OK, trying to track down the no-start problem I'm having with my car. Actually, it's a start, rev, then die problem :P


So, today I was checked the resistances on the 2 E2 connectors that go to the AFM. One was giving me a ~40ohm reading between the harness and the block, the other gave me a ~20ohm reading. Is this normal?

Also, when checking the grounds for the ECU, they change resistances when the key is in the "on" position and when it's in the off. Is that normal? I can't figure out WHY it would do that, but the resistances on all but 1 of the grounds DOUBLE when the key is turned to on. The 1 that doesn't double is actually halved, but the polarity of the circuit reverses! I guess I could be check the wrong pins, but I don't think so...

 

Always check grounds with the key to off.

The 20ohms sounds waaaay high. Sorry, I can't remember ever checking those at the AFM plug before. AFM plug, not the afm jack.

Tell you what, pull the middle plug off the ECU and ring from those E2 at the afm plug, to pin 2C of the ECU plug.. In my mind the reading should be something like 0.1 or 0.2 ohms discounting the meter leads.

If you pull the ECU plugs off are the grounds on 2R, 3A and 3G less than one ohm. Closer to .3 or so ohms????? Key OFF. The plug, not the jack on the ECU.

I might take a look at my car tomorrow for grins.

 

So when I checked the ECU grounds before they were all about ~.7ohms or lower. Today when I checked, they were all 7ohms! I couldn't figure it out!

Then, I finally figured out what happened. Previously I had checked the grounds with the negative battery cable disconnected and resting on top of the battery. With the negative battery cable connected, the resistance went up to 7ohms. That seems really weird to me...

I'll go check the resistance through the harness to the AFM.

 

K, I just checked the resistance through the harness too, and it's where it should be (.3ohms) from the E2 to 2C.

 

Why is that weird??? Its simply that the resistance is changing with voltage on the wire.

pretty normal

 

The resistance at either of the E2's at the PLUG is 0.3 ohms. That's with the negative lead of the meter on the battery negative post and the pos on the E2 and the plugs on the ECU connected up.

Most of that 0.3 is my meter leads/alligator clip/probing pin.

If I were you, and had doubt about the afm, I'd put a meter lead on the output of the AFM and with the key to ON push the vane in the afm from full close to full open. The voltage should move from approx 4vdc at close to about 0.5v at full open and no *opens* inbetween.

Just a note: around 86/87 they had a factory service bulletin that added a ground to the boost sensors brown/black wire. This was NOT done to correct a boost sensor problem. It was to add an additional ground to help the AFM out. They put a ground from the brown/black of the boost sensor and the other end to the water filler neck on the engine.

I do notice something about my E2's on the afm plug. The E'2's are the third from either end. They are SUPPOSED to splice together in the harness somewhere along with the other brown/black from the other sensors in the engine bay.

Well I notice the E2 on the right of the plug read 0.3 ohms and the other E2 read 0.3 ohms. IF I removed the extra ground to the boost sensor I just described above, the E2 on the left of the plug reads 3.8 ohms now but the other E2 still reads 0.3 ohms. Quite a jump from 0.3 to 3.8ohms.

Especially since the wiring diagram shows both tied together inside the harness. So I'm making sure I reattach that extra ground to the boost sensor brown/black. By the way, later cars did not use a color of brown/black. They used a pure black wire. Go figure.

 

..

 

Thanks hailers.

So, I went out and checked the resistances again. With the key to off, the E2 connectors on the end of the harness are both below 1ohm in resistance (one's ~.3, the other is a little higher like ~.7). So they're probably OK.

But, when I checked the ground for the boost sensor (just a black wire on my car I think) the resistance was 3.8 ohms. So even though my car is an 88 (TII), do you think I should add an extra ground wire for the boost sensor?

Also, when I disconnect the harness at the ECU and check the grounds, they're all about 7 ohms. Would it be a good idea to splice another ground wire into the ECU grounds to get it closer to <1ohm?

Finally, I checked the AFM voltage using the sensor check function on the SAFC. Closed it's at 3.8volts, fully opened via my special AFM checker (screwdriver) it's showing ~.32 volts. There weren't any opens that I could see, it was nice and smooth the whole way.

 

Yah, I was thinking backwards. Been far too long since highschool electronics classes