Blue smoke on Decel, Think I understand now Geoff Options

[DNHunt]

Got the bad news yesterday. Geogg Bleyseng followed me to lunch from the AX and said "Blue smoke when you slow down, bad rings or valve guides".

I calmly say "Thanks I was wondered where all the oil was going". Meanwhile I'm thinkin "Aw $hit, more $$$".

He says "Do a compression check then do another one after you squirt some oil in the cylinder. If it improves its bad rings if it doesn't it valve guides".

I proceed to ask several questions that show how little I really know but, I got to thinkin about it last night at a wedding reception (damn this 914 thing is an obsession) and I think I understand it now.

2 ways for oil to get into the cylinder, past the rings from the crankcase and past the valve guides from the valve covers (from crankcase via pushrod tubes). On decel there is a high vacuum in the cylinder (and intake) therefore oil is sucked into the cylinder from one or both worn parts and burned leaving blue smoke from the exhaust and extra oil usage.

Compression should be lower than desired because of leakage past the worm parts. Squirting oil in the cylinders will help seal the worn rings & cylinders and result in improved compression. But, if the valve guides are worn it will not help compression.

Low oil pressure at idle results from more oil escaping at the bearings and therefor less oil reaching the sending unit at the oil cooler.

Guess I'll do the compression checks Wednesday. More to follow.

And I repeat "Ah $hit more $$$".

Dave

[Lawrence]

That's a nice explanation. You should save that and post it for newbies.

-Rusty

[DNHunt]

Which part Rusty? The thoughts (whats going on in the engine) or the feelings (Ah $hit more $$$). Or maybe we should post if you own one of these cars you'll learn whats going on in the engine and you'l feel "Ah $hit more $$$. Have one long enough it's gonna happen.

Sorry about the rant

Dave

[Lawrence]

The explanation of where oil goes, and why. Nice and concise and doesn't require a degree in rocket science to understand.

[Bleyseng]

Yup that was good Dave, you compressed our 1/2 hour lunch topic into a paragraph without all my rambling and hand waving and your "Huh??'s"

Geoff
Still don't fix the problem but its fun too try to figure out.

[JeffBowlsby]

Guides or rings...either way the heads come off...

Although, does it really need to get fixed now?

If so its a perfect opportunity to upgrade...

(IMG:style_emoticons/default/cool.gif)

[DNHunt]

Its gonna take some figurin. Besides the blue smoke the oil pressure is low at idle at least according to my gauge and light. I added the gauge last winter and changed sending units. Prior to that, I had the light only and I only saw it on a couple of times when the oil was low so, I suspect that the new sender might be wrong. Keeping my fingers crossed

The interesting thing is the car really runs very well and just dyno at 80.5 hp so the performance is not that of a tired engine. True the fuel injection was just "upgraded" to Megasquirt, but, it ran well with old D-jet and I'm convinced that the new fuel system isn't masking problems. Still I remember a old saying "They run the best just before they bust".

So my plan is this. First, change back to the old sender and see if the idiot light still comes on when warm at idle. If so according to Geoff, I should suspect the bearings and so it looks like rebuild time in the not to distant future. If the idiot light doesn't come on I'll try to find a way to check the pressure with and accurate gauge and see if there is a way to recalibrate the VDO unit. Second, do the compression check and find out the source of the smoke. Either, redo the heads or rering or rebuild.

This may rearrange my plans since I wanted to do the suspension this winter. I've got a lot to consider. Should I stay with a suspect engine and try to stall big engine work while improving the handling or put off the suspension and do a new engine. Hopefully, I can find some kind of compromise, I doubt I can do it all.

Dave

[Brad Roberts]

My wifes car smokes on decel and gets 31 MPG. I figured out why it wont idle at startup (cold).. its fouling plugs with oil when cold (high vacuum). They clean up when the car warms up.

B

[DNHunt]

(IMG:style_emoticons/default/idea.gif) Maybe this explains my difficulty trying to tune my fueling map. I blamed the difficulty tuning overrun on the 2.0l injectors being too large. Maybe the problem was it was trying to burn gas and oil. Spent a lot of time and energy getting to a VE table that worked. Maybe it shouldn't have been so hard (IMG:style_emoticons/default/headbang.gif) (IMG:style_emoticons/default/headbang.gif)

Dave

[Brad Roberts]

Dave,

You have stepped thru the time portal in 914 learning. Your on the accelerated path and it sounds like you "enjoy it".. LOL

B

[tryan]

sorry to hear about the blue smoke.

is there a electrical tap on the mega squirt brain for a de-acceleration valve? ( the electrical actuated valve from a 944 might work ).

[DNHunt]

There isn't one in its present configuration. However, there are unused out puts that could run a solenoid. The instructions for this would have to be coded into the firmware using assembly programming. I don't have the foggiest idea how to do that so its a dead end for me.

There is an offshoot of Megasquirt called Megasquirt AV that is programmed in C and also has more output including extra outputs that can controll stepper type motors.

I am waiting for an Ultramegasquirt that being developed now. It will have plenty of outputs including extra pulsewidth modulated outputs (sequential multiport injection ) and ignition. This also will be programmed in C so the sky's the limit.

I'm kind of ahead of myself since I may be taking several steps backwards with this engine.

Dave

[garyh]

My 2.0 'blue-smokes' on de-accel. Especially on sweepers.

Somebody wiser than me explained it to me a while back.

1) The valves are at the bottom of the motor. (That's where the oil is.)
2) These motors do not have valve guide seals.

You are going to get some blue smoke. Especially at high vacuums during cornering.
G. (IMG:style_emoticons/default/dance.gif)

[Bleyseng]

Another test is to use a vacuum gauge to see the condition of the engine. What's the vacuum at idle? Does it fluxuate wildly or is it steady? It can tell you alot. I wasn't trying to alarm you telling you about the blue smoke it was just that you said the engine was rebuild not too long ago.
The type 4 motor can go 150k easy with the proper maintanence (few have got that) and run seemingly forever. Blue smoke isn't the end of the world but it is nice to know why it doing that.

29 mpg (at 70-85mph) is the best mine has gotten cuz I have such a leadfoot.

Geoff

[DNHunt]

Keep it up you guys are making me feel better all the time. Geoff, the vacuum when warmed up at idle, taken off of Megatune (the tuning software) is 41-46 kPa or 5.9-6.5 lbs/sq in. It doesn't move around much.

Still gonna do the compression checks Wednesday.

Dave

[Bleyseng]

Hmmm, that doesn't mean anything to me. On a vacuum gauge you need about 15lbs hg of vacuum steady. If the needle wobblbes, or is reading low it tells you alot about the condition of the motor.

Geoff

[DNHunt]

Geoff

That equals13.28 inches of hg which I think you are referring to. Its how much a column of mercury will move in response to a change in pressure. Like a blood pressure cuff when the doctor pumps up the little ball.

So this could be a little low and the needle moves some. It moves thru a range of 10%.

Dave

[rhodyguy]

oil is cheap. carry a couple of quarts. save the engine pull for the winter. you know things will get out of hand when you start.

kevin

[RustyWa]

It's taking me a while to figure this all out..but here goes.... Just drive the hell out of it.

[Dave_Darling]

Smoke on overrun (throttle closed, coasting at high RPMs) is more likely due to bad valve guides than rings. I don't think you should get noticeable smoke just because there aren't any valve stem seals--I think it means the guides are wearing.

The guides provide one of the main paths for heat transfer out of the valves. Good ones help keep you from burning a valve.

--DD