Pesky P1131 on B2500


CodyDance

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Hello Everyone,

First time posting, but I have been reading and getting a lot of help from here for awhile.

I have a 2000 Mazda b2500 4 Cylinder 2.5L Manual with a P1131 code. My understanding of this code is that it is a lean reading at the upstream o2 sensor. Noticeable symptoms are bad gas mileage, low idle when moving slow, low power going uphill, and a somewhat erratic idle. I have tried quite a few things to fix this with no luck. This is what has been done on the truck recently:

-new upstream o2 sensor
-new egr valve
-new pcv valve
-new iac valve
-all new electrical parts (plugs, wires, and boots)
-new fuel filter

I tested all the fuel injectors and they are all firing. Also it runs much worse with the MAF unplugged, so I don't think it's that. MAF and throttle body are both clean. I had a smoke test done about 6 months ago and there were no leaks. I just sprayed carb cleaner around the fuel injectors and the obvious vacuum lines and found nothing.

What next?? One idea is to have another smoke test. Another idea is the fuel pressure regulator, but I haven't been able to find one for this truck anywhere (not even parts geek has one, nor 1aauto or O'rielly). Also there is a tube coming out of the fuel pressure regulator (not the fuel line going in, but a thicker black tube in the back) that might be glued on? Not clear to me how it is connected or how I would get it off.

Anyway, I'm open to any suggestions.

Thanks,

Cody
 


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adsm08

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You already replaced the fuel pressure regulator. On a mechanical returnless system the three-port fuel filter is the pressure regulator. The smaller rear-facing port is a return to the tank, and there is a bypass valve that closes and diverts fuel back to the tank when the pressure in the forward part of the system reaches a certain point.
 

CodyDance

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Hey adsm308, thanks for the response.

Are you sure? Yes, there is a 3-port fuel filter, but there is also this thing attached the fuel rail that looks (to me) like a fuel pressure regulator
KIMG0070(1).jpg
 

adsm08

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That does look like a vacuum pressure regulator. It would help to know where that other larger line off it goes.

I know that is how it works on the later ones.
 

curtis73

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Did you test fuel pressure? If the pump is dying it might not be giving enough pressure to supply the necessary fuel.
 


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