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AFRs high...but midrange only


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Any ideas what would cause AFRs to be high in the mid-range rpms, but fine in the lower and high rpm ranges?


Background: My car was on the dyno after the latest goodies purchase. Come dyno time, and 2 hours later, the tune has to be called off because of this issue. Now the tuner, is a god. he has tuned over 3000 subies and has never seen anything like this. The whole shop crew, who are very very good, was looking over trying to figure it out.


They check/replaced the fuel pump again, no fix

They swapped out intakes, no fix

They swapped out MAF sensors, no fix


They think it may be an injector (DW 850), and will look at it again this week. They may try to get another set from the supplier. Any input form the forum? and no, i dont have any logs. List of mods can be provided if you think it is useful.

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Replaced. It is a pretty small metal box bolted to the side of the trunk. The signal to it can be logged, but unless they really screwed up the tune he signal to it should be fine. The thing runs 3 duty cycles - 33, 66 and 100, corresponding to idle, part throttle and WOT. It might be skipping the 66. There is only one way to find out - measuring fuel pressure. Just about any 02+ Subaru has one, so a swap is easy.


Either way a check of fuel pressure is needed.

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Could it be FPR? My symptoms were a bit different, but that was the problem...the vac/pressure hose connecting the FPR to manifold popped off.


Not to be dumb, but you are using a Wide Band O2 sensor, and comparing AFR of the wideband to you fuel map, right?

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