# CIS-E oxygen sensor testing



## Scott555 (May 10, 2007)

Attempting to test control unit response. Per the Bentley - bridged the temp sender circuit with a 15k ohm resistor. Manual says DPR current should read 9 - 11mA. With the bridge in place it reads 60 mA. (For comparison, with the temp sender circuit open, it's 85mA.)
Now, *without* the bridge in place, and the sender plugged back in, DPR current is as expected - about 10 mA.
Am I interpreting the Bentley procedure incorrectly?
FWIW - I'm trying to track down a spurious performance issue. Symptoms include:
- low power in the 2k to 3k RPM range (that's as high as I typically rev her.)
- low idle on cold start
- hesitation after hot start (goes away after a minute or so.) Sometimes accompanied by a back fire or two.


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

You use a 15k ohm resistor to simulate cold conditions. It should result in 50-80ma through the dpr. Your 60ma is completely normal.
When you do have the sensor plugged in and the car warm, what's your dpr's behavior? Assuming proper tune, you should be seeing dpr current oscillate between 9 and 11ma.
Some day, I'm going to take a short clip of what a properly oscillating dpr current should look like on an everyday multimeter.
onto your symptoms:
low power 2-3k. is this only when cold or always?
low idle on cold start. have you watched your dpr current from a cold start until it's warm to see its behavior? fueling problems could cause low idle. but if it drives fine otherwise, it's likely your aux air regulator isn't up to par. you can take it out and try to clean it and see if you can get the hole to start a little bigger.
hesitation after hot start. again, when this is happening, you should be watching the dpr current to understand how the system is trying to fuel.
with a fully warm cts signal, the max the dpr should get to is 20ma. I've seen a bad o2 sensor cause the dpr to peg 20ma sometimes.

I'd say, start with a new bosch cts and go from there. Assuming the mixture is set properly, you could try unplugging the o2 and seeing how the car drives (should result in 10ma constant)


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

CTS resistance cold - 3500 ohms
Hooked up the DPR and tracked the current from a cold start until the fan switched on. 
In 15 second increments:
Start - > 50 mA
15 - 26 
30 - 25
45 - 23
60 - 21
1:15 - 19
1:30 - 17
1:45 - 15
2:00 - 17
2:15 - 20
2:30 - 20
2:45 - 18.5
...at this point, and for the next 3 minutes until the fan switched on, the DPR current fluctuates between 16 and 18 mA.
CTS resistance hot - 230 ohms.
As for the hot start weirdness - for the first 15 seconds or so after start, the DPR current sits at 9.5 mA and the engine struggles to stay running. A goose of the pedal will usually invoke a couple (what seem to be) backfires. After 15 - 30 seconds the DPR current creeps up to the range noted above, and it starts to run "normal."
Also of note - at high idle the DPR current pegs to 19.3 mA and does not fluctuate. Should I discount the .7 mA difference and assume it's pegging to 20 mA? My meager grasp of this system leads me to conclude the o2 is detecting a lean condition and is instructing the DPR (via a higher current) to enrich the mixture.
As for unhooking the o2 sensor, the engine struggles to stay running and will not accelerate - in fact it's the exact same hot-start symptom I describe above, except it doesn't self-resolve after 30 seconds or so.
Thanks for your time. I think I'm understanding things a little more at a time, but I'm still pretty confused, can't tell where the problem is, and can't afford to just replace everything.








Will work on cleaning the aux air valve and test again.


----------



## WaterWheels (Aug 14, 2005)

*Re: CIS-E oxygen sensor testing (Scott555)*

50mA at cold start seems to be to little, could be the CTS, but the values you indicate seem OK. Could be wrong, but I seem to recall the cold start should be more in the 65mA or more? In any case the engine is set too lean based on the rest of your readings. That 9.5 for the first 15 seconds after hot start is the ECU sending a fixed mA signal until the O2 sensor is warm enough to read correctly. The same should happen if you disconnect the O2 sensor and check the mA reading at idle. Book says 10mA but they don't all read exactly 10. 
I would turn the mixture screw in a halfl turn and see what readings you get then. One half turn may be too much or to little, but it should at least make the readings change and get you in the right direction.


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (WaterWheels)*

Thanks for the info - 
The value "> 50 mA" was to indicate that it was well above 50 at start, but by the time I got from the key to the workbench to grab my notebook and start writing stuff down it had crept down from above 50. That 65 mA or more value you cite sounds about right.
I'm leery to fool with the mixture until I've ruled out any faulty components, but I guess it can't hurt to try it. \famous last words\


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

Don't go tampering with the mixture just yet.
Your set mixture is too lean for your conditions. This is most likely the result of vacuum leaks you need to find, vs the mixture actually needing enrichening.
The most common point of failure for the foxes is the bellows in the rubber boot. It'll probably look cracked all over, and when you go to flex it, it'll show rips and tears.
These boots are real hard to source. I found a good one from the local junkyard. Some people have gotten a fox2 rubber piece along with a traditional vw cis piece with some sort of pvc straight tube connecting the two.
Of course, you could have other vacuum leaks as well, so check everything out. Watching the dpr current as you monkey around with the vacuum hoses helps a lot.
The initial warm start problem is because the o2 sensor has not come online yet, but the CTS is reporting warm conditions, so the ecu is sending nominal 10ma through the dpr (same as when you unplugged the o2).
So it's fairly safe to say you probably can keep the o2s and cts longer and just find your leaks.
Once you've done all you can do, you can try dialing the mixture if you wanted (longitudinal's power tuning guide etc).


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

Ok, will revert to searching for vacuum leaks. However, I've spent nearly an entire can of carb cleaner so far looking for them, and thought I had them all rooted out. Most of the vacuum tubing has been replaced, and I did replace the intake boot with a salvage one that appeared okay, (no cracks.) I replaced the injector o-rings as well. 
Wonder where I'm missing something?


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

Aux air valve; removed, cleaned, checked by hooking up to 12 volt source and watching it close. When closed, very difficult to blow through it. Was pretty sure that was a red herring as I've checked and re-checked the aux air valve on numerous occasions.
Vacuum leaks; Can't imagine that's my problem. I've traced every hose on this ephing car upwards and downwards, soaked them with gumout and noticed no change in RPM or DPR current. As noted, I replaced the intake boot. I confirmed there are no leaks or tears. Even gave it a once-over with armor-all and a q-tip to help keep it from drying out. 
Again - what am I missing?


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

Sorry on my phone. You said you changed the fuel filter? There's also a little mesh screen at the fuel inlet to the distributor. Beyond that requires an expensive fuel pressure gauge so just play with the mixture at this point


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

On your phone? Unacceptable!! </stewie griffen>
Yep, fuel filter is about a month old. Fuel inlet filter has already been extracted and done away with. 
I have a pressure gauge from JCWhitney - I made the salesperson on the JCW chat swear up and down it was the appropriate kit to test CIS-E. Of course it's some bogue BS. Maybe 3 or 4 trips to the hardware store and I can make it work. Once I get some pressure numbers I'll post 'em.
Thanks again for the feedback and advice.


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

just give the mixture a tweaking and go from there. was the tamper plug ever drilled out?


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

Tamper plug was in a weird state - hadn't seen one that looked like this before. It was there, but there was a thick glob of caulk or something pasted over the top of it. Wondering if it ever got removed and re-placed.
Anyway, yeah - drilled it, yanked it, and tweaked the mix to a DPR current of about 13 mA. I know that's still a bit lean, but thought I'd make a small adjustment and see how it drives for a day while I shuttle back and forth to the hardware store for the bits and bobs to make my half-assed JCW pressure tester workable.


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (Scott555)*

If it wasn't for my parts car out behind the shed I'd have been SOL trying to hook up this POS pressure tester. Looted some banjo fittings and got some fresh hose clamps and it held up. The gauge leaked a bit at first, but all my rig job held up sweet.
Result - 5.5 bar system pressure, 5.2 differential pressure. Seems to fall exactly within Bentley-recommended operating parameters. 
BTW - the Bentley recommends hooking up the DPR harness and watching DPR current, but it doesn't say what to look for, or why. On top of that, the test procedure doesn't say to turn on the ignition, which is necessary to get current at the DPR anyway. I don't get it.
Still no answer to my performance question.


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

What performance issue?
Hesitation after hot start is because of hot cts reading before o2 sensor comes online resulting in ecu running 10ma through dpr, which is too lean.
Low idle on cold start could be either lean or AAR that doesn't open wide enough. You said you took it off and sprayed it clean. If you got a small screwdriver or something to stick in there and kind of pry at it, you might be able to free it from any further sludge. I've gone through 4 different junkyard AAR's before I found one that was acceptable.
Low power in 2-3k range should be fixed with a proper mixture adjustment. How does it run beyond 3k? If you never rev it past 3k, it might be an especially good idea to do a seafoam treatment of the intake.


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

Hesitation on hot start due to lean mixture - makes sense
Low idle on cold start - I don't doubt the AAR isn't opening wide enough. I'll fool with it and see if I can get it to open wider. I was more concerned that it wasn't closing completely and that might have been the source of my lean air. 
Seafoam - never heard of it, but now that I searched it looks like a common remedy.
Cheers.


----------



## ziddey (Apr 16, 2006)

*Re: CIS-E oxygen sensor testing (Scott555)*

AAR not closing will NOT cause a lean condition. It just allows air to bypass the throttle plate. The air is metered. It will just cause an elevated idle when warm.


----------



## Scott555 (May 10, 2007)

*Re: CIS-E oxygen sensor testing (ziddey)*

Okay, got it. 
Well, I enriched my mixture to within specs. Runs a little rougher now, and throttle response seems weaker. Still struggles between 2 and 3k. Getting on the expressway isn't any more fun that it was a week ago.
I'm questioning my judgement regarding the spray pattern on the injectors. They *seemed* fine when I did a quick check, but honestly; I don't have much experience in that area. My conclusions are likely flawed. Guess my only option there is to buy new ones and then take a look. More $ I don't have.
This engine has 210k miles on it. Last time I checked the compression was at 153k. Maybe the engine's just plain ol' worn out?
Anyway, seems like I've gone over every last item. Even at slave wages, I probably could have paid to have this fixed with all the time I've spent screwing around.


----------



## WaterWheels (Aug 14, 2005)

Sitting where I am and you being where you are, "runs a little rougher", is a hard thing to determine just what you mean. The fact that you can adjust the mixture, the mA reading anyway, to where it should be is a good sign. Yo don't say if it holds there or starts to wander again, but I think you would have added that if it did. And yes, the plug had to have been tampered with if it was sealed over with something.
210k is a few miles, but I have seen engine with much more still run fine. Have you looked into the ignition at all? If the mixture can be adjusted at idle to where it should be you problems could be in the ignition system. What was the compression when you tested back at 153k, low or good? If it was low then the wear could have gotten worse. At 210k you for sure have some worn items in the cylinder head also, valve guides, valves, followers, camshaft and every tiny bit could add up to rough running also.
If it is not running like a mix-master, I would check the current engine compression and check the ignition over good (timing set right?). If the injectors were so bad in the spray department I doubt the mixture would adjust very easy to being correct.


----------



## Scott555 (May 10, 2007)

*Re: (WaterWheels)*

Sorry - "runs a little rougher" is subjective prattle; and was just my mild frustration speaking.
Today's hour-long commute seems to have smoothed things out a bit. I put a good half-can of seafoam through the intake. I'm wondering if that took a few miles to work all the way through and do its magic.
So currently - Throttle response isn't great, but isn't terrible. Power is moderately better than before the mixture change and cleaning.
Compression at 153k was good. I do have the typically noisy valvetrain for the miles. I don't doubt I have cylinder head issues. Not sure I'll be investing a lot of time and effort in the mechanicals here; likely just nurse it along while I search for an ABA or something to swap in.
As for ignition; timing is spot on, and there's a new set of plugs in there. I am due for a cap, rotor, and wires though; pending $.


----------

