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1989 7MGTE Ice Blue Pearl,
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Discussion Starter · #1 ·
Can anybody explain what the Stock ECU does when you have the AFM unplugged? Like what is it doing with fueling and timing and such. Car runs terrible with AFM plugged in and vacuum around -15. unplug it, Idles great, Vacuum and AFRs are good/on the rich side. Plug AFM in it dies/ will not stay running. I have used 3 different AFMs and all end up with the same result.
 

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If no AFM is present, TCCS goes into limp home mode. It should not be able to spin past 2000 rpm (or was it 1500 rpm).

Things to look at;
make sure someone did not upgrade to the lexus AFM and not upgrade the injectors.
wiring.
vacuum leaks AFTER the AFM.

the AFM is a frequency based output and that is how the TCCS calculates engine load.
 
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plug it everything in and try to run the engine


is the check engine light on ? shut the car off and pull the codes and see what faults the cars computer is detecting
 

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1989 7MGTE Ice Blue Pearl,
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Discussion Starter · #4 ·
@madisonMK3 No codes. Only codes that will ever come up is if I unplug AFM. Other than that if I go above 2500 RPM it throughs a Code 52 for Knock sensors. I plan on rewiring them when weather permits.

Also No vacuum leaks checked 5 or 6 times per TSRM vac routing. Timing is set as per TSRM, Injectors and AFM both upgraded together, Maybe wiring but before it got cold I pined out each wire from AFM to ECU and was all as it should be.

The thing that I dont get is how it runs perfect with afm unplugged at least from cold start up to temp. but with AFM plugged in it will not run / sounds like it has a huge cam.
 

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If you've honestly tried 3 different AFM's and it runs like that, 99% of the time it's a post-AFM intake leak.
I'd bet on a popped IC pipe coupler, a torn IC soft pipe right off the turbo (the stock one fails all the time due to heat and age) or a cracked accordion hose between the AFM and turbo.
 

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1989 7MGTE Ice Blue Pearl,
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Discussion Starter · #6 ·
Still no luck on this. Have rechecked all wiring from AFM to ECU all in spec per multi pages of tsrm. Have since tried another TPS. No change. Afm is reading 122hz at choppy cold start idle. Is this in spec? Rechecked intake piping no leaks. Since last post I have taken off IAC cleaned and tested. Tested good. Still same issue. Was thinking of taking lex afm housing and 550 injectors out but worried of same result.
 

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90T
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With no AFM signal you will get a code 31 and the ECU will default to a 3 point map. Fuel cut will be 3000 rpm.

At fast idle AFM (900rpm) should be 30-60 Hz max and at hot idle maybe 20-30 Hz. 122 Hz is way too high.

I've attached some typical logged values at hot idle here.

258740
 

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Discussion Starter · #8 ·
@3p141592654 Thanks for the great info! Glad to see your still around! Yea I have been thinking that value is too high... I get same results on 3 sensors so that leads me to think its the AFM housing or wiring but all wiring to ECU checks out. Could a bad AFM ground cause something like this? Honeycomb is installed on the Lex AFM housing. Cold start idle is at 700 to 750 and then after about 10 seconds drops to around 450 500 to 650 700. In this condition when its hunting it will stall. Only thing that changes it is unplugging AFM so I know that is where my problem is.
 

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@3p141592654 Thanks for the great info! Glad to see your still around! Yea I have been thinking that value is too high... I get same results on 3 sensors so that leads me to think its the AFM housing or wiring but all wiring to ECU checks out. Could a bad AFM ground cause something like this? Honeycomb is installed on the Lex AFM housing. Cold start idle is at 700 to 750 and then after about 10 seconds drops to around 450 500 to 650 700. In this condition when its hunting it will stall. Only thing that changes it is unplugging AFM so I know that is where my problem is.
very doubtful. For it to be reading higher means that there is MORE air going into the engine.
Since it is a digital signal, it either works or not, reading high means it has to be measuring that much air going into the motor.

Silly question but are you sure you are not on OEM AFM and 550cc/min injectors?
 

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Discussion Starter · #10 ·
@figgie Thats what I was worried about a month or so back, double checked the part numbers and believe I am using the lex AFM housing Part Number on it is 22250-50010. Went and compared it the stock AFM housing and it is larger.
258756
258757
Took Apexi Filter off and no difference. Rubber line in the back is a power steering line. PS not hooked up. Just incase that raised any questions lol
 

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90T
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I was wondering if it could be turbulence from the fan, but it looks like the shroud is in good shape. You might still try placing a shield of some sort temporarily between the fan and the AFM intake to block any air from the fan spilling over.
Also normally the AFM is usually rotated 90 degrees although I am not sure gravity play any role in its operation.
There are no codes set?
 

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Discussion Starter · #12 ·
@3p141592654 I saw somebody had an issue with that in the past. I have not blocked it off to test. When the Apexi air filter is on, it puts it right up behind the headlight and have not felt much air from the fan there. But it is another thing to try so I will do that! Yea I have noticed stock is usually turned 90 Degrees. I have not tested that either! but will. No codes in ECU unless I unplug AFM then I get the 2 AFM codes. Plug it back in light goes off. ( unplug battery to reset ecu ) and test and no new codes after letting it run with everything plugged in. Will do these tests and report back Thanks!
 

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90T
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All evidence seems to point to a bad AFM, but after trying 3 of them with no improvement I'm stumped.

You should confirm 5V on the VC pin during operation.
 

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Discussion Starter · #14 ·
Yea I hate the thought of having to spend the $$$ for a 4th AFM lol.
 

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Yea I hate the thought of having to spend the $$$ for a 4th AFM lol.
I would start troubleshooting the wiring as Pi (3p14) mentioned.

is there a solid 5V and 0v to the AFM? I say 0v and not ground as the TCCS should supply the 0v reference for most sensors.
 

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Discussion Starter · #16 ·
Did more testing. I think I may have been thinking my problem was in the wrong place.
VC - E1 = 5.01v
VC - Chassis Ground = 5.01
Same voltage at sensor side of connection also.

As mentioned above I decided to turn the AFM housing 90 degrees with the AFM from the picture above and reinstall apexi air filter. This resulted in the same rough idle but then revved to the moon. Turned car off at 4000 RPM. This is the AFM that reads 120 to 130 hz and AFR of 10+. I then decided to try one of the other AFMs I have again. Its one with the white outline around it (Original to this motor) when car is cranking / cold start / Idling it is at 29 to 40 hz. So this is the sensor I am staying with since it seems to be within spec. Problem however is with this sensor my AFR are 20+. I decided to hook up the SAFC and give it fuel and at 40% to 50% fuel at 1000rpm I was able to get the car down to 14.6 to 15.0 AFR and idle was perfect. Revving it would go lean. I let it get completely up to temp. Then checked VF, kept going from 3.25v to 4.99v. Rechecked for any air and vacuum leaks none were found. Should 550CC Injectors be this lean with lex AFM housing? I thought with lex and 550 I would need to remove fuel not be adding that crazy amount?
 

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what are you using to read AFR?

Are you sure it is in the correct scale (gasoline and not ethanol, methanol, diesel scales)?

If it is reading lean out of the box then you have a leak between the AFM and the intake vales. No way around that.
I personally would put the AFM correctly (the AFM should have the connectors pointing straight down).

Take a wide angle picture of the engine bay.. one shot. All of it.
 

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90T
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You are running the lexus afm housing? What is the situation with your bypass screw? I will tell you that someone on supramania did a FEM analysis of that housing and concluded that the screw is being used to damp out some nasty resonances. Twidlling the screw to adjust the mixture throws a lot of things out of whack. Also, the calibration table for the lexus afm is quite different from the supra housing. Any chance you can temporarily go back to the supra housing and then adjust fuel pressure to compensate for the 550s?
 
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