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Rich / Lean condition - Update - O2 sensor
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hansh
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PostPosted: Tue Nov 25, 2008 9:07 am    Post subject: Rich / Lean condition - Update - O2 sensor Reply with quote

I have the mixture perfect at an operating temp idle. No blips, great performance, good temp. Then on hot restart it is slightly rich for the minute till the O2 sensor takes over. On cold restart it is way, way too rich. It is just begging me for more air. I'm leaning toward this being a cold start issue since I can't come up with a scenario that would make sense otherwise. This isn't a new condition that I've created. It's something that has been there but, I thought would be fixed with my new FPR as the old one was leaky and had high pressure at idle.

The temp sensor II doesn't seem to make sense as its job is to richen at cold start and then handover to the O2 sensor when warm. Failure would mean too rich at operating temp also. The O2 sensor would cause a too rich condition at operating temp had it failed (read below though). The easiest answer is that it is not getting enough air at cold start and hot restart. The cold start valve is doing its job as I tested it yesterday. I don't know where else to get it some air at startup.

I was having another issue with having zero power when starting on even the slightest uphill from idle rpm. I disconnected my O2 sensor and the that issue was solved. Without the O2 sensor it bucked and jerked on deceleration. I'm going to pick up a new sensor today although, this one is only a couple months old.
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Last edited by hansh on Tue Nov 25, 2008 7:36 pm; edited 1 time in total
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hansh
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PostPosted: Tue Nov 25, 2008 7:35 pm    Post subject: Reply with quote

Long day away from the computer today. I was able to do a little testing on the van and found some good information.

I borrowed my neighbor's factory sealed, known good AFM. I had borrowed it before but, only tried it on a hot engine to see if it resolved a stutter. I tried it on the engine cold and hot start this time and everything was great with the mixture!

when driving, I was still experiencing the absolute zero power condition when starting from idle rpms. Every time, even on the slightest of uphills. It became dangerous so I disconnected the O2 sensor. Suddenly, all was good in the world. No issues with anything at all. Great cold, warm, and hot idle. Great power, no lag on acceleration. Also tried bypassing the DIS both with and without the O2 attached. Neither was better and with both disconnected (DIS into itself) it was ridiculously powerless.

This is a brand new O2 sensor that I put in today. I checked the coax and the outer braided shield is not touching the center wires. However, I did measure the center connector to a ground and got about 149.5 ohm on a 200k scale. Does this mean that it is somehow grounded? I guess it would mean that since the ohmmeter measures 1 if there is no conductivity. Where would I look for the ground?
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hansh
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PostPosted: Wed Nov 26, 2008 9:01 am    Post subject: Reply with quote

Coo Coo Cachoo

Our family has to take a trip out of state next week and while I'm confident in the van's ability to make a trip, I'm worried about the amount of fuel that we'll use. I need some help tracking down why the van would run so poorly with the O2 sensor connected and so well without it. I could use some help hunting this down so that the van isn't hitting us as hard in the pocketbook with fuel as it has with parts!

Here's a rundown:

- O2 sensor seems to be working when disconnected and checked with ohmmeter

- 0 ohms between green coax and ECU connector

- 139.5 ohms between green coax and ground when ECU connected

- Checked with known good ECU

- O2 sensor is new yesterday
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Wildthings
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PostPosted: Wed Nov 26, 2008 11:10 am    Post subject: Reply with quote

When I first put my 87 Syncro together it would do about the same as what you are seeing. It would run well until the CPU started listening to the O2 sensor and then would barely run. It would run fine with the O2 sensor disconnected, good smooth power. I swapped EVERY FI and ignition part out between my 91 and the 87 without success until I changed out the new set of aftermarket spark plug wires. The problem was the wires, don't know why the engine wouldn't run with them. They were high quality, checked out A-OK, and there was no misfire at idle. A new set of Bosch wires solved the problem.
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hansh
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PostPosted: Wed Nov 26, 2008 11:15 am    Post subject: Reply with quote

Thanks Wildthings. What did you switch from and to? I have Bosch Ultra Premium wires that are about 2 months old.
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hansh
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PostPosted: Wed Nov 26, 2008 12:06 pm    Post subject: Reply with quote

I'm also verifying the correct part numbers for my ignition system parts. I noticed that there are black marks between the posts in the distributor cap. Big deal / no big deal?

I have Bosh spark plug wires # 0 356 301 031. I can't find a cross reference to see if these are part #9180.
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Wildthings
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PostPosted: Wed Nov 26, 2008 12:47 pm    Post subject: Reply with quote

hansh wrote:
Thanks Wildthings. What did you switch from and to? I have Bosch Ultra Premium wires that are about 2 months old.


Have no idea as that was 12ish years ago. You might check that all your other ignition parts are A-1 as well. Never truly understood what made the difference in the wires, but I have also found that Vanagons have particular likes and dislikes in spark plugs as well. Can't say why there either. I guess a scope would tell me a lot.
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presslab
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PostPosted: Wed Nov 26, 2008 12:48 pm    Post subject: Reply with quote

hansh wrote:
I'm also verifying the correct part numbers for my ignition system parts. I noticed that there are black marks between the posts in the distributor cap. Big deal / no big deal?

I have Bosh spark plug wires # 0 356 301 031. I can't find a cross reference to see if these are part #9180.


Black marks, like carbon tracks? No bueno! You could try cleaning the entire inside with some alcohol, but if it were mine I'd throw on a new dizzy cap.

With your problems, my bet is on something in the ignition system.
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hansh
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PostPosted: Wed Nov 26, 2008 1:06 pm    Post subject: Reply with quote

Ya. They are kind of sooty black spots. I was able to just wipe them out with my finger. I'll grab a new cam and see what happens.

I'm really curious about the plug wire numbers as I just can't find a place to verify them. I'm 99% sure they are the correct wires but, I'd like to know for sure.
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PostPosted: Wed Nov 26, 2008 1:19 pm    Post subject: Reply with quote

Check to make sure your rotor and/or the center contact in the cap isn't burned up. The resistance strip on top of the rotor can fail as well. There are several different caps and rotors that will kind of interchange and look the same, but will not work correctly. Aftermarket places often do not sell the correct OEM stuff, though it may still work. This is one place I have sometimes gone to the dealer for parts.
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hansh
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PostPosted: Thu Nov 27, 2008 9:02 am    Post subject: Reply with quote

Happy Thanksgiving Samba! Let me say that I am thankful for all of you good people. Hope your day is filled with family and friends.

I pulled the entire ignition system yesterday (at least what's in the engine bay). I saw online that many of the parts are very specific to an '84 as opposed to even an '85. It took a while to cross-reference all of the numbers but, every part checked out. I also checked the resistance on each and they were all good.

I found that while the engine is running better with the other AFM, it is still running very rich (as evidenced via voltage from the new O2 sensor). The new O2 sensor is working but, if attached the engine runs terribly still.

The temp sensor II specs out just fine across the heat range but, it is all I can think of that would cause the engine to run that rich. Oh, and the fuel pressure. I haven't rechecked it since I got the new FPR. I was having a heck of a time trying my pressure gauge not to leak from the hose. I finally bought some new hose but, still need new hose clamps (bought some at Autozone that the guy handed to me but, they are barely too big for the hose line he sold me).

I can't imagine what would cause a constant rich other than these things. It's definitely not the AFM. I can slide the potentiometer clockwise a considerable ways and get the mixture lean and the idle smooth. The distance that I have to push it is just too far for any reasonable adjustment to it.
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Terry Kay
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PostPosted: Thu Nov 27, 2008 9:16 am    Post subject: Reply with quote

On an 84 there are two throttle postioning switches--

One for low speed enrichment , one for high speed enrichment.

IF either one of them isn't set up right, this will cause all kinds of problems.

Your getting close with the transfer of the AFM--but I don't think you've landed on the real source of the problem yet.
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PostPosted: Thu Nov 27, 2008 9:18 am    Post subject: Reply with quote

When you check things like the Temp II sensor resistance, are you doing it at the sensor or at the ECU? Wiring and corroded connectors can make all this moot. Especially with the rich condition you are seeing. The O2 takes over when the Temp II makes it to its pre-determined resistance value. Does your 84 have the two Throttle Switch set up? I know you checked the switches earlier, but the switches should be checked again, at the ECU connector. It may be your WOT signal from the full open switch is putting the engine in enrichment mode (grasping here).

As I found out the hard way, the WBX is very, very sensitive to ignition components. The Bosch Ultra Premium ones may not be the ones recommended for the 84. They have the proper connectors for the later style cap. Go to the Van Café web site and read the blurbs about the different wire sets. 84's have specific caps that must be paired with specific wires.

http://www.van-cafe.com/home/van/page_223_242/spark_plug_wire_set___bosch___fits_all_years.html
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PostPosted: Thu Nov 27, 2008 9:24 am    Post subject: Reply with quote

A gagillion times I've checked those switches. They have been dismissed from the line-up of suspects. No issues with either. Coming off idle the resistance goes to 1 (infinity). I sure wish that thing was the answer.

You're right that I'm getting closer though. It feels good to have things narrowing down to a singular problem that eats at me day-in and day-out, rather than a host of problems.
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Terry Kay
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PostPosted: Thu Nov 27, 2008 9:24 am    Post subject: Reply with quote

<< Does your 84 have the two Throttle Switch set up? >>

Unless somebody did some TB & harness swapping, an 84 has two switches on the throttle body, and a pain to get dialed in correctly.
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hansh
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PostPosted: Thu Nov 27, 2008 9:28 am    Post subject: Reply with quote

Dogpilot wrote:
When you check things like the Temp II sensor resistance, are you doing it at the sensor or at the ECU?


Good point, I have not.


Dogpilot wrote:
84's have specific caps that must be paired with specific wires.


This I have checked. You are absolutely right that the parts are very specific for this year...right down to the month that it was made. Mine was made in 1/84 so it doesn't fall into a gray area.
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PostPosted: Thu Nov 27, 2008 9:30 am    Post subject: Reply with quote

Terry Kay wrote:
Does your 84 have the two Throttle Switch set up?


It does have the two switches. They are adjustable exactly per Bentley. The idle switch clicks on even when the throttle is closed very gently.
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PostPosted: Thu Nov 27, 2008 1:05 pm    Post subject: Reply with quote

Check the switch function at the ECU plug, not at the switch.
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PostPosted: Thu Nov 27, 2008 1:15 pm    Post subject: Reply with quote

I thought I had it. The idle/WOT switches were not working at the ECU connector pins. I found a yellow/brown wire disconnected near the grounds on the driver's side head. Connecting caused the two switches to work. Without checking the rest of the pins, I started the van and things seemed pretty good until the O2 sensor kicked in.

Checking the O2 circuit:

It is supposed to be an open circuit when connected - check
It is supposed to be 0 ohms when disconnected and grounded - no check - still open circuit

I'm trying to figure out what is missing but, I'm having some difficulty figuring it out. The inner green coax measures 0 resistance to the pin at the ECU. The outer of the coax measures open circuit everywhere.

Everything checks out other than all of the injectors measure 18 ohms rather than the spec of 16 - 16.5.
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PostPosted: Thu Nov 27, 2008 2:17 pm    Post subject: Reply with quote

hansh wrote:

Checking the O2 circuit:

It is supposed to be an open circuit when connected - check
It is supposed to be 0 ohms when disconnected and grounded - no check - still open circuit

I'm trying to figure out what is missing but, I'm having some difficulty figuring it out. The inner green coax measures 0 resistance to the pin at the ECU. The outer of the coax measures open circuit everywhere.

Everything checks out other than all of the injectors measure 18 ohms rather than the spec of 16 - 16.5.


I'm having some difficulty figuring out how you're checking the O2 signal circuit. To be completely clear, I'll spell it out. Check it exactly like this:

Disconnect the single-wire signal lead of the O2 sensor from the green coax (you can leave the two-pin heater plug for the sensor connected; it has nothing to do with the signal circuit).

Leave the disconnected end of the coax hanging free. Make sure it won't touch ground inadvertently.

Ignition off! Disconnect the multi-pin connector from the ECU.

Put VOM in ohms mode, lowest-range if not auto-ranging.

Connect one VOM probe to the free end of the coax center wire.

Touch the other probe to ground. You should only ever see infinite ohms (open circuit). This verifies that the signal wire is not inadvertently shorting to ground. Move the coax wire with the probe attached around a bit and watch that there is never any continuity to ground.

Leave the probe connected at the signal wire of the coax. Now touch the other probe to the O2 signal pin at the ECU harness plug. You should see zero ohms. This confirms that you have a continuous signal circuit.

Now take the first probe from the signal wire at the end of the coax, and touch it instead to the coax sheathing braid. Touch the other probe to ground. You should see zero ohms. This confirms that the noise-suppressing sheathing is properly grounded (it is grounded up near to the ECU harness connector).

That is the complete, isolated test of the signal circuit and noise-suppression. Don't concern yourself with checking the resistance of the O2 sensor to ground (irrelevant), the resistance of the O2 signal circuit thru the ECU (also irrelevant). Confine your tests to the signal coax in isolation.

The reason I'm spelling this out, please don't take insult, is because I've read this and it's quite unclear to me whether you have been testing this circuit properly. That's how you do it properly.

Now, there's another functional test for grounding of the O2 signal circuit with the engine running, everything connected as normal including the O2 sensor. Under those conditions, you take a jumper from ground and connect it to the O2 signal connection. The engine should noticeably alter speed and run stink-rich. If it doesn't, then there is already shorting to ground somewhere of the O2 signal. If it does go to a very rich idle, then functionally, all is well with the circuit. This does not confirm anything about the quality of the O2 sensor output, only that the signal is reaching the ECU cleanly.

Don't be tempted, by the way, to ground the free end of the coax's sheathing braid. It is grounded up near the ECU, and to cancel noise a sheath like that can only be grounded in one location.

If you ever want to test whether a TB switch is functioning, you can always disconnect the switch connectors at the TB, both if yours has two TB switches, and jumper one pair of the wires together to simulate the switch closing, and open that circuit to simulate the switch opening, since all the TB switch or switches do is to open and close that circuit to the ECU. If you have two switches, they are in parallel to each other and the signal, whether open throttle or closed, is the same signal; the ECU merely interprets it differently depending on present and recent engine rpm.

Finally, what the hell are you doing working on the damn van? Go inside with your family and eat, you turkey!!!
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