If it is only oil, there really isn't much to worry about at all. Oil can collect in the lower intake plenum due to the somewhat open nature of the plenum and the fact that these engines have a PCV (positive crankcase ventilation) system. Air with entrained oil that is pulled from the crank case via the PCV valve gets sent back into the intake plenum to be burned in the cylinders.

If this is excessive, it could mean that your engine is having problems with excessive blow by which would force abnormally high amounts of oil through the PCV system.

 

Never thought of the PCV. But in order for it to puddle wouldn't their have to be an excessive amount of blowby to create alot of pressure in the crankcase?

spyderlock - You should do a compression test and get back to us

 

You have to consider that once the oil gets into the lower section of the plenum, it has no way of leaving. Over time, even a healthy motor passes quite a bit of oil through the PCV system.

 

true, so do you think that a oil stabilizer additive (Lucas) will help keep some of his oil in the pan opposed to the intake? So I see it as if the oil is a bit thicker and heavier then it wont be sucked up the PCV as easily, correct?

 

I'm still somewhat new at working on motors so... I noticed I was losing coolant at a fairly quick rate, and couldn't figure out where it was leaking. I took the whole plenum off and realized the lower intake gasket on the passenger side was destroyed allowing antifreeze to go where it shouldn't. I replaced both sides and it fixed the bad miss I had as well as the liquid in the plenum. I guess it was coolant mixing with carbon, or maybe oil?. There was a ton of carbon build up blocking 90% of one of the exhaust ports wich I cleaned out. Thanks for all the advise. I'm sure I'll have another question soon. THANKS!

 

and thank you for posting up that the problem is solved too!

 

'94 blazer 2wd automatic, vin w .... CPI!!!
(Lets hear it for central port injection !!!) .... YAY!! ..... YEAH!!!!

i have had this exact same issue. oil in the plenum, causes surging/hesitation... when the issue first starts if you drive it like a grandma, very slow acceleration, you may not get it much.

the harder you hit the gas the more likely it is to hesitate. it will start and idle just fine, you can even play with the throttle in park/neutral as much as you like and not duplicate the issue. except for 1 of .... 5 or 6 times i've had this problem.

on doing some internet research i've found the CPI motors have a common issue of the spider injectors, or the nut kit (things connecting to the spider!), to leak. so... took it apart the first time, replaced the injectors.

blazer ran great for somewhere around 3 months. exact problem began to resurface and i figured i knew the problem and got a faulty part. put a new spider injector in, of course cleaned up the fluid. ran great for another (about) 3 months and same thing.

this time, the engine actually stalled while driving. it started up again after waiting about half an hour, then i could drive it home and do spark/fuel psi/compression tests.... all tests came out normal, even while the problem was occuring. the sparks slowed w/ the hesitation as you would expect. took it up the highway real quick for a test drive w/ gauges hooked up and it stalled again after a few miles. couldn't restart the engine no matter how long i waited, and again the tests were all fine / inconclusive.

Took apart the plenum.... sopped up the oil i knew would be in there, and replaced the spider injectors again.

ran great another few months, did it one more time. then, yes for a fifth time the issue reappeared. the 1 year warranty on those injectors has now expired, and even if it hadn't i am sure something else is the problem.

the egr valve on this engine had been blocked off for years, it was just a check engine light that came on when you've been on the highway a while. completely unnecessary (exhaust b/s..).

so this last time, i opened it to the plenum (which is needed to change the egr valve anyway), i sopped up the oil, and i changed the egr valve.

i was interested to see if maybe this is some weird engine design and the egr was supposed to open to prevent a buildup of fluids in the plenum or something crazy like that.

of course, i'm wrong, the egr valve is completely and utterly useless and unnecessary. another few months and here i am today!

the engine is hesitating again, i am about to open the plenum and sop up that oil that i KNOW is there.

I HATE YOU!

OIL IN MY PLENUM!

why don't you want to take a nap in the oil pan? it is so much more peaceful down there, i swear to god!

so... i did more googles and stuff this morning.

i found a couple posts online saying the seals or oil rings are bad, therefore allowing oil droplets to make it to the plenum.

i do very, very slowly lose oil... a respectable portion of a quart of oil per few months (this is the time interval, and about how much oil is in the plenum..)

so, i believe the solution to my problem is an engine rebuild.... this engine does have a lot of miles, the odometer has been altered but probably has 300k+miles. though this problem has been going on for probably about the last 50K miles.

 

I have the exact same problem to the exact same steps. Except I just rebuilt my motor in Jan 2010. I now about to put another injector in. I was thinking blow-by but compression is good. I had someone build it so you never know. It seems to be coming from the PCV. Have you had any luck?

 

Mine was puddles of gas from my spider leak when i took it apart. Just clean it up now and take apart in a week and see if its in there anymore. My guess is just gas from your leak.

 

Sorry I haven't replied, sold the Blazer and bought a Cherokee for $250. I finally tracked down my problem before I sold it though. The oil I was wiping out was mixed with coolant and coming from the intake gasket (it sets under the plenum). It was blown, and blowing oil / coolant back up into the plenum. I assumed it was gasoline every time I opened it, my bad. Also... I've heard that you need to run the EGR vavle open like it was designed. I bought an EGR gasket at the auto parts store with a screen on it for $2. After I changed the intake gasket it loosened up a ton of hardened carbon which kept clogging the valve open and giving a check engine light. Made it very hard to start as well.. The EGR is controlled by the ECU so blocking it off will cause more harm than good. A buddy of mine had his intake gasket blow in the same place, so take the plenum off and see if it isn't torn up near the rear of the plenum. Hope this helps. E-mail me at spyderlock15@yahoo.com if you need anymore help. I don't check this website much anymore.