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View Full Version : Boost Leak or DV Leak?



Nateness
11-13-2010, 12:44 PM
I recently tried out the log option with VAGcom and noticed some odd boost request/actual data.

Background info:
1. 2001 1.8TQM w/ 80k
2. Cone intake with Evolution Racewerks Turbo Inlet Pipe
3. Everything else stock (? that I can observe?)


Description of Issue:
1. Trending boost request/actual has shown that for the majority of the time, I am not making more than about 4 to 5 PSI (requested as 0). Note that I am trending this data for a full 30 minutes of driving around town/highway with occasional sprints when traffic is clear.

2. The boost log shows that there are times when the Boost Specified approaches 15 to 16 PSI (rarely, but maybe this is due to the casual driving around). Peak specified is recorded as 16.3 PSI.

3. The boost log also shows that my peak actual boost for the trip was 11.99 PSI (far below boost spec). I noticed a trend that whenever boost specified approached 16 PSI that the boost actual never acheived this value.

4. Peak air mass flow acheived: 151 g/s

5. I have noticed poor fuel economy lately, in the realm of 19 to 21 mpg. I have recently replaced spark plugs and the air filter is new. No CEL's. This could be from a lot of in-city driving or maybe driving around to hear the recently installed intake? Not sure.


Questions:
1. How can you tell if your car is chipped (or flashed in my case) versus a diode mod?

2. On other cars that I own, boost leaks are usually noticible around a consistent boost pressure. You generally hear a rushing air noise followed by a huge drop off in power. Do the above observations seem like a boost leak to you guys?

3. I have not experienced a leaky DV. Do the above described symptoms match?


Thoughts anyone?

walky_talky20
11-13-2010, 09:30 PM
If you could share some logs, that would be helpful. When logging boost, you want to log in a specific way. In general you want a "3rd gear pull". That is: cruise in 3rd gear at about 1500 rpms, start the log, floor the pedal (full throttle) up to about 6k rpm, upshift, slow the car and stop the log. Do at least 1 run where only block 115 is logged, for best resolution of the boost curve.

You can do a slightly different log to check a DV: Cruise at 1500, start log of block 115, full throttle to about 3,500 rpm, shift to 4th and continue full throttle for a few seconds, let off throttle, stop the log. While logging, both times you let of the gas, make sure to let off the gas as abruptly as possible, so the throttle plate slams closed quickly at full boost. That way the DV is tested fully.

Also, make sure you note any stored codes (whether the Check Engine Light is illuminated or not), and also note your long term fuel trims (take a glance at block 032, no need to log).

Fender0122
11-16-2010, 09:51 AM
My car is running about 16psi too and the stock DV gave out above 10psi and was very inconsistent in boosting pressures. Mine wouldnt go above 10psi until I switched it out for a Forge Splitter. I also noticed a slight groaning noise as I waivered the throttle around 0psi and much louder at WOT. I figured what the hell, might as well get a Forge and if that wasnt it I still had a better DV.

Nateness
11-18-2010, 11:35 AM
I installed my Podi electronic stepper boost gauge last night (VERY awesome product BTW) and noticed that I will spool to 10 PSI very quickly around town.

For a while it looked like boost was limited to about 10 PSI until I hit the highway. On the highway if I go WOT for about 2 or 3 seconds, I can see the boost gauge slowly creep up until about a peak of 12 to 13-ish PSI.

I will be putting on the APR R1 diverter valve this Friday. We'll see how it goes.

Nateness
11-20-2010, 12:48 AM
Installed the R1 diverter valve today. I also tightened some "loose" couplers on the compressor discharge and the hot/cold sides of the SMIC. These were tight if you used a flat head, but when I checked with my 8mm, they had a way to go before being as tight as the couplers on my RX-7.

Boost seems to come on a little faster now. I notice that I consistently achieve 10-12 PSI before 3k @ WOT. Boost apears to max out at around 12 PSI.

I have no idea what sort of combination would lead to a peak pressure of 12. Apparently 11-ish PSI is what other stock AWM guys are getting, so maybe the extra 1 PSI could be attributed to the ridiculously cold weather we're having in Seattle... (low of 28*F expected on Monday...)

So it looks like the conclusion to this is neither a boost leak or a DV issue. 10-12 PSI is normal if you have a AWM motor.

2001A4QUATTRO
11-21-2010, 11:11 AM
^ He stated that the logs showed a requested boost of 16 psi. If the ecu is requesting 16 psi it is chipped. His issue is that it is requesting 16 and only boosting 10.

Nateness
11-21-2010, 04:12 PM
^ He stated that the logs showed a requested boost of 16 psi. If the ecu is requesting 16 psi it is chipped. His issue is that it is requesting 16 and only boosting 10.

I have logs from BEFORE I installed the ER TIP that showed I was specifying 16 PSI and achieving 18 PSI actual.

The silicon hose that was provided in the kit to connect to suction side of the pipe to the N75 valve was a 3.5mm when it needed to be a 6mm. I was able to expand the hose to fit over the 6mm nipple on the N75. I wonder if the under-sized vaccuum connection could affect the N75 valve's ability to regulate boost pressure. If the N75 was disconnected, would the car only achieve the pressure specified by the waste gate actuator?

walky_talky20
11-21-2010, 06:15 PM
Yes, if the N75 is unplugged electrically, you will be limited to spring pressure. On a stock turbo that will be around 3psi or so. And stretching the TIP connection over the N75 nipple shouldn't cause any problems as long as the hose isn't kinked somehow. It has to have access to atmospheric pressure: that connection is it's "vent". If it is plugged you will underboost as the pressure from the actuator cannot be vented.

Nateness
11-21-2010, 09:11 PM
Yes, if the N75 is unplugged electrically, you will be limited to spring pressure. On a stock turbo that will be around 3psi or so. And stretching the TIP connection over the N75 nipple shouldn't cause any problems as long as the hose isn't kinked somehow. It has to have access to atmospheric pressure: that connection is it's "vent". If it is plugged you will underboost as the pressure from the actuator cannot be vented.

I suspected as much, but I'm really stumped as to why boost pressure is limited to 12 PSI when I have logs showing a spec of 16.

I'm going to replace the vaccuum line from the TIP to the N75 valve anyways. Could be that there is a kink that I cannot see that could be messing with the reference that the valve is seeing.

Nateness
11-22-2010, 12:58 AM
I did a little bit of homework on how the N75 valve works and found this nice article:

http://s4wiki.com/wiki/Wastegate_bypass_regulator_valve

If the line to between the TIP and the N75 is kinked or undersized, then I can imagine that it would hinder the valve's ability to divert pressure away from the wastegate and raise boost pressure to the desired set point.

I will let you guys know what I find out after I replace the line w/ a 6mm line that is matched to the N75 port OD.

Nateness
11-25-2010, 05:15 PM
I replaced the kinked 4mm line with a new 6mm line and now I am getting a peak boost pressure of around 14 PSI now... Is it possible that the N75 is failing?

What is the characteristic of a failing N75? Do they just fail open/closed, or do they slowly lose their ability to actuate the valve?

If this is a case of a failing N75 valve, are there any recommendations on which one of the many valves I should replace it with?

Nateness
11-26-2010, 06:05 PM
N75 was initially connected to a vacuum line that was higher up on the TIP. This vacuum line is not port-matched to the N75, I had to stretch the line to fit.

I switched the N75 to the lower vacuum line that is port matched to the N75 nipple diameter. This seemed to cure my missing boost.

I now spike to 18-20 PSI in gears 1-3, and up to 24 PSI in gears 4 and 5. Can anyone tell what chip/program my car has based on that information? N75 appears to be OEM with the factory clips still connected to it... Previous owner of this car had no idea that the car's ECU was flashed.

walky_talky20
11-26-2010, 09:23 PM
Wow, that is a lot of boost. So it was the atmospheric input the N75, eh? Good to know.

I'd like to see a boost log on this car, as 24 psi seems way too high. Most chips spike to 20 and hold about 16-18 and it tapers off at higher revs. If the N75 is original, they can fail such that they don't regulate the boost properly, either under or overboost condition. I've seen the overboost failure more often. It seems the internal spring which opposes the solenoid weakens over time. So a small input to divert the pressure becomes much larger than normal as the spring tension isn't there. The internal slug moves further than it ought to and overboost results. That's just my guess on what is going on. On an '01, if it spikes to high it may put it in limp mode after a bit.

Nateness
11-26-2010, 11:29 PM
Yup, the N75 operation surprised me too. Apparently it needs to relieve a certain mass flow rate to achieve a certain effective waste gate pressure. Coming from owning a number of Japanese turbo cars, I'm used to the predictable onset of boost consistent with RPM. Of course throttle position plays a part, but the output is more predictable than the N75 =[

24 PSI seems like a lot to me too... So far I have not experienced limp mode. Brief logging shows that my peak requested boost pressure is around 17 PSI. I'm curious to know if I can identify which ECU I have based on the spec boost.

I will try to get a clean log. All of the logs I've run so far do not have very good resolution (sampling rate of only 1 point per second). Is there a trick or method to get the clean high resolution data logs that others on this website are getting? I'm using the latest version of VAGCOM, logging with the measuring blocks button under Engine parameters. I noticed that I'm limited to only 3 blocks at a time... is there a way to get more?

What blocks would you like to see me log?

Interesting to note that when I did a quick run that I achieved a peak air mass flowrate of 173 g/s at 5,100 RPMS and 17 PSI. I let off the throttle at 5,100... I wonder if I would have achieved a higher mass flow rate if I had held at WOT longer.