That's why you buy flow-matched sets. Linder Technical Services in Indianapolis puts on very expensive, high-level classes all over the country. They have solved a lot of problems by providing replacement injector sets after they have found no defects with those sent to them. They just flow different rates leaving one or two cylinders lean compared to the others. Their biggest sellers are by far for GM products and they claim many of the car owners are surprised by how smoothly the engine runs with the matched injectors. Chrysler buys their injectors from Bosch in flow-matched sets. GM grabs a handful out of a big bin. That is the word from the experts, not me. To be fair, there's a lot more GM products on the road so of course they're going to sell more injectors for GM vehicles. No mention was made that I recall about other car brands. Check out their web site and their "Dirty Dozen" most common failures.
It seems too many mechanics rely on resistance readings to determine if an injector is bad and they condemn way more than necessary. I don't have an issue with replacing just one defective injector but when you're looking for the cause of an intermittent problem, I'd look at the ignition system first and compression problems last. If one cylinder is running a little lean, you are less likely to feel that compared to a loss of spark, but the Engine Computer can pick that up. That's the most common cause of misfire codes that you can't feel.
A lab scope can show if an injector is opening at the right time but it won't show a restriction. If you're good with a scope you can also look at the oxygen sensor waveform to tell if a problem is due to ignition, fuel, or compression. Most of us will never be that good. It's one thing to watch a slide presentation in a class but quite different to try to do it on a customer's car when you're charging by the hour. Even those instructors have to fiddle around for a long time to show what they want us to see, ... BUT, in my case the instructor owns a specialty shop that only solves the one in a hundred no one else can solve. Their customers are other shops, and they have plenty of time to experiment and put together a presentation on their findings. We don't have that luxury.
For the injector balance test, are you going to cancel one at a time with a scanner? How would the results of a restricted injector be different than from low compression? Are you watching the drop in engine speed or are you doing something else?
Given that this is an intermittent problem, measuring the injector's resistance is useless unless you can do it at the instant the Check Engine light turns on. That's not practical. You COULD replace the suspect injector and hope you didn't waste $290.00, or you could just swap two of them and let the Engine Computer tell you if you're on the right track.
The computer is the last thing I would suspect. If one injector is not firing due to lack of current flow, the diagnostic fault code should reflect that. I'd suspect a corroded connector terminal first, especially for an intermittent problem. As it is now, it's just detecting the misfire, not the cause. On engines that batch-fire the injectors, two or three would quit at the same time and you would definitely feel that. Too many people, it seems, jump on the computer right away as the cure-all for problems that haven't been properly diagnosed. I'd want to rule out every other possibility before I bought a computer.
Saturday, February 16th, 2013 AT 12:28 PM