Possible bad O2 sensor?

[AirCooledCurtis]

I found a used Bosch rotor in my stash and threw that in hoping that my Chinese AutoZone one which didn't fit snug was the issue. No change. I checked for vacuum leaks again, now the whole system up to the AFM has been checked (previously I did just to the throttle body) and it's a sealed system.

The engine harness is the only thing that I have not swapped out or thoroughly tested at this point. My Syncro is manufactured in June of 1985, it's one of the earliest Digifant vans, but it has the heater for the PCV and the snipped black and white wire at the coil as per the dealer update. I've been reading that there are some issues introduced with this update. Tomorrow I'm going to check the wiring and see if the ECU relay is operating, and try to see if making it operational again will increase voltage at the ECU. I've also found a '90 harness near me but I'd rather poke around with this one first.

[AirCooledCurtis]

I spent some time to go over everything piece by piece.

Spark plugs swapped out from BP6ET to WR7DC+ with the correct gap. I had checked the plugs a few days ago after some more average around town and short highway driving, the plugs looked good. After cold starting and troubleshooting this problem the plugs were black and wet with fuel.

I followed the Bentley to test the Temp II and TPS at both the ECU and Idle Stabilization Control Unit. Both circuits are good. Temp II is swinging along the graph correctly.

The IAC valve isn't functioning right now, it's stuck closed. I believe it's the valve itself, I have already replaced the transistor in the control unit that was fried, I'll troubleshoot this later but I cannot image this would cause this issue. I've driven Digifant vans with the control unit removed.

I did a compression test and it's lower than I'd like but it was very consistent and wouldn't be causing absolutely terrible drivability issues. 120-124 across all 4. This van has sat for the better part of 10 years, I'm sure that with some driving and temp it'll come up a little.

I was getting 11.7V at the power to the coil. I jumped 12.7V from the alternator to the coil and that didn't cure the issue. I am getting 12.5V to the ECU though with the wiring how it was. This van does not run without the ECU relay unlike another post about an early '86 van that I read. It's had the update to add the PCV heater, so the wiring to the coil has been messed with. I get 12.3V to the black/white wire that's been snipped that has previously supplied key power to the coil.

When jumping 12.7V to the IAC valve, after getting unstuck the idle does bump up about 200rpm, and often time the van stumbles just from opening the IAC valve, so I know that it's not strictly TPS related. I also know it's not TPS related because it does not want to have large throttle load under 2k rpms.

I have found that unplugging the Temp II improves the stumble/stalling a lot, but it does making it run choppier across the whole rev range. I'm guessing that unplugging the Temp II would make it run richer. The Temp II works, and I've tested 2 ECU's today.

I also did yet another vacuum leak test. Just the throttle plate like I knew.

[AirCooledCurtis]

[1988M5]

The voltage readings are not ideal but it's an old car so some loss is expected but checking the voltages while running wouldn't hurt. I think you threw everything at it, does that include a full tune-up on the secondary ignition system? That would be cap & rotor, spark plug wires (attached properly) and sparkly plugs gapped right and just for fun a new coil.

BK
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[AirCooledCurtis]

I had ordered a cap and rotor a week ago, I got them installed today. Yesterday I pulled the distributor and did a thorough examination of it and the drive gear. The Chinese cap that came on the cheap aftermarket distributor that this van came with wouldn't fit straight, it would foul on the hall sensor plug meaning that the cap was crooked just barely. New German made cap on, and Bosch rotor and the hot stumble is ironed out, cold stumble and sluggishness below 2500rpms is still there. I checked AFM voltage, again, as it now clearly feels like a fueling issue now that the ignition issues are resolved.

When I tested fuel pressure earlier, I did it with the van off, just jumping the pumps and applying vacuum to the regulator. I got the full swing, but today when I tested it on a hot running van, I found the culprit. The van will start and idle around 32psi, but as you blip the throttle, it will slowly climb to 39psi and it won't return to the lower threshold with any amount of vacuum to the FPR. This has to be what's causing the strange fueling that's throttle position and rpm related. If I'm easy on the gas down low it's fine, as the rpms increase the amount of throttle and power that's available increases.

I'll buy a FPR right now, I've heard some horror stories about cheap ones. I don't particularly like how vendors like GoWesty charge high prices for "trust us, this isn't aftermarket crap" just to find out the same one is on RockAuto for 1/2 the price.

[ALIKA T3]

I just spent an hour reading everything here, I stumbled randomly upon this thread and strangely I have the exact same issue on a free van I just finished to put back together. 1986.

I didn't do as many wire tests as with experience, I'm more pragmatic but everything seems kosher.

I went through the whole dance of parts swap. A lot of new parts.

Still runs like crap, I can tell power is lost, cycle the key, sometimes better! All symptoms identical from what I read.

I was about to swap out the dizzy just in case, but I'll prolly go straight to swapping out the harness. I have a used new harness I saved from a Subaru conversion, I know it's a good one.
At this point, I don't feel like trying a used harness (I got many).

I always wondered how all these different wiring on Digifant over the years don't affect anything when you swap components, it's all interchangeable. I find it fascination bc I'm not much educated about the EFI theory. I know how to repair problems, but don't ask me too much about how everything works. I know the basics, it has served me well for 16 years on WBxer's until now.

I will say, I had 3 fuel pumps in this turd, the previous 2 were original Bosch, not pushing enough fuel pressure, even with a new cheap chinese regulator, even with returned hose clamped.
I finally put a cheap pump, pressure is now good. Been using these pumps for years, no issues.
The FPR, that's the first time I'm trying one... I wonder if that could be it too as it feels like a fueling issue more than a wiring issue from the seat of my pants. Doesn't run rich, just feels weak, and sometimes a backfire.

I'll follow very attentively this thread, i'll be back on this van tuesday, maybe by then you will have the problem!

Good luck!
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget

[AirCooledCurtis]

So new FPR from busdepot is installed. It's one of the FPRs that the body is too large to fit through the bracket and the vacuum port is also larger than original, not happy. No change at all, maybe even worse than before. I've had fuel delivery issues run out of flow up top, never with transitory throttle. It's not that it's not getting enough pressure.

I'm now thinking that the fuel pressure tester from Auto Zone was broken, I had tested fuel pressure earlier and it was okay and now I'm out $100.

The engine harness is the last thing. Besides the temp II but the resistance of that is fine at the ECU plug.

[DanHoug]

[ALIKA T3]

Well I'm gonna add to the sauce here with my issue, maybe it'll be useful.

I went back to a stock used FPR bc the new one leaked at the crimp when pressure was built up engine off ( manually activated fuel pump relay ).
I replaced the coil with a good used unit.
I replaced distributor cap/rotor with new Bosch.
I tried another used distributor.
I tried a 3rd AFM.
I also replaced the entire EFI harness with a semi new one I took off from a Syncro a while back) converted to Subaru.
It didn't change a god damn thing.
Almost chugging as soon as I accelerate.
Gotta pump the accelerator to rev it and go into high rpm. Idles ok sometimes, until it gets hot, then there's backfiring when I try to accelerate.

Oh and the valves got adjusted, also replaced the adjuster screws which were chewed up beyond recognition, like 3 mm deep into the screw.
Installed lash caps.

Removed exhaust to look through the catalytic converter, I can see through just fine.
Tried with muffler off, OXS off, same shit.
AFM unplugged, temp 2 unplugged ( tested good at many different temp ranges).

Starts great no matter what, but when it gets hot, it is just horrible.
I'm gonna try a Bosch fuel pump next., and revert to stock injectors ( I have 2L ABA 4 inline injectors, rebuilt. It's an upgrade I saw sold in Germany so I gave it a shot buying my own in the US).

I'm loosing it.
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget

[AirCooledCurtis]

That does sound similar to mine, the issue where it needed a key cycle was solved by the AFM, after the AFM it would want to stumble when cold and hot, there was a moment that it would be okay stone cold. Yesterday I got it to consistently stumble off idle while hot, so I took the moment to unplug the o2 and that didn't do anything. The ECU is getting the signal from the o2 I've tested it on the physical ECU board while running. I double checked injector spray yesterday, all good. There's nothing else with Digifant to go over on this van, the stumble doesn't seem like it's a wiring issue, I'd expect wiring issues to cause intermittent issues that are worse than what I've got now which is pretty minor.

My current theory is 2 parts:

1: This van has sat for about 10 years. The engine only has 5k miles on it since it was rebuilt around 2006. Judging from how much hackery the EFI system had, it hasn't been running right in a very long time. I'm a little worried the bores are already damaged (rich mixture will kill bores), but I'm hoping that since it doesn't look or smell like it's burning oil, that isn't not the bore condition and just that the compression rings are stuck. I blasted half a can of Seafoam through the vacuum port at the throttle body while at temp and heavy throttle, I hope some of it has gotten though the rings and with some more driving it will help.

2: My last van was an '86 automatic tin top, and I think that the stall speed masked the torque dip at 2k rpms that I've felt like was a mixture problem. GoWesty has a dyno graph of a stock 2.1 WBX and to my surprise it's actually quite bad around 2k rpms, and actually dips. A lot of what I'm feeling with the poor performance under 3k rpms is probably just the nature of this particular engine, less than perfect compression at this moment and a very non linear torque curve.

[AirCooledCurtis]

I put maybe 30 or so miles on the van this morning, all highway but there was 50/50 traffic. This is the most I've used the van since buying it and on this journey to fix it. It's been raining heavy, I feel like I should say that but I don't want to mislead anyone by giving the idea that it's water related.

about 15 miles in it developed a mixture issue. It was down on power, and it would phase in an out over the course of 3-5 minutes then go away. It's not fuel flow related, I could still rev it out to redline. While it was acting up I could feel the o2 swing and correct the mixture in 1st gear at 3000rpms. I've been over the o2 circuit too many times, it's not that. There's an intermittent issue with either the AFM or Temp II. The mixture issue is sometimes worse than other times. When it's bad it acts like it has been, off idle response is poor, making hill starts hard. Now I have to diagnose an intermittent issue that pops up while on the highway, in a dense urban area (NYC) where I can't just pull over test something.

[AirCooledCurtis]

I had a 10uF cap on hand so I figured I'd solder it in but this AFM already has a tantalum cap soldered in. Also the traces are worn. I feel uneasy buying another Fuel Injection Corp AFM, I don't know exactly how many miles were on this but I was told very little miles.

[ALIKA T3]

Doesn't look that bad.

Use a HB2 pencil on the carbon board traces, that helps for a bit.

I too feel like it's fuel related. The other day it wouldn't go up the driveway, cycling bursts of half ass power.

I'm getting back to it tomorrow, gonna test the fuel pressure since I had put a used regulator, marked OK by me but who knows after sitting....

Next, replace injectors.

Last time it died at idle, plugs were wet AT, it flooded the cylinders to the point the starter wasn't powerfull enough to spin the engine. Took the spark plugs out to flush the cylinders with the starter running, Hall sender disconnected.

It wouldn't restart until I tool the left fuel rail off away from the intake runners to start it, spraying from outside the manifold, basically sucking in more unmetered air, cranking from the engine bay with a trigger wire in the other hand. Took a while but that did the trick.

POS...
_________________
Silicone Steering Boots and 930 Cv boots for sale in the classifieds.
Syncro transmission upgrade parts in the Classifieds.
Subaru EJ22+UN1 5 speed transmission
http://www.thesamba.com/vw/forum/viewtopic.php?t=416343
Syncro http://www.thesamba.com/vw/forum/viewtopic.php?t=4...num+gadget

[AirCooledCurtis]

Link


I picked up a cheap analog voltmeter to do some testing with o2 swing and AFM signal. I cannot find any signal drop out with the AFM. This o2 was brand new Bosch 150 miles ago. Ground strap from head to chassis is new, o2 signal wire (Vanagain) is new, I had replaced the ground wire from the ECU to the head but I've reverted back. I don't want to parts cannon another AFM, there is some resistance between pin 4 of the AFM and the chassis when testing between pin 2 and 4 versus pin 2 and chassis, I'm unsure if this is normal, about 200mV.

[AirCooledCurtis]

I think I've narrowed it down, or at least I've found an anomaly, I'd appreciate some advice whether or not this is how it's suppose to work. I've measured the AFM from the voltage signal, and there were no drop outs. People poo-poo the Bentley's method of testing the AFM, probably because it's vague and only says that the resistance should change. My test shows resistance has a large peak right off idle in the low range, it peaks around 2.7k Ohms, only in that spot where the board is worn.


Link


I've found another video of the same test being done, and this AFM here doesn't have any large peaks, it just swings between 2 thresholds while moving through the range.


Link


The placement of this area of high resistance is where the off idle dead spot is, and possibly my loss of power around 2k rpms. I'm going to spend a few minutes to see if moving the board can fix this issue, otherwise I think I've found enough evidence to convict this "good tested recently rebuilt" AFM.

[1988M5]

They both look like doggy poop. It's as if there is a bleeding capacitor in the circuit.

https://www.clarks-garage.com/shop-manual/elect-22.htm

https://www.youtube.com/watch?v=4pFxhJO4jXc

BK
_________________
1991 tin top GL
2002 Winnebago Vista. VW VR6 24V Eurovan front clip powered class C 21' RV.
Some BMWs.

[AirCooledCurtis]

That is just how the resistance looks when you test it like the Bentley says. I moved the swiper board down and took the 500ohm peak out where the patch is bare, but that didn't change how it runs, it might be stronger above 2200rpms, still a hole underneath that. I removed the throttle body, I knew it has a leak from the throttle shaft, so even though I had felt like it's minor enough to not be causing this issue I'm going to replace it.

I'm talking with someone I know who tunes Bosch Jetronic cars about developing a hot wire MAF for Vanagon Digifant. I know GoWesty has done this previously. As someone with an LH-Jet daily driver, I personally don't think custom EFI is the solution to Digifant, it just needs higher resolution sensors and all of the hackery of previous ownership to be undone.