16785 - EGR System: Insufficient Flow

Jimbo70

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I thought the timing issue was going to be the stickier wicket, but it isn't. I cannot solve the CEL I'm getting for a 16785 - EGR System: Insufficient Flow. Now before you send me to the Wiki or the FAQ, I've been there and:

- Replaced the EGR last year because it was plugged solid.
- Had the rest of the intake cleaned, again because it was plugged.
- Recalibrated the EGR in adaptation per the instructions in the FAQ.
- Replaced the MAF... twice. First time with a Pierburg, then after reading the FAQ with a Bosch unit.
- Reset the EGR calibration to the factory setting thinking that was causing the insufficient flow issue.
- Inspected all the vacuum hoses.

All I have to show for this is a (probably) good spare MAF, a clean EGR and a CEL.

What would my next step be?

Jim
 

DanG144

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Jimbo,
Take a log of the MAF data, from an idle to 4000 rpm or so, going through the gears at full throttle.
look for a basic setting button for a MAF data block, and use the basic setting test to grab another log.
Graph your logs, and see if that will help make a call.
Dan
 

Jimbo70

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DanG144 said:
Jimbo,
Take a log of the MAF data, from an idle to 4000 rpm or so, going through the gears at full throttle.
look for a basic setting button for a MAF data block, and use the basic setting test to grab another log.
Graph your logs, and see if that will help make a call.
Dan
Will do.
 

Jimbo70

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Thanks to Office 2007, making charts isn't as intuitive as it used to be. That being said, here is my MAF chart:


After listening to the car while going through the gears, it sounded to me like it was slow to build boost, then slow to let the boost go on decel. Here is a chart of the manifold pressure and MAF versus atmospheric pressure:


This second boost chart is a sample of a larger log. With the exception of 160.06 seconds, where I shifted, I was at full throttle the entire log. Seems to me something isn't kosher here.

Jim
 

DanG144

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Jim,
That does look a bit suspicious.
The 400 actual MAF when you have 250 specified is about what you would get if your EGR valve was closed. What was your N18 duty cycle doing at that time? It was logged also, wasn't it? From your earlier posts, it seemed you were expecting to have the EGR opening?
It might be worth making a graph of MAP specified vs actual as well. I don't see why your MAP would die off at higher RPM, then spike upwards again.

Did you find the basic setting test for the EGR/MAF? A log of that could help, too.

Dan
 

Jimbo70

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I have all that information... on my thumb drive at work where I have Office 2003 that is so much easier to graph with. I'll post those tomorrow. That being said I wouldn't expect a relatively new (and really clean) EGR to stick. It moves when a vacuum pump is used.

Jim
 

DanG144

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and the MAP data? specified and actual on the same profile? Or a full throttle run from idle, through the gears to as fast you care to go, taking RPM up to 4k or so.
 

Jimbo70

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I hope I'm getting this right. These two charts come from the same 12 second full throttle pull. You will see one dip at the very beginning from a shift.

Chart 1 is the EGR and MAF


Chart 2 is the MAF again but with atmospheric pressure and boost.


What my untrained eye is seeing is that my boost is all over the place under full throttle. Wouldn't that normally be a steady curve up to the point where of maximum allowable boost? Could it be an issue with the N75 valve?
 

DanG144

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N75 or turbine vane controls.

But we really should see SPECIFIED MAP as well as ACTUAL MAP.

Please look for another group that has RPM, specified MAP, actual MAP and N75 duty cycle.

Any luck on basic settings test for the EGR? There should be one for the N75/turbine charge pressure control, too.

Dan
 

Jimbo70

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My tentative diagnosis is a bad N75 valve, and without posting more charts here is why:

- I hooked up the VAG-COMM to my '03 Golf TDI and started looking at basic settings at idle. While idling the EGR cycles on and off. As this happens you can watch the corresponding mg/R number go up and down as the EGR cycles (I thought it was the MAF number, but I don't have the data in front of me). You can also hear a "click" while the engine is idling that corresponds with the indicator in the basic settings changing from EGR On to EGR Off and back.

- With my wife's car, however, although the indicator in the basic settings says that the EGR is turning on and off, the corresponding mg/R number does not change, nor is there the clicking noise as the valve cycles. I traced and inspected the vacuum lines going from the the EGR to the N75 and from the N75 to wherever those lines go, and they appear to be in good shape.

Before I sink another $70 or so into a piece I think I need, can anyone think of anything else that would cause what I am admittedly poorly describing?

Thanks,
Jim
 

DanG144

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Jim, are you meaning the N-18 solenoid for the EGR?
The N75 drives the turbo controls.

Your MAF readings at low power and idle are what I would expect with the N-18 not working, and the EGR stuck closed, so that does jive.

A bad N18 is supported by the test information you gave.

Find the N18 and the N75, and verify the N-18 solenoid is electrically plugged in. It would be embarrasing if it had just come unplugged.

Dan
 

Jimbo70

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Did I say N75? Of course I meant N18 :eek:

I will take a closer look at the connection. When I checked the vacuum lines it wasn't hanging off or anything like that.
 

Jimbo70

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SUCCESS!!!

I replaced the N18 tonight, cleared the CEL and brought up the Basic Settings for the EGR. The number that corresponds with the EGR opening and closing now goes up and down when the EGR opens and closes. I'll know for sure tomorrow when my wife drives to work tomorrow but for the first time I'm confident I've solved the problem.

Now for your Top Gear "Top Tip of the Day". If you get an EGR-related CEL, after you check your EGR but before spending $100 or more on a new MAF, test your N18.

Dan, thanks again for your assistance on this.
 

eRock

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ok i get the same intermittent code i check the duty cycle of the egr and it stays at 83 % almost all the time idle or cruise what else to check on the n75 or n18 what meas block is it and what duty should the egr be? the egr also needs to be cleaned and im getting some serious blow by oil in the intercooler pipe
 

PDJetta

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These are what you should check:

EGR valve, is it working? Apply vacuum to the diaphragm. Does it open?

The EGR cooler tubes could be clogged with oily soot, preventing EGR flow.

The intake manifold could be clogged.

The vacuum to the EGR valve could be non-existant.

--Nate
 

NarfBLAST

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eRock said:
ok i get the same intermittent code i check the duty cycle of the egr and it stays at 83 % almost all the time idle or cruise what else to check on the n75 or n18 what meas block is it and what duty should the egr be? the egr also needs to be cleaned and im getting some serious blow by oil in the intercooler pipe
It could just be that your MAF sensor is reading too low all the time.
 

djturbulence

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16785 - EGR System Insufficient Flow (lets start at the beginning)

I have the same code but am at the beginning of working on the problem and need some beginner advice.

here's the short story:

-2004 BEW Jetta Wagon (92K) was running great about a month ago with no codes
-timing belt was replaced with 100K kit by a well respected guru who also found the intake to be clean
-same day, the car was chipped to RC1+ by Jeff
-on the drive from Oakland to Santa Cruz the MIL came on
-car continues to run great
-with help of club member, we ran fault codes and found 16785 (P0401-000)
-turned off the MIL but it came back on 20 mins later

I'm not sure if the TB job or chip have anything to do with the MIL, but thought i should mention it. I assume that Jeff tinkered with the EGR during the process.

I have read every thread that I could find on the topic, looked at the Ross Tech wiki, but couldn't find an FAQ as stated in the original post. I would really appreciate it if someone could start me off at the beginning with the first things to check, any instructions as to how to check them, and so on. I do not have a Bentley and its a little tough to get VCDS help, so i would like to do the easier things first before trying to clear the code again.

Thanks for any help!
 

DanG144

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Take a good look at the EGR electrical connection. Is it completely plugged in? Solid?

So I guess you left your EGR working, and told Jeff that you needed/wanted it to function when he was designing your tune?

The code means you are getting not enough flow through your EGR; your MAF air flow is remaining too high - when it should be dropping as the EGR opens.

The valve could have gotten stuck from small piece of crud getting in the wrong spot during the inspection.

So you might pull the EGR out of the manifold and clean it carefully. Then put it back in. Take great care not to allow crud to fall into the intake. Maybe onlly clean with a vacuum tip, when working in the intake?

The best way to troubleshoot this is with the VCDS. Go to basic settings in block 3 and do the test. You should see your EGR demand go up and down, and your MAF flow oscillate up and down.

You might also check your MAF connection, and make sure it is on good, too.
 

djturbulence

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thanks Dan.

I will check the EGR. I actually didn't talk with Jeff about the EGR, so I'm not sure what he did or didn't do with it.

the MAF is solid and the engine doesn't exhibit any lack of power.

Is there a how-to for locating and cleaning the EGR? it was also suggested that a vacuum or other line may not have been reconnected during the TB job, so i'm going to try to check those connections.
 

DanG144

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[/IMG]

The EGR is sort of in the top center of the photo. You can see the electrical connector on the top left portion of it. There are 3 allen socket head bolts that hold it on the manifold. (either 5 or 6 mm). You can see two of them in this photo, one near the top, one peeking out from the lower left of the EGR, and the third one is hidden by the EGR on the lower left.

To clean it, simply undo the three bolts, carefully slide it out, then clean it, and vacuum the hole it came out of. There is no need to get dynamic getting all of the black nasty goo out of the intake manifold; just vacuum up any loose chunks.

But do carefully and fully clean the EGR valve that you removed. Brake cleaner, or diesel fuel is good to clean it with.

Wear old clothes, and gloves. Expect to get filthy.

Dan
 

djturbulence

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So, I checked the EGR. You were right, what a mess! Gave it a thorough clean and am curious to see if the CEL will go off now.
 

djturbulence

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Unfortunately, the CEL came back on. And, has now been on for two years. I now have to get the car smogged in CA, so I need to sort this out. I'm wondering two things.

One, is it likely that Jeff may have turned off the EGR as part of the RC+1. In that case, can I just turn it back on via Vag Com which might resolve the code and also show "readiness" to the computer at the smog station? How might that affect the tune, or can I just turn it back off after the smog? Second, with the smog issue aside, any suggestions on the next thing to try to resolve the original code issue?
 

DanG144

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Did you ever do the basic settings 003 test? That specifically tests the EGR, and will test it no matter what Jeff did in the operational portion of the tune. Even on off-road tunes this test still works.

If this test works, then I think you may need to get an updated tune from Jeff. If it does not work, then you have system problems to fix. Either a bad EGR valve, or plugged cooler, perhaps.
 
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