I started the day with three automobiles to take a look at. The 08 Mazda CX-9 had a misfire complaint. The 07 Chevy Impala had a no-crank complaint. The 02 Buick Rendevoux had to be battery boosted to start. No problem. I'll just grab the machine that tells me what is wrong with a car and get started. Oh wait, there is no such thing. It would be kind of cool to grab a tricorder and run diagnostics quickly just to see what the problem is. That isn't in the real world, though I do know a lot of people believe that to be how it works.
I'll explain how I do diagnostics and repair. At least, I'll give a few examples. First, I guess it is similar to triage. I have to take a look at each job on the schedule and see how to best get the work done. The 07 Impala had been towed in as a no-crank. I should explain no-crank. The starter is supposed to turn the engine, or crank it over. If that doesn't happen it's a no-crank. If the starter does turn the engine fine but the engine doesn't start, that's a no-start. The Impala, for me, did crank but very slowly. It did start as well and I drove it into the shop. Because it cranked slowly I suspected I might have a low battery condition. Low battery could be caused by an alternator not working. Since the car was runnning and might not start next try it seemed like a good time to see if the alternator was working. I put a voltmeter on the battery and could see just over 14 volts so the alternator should be ok.
You want to see the battery voltage reading with engine running to be more than battery voltage with engine stopped. The meter was already connected so I just had to notice the reading after shutting the engine off. Just under 13 volts and steady even with lights and key on. Basic testing, but looked like the alternator and battery were probably ok.
I still had two cars outside that needed checked so this was a good stopping place. I'd probably be looking for a bad connection or a starter problem on this one. I went to the Buick that was having to be jump started. I tried the start first with no booster and it cranked fine. Not even a slow crank, a nice normal fast spin and started right up. I drove the Buick into the shop. I tried restarting several times and found no problem. A basic rule of diagnostics is to "verify the complaint". It's nearly impossible to find a problem that you can't re-create. My plan with the Buick was already formed though. Open the hood, pull the key, shut all the doors and let it sit right there at least 3 hours. After that I would test for battery current draw. Maybe the battery was being drained while sitting.
I now had two of the three vehicles situated and had to take a look at the 08 Mazda. The Mazda was towed in but only because the owner did not want to drive it with a misfire. The complaint was a misfire. The car started and ran fine with no miss. I tried to load the engine a bit by power braking but still no miss. I decided to let the Mazda sit inside as well and rest. When the engine was cool I would use a scan tool to see if a particular cylinder had triggered a misfire code and begin checks with that cylinder. So.... back to the Impala since it was the only one with the complaint verified and present.
Now the Impala was the no-crank complaint that had cranked slowly for me. I tried to start and now it was no-crank. I didn't hear a sound from the starter solenoid which is usually a click. I watched the lights and they didn't seem to be losing power. The headlights go out normally on crank with this model so there was a bit of room for error in judgement. If the lights go out on a crank you probably have a bad connection. Here they seemed ok but since I wasn't sure I wanted to test the battery connections. You can make things complicated or you can make them easy. I prefer to work with easy and let any complications come from the car, not from me. I could take the connections loose, clean them and try again that's one approach. I could even do voltage drop tests with a meter while trying to crank. What I did was put a booster/jump pack on the battery connectors. If it then cranked I had a bad battery connection. It made no difference. I put the booster negative cable directly to the engine block and no difference so the negative cable was probably ok.
Next up would be to check at the starter for battery power to the solenoid. I ran a jumper wire down to the starter and to a test light placed where I could see it from the driver seat while cranking. I had power to the starter battery terminal and I had power to the solenoid wire from the starter relay. I could have enough voltage to light the test lamp but not to engage the starter and I could do voltage drop testing at the starter but I chose the tap test or whack it with a hammer method next. After tapping the starter with a hammer it did engage on a crank and did crank slowly. Bad starter.
Diagnostic tools needed:
Tools needed to repair:
Thanks!
G&G Auto Repair
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