Liquidog

Hi all. I have reason to believe that the ECU is not getting the correct voltage from the AFM. How would I go about testing that with a multimeter? Take your time and speak slowly because I'm an electricity noob.

Background:
1990 with 1.8 swap. Car ran fine for a few years, maybe a little rich, not sure, back in Illinois I didn't have to do emissions testing. Eventually I installed a DIYPNP and turbo setup. That worked fine but I always had to keep my fuel tables insanely low to get the car to run right. Fast forward to now and I'm in California trying to pass smog. I put the car back to stock. It failed smog. Running way rich. I went through the entire fuel system and afterwards installed a fuel pressure gauge. It reads about 41PSI at idle. I've done the timing belt a couple of times to be sure. Dead nuts accurate. AFRs in the 10s for no apparent reason. This continued until I took off the AFM and adjusted it much leaner. This way, the car would run fine, albeit with awful gas mileage and still not passing smog.

The other day the car started behaving the way it did before I adjusted the AFM, super pig rich. I checked the timing. Still dead on. Swapped in a spare CAS and verified timing with light, still pig rich. Plugs fouling bad. Then I checked codes and noticed it was throwing 10 and 8. Research led me to check the AFM grounds underneath the brake booster. I took that clip apart and did some cleaning, cleaned the threads in that hole as best I could, and used a fresh bolt. Even tried a completely different hole nearby that was more accessible and therefore more cleanable. The codes are gone but the car is still running pig rich. I also have a brand new AFM and it makes no difference if I install it or use the old one. So, I suspect that the signal is getting compromised somewhere between the AFM and the ECU. Since running rich was also a problem when I had megasquirt installed, I think I can also cross off the ECU as the culprit. With megasquirt installed I ran the typical GM IAT - plugged into the same problematic AFM pigtail. So I'm pretty sure something is up with my AFM grounds or AFM wiring. How can I get to the bottom of this?

Z_WAAAAAZ

Have you diagnosed any wiring concerns aside from the the grounds beneath the brake booster? Based off of everything that's been done/checked already, there's not many other steps left except to bust out a multimeter and start testing the AFM wiring. I'd probably ohm out the AFM signal wire to the PCM and see if there's high resistance in the wire or a short to ground. Second, I'd check for voltage at the AFM connector and make sure you're getting 12v with key on engine off, or as close as possible to whatever the exact battery voltage is.

Liquidog

Thanks for the pointers - yep, did some testing today with the multimeter. AFM connector is getting power. Continuity between the AFM signal wire at the connector pigtail, and the AFM signal wire at the ECU plug, is very shaky. I was able to get the pin out of the connector and it looked fine and did better with continuity out of the connector, but after reinserting it in the connector and plugging that back into the ECU, the richness problem persists. I ordered new ECU connector shells from Ballenger along with terminal pins. This car has a lot of hard midwest miles on it and I noticed a lot of the wire strands at the pins are covered in corrosion. I suspect not just the AFM signal wire but probably also other wires are developing issues transmitting voltage - or will eventually - so I'm going to cut the wires right at the connector and crimp new pins on to nice clean copper before inserting into the new ECU connector shells. I figure this 33 year old ECU connector assembly has done it's duty and it's time for full renewal.

Z_WAAAAAZ

Heck yeah dude, that's proper! Yeah, 33 years for a little piece of plastic being exposed to constant heat cycles and moisture is pretty good. I'm always impressed that more of the connectors in my car's engine bay aren't completely disintegrating haha.

Let us know what happens after you splice the new connector in.

Liquidog

I replaced the ECU connectors with the kit from Ballenger. Continuity at the connector is solid now. However, the rich issue persists, so there has to be an issue somewhere else.

How do I check the voltage the AFM is sending to the ECU connector? I know it's supposed to be 4-5 volts with the key turned to ON, and zero volts at WOT. But I don't know where to put the other multimeter - one probe goes to the red AFM wire and the other one goes to...? Do I stick it in one of the ground pins at the ECU connector? Sorry for this unbelievably basic question. I'm just trying to figure out why there's apparently no voltage going down the red AFM wire to the ECU, but there is continuity? Could this be an issue with the 5-piece ground under the brake booster? I did do some work on it, but maybe I should cut the connector out and have all the wires go into a single big ring terminal? My electronics understanding is obviously very basic and I'm tearing my hair out over here.

curly

iTrader: (25)

Yes, you’d connect the other probe to ground, and monitor volts while running. I don’t know a whole lot about the AFM, but if it is 4-5 volts off, 0v WOT, then I’d expect nearly the off voltage while idling, because there’s very little airflow. You can adjust the spring tension to adjust idle fueling, but I’d expect something else to be going on. What fuel pump is in it?

Liquidog

Into one of the grounds on the ECU connector itself? Is there a specific one that’s best?

I’ve tightened that AFM spring 5 clicks and it did help for a while, but whatever this issue is, it’s gotten progressively worse and that adjustment is no longer able to overcome the voltage drop, which is why I am now forced to learn how electricity works.

Everything in the fuel system is brand new, there’s a fuel pressure gauge installed, it’s around 38-40psi at idle, so I don’t think that’s the source of the issue.

Right now I am cleaning up grounds. There’s two at the passenger rear of the engine: one two black wires (ECU ground?) and one with a black wire and a black and green wire (Sensor ground?). Both had been mounted on the back of my intake manifold, on the EGR block-off plate. Research seems to indicate I should mount the black/black on the rear of the head and the black/black&green on the rear of the intake manifold. Keep in mind it’s an NA6 chassis with an NA8 engine.

Any thoughts welcome!

Liquidog

Cleaned up passenger side grounds. Rigged up a little bracket from the parts bucket for the black/black grounds and did the black/black&green directly to the manifold instead of the block-off plate. Cars seems to run ever so slightly better but still incredibly rich. On to the JC-01 white plastic block under the brake booster next.

Liquidog

I completely redid the grounds under the brake booster and code 18 is gone. The car continued to run very rich but I traced this to a bad coil pack not firing two of the spark plugs. Luckily I had a spare coil pack. I swapped that in and the car is now throwing a code 1, no ignition signal. It will start and sounds better, but won’t idle for long and then stalls. I bench tested the coil pack and it seems fine. It’s definitely getting good voltage at its connector too. Plugs are new and I cleaned them again before this start. Here’s the weird thing: voltages with key turned to on.

• Voltage for the AFM signal both at the AFM and at the ECU is 3.87. This is slightly out of the 4-5V spec but seems close enough for now.
• voltage for the IAT signal at the AFM and at the ECU is 2.42 - over the spec of 2.18
• voltage for the IGF at the ECU, yellow/blue wire at pin 2I, is 5V. My understanding is it should be at .5 so it’s very far off.

so what’s going on with the Code 1 and ignition voltage being so far out of spec? Does the voltage regulator in the alternator handle this? I have other reasons to suspect the alternator - I notice the battery light is on now. The battery is fairly new and stays on a trickle charger at all times so I don’t know what else it could be. The original problem, my AFM wiring, seems solved, but I’m worried that my alternator - which was used when I bought it - has crapped out. Thoughts?