Can an MFI pump push oil into the fuel ?

[michel richard]

Just started up my just-rebuilt 911 E engine. I'm getting huge amounts of blue smoke and actually have black oil leaking out of the headers at the muffler (will need to make sure the flanges are flat).

Initially I had way too much oil pressure, 10 bar or even more, but we figured that one out and the pressure seems to be under control now. It's a 1971 case, so there are squirters, which must have been dumping huge amounts of oil onto the pistons.

However, the blue smoke continues, although I'll say I have'nt run the engine more than 10 or 15 minutes total and I'm not sure if the blue smoke is diminishing now that the pressure issue is under control.

The plugs are oily, which tells me the oil has been through the combustion chambers and was not just sitting in the headers.

So, is it possible that oil somehow is getting pushed past the injection pistons or past a seal somewhere in the pump and is being injected along with fuel into the engine ?

Of course it may be that the oil got past the rings but compression and leakdown both check out: all cylinders between 150 and 160 and less than 10% leakdown, on rings that have not been broken in yet.

Any thoughts anyone ?

Michel Richard

[Early_S_Man]

Michel,

No, I don't believe your hypothetical about oil/gas from the injectors!

Are you POSITIVE that your oil tank level is NOT OVERFILLED?

Two possibilities for oil from the squirter holes/passages past the rings into the combustion chamber and onto the spark plugs ... come to mind.

1. If your crankcase was hot-tanked for cleaning ... is it possible that the oil squirters were loosened and fell out? The high oil pressure you cited does disturb me, and I suspect it has very serious implications, especially if the squirters might be laying loose on top of the windage screen above the sump!

2. The compression numbers are VERY BAD for a newly rebuilt 9.1:1 compression engine, and I suspect that the rings are NOT seated ... due to the extremely high volume of oil they had to deal with in the first ten minutes or so of running, when they should have been breaking in! Just for comparison ... my 70K mile, 8.5:1 engine had 192 psi mean, and ranged from 185 psi to 200 psi when tested last! Other 8.5:1 engines I hjave seen had compression mean numbers from 180 psi to 195 psi.

Sorry, but I believe a teardown may be called for in the near future. Even if the squirters are OK, the extremely high oil pressure you cited ... above 150 psi would mean an extraordinarily high volume of oil overwhelmed your rings, and prevented them from seating properly.

I suggest driving the car another 500 miles or so ... at 200 miles change the plugs, and again at 500 miles and carefully check them again at 50 - 75 miles afterwards to check the continued progress as to whether the oil-fouling is getting better, worse, or staying about the same. Good luck!

[michel richard]

Warren,

Thanks, I was hoping for an answer from you.

We thought about oil level too. Oil was competely drained and refilled. The amount that drained was normal . . . I had counted the amount that went in.

The info about your compression numbers is news. I guess I'll put some miles on the engine and see if the smoke goes down, as you suggested.

Engine was assembled professionally, and the gentleman who did it is beign very good and helpful with the diagnostics and repair of it.

I'll report further !

Michel.

[Wayne 962]

You said you solved the oil pressure problem, what was the cause?

-Wayne

[michel richard]

The mechanic who did the rebuild tells me that he usually modifies the oil pressure relief system as was done in the later engines. He also puts a couple of small washers under the relief spring, as shims, to bump up the oil pressure. The combination seems to work.

In my case, I asked him no to do the crankcase modification because I did not have the later oil pump and I had read here it could result in low oil pressure. I did not realize he was gonna put shims, which he probably did out of habit.

So, it looks like we had a failure to communicate.

Took the washers out last night and pressure came down to more normal levels.

Following Warren's post, my current thinking is that oil got by the rings on account of the high pressures, was partly burned, and then was pushed into the exhaust headers. I suspect that there is still oil in the headers from beofre we fixed the pressure thing, which would account for the continuing smoking.

Have'nt been able to check this out as work kept me away from the engine today and this evening.

I would hope we have'nt damaged anything permanently and that compression will increase once the rings seat. Total engine time is probably 10 minutes under high pressure and 5 afterwards.

Michel Richard

[Wayne 962]

You should run the engine regardless right after turning it on for 20 minutes at 2000 RPM - use a stopwatch...

-Wayne

[michel richard]

Short update

Swung by the shop on my way home tonight. We pulled a couple of the plugs and though they are still oily, they are a massively better than what they were like right after we had run the engine with the high oil pressure.

This is consistent with the "current thinking" outlined above.

Keeping my fingers crossed.

Michel Richard