# 16V CIS-E Motronic - DPR current inconsistencies and questions...



## Legoguy (Sep 18, 2002)

I've been having to do a lot of research to figure out my current issue, but one thing that bugs me is the inconsistencies in the description of what the DPR current actually means in terms of a richer or leaner mixture.

90% of user-contributed material (for example: http://gtitoolbox.com/handbook/fuelmix.html) states that a higher current means *leaner* mixture. I can understand this, and see how it could work in theory... however, The Bentley, on the other hand, states that during cold acceleration _*enrichment*_, the current increases, and during deceleration _fuel shutoff,_ current goes _negative_. I've got this issue where no matter what I do, the DPR current is negative, which one source says I'm running super duper rich, but another source says I could potentially be running very lean (and this is even with the OXS disconnected!) And yes, I do have the test leads hooked up right - the DPR gives a current of ~100ma with ignition on before starting the engine, as appropriate. Through my own tests, I can confirm that cold acceleration and high load situations cause the current of the DPR to increase to a positive value, indicating a richer mixture.. but yet according to some, that means lean... :banghead:

Clarification is needed.


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## WaterWheels (Aug 14, 2005)

First to what may be confusion or wrong poop about the mA reading at the differential pressure valve. You have to look at it in two different perspectives, idle and anything off idle. Anything off idle it is true that positive readings are rich and negative lean. So as the numbers increase so does the fuel mixture and as they decrease it’s getting leaner. You can say negative readings are cutting off fuel but fuel is still getting through until some point when it really is cut off. At idle though you have to think of it in a reverse kind of way. The computer reads the signal from the O2 sensor and is trying to correct it back to the ideal mixture. So if the O2 sensor says the mixture is a tad rich then it leans things out until it starts reading lean and goes the other way, over and over very fast. That’s why at idle, and only at idle, as you turn the mixture towards rich, to the right, the mA readings go down. You are making the mixture richer but the computer is trying to compensate. It knows you are at closed throttle by the installed switch or potentiometer.

As for your problem with the reading you are getting, I can’t help a lot right now. The first thing I thought of was the wires being connected backwards, but you said they’re not. I doubt that it is set way too lean, but have you tried to adjust the mixture screw to bring it back? You don’t state just what the reading is except for when you first turn the key on when cold (assume it is cold). You also said something about the O2 sensor being disconnected, is this always or just while checking things? I am not sure as this is just off the top of my head, but with the Motronic system, with no O2 sensor input the default is I believe 0mA. So right now it is real hard to say just what could be your problem.

Sent from my computer at work via the keyboard


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## Legoguy (Sep 18, 2002)

Well, to clarify my situation further:
1.8L 16V, with CIS-E Motronic swapped in by previous owner prior to the swap into my Cabriolet.
This raises concerns about whether the 1.8L engine differs greatly from the 2.0 that Motronic would usually power in terms of fuel amounts and other variables, notably the knock sensor. I have the second knock sensor mounted to the back side of the block; seems to work well enough so far, but I am dealing with quite a few issues.
The most upsetting is that my exhaust manifold is cracked. As was explained in another thread this should not make a _huge_ difference in driveability when the engine is cold and the system hasn't gone into closed loop yet. Of course it will make the O2 sensor think the mixture is lean due to some exhaust gasses escaping (or will it make it think it's rich because of outside air entering? My logical guess is that pressure from the exhaust will mostly prevent air from entering the exhaust, only escaping). Regardless, I'm trying to find a replacement manifold (A2/Passat 16V, if anyone has one in good shape, let me know...). 
Quite a while ago I swapped the whole air metering assembly with one from another Motronic passat, in an attempt to remedy some other issues (poor power) and for a while it seemed to do the trick. The mixture tamper plug was and still is in place, I plan to pull it out tonight. The problem is that I'm experiencing this horrible hesitation and lack of power when cold _and_ warm, but as I understand it, I can only use the DPR as an adjustment reference while the engine is warm and there is no leaking exhaust manifold or other vacuum leaks for that matter. So it sounds like if I fiddle around too much right now with the manifold the way it is I might actually be just poking around in the dark. Must get that manifold replaced!

DPR values that I see:
Hard accelerating: ~20ma
Cold start: ~70ma gradually dropping in ~5ma increments to 0, then a sharp drop to ~-10
Deceleration: Sharp drop to negative
Acceleration after deceleration: momentary spike up to ~25ma
Running, with O2 plugged in: ~-10ma
I'm not 100% sure of these values, I've been using an anolog meter that doesn't show an actual reading for negative, just the needle goes the other way; I did use my digital for a while which is where I get this reading from but needed it elsewhere thus I haven't been driving with it much, I will reconnect it later this evening and take another nice test drive to get some solid numbers.


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## Legoguy (Sep 18, 2002)

Did some testing this morning with my digital multimeter and the O2 sensor plugged in:
When started cold, DPR starts at 70ma, drops over the course of 5 minutes to about -14ma, at which point the engine stumbles at idle and on acceleration. As the car warms up, the stumble goes away from idling, but comes back on acceleration, until the DPR adjusts its value to around -8 or so. Eventually when the car is completely warmed up, the DPR sits at exactly -16.1 ma on idle and for about half a second while accelerating, until it rises to -6 or so. While driving on the highway it sits between -6 and -9 ma, and when at WOT, it rises to 0.2. Sounds like I need to fiddle with the mixture but I think I will wait for that until I find a sound manifold.

-16.1 seems to be the maximum negative adjustment the ECU will make before throwing an "outside adjustment range" code. It drops to -74ma during deceleration fuel cutoff, which the ECU must treat as a special case.


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## ziddey (Apr 16, 2006)

Especially with cis motronic, you can look at the dpr as a way of fine tuning / compensating for a more desired mixture. When speaking of DPR current and associated rich/lean, it's relative to the set idle mixture. CIS motronic is supposed to have a running dpr current around 0mA, so if the system fails, you should still be in good shape to drive as long as the mixture is set properly.

If you see a high positive DPR, it means the ECU is calling for extra fuel to achieve stoichiometry, and thus the set idle mixture is "lean". Vacuum leaks would cause such a condition-- unmetered air is being compensated for by increasing DPR current.

But in your case, you're seeing negative DPR current when warmed up, suggesting the set mixture is overrich and the ECU is compensating. That's pretty rare to see with an untampered mixture setting. Do you see DPR oscillations as well that would indicate it's cycling around stoichiometry in closed loop?

Have you tested the resistance of the coolant temperature sensor at various temperatures? I'm not sure about cis motronic, but I'm imagining that with a hot engine that's not started, you should see 0mA?



> DPR values that I see:
> Hard accelerating: ~20ma
> Cold start: ~70ma gradually dropping in ~5ma increments to 0, then a sharp drop to ~-10
> Deceleration: Sharp drop to negative
> ...


Hard accelerating, you're activating the WOT switch?
Cold start, the steady dropping suggests the CTS is in working order. How long does it take before it goes into closed loop though? I understand it is winter time.
Deceleration sounds good. You're tripping the idle switch -- fuel cutoff

Running with o2 plugged in, again is it oscillating? And without it plugged in on a warm engine, you're at a fixed 0mA? Does it idle better at -10ma or 0ma?


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## idubse7en (Aug 19, 2012)

*DPR*

What is "DPR"???


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## nbvwfan (Aug 15, 2007)

idubse7en said:


> What is "DPR"???


I hope you are joking.
*D*ifferential *P*ressure *R*egulator.

To the OP, thanks for the really good content, it seems as though you are trying to figure it out, instead of looking for the fast secret tweak.
I'll chime in a few things that come to mind.
DPR current goes both ways especially on Motronic.
As I understand it, the DPR's primary function is, WOT Fuel enrichment, Fuel cutout, and fine metering at idle and throttle tip in and O2/Vacuum signal degradation.
What you seem to describe indicates to me that oyur base mixture is off. Even if you still have the tamper proof plug in place, there are other ways to have the system out of sync.
My hunch is oyur control plunger stop depth. On CIS-E the magic number is 19mm, on 2.0 Motronic it is ~23mm, but you can dial it in by doing the following.
Remove the snake head
Set rest position (nickel thickness)
Center sensor plate
Validate down travel (backfire spring)
Measure pivot bearing depth at rest position
Prime pump and measure plunger protrusion, back out or screw in slot until this measurement is ~.35 less than the pivot bearing stop depth.
Put it all back together less snake head.
Prime the fuel pump a few times.
Gently lift senor plate until it makes contact with tip of control plunger (freeplay should be .25-.5mm)
Adjust plunger stop depth if need be
With this set, prime the pump once more; the sensor plate should reach just under the cone transition from vertical to first angular draft.
Re-install snake head and drive it around.
You'll probably have to adjust the IAS (idle air screw IIRC CCW)

Part of what you are troubleshooting may have to do with the cracked manifold. From my experience, an exhaust leak upstream of the O2 will cause a false lean signal (due to scavenging). This causes a false rich condition the ECU then tries to compensate. 

This is part of why I went with a WB (LC-1) and stopped chasing DPR adjustment. 100% of the time I can glance down and see what A/F my car is running, and being F/I it was the best investment I could make.
Hope this helps, sorry if it was TMI (too much information)


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## kwak (Apr 7, 2005)

idubse7en said:


> What is "DPR"???


CIS-E and CIS-E Motronic are both mechanical fuel injection. The "-E" part means there is Electronic mixture adjustment. The computer sends a signal to the fuel differential fuel pressure regulator (DPR) to increase or decrease the fuel pressure as needed.

Reading posts 1 and 2, both are getting confused in their use of terminology. Remember that thing with Einstein and relativity and frame of reference? It matters what part of the system you are referring to when you say rich or lean.

The mechanical mixture, which the Bentley calls "idle mixture" because it is set at idle, is the mechanical mixture used at all RPM's. If no electronic mixture correction is being applied this mechanical mixture can be lean, or good, or rich, and you will see this at the O2 sensor. Once you add the computer in (electronic mixture adjustment), if this mixture (measured at the O2 sensor) is different from what the computer wants it will tell the DPR to increase or decrease fuel until the mixture at the O2 sensor is what the computer wants.

So if the DPR value is below normal (for a given situation) this means the computer is reducing the amount of fuel because the mechanical mixture is too rich. And if the DPR value is above normal the computer is adding fuel because the mechanical mixture is too lean.


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## stija (Aug 20, 2011)

kwak said:


> The mechanical mixture, which the Bentley calls "idle mixture" because it is set at idle, is the mechanical mixture used at all RPM's. If no electronic mixture correction is being applied this mechanical mixture can be lean, or good, or rich, and you will see this at the O2 sensor. Once you add the computer in (electronic mixture adjustment), if this mixture (measured at the O2 sensor) is different from what the computer wants it will tell the DPR to increase or decrease fuel until the mixture at the O2 sensor is what the computer wants.
> 
> So if the DPR value is below normal (for a given situation) this means the computer is reducing the amount of fuel because the mechanical mixture is too rich. And if the DPR value is above normal the computer is adding fuel because the mechanical mixture is too lean.


Thank you for explaining it so simply, you seem to have the concept under control. 

What is the best way to increase the mechanical mixture, should one experience a higher than normal reading at the DPR after, for example, running on a heavily ported head with bigger valves and long duration and high lift cams, all of which increase air flow through the engine making the mechanical "factory-preset" mixture lean. Is there a simple adjustment to increase the mechanical mixture? Is that what the DPR mod is about? (involving taking apart the DPR and drilling though it to turn clockwise the 3mm screw by like 1/2-3/4 turns?)

You also mention that computer wants a specific mixture, or is factory-preset for one, or a range perhaps, but you failed to say what this is. Do you know what this preset mixture is, and how is it measured, in what units and range of normal operation?

And as i understand this, and correct me if i am wrong please, the mechanical mixture is constant at all rpms + "dynamic" mixture enriched through the "-E" reading the O2 sensor and sending a signal to DPR to "dynamically" enrich or lean out the mixture, right? So mech + dynamic pressure (adjusted constantly). My question is following, what happens at WOT? Does the -E just enrich a preset amount? And if so, do you know it is, or its value measured perhaps? 

I am asking these questions because i am trying to understand exactly how this works so i can build my own -E.....:laugh:

Thank you, and i hope you chime in and help us all understand what is really going on in there. So far, for example, i interpret above negative DPR readings on deceleration as rich mixture due to no actively open throttle and air suffocating the engine down....but maybe i am wrong.


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## stija (Aug 20, 2011)

I just reread the thread and i think that it depends on the frame of reference, or the context of what you are talking about, like the other poster said.

A high DPR reading indicated NOT a rich mixture, but a lean mixture at the O2 which is therefore electronically enriched at the DPR resulting in a high reading. High reading in this instance means the mixture is being enriched electronically through the DPR because it is lean, rather than the mixture being rich in the first place.

I hope that is right and that it makes sense.


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