, sometimes if just gets worse and belches black smoke.
I am getting a good 5 volt signal on wire "c" with the sensor disconnected ("c" = signal wire). Hook it up and check the signal and I get 2.18 volts. Man am I confused with this one. Can anyone help??
Can someone please scan their car with the key on engine off and tell me what they read for MAF grams. Any ideas will be appreciated.
I am getting a good 5 volt signal on wire "c" with the sensor disconnected ("c" = signal wire). Hook it up and check the signal and I get 2.18 volts. Man am I confused with this one. Can anyone help??
Can someone please scan their car with the key on engine off and tell me what they read for MAF grams. Any ideas will be appreciated.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
On my 88, I always see 23 grams/sec with the ign in run engine off, so I guess that is normal.
During crank, before the engine starts, I will start seeing actual flow values well below the 23 gram/sec initial offset.
I have also recalibrated my MAF tables to better fit my cars behavior.
Note:the first value in the stock MAF table #1 is artificially high (it kicks up to 8.4 gm/sec at 0 volts), which causes an overestimate of the airflow. This could be part of your rich condition.
Crank fueling is not dependent upon MAF flow. If you're too rich after it fires then the MAF calibration and start-up fuel enrichment and or fuel pressure could be responsible.
During crank, before the engine starts, I will start seeing actual flow values well below the 23 gram/sec initial offset.
I have also recalibrated my MAF tables to better fit my cars behavior.
Note:the first value in the stock MAF table #1 is artificially high (it kicks up to 8.4 gm/sec at 0 volts), which causes an overestimate of the airflow. This could be part of your rich condition.
Crank fueling is not dependent upon MAF flow. If you're too rich after it fires then the MAF calibration and start-up fuel enrichment and or fuel pressure could be responsible.
Thread Starter
Instructor
Joined: Apr 2002
Posts: 249
Likes: 0
From: Broken Arrow Oklahoma
Thanks for the reply. I threw my hand held scanner in the corner and broke out the Diacom. Saw what the hand held couldn't show me. You are right. My sensor would not show cranking air flow. Just the high pre-start number. Replaced it and all is good. Autozone had a really good sensor. I checked the calibration and air fuel ratio's all the way up to redline. Thanks again.
Melting Slicks
Joined: Aug 2003
Posts: 3,395
Likes: 393
From: Lakeville MI
Any chance your Auto Zone MAF is a Micro-Tech product?
I just got the non-adjustable one from ZIP products and the calibration is way off.
+ 17 % Flow error as compared with my old OEM Bosch MAF.
I'm now rescaling my MAF tables by a factor of 0.85 to get the flow back where it should be. The raw signal is pretty noisy for flow over 230 gm/sec, it will jump up and down about 20 gm/sec, but the filtered signal looks ok.
With the bosch MAF the filtered and unfiltered values were almost identical, so I disabled the filter. This had to be reversed for the new MAF.
Strangely on the first drive with the artificially increased flow, I was seeing blms in the lean range (130-136). This is the opposite of what I would have expected, with an inflated MAF reading. Load is also skewed high.
The car runs ok, but not quite right. The idle and throttle response is a bit off. Hopefully this will improve with the new MAF table cals.
I just got the non-adjustable one from ZIP products and the calibration is way off.
+ 17 % Flow error as compared with my old OEM Bosch MAF.
I'm now rescaling my MAF tables by a factor of 0.85 to get the flow back where it should be. The raw signal is pretty noisy for flow over 230 gm/sec, it will jump up and down about 20 gm/sec, but the filtered signal looks ok.
With the bosch MAF the filtered and unfiltered values were almost identical, so I disabled the filter. This had to be reversed for the new MAF.
Strangely on the first drive with the artificially increased flow, I was seeing blms in the lean range (130-136). This is the opposite of what I would have expected, with an inflated MAF reading. Load is also skewed high.
The car runs ok, but not quite right. The idle and throttle response is a bit off. Hopefully this will improve with the new MAF table cals.
