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Jim Testa's TroubleShooting Logic


If you compare the following with the factory troubleshooting tree, you will see a lot of similarity, but, this may be easier to follow-certainly makes a lot of sense to me.  BTW, I always check the ECM-IGN, CCCI, and FP/INJ fuses-the latter if the pump does not run.  If the pump does not run, you are not going to have any fuel pressure and the car will not start.  Steve W.

"OK, to diagnose ANY car, you need to find what you have and don't have. The way *I* usually go about it (which might not be right to some people, but it's methodical and consistent so I stick to it.

1) Note the check engine light (if EFI). If its not on, STOP and find out why. Listen to how it cranks. I can pick out compression problems doing this. If you are in tune to your car, you can too. Listen to the starter as each cyl comes up on compression stoke. You'll hear the starter slow down a little at that point. You might hear deerdeerdeerdeer, where a dead cyl might sound like deerdeeeeedeerdeer (great sound effects huh?)

2)Depending how accessible the intake is, I'll shoot 3 or 4 seconds of carb cleaner into the plenum. Either thru the throttle body, or, the brake booster vacuum port.  If it's a lack of fuel problem, the car may start, or it may simply kick.  If it does either, it's time to look to at the fuel system (usually, although enrichening can bring out a low secondary output problem too, so don't take my suggestion of fuel as law)

3) If the car kicked, I'll put a FP gauge on it. If fuel pressure isn't in spec, now you need to see why. Fuel pump, filter, restricted line, bad reg, low batt voltage, bad relay, blown fuse etc.  If FP is in spec, it's time to hook up a noid light and verify our injectors are getting pulsed. If you're not getting a pulse, you will want to hook up a scanner (or tach) and look for RPM during crank. If you are getting RPM signal, check for spark. If you're getting spark and no fuel, although there is a commanded PW (see below) you probably have a bad ECM. How fast it cranks isn't as important as the fact you get a RPM signal. Next you'll look at Coolant temp to see if it coincides with ambient ) if the car is cold), and verify TPS isn't shorted to Vref which will put the car in clear flood and cut off fuel.  If these all look OK, you'll want to take a look at commanded PW. (If there is no rpm shown during cranking-I immediately suspect the module-but, read on, Steve)

4) If the car didn't kick, I'll yank a plug wire and see if I got spark. If I got no spark, then I'll check also for inj pulse using a noid light   (Noid light that is labelled G.M. PFI or G.M. PFi-B). If I have neither its usually due to a dead crank sensor. If I have no spark, but I have injector pulse, its usually a module.

No start - no spark, has inj pulse ; Module
No start - has spark no inj pulse -; ECM / cam sensor prob
No start - no spark OR inj pulse - crank sensor or module

Oh, and if the module is dead, I suggest putting a coil pack on it as well as most of the module failure are caused by an overheating or arcing coil."