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View Full Version : Weird numbers from my ECU regarding power and boost



TheRedGlacier
08-19-2016, 08:00 PM
When I got my B5, the owner knew little about it, and said he believed it to be stock. Well few months in, I saw I had a chrome, unbranded (to what I can see) diverter valve. So I plugged in one of those OBD diagnostic tools (NOT VAGcom) and it was reading that I was making 15 to 18psi MAX, giving me roughly 205-215 horsepower, and ~240-250 lbft, which seems to line up with APR stage 1. However, I just installed a boost gauge and that runs up to about 9-10 and then tappers down. Is it possible that the ECU could be "lying" about those numbers? It reads the correct Engine RPM, Road speed (not via GPS), fuel flow, mpg..

I'm not sure what the issue is. I figured it could be a boost leak with the gauge installed.. But I haven't checked the ECU yet. I would assume it would not consistently run to 9 / 10 psi (k03Sport) if it were a leak sucking away the power. I also have a light rattle/ plastic/aluminum sound on the engine's deccel at idle (when revving), somebody mentioned possible loose wastegate (or cracked gasket/loose bolts at the downpipe where it is loudest), but I'm unsure that once again that it would show stock numbers for psi.

Any ideas on what is going on? The car feels just as fast as the day I bought her.

Edit: Probably be helpful to list mileage.. Right? Haha 201k miles 2001

SynapticA4TQM
08-20-2016, 03:24 AM
You can open the ecu box to see if anything has been written on the ecu itself... If it's been flashed some companies will write the tune on the outside of the ecu housing. It would be good to check that.

When you say that it shows the right road speed (not via GPS), are you saying it doesn't match GPS? Or just that you've confirmed via GPS, but by police "your speed is" signs or something like that... Not that it matters much in this case, more curious bc of the wording.

When does it taper out? If it's after 5500 or so rpm, that's extremely normal. What obd diagnostic tool did you use? I'm assuming that it's a 2001 a4 with a 1.8t in it? 2001 has a MAP sensor in it that actually reads the amounted of boost at the intercooler. If you are able to read specific measuring blocks, or can get ahold of someone with a vagcom, you can log block 115. It has 4 sets of numbers in it that reads RPM, "Last", boost value specified (in milli-bar "mBar"), boost value actual (in mBar). If the actual is substantially less than the specified boost value, you've either got a leak, or the turbo could be failing.

Another way to find out if you have a boost leak is to either purchase or make yourself a boost tester (there are a number of DIY's on it). Using that, you wet down the boost plumbing with soapy water and look/listen for air escaping (i.e. Bubbles). With our cars being 15 years old (and older in many cases) it's very likely that tubes and hoses have gotten dry and cracked.

Also, without knowing anything about the diverter valve, it'd be very reasonable that it could be defective and is a leak in the system. Most (if not all) aftermarket DVs can be opened and (should be) greased periodically. So it wouldn't hurt for you to take it off and see about opening it up. Also a very common place for a leak is the hose that goes from the manifold to the top of the DV.

As for consistently getting 9-10psi, it is very possible that there is a leak, if hoses are dry and brittle, cracks may not open enough until it reaches 9-10ish psi... Which is why a boost leak tester is a good idea. Using it you start at a steady 5psi and look for leaks. Any leaks at 5psi are going to be substantial. From there you slowly increase the air pressure until you're at around 20-25psi... In your case since 18psi is what you're expecting, you'd definitely want to test at least to 20psi.

While noises while rev'ing can be aggravating, what I'd really be concerned about is whether you hear any chattering during wide open throttle (WOT), engine braking just after having it WOT, or at any specific boost level while driving part throttle.

If you're capable, if recommend unbolting the downpipe from the cat and inspecting the gasket. It is a pain to get to, but gaskets are cheap. Also, if you uninstall the catalytic converter (assuming you don't have a test pipe) you can visually inspect the wastegate with a flashlight and a mirror. It's not the most convenient thing to do, but it's a tad less effort than taking the whole turbo off...

Personally, I'd be surprised if you're getting 205-215hp and 240-250tq while only reaching 10psi. That is unless the turbo is not a ko3s, if it were something like a Garrett eliminator turbo, GTRS or something of the like, that would make a bit more sense. It would also fall in line with some of the kits APR sells, since you mentioned it.


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TheRedGlacier
08-20-2016, 02:34 PM
Thank you for the quick and detailed response!! Okay, so I just got out of work and I have to run a few errands before I can get dirty. But for starters I will check the ECU sleeve as stated. I didn't really word it well enough, but I have one of those apps that you can use on your phone. It reads the speedometer and displays that along with the engine Rpm, and the phone I used was an old iPhone, that is deactivated and has been since I went back to Android. And also was in airplane mode anyway. But the app displays the boost pressure (read up to 15-18 last I saw it) It was throwing 210 hp, 250 tq (approx) too. However the boost gauge says that I am making (sorry I made a mistake...) 8 to 9.5 psi.. But as stated the ECU OBD tool and app were stating much higher (the 15 to 18... It was saying my car was actively making that under WOT)a few months ago, and the car does not feel any slower. The car does run well to 5500 then it tappers down, so K03..

I'll check to see if the line from the Intake manifold to the DV is loose or something, but if none of the above stated work, I'll try a boost leak tester. Just out of curiosity.. If my diverter valve can open, how would it? And what type of grease would I need to regrease it?

Once again, thank you! This is a lot to try, so I'll be sure to post progress.

EDIT: just going off of looks alone, my fdiverter most closely resembles a 034 billet aluminum one, and I might be an idiot... Would such a diverter even make noise with the stock intake? Cause the car makes a woosh in the background of the engine rev/intake. I could try to get a video but it might not be apparent. Other than that no noise out of idle

SynapticA4TQM
08-20-2016, 03:37 PM
Okay, so there an iPhone app you're using, does it have something like a Bluetooth connector that plugs into the ODB port? Or does it measure things via the accelerometers (i.e. Measure rate of acceleration and then calculates things with things like weight, engine displacement, etc having been provided).

Apart from the iPhone app, you also have an OBD scan tool?

Regarding the DV, what happens is there is a spring in it that holds it close mainly during steady state driving (cruising at pretty much the same speed) and during idle. In other words, mainly when vacuum is low. The line from the top of the DV to the manifold sends compressed air to the top of the DV wen you're in boost. It also "sends" vacuum to the top of the DV when your in vacuum... Coasting, engine breaking, idling. The moment when the DV really does what it's designed for is after accelerating, when you let off the gas, there is a moment when the turbo is still compressing air and the throttle body is close. Without getting into all kinds of gas flow and bernoulli's principle (which is a bit redundant actually) let me summarize by explaining that when the compressed airflow hits the closed throttle body it sends a pressure wave back to the turbo. That pressure wave can damage the turbo of its strong enough, or if that happens enough. At the moment though when the throttle body closes the manifold instantly goes into vacuum. That tube sends the vacuum to the top of the DV and along with the compressed air that is on the other side of the DV opens the DV which vents that compressed air back into your intake path. So that's how it opens.

For lubricant, I've heard of folks using a thin layer of grease. The recommendation though is for something like graphite lubricant. The few I've had have looked like they used graphite lubricant from the factory. However in a pinch, I've simply cleaned it well and sprayed it with some WD40. Just don't leave it like that for long, the WD40 dries out and what not.

Regarding sound... The stock DV can make an audible sound on occasion, most often it'll be a moment you get the slightest sensation of having a blow off valve... But that is pretty rare. An aftermarket DV won't add much noise by itself, but with higher boost, you'll have a better chance of hearing it.

However, the woosh you're hearing when hitting boost will be the turbo itself... It could also be a leak opening up once boost is made. It's just hard to inspect things while driving the car right LOL... Which is why we have boost leak testers! :thumb up:


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TheRedGlacier
08-20-2016, 06:12 PM
I see.. I have a bluetooth setup via the obd port. I follow what you are saying. Alrighty, I'll give it a look in a bit. But you definitely have me convinced with a boost leak tester! I went to pull out the DV earlier, but one of the rubber hoses is stuck on it, so I'll go back and heat it up.

You sir really deserve a slice of pizza by the way! I greatly appreciate your assistance!

SynapticA4TQM
08-20-2016, 06:14 PM
Looking forward to hearing what you find out.


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TheRedGlacier
08-20-2016, 08:18 PM
Okay so.. All I've had time to do was attempt to remove the diverter. Well no luck. The hose on the nipple and one of the large hoses (bulging around the dv) are stuck completely. I can't get the big hose to move and both look like the are barely on, but I can't even get them to go on more..

SynapticA4TQM
08-20-2016, 08:34 PM
The big hose that the DV goes into is an intercooler hose that connects the turbo outlet to the crossover pipe. The discharge from the DV goes back up to the turbo inlet pipe/hose just after where the n75 is. On occasion, I've found it a bit easier to take the entire conglomeration out. Hoping for your sake the clamps aren't still the oem pinch clamps, loosen the clamp on the turbo outlet and the crossover inlet, disconnect the n75 (for room to maneuver, loosen the clamp holding the DV discharge pipe in the turbo inlet pipe and pull it out. Be careful, the hose actually connects to a plastic elbow that then goes into the turbo inlet pipe, it can break if it's too brittle. Pull the intercooler hose off the turbo outlet and the crossover inlet. At the point all you should have to contend with is the boost/vac line from the front corner of the manifold. IIRC, that line has quite of bit of extra length to it... Be sure before you follow my next instruction... Cut it a little bit (a half inch maybe) above the nipple of the DV. You should be able to pull it all out of the bottom.

Now with it out of the car you can put some pliers on the stubborn boost/vac line on the DV. Then work the DV out of the intercooler hose. It's a pretty stout hose, so you should be able to twist and pull for all your worth on the DV to get it out.

Good Luck


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TheRedGlacier
08-25-2016, 04:31 AM
Hey, sorry for the delayed response. I got caught up in work. Anyway, last night I did have time to load up the old phone. Still reads 15 average 18 max. 210 / 250 average (hp/tq)

Yet the boost gauge reads max of 10, will drop to 8 or 9 around 4500, and go down around 5500

SynapticA4TQM
08-25-2016, 04:34 AM
There's a chance your boost gauge is faulty... Is it new or used?


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TheRedGlacier
08-25-2016, 05:22 AM
Possibly.. It is a new gauge.
The app says my idle vaccuum is approx 10-12, and the gauge says 15 to 20

SynapticA4TQM
08-25-2016, 05:31 AM
Where did you "t" it off to get a signal?


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TheRedGlacier
08-25-2016, 05:40 AM
I put the tee right off of the intake manifold vacuum line

SynapticA4TQM
08-25-2016, 05:40 AM
That's a good place... Does it sit at zero when the car is off?


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TheRedGlacier
08-25-2016, 05:48 AM
Yeah, flat at 0

SynapticA4TQM
08-25-2016, 05:56 AM
If you've got a bike tire pump, you can dig it up to feed the boost gauge. You can then pump up pressure and then verify the gauge against the pump's gauge. Once you know the gauge is reliable or not (and I personally think a mechanical boost gauge is going to be more reliable than electronics) you can then start looking for leaks or a new gauge.


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TheRedGlacier
08-25-2016, 06:16 AM
I have an electric bike pump, I'll check it out in a bit and let you know my findings.Thanks again!

TheRedGlacier
08-25-2016, 08:21 AM
Okay, I still have not tested the gauge, I apologize for jumping around.. But I pulled the diverter for the first time, unscrewed the cap, and it has a very faded red spring. Piston diverter.https://twitter.com/TheRedGlacier/status/768830664749842432

I've never posted a picture here so if it isn't visible please let me know. Sorry for being sorta new haha

SynapticA4TQM
08-25-2016, 08:25 AM
The red spring is typically for when you're running 25+ psi... Looks like it could use a cleaning and re-greasing.


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TheRedGlacier
08-25-2016, 11:38 AM
So I inspected the diverter valve further upon cleaning, to find that the o ring is torn and a chunk about .5" long fell in to the assembly.

SynapticA4TQM
08-25-2016, 11:42 AM
That will cause a problem... That'd mean compressed air could leak past the piston back into the intake pipe.

If you've got a decent hardware store near you they might have an o-ring that you could replace it with. I'd take the piston and what's left of the o-ring with you... Or, you could order a replacement DV.


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TheRedGlacier
08-25-2016, 12:01 PM
I'll go to Valu and see what they have. Looks like either 1.5 or 2" diameter.

SynapticA4TQM
08-25-2016, 12:02 PM
I sent you a pm with what should be a direct replacement


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TheRedGlacier
08-25-2016, 04:03 PM
Okay thank you much! I cleaned and regreased my unit and swapped a new o ring in and it still boosts 10 holds 8 or 9. Might just be worth buying that new one.

EDIT: I bought the car with the valve in it. I thought it was stock at first.

SynapticA4TQM
08-25-2016, 04:04 PM
Unless you find a way to replace the o-ring... Getting a new one is a good way to go


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TheRedGlacier
08-25-2016, 04:05 PM
The oring itself on top of the piston was easy to swap in, but the numbers are still the same as before.

SynapticA4TQM
08-25-2016, 04:05 PM
Ahh I see


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TheRedGlacier
08-25-2016, 04:08 PM
Could the valve? Otherwise I'll try the gauge with a pump on it.

SynapticA4TQM
08-25-2016, 04:10 PM
Could the valve?? It would hurt to double check your gauge regardless


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TheRedGlacier
08-25-2016, 04:13 PM
Sorry I thought I typed could it be the valve? (Going out?)
Gotcha.

SynapticA4TQM
08-25-2016, 04:14 PM
The spring may be weak if it's pretty old. That'd be another thing about getting the new one... You'd have the other springs...


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TheRedGlacier
08-25-2016, 04:15 PM
Alright. Ill go for it. Sorry if I'm getting annoying

SynapticA4TQM
08-25-2016, 04:16 PM
Nope not at all


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