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Rough Running Stalling Using a Scan Tool to Diagnose the MAF in Your Car

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Created on: 2020-11-30

Andy shows you how to diagnose a rough engine by graphing the mass airflow sensor (MAF) output, and he discovers the simple cause!

Does your vehicle run rough and even stall at times? That's what this vehicle is doing, and we're gonna check it out in this video.

The first thing I'm gonna do is do a quick preliminary check. Just look under the hood, see if there's anything obvious. If there's anything loose, any wires that looks like they're disconnected, any hoses. That looks good. This is off right here. Although this just is an air intake into the airbox that needs to be secure, but that's not gonna cause an issue. And I'm definitely gonna check the oil level. Just take a look with the dipstick. And the oil level looks good. It's right in between the hash marks. It's not too much and it's not too low, and it looks fairly clean. So, I don't see anything obvious. I don't wanna take anything apart because I don't wanna fix anything by accident and not know what I fixed. So, the next step, I'm gonna scan the vehicle.

So, we did have a check engine light. So, we knew there was gonna be codes in there. And we happen to have a mass airflow sensor code, which is good that we have something to go on. So, that's the direction we're gonna look at. So, under the hood, this is the sensor that that code is related to. This is the mass airflow sensor, or MAF. This is the sensor that actually reads the airflow going into the engine so that you can get your air-fuel ratio dialed in correctly. And something is going on with this, so let's check it out. With a scan tool, I can actually graph what the reading is for the mass airflow sensor. We have 0.13 g/s, and that's with the vehicle not running. Now, I'm gonna start the vehicle up. And we're gonna let it stabilize out a little bit. You can see it's jumping all over the place which that's not good. So, this actually looks like it's running worse right now. It's jumping all around, the engine is running really rough and it doesn't look good at all. See, it just spiked right there.

So, this is what the mass airflow sensor is doing. And if I accelerate the engine a little bit, rev it up to around 1,500 RPM and try to hold it there, it's not easy to hold it there. If you look at it, it looks like it's bouncing all around. So, what we can do is we can monitor this flow on the graph. And what I'm gonna do is just wiggle the wires and see if I get a spike. See if it goes up. If I wiggle it just a little bit, just move the connector a little. There we go. That's not supposed to happen. So, there's a big spike. There we go. So, just wiggling the connector is causing all these spikes and it's causing the engine to flare up and down and stuff. So, that being said, the most likely cause for this issue is probably just the connector. We just got to replace the connector. That right now. Oh, it was down to nothing a second ago. Yeah. Right there. It was nothing and it just spiked back up. We did have that couple of spikes and caused it to stall. So, it's not getting any better. I'm gonna replace that mass airflow sensor and we'll go from there.

Now, we put a new mass airflow sensor in and a new connector. And if I accelerate the engine to around 2,000 RPMs, this is significantly smoother. It's not jumping all around like it was, which is great. And it hasn't stalled on us at all. Overall, the car runs a lot smoother.

So, in our case, it happened to be the connector for the mass airflow sensor. Now, because there was a problem with that connector and there could potentially be something wrong with the terminals in the mass airflow sensor, we replaced both. Here's some other things you can check if that wasn't the case.

I'm gonna check the airflow to the mass airflow sensor. So, I'm gonna take the airbox cover off, take a look at the air filter. It looks pretty good. Although there is a lot of leaves and stuff in here. You wanna make sure it's not plugged up. Doesn't look too bad. The airbox has a bunch of leaves in it, so I'm gonna clean that out. I don't believe that the leaves are the issue, although if a leaf somehow got past the air filter and were sitting on the mass airflow sensor, that can block the airflow and cause a situation just like this. All right. Take that out and slide out the sensor. And this is where the sensor actually reads the air. So, that's what we're concerned about. If you saw a little leaf right on there, that's gonna be your issue. I don't see any debris in there or anything. They do make something called mass airflow sensor cleaner. You're gonna wanna follow the directions on the can. You wanna make sure you don't touch the sensor itself with the straw or with the can. And just like I said, follow the directions on your particular cleaner.

I hope this video helped you out and gave you some information about mass airflow sensors and some of the things that could go wrong with them. If you enjoyed it, make sure you subscribe to our channel. Make sure you ring that bell and turn on all notifications so you don't miss any of our videos.

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