86-95 has an AFM not MAF!! Interior pics and explanation
12-23-2010, 11:25 AM
#1
Registered User
Thread Starter
Join Date: Dec 2010
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
86-95 has an AFM not MAF!! Interior pics and explanation
After learning my lesson, I see that a few people have mentioned online that this generation of vehicles has a mechanical AFM (Air Flow Meter, aka VAFM), and not a MAF (Mass Airflow Sensor). However, I found this information few and far between in hundreds of posts discussing how to clean a MAF. I just wanted to put the information out there very clearly... THESE VEHICLES DO NOT HAVE A MAF!!!
------
Before knowing this, I had decided to clean the MAF on my 94 Pickup 22-RE... I unplugged the little thing off the airbox with the two screws, and was horrified to see wires being pulled out and nothing like a MAF at all. If this happens to you, don't fret, you can fix it.
-WARNING- There isn't really anything serviceable in here or anything to clean. But if your little air rudder doesn't rotate smoothly (without clicking/catching/sticking) or if you pulled out the wires, you'll want to take it apart and fix it. Otherwise leave it be!
As you read, follow the pictures and this service manual PDF:
http://www.ncttora.com/fsm/1993/engine/33volumeai.pdf
Remove the air hoses and the four or five bolts holding the AFM to the airbox. Then use a utility knife and cut the silicone sealer around the top, like in this pic. Grab an edge with a screwdriver and pop it out, being careful not to jam the screwdriver through and into the delicate circuits beneath!
Now once inside, it should look something like this below. When there is no airflow, the two pieces of flexible metal should be separated by a tiny gap (pins FC and E1 in the manual diagram). When air flows from the engine vacuum, these are allowed to touch. This signal turns on your fuel pump. If your engine will catch when you start it but then immediately run rough and die hard, you probably messed up something with this. This is what happened to me. If you go to the diagnostics box by your engine fusebox (by the battery) and short "FP" and "+B" with a paper clip and you hear the fuel pump, but it doesn't run without the jumper, then this is probably broken inside the AFM.
The metal piece in the middle that rotates is just a potentiometer (variable resistor). Its common output comes out of it, is held by a little rubber loop, and goes to the big gold connector (as shown, pin VS). This was also a problem for me, as when I pulled the connector, this wire popped off and was interfering with the air vane movement. I never woulda known this even existed without taking it apart. I went ahead and soldered that connection.
Next there's the temperature sensor. It is at the top right of the pic, near the screw. It goes down into the air chamber and measures air temperature. Its output wires (shown unconnected) go to the metal tabs on the outer extremes (the far left one and the far right one, E2 and THA). It doesn't matter which is which, it's just a resistor. I also soldered these.
Okay, saved the most annoying for last. Pins E2, VB, and VC have a little flaky foil connector to the main PCB. (E2 has both the foil pad and the terminal for the temp sensor that I just talked about). I think these are supposed to connect by contact, and basically connect just through flexing like a spring. This is a terrible design, and when I opened mine at least one was completely torn. It is gonna take a little time and patience (or just more skill than I have), but you're gonna wanna solder the pins coming through to the PCB landing pads. This will make it so you can't take out the connector. Don't worry, once you put this thing together again working, there is NO REASON to take it out! You don't clean this like a MAF, which works completely differently. Take your time and solder each one down, making sure you don't short them at all.
When you're all finished soldering all the connections, go through the manual troubleshooting and take all the measurements as described there between the various terminals; make sure they are in range. As they mention on the 2nd page of the manual, the resistance between E2 and VS should start lowish, then go higher somewhere near the middle of the vane's range, and then taper down again.
Finally, when you're all done, make sure it works in your truck first. With the key in the ON position, you should be able to move the air vane and hear the fuel pump turn on. If everything works as it should, go ahead and pop the plastic cover back on and seal it up with some good silicone glue. I finished up by using my label-maker and putting a big "DO NOT REMOVE THIS CONNECTOR!" label on the AFM, in case anyone owns my truck after me I don't want them to learn the same painful lesson.
Hope you found it helpful, and remember, if you see anyone talking about these years having a MAF... correct them please!
------
Before knowing this, I had decided to clean the MAF on my 94 Pickup 22-RE... I unplugged the little thing off the airbox with the two screws, and was horrified to see wires being pulled out and nothing like a MAF at all. If this happens to you, don't fret, you can fix it.
-WARNING- There isn't really anything serviceable in here or anything to clean. But if your little air rudder doesn't rotate smoothly (without clicking/catching/sticking) or if you pulled out the wires, you'll want to take it apart and fix it. Otherwise leave it be!
As you read, follow the pictures and this service manual PDF:
http://www.ncttora.com/fsm/1993/engine/33volumeai.pdf
Remove the air hoses and the four or five bolts holding the AFM to the airbox. Then use a utility knife and cut the silicone sealer around the top, like in this pic. Grab an edge with a screwdriver and pop it out, being careful not to jam the screwdriver through and into the delicate circuits beneath!
Now once inside, it should look something like this below. When there is no airflow, the two pieces of flexible metal should be separated by a tiny gap (pins FC and E1 in the manual diagram). When air flows from the engine vacuum, these are allowed to touch. This signal turns on your fuel pump. If your engine will catch when you start it but then immediately run rough and die hard, you probably messed up something with this. This is what happened to me. If you go to the diagnostics box by your engine fusebox (by the battery) and short "FP" and "+B" with a paper clip and you hear the fuel pump, but it doesn't run without the jumper, then this is probably broken inside the AFM.
The metal piece in the middle that rotates is just a potentiometer (variable resistor). Its common output comes out of it, is held by a little rubber loop, and goes to the big gold connector (as shown, pin VS). This was also a problem for me, as when I pulled the connector, this wire popped off and was interfering with the air vane movement. I never woulda known this even existed without taking it apart. I went ahead and soldered that connection.
Next there's the temperature sensor. It is at the top right of the pic, near the screw. It goes down into the air chamber and measures air temperature. Its output wires (shown unconnected) go to the metal tabs on the outer extremes (the far left one and the far right one, E2 and THA). It doesn't matter which is which, it's just a resistor. I also soldered these.
Okay, saved the most annoying for last. Pins E2, VB, and VC have a little flaky foil connector to the main PCB. (E2 has both the foil pad and the terminal for the temp sensor that I just talked about). I think these are supposed to connect by contact, and basically connect just through flexing like a spring. This is a terrible design, and when I opened mine at least one was completely torn. It is gonna take a little time and patience (or just more skill than I have), but you're gonna wanna solder the pins coming through to the PCB landing pads. This will make it so you can't take out the connector. Don't worry, once you put this thing together again working, there is NO REASON to take it out! You don't clean this like a MAF, which works completely differently. Take your time and solder each one down, making sure you don't short them at all.
When you're all finished soldering all the connections, go through the manual troubleshooting and take all the measurements as described there between the various terminals; make sure they are in range. As they mention on the 2nd page of the manual, the resistance between E2 and VS should start lowish, then go higher somewhere near the middle of the vane's range, and then taper down again.
Finally, when you're all done, make sure it works in your truck first. With the key in the ON position, you should be able to move the air vane and hear the fuel pump turn on. If everything works as it should, go ahead and pop the plastic cover back on and seal it up with some good silicone glue. I finished up by using my label-maker and putting a big "DO NOT REMOVE THIS CONNECTOR!" label on the AFM, in case anyone owns my truck after me I don't want them to learn the same painful lesson.
Hope you found it helpful, and remember, if you see anyone talking about these years having a MAF... correct them please!
12-23-2010, 01:13 PM
#2
Registered User
Good post, but I haven't seen an actual argument stating that it's a MAF and not an AFM. Really, people just tend to stick with terminology that they know, which then spreads like wildfire through forums. N00bs read MAF and automagically, the truck no longer has an AFM, but a MAF instead.
A simple look at the FSM would have told anyone actually wondering that it is indeed an AFM. (The style of it alone should have made it abundantly clear) But I digress...
that all being said, I usually correct people when I see it, and if I care enough to fight the inconsistencies at that moment. At times, it really is an uphill battle.
A simple look at the FSM would have told anyone actually wondering that it is indeed an AFM. (The style of it alone should have made it abundantly clear) But I digress...
that all being said, I usually correct people when I see it, and if I care enough to fight the inconsistencies at that moment. At times, it really is an uphill battle.
01-01-2011, 06:49 AM
#5
Registered User
Thread Starter
Join Date: Dec 2010
Posts: 12
Likes: 0
Received 0 Likes
on
0 Posts
Good post, but I haven't seen an actual argument stating that it's a MAF and not an AFM. Really, people just tend to stick with terminology that they know, which then spreads like wildfire through forums. N00bs read MAF and automagically, the truck no longer has an AFM, but a MAF instead.
01-31-2011, 10:43 AM
#6
Registered User
Join Date: Oct 2007
Location: Durham, NC
Posts: 63
Likes: 0
Received 0 Likes
on
0 Posts
Since this is the best AFM screwup thread on the site, I wanted to chip in. I pulled out my connector and ripped the foil from the circuit board. Before repairing it, I put the thing back in and started the truck. It ran for a second, then died.
Somehow I blew the EFI fuse, and it took me a couple hours to figure out why the truck still wouldn't run even after I repaired the AFM. Just another thing to check, and maybe I can save someone else a headache.
Somehow I blew the EFI fuse, and it took me a couple hours to figure out why the truck still wouldn't run even after I repaired the AFM. Just another thing to check, and maybe I can save someone else a headache.
01-31-2011, 07:18 PM
#7
Registered User
Just wanted to emphasize that word. Neither term is any more or less correct than the other.
Subaru always called it a MAF, even though the first few years was a flapper-door style, before switching to a hot-wire style.
Full-time 4WD, AWD. TBI, SPFI. Knuckle, spindle. blah blah blah....
Subaru always called it a MAF, even though the first few years was a flapper-door style, before switching to a hot-wire style.
Full-time 4WD, AWD. TBI, SPFI. Knuckle, spindle. blah blah blah....
Thread
Thread Starter
Forum
Replies
Last Post
RedRunner_87
95.5-2004 Tacomas & 96-2002 4Runners (Build-Up Section)
84
06-01-2021 01:51 PM
