AFM questions.

[IndigoMKII]

Alrighty so I started my car up to go somewhere and went to pull out and the car started to buck like mad at part throttle. So after I limped it home I didn't have any CEL come on but I ran a test and sure enough, code 31. Switched it with another AFM I had here and now the car doesn't want to idle unless I barely hold the throttle open. I haven't checked the ISCV but it was JUST working fine. Anytime you get the car near positive manifold pressure it bucks and freaks out like someone is trying to drag me backwards. Could just a AFM cause this?

 

[WillWorkFoBoost]

yea definitely, I've had afms that wont idle, some that will idle fine, some idle high.... depends how they're broken. have you cleared the codes to see if it comes back with the spare one? The generic tsrm only has the test for intake temp THA to E2, this is for the entire sensor. Test it per this here.

http://www.supra.co.nz/87tsrm/EFI/efi98.htm

If they dont match, theyre no good.

 

[IndigoMKII]

Sweet thanks, I was looking for this but couldn't find it. I didn't like the TSRM only has 1 of the tests in it..

 

[IndigoMKII]

Okay so with that test I have these readings.

KS -> E1 Infinite
E1 -> KS 490.9k
VS -> E1 173k (Assuming VC is VS)
E1 -> VC 172k
THA -> E2 2.7k at 72 degrees.

According to these readings if I did it correctly, I'm searching for a new AFM it seems lol

 

[jetjock]

You understand what those arrows mean right?

 

[IndigoMKII]

Correct. Positive one side negative other side. It's to measure resistance one way then another way.

 

[Chrisco]

Just out of curiosity, have any of you out there with a known good AFM (car runs right and no.codes present) check your AFMs using the above posted test?

My AFM came off a healthy running 91 GTE, but I just tested it and it failed the same three specs as the OP.

 

[IndigoMKII]

Just out of curiosity, have any of you out there with a known good AFM (car runs right and no.codes present) check your AFMs using the above posted test?

My AFM came off a healthy running 91 GTE, but I just tested it and it failed the same three specs as the OP.

This makes me wonder then.. If your AFM is more out of spec then mine, could mine be good then? According to these tests it's not but yours came off a running engine with no problems.

I can further explain my symptoms as to why I think it's my AFM. When I was driving my car up a slight incline, it started bucking like mad which caused the turbo to spool as the engine load increased. When the PSI climbed to around 2-3 psi it seemed as if I was dragging something up the hill with me. The car will drive fine out of boost and under half throttle but anytime you put the engine under a load aka climb a hill it gets VERY mad.

I've recently rewired my knock sensors using the guides floating around. Bought rg6 coaxial cable along with new solder and made sure to heat shrink and electrical tape everything. I'm not getting any other codes besides 31.

It's really frustrating as I haven't even broken the engine or turbo in yet and I'm scared to put any more miles on it with the car acting like this.

 

[Chrisco]

Everything you've described both now and previously make me think that you have a massive boost/vacuum leak somewhere past the AFM. That, or the wiring to your AFM is bad, because the car will act just like you describe if you try to drive it without the AFM plugged in.

 

[DHeath0013]

I had a very similar issue after rebuilding my 3SGTE MR2 (metered air). Same exact condition you described. I tested the MAF meter and it checked okay. I actually cracked it open and adjusted the door and was then able to get it to operate okay until the turbo started to spin up. Took a fresh look at it the next morning and found a loose intercooler pipe clamp. It's worth a look. I will test that Lexus AFM for you and see how it comes out. Keep us posted on your findings.

 

[IndigoMKII]

Guess I need to make a boost leak tester and report back. I'll see what kind of PVC piping I have laying around. Just to refresh my memory, unplug and cap the breather to the valve covers and cap the 3000 pipe near the TB, right? Pressurizing the turbo inlet without it moving won't hurt the labyrinth seals of the turbo right?

 

[Nick M]

Everything you've described both now and previously make me think that you have a massive boost/vacuum leak somewhere past the AFM. That, or the wiring to your AFM is bad, because the car will act just like you describe if you try to drive it without the AFM plugged in.

He has a 31 and not a 34. You are correct about the symptom of a false air reading. He should put the DVOM on Hz and compare it to a known good unit.

 

[IndigoMKII]

Put it on Hz and measure what? I'm up to any ideas, I can borrow my friends 87 AFM to do the test.

 

[Nick M]

Measure the airflow reading. The karman vortex air flow meter measures volume and puts out a frequency varied signal. More volume, more Hz. There is a book spec, that I don't have in front of me. It is something like 30Hz at idle, and a lot more at 1500 rpm. It isn't in the repair manual. Sadly.

 

[AJ'S 88NA]

Correct. Positive one side negative other side. It's to measure resistance one way then another way.

Resistance is resistance, doesn't matter which way it's measured.

 

[IndigoMKII]

Resistance is resistance, doesn't matter which way it's measured.

Wrong.

 

[AJ'S 88NA]

Wrong.

How so?

 

[Chrisco]

While "resistance is resistance," sometimes a circuit as a whole will provide different readings when checked in opposite directions because of the presence of things like diodes; which are current limiting devices that limit current flow in a certain direction.

 

[DHeath0013]

LED lights are diodes. Light Emitting Diode, Wire it in reverse and see what happens.
------I>----- (i.e. current will travel from right to left but not left to right)
------<I-----(i.e. current will travel from left to right but not right to left)

so infinite resistance one way and near zero the other.

 

[IndigoMKII]

LED lights are diodes. Light Emitting Diode, Wire it in reverse and see what happens.
------I>----- (i.e. current will travel from right to left but not left to right)
------<I-----(i.e. current will travel from left to right but not right to left)

so infinite resistance one way and near zero the other.

Exactly my point. I didn't mean wrong as like BAHAHA WAY OFF. I didn't have the time to type a more detailed response.