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Suspecting backpressure in exhaust. Good place for vacumm ck or diag. 850 1995

posted by  Three5bangers on  Sun Dec 6 12:24 CST 2015
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last visit: Thu Jan 17 20:50 CST 2013
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I'm going to crawl under the car soon (will take me hour to clear garage) , but not much daylight left so I though I'd leave this. Power seems low all the sudden. Blowing sound with higher revs. One idea is always that a animal took up residence in the exhaust as car has sat for 5 days at a time. Good vacumm port (i have a gauge somewhere, last used 1985)








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    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

    Critters really don't like crawling into a dirty, smelly exhaust. Cat converters do fail, so I suggest banging it with the side of your fist and listen for loose stuff inside. Check the exhaust for breaks before and after the cat. If the exhaust was really clogged, your wouldn't be able to rev the engine much above 3-4K.

    Mice will find the air filter much more to their liking.
    --
    Keeping it running is better than buying new



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      posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

      12 inches at idle
      12 inches at 2k
      at 3000 rpm gauge starts to bounce between 10 and 12 inches. Shaky needle now.
      4000 rpm 10 inches vacuum.

      I took off some plastic shield near the trottle cable and found a unused port on a vacuum T.

      Next test it with my IR thermometer, temp should be higher on cat outlet , if I can avoid the cat shield.

      So doesn't sound to bad. COuld be my imagination. I fixed a terrible wheel bearing recently so I hadn't heard anything for 6 years prior. I was even hearing light detonation so I mix in a little premium gas.



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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        Cheap Newbee IR thermometer read 340F on input and 141 on output after a while of idle. Anyone want to try this on their own car for baseline? The cat is 20 years old but only 117K miles. Apparently in NY 1995 is the only year where an EPA cat can be installed. Even 93 and 94 require CARB cats or the shop can be fined $26K per cat incorrectly installed. With that - i bet shops will even be afraid to install an EPA cat in my car. I bet the upstaters in watertown NY complained about the CARB cats do it was dropped but ODBCII in 96 brought them back.



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          My cheapie scanner read 278F/260F front/rear. Upper part of the down pipe reached 330F. This was after 5 minutes of idle with a 'warm' engine, I ran an errand prior to parking.

          The rear O2 sensor is a foot behind the Cat.
          --
          Keeping it running is better than buying new



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            posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

            Eric the car guy had to find a new car to find higher output temps.

            https://www.youtube.com/watch?v=9VZ5K8n5jj0

            at about 7:20 into the video.

            SO maybe old cats don't work that well, but no indication if they are clogged or open. Just ineffective.




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        posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

        I found this in my 850 online owner's manual for diagnostics:

        Exhaust System Backpressure
        1) Exhaust system can be checked using a vacuum or pressure gauge. Remove oxygen sensor or air injection check valve (if equipped).
        2) Connect a 1-10 psi pressure gauge, and run engine at 2500
        RPM. If exhaust system backpressure is greater than 1 3/4-2 psi, exhaust system or catalytic converter is plugged.
        3) If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steadily. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.

        So your car sounds "normal". I would expect slightly less vacuum with the butterfly valve open and allowing more air into the intake.

        --
        Keeping it running is better than buying new



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          posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

          I was looking at an old book, says 21 inches. Eric the car guy is getting 22 on his sub.
          https://www.youtube.com/watch?v=d-jp1IIJVVk


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            posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

            I was thinking that the vacuum pressure for the 5 banger should be around 17psi at idle, warm engine.

            Checking back pressure in the exhaust is interesting:

            https://www.youtube.com/watch?v=Lafv2c4szZY
            --
            Keeping it running is better than buying new



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              posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

              The o2 sensor I though I might bust if I heated it up too much. There is a bong opposite it with a 14mm hex which I heated up , but which does not want to loosen. I might drill a hole after the cat to see if clog is in muffler.

              btw - no 2nd o2 sensor found after cat

              http://s1314.photobucket.com/user/84quattro/media/PostCatPipesV850GoodShot_zpspuxjsiiz.jpg.html


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                posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

                The 'bong' needs to stay there. I don't like putting holes in stainless steel. If I remember, I will crawl under and take temp readings of before/after cat.

                The rear O2 sensor, yes you do have one, is covered by a plate with 4 12mm(?) screws. The plate goes across the car and covers part of the exhaust. The sensor wire actually has a holder to that plate.

                Remember, you also have an EGR, which may be clogged or has a bad vacuum line.
                --
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                  posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

                  My 84 country squire, which I still have of course, I believe the EGR might stick open causing a lean out stall when returning to idle which pissed of my wife to no end. She got another car in 2000. So I cleaned the EGR valve often. Could it cause a more serious problem with the 850? BTW: I did the pcv check with a glove.

                  The car is going to a local mechanic tomorrow. He should have better luck poking around. Hopefully they just pull a dead rat out of the muffler but I ran a electician's snake wire up there and nothing hairy came back.

                  I didn't drill any holes, I didn't have a pressure gauge to insert anyway.

                  steve



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                    posted by  someone claiming to be on  Wed Dec 31 18:00 CST 1969 [RELATED]

                    I hate EGRs, they clog up everything. And if the mixture is super rich, when the EGR valve opens, the unburned gasses are introduced to the intake and make it even richer! Of course, the EGR valve tends to clog up and it doesn't work at all and they you get a CEL!. Those poor spark plugs, trying to burn all that junk, just to get completely coated until they can't fire any more.
                    --
                    Keeping it running is better than buying new



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