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SAI sound (video)

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sai sound video
6K views 17 replies 6 participants last post by  2004 1.8T BBS 
#1 ·
Having some issues with cold startup lately on my 1.8t tip.

As a preface, the SAI pump started going out months ago, and I finally unplugged it when it triggered the CEL for the annoyingly loud sound it made. Just before the CEL however, it started making a lot of extra noise during the SAI cycle.

When the car is put in gear and the SAI system is running, I get this loud raspy rattling exhaust sound and sometimes smell it in the cabin. It completely disappears under load however. As soon as the cycle completes, the sound goes away and everything is business as usual.

I have replaced the SAI pump with a new unit that works fine, and I could find no moisture in the hoses leading to the EGR during the installation. I trolled cold start issues as best I could but figured a learned ear could distinguish the problem before I go ripping out valves.

Thanks everybody for any and all pointers. Can't wait to get it resolved.

 
#2 ·
Is the noise only there during the SAI cycle ?
Does it happen again a few minutes after starting, during the SAI test ?
Does it make the noise on a cold start with the SAIP fuse removed ?
Can you use a stethoscope to narrow down where the noise is coming from ?
What valves are you considering ripping out ?
 
#3 ·
Thanks for the prompt reply. I hadn't had the time to investigate the sound any further since the holidays.


Is the noise only there during the SAI cycle ?
--Correct. Only during cold starts.
Does it happen again a few minutes after starting, during the SAI test ?
--It only occurs the one time (immediately at start, for a minute or so) when the car is cold enough to run the cycle. Can I force a test with vagcom?
Does it make the noise on a cold start with the SAIP fuse removed ?
--I don't have access to a garage right now to perform this check, but since the sound was still present with the pump harness unplugged, I am sure it does.
Can you use a stethoscope to narrow down where the noise is coming from ?
--Noise seems to be coming from the front, same area as the SAIP.
What valves are you considering ripping out ?
--From what I have read it may be the Kombi valve leaking due to some sort of seizure, but in that case the sound wouldn't go away after the SAI cycle, would it? Pump hoses? Vacuum hoses?

For reference, I still have a recurring SAI error code even after replacing the broken pump:

16795 - Secondary Air Injection System: Incorrect Flow Detected
P0411 - 002 Lower Limit Exceeded

Thanks again.
 
#4 · (Edited)
It's nice that you posted a video, but what I don't understand is why there is a change in sound and possibly revs between 6-7 seconds in. Later on it looks like you rev the engine a bit which is fine, but it's unclear if you did that at engine start as well. Are you off the gas pedal completely during this video? If so, then aside from a SAI issue, you have an idle issue also (at least while the SAI is activated). Can you elaborate on how your car idles when cold and hot?

If you have a 411, the problem is not fixed. You need to test your combi at a minimum, including the vac line to it but it would be best that you take it out and clean it thoroughly, test it and reinstall it. It might be useful to connect a vac gauge at the combi with a T to measure what it is there, and compare it to what it is at the manifold.

My guess is that you have some vac leak either on the diaphragm inside the combi, or the vac hose to the combi.

vcds allows you to run output tests on the SAI system.

post all other codes you get as well.
 
#5 ·
The change that you are seeing/hearing at 6-7 secs is the engine being put in gear (from then on it stays in gear), which is what really emphasizes the sound. I begin reving at 29-30 seconds to illustrate how the sound subsides with a load. The car's idle rev behavior has not changed. Everything operates normally except for the sound when cold. When its hot there are no issues because the SAI system is not in use.

The only other code is 16840 - EVAP System: Very Small Leak Detected P0456 - 001 - Upper Limit Exceeded , which is a condition that has been present since I bought the car 8 years ago.

I will have the chance to get into the plumbing this weekend and hopefully there will be a glaring leak. I would just like to know what is actuating that sound at startup, since that indicates that at least something is opening up during the cycle.
 
#6 ·
Also check that there are no breaks in the tubing from the air pump to the kombi. That will effectively turn that tubing into an unmuffled exhaust which is similar to what this sounds like.

The SAI system is tested shorty after it is actuated, when the engine is idling. The test is a cycling of the system from on to off for about 5 secs. You should hear the clatter sound again during that cycling. You may want to listen for that test mode and what sounds it makes.

The SAI system is activated on a cold start, based on coolant temp reported to the ECU. Activation involves a couple of coodinated actions taken at engine start: SAIP relay is actuated (turns on blower motor), and kombi solenoid actuated (applies vacuum to kombi valve to open it). So the combi is what stays open during that time. The ecu can't know how well the esystem is performing at engine start. Any SAI codes post only after a test cycle completes.
 
#7 ·
Check your flex joint on the down pipe. Mine is leaking and makes that sound the entire time the SAIP is on. Quiet otherwise. No CEL.
 
#8 ·
Is the noise only there during the SAI cycle ?
--Correct. Only during cold starts.
Does it happen again a few minutes after starting, during the SAI test ?
--It only occurs the one time (immediately at start, for a minute or so) when the car is cold enough to run the cycle. Can I force a test with vagcom?
You can force a test with vagcom, but the above suggests the SAI system is not causing the problem.

Does it make the noise on a cold start with the SAIP fuse removed ?
--I don't have access to a garage right now to perform this check, but since the sound was still present with the pump harness unplugged, I am sure it does.
This proves that the SAIP is not making the noise.

Can you use a stethoscope to narrow down where the noise is coming from ?
--Noise seems to be coming from the front, same area as the SAIP.
A stethoscope could help locate the source.

The noise does sound like it could be caused by exhaust, the combi valve might be stuck open.
I can't see why this would cause the noise only on a cold start.

Sometimes a failing bearing will be noisy only on a cold start, I suggest you check the accessory belt and timing belt tensioners and rollers etc.
 
#9 ·
I will prioritize investigating the corrugated hose between the pump and the combi. I am convinced that it is an exhaust sound (especially since an exhaust smell whofts in when in motion during the sound). Really hoping that's the culprit. Any hints for getting in there?

Also, I haven't personally seen the N112 solenoid. Is that something I could easily unplug to diagnose what creates the sound?

Due to my job I'm just struggling to align free time, daylight, warmth, and a cool engine to troubleshoot. Counting on borrowing a garage this weekend.

Thanks all for the continued insight.
 
#10 ·
you could do one thing that does not require much prep, just removal of the belly pan.

locate the secondary air injection pump (SAIP) below the passenger headlight. you don't need the engine running. you can test if there is an air leak on the path to the combi in one of two ways, whichever you find to be easier to you:

1) unplug the connector to the pump, and take two wires from the battery to the pump, and activate it (using the correct polarity). Then, in the engine bay look for air leaks all along that path. part of that path will be the corrugated hose from the pump to the hard pipe and it will be hard to get to it, but you should be able to feel air flowing out if there is a leak.

2) gently press the tabs of the corrugated hose from the outlet of the pump, then gently twist it back and forth as you pull it out. blow into it with your mouth and hopefully you feel like you can't pressurise the pipe you have an air leak. You may need a second person for this.

I don't think you need to worry about the N112 solenoid. It's probably working fine, and perhaps the combi itself is okay. an air leak may be all you need to fix.

also, say more about the evap problem you've had for 8 years. it might not be that hard to fix, and you will have a better car. It's best to have no ongoing CELs.
 
#11 ·
Those are good options, I'll give that a try! I suppose it would have been prudent to test those hoses while I was replacing the SAIP with the bumper cover off, but hindsight is 20/20.

The evap problem never seemed to trigger a CEL, and emissions have always passed fine. Visual inspection of evap hoses didn't really turn anything up. Checked that N80 clicks, etc. I suppose I didn't feel like replacing the gas cap because it didn't fix my dad's identical problem on his 08 2.0t, however silly that sounds (also, isn't that the purpose of the gas cap light? I never see it with or without the cap on).
 
#12 ·
The gas cap light???

There's the fuel light, which looks like a gas pump. It comes on when you're about out of gas.

There's the light on the gas cap switch, but it comes on with the headlights so you can see the switch in the dark.

But there's no gas cap light... What are you referring to?
------------------

Also: you didn't give the year of your Passat, although I'm guessing it's a B5.5 since you've got the battery tray cover.
In the early B5.5s, at least, a few of the vacuum hoses tend to turn hard as a rock. I got my first P0411 because the vacuum hose to the combi had hardened and was leaking. If yours isn't pliable, replace it (see my DIY in the info base).

Here's a picture so you can see where N112 is (my replacement vacuum hoses are blue):

 
#13 · (Edited)
Haha. Yes an 04 B5.5. And yes, gas cap loose light.

It's a thing:
Vehicle Car Auto part Odometer Display device



I digress. I was miraculously able to get eyes on the plastic combi hose when I got home this evening. Visual inspection: FAIL. I'd say 350 out of 360 degrees are sheared from some typical plastic baking. Lucky for me it was a section that is visible.

My new project is going to be finding a replacement part that costs what its worth and doesn't take a month to arrive. Or you can tell me now if this is my best bet: sai outlet hose.
 
#14 · (Edited)
Dropped by the dealer Saturday and picked up a new SAI outlet hose. Got the car all buttoned up last night, and the sound is finally gone. Thanks all for sharing all of your diagnostic ideas and experience. I'm never disappointed with the community. It's running like the day I drove it off the lot again (with 110k on the clock)!


First hand warning to those hearing sounds who haven't inspected the plumbing before. Your car is old and those brittle hoses will be failing with certainty. Only a matter of time.

Snake Plumbing fixture
 
#16 ·
VAGguy, I am curious to know what it turns out to be. If there was a leak on that hose where abrasive found his, it should light up the CEL. All it takes is two failed SAI system tests.

Having said that, the SAIP does NOT get activated on very cold starts, but maybe the test doesn't run either following those very cold starts (I don't remember and not close to my Bentley to check).
 
#17 ·
It has done this for well over a year to me. No CEL, no codes.

Correct. Somewhere around 30f and under it does not kick on and maybe above 80f?
 
#18 ·
FWIW, I had the EXACT same codes about 2 years ago before I got my APR tune. Cleared the codes after finding the problem. It was, INDEED, the hose going from the airbox down to the SAIP (INLET hose, AWM engine). I have had it temporarily fixed for about a year now. I went to Lowe's and had to buy a 6ft 1 1/4" OD corrugated hose and a couple of clamps/silicone...

Code is gone, and only costed me <$20.

Maybe one day I'll buy the whole hose kit, but right now I can only find them as Genuine VW/Audi. I don't feel like spending $100.62 on a single piece.
 
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