Rex4Life

Well this problem is not good at all. I've had it since I installed the engine and thought it would get better but it hasn't. Last oil change was about a little over 1000 miles and the freaking gas must of been at least 5/8" over the full mark. Best I can tell there is also premix in the crankcase oil/gas mixture. I've pretty much done my homework on this project and don't think I missed anything, but, I must do something to fix this problem.

As you can tell from my sig, I have a stock S4 system with the few mods that are listed. The car runs great, develops good power and boost, doesn't smoke, and idles at 800 rpm with a slight bump every so often. Getting about 17-18 mpg mixed driving and I premix 14 oz of Penzoil premium plus synthetic TC-W3 2-stroke oil in about 14.7 gallon fill-up. No OMP is installed on the engine.

The engine was recently rebuilt and has about 5300 miles on it. Idle vacuum is about 11.5" per a new Stewart Warner mechanical boost/vacuum gage (engine off reads dead zero). I consider this reading to be low. A second gage read about 12.5". I have pressurized the intake system to about 3 psi and confirmed there are no substantial vacuum/boost leaks. Going higher than 3 causes the stock TID to pop off the turbo as there is no groove on the turbo inlet to hold it on. There is some small seepage of air from the TB bushings. Front rotor and rear rotor both have three solid pulses to 82 psi at 2000 miles of the break-in. Good that the pulses are the same. Procedure was: Removed both trailing plugs. Pulled both EGI fuses. Throttle held wide open on a warm engine. Watched pulses while cranking. Used standard compression tester with check valve removed. Couldn't check the peak pressure as the check valve is gone.

The FPR is adjusted to about 33 psi which is lower than stock 37-1/2 psi. The stock pressure is measured in the fuel line before the injectors whereas the 33 is measured at the FPR gage port (which is after the injectors). The car seems to run better with the slightly lower fuel pressure.

The fuel injectors (4x550cc) were recently cleaned and tested by the Injector Perfector. The engine has new Atkins viton oil o-rings on the rebuild and as mentioned it does not smoke.

After this last oil change I started using the fuel kill switch to stop the engine and on startup I let it crank a few before turning it back on. After shutdown, FPR pressure bleeds down to zero but the engine heat cooks the fuel lines and pressure goes back up within a few minutes. Eventually the pressure goes back to zero. Right after the rebuild the fuel kill switch was helpful but now its very rarely needed to start the engine and I haven't had any trouble with flooding.

Last week I changed the oil/filter and left it at about 1/2 full with no gas in it. Edit: (the fuel switch trick seems to be working after one week--we'll see if the oil level holds--so far it hasn't increased much).

One guess is I have a bad injector that is leaking fuel into the combustion chambers. What I don't understand is that if the oil rings are working as evidenced by no smoking problems, how is the gas leaking to the center of the rotor and into the crankcase? Even if an injector was leaking, chances are it wouldn't go right to the center of the rotor and force its way to the rotor center, it would drip down the side of the combustion chamber and pool up in the bottom.

Another possibility is the engine isn't sealing very good and combustion product blowby is causing this. I need to do another compression check and see if there is any difference from the 2000 mile test.

What do you guys suggest I do to solve this problem?

TIA for your help,

Scott

Impreza2RX7

Sounds like flooding, my car used to do it..

WAYNE88N/A

I've got the same thing going on, but it doesn't sound near as bad as yours. I use a little over an ounce per gal of premix (about a 105:1 ratio), and true to form, some of it finds its way into the oil supply. Gotta remember, the compression pressures will override the oil system pressures during the compression & combustion strokes, resulting in a little blowby even with perfect rings. I'm getting about the same amount of blowby as I was before the rebuild (got about 6K on her now), so new control rings don't factor a whole lot in any blowby protection (but used side housings just might). It's just something I accept as "normal" on an otherwise healthy engine (110 psi cold), and I deal with it by changing the oil more often.

I would definetly do another compression check, because 82 doesn't sound real good to me, and you're right, 11 or 12 vac is kinda low also....

You could try to cut back a little on the premix, as I have done, it seems to help a bit (was running about a 90:1 ratio), but you've got to anticipate that at a certain ratio, you'll be doing more harm than good. I would much rather "overlubricate" with premix and deal with the blowby, than low-ball it and perhaps accelerate engine wear.

So, I didn't really prescribe a fix there, lol, just thought I'd let you know that you're not alone

Rex4Life

^^

Mr. Gadget

what kind of oil o rings were used. I experenced the same thing with viton rings however all was fine in another engine with oem orings.

Rex4Life

They are new Atkins viton oil control rings.

Anybody got advice on this fuel in oil problem?

TIA,

Scott

RETed

All the major points have been made...

1) Vacuum at idle is a bit low - check compression.

2) 5,300 miles is decent break-in mileage, but I'd wait till 10,000 miles to see if the problem totally goes away. Earlier flooding could be the culprit.

You're running a pretty huge fuel pump for your needs right now.
Can you confirm the engine isn't running ultra rich???
If it is, there explains all the extra gas in the oil.

What causes fuel to end up in the oil?
1) flooding
2) engine running too rich
3) bad oil control o-rings

We can pretty much eiliminate #3.


-Ted

Rex4Life

Thanks Ted,

I'll check into the compression and running rich.

I know the best way to check AFR is a wideband and dyno, is there any other way to that gives a good indication? The plugs haven't looked really sooty so my guess is it's not ultra rich. I won't be on a dyno till November.

What about the leaking injector theory--do you buy into that? Not sure I do.

TIA,

Scott

Rex4Life

Front and rear rotors have the same compression results: 102 psi max with bleed valve closed, even pulses to almost 60 psi with bleed valve open.

Looks to me the compression is not the problem. Not the best compression but definitely acceptable. Now have 5900 miles on the rebuild.

Now all I got to look for is why I may be running rich.

p.s. I used the Rotary Resurrection test method.

WAYNE88N/A

If all else fails, read the O2 sensor from the ECU with a meter while running, and at cruise...

During 5th gear cruise (closed loop), you shouldn't be over .5 volts...Out of closed loop, she'll jump all over the place during throttle transients, but you should still see an average of around .5v...During idle, .8 (rich) seems to be normal with my car...See if this helps,

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/troubleshooting-your-car-ecu-340578/

Mr. Gadget

I am actually leaning toward #3 as a culprit - let me explain. The viton oil rings sold and included in some of the kits are not true metric orings. The size is real close and with careful installation will work better than oem. HOWEVER, due to the slight size difference (larger and thinner) they will move about in the oil control ring during installation. I myself have cut a few during installation. If the rebuilder did not check to insure the vitons were installed properly, the motor could have a few cuts in the vitons.

With all of that said, teds advise is correct - make sure you insure your car is not excessivly flooding or running too rich and run it out to 10K - just keep an eye on the oil during that period so you dont ruin any bearings.

One other piece of advise - watch your premix. I have had a few guys with the same problem only to find out they are premixing too heavy. If the % of fuel to oil is way off it will not burn as well. Fuel will pass by the oil control rings in a older engine (even rebuilt) easier than oil.

WAYNE88N/A

That was my problem early on in my premix days, Mr Gadget- I was trying to find the ultimate ratios for fuel economy, and had her down to about 80:1 at one point. The fuel economy definetly improved, but the excess "oil" was just overwhelming. It's like a big "catch-22" situation, and your blowby surely decreases when the ratios are brought closer to the 128:1 (once per gal) level. You gotta figure, that premix is "spraying" all over during combustion, even onto the side housings that probably didn't see a whole lot of OMP oil in those days. And if you have an oil film on the side housings, then you have a path for oil/fuel ingression, because the side seals will be "riding" on the oil film. Like I said above, I would much rather have too much lubrication than not enough.

Good point on the Viton control rings, but I had the same thing happening with the OEM rings before the rebuild (not gas so much as premix blowing by). I'm beginning to think the wear on the side housings has more to do with it than we give 'em credit for...

Rex4Life

Well I don't feel any closer to solving this problem. I think I will try and get the car on a dyno and see what the AFR is at.

I have a couple more months on this engine rebuild warranty and if it is the engine I need to know soon.

I don't think this is a problem I can live with. At 1000 miles there was way too much gas in the oil--I should get more than four fill-ups on an oil change--this is just riduculous.

As far as the premix is concerned, I'm running a little less than 1 oz. per gallon--this seems to be typical for those that premix. Maybe I'll try a little less or a different brand.

I was reading over in the FD section and some of those guys suggest it could be related to bad clearances of the side seals. Normal compression would look OK but then under turbo boost the side seals give way and allow blowby--maybe.

One way or another I'm gonna get this fixed.

Again, thanks for all your help.

Scott