Help with code 48 MAF
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Registered User
Joined: Aug 2019
Posts: 7
From: Missouri
Help with code 48 MAF
I have 2 questions on a 1995 LT1 with code 48,
#1. I have checked the voltages, 12, 5 and ground. The 5 volt signal drops as engine RPM increases. I have tight connections on the connector to the sensor, I replaced the wires, hot straight to fuse, ground straight to ground block, signal wire all the way to within 1 in of PCM original wire cut off and new one soldered on. I have swapped the MAF with a known good one off of my 5.7L vortec. All with no change. I wrote down the numbers from the live data of the sensor and O2 sensors at every 500RPM, I don't have them with me will post later. At this point I am thinking PCM.
#2. Looking for a PCM 16209461, doesn't seem to be a popular number is there another number that is the same hardware that can be programmed to this specification?
Background: Fresh build of the LT1 from a 1995 Z28, with 383 rotating assembly and LT4 Hot cam kit, headers, original stock PCM (as far as I know), otherwise stock with manual transmission dropped into an 83 Z28. All was running well, only a few hours on the engine and all codes (that will set the light) were clear. I was preparing to adjust the valves, when I pulled the negative battery cable off with the engine running (don't ask why) at that point instead of dying it ran rough for about 15 sec then died. After that it was hard to start, I finally got it to run long enough to set a code which was 48. The MAF was fried, it would not work an another car and a new one made this one start and run, but now with a code, and not running as well as it did before. So that is where I am now.
Thanks
#1. I have checked the voltages, 12, 5 and ground. The 5 volt signal drops as engine RPM increases. I have tight connections on the connector to the sensor, I replaced the wires, hot straight to fuse, ground straight to ground block, signal wire all the way to within 1 in of PCM original wire cut off and new one soldered on. I have swapped the MAF with a known good one off of my 5.7L vortec. All with no change. I wrote down the numbers from the live data of the sensor and O2 sensors at every 500RPM, I don't have them with me will post later. At this point I am thinking PCM.
#2. Looking for a PCM 16209461, doesn't seem to be a popular number is there another number that is the same hardware that can be programmed to this specification?
Background: Fresh build of the LT1 from a 1995 Z28, with 383 rotating assembly and LT4 Hot cam kit, headers, original stock PCM (as far as I know), otherwise stock with manual transmission dropped into an 83 Z28. All was running well, only a few hours on the engine and all codes (that will set the light) were clear. I was preparing to adjust the valves, when I pulled the negative battery cable off with the engine running (don't ask why) at that point instead of dying it ran rough for about 15 sec then died. After that it was hard to start, I finally got it to run long enough to set a code which was 48. The MAF was fried, it would not work an another car and a new one made this one start and run, but now with a code, and not running as well as it did before. So that is where I am now.
Thanks
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Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Re: Help with code 48 MAF
Did you clear the code from the PCM after installing the new MAF?
The signal output from the MAF sensor is a variable frequency.
Did you check:
- 12 V on pink wire (pin C), measured to ground (pin B)
- 12 V on pink wire (pin C) measured to chassis ground
- ground on black/white (pin B)
- measure frequency between yellow wire (pin A) and ground.
You should get about 2,200 Hz at idle. A scanner would indicate a flow range of 6-10 grams/second
DTC 48 sets when the PCM detects pulse signals from the optical cam position sensor in the Opti distributor, but no frequency signal from the MAF sensor. The PCM provides a 5 V reference, but the variable frequency rides on that reference.
Is the MAF sensor installed facing in the correct direction? Are you sure there are no leaks between the MAF and the throttle body? Should not set DTC 48 in either case, but just checking.
The signal output from the MAF sensor is a variable frequency.
Did you check:
- 12 V on pink wire (pin C), measured to ground (pin B)
- 12 V on pink wire (pin C) measured to chassis ground
- ground on black/white (pin B)
- measure frequency between yellow wire (pin A) and ground.
You should get about 2,200 Hz at idle. A scanner would indicate a flow range of 6-10 grams/second
DTC 48 sets when the PCM detects pulse signals from the optical cam position sensor in the Opti distributor, but no frequency signal from the MAF sensor. The PCM provides a 5 V reference, but the variable frequency rides on that reference.
Is the MAF sensor installed facing in the correct direction? Are you sure there are no leaks between the MAF and the throttle body? Should not set DTC 48 in either case, but just checking.
Administrator
Joined: Nov 1998
Posts: 71,094
From: Hell was full so they sent me to NJ
Re: Help with code 48 MAF
Are you sure that is the PCM part # you have? I thought the 94/95 PCM was either 16188051 or 16181333. These are readily available used or rebuilt.
http://lt1pcmtuning.com/service/
Further to discussion above, when DTC 48 sets for the MAF, the PCM defaults to speed density. Your PCM would have to be tuned for the 383, particularly the volumetric efficiency table and displacement, and the IAT and MAP sensors would have to be functioning correctly for the engine to run well.
http://lt1pcmtuning.com/service/
Further to discussion above, when DTC 48 sets for the MAF, the PCM defaults to speed density. Your PCM would have to be tuned for the 383, particularly the volumetric efficiency table and displacement, and the IAT and MAP sensors would have to be functioning correctly for the engine to run well.
Last edited by Injuneer; Aug 15, 2019 at 05:22 PM.
Thread Starter
Registered User
Joined: Aug 2019
Posts: 7
From: Missouri
Re: Help with code 48 MAF
Thanks for all the great info, and sorry for the delayed response. Looks like the problem was an inferior cheap MAF, and the reason I had trouble finding it was the way I was doing the voltage checks. I was checking the connector with the sensor unplugged in which case I had 5 volts. With the MAF plugged in that 5 volts drops to 2.5 volts, the 12v and ground are still good. I assume at the 2.5 volts the PCM was on edge of being able to detect the pulses, because some days the code would set right away, some days it would go 30 minutes before setting. It is now 3 days code free running on an AC Delco MAF with 4.95volts on pin A with key on and engine off. At idle I have 2800 Hz, and shows 10 g/s.
I don't believe I need a PCM at this point but I got the # 16209461 from the scanner info (Scan94/95), as mine has no sticker or other external numbers.
I hope to get it tuned this week.
Fun fact my 1998 K1500 runs decent with the bad MAF, in fact I have had a SES light on for 2 years for low cat efficiency, and it has been clear now for 2 days. Don't worry, I do have a new AC Delco on it's way.
Thanks again for your time and information.
I don't believe I need a PCM at this point but I got the # 16209461 from the scanner info (Scan94/95), as mine has no sticker or other external numbers.
I hope to get it tuned this week.
Fun fact my 1998 K1500 runs decent with the bad MAF, in fact I have had a SES light on for 2 years for low cat efficiency, and it has been clear now for 2 days. Don't worry, I do have a new AC Delco on it's way.
Thanks again for your time and information.
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