Hi, I need some advice on an airflow meter problem. I have a 95 4runner, 4WD V6, and with the engine running, I'm reading 20 volts AC between the meter housing and ground. I've replaced the airflow meter, still same problem, and the alternator diodes test good and no AC is detectable between alternator output and ground. Any ideas would be appreciated...

 

It not actually AC its variable resistance. It's your multi meter that gets confused when it sees the changing states. Non issue unless there some thing wrong with your engine performance.

 

My engine performance is definitely bad, and fuel economy is down to about 11mpg. I have a Celica with similar airflow meter and it doesn't show any voltage so I was wondering...

 

I have pulled the codes from the ECM? The volume or vane air flow meter is check via resistance not voltage.

for example if you open the connection at the AFM and put your ohm meter leads on Vs & E2 you should have 200-600 ohms (doesn't matter what temp it is). Vc & E2 should be 200-400 ohms (doesn't matter what temp it is).
Leads THA - E2 will varry with temp, as examples;

10-20K ohms for 4f
4-7k ohms for 32f
2-3 k ohms for 68f
.9-1.3k ohms for 104f
.4-.7 k ohms for 140f

the AFM terminal will start from left to right Fc E1 E2 Vc E2 Vs THA. Good luck.

 

I did that and all terminals read as expected. Also, there is no continuity between any terminal and the AFM housing. I only checked voltage between the housing and ground because I could feel it shocking me (tingling) sometimes. The ECM gives a trouble code for the VAF and the Air Temp Sensor. Do you think an engine fire might help?

 

If you use the pinout number in stead of the abbrivated connector ID's,
1 is ground,
2 goes to the A/C
3 is not applicable
4 goes to the TPS, pin
5 goes to throttle position sensor
6 goes to ECM
7 goes to the ECM

Which lead positive giving you 20 volts?

An engine fire? Explain, cause this is getting starting to get a little weird.

 

I'm not sure which lead is giving the 20 volts, because it only happens while running and I didn't want to start cutting insulation. I'll check tomorrow and let you know. I was thinking that if I set the engine on fire in the morning I wouldn't have to troubleshoot anymore, and that sounds like a good option because everybody thinks I'm an idiot when I tell them these symptoms.

 

Your sarcaism wasn't lost to me. I was just lost in the translation of fustration.

Check lead 4 (Vc) on the throttle position sensor ... it's a shared ground with AFM. The ground combines TPS, AFM and ECM.

Check lead 1 on the AFM. It's the ground that goes to the ECM and the data link (where you pull engine codes).

Check lead 2 on the AFM for positive 20 vdc. It's from the A/C relay under the hood. It could a good place to start tomorrow. It's pin 4 on the A/C relay. Infact if I was a betting man, I would replace the A/C relay. That's me and it's just a suggestion.

Worst case the ECM has a problem
Best case A/C relay

 

All the AFM wires are normal. The problem seems to be high resistance in the secondary ignition system. If I remove wires from the distributor cap individually, the voltage increases. I think because the AFM is isolated from ground, it was showing some sort of capacitive effect (hose clamps are reading 2-8 VAC). Time to start replacing parts it seems...

 

If AFM is normal resistance than I wouldn't replace it. It's ok to gain voltage with disconnecting wires from the distributer because it places load on the battery. If you are still getting 2-8 VAC when the key is turned to ACC, then a floating ground is present. You can isolate the ignition coil and check for floating ground. The amount of resistance for the primary ignition coil as measured between the positive and negative poles are 9-14.5 k ohms. The coil insulation should be more than 10 mega ohms. You can also test the secondary between the postive post and high tension. It should be .33 - .55 ohms.

I am thinking two things .. the A/C relay is not the problem if the lead was tested good to the AFM. And if alternating current is still be read when the engine is turned over I would suspect the diode bridge in the alternator to be the fault.

good luck

Please make sure you indicate wether the tests where done without battery, with battery, or engine running. Thanks.