{"id":216,"date":"2010-03-05T22:02:27","date_gmt":"2010-03-05T22:02:27","guid":{"rendered":"http:\/\/autotechdiagnostics.com\/?p=216"},"modified":"2010-03-07T22:02:57","modified_gmt":"2010-03-07T22:02:57","slug":"2000-toyota-tundra-3-4-p0171","status":"publish","type":"post","link":"https:\/\/autotechdiagnostics.com\/?p=216","title":{"rendered":"2000 Toyota Tundra 3.4 P0171"},"content":{"rendered":"

I arrived to a 2000 Toyota Tundra 3.4 running rough with a P0171 that was cleared by the shop. They had in hand fuel fouled spark plugs and no explanation as to why. <\/p>\n

I connected my scan tool and observed the fuel control and feedback PIDs. I found fuel trim to be positive (indicating a lean condition) at idle and at 2500 RPM. This ruled out a vacuum leak. <\/p>\n

The engine air flow was 7.56 grams per second (GPS) at idle. With an engine size of 3.4 lites I expected to see a GPS number close to that. A general rule of thumb: An engine flows about 1 GPS at idle per liter. For example a 2.0 liter engine would flow about 2 GPS at idle. <\/p>\n

\"DSCN3175a\"<\/a><\/p>\n

With a reading twice what it should be normally I wanted a close look at the sensor. Gaining access was easy, the mass air flow sensor is mounted in the air intake after the air filter near air box (arrow<\/strong>).<\/p>\n

\"DSCN3188a\"<\/a><\/p>\n

Once removed the mass air flow (MAF) hot wire was clearly covered in debris. This can lead to a skewed reading. When the hot wire is covered in dirt at idle (low air flow) the dirt acts like a radiator, cooling the wire and reporting a higher than actual reading. Off idle, the dirt acts like an insulator, protecting the hot wire element from the passing air and it’s cooling effect. This leads to a lower than actual air flow calculation.<\/p>\n

\"DSCN3181a\"<\/a>” \/><\/p>\n

The dirt was cleaned and the MAF sensor was installed.<\/p>\n

\"DSCN3186a\"<\/a><\/p>\n

The reading dropped a few tenths of a volt but not quite enough. <\/p>\n

\"DSCN3189a\"<\/a>
\nAfter confirming the reference voltage and ground was good to the MAF sensor I suggested replacing it. The MAF sensor itself was faulty. <\/p>\n","protected":false},"excerpt":{"rendered":"

I arrived to a 2000 Toyota Tundra 3.4 running rough with a P0171 that was cleared by the shop. They had in hand fuel fouled spark plugs and no explanation as to why. I connected my scan tool and observed … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[106],"tags":[109,110,108,107],"_links":{"self":[{"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/posts\/216"}],"collection":[{"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=216"}],"version-history":[{"count":8,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/posts\/216\/revisions"}],"predecessor-version":[{"id":686,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=\/wp\/v2\/posts\/216\/revisions\/686"}],"wp:attachment":[{"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=216"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=216"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/autotechdiagnostics.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=216"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}