Can't figure it out

[Fatmobile]

A vacuum gauge would let you know if a clogged fuel system was the problem.
I don't like running without the tank screen in place.
There is another screen below it with less surface area, that clogs easier.

[stopping]

mon dude ... if you are in there already why not put a screen in?

You should change the fuel filter to the largest most expensive one you can find (about $15) and see what happens then... it should help. Are you sure ALL the glow plugs are working? I can't comment on compression or valves.

I checked the vacuum pressure on my fuel line after filter(btwn pump and filter) and it was -5 psi... I haven't checked it since I change to the good filter but there is no more air in my lines.

Have you been using paraffin wax?

[Hans]

I've got a compression tester and vacuum gauge in the mail, so I will soon be able to diagnose some of these issues better. I will also try to get my hands on a better fuel filter.

I had to use the car so I put things back together w/o the tank screen. I'd like to put one in, but I have no idea where to get a replacement. Any ideas? I also didn't see the secondary screen that Fatmobile was talking about.

The car started right up after doing all this work in a heated garage...so I'm not sure why it wouldn't start with the block heater. I do know the block heater works....you can hear coolant bubbling when it's plugged in for a while. I am 99% sure that the glow plugs are good, but I will verify that when I do the compression test in the next day or two.

[tylernt]

I'm pretty sure that you should not see vaporized fuel coming out of the intake! Perhaps one or more intake valves are not sealing properly against their valve seats due to wear or carbon deposits, and this results in low compression.

Also, you needn't worry about flooding a diesel. I always start mine with the pedal floored. Just be ready to back off once it fires, so it doesn't overrev.

[Fatmobile]

I'd like to put one in, but I have no idea where to get a replacement. Any ideas? I also didn't see the secondary screen that Fatmobile was talking about.

They used screens in all the gasser cars to so I'd check the vortex for someone parting out a Rabbit or Jetta.
The secondary screen is flat, round and sits at the bottom of the stock screen. At least I think I saw one there. It's been awhile. I know they can be broken by fuel being pulled toward the pump.

[Hans]

Just did a compression test with the engine warm. I recorded compression after 6 cranks and 10 cranks for each cylinder. 10 cranks seemed to give me the max reading for each cylinder.
The number are (@ 10 cranks):
390, 390, 300, 410...going from cylinder 1-4

Obviously cylinder 3 seems rather low. I do have a oil leak coming from the headgasket between cylinders 2 and 3. Could this be the cause of the low compression on #3...if so I would think that #2 should be low as well?
What could be the other causes of such a low reading in only one cylinder?

I'm pretty sure that you should not see vaporized fuel coming out of the intake! Perhaps one or more intake valves are not sealing properly against their valve seats due to wear or carbon deposits, and this results in low compression.

How would I go about checking if I have a poorly seating valve?

[tylernt]

To check the source of low compression, you can go to the next step beyond a compression test and do a leakdown test. Get an adapter so that you can hook up a compressed air source to your injector or glow plug hole (you may be able to use your existing compression tester fitting). Then see where the air is coming out -- either the oil filler cap in the valve cover (meaning rings are at fault) or out one of the intake runners (intake valve at fault) or the exhaust pipe (exhaust valve at fault) or somewhere else such as bubbles in the coolant (head gasket is shot). Obviously you need to make sure you are near TDC for cylinder #3 for this test so both valves are closed.

If it does turn out to be a valve, I'm not sure how it could be cleaned short of pulling the head off. I have heard of a product called Seafoam, maybe you could pour some of that down the intake runner to break loose some of the deposits. You have to be really careful with the stuff, though, so that you don't hydrolock your engine. You might need to vacuum it out of the cylinder when you were done, or something.

But if you do have a leaking head gasket, the head's gotta come off anyway. Usually when a VW diesel gasket blows, you get compression pressure in the cooling system. Sometimes this will cause your coolant resevoir cap to boil over, sometimes not. To test, start a dead cold engine (first thing in the morning) and run it for 15 seconds or so. Shut it off before the coolant can get warm. Then unscrew the coolant resevoir cap. If you hear pressure escaping, your gasket is blown. The coolant may also be turning interesting colors, but you won't always see oil in the coolant or coolant in the oil as with gas cars.

[Hans]

Thanks Tylernt, I'm going to look into the leak down test.

I should also add that sometimes when I was testing cylinder 3 the needle on the compression gauge would climb a lot slower and the final reading would be a little lower. Other times it seemed like the needle would climb much faster and would rest at the number I listed above. I noticed this twice.

I will see if it happens again when I test compression with a cold engine.

Could this be a sign of a poorly seating valve?

[Quantum-man]

Thanks Tylernt, I'm going to look into the leak down test.

I should also add that sometimes when I was testing cylinder 3 the needle on the compression gauge would climb a lot slower and the final reading would be a little lower. Other times it seemed like the needle would climb much faster and would rest at the number I listed above. I noticed this twice.

I will see if it happens again when I test compression with a cold engine.

Could this be a sign of a poorly seating valve?

Quite likely!
I don't think that significantly low pressure readings are ever down to head gasket problems... Unless its a major leak; in which case you'd pump the water out of the system in seconds [minutes perhaps:) If you consider that your rings are good then for your low pressure to be down to a gasket means that 25% of the cylinder volume is escaping or 100cc every stroke...rad hose would blow up like an innertube if this was going into the coolant

[Hans]

I'm pretty sure that you should not see vaporized fuel coming out of the intake! Perhaps one or more intake valves are not sealing properly against their valve seats due to wear or carbon deposits, and this results in low compression.

I'm not sure why but what ever the problem I am having with this car seems to be getting worse. I drove it 80 miles this past monday and it drove fine except for starting... but once I got it started it seemed fine.
Now the past three days it has been sitting in a 50 F garage and it will not start. Once again I see lots of smoke that smells of diesel coming from what looks like the intake. So I got out and removed the intake cover and air filter and had someone crank it while I watched. When cranking there are large plumes of smoke pouring out of the intake, I can't see from where exactly but it seems to be coming out of one of the little holes on the bottom of the manifold centered between cylinders 2 and 3.

I am going to be removing the head in a few days so I will hopefully find out what is going on then, but until that time I am wondering has anyone ever experienced this symptom?

[Hans]

Just pulled the valve cover to double check the valve clearances and they checked out. Then I turned the engine over by hand and when the cam for the third cylinder intake pushes the valve open there is a definite creaking. All the rest of the valves are silent.

[tylernt]

Broken valve spring or bent valve comes to mind.

[Quantum-man]

If that valve was bent then it wold not seat properly if bad enough. If it is the intake then cranking would suck in air (normal) and squirt it back into the inlet manifold with injected vapour...Guess guess guess

[Hans]

Well after talking about it I finally removed the head and pistons from my engine.

I haven't done much with the head yet, but I did do what libbybapa has said in other threads and sprayed pb-blaster into the intake ports to check if the valves are poorly seating and none of them leaked. So I guess thats good.

On the other hand when I pulled the pistons I had broken compressions rings on three of the pistons. Each one was one of the middle rings. This doesn't really seem to fit with my compression testing numbers but then again maybe I did a poor compression test.

In any case it's kind of nice to find the culprit of my problems.

[surfcam]

I was wondering what the cylinder bores looked like with broken rings running in them.

4BTA 3.9 Cummins Stepvan
86TD Golf
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