Cylinder Differential Test - Fuel In Oil!?

[mhyphenl 10 1 Cars]

I have a slightly perplexing issue. Trying to get to a core running issue I performed a cylinder diff test and used a scope to listen for where air might be leaking. While the diff test showed around a 6% difference and with all cylinders the same it seems that all the air is escaping into the crank case. Head was re seated and new valve guides / seals so confident that little or no air is getting into there via the head. No noise at inlet or exhaust.

Now if all the air is escaping past the piston rings, (which are new) and liners (which aren't) does that suggest ovalling of the liners? Will this improve over time? (engine has done 400 miles since rebuild). As the air was coming up to the oil filler cap I put my hand over the cap which built up a tremendous amount of pressure and pushed hand off with a big burst of air and gunk! Also the oil smells of fuel contamination! and is slightly mayo ed!?

Now the instruction on the tester say a difference of 10 psi at 100 psi is within tolerance but if you start the engine and take off the filler cap you can see puffs of fumes coming out!? How much is too much?

 

Now the engine was running very rich as the AFM had been tampered with pre build to get it through mot. Maybe the now excessive fuel has been forced into the crank case and contaminated the oil, I adjusted the AFM today with the help of gas meter and making the engine run open loop so it should be about there! Strangely the spark plugs aren't black or wet, quite the opposite and greyish!? Can you have an engine run rich but not get damp sooty plugs?

 

Bloody thing!

[PhilNW 44]

There is going to be a lot of air in the crankcase being pushed around because of the pistons moving up and down

Have you check the crankcase breathers to make sure the crankcase is not being pressurized,

Check the small connection on the throttle body to make sure its "sucking" on the crankcase

Have you any oil leaks anywhere? (possibly due to pressurization)

[Spesh 31 1 Cars]

new rings and old bores? Were the liners honed? If not and they are glazed then its entirely possible you've not got a good seal with the new rings as they wont have bedded in correctly, if at all.

 

Also if you were running very rich then bore wash is possible so that could have damaged your new rings and/or the liners.

[mhyphenl 10 1 Cars]

No oil leaks. The breathers are clear and letting pressure through. My main concern with the leak down test was that the valves are excellent, all the leakage is down the cylinders!

I think cylinder wash is occurring which would explain the leakage into the crank case and the clean spark plugs! Now I've only done 300 miles since rebuild so how much damage could have been done!?

[PhilNW 44]

Is 100psi the actual readings on the individual cylinders

[mhyphenl 10 1 Cars]

It's a leak down test so 100 psi in and 94psi holding pressure. That means 6% leakage which reading the instructions thoroughly is a good result! Anything up to 10%! Also the fact that the leakage is down the piston is very good, means the valves are very well seated!

So looks like the over fuelling hasn't done any damage yet but as there is fuel in the oil it probably has been washing the cylinders. I need to rectify the fueling urgently before damage occurs!!

[PhilNW 44]

Have you done a compression test?

 

Never done a leak down test, does the held pressure mean there is no further leakage after that?

Edited June 24, 2016 by PhilNW

[mhyphenl 10 1 Cars]

Yes, compression was good! A leak down test is just a more in depth compression test. You put a constant psi in and it tells you what psi it's holding on to. You have to supply a constant psi as cylinders always leak, if you just put a burst of air in it would all be gone in a second or two! So on mine I put a constant 100 psi in and the pressure in the cylinder at tdc was 94 psi so a leak percentage of 6%!

[PhilNW 44]

How long have you run the engine for to date?

Are you losing any water?

[mhyphenl 10 1 Cars]

No water loss and about 300 miles in a month after engine rebuild!

Before I built the engine the AFM was altered to to richen up to compensate for air leak/s. I've put it back on to an engine with no leaks and so was far too rich!!

[Spesh 31 1 Cars]

still curious as to whether you honed the liners (or at least deglazed them) before fitting new rings.

[toolie72 67 1 Cars]

Is adjusting the afm going to make much difference when you're moving? Would it not just be rich at idle? Put your foot down and the flap opens-is the mixture screw not just a form of air bypass for when flaps closed at idle?

If however the guts have been played with that's a different matter lol

New rings should always have honed bores-different opinions are out there on the angle of attack that you take but new rings won't bed in to glazed/shiny bores

[mhyphenl 10 1 Cars]

Yes, I had the liners honed. To be honest I'm happy with the test now having read up. The readings are good in term of air leakage. I'm more concerned about over fueling and fuel in the oil. It was running very rich so cylinder wash is possible. Also could have a leaking injector when the engine is switched off. Are there any othe routes for fuel to get in to the oil?

Just a note on the AFM. Changing the spring tension will affect fuelling accross the whole range as the spring tension will be higher / lower all the time! Mine has no air bleed screw as its a DKZ engine with lambda. The ECU governs mixture and there's no adjustment at all on the AFM. My ECU will not enter closed loop mode as it's not able to bring the mixture into line by adjusting to what the lambda is saying. Now I've tried moving the spring on the AFM back incrementally to bring it back into line but it's not having it at all.

I'm going to get the local garage to set the emissions as close as they can with the lambda disconnected so the ecu is in open loop. At least I know then that it's close and running ok in open loop. I'll then need to tackle any other issues to bring the lambda back in and get it spot on. Apparently the ECU will only allow an adjustment from the lambda of about 10% from what it's expecting before it comes out of closed loop and puts the ECU light on!

If compression test is good and leak down test is good are there any other checks I can or should do to make sure the core of the engine is in good working order without dismantling the whole thing AGAIN!