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Rich / Lean condition - Update - O2 sensor
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hansh
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PostPosted: Thu Nov 27, 2008 2:44 pm    Post subject: Reply with quote

Thanks Tencent. I'm in between inside and outside. Due to my job, this is my last week/weekend that is free until the middle of April. Plus, my wife is picking her brother up right now...

So long as the single-wire coax is the same as the heated O2 sensors, I am missing a ground for the outer sheath of the cox. Everything else checks out.

I'm not good at these: http://shoebox-electronix.com/sitebuildercontent/sitebuilderfiles/86FWD.pdf

I believe that the sheath somehow goes to 5 and 6? The sheath does have continuity to 6 but not to 5. Actually, maybe that is how it is supposed to be.
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PostPosted: Thu Nov 27, 2008 8:23 pm    Post subject: Reply with quote

Yeah, that diagram isn't that clear. Bentley shows it better, but mine's not here. The sheath has to test out as common with ground in any case.
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PostPosted: Fri Nov 28, 2008 1:01 am    Post subject: Reply with quote

I've fixed quite a bit but, I'm not out of the woods yet.

The O2 coax was cracked just below the end of the outer sheath at the end that connects to the O2 sensor. I fixed that and re-tested. I checked the coax at the ECU connector end as well and it was in good shape. The sheath runs to pin #6 of the ECU connector. I now have continuity from the outer sheath to pin #6 (didn't before). Pin #6 is listed as the "sheath ground" but, it shares that pin with a wire that goes directly to the AFM. I can't find that it actually grounds anywhere at all. Testing continuity from pin #6 (O2 sheath) and a ground shows an open circuit (infinite ohms).

The outer sheath of the coax is still not common with ground. When I test the disconnected coax center wire to a ground, it is an open circuit (infinite ohms). I believe that this should result in 0 ohms when the O2 sensor is disconnected. I don't know where the ground is supposed be.

I know I'm missing either a ground wire or a connection to a ground somewhere. I just can't figure out where the outer sheath of the coax actually grounds. Is it supposed ground somehow via the AFM?
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PostPosted: Fri Nov 28, 2008 9:15 am    Post subject: Reply with quote

Quote:
The sheath runs to pin #6 of the ECU connector. I now have continuity from the outer sheath to pin #6 (didn't before). Pin #6 is listed as the "sheath ground" but, it shares that pin with a wire that goes directly to the AFM. I can't find that it actually grounds anywhere at all. Testing continuity from pin #6 (O2 sheath) and a ground shows an open circuit (infinite ohms).


I keep forgetting you're on a Digijet. The instructions I gave you were what you would do on a Digifant. On Digifant, the sheath ground goes to a pin that also shares a wire directly to ground.

The sheath wouldn't ground thru the AFM. What the layout probably is, in the absence of my book, is that the sheath and AFM grounds connect to a grounding bus inside the ECU. So, if you reconnect the ECU you will then see continuity between the sheath and ground.

Quote:
. When I test the disconnected coax center wire to a ground, it is an open circuit (infinite ohms). I believe that this should result in 0 ohms when the O2 sensor is disconnected. I don't know where the ground is supposed be.


No, the center wire should always show infinite ohms with any ground when the ECU is disconnected, never zero. It is the signal carrier from the O2 sensor into the ECU and it has to be a clean shot. Yours sounds like it is OK as far as the center wire is concerned, as long as it has continuity to pin 5 on the ECU plug.

Since you've established that, leave the O2 sensor disconnected, but reconnect the ECU. Now test that the sheath has continuity to ground; it should. If so, then it is grounding thru the ECU internal grounding bus. They do this with a lot of things anyway, but on Digifant the sheath has a direct external ground so I misled you before.

So when you go to reconnect the O2 sensor, make sure the ends of the sheathing braid are trimmed back away from the center wire such that they can never touch it or the connector. I'd say most of the O2 signal-short-to-ground problems are due to manipulating the connection and having a braid wire come into contact with the signal connector. This is how I discovered the problem on my own van. I was getting 5mpg! with black smoke spewing out the tailpipe.

You definitely had a major problem with the ignition. If you see carbon tracking inside the diz cap, that means the spark is jumping to an adjacent pole rather than the one the rotor is pointing towards, suggesting that the spark current path is far too resistive on the firing cylinder. You might want to pull your plugs and check the gaps. Spec is .028" if I remember right, but you could close them down to .024" to make it easier for the current to jump the gap. This could indicate a weakening coil, but of course it could be due to high resistance on the high-tension circuits, or a concert of factors.

I can't remember if the ideal wires are the Bosch Super Premium or Ultra Premium. I wish marketers wouldn't use such confusing redundancies when they brand their different grades. I mean, super and ultra mean very nearly the same thing to normal people, don't they?

Anyway, if you saw the severe carbon tracking you describe, I would be renewing the entire high-tension side at once: rotor, cap, wires and plugs. Maybe even a new coil; they do lose power with age as the insulation breaks down, even though they check out fine with an ohmmeter.

Finally, I would reconnect everything and try making gradual CO adjustments on the AFM, using the hex screw intended for this, not messing with the internals. One full turn at a time. The others who have reported symptoms like yours, where the thing runs good until the O2 signal comes on line, have fixed it by just altering the base mixture a bit.

But, using the O2 sensor signal is not a reliable way to monitor mixture when disconnected, since it will only read a middling voltage if base mixture is pretty much perfect lambda. You don't want base mixture to be lambda, you want it to be rich from there, the amount varying with altitude, and you can't see that variance on a narrowband O2 signal with any reliability.

What you can do once you set a base mixture is measure the O2 voltage while it is connected and watch the lambda feedback working. Voltage will rise and fall cyclically around the 0.45V of perfect lambda, but it will never settle there. It's just a confirmation of the whole system working. But watching O2 voltage independently of that will only drive you crazy; it's just not a way to tune base mixture, I've found. Your ear is better than that.
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hansh
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PostPosted: Fri Nov 28, 2008 9:49 am    Post subject: Reply with quote

Thanks Tencent. I appreciate all of the thought you put into your description. You're correct, with the ECU connected the sheath ohms do read zero when grounded. When I started it last night after the O2 repairs it started great but then soon began running like crap with or without the O2 sensor connected. The potentiometer on the AFM was winging every which way. I incorrectly assume that it was a mis-wiring of the O2 sensor.

the plugs are the NGK bp6et (or whatever). I pulled them and the weird thing is that on each plug, two of the prongs are brown/black while one is white. Is this because the spark can only travel through one prong at a given time and it tends to favor one? (the NAPA guy told me about the 1 prong at a time thing but, he didn't say that they use only 1 prong all of the time...that part is my question)

BTW, I did go through every piece of the ignition system yesterday and verified each part for my monh/year van. They all check out and are new other than the coil which specs correctly but, is not new. the center wire to the distributor arcs a blue spark when disconnected and held to the block.


WAIT!: I pulled the plugs again to re-check them and the right side 2 are sooty as hell while the left two are the brown-brown-white combo. checking FI now.
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PostPosted: Fri Nov 28, 2008 10:29 am    Post subject: Reply with quote

AFM wiper position fluctuating more than about 1mm (measured at the tip of the wiper) says that manifold vacuum is very erratic. Those wipers are dead steady on a normal-running engine.

You've got the best plug available for a Digifant, in my opinion, but I'm not positive I've tried those on a Digijet. I believe I put a set in a customer's new engine, and if so it test-drove fine, but I would have to check my records and unfortunately I'm away from home. The ignition systems are entirely different early to late. If the BP6ES is listed as correct for your vehicle as a match for the OEM Bosch plug, then I would say the BP6ET is suitable, as it has the same spark characteristics, but has the triple grounding electrode.

The idea with multiple grounds for spark is that the spark erodes the gap when it jumps it, but with three grounds encircling the center pole, it will fire off to one, then as that gap widens another is closer, so it will fire off to that one, and so on. Overall plug life is extended because there are multiple paths to ground so all the wear isn't concentrated on a single gap.

The same benefit accrues to the center pole. Spark is best when it fires off the sharp top edge of the center pole. A sharp edge or a point focuses spark energy as it jumps. This is the idea behind platinum and other exotic metal center poles. They are tiny and bring the energy to a sharp point. The metals are very hard compared to copper, so they erode very slowly, meaning the sharpness of the point is maintained longer, the net result being that spark energy stays sharply focused for much longer. The metals have other properties that provide benefits, but it's the physical shape they can maintain that is the principle reason for using them.

With triple grounding paths, the top edge of the center pole is used round and round instead of wearing constantly in one area, so plug life is extended by forestalling the physical erosion of the top edge of the pole. Plus, if one gap is fouled, there are other gaps where spark can hopefully jump.

So the triples use one gap at a time, and alternate freely among them according to the surface conditions at that instant.

In a normal complete burn, all three prongs will be exactly the same color. With one prong white and the others dark, I would think that what's happening is incomplete combustion. The plug surfaces are like a snapshot of the inside of the combustion chamber. They don't reflect spark release as much as the burn conditions after the spark. What yours are saying is that hot combustion is concentrated in one geographic area of the chamber but is too cool and incomplete in other areas. That makes me think that spark intensity is weak, or spark is mistimed (probably too late), or the injection pattern is pretty bad, so fuel atomisation is spotty, resulting in a very heterogenous mixture which burns very unevenly.



The AFM wiper fluctuations may be a secondary effect of the incomplete burn. Or it indicates that the burn is still ongoing as the intake valve opens so there are back pulses of pressure out the intake tract. This is of course assuming that all valves are closing completely and on time. Have you check your ignition timing and confirmed total advance afterward? It's all well and good to set it by the book specs at idle, but then you really have to confirm that there is 35-40deg. total advance at 3000-3500rpm. 35 deg. is 2" to the right of the TDC dish (not the idle retard notch) on the rear pulley.

Anyway, just thoughts.
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PostPosted: Fri Nov 28, 2008 10:50 am    Post subject: Reply with quote

Okay, for the sake of troubleshooting, let's just assume that we are talking about an incomplete burn problem causing the AFM issue. Given that left plugs are whitish, and right plugs are black as black can get, where the heck to I begin looking for the lopsided burn issue? It seems like a problem with spark given carbon between the posts in the cap.
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PostPosted: Fri Nov 28, 2008 11:32 am    Post subject: Reply with quote

Without an ignition scope, it's relatively difficult to accurately diagnose ignition net effect. As an at-home mechanic, what you can do pretty much is just install good components, set up timing correctly, and leave it a that, because you can't actually see what power flowing thru that system is doing under load. Also, ignition problems aren't as likely to be geographically inconsistent; if one plug fires poorly, all else being equal they all will probably fire poorly.

If you've covered that, and it sounds like you have other than to verify total advance, I would concentrate on fuel delivery first. And the quickest, easiest things to do are to verify fuel pressure, and then look at the injector spray patterns. Spray pattern problems manifest as bad combustion patterns most severely at idle and low rpms, because the high-velocity airflow isn't present that helps to cover up these problems at higher rpms.

So, take out the injectors and check the spray patterns. If you see inconsistent patterns side-to-side, then you're onto something.

If you don't know how to go about that let us know and we'll talk you thru it. Make sure you've nailed down fuel pressure first, though. Just having a new regulator doesn't guarantee that it is correct.

Since you have a unilateral problem, you can also selectively swap components, one at a time in a controlled fashion, test-running in between to see whether your bad plug colors move around. It's time-consuming but with limited means you might be able to nail down which components are contributing to the bad burn.

Also, when you pull plugs after idling, you see what the idle burn looks like, but it tells you nothing useful about the running burn. Best way to do that is go out on the road, run under load for several minutes to burn off residual carbon and kill the engine while still in the mid-range revs and coast to a stop. Then look at the plugs, right there on the side of the road. Then they will give you a snapshot of the burn conditions under load instead of at idle.

Another test concerning the injectors is to see that they are all receiving the same trigger voltage. Unplug all four (the plugs can be mixed up; this is a batch-firing system), connect your voltmeter to a good clean ground with one probe, switch on the ignition and probe each injector plug. One pin in each will show a positive voltage, about 5V. Make sure they're all seeing the same voltage, I would say within a couple tenths of a volt. If you see lower voltage on one side than the other, there's a problem in the wiring harness where the leads are all common. You can also test the grounding side, which is how the ECU triggers the injectors, by ohm-checking te non-hot side of each injector plug back to the pins on the ECU connector according to that diagram you have. This isn't a place you're likely to turn up a problem, but it's not impossible and you seem to be in leave-no-stone-unturned mode, so have at it.
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PostPosted: Fri Nov 28, 2008 1:46 pm    Post subject: Reply with quote

Sorry Tencent. I know you are more familiar with Digifant. Can you, or anyone else for that matter, verify that the injector connections in a Digijet system should see 5V with the ignition just at "on" (not turning over).
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PostPosted: Sat Nov 29, 2008 4:41 am    Post subject: Reply with quote

tencentlife wrote:
Without an ignition scope, it's relatively difficult to accurately diagnose ignition net effect. As an at-home mechanic, what you can do pretty much is just install good components, set up timing correctly, and leave it a that, because you can't actually see what power flowing thru that system is doing under load. Also, ignition problems aren't as likely to be geographically inconsistent; if one plug fires poorly, all else being equal they all will probably fire poorly.
You can also test the grounding side, which is how the ECU triggers the injectors, by ohm-checking te non-hot side of each injector plug back to the pins on the ECU connector according to that diagram you have. This isn't a place you're likely to turn up a problem, but it's not impossible and you seem to be in leave-no-stone-unturned mode, so have at it.

Pretty good stuff there Chris!
I noticed you said: "without a scope" I've not heard on anyone using a scope for years. I know they used to be a big part of the Sun machines.
Does anyone still use them? I realize a good tech with a scope could find problems easily, just haven't heard the word for a while.
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PostPosted: Sat Nov 29, 2008 9:32 am    Post subject: Reply with quote

hansh wrote:
Sorry Tencent. I know you are more familiar with Digifant. Can you, or anyone else for that matter, verify that the injector connections in a Digijet system should see 5V with the ignition just at "on" (not turning over).


OK, home again so I have my Bentley in front of me (where's yours?).

Digifant powers the injector 12V bus (12, not 5V!; turkey and stuffing on the brain...) off the main FI power relay so one pin of each injector connector goes hot with key on.

However, Digijet powers it off the fuel pump relay, so it would be hot for a couple seconds with key on (simultaneous with hearing the fuel pump run) but is shut off if there's a no-start, because in both systems the pump relay is grounded by the ECU. So, if you want to test that supply at the injector connectors, you would have to do it two seconds at a time, or jumper the pump relay for your test, the same thing you would do to test fuel pressures and delivery without running the engine.

Hansh, this isn't a place you're at all likely to turn up a problem, I just suggested it since you're getting all your little ducks in a row. Nail down that all injectors spray evenly, and you can pretty much blame the ignition, is what I'm saying. All of this is assuming there is a good engine under there. Can't remember if I read that you had done a compression test or not.

One thing to consider, though, and this is not at all uncommon, is that if there is a miss or incomplete burn on any particular cylinder or cylinders, there will be an excess of oxygen in the exhaust. The O2 sensor will then produce a low voltage corresponding to a lean condition (until it gets fouled by the excess fuel, anyway), and the ECU will respond by enriching mixture. So the bad running that starts when your O2 comes online may well be an artifact of your incomplete burn on some cylinders. Get that fixed and it will probably settle in to normal running in closed-loop.

Al, I don't know what service shops are using these days, I hardly set foot in one anymore, but I'm pretty sure a lot of them have their old Sun machine in the back gathering dust. I suppose the factory diagnostic machines must provide this function, and I know a lot of data can be accessed by OBDII, maybe you can graph ignition on a laptop, even. But you can sure tell a lot by watching those power curves, so shops must have some way of graphing them. That would be a "scope", in my book.
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PostPosted: Sat Nov 29, 2008 10:51 am    Post subject: Reply with quote

Thanks Tencent. I'm embarrassed to say that I still don't have a Bentley manual. I'm buying a used one, which is coming with a parts van, that a neighbor is purchasing. It will save me money but, right now it is biting me in the a**.

This problem has really been a rabbit hole. I've been through the wiring inside and out and found many little things to repair. It still doesn't like the O2 sensor. It runs great on startup but, once the O2 sensor begins to manage things all hell breaks loose. Once it warms up, it just wants more fuel.

I was obsessing over the wiring again this morning and couldn't find anything. I decided to check the fuel pressure as I hadn't checked it since getting my new FPR (I needed new hose clamps and just kept forgetting). The fuel pressure is 34 with the vacuum hose and 39 without. Looks like I'll begin exploring the fuel system. The old FPR was literally leaking fuel so, I also just assumed it was the problem.
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PostPosted: Sat Nov 29, 2008 11:45 am    Post subject: Reply with quote

I think you may be completely missing the point 10 is making earlier. If your engine is in bad mechanical shape you may be barking up the wrong forest. If you have poor compression due to worn rings/valves. Your engine will never run right, no matter how much adjustments you do to anything. Poor compression will give you a bad burn, and the ECU will pump more fuel in, you run rich and incomplete.

You are using a ton of bandwidth here and need to get down to basics on the engine. We all love to help troubleshoot, but then if you don't follow doctors orders, you will remain sick. We can only help if you do follow what is asked. Hints you gave is a jumping wiper, this indicates your induction of air has some issues, like perhaps a leaking valve. So unless I missed it someplace, do a compression test and then get back to us.

The down side of that, it is like a cancer biopsy. If the test is bad, your dead until you rebuild the offending parts.

When you do the compression test, do it twice, cold and warmed up. Also, when you do it, do the test clean and then squirt a shot of oil in the cylinder to see if it gets better afterwards, kind of a ring health check.
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PostPosted: Sat Nov 29, 2008 12:11 pm    Post subject: Reply with quote

You're right Dogpilot. Vacuum is the problem...my lips hurt.
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PostPosted: Sat Nov 29, 2008 3:25 pm    Post subject: Reply with quote

Sad I did a compression check. 2 & 4 are around 130-140 psi. Cylinders 3 & 4 were kind of weird. I had adjusted all of the valves the other day. When I checked 3 & 4 today, each was 120 psi on the first check. On the 2nd each of them was 0 psi. For both of them, I had to set the exhaust valve to 0 lash in order for the compression to rise back to 120 psi. If I put the exhaust valve(s) back to their original position, they each read 0 psi still.
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PostPosted: Sat Nov 29, 2008 4:31 pm    Post subject: Reply with quote

Lifters seem to make sense for this problem. The exhaust lifters on 1 & 3 have been clicky-clacky. What's baffling me is that they went from 120 psi to 0 psi in between consecutive tests. Slow to adjust lifters would make sense except for the sudden change as far as I can figure. For a slow to adjust lifter, zero lash would allow the exhaust valve to close all the way while anything more would keep the valve open a bit.

The change from 120 psi to 0 psi could only be accounted for by lifters that are very quick to pump up but, slow to adjust down. The van is out of commission until Tuesday morning now...since that is when Napa can have an expandable push rod tube in. I destroyed the tube on cylinder #1 in order to get #1's lifter out.

Also, I found this thread posted by someone who had a very similar problem.

http://www.itinerant-air-cooled.com/viewtopic.php?t=2266&highlight=

As far as I can tell, the resolution, even after cleaning the lifters, was to run with 0 lash (later he was able to adjust to 1/4 lash).

Just remembered: the engine was cold for the compression check.
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PostPosted: Sat Nov 29, 2008 5:13 pm    Post subject: Reply with quote

Read this little write up by our sorrily missed Boston Bob:

http://www.bostonengine.com/articles/hydraulicll.htm
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PostPosted: Sat Nov 29, 2008 5:32 pm    Post subject: Reply with quote

Thanks Dogpilot. It's been years since I last read that and I had forgotten about it. I was just sitting here pondering whether I should mess around with these lifters or just get a couple new ones. These are the old style with the little "paperclip" retainer which I worry about. I've also never had great luck with problem lifters. I don't know...a lifter is a lifter. Anyone have opinions on which to do?

Bob has left quite a legacy...I was just looking at his instructions for WBX head replacement before I switched to accusing the lifters.
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PostPosted: Sun Nov 30, 2008 9:14 pm    Post subject: Reply with quote

Just for the good of the group and to show my humility:

http://www.itinerant-air-cooled.com/viewtopic.php?p=88868#88868

Embarassed
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Wildthings
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PostPosted: Mon Dec 01, 2008 11:14 pm    Post subject: Reply with quote

hansh wrote:
Just for the good of the group and to show my humility:

http://www.itinerant-air-cooled.com/viewtopic.php?p=88868#88868

Embarassed


If this got your engine running right then great, but I question what was actually happening. If you set your lifters at any place other than on the base circle they will end up too loose and not too tight. Too loose and they should either run 100% normal or they would make a lot of noise because of lash. I see no way that they should tighten up and cause the valves to be held open.
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