Everybody wants inexpensive repairs. Unfortunately that's not a choice we're given. If all it took was a can of chemicals to solve a problem we wouldn't need mechanics and they'd all be out of jobs.
Fuel injector cleaners in a can are just concentrated versions of what's already in high-quality gasoline. The really effective cleaners are in a bottle that is attached to the fuel rail. The fuel pump is disabled, then the engine runs on that bottle for about 20 minutes. I've heard of that stuff solving hesitation problems on GM engines. They have their own problems. Chrysler has very little trouble with their injectors.
The first thing you have to figure out is why there's a misfire. Every cylinder needs compression, and the right amount of fuel and air. Lack of compression is a mechanical problem and the least likely cause of misfires. Loss of spark is the most common cause but you also have a clue in code 201. The Engine Computer can't detect what the valve inside the injector is doing. The only way it can set a code is if it sees something wrong with the current going to the injector. It still doesn't know why there's something wrong with that current flow. That's where the mechanic comes in. He is trained to diagnose the cause with various tests and measurements.
The best guess is there's a break in the circuit someplace. The list of possible causes of a break include a cut wire, a corroded splice, a corroded or stretched terminal in the connector on the injector, a broken wire inside the injector, and a stretched or corroded terminal in the Engine Computer's connector.
Most mechanics would unplug the computer's connector, then measure the resistance in the wiring for the problem injector circuit. The injector itself is by far the least likely thing to cause an open circuit, (break in the circuit), but some people go right to the injector and unplug it first to measure it because it's easy to get to. The problem with that approach is it is more likely a terminal in that connector has a light film of corrosion. Once testing proves the injector is okay electrically, plugging the connector back in causes a scratching action between the terminals and will often solve the problem, ... Temporarily. Now the engine runs fine, there's no problem to be found, and any further testing will be fruitless. The mechanic may not know what he did, and for sure he would never call it "fixed". The goal is not to simply make the engine run right; it is to know what it will take to make it run right, THEN do what it takes. Without knowing what it will take, there's no way to know if anything you did will permanently fix the problem and there's no way to guess if or when the problem will show up again.
Getting back to that plug on the injector, logic would say if the engine runs right after unplugging the connector and plugging it back in, something changed by doing that. This is where you look for signs of corrosion or a stretched terminal. The male terminal fits snugly inside the female terminal. If the female one loses its tension, the two will make no or intermittent contact. This happens most commonly from do-it-yourselfers sticking test probes, paper clips or some other wire in them to take measurements. If those things are too fat, they can stretch the terminal. Usually they can be removed from the connectors and tightened with a small pliers or pick. It's hard to get in there to sand them clean so if corrosion is suspected, a contact cleaner works best, then you plug and unplug the connector multiple times while the terminals are still wet.
The smarter mechanic will start right at the Engine Computer's connector and take the resistance measurements there. Those connectors are well-protected against water entry and the terminals are very high-quality so that's not a common place to find a problem. If measuring there shows the proper resistance, that entire circuit can instantly be ruled out as the cause of the problem. It's more likely the resistance reading will be incorrect, then the mechanic knows he just has to narrow it down. I used to run into this all the time in tv repair. I'd start by gently wiggling any related connectors while watching my meter. If the reading changed, that connector got examined. If the reading didn't change, that's when it was appropriate to unplug them and measure the individual wires and parts in that circuit.
All of that took WAY longer to type than it takes to do. Inexperienced younger mechanics jump right in like a do-it-yourselfer. Experienced mechanics know to avoid making the problem clear up so they can find the cause.
If you don't have the test equipment and know how to interpret the readings, there's only two ways to approach this. One is to throw random parts at it in hopes one will solve the problem. That is never a good choice unless you have some valid reason to suspect a specific part. You will find out that is the least effective and most costly method of diagnosing a problem. We read about those here every day where someone replaced $600.00 worth of the wrong parts and it's still not fixed. At some point you have to know it would be less expensive to let a mechanic diagnose it. Also, with every new part you introduce more variables that can easily compound the problem. That's a whole 'nother chapter in how the Engine Computer learns the characteristics of those new parts.
The second method that involves more time than money is to swap parts. Beginning with all '96 models, the Engine Computers can detect which cylinder is misfiring so you have that advantage. You know it's cylinder number one. Instead of removing the fuel rail to switch two injectors, you may be able to just switch the plugs between number one and the one next to it. Both injectors will fire at the wrong time but that timing is not important. Now, if the misfire code is still for cylinder one, you know the cause is not the driver circuit in the computer or the wiring because cylinder one injector is being run by the circuitry for cylinder three which was just working fine a minute ago. That leaves the injector itself or a spark problem.
Most of the time mechanics are looking for an injector mechanical problem instead of an electrical problem, so they will remove the fuel rail, then switch the suspect injector with one of the other ones that are known to be working correctly. That takes longer to do, but if a code pops up now for the different cylinder, they know for sure that injector is defective and they can order a new set with confidence.
You see how much I just typed about one possible condition for one fault code. There are many pages of diagnostic tests for each code, and there are almost 2000 fault codes that can be set in just the Engine Computer. There's dozens of other computers each with their own sets of fault codes. There's a 2" thick diagnostic manual for just one engine size on one car model for one year. We can't hope to cover even a tiny fraction of those things in a 200-hour Automotive Electrical class and a 240-hour Engine Performance class. All we can hope to cover is how to do the testing and interpret the results. Once in a while we will run into a "pattern failure" meaning the same common failure on the same engine and car model over and over. That's what you're hoping to find but it's not going to happen. There ARE many pattern failures that are so common we can tell people exactly what to look for or which part to suspect based on their detailed description of the symptoms, but that's not the case with code 201.
One last thing I should point out is fault codes never say to replace parts as way too many people think. They only indicate the circuit or system that needs further diagnosis. That pertains to this code too. It doesn't say which part is defective or what is wrong; it just says something is wrong and it narrows it down to one cylinder.
Friday, December 7th, 2012 AT 8:34 AM
