Due to a major house fire, I don't have internet at home. I drive 10 miles to town each day to help here, but I only do that a few hours per day. Today I'm here a lot earlier than normal to see if I can help. Most of the other experts are at their regular jobs so they won't respond until later.
When I need to post diagrams or drawings, those need to be copied and have arrows and callouts added, then they must be transferred into a format that can be uploaded. In some cases, especially for engine performance problems, that can include up to 12 to 24 separate diagrams, with each one taking 15 minutes or more to complete. I can do that at home, but it often takes until the early morning hours. That's why I don't show up here again until early evening the next day.
As are a few of our other experts, I'm a former instructor. As such, I'd be happy to help you understand how fuel injection systems work. I'm more familiar with Chrysler systems up to the late 1990s, but I have two 2014 models, including a Grand Caravan. I started following your question in hopes of learning the solution in case mine develops the same problem.
I have three areas of expertise, but engine performance is not one of them. That's why I'm quite happy to let Steve lead the way. He's a lot smarter than I look, especially in this area. As for how these systems work, for the most part, GM and Chrysler did everything the same except for a long time Chrysler didn't need a mass air flow sensor to make their engines run right. GM had a couple of models that also didn't use a mass air flow sensor, but almost all other brands and models do. Those measure the weight of the incoming air and provide the most important variable in the fuel metering calculations. If there's an air leak anywhere after that sensor, which sits in the intake tube, the air won't get included in the calculation and there won't be enough gas to go with it. In the earlier years, Chrysler only used the MAP sensor to calculate the load on the engine. It measured intake vacuum. That was their most important variable when calculating fuel needs. Many other brands used the MAP readings as a backup strategy when the computer detected a problem with the mass air flow sensor. Chrysler also takes a MAP reading before the engine starts to know barometric pressure.
The biggest changes in engine electronics showed up on 1996 models sold in the U.S. It incorporated a lot of new emissions systems and monitors. Those became more refined later, but now we're running into mechanical advancements that are new to many of us. The big one is variable camshaft timing. Technology is squeezing more power at different rpm ranges along with improved fuel economy, but with increased complexity and questionable reliability. This is why we're seeing so many hard-to-diagnose problems we never saw before. Along with that is a whole new series of diagnostic fault codes that we're unfamiliar with.
Most of us would not want to go back to the days of carburetors, especially once we understand fuel injection systems, but consider that among the huge list of Chrysler's innovations, they were the first one to use an Engine Computer in 1977. All they did was adjust ignition timing. Since the late '80s, all of the computers could detect certain defects and set diagnostic fault codes related to them. The biggest confusion with those codes, including those you found, is they never, ever say to replace a part. Way too many competent do-it-yourselfers see a fault code and instantly take it to mean the part referenced must be replaced. in fact, when a sensor or other part is listed in the code, it is actually the cause of that code about half of the time. It's just as likely to find a corroded connector terminal or cut wire. Those are a couple of things we have to check for before spending our customer's money on a new part.
There's a couple of thoughts to get you started. This really isn't the place to continue this part of the conversation as we try to stick to one topic per question. That's for a couple or reasons. First, others researching a similar "how-it-works" concern may not find your question because it's categorized under a different topic. They'll miss my wondrous wisdom here. Second, unlike how other forums work where anyone can show up and add a confusing comment, here it becomes a private conversation between you and just one or two other people. As such, none of the other experts are going to see your newest desire for knowledge or have a chance to reply. Often that may not get you the best help. By starting a new question just for system operation, more experts will see your request, and only those who feel they can do a good job will offer a reply. There are even some people who are smarter than me, although only I can make it easily understandable. (Eye roll appropriate here).
Keep in mind too that while we all have areas of expertise, models change every year and we will run into designs we're not familiar with. One of my specialties is Suspension and Alignment, but when helping a friend, I see new things all the time that I don't have any formal training on. My friend has a body / repair shop where he specializes in rebuilding smashed one and two-year-old Ram trucks, and other Chrysler models. I help him with electrical problems, but I get to see new suspension and brake systems all the time. I rely on following a lot of questions here to learn what kinds of problems these new designs are running into and how they get solved.
A good place to start when researching how something works is with this list of articles:
https://www.2carpros.com/articles
By necessity, these have to be short and inclusive of all appropriate brands, models, and years, so they're just a starting point that can start a conversation. We don't like to ask, but it's really helpful to know your experience level with the topic, and whether you know how to use certain test equipment and have access to it. Scanners and voltmeters are the two best examples. That helps us tailor our replies so we don't make them too confusing or overly simplified. I can type a reply to an electrical question a lot faster when you understand basic electrical theory already. When you don't, I can work with that, but it may be necessary to include some basic theory or generalizations to make it understandable. Most of us here are not satisfied with just spewing out a solution. We like to include details as to why something failed, how it's supposed to work, or some other details that may be relevant. That knowledge can be useful when working your way through a circuit, and it can prevent you from wasting time with unneeded tests.
To get back to the original problem, Steve will handle this better, but I can offer a couple of observations for you to mull over. If you're seeing too much unburned fuel leaving the tailpipe, there's two causes to start with. One is too much fuel is being sprayed by the injectors. The other is it's the right amount of fuel, but it's not being ignited. The injectors are pulsed open and closed by the Engine Computer. On most engines, fuel pressure is not monitored but it is carefully controlled by a fuel pressure regulator. That makes pressure a variable that is programmed into the software, so the computer knows it. Based on all the other sensor readings, the computer calculates how many milliseconds to hold the injectors open. When closed, an injector can leak, but that will be too slowly to show up while the engine is running. When the engine is stopped, that fuel pressure should hold for days or weeks. With a very small leak from an injector, pressure will bleed off within a few minutes. Most of the time the only complaint is a long crank time because pressure has to build back up before the engine will start. With what you're describing, the better suspect would be an injector control wire shorted to ground. That would hold the injector open constantly, and that would allow way too much fuel to enter one cylinder.
We also have to look at the ignition system. Most engines use a camshaft position sensor and a crankshaft position sensor. They develop voltage pulses. The actual voltage isn't important. The computer looks at when the pulse goes up or when it goes down to know precisely when to fire an injector and a spark plug. Some engines will start and run with one failed sensor. Some will run until stopped, then they won't restart. Others, especially older engines will stall if either one sensor fails. Some of these sensors have electronics built in, so all kinds of unusual problems can occur. We even used to hear stories of a cracked magnet inside a crankshaft position sensor that caused it to develop multiple and erratic signal pulses, and that resulted in the computer firing the injectors too many times. Spark timing would be wrong too.
I don't mean to jump in ahead of Steve, but some things he is likely to suggest include measuring fuel pressure, and unplugging injectors to see what affects the symptom. Ya gotta have fuel in the right amount, spark, compression, and all of those things at the right time for the engine to run. Various tests will show if one of those is not correct. If two are incorrect, specifically fuel and spark, at the same time, he will go in an entirely different direction with what they have in common. Most commonly that is the two sensors I mentioned.
Rest assured we will not abandon you. We've all had questions that have taken months before we arrived at a solution, but no one gave up. We can enlist the help of others too if that becomes necessary.
Friday, February 2nd, 2024 AT 12:59 PM
