Engine electrical system testing?

[Phaedras]

I've been wondering if anyone has experience with testing the electrical components such as MAF, IAC, TPS, CTS, etc. I don't feel like replacing random parts to fix the problems I've been having (idle, mileage, hesitation). Testing some of the components has yielded values that differ wildly from what is considered nominal by both Haynes and Chilton. I feel that this means I am doing something wrong. So before I spend big bucks, are there reliable ways of testing these components?

[Cougar]

What kind of tests are you doing, and what kind of meter are you using?

[Phaedras]

Just a regular multimeter. The manuals say to check for continuity and voltage by testing certain terminals on for instance the MAF, where it's like "check for a certain resistance between terminals A and D with the key in the off position", etc.

[Hank Roberts]

Just a regular multimeter. The manuals say to check for continuity and voltage by testing certain terminals on for instance the MAF, where it's like "check for a certain resistance between terminals A and D with the key in the off position", etc.

 

I bought the TSBs for my 1988 GL from Alldata ($25/year) and it's full of info I haven't seen anywhere else -- which may or may not be helpful. I can't judge, this is my first Subaru and it's still mostly in the shop trying to get working.

 

But -- things like, if you jumpstart the car with either engine revving up, or if you open the doors or windows while doing the jump, you can damage the computer.

 

Use a digital or analog multimeter with a minimum 10k ohm resistance. (because lower resistance, like on the standard over the counter meter, can damage the computer)

 

and so on and so forth.

 

Nobody takes sufficient precautions with electrostatic damage and computers, according to the real professional computer experts I know. Nobody, unless you stand over them with a shotgun watching every move. It's just too damned easy to touch something and zap it a little out of spec, with semiconductors.

 

Once that happens, nothing else is going to be exactly right in all circumstances.

 

So, you might want to try looking at the exact TSB for your vehicle, if you don't have all those yet.

It includes, for mine, some corrections to the older tech service manuals -- make sure yours aren't the old outdated ones!

[Cougar]

You may find that using a digital meter, for resistance tests especially, will give you better results. They are designed so they will not exceed the the threshold voltage of a diode unless in the diode mode. Using a analog meter may give a false reading in certain circuits.

 

Your meter should have a 20,000 ohms/volt sensitivity for voltage. If you have a cheap 1,000 opv meter that can cause errors also in high impedence circuits. A decent DVM can be purchased for around $30 dollars if you need one. I like Fluke models myself but they cost more.

[Bill90Loyale]

I agree with Phaedras and have long believed that it would be excellent to have a knowledgeable electrical person write up a tutorial for publication in the the USRM repair and mod. electrical section. I, for example, have a Sears digital multimeter in my toolbox that I've owned for about two years and barely know how to use. Sure, I've tried sticking the probes into various things and trying to figure out if I accomplished anything. And I even sucked into paying another $10 for the Craftsman How to Use a Multimeter booklet - which was written for someone other than me. In my book, the ideal would be a multimeter users guide for old subarus that would be written at about a sixth grade level to explain:

The best way to test:

1. A possibly dead purge or egr solenoid.

2. A possibly dead throttle position sensor and idle air control valve.

3. A possibly dead battery, coil, or ignitor.

4. A possibly dead ignition switch.

5. A possibly dead fuel pump.

6. And any other neat and particularly helpful things a person can do with a multimeter.

 

Anyone out there interested in writing the book on this subject?

[Cougar]

There are a number of books already available to learn about using a meter and troubleshooting technics. Half.com has some good prices on used and new books.

[Hank Roberts]

After I bought the TSBs for my 1988 GL, I started quizzing the mechanic by referring to them --

 

"The whoozywhatsis is giving a code? Before you swap in a new part, did you check the connections by the book? What did you measure when you went through the flowchart, for each of the different terminals it tells you to check?"

 

Generally I've been reassured, they actually do the procedure. Probably we should too.

The TSBs have a flowchart test procedure specifying exactly what to set and what to test, step by step, branching off depending on the result.

 

They also set out a procedure for checking and testing and fixing the electrical connectors and specify when to replace them, and how.

 

But they do cost $25 for the first car, $15 for each additional model, per year, from Alldata.

[Cougar]

Here is a link to a book that may be of interest to you. I have this book and it is pretty good.

 

http://half.ebay.com/cat/buy/prod.cgi?cpid=1173023&domain_id=1856&meta_id=1