Jump to content

2.5 tbi losing oil, gas in oil, don't know where to start...


Recommended Posts

I have a 1987 MJ with 2.5L. I will start at the beginning of my issues. Sorry in advance for being so long, just wanted to give as much details as possible.

 

Last year I started noticing oil in the throttle body and in the breather box. I never could find any obstruction in the ccv system, so I just replaced the ccv "elbows" in the valve cover with breathers, I plugged the hose attachment on the breather box, and regulated a hose down to approx. 2mm and put a filter on the end it of where the hose would have attached to the throttle body. This (as dumb as it may have been) seemed to eliminate my issues, and did not effect the way the truck ran (if anything the idle smoothed a bit.) The only downside to this was that some oil would bubble out of the rear breather and run down the engine when the oil level was at the tip top of the full range on the stick. I have no smoke out the exhaust pipe so I figured all was well. Oil was never low either always between add and full. So other than oil on the engine, and smelling oil at interstate speeds no obvious downside.

 

Fast forward to now: I have detected the scent of no small amount of Fuel in my oil. I had to put 1.75 quarts of oil in my truck 2500 miles after an oil change. It has never used oil, and this is totally new. I don't recall detecting the smell of gasoline before. I would immediately assume blow by, but again no smoke out the exhaust, (if you can have blow by, and no smoke, this is unknown to me.) I would think bad valve seats, but wouldn't explain the gas in the oil I wouldn't think.

 

I have scoured the internet for any sort of COA, but everything is pretty foggy, or the scenarios presented in the articles are no exactly like mine.

 

My first thought was fuel pressure regulator, then I thought leaky injector, then I thought I need to attempt to diagnose the problem before I throw parts at it. I am currently thinking of purchasing a leak down tester, do you guys think this is smart, or I am more likely to find that it is an issue somewhere else. Could my CCV modification/elimination cause this problem? It is possible that the fuel in oil, and oil leaving the engine (somewhere, burning or not) problems are unrelated, I just felt it doubtful.

 

The only other issue I have noticed that may help guide those of you with the extraordinary constitution to read this extremely long post, is that a couple time over the past couple months I have had a really strong smell that I cannot identify would fill the cab (if the window was down, or the vent was on) and burn the crap out of my eyes, and I would have to pull off. This seemed to only happen when I was accelerating up a steep hill, and only happened twice then, and no power loss has been observed.

Link to comment
Share on other sites

No, I have not. I am currently under the impression that a "leak down tester" will tell me everything that a compression tester would tell me and more. If I am mistaken in this, please advise. I am at the understanding that: A leak down tester could actually show me what component of the cylinder is leaking if that is indeed the issue, ie: leaking down exhaust=exhaust valve seat, and so on and so forth.

Link to comment
Share on other sites

Since my valve cover has two breathers in the top of it, and no ccv system connected at all, should I have pressures in the valve cover high enough to push oil out the rear breather? or could this suggest a valve seal/seat issue with compression being pushed into the valve cover via a valve? Could an intake valve seal failure push fuel into the oil if this is indeed the case? :???: so terribly confused. (The term "knows enough to be dangerous" is me to a "T") I should probably just stop thinking now, and listen to responses.

Link to comment
Share on other sites

Update: I have went ahead and purchased a leak down tester. It has been shipped I expect it Monday. In the mean time I was researching how to check for a bad fuel pressure regulator diaphragm. All the how to's I found said pull the vacuum line from the regulator and check to see if fuel is present, if so: bad diaphragm. I cannot find a vacuum hose going to my fuel pressure regulator, have I been struck stupid or is there no vacuum line? Is this the correct COA to checking the diaphragm?

Link to comment
Share on other sites

There is no vacuum to the pressure regulator on the TBI system. There is a diaphram, spring and a adjustment screw on the throttle body assembly. I'm not sure where the pressure gauge would connect to.

The leak down tester is a good tool, you can learn a lot about the condition of the engine. Be sure that engine is TDC #1 and don't leave the socket wrench on the crank, that motor will spin real fast with 100psi in the cylinder if you are off TDC ever so slightly. I use a plastic stick through the plug hole to feel the piston at TDC and just keep going around 1, 4, 3, 2.

Link to comment
Share on other sites

Thanks for tip airspeed. I wish i had read the take the wrench off the crank part before I did the test. It scared the crap outta me but no one was hurt and nothing was damaged thankfully.

 

I conducted the leak down test:

The first thing I noticed was the spark plugs showed a bit lean, pretty white. Then I conducted the test and nearly every cylinder leaked out the exhaust (went back and made sure I was not on the exhaust stroke). So I figured the exhaust valve seats and or guides are in pretty bad shape.

So I remove the head, the valves are WHITE! So this is pretty lean (or that is how I am reading it, please chime in if I am missing something.)

 

So my understanding of this situation is the exhaust valve are leaking so bad it is putting pressure in the valve cover which is pushing oil out of my valve cover which explains the oil loss. With the exhaust valves leaking The whole time the compression stroke is taking place is pushing fuel out the exhaust valve and into the valve cover, thus explaining the gas in my oil. Since a portion of the fuel is being pushed out the exhaust valve/exhaust port this would explain the lean condition.

 

Am I on the right track, or is this totally wrong?

Link to comment
Share on other sites

The exhaust valves will be the first thing to fail if the engine is running too lean. You will need to pull the valves out of the head to see if the seating surface is burned. How high are the valves sitting in the head? Is the valve surface a little above the head chamber, even or below? This is another indicator of how bad they are worn.

 

If the exhaust valve is leaking it won't put pressure in the valve cover, it will leak to the exhaust system. The leak down test would have to go by the piston rings to put pressure in the valve cover.

 

The CCV on the 2.5 TBI is the 2.2mm grommet on the back of the valve cover, make sure that is open, I used an .092 drill bit on mine.

 

How many miles are on this engine? If you rebuild the head and put it back on then you might find that now you have bad rings.

Link to comment
Share on other sites

In addition to mileage are you sure it's the original engine? My '87 MJ had an engine out of an '86 (V belts instead of Serpentine). The reason I ask is that you have a condition that causes lean running. You can treat the symptoms (fix the valves, etc) but you may burn the valves up in short order if you don't find the cause for lean running.

Link to comment
Share on other sites

The truck has 130,000 miles on it. I am not 100% that it is the original motor, but I am 99.9% sure. It is serpentine belt, not v-belt truck. I am hoping that a new t.b. will help ensure that the valve work will eliminate the problem. The machine shop has said that the valves "looked" fine, and white valves are normal (well i have never seen them look like these.) I have a theory that the way I have my ccv system eliminated might be causing or adding to a lean condition. It may be getting significantly more air under the butter fly of the t.b. that it should be. That doesn't however explain the gas in the oil. I am probably going to go ahead and rebuild the bottom end of the engine while I have the head off even though I don't have any smoke.

So if anyone has any advise beyond what the repair manuals tell please let me know, as far as the bottom end rebuild is concerned. The cylinder walls are very smooth, so I think I can get by with honing and re-ringing, plus normal other work ie: rod bearings and etc. Also, do I understand correctly that you can make an ax4 into a ax5 by just adding a couple parts to the case? Is that very involved, that may be something I do while i have the motor out. Thanks for all the responses.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...