my van was running well til last week.it allegedly has 77000 miles on it.it started running really rough within a 50 mile period.ive quit driving it til im sure im not harming it.i put a vacuum guage on it.it wildly flutuates between 3 and 7 pounds at idle.ive tried plugging the four vacuum lines one at a time to eliminate the accessories as the problem.the check engine light is off and my scan tool shows no codes.i unhooked the exhaust at the manifolds to make sure the cats aren't clogged.it doesn't have egr.theres no water in the oil or bubbles in the radiator.i have a compression tester but id like to avoid trying to get to the plugs unless nesessary. any ideas?thanks.

 

One vacuum leak that's hard to find is the line from the fuel vapor recovery canister. It's a pretty stiff line that runs from the canister mounted below the big intake air hose on the passenger side frame rail to the intake driver's side of the intake manifold. It's buried under all the wires and lines near the front of the engine, behind the thermostat housing, so it's kind of hard to see of get to. The line has a solenoid that opens it to the intake at appropriate times.

I assume you've already checked the vacuum tree at the rear of the upper intake manifold for loose lines or missing plugs.

Another possibility is that the EDIS has failed. The only way to test that without instrument is to get a replacement. I would check the local scrap yard for one.

 

Another vacuum line that fails often is the one from the vacuum tree to the auto transmission vacuum modulator located on the passenger side behind the CAT. the vac. line takes a real beating from the CAT exhaust heat and the flying road debris

Also, the vacuum line to the FPR fuel pressure regulator located on the passenger bank fuel rail.

If the vacuum diaphram breaks in either device, the engine either sucks in auto tranny fluid or raw gas.

 

a bad upper intake gasket will cause the same symptoms in the 4.0 liter.

a way to replace the intake/butterfly-nipple-to-canister plastic hose is to find plastic fuel hoses from Hondas, they use a similar diameter tubing. A few splices with plastic splicers and you can get it fixed.

 

thanks.i guess i missed several vacuum lines.

 

i did a compression test on it today.i could only check five cylinders because i couldn't get the hose screwed into the passenger rear plug.all checked high except the front drivers plug.no compression at all on it.that combined with the ultra low vaccum tells me i have a stuck or bent intake valve.btw a carfax check revealed it has 177000 miles not 77000 miles.

 

i finally pulled off the valve cover.the intake valve spring on the front cylinder broke and collapsed.the valve has been open ever since.i pulled it back up but i will have to do a compression test to see if the valve is bent.the spring retainer and valve keepers were laying in there.the push rod and rocker look good.i hope to install a new spring and keepers and get it going again.