thats 100psi across both banks with a variation of no more then 20-25%.small/large plenum leak needs to over come the blow-by in order to register on a gauge.increased blow-by the less likely hood of finding a leak with a gauge.you could have both bad rings in #8 and have a plenum leak.theres also a dye we used(available from mopar or summit)with a black light.you add it to the oil and drive then shine the light down the tb.pcv should be disabled.you can also use a vacuum gauge to test for worn rings along with other issues.hook the gauge to manifold vacuum with a warmed up motor and blip the throttle.good running motor gauge should read about 2in then jump to 25in.bad rings youll get 0in then 20in or less.in lue of this a leak down should be done.

 

ok ill see if i can get hold of some of this dye.

i have done a vac reading. i get about 16 in of merc at idle. when i blip the throttle it drops then spikes then goes back to 16, however i forget what it dropped and spiked to. so ur saying if when i blip the throttle it drops all the way to 0 and spikes at 20 then rings are likely bad?

yea i agree there is a 44% variation among cylinders, however i had trouble getting the tester into the #8 cylinder since its in a tight spot, and it was the last cylinder tested so it did have alot of time to cool off. if it was cooler would that give a lower reading?

 

http://www.summitracing.com/parts/DCC-05010042AA/

iyes. just another way , combined with a compression test to point you in the direction of bad rings.to pin point the loss of psi exactly a leak down on those 2 cyl is the only way.try it again and note the readings.full warmed up is very critical.16in at idle is low.good running stock motor should show 18+@idle.


yes you would get a lower reading.needs to be fully warmed up,all plugs removed,tb wide open.theres also a dynamic compression test with the motor running but again a leak down is much better tool.edit...if you do another compression test note how the gauge jumps up or lack thereof and how many strokes to reach psi.good cylinder will jump up quick.

 

theres a local shop that will do a leakdown for free so ill see how that turns out. as well as re run a vac test. some of the cylinder's pressure took quite a few strokes to build. with good rings how many jumps shuld you get? for example 90-120-140-165 or fewer than that or what?

 

redid a vac test. steady 16 in/hg at idle, when i blip the throttle it rapidly hits 0 then rapidly rebounds to about 20 then goes back to 16

 

Matt,

On my 2000 Dodge Quad Cab 3/4 ton 4x4 5.9 V8 Canadian built pickup, I didn't even bother doing the plenum test to verify I had the leaking plenum problem.

Mind you when I got the Dodge, it was using oil but not leaking it externally and not smoking out the tail pipe at all due to the Catalytic converter catching it first. Finally I had enough because I changed the oil and filter and then in 600 miles it was a quart low.

I went and bought the Mopar updated metal intake plenum gasket kit, plenum bolts, intake bolts, thermostat, and o-ring for the water pump pipe and changed it. As soon as I got the intake bottom plate off I could see where the oil was leaking past the factory intake plenum gasket.

Now my Dodge doesn't use any oil at all, so I'm very glad I finally changed the plenum gasket.

 

yea i guess i culd just get an airgap and if that doesnt resolve the issue i can just swap it over to a new engine, however im now starting to think it may be a combo of rings and plenum.

it does have 176k on it so wouldn't an engine rebuild be in the near future anyhow? the tests seem to point to rings but im still not sure

 

My Dodge has 155k on it and it still has 170# of compression in all 8 cylinders, but I don't know if it is the factory engine or if it has been rebuilt or replaced before I got the pickup.

The plenum gasket is far less intensive compared to pulling the engine and rebuilding it, so IMO, I'd change it out first and go from there. It was only $120 for all the parts for me to do the Mopar plenum updated gasket kit on my Dodge.

 

cant beat free and a leak down is what you need to do.it will tell you were and @ what % that cyl is lossing psi.good cyl should jump up quick 4-5 strokes

that confirms theres an issue just doesnt tell you what cyl.from all the info so far its the rings or out of round bore.if dodge would of put a water passage cross over in the back mani #8-7 would run alot cooler