legacycentral bbs

I have a 92 Legacy NA. I have been having trouble with starting lately and decieded to investigate my code 24. I took the IAT off and swapped it with a known good one but I still got the code. I then swapped the ECU with a known good one. I still got the code. So I did some more digging and according to the FSM, I am supposed to have 6 volts and 7 volts on Pins 1 and 3 of the IAT connector, or at Pins 1 and 2 of the F47 on the ECU with ignition on and car not running. I have 2 and 5 volts. I think this is causing my IAT to act up and my starting troubles.

If I put in a 90-91 ECU the voltages are closer, 4 and 6 volts, and the car starts and idles fine, but with the 90-91 ECU I have a different set of driveability issues.

The FSM says "Repair ECU terminal poor contact [Replace ECU.]" I'm not sure which contact to repair

Either I am not getting enought power to the ECU (poor ground connection or related), or some other device that is hooking into the ECU is pulling the voltage down.

I think this is also causing my intermittant code 32.

Any thoughts.

I'd suggest checking your wiring harness. either to the ECU and/or to the IAC valve.

I checked the continuity for the two wires that go to the IAT and they both seem fine. I even tried jiggling them and my multimeter said they were fine.

I did some more testing, and I wasn't reporting the voltages correctly. They were at .2 and .5 volts. Not 2 and 5 volts. But I went to my working car and they were even less. Like .06 volts. I can't figure this out for the life of me. The FSM says that the wires should be at 6 and 7 volts. Is this supposed to be with the IAC plugged in?

Also, if I go out on the highway and punch it, when it gets in the upper 5000's the tach starts to jump around. Sometimes even dropping to 0 for a while. The car is still running fine, and Vrg's app shows good RPM values.

Do I have some sort of grounding issue? Does anyone know where the ground points are for the ECU or the tach?

Thanks

Sounds like you may have intermittent connections on your wiring harness. As far as your measurements, make sure you have your meter set correctly. You may be measuring AC volts, but you should be measuring DC volts.

Are the connector pins clean and shiny? Is there any corrosion? Are they tightly connecting together?

You really can't directly measure the voltage of the IAC valve pins when the engine is running. The reason for this because the signal is a PWM signal. You need a special meter to read that.

Are you doing your testing when the engine is running or engine off, and key in the ON position. You should be testing things with the engine off, and key in the ON position.

I'm assuming you're using these pages to test the IAC valve
http://www.main.experiencetherave.com/s ... C_Diag.zip

What resistance are the IAC valve pins showing?

That is the diagnostic test I was running. I am doing the tests with engine off, key in the on position. What I was asking was if I should be taking the reading from the F47 terminal with the IAC valve plugged in. I am not trying to do the test wth the engine running.

I have been taking the measurement with the IAC not plugged in. I'll try it again with it plugged in.

An a side note, after running *okay* for a few days, the car is not starting again today. I know the only codes that will show will be 24 and 32.

I have tried swapping CAM sensor, Crank sensor, MAF and IAC. I also checked the fuel pressure, it is up over atleast 30 psi before after turning the key forward, and holds its pressure.

Pretty sure the IAC valve needs to be plugged in. Are you back-probing the ECU connector to check these voltages?

Also, are you sure you have the correct pins on the ECU connector?


Have you tried the continuity tests for the wiring harness

If you've done all the tests, please post the results of each

I checked the continuity on the wires from the ECU to the connector harness and they seem fine. I will check the voltages at the ECU with the IAC plugged in.

So I think I have head gasket issue which I guess may be setting the codes. Regardless, the head issue needs to be addressed first. I have the FSM and I have done this type of work before on Chevy V8's so I think I will attempt it. Also, according to the FSM its is a only a 5.5 hour job (for a professional) so I figure I can get it done in two days.

Are there any good threads in the forum that discuss a head gasket replacement? I searched twice but didn't really find much.

Thanks

I'm not sure if there's a thread specifically noting head gasket replacement/work. I'd start with searching the engine forum. If you don't find anything, and have specific questions, post there.

After chasing the electrical problem to no avail I performed a cylinder leak down test and everything seemed okay. I tried a bunch of other stuff then decided my no start and erratic idle could be due to some sort of major vacuum leak and decided to replace the intake gaskets and TB gasket.

While in the process of pull the intake I discovered that there is a ground wire that connects to the back-drivers-side of the intake manifold. The bolt holding the wire had backed out quite a bit and the wire was not making a good connection. I was half way through tearing the intake off so I said f--- it and deceided to finish what I had started.

The intake gaskets looked fine, but will soon be replaced. I will let you know what happens, but I did some research and that ground wire is the primary ground wire for all of the sensors and switches and the ECU it self. I am pretty confident that this will alleviate all of my starting and idling issues, as well as the mystery 32 and 24 code problems. I'm putting it back together this weekend....fingers crossed.

The ground wire in question is referred to in the FSM as 'GE'. This wire connects to B48 - pins 11,21,22 and F47 - pins 14,15,24,25 on the ECU.

I'm honestly pretty surprised that I have never heard anyone talk about this ground point. From now on it will be the first thing I check whenever I get an ECU code.

B48 Pin 21 does not connect to that ground. Pin 21 provides a ground for the water temp sensor.

That ground in question is the engine sensor ground, however I'm not sure if it will affect starting.

Do let us know how things turn out.

Everything back together and running strong. I'm 99% sure it was the ground wire which was causing the intermittent no starts and hard starts. I am no longer getting the 24 and 32 codes either. It idles like a dream.

Thanks for all the help.

Nice work!