A lot of cars have a MAF sensor AND a MAP sensor. If you introduce exhaust or air into the intake it will change the MAP to a pressure that the PCM will interprete as a larger throttle opening...and therefore more fuel will be added.
It def affects o2 sensor function, albeit briefly, you can see the valve open on the o2 waveform. I dont see how it couldn't affect fuel trims. You can test by applying vacuum to egr, hold at 2k rpm & watch fuel trim change while open.
The thing is, on some cars, it doesn't affect fuel trims at all. Here's why, it's not the exhaust gas that changes the fuel trims. Exhaust gas doesn't have appreciable amounts of o2 in it, so it doesn't change the o2 sensor reading on some cars. If the egr system is capable of flowing enough volume, relative to the cylinder charge volume at a given rpm, it will dilute the charge enough to cause a misfire. It's the extra 02 from the unburned charge that makes the effect happen. However, if you do a web search, most reputable sources simply say that egr flow will not affect fuel trims on a maf engine. It depends on displacement, maximum egr flow, intake design etc..... The bottom line is, you can not rule out unwanted egr flow, as the cause of a fuel trim issue on a maf system, without testing it by some other means. If your smoke test comes back good, but it still looks like a vacuum leak on the trims, you better look close at that egr.
@@tradito Technicians analyze fuel trim data when trying to get a direction to start more pinpoint type testing. Some literature on the subject has (erroneously) led people to believe that (on all maf systems) egr flow has no effect on fuel trims. This proves otherwise. It may help prevent many technicians from making a mistake due to misinformation that is sometimes presented as fact.
that was pretty good.
Thank you for the information!
No problem, hope it helps some people!
A lot of cars have a MAF sensor AND a MAP sensor. If you introduce exhaust or air into the intake it will change the MAP to a pressure that the PCM will interprete as a larger throttle opening...and therefore more fuel will be added.
It def affects o2 sensor function, albeit briefly, you can see the valve open on the o2 waveform. I dont see how it couldn't affect fuel trims. You can test by applying vacuum to egr, hold at 2k rpm & watch fuel trim change while open.
The thing is, on some cars, it doesn't affect fuel trims at all. Here's why, it's not the exhaust gas that changes the fuel trims. Exhaust gas doesn't have appreciable amounts of o2 in it, so it doesn't change the o2 sensor reading on some cars. If the egr system is capable of flowing enough volume, relative to the cylinder charge volume at a given rpm, it will dilute the charge enough to cause a misfire. It's the extra 02 from the unburned charge that makes the effect happen. However, if you do a web search, most reputable sources simply say that egr flow will not affect fuel trims on a maf engine. It depends on displacement, maximum egr flow, intake design etc..... The bottom line is, you can not rule out unwanted egr flow, as the cause of a fuel trim issue on a maf system, without testing it by some other means. If your smoke test comes back good, but it still looks like a vacuum leak on the trims, you better look close at that egr.
sorry, i'm a newb at cars. what does this mean?
@@tradito Technicians analyze fuel trim data when trying to get a direction to start more pinpoint type testing. Some literature on the subject has (erroneously) led people to believe that (on all maf systems) egr flow has no effect on fuel trims. This proves otherwise. It may help prevent many technicians from making a mistake due to misinformation that is sometimes presented as fact.
@@JessClearyAutoRepairLLC thanks. so deleting the egr can have effect on fuel consumption?
The point is, when analyzing fuel trim data for drivability problem, a defective egr system cannot be ruled out simply because it's on a maf engine.