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Rich / Lean condition - Update - O2 sensor
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hansh
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PostPosted: Tue Dec 02, 2008 9:58 am    Post subject: Reply with quote

Thanks Wildthings. If you are able to formulate a theory, I'd be interested in hearing it. The valves were able to adjust properly and the lifters were pumped (although exhaust 3 lifter continues to click). I plan to just some cleaner through with an oil change and filter. I feel like the compression in the cylinders should be able to produce enough vacuum to get the fuel pressure lower than 34 psi. I do need to recheck though.

The problem still exists with vacuum pressure. I'll need to recheck the compression on each cylinder and see what I'm dealing with. I've adjusted the valves to 1.5 turns past 0 lash. I'll also get a vacuum gauge today to see what I am actually dealing. I don't know how much sucking it should take to produce 28 psi but, it sure seemed like a hell of a lot! If anyone has any qualitative experience with this (appropriate), let me know.
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tencentlife
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PostPosted: Tue Dec 02, 2008 10:23 am    Post subject: Reply with quote

Dude, if your FPR doesn't ride along at 35psi with no vacuum, you could suck your own guts out your mouth and you'll still never see 29psi. If you trust the gauge you're using, then you are already in the market for a new FPR, plain and simple. If you haven't nailed that down yet you are completely wasting your time trying to fix a rich burn. Fuel pressure is the foundation of everything the FI does.

Also, don't even think about doing any compression checks after adjusting lifter preload until you've actually heat-cycled that engine at least twice, with oil temp going above 180F. I watch in amazed amusement (or amused amazement) every time I see someone fiddling with the preload and then compression checking and expecting the numbers to be valid; you'll be a very lucky lad if they actually reflect how that engine will run, but the problem is you have no way of knowing if you've been lucky or not. I don't believe they're even valid from one cylinder to the next unless the lifters are holding oil perfectly, and there's always one or two that don't hold statically, but work just fine when running. I've always said that you can't reliably assess one of these engines with hydro lifters by comp-testing. A cylinder leakdown is the only truly valid test of containment integrity.
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Alan Brase
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PostPosted: Wed Dec 03, 2008 5:09 am    Post subject: Reply with quote

tencentlife wrote:
A cylinder leakdown is the only truly valid test of containment integrity.

How true.
Also, it continues to amaze me why people think the hydraulic pressure inside a lifter will work so well as to open a valve that was previously seated.
The area of the sliding piston inside the lifter could not be more than .3 sq. inches. multiply that by the hydraulic pressure and you get maybe 12 lb at 40psi. Why would that open a valve spring that has a seating pressure of probably 100+ lb?
What I suspect is that you are incorrectly finding the zero lash point, then tightening them too tight.
Or, perhaps somebody put solid lifters in it.....
These hydraulics will actually tolerate quite a bit of misadjustment. I once readjusted a set that were at 4 turns past zero. And it ran okay. But it sure looked funny because there was no screw left above the lock nuts.
Al
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tencentlife
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PostPosted: Wed Dec 03, 2008 8:36 am    Post subject: Reply with quote

Right, Al, that's exactly why I think it's not really possible for a lifter to over-pressurise and hold a valve off the seat. The seat pressure is 100lb at full lift (I've measured it), so it's somewhat less when seated (haven't measured that), but it's still in excess of 50lb, easily. There just isn't the force available down inside the lifter to do that.

The exceptions might be what Wildthings said, that the valve springs are tired or overextended, and the other possibility being when a valve sticks a bit and doesn't close completely, even just for a few cycles. That would of course be exacerbated by weak springs. Then the lifter could "sneak in" underneath the slack in the valvetrain and overfill. But it would correct itself in a handful of engine cycles if it did. I actually doubt this ever happens but those are the only possibilities I can imagine.

The total range of plunger movement inside the lifter body is 4mm, so if the adjustment is taken all the way down it bottoms out and the thing acts like a solid lifter. But within that range, it shouldn't matter where the plunger rides as long as it doesn't hit either end limit, the bottom of the bore or against the clip.

When a valve is parked on the lobe, which is at least two valves in the engine no matter where the crank comes to rest, its lifter will bleed down, either quickly or gradually depending on the tightness of its plunger-to-bore tolerance, the quality of the ball valve fit, and the viscosity of the oil inside it. When it reaches bottom, the valve will still be opened when the cam turns again, just not to full lift. That's the clattering you hear on a cold startup after letting an engine sit awhile. During the slack episodes of valvetrain movement after the restart, the internal spring may raise the plunger higher to take up the slack, and draw air in thru the ball valve as it does if there isn't sufficient oil delivery yet to the inside of that lifter and the oil in the prechamber has drained away and been replaced by some air while the engine was stopped, but once oil is filling the prechamber under any pressure, it will purge the air out pretty quickly as long as the oil inside the lower chamber isn't an oil/air emulsion. Under pressure even that will sort it self out as the high valvespring counterforces compress the air bubbles and the aerated oil, having a lower viscosity, is forced out thru the bore tolerance as it is designed to do. Eventually the lower chamber is completely filled with pure unaerated oil and the bleedoff rate thru the tolerance normalises for that lifter, and you're on your way.
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Wildthings
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PostPosted: Wed Dec 03, 2008 10:29 am    Post subject: Reply with quote

I have tried to understand this issue. I would have thought myself that lifters couldn't overpump, but having seen it happen, I have tried to come up with theories to explain it. What may well happen is that if and when valve spring tension is low the lifter does not bleed off normally as engine temperatures change. Solid lifter T4 engines used aluminum pushrods to try and keep the valve adjustment from varying too much as the engine heat cycles, while hydraulic engines depend on the lifter to bleed and refill with oil as needed.

When I have seen this happen it has not fix itself with time. To me this rules out the idea that it could be entrapped air, but neither does it seem to fix itself after the engine is shut down and allowed to cool, which might void my theory about the phenomenon being caused by changing engine temperatures. I have never seen it happen on engines with known good valve tension.
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hansh
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PostPosted: Wed Dec 03, 2008 11:01 am    Post subject: Reply with quote

tencentlife wrote:
Dude, if your FPR doesn't ride along at 35psi with no vacuum, you could suck your own guts out your mouth and you'll still never see 29psi.


Very true, that is exactly what it felt like as I passed 30 psi going down the scale. Make no mistake, I did it, and was incredibly unpleasant.

The saga continues. I'm getting pretty frustrated with it. Last night I ran 50/50 ATF with oil through the engine for a bit and then changed the oil and filter. The exhaust valve lifter on #3 was still clicking. The vacuum pressure from the plenum (measuring the FPR vacuum hose) is about 6 Hg. I did a compression check after that and didn't make it past 1 & 2. Cylinder 2 made it to about 140 psi. I tested the rocker arm settings by going in 1 turn out and 1 turn, by .5 turn increments, from my current setting on the rocker arm screws. Nope. Cylinder 1 tested at about 120 psi the first check (maybe 2 checks...I can't remember). I then moved the rocker arm screws as I did with #2, but adjusting by .25 turn increments. Starting first with a .25 turn in, I got 0 compression. Then I backed them out .25 turns beyond my original setting. Got 0 compression. I moved them both back to their original settings. I finally did get it to put out about 100 psi but, and honestly I can't remember now, I think it was again at 0 lash. I did double check each of the valves for TDC using a long screwdriver the last time I adjusted the valves just to be sure. When adjusting the valves, I use my fingers to back the screws out to just past 0 lash and the tap the rocker back in until it just touches the valve spring. Then 1.5 in of course.

I did not bleed the lifters previously. I did pull #1 exhaust out to check it. It was rock hard, the keeper was in good condition and there was nothing apparently wrong with the lifter. I reinstalled it and opted to just use the ATF to make sure everything was clean and pumped up. Any compression test mentioned here was done on a warm engine after driving until the engine was at operating temp and the lifters should have been fully pumped up.

I did find that there is a small vacuum leak on the 1/2 cylinder head. I found it using starter fluid spray. The idle would raise when I sprayed behind the intake runner where it meets the head. I couldn't find the actual leak though. I first tried tightening the runner bolts. I pulled the runner to check the gasket. It is correctly aligned and no cracks (it is brand new). I felt around the head and runner surfaces and they were both smooth. I examined the crap out of the runners and did not find anything. The runners were also inspected very, very, closely (inside and out) when they were off the engine about a month ago. I couldn't find anything leaking at the runner. Even starter fluid sprayed directly at the runners only would not elicit a change in the idle. I looked as very closely at every potential leak in that area. I tested the cold start valve and all hoses in that area. The problem was definitely behind the runner somewhere. I tried pinpointing the leak with propane but could not get the idle to rise as I had with starter fluid. I'd like to be very clear that I tested everything around that area with the starter fluid and there were no other areas that would cause the idle to rise. The problem was not caused by drift of the fluid spray otherwise I would have identified it by a more direct spray. The leak was definitely behind the intake runner. The problem could be something else back there but, I couldn't get anything to happen with propane so I couldn't narrow down the options. I didn't see anything obvious when inspecting the area behind the runner. I also checked the spark plugs were tightened and looked around/in them for a crack. I could not spray directly at #1 but, it is very unlikely that the leak is there.

I don't think that the leak I found down there is directly related to the compression readings from #1. The leak could not have caused the compression readings to go from 120 psi to 0 psi. The leak was small enough that the cylinder would have given, at least, just a reduced psi. I just thought I'd mention it as it could be related to my stumbling idle. The fuel pressure gauge is still rapidly dancing back and forth between between around 28-34. I trust the fuel pressure gauge reading due to the vacuum gauge reading. There is obviously a vacuum leak causing it. It could be this one on the head but, that still doesn't mean that the leak is causing the drop in compression on #1. Again, I didn't even make it to #3 last night because it got dark on me.

I am not able to do a leak down test without getting a threaded hose connector to fit in the spark plug hole. I've never done a leakdown test, and there may be much more to them, but this simple method could help me identify the vacuum leak in #1.
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Dogpilot
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PostPosted: Wed Dec 03, 2008 11:10 am    Post subject: Reply with quote

Dumb question, but are you sure the injector O rings are really doing their job? They are quite close to where you are testing.
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Wildthings
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PostPosted: Wed Dec 03, 2008 12:52 pm    Post subject: Reply with quote

Try backing off your adjusting screws until you have just a little lash, like .006" and then do a compression test. This should guaranty that the valves are closing. It kind of sounds like an intake valve is the culprit, as an intake valve not closing will cause strong pulses throughout the intake system.
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hansh
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PostPosted: Wed Dec 03, 2008 3:03 pm    Post subject: Reply with quote

I'll check the intake valve separately of the exhaust when I get a moment.

Dogpilot: I did suspect the injector gaskets. I took them both off to look. The injectors are brand new as are the gaskets. I pushed their hoses a bit forward on the rails to create a little more pressure pushing the injectors into the runners. No luck spraying either with starter fluid.

A thought occurred to me. If the fuel pressure gauge needle is jumping all over the place, then shouldn't the vacuum gauge needle be doing to same? Wouldn't fix the low vacuum but, just curious.
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hansh
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PostPosted: Tue Dec 23, 2008 10:46 am    Post subject: Reply with quote

We left on our first trip in the Westy yesterday. We did about 8 hours of actual driving from Bend, OR to Wallace, ID. I was amazed that the van drove beautifully. Up steep grades or passes, I'd need to use 3rd gear but, other than that we could pull a solid 65mph on flats and up hills. The temp gauge sat solid with the needle covering the top 1/4 of the light, other than on downhills when it would cool quickly. We were heavily loaded with 3 adults and 2 kids, luggage for 5 days, Christmas gifts, snowboard equipment for everyone, and the Thule box newly mounted to the poptop. We averaged 19mpg even with all of this.

It still has the problem of being either too rich on warmup or too lean at operating temp. Seems to be mostly at idle though. I have adjusted the mixture to be rich enough while running but, it is still too lean at idle at operating temp and thus, too rich at warm-up idle.

I can't imagine that this could be attributed to anything but, the AFM. Everything else checks out and all of the wires running to it are in spec. I checked the resistance of the pins from the AFM which are supposed to be "variable" from the AFM (2 and 3 I believe). There were a couple of spans at which the ohms read infinite (open circuit). I pushed the potentiometer contacts onto the plate and it stayed closed circuit most of the way. I think I said earlier that the AFM was all that my mechanic could come up with also.
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PostPosted: Wed Feb 08, 2017 12:48 pm    Post subject: Re: Rich / Lean condition - Update - O2 sensor Reply with quote

im going to beat this dead horse just in case someone else is reading it just now like i am.

check your timing and then familiarize yourself with pro-training manuals for digifant/digijet. it goes through all the testing easily explained for the fuel delivery/ignition system. this should take care of all sensors and parts external to the engine. after the COMPLETE diags make sure you again check/adjust your timing. if this does not resolve your issues your engine mechanicals need to be thoroughly inspected. and get yourself a bentley....

im in the process of doing this on a late 1.9L digijet and the pro-training manuals are a good read.

www.vanagonauts.com/files/Digijet_FI.pdf
www.vanagonauts.com/files/Vanagon%20Digifant%20Fuel%20Injection%20System.pdf
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