Author Topic: Blowby and high revving! Help! (Read 21688 times)

vegfuel · « **on:** March 26, 2007, 03:49:03 pm »

My 1981 VW Rabbit diesel runs and drives but it has a problem with lots of smoke and high reving at hard acceleration. Like when you rev the engine up to let the clutch out it will "run away" on me. It only does this when you rev the engine up high, other wise it idles fine and drives at low speeds ok. I'm thinking that I have excess blowby, it's buring oil because it is like 50 degrees out and it's still puffing blue smoke. I checked the vent on the valve cover and there is no smoke and almost no oil coming out, just nice warm air. I havn't tried it at higher speeds though. I'm thinking that I might have to do a minor overhaul and replace the piston rings. Has anyone on here done this? My question is, is it only one or two piston rings that are worn or all four? Can anyone give any input? Would it maybe just be the air intake clogged?

saurkraut · « **Reply #1 on:** March 27, 2007, 09:28:29 am »

Search for "runaway". There is a plastic oil deflector that goes under the valve cover to reduce the possibility of oil vapors going into the intake and cause the runaway. If you don't have one, get one. If you do have one and your getting the runaway problem, the show is over. Ring time.

jtanguay · « **Reply #2 on:** March 28, 2007, 12:51:42 am »

you might as well do all 4 piston rings while you're in there... why do one or two cyls, just to find out that a couple of months later you've got more blowby in the ones you didn't do???

rings can be done by simply removing the pan correct?

jimfoo · « **Reply #3 on:** March 28, 2007, 01:00:35 am »

Quote from: "jtanguay"

you might as well do all 4 piston rings while you're in there... why do one or two cyls, just to find out that a couple of months later you've got more blowby in the ones you didn't do???

rings can be done by simply removing the pan correct?

Only if you drop the crank first. Even then, you really should hone the cylinders, and it's better to do that with the head off. If there are any ridges, they need to be removed also, which HAS to be done with the head off. Plus all that stuff has to be cleaned really well.

vegfuel · « **Reply #4 on:** March 30, 2007, 12:27:55 am »

Hey guys, I think I may have found something that will stop my over revving. The Rabbit never takes off on me it just over revs when I let out on first!

To quote a VW manual on Diesel Fuel Injection: " The maximum engine speed adjustment prevents the engine from over-revving and self destructing.

So these would be the maximum and idle speed adjusters on the IP.

Also the guy I bought from, evidently screwed with the IP.

saurkraut · « **Reply #5 on:** March 30, 2007, 12:18:28 pm »

If you turn up the fuel screw, and don't adjust the residual fuel screw (idle stop screw) the rpm will drop very slowly after winding it out in gear.

If the "lots of smoke" you are seeing is black, it sounds like your previous owner turned in the fuel screw and didn't adjust the residual fuel screw.

Try backing out the fuel screw 1/8 turn at a time and see if you "overrevving" goes away.

Or you could putz with the residual fuel screw (idle screw) and that should also reduce your "overrevving" but won't reduce your "lots of smoke"

Did you try running it with the breather hose disconnected and see if your "overrevving" went away.

The things that need to be clarified are: "lots of smoke", is it black or white? Is your "overrevving" a very slow reduction in RPM after accelerating, or is it a runaway, uncomanded acceration, when you take the engine to high rpm?

vegfuel · « **Reply #6 on:** March 30, 2007, 02:34:39 pm »

Would it be better to hook a tachometer up (Rabbit does not have a tach) to check rmp before fiddling with the screws?

The Rabbit can drive. I can shift out of the high rev when gaining speed. It just leaves a bunch of blue smoke when it does over rev.

saurkraut · « **Reply #7 on:** March 30, 2007, 03:29:56 pm »

"I can shift out of the high rev when gaining speed."

What happins when you take your foot off the accelerator and leave it in gear when its doing the high revving?

vegfuel · « **Reply #8 on:** March 30, 2007, 04:00:00 pm »

yeah, it does stay up there when I let off of the peddle....

but it doesn't take off on me.

What I like to do to test the problem is just pop the hood while it's on idle and press on the IP lever and see how far I can get the rpms before it starts to take off, and then I have to turn it off with the key because it won't rev down.

But it's funny because it doesn't take off on me and it will still drive in most of the gears.

saurkraut · « **Reply #9 on:** March 30, 2007, 04:06:21 pm »

Black smoke, too much fuel.

Blue smoke, rpm staying high when the accelerator is relaxed, its looking like a runaway.

Disconect the breather hose from the air cleaner and see if it solves the problem.

Revving the greegree out of the poor thing in nuetral will not help the matter.

Isolate the cause, attack the cause, enjoy the bennifit.

There is an outside chance that the throttle shaft is sticking in the injection pump. The 1.5 pump used to do that. Hose it down with WD40 and work it back and forth(engine off) and see if it frees up.

vegfuel · « **Reply #10 on:** March 30, 2007, 05:01:57 pm »

Thanks saurkraut I will try that,

I bought this Rabbit for 400 bucks. I needed a car to run my biodiesel for my senior project. The rings are most likely worn for some reason. One thing I found was that the oil pan had really bad leak and the oil level was always extremely low with me having to fill it up all the time.

I think maybe the rings got worn because of the lack of lubrication, I don't know.

But do you think it would be safe to use it for my biodiesel project until I graduate? And then I can worry about a minor overhaul. It does have a little of 200,000 miles on it.

saurkraut · « **Reply #11 on:** March 30, 2007, 09:00:13 pm »

Find the oil baffle that goes under the valve cover. It completely covers the cam shaft and has successfully worked for others with far worse symptoms. I have them in all my diesels. i tried to find a picture of one, but couldn't find one. You can post a WTB for one in the for sale section of this web page. Or Email [email protected] and he can send you one.

The oil baffle may solve you problem for now.

Why rings wear out. There are two causal factors.

Driving too conservatively. Carbon deposits form in the ring lands, behind the rings. Eventually, the carbon becomes so thick it pushes the rings out and they wear faster. Some times they even stick in the ring grooves and the compression goes by by. This can occur at 80,000 miles or less, if someone drives like a real sausage.

Solution: drive it like you stoll it.

Causal factor 2, long hard life 300,000+ miles. The bores in the block become egg shaped, the rings have to do a lot more booging in the ring grooves. Piston clearance becomes excessive. Death rattle sets in, and if its pushed to its limmits, skirts break off the pistons and the show is over.

Oh, and one more. never changing oil, and / or running S rated oil instead of C rated oil. Soot particles build up in the oil, the oil either doesn't have the ability to break down the soot particles, our it lost the abilty to do so. The soot particles actually machine the inside of the motor: bearings, bushings pistons, ring and bores. Eventually the compression is so low, it won't start any more. once again, show over.

how bad is your moter? hard to say. One the pluse side, it still starts. On the negative side, you have enough blow by to get the overreving thing, but apearently not enough to get the full blast runnaway, complete with overheated breaks and a really wild ride.

so, it may live for a while, maybe a long while.

Find the oil baffle and give it a try. Don't baby it too much, but don't thrash the living beejeepers out of it either. Run a C rated oil and keep your finger crossed.

vegfuel · « **Reply #12 on:** March 30, 2007, 10:19:28 pm »

Hey thanks

Are you a mechanic? Not to question your validity in knowledge, you just seem to some good stuff. This has gives me some hope. I don't want to screw around with the IP with first checking the rpms. I havn't really done a good "checkup" on this little Rabbit. I will research the oil deflector or what ever it is and that might get me by for my project. After that I'm thinking about doing an overhaul and re ringing it.

vegfuel · « **Reply #13 on:** March 30, 2007, 10:22:57 pm »

How would I go about seeing if I have a oil deflector, just by taking the valve cover off? What does it look like? Is it ok to take the valve cover off and then on again?

jtanguay · « **Reply #14 on:** March 30, 2007, 10:58:23 pm »

Quote from: "vegfuel"

How would I go about seeing if I have a oil deflector, just by taking the valve cover off? What does it look like? Is it ok to take the valve cover off and then on again?

if you take the oil cap off and you can see metal, then you don't have the oil deflector...