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Discussion Starter #1
Hey there.
I have a 2004 Golf TDI with BEW engine that has the following history:
1. Converted from auto to manual gearbox four years ago (it's how I bought it)
2. PD150 Intake
3. Replacement Borg-Warner KV39a turbo
4. Malone Stage 1 tune w/ EGR DELETE

It's ran great for whole time I've had it until this winter. Whenever it rains, the turbo boost disappears. If the weather warms up the boost comes back. Ugh.

I've been doing my best to diagnose what's what but it's a bit out of my league. I need help.

1. To start, I found that the turbo vacuum line pulled no vacuum according to my gauge. Eventually I disconnected N18 and N213 EGR solendoids and now have a much simplified vacuum system consisting of only the vacuum from the pump, the vacuum reservoir, and then feeds through the check valve to the N75 solenoid and the turbo (or my vacuum gauge). That at least for testing purposes gets me 20lbs of vacuum at the actuator or gauge. When I run the N75 test from within VCDS it cycles correctly, verified when using my vacuum gauge connected instead of the actuator. The test pulls and holds vacuum, releases it, pulls it again, repeats. Great. N75 seems fine as the does the simplified vacuum system.

2. Test drive showed no boost.

3. If I pull the electrical connector from the turbo actuator I do get some boost, but not full boost.

4. I ran the MAF test in VCDS based on the FAQ from this site. Also ran a test to see what the boost pressure looks like. They're both weird and I don't know how to interpret them. Here are the screenshots:

8514


8515


The value of 2193mbar for boost pressure does not deviate when I blip the throttle. Somehow I doubt that a value of zero for the MAF (actual) field is what I want.

Where to go from here?

Thanks!
 

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Discussion Starter #3
Have you tried removing the connector from your MAF and see how it runs?
Hi. I did not but I can do it right now. Reading through the FAQ it said that on TDI cars disconnecting the MAF may not make a noticeable difference in how it drives. But it won't hurt to try. Stay tuned.
 

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Discussion Starter #4
Have you tried removing the connector from your MAF and see how it runs?
Okay. Just drove around neighborhood up and down hills and along level roads. No change. No boost. It doesn't drive any different whether or not the MAF is connected.
 

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Hi r3dplanet! After reading all of your stuff here I have determined that you are more knowledgeable than me about TDI BEW cars. I have an ‘04 Jetta TDI BEW and I currently have a minor boost issue in 5th gear going up steep mountain highways. I’m pretty sure that short pipe that connects between the pancake pipe and the intercooler isn’t sealing properly on mine causing a temporary loss of boost on the high end under heavy load. Have you checked all of your piping connections going from the turbo to intercooler to intake manifold? Maybe one of those connections isn’t sealed causing no boost?

You said you did the Malone Tune with EGR delete? Did you actually remove the EGR and piping and block off those holes, or is the EGR still there and working? If it is still there, check those 2 flex pipes (I think I recall those thin metal pipes are called flex pipes) for cracks or holes. My lower flex pipe broke in half causing no boost, limp mode, and exhaust smell when idling. I have completely removed the EGR and EGR cooler since then, and still need to do a Tune and EGR Delete.

Just a couple thoughts since it looks like all the other smart guys are out of ideas.
 

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Discussion Starter #6
Hi r3dplanet! After reading all of your stuff here I have determined that you are more knowledgeable than me about TDI BEW cars. I have an ‘04 Jetta TDI BEW and I currently have a minor boost issue in 5th gear going up steep mountain highways. I’m pretty sure that short pipe that connects between the pancake pipe and the intercooler isn’t sealing properly on mine causing a temporary loss of boost on the high end under heavy load. Have you checked all of your piping connections going from the turbo to intercooler to intake manifold? Maybe one of those connections isn’t sealed causing no boost?

You said you did the Malone Tune with EGR delete? Did you actually remove the EGR and piping and block off those holes, or is the EGR still there and working? If it is still there, check those 2 flex pipes (I think I recall those thin metal pipes are called flex pipes) for cracks or holes. My lower flex pipe broke in half causing no boost, limp mode, and exhaust smell when idling. I have completely removed the EGR and EGR cooler since then, and still need to do a Tune and EGR Delete.

Just a couple thoughts since it looks like all the other smart guys are out of ideas.
Hi there.

I would certainly not describe myself as knowledgeable about any of this. "Bumbling" is a better word. I can get readings from VCDS but don't know how to interpret them. I find modern auto electronics a total PITA. For reference, my next oldest car is from 1971.

Your questions are good ones and I'll answer them here: the intercooler pipes and whatnot are all secure. I have a Dieselgeek bracket that holds the intercooler pipe to the ASV, the rest of the pipes are secure as well. The EGR bits and cooler are completely removed and replaced with a "race pipe." I lost boost once before and like you say it was a loose hose at the intercooler. That was the first thing I checked. I'm still at loss in general but especially because I lose boost when it rains, and then it comes back when the weather dries up. That makes zero sense to me.

Something I failed to mention is that when I loose boost I get a CEL code P0652. When I look that up all I get are references to Ross-Tech but nothing is explained. Apparently this is a generic wiring error entitled "Sensor Reference Voltage B: Too Low" but it's super vague. I replaced the MAP sensor because I read elsewhere that a bad MAP sensor will cause this error but it didn't fix the problem.

I tried to get access to the Ross-Tech forums but apparently I'm a terrible person because I didn't go through the absurd four-step process of getting my account verified. I asked for help and handed over my name and serial number to the admin and got a snarky answer several months later. Screw that.

Today is the first day of sunshine in three weeks, so tomorrow I'll carve out some time to trace wires in the harness from the MAF sensor to the ECU. I have no idea if the MAF is even involved and I can't get any answers. I posted a similar thread months ago on TDI Club and VW Vortex but got no responses. Finally I took the car to a VW mechanic but the car dried out in the five weeks he had it before looking it, so it ran fine for him. It seems like a lot of the brainy Mk4 guys have moved on. But that's me - always late to the party.

Thanks for chiming in.
 

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I’m wondering if a connector such as the plug to the turbo is getting wet and causing an electrical issue. Maybe try putting some dielectric grease on the plug? I was ATV’ing with a friend years ago up a wide but shallow creek and every time we crossed the water and splashed, his ATV would cut out and die. He would sit there cursing for a few minutes while trying to restart the machine. Eventually he figured out that a plug was getting wet and cutting the power. He put some dielectric grease on that plug and had no issues crossing the water after that.

Or maybe you have an exposed wire that is getting wet instead of the plug.

I would rule out the MAF. It seems like a bad MAF can be the culprit for pretty much everything, but I have never read a diagnosis where the MAF actually was the issue. It’s got to be an electrical issue.

Maybe the ABS wire or connector is getting wet and telling the computer to not give you full power because it’s wet and slippery. I notice my car won’t give my it’s normal acceleration output when it senses it’s slippery out.
 

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Discussion Starter #9
At this age I would guess wire. But I see lots of detail for that code, including special notes for the BEW.
Right. I've seen that page but I don't understand this part:

"Check Atmospheric Pressure (MVB 010.2) and Intake Manifold Pressure Sensor (MVB 010.3). Compare both Values with Engine OFF, the Tolerance should be +/- 50 mbar."

Great, but how do I do that? I don't understand VCDS well enough to know where to do test it.
 

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Discussion Starter #10
You actually have it in the first screen shot above where you started the discussion. MVB is Measuring Block or "Group" and you have 010 in that box. Across from that the second and third item, (10.2 and 10.3) correspond to "atmospheric pressure" and "Intake Manifold Pressure Sensor" which I'm pretty sure is "Boost Pressure." In any case, the numbering system in VCDS is Group is before the decimal, and item in the group (horizontal across the page for that group) come after the decimal. So in your example, you would be comparing 1009.8 with 2193 (if your car was off when you measured). This example would fail their test.

To verify if "Intake Manifold Pressure Sensor" = "Boost Pressure", after you open the Engine Controller, click on Adv. Measuring Values. A list will appear to the right. The numbers on the left edge are the group/item combinations, then their descriptions. Scroll through until you see the values you want and check all you want, and they will appear in the larger box with their measured values. Hope all that makes sense.

What do the notes say to do if this fails?

The item to find next is "Boost Pressure - Specified" and compare that to - Actual.
THANK YOU! I had no idea how the annotation worked and I didn't find anything explaining how that worked. Mystery solved at last.

Here the latest screenshots armed with the new data gathering. As you can see both with the engine not running and with the engine at idle the values don't change. Since the MAP sensor is brand new, I think it's reasonable that either I have (less likely) two bad MAP sensors in a row or (more likely) it's the wiring from the sensor to the ECU or wherever. Correct?

Progress at last!

8519



8520
 

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Discussion Starter #11
Electrical issues are the worst. VW makes it the absolute worst with the world's worst wiring diagrams. Mitchell 1 DIY (or the library version) makes it bearable, and it may help you to map out common grounds and trace the paths you need to check.
Right? I'm in the Bentley manual right now and my eyes feel like they're bleeding. I'm able to navigate the manual to a degree. I finally found a reference for the G71 MAP sensor in the 2001 ALH diagram, but it isn't mentioned again after that for any year or model. The inference I suppose is that it wasn't changed in later models like my 2004/2005 but that isn't clearly stated. The diagram No. 65/5 shows the G71 MAP sensor as the G72 IAT sensor at the same time. Not confusing at all. Ugh.

I'll take your advice and see if I can map a common ground for N75, maybe N18, the MAP sensor, and the turbo actuator sensor. That makes a lot of sense. Before starting any of this I did remove the battery and cleaned/lubed all of those clusters of ground connections and the one on the engine block. I see the manual shows two others ground points. I'll check those also.

What a damn nuisance.
 

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Discussion Starter #12
Oh wait. At first I didn't catch that the MAP sensor is actually the "Charge Air Pressure Sensor" in the BEW models. Helpful tip.
 

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Hi. Yes, the descriptor as far as I can tell for the CAP sensor is G31. Does that mean I've been testing in VCDS wrong the whole time?

The tests are in, sort of. Continuity between the charge air pressure sensor (CAP sensor I guess) is good along all four pins of the connector and their corresponding pins on the ECU. I cleaned the connectors with electrical cleaner, dried with compressed air, re-attached. Great. I pulled the three ground wires from the threaded terminal under the cowl, cleaned them, and reinstalled them with carbon conductive grease. While I was out there testing, for kicks I ran a turbo actuator test with my Mityvac and it works correctly as it begins to draw the actuator rod at about 3psi and stops at about 19psi. Right on the money.

So, no obvious wiring fault that I can find. I did find a bucket full of wet leaves in the cowl though. That tells me two things. First, it was gross and home to millipedes and way too wet in there. Second, the mechanic I brought the car to is a lying sack of s#it because he said he tested and cleaned the ECU connector.

I'll get the bits put back together and see if it brings back the boost but of course I'm doubtful. I'll report back with that info.
 

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Discussion Starter #14
Peeps,

I'm reporting back in to say that I've driven 400 miles since yesterday with ALL THE BOOST. But there's no way of knowing why just yet because the weather has been hot and dry for a week. So maybe it dried out? I wonder because I had a perfectly consistent lack of boost until immediately after the troubleshooting session.

The morning after checking all the wires and cleaning out this and that it cranked right up with a reassuring whistle. I cleared the CEL and it hasn't returned. Until it rains again I won't know if it's "fixed" or not. Right now it's just a blast to drive the Golf again for the first time in six months.

It could very well be that maybe the CAP sensor wiring is dodgy, although it did check out fine and visually there's no corrosion or junk on the connector or wires. The setup is not satisfying. No Chekhov gun in this story.

I worry that there's a kink or something maybe. Probably not. Why would wet leaves and bugs cause so much trouble? How do I keep them out? Is anything actually rectified? These are the questions pinballing around my head.

The new plan then is to let it be for now and I'll report back if the problem re-emerges after some wet weather. In the meantime I'll renew my plates and start another thread on resolving the lack of cruise control.

Mostly I came back to thank you all for the excellent guidance and ideas. I'm so lost with modern auto gadgetry. So at least the troubleshooting became doable. That's worth it by itself.

Cheers to all!
 
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