3.8 engine trouble

**mjacob** · 10-08-2011

Got a 97 GP with a 3.8 engine. The engine is not running correctly. When I take the air filter housing loose and let the motor draw non filtered air, it sounds and feels like it is struggling to get air. I am also having vaccum pulled through the oil fill cap. When you take the oil cap off,it relieves the motor and the motor no longer acts like it is struggling to draw air,but still doesnt run right. I changed the pcv valve and maf sensor, but nothing changed. The engine isnt running right all the while and I think I may have a clogged cat convertor causing excess preasure in the cylinders. Am I thinking right on this, or does anyone else have any advice on these issues. I am relly scratching my head on this one.

Thanks

**matt5112** · 10-08-2011

Oil cap issue sounds like a PCV issue.

**vern85** · 10-08-2011

do a vacume test
find out what your vacume is that will tell you if you have a clogged cat because if it is clogged cat you wont have any vacume.

**Fivefingerdeathpunch** · 10-08-2011

Originally Posted by vern85

do a vacume test
find out what your vacume is that will tell you if you have a clogged cat because if it is clogged cat you wont have any vacume.

orly?

If he had NO vacuum, the motor wouldnt even run home boy.

**Fivefingerdeathpunch** · 10-08-2011

try another pcv valve and make sure you replace both the o rings.

If he has a clogged cat, the car would still have vacuum ( IT ALWAYS HAS VACUUM WHILE RUNNING) but would have access back pressure.

To test this either take the up stream o2 sensor out and go drive the car and see if it runs better or, take the sensor out and put a pressure gauge into the o2 bung and read the pressure. If it reads more than 1-2 psi, the cat is more than likely clogged. Modern day cars make less than 1 psi of back pressure.

**vern85** · 10-10-2011

back pressure test is by far the most acurate but a vacuum test is good to and is easier hook a vacuum tester up to manifold vacuum. watch at idle the vacuum, if the needle drops near zero when the engine is accelerated rapidley and then rises slightly to a reading below normal indicates that you have a restiction in the exaust HOME BOY

**ZR1Vette09** · 10-10-2011

Originally Posted by vern85

back pressure test is by far the most acurate but a vacuum test is good to and is easier hook a vacuum tester up to manifold vacuum. watch at idle the vacuum, if the needle drops near zero when the engine is accelerated rapidley and then rises slightly to a reading below normal indicates that you have a restiction in the exaust HOME BOY

No one is going to take you seriously with your first grade spelling.

**chev1988rolet** · 10-10-2011

this probably wont be your fix but its worth a try. i worked on a vehicle that had vaccum at the oil fill cap and it turned out to be a cracked head. do a compression test and find out. or you could also just take off valve covers on both banks, remove all spark plugs and connect a compressor hose into each sp hole while both valves closed ( both pushrods at the lowest point of their travel. you should hear hissing when u apply air. engine might spin when u apply air so keep ur hands away from moving parts

**chev1988rolet** · 10-10-2011

also, you might hear hissing on the exhaust manifold or the intake manifold. thats just due to slight worn out valves or carbon deposits. you will also hear hissing at oil pan small amounts is normal but it shouldnt be to excessive unless you have real bad piston rings or a broken compression ring

**BillBoost37** · 10-10-2011

That type of vacuum pull is either pcv missing o-ring on the cap or under/on the valve. Or .. we not too long ago saw a missing LIM bolt that allowed this same type of issue.