Possible Damaged Vane Type AFM

[Big Rob]

When measuring the resistance across terminals E2 and VS of a 7MGE AFM should the resistance only increase from fully closed to open?

I am having engine trouble with my 1GGTE which shares essentially the same engine management system design as the 7MGE. Whilst trying to diagnose the system I have noticed that the resistance does not just increase, it will however increase, drop, increase and drop as the vane is opened further and further.

For a more detailed explanation consider this similar example:

Fully closed - 200 ohms

10% open - 280 ohms

20% open - 400 ohms

30% open - 350 ohms

40% open - 450 ohms

50% open - 400 ohms

ect

Finally close to fully open is 600 ohms and 100% open where the vane is mechanically limited in its travel by the housing the resistance drops again to approximately 380 ohms.

Ignoring the fact that this is a 1GGTE AFM would this operation on a 7MGE AFM indicate that it is faulty?

Addition information:
Part number on 1GGTE AFM - 22250-70200.
Both AFM's appearance is identical 1GGTE <-> 7MGE.
The air temp compensation cal curve is identical 1GGTE <-> 7MGE.
The documented resistances across the AFM output are identical 1GGTE <-> 7MGE

Thank you in advance for any assistance.

Rob

 

[Nick M]

Is your's a 5 VC signal? I don't believe yours is 12V, but you never know.

It isn't supposed to go up and down. Make sure the wiper isn't moving when you think it is holding still. Voltage goes down as the wiper opens, so resistance should go up as it opens.

 

[jetjock]

Sounds like a worn wiper. Common on those things as they age. Bad news because the load signal is one of the two critical signals used for calculating basic injection duration.

 

[Big Rob]

Out of curiosity whats the timing referenced to? Just the CPS?

 

[Nick M]

Cam and crank time come from the cam position sensor. Assuming you mean ignition timing and not engine timing.

 

[Big Rob]

Ignition timing would be based on the AFM voltage would it not? If it was just based on engine speed how would the TCCS account for load and boost?

So an update on the situation: I believe the AFM is fine. I measured the voltage at the VS terminal which proportionally decreases from ~ 4.9v -> 0.1v as the vane is moved from fully closed to fully open. This suggests now that the AFM is working satisfactory.

Now that this not the cause of my problems I am pretty much at a point that there is nothing else to check.

 

[Nick M]

Ignition timing would be based on the AFM voltage would it not? If it was just based on engine speed how would the TCCS account for load and boost?

Boost on GE? But yes. Engine load is an input factor for the base angle. Initinal timing + base + corrections = total advance.

Now that this not the cause of my problems I am pretty much at a point that there is nothing else to check.

You never said what is wrong. You just asked about the airflow meter.

 

[Big Rob]

You never said what is wrong. You just asked about the airflow meter.

This is true.

Problem: Intermittent poor acceleration, antilag like engine response during engine warm up and power surge above approximately 5200rpm.

Detailed description:

The engine will run fine after an ecu reset i.e disconnect battery for a period of time. After a number of random engine start cycles the engine will perform less than satisfactory where upon start up will behave like an anti-lag strategy has been enabled but is most extreme only during warm up. The car will have very poor acceleration and the turbos will audibly build boost, I believe this is due to a timing retard as the AFR's measured are leaner than at same loads when the problem is not occurring. This indicates to me that there is a substantial mass of fuel not being combusted due to an extreme ignition timing retard.

Once the car is warm the anti-lag is much less noticeable but throttle response is poor, fuel economy is not so good and acceleration is also average. Strangely at approximately 5200rpm engine power surges so violently that the car can break into wheel spin like the clutch was kicked however I think this is due to ignition timing being rapidly advanced.

These issues can temporarily be resolved by disconnecting the battery and resetting the ecu but after a random period of time the engine will begin to exhibit the same problems. Usually it seems that the problem always comes back when the car is restarted from dead cold. i.e its been sitting over night and started in the morning.

Action so far:

Replaced rotor button
Replaced distributor cap
Measured ignition lead resistance - very acceptable.
Replaced and gapped spark plugs - using laser iridiums so iridium center electrode and disk on the ground electrode.
Replaced timing belt, tensioner ect.
Verified TDC and '0' mark on crack pulley, reset cam timing and set valve lash.
Reset base ignition timing with diagnostic terminals T1 and E1 shorted.
Completed a compression test with results within a few psi of each other in the hight 170's if memory serves right.
Completed a leak down test with excellent results, average leak down was 5/6%.
Reset cam sensor pickup gaps to 0.2mm.
Pickup coil resistance checked out according to the tsrm.
The igniter and coil checked out according to the tsrm.
Injectors were cleaned.

TCCS trouble shooting:
With the car at operating temp
Disconnected the water temp sensor - no change other than slightly leaner AFR's and diag code 22.
Disconnected the O2 sensor - no change other than slightly leaner AFR's no diag code.
Disconnected the rear knock sensor - at approximately 2000rpm there was an initial timing retard with the CEL appearing but the engine performance was fine and there was no noticeable change in AFR's. After two on/off engine cycles the CEL disappeared as did the timing retard at 2000rpm but diag code 52 still existed until the battery was disconnected.
I completed the troubleshooting guides for both the AFM, water temp sensor and 02 sensor at the ecu which all check out.
There is continuity between the ecu ground on the intake manifold and the ecu.

Currently the engine is stock other than a FMIC. It did have a restrictor type boost valve which has been removed for the problem diagnoses. With it on the engine it did seem like the rate at which the problem would become apparent was sooner.

The only thing that I can think of which I have played with was the dashpot on the throttle as it over damped the throttle blade on 'off throttle' motions.

I also noticed one of the pickp coils a small amount of potting material missing on the top surface next to the core.

The other interesting thing is all these problem will always be briefly resolved by disconnecting the battery for a few minutes and reseting the ecu.

 

[Big Rob]

No body?

 

[3p141592654]

I think you already found your problem. The AFM is bad in post #1, then post #6 is good. I would suggest it is intermittent. Try putting it in a freezer for an hour then remeasure before it heats up.

 

[Big Rob]

I'll try this BUT I was a little surprised when I measured 20+ AFM's at the wreckers the other day and the resistance vs vane opening was as described in post one.

I believe measuring the resistance is misleading but the voltage is accurate.

 

[Big Rob]

The intermittent "anti-lag" appeared again today.

What sub-system of the TCCS is able to retard timing so that it is able to perform like an anti-lag strategy?

I'm sure this is a timing issue, as described above the AFR's during "ant- lag" are lean indicating an incomplete combustion as a result of a ignition spark retarded.

As I understand it the AFM output voltage and RPM signal from the distributor is used to estimate load and set base timing, but is there any other sensor or electrical device that would have the ability for such a large adjustment?

I'm sure this is an electrical issue as the problem will always disappear with an ecu reset.

 

[3p141592654]

If its like the 7MGE ECU, then the AFM and NE signals are used to compute VE. There are a few correction tables based on coolant and air temp, as well as battery voltage.

Given the way the AFM operates, the voltage returned is linearly proportional to the resistance. The voltage cannot be smooth unless the resistance is also smooth, and vice versa.

Any codes set? Resetting the ECU clears codes and learned values. A crappy AFM signal could send the learned values into unknown territory, and then they would be cleared upon reset back to nominal.

 

[Asterix]

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=FI&P=95
I quote: Resistance between VS and E2 will change in a wave pattern as the measuring plate slowly opens.
That is, it's not a monotonic sweep through resistance as the flap moves from closed to open. Page 94 of the TSRM shows what other resistances you should see. One depends on temperature.

 

[3p141592654]

You are reading too much into a translation from Japanese to English. What they mean is that the resistance varies smoothly (like a wave) through the range of motion of the flap. Rest assured that it is supposed to be monotonic, otherwise it would be useless as an AFM.

THA, discussed on page 94, which is the air temp sensor built into the AFM, better be sensitive to temperature!

 

[Asterix]

IIRC, my AFM does just that. The resistance goes up and down as I open the flapper, though overall the trend is up. It's done that every time I've checked it over the past 10 years. I can check it again this weekend. I thought it strange, but the computer doesn't complain about it and the car runs fine. It passes Virginia emissions just fine.
Now, if someone has a new AFM to check, that'd be great. Everything I have (which isn't much) says it's right that the resistance goes up and down as the flap moves.
Maybe the TSRM for a different car that uses the same AFM was translated by a different person...

 

[3p141592654]

Typically the resistance strip is scalloped with about 8 steps in the full range, with shunt resistors used to tailor the resistance for each segment, so the rate of change (second derivative) varies with position, but the resistance must be monotonic (first derivative>0) . This photo shows the resistive strip shape since this is hard to explain in words.

The proper way to test these things is to put 5V across Vc and E2, and then measure the voltage on Vs. It must be monotonic or it is broken.

 

[Big Rob]

My AFM is behaving exactly as described by Asterix. The resistance measured across VC and VS is not monotonic and is much more like a wave but with an increasing trend.

However, measuring the voltage output of VS is monotonic and decreasing with measuring plate opening. That is only half the story to determine if the AFM is functioning correctly and I'm guessing there is no readily available or documented method to determine if the AFM output voltage is correctly proportional to mass flow.

Could this be as simple as a loss of tension in the AFM spring? The engine runs very rich and could be due to a "false metering" of air mass by the AFM due to the AFM spring.

 

[Big Rob]

If its like the 7MGE ECU, then the AFM and NE signals are used to compute VE. There are a few correction tables based on coolant and air temp, as well as battery voltage.

Any codes set? Resetting the ECU clears codes and learned values. A crappy AFM signal could send the learned values into unknown territory, and then they would be cleared upon reset back to nominal.

Forgot to add, thanks that is great information!

Also there are no codes to clear or reset but the "anti-lag" can be cured for an unspecified time with an ecu reset.

BTW what can the ecu actually 'learn'? And the NE, G1 and G2 signals do they trigger the ecu on a falling or rising edge?

 

[3p141592654]

NE is clocked on the rising edge at the MCU, but I can't remember if there is an inverter in the signal conditioning amps between the CPS and MCU.

G1 and G2 are asynchronously latched, and checked at each NE event.