Case Study Using a KV tester
Where do you go first, when you have one that runs bad? I usually look at O2 first, it will tell you a lot about whats going on. Another approach, is to look at tailpipe readings to give you an idea. I suppose most shops require hooking up the big scope and start there. Once you have an idea whats going on, rich-lean, etc. you know where to start looking. The above image is an 89 Chev Corvette 5.7 PFI 79k miles O2 at idle, engine at operating temp, pegged rich. I knew the engine was rich, I had the Mastertech on this one looking at the readings before looking at the O2 on the scope. When this thing went closed loop,(barely) it ran even worse, PCM was trying to turn off the injectors by adjusting ontime to its minimum, about 1.10ms integrator was pegged full lean, at 90. A definite rich exhaust, based on the O2 reading, but why? How many things will make this thing pig rich in open or closed loop? I usually look at the Evap system first to make sure its getting purged and doesn't have a saturated canister. Then the fuel pressure, fuel in the oil (makes sense on this one). All were good except the oil was a bit overloaded with fuel. So, whats left? Injectors... It was easy to ohm check them on this application, here's the results.
This is my Fluke 123 in its resistance mode, and all the injectors were in this range except for number four,
at 2.1 ohms. Here's the cause of the rich engine. Not quite shorted enough to shut off the driver for that bank in the PCM, but enough to flood the engine with fuel. Here's the Injector pattern.
Missing spike is at number four injector. Now just unhook that injector and,
the pattern returns to normal on that bank of injectors. Problem found. But wait, isn't this about KV testers? Remember I said these injectors where easy to get at and ohm test? What about those that are near impossible to get at without removing the top of the manifold? Even to do a balance test on them you would have to do the same (in most cases). Lets try to find the offender with the KV tester.
Since this has the enclosed coil, I need to look at each plug wire individually, most of them were in this range and are somewhat low (8-12KV is average at idle) at 6.6KV average and a low of 5.1 (all the plugs were fuel fouled).
Here's number four plug, clear down to 2.2KV minimum. Easy to see its the lowest, Its where I would look first. If I couldn't get to the injectors easily. Now, can I get the connector off that injector? Maybe... Can I get my test leads down in there? Maybe... Sheesh!!!