p0491 Questions

[pyrael]

As the title reads, I've go only p0491. But first some background...

I bought this car ('02 325ci) in april for $800. The guy I got it from had already replaced the SAP nad said that the only code coming up was a MAF code. I bought it after test driving because it seemed to have all the tell tale symptoms and if that's all that was wrong it was a good deal. It needs a bit of body work and interior work. He even drove it to my house and removed his plates there.

So, I threw it on my scan software, I use ScanMaster and have an ELM327 usb cable. The codes that came up were SAP, MAF and a misfire on a couple of cylindars. I bought a new MAF and spark plugs and discovered the fuel pump was bad. So I bought a pump and a filter. When I changed the filter I noticed the vacuum line was rotted off. So I replaced that. MAF and Misfires are now gone. no problem. But the SAP p0491....

So I watched a bunch of youtube vids (most from the 50sKid) and started troubleshooting. I have replaced EVERY vacuum line, tested the switch at the back of the intake, discovered a vacuum plug missing and fixed that. The hose from the pump to the valve he put on was not correct and crimped where it needed to bend so I replaced that with the correct hose. Still have the code!!!

I removed the valve, which looks new on the outside, and discovered that the metallic gasket was shot and it looked like he tried to use form-a-gasket or something to fix it. I put vacuum on it, did the blow test, valve works fine. The gasket "goo" was bulged out and partially blocking the port on the valve. I have ordered a new gasket and will replace it regardless.

I have read that sometimes a "working but weak" O2 sensor can cause this issue as well. so my question is this...

After all I have done, Would this gasket be a logical reason for the code or should I start looking at the O2 sensors or other places? Also, it passed a smoke test so that's off the list too.

Thanks in advance for any help!

Steve

[MarcoZandrini]

The code is for insufficient flow in bank 1 from the SAP. I bet the previous owner mucked up the piping to bank 1.

[randy72877]

Check exhaust backpressure. If the catalytic converters are clogged, the sap won't be able to push air into the exhaust against the backpressure. This can cause misfiring codes as well. Your car would also have a noticeable loss of power especially at higher rpm.

Sent from my S61 using Tapatalk

[pyrael]

The code is for insufficient flow in bank 1 from the SAP. I bet the previous owner mucked up the piping to bank 1.

It certainly appears that was as far as the gasket goo goes. I don't see anything else wrong otherwise though.

Check exhaust backpressure. If the catalytic converters are clogged, the sap won't be able to push air into the exhaust against the backpressure. This can cause misfiring codes as well. Your car would also have a noticeable loss of power especially at higher rpm.

My neighbor put his "fancy psi gauge" on the exhaust when I first got the car. He said the readings were fine, I'll ask him to check it again, maybe its an underlying problem that wasn't presenting before when I had the fuel filter/pump issues? Based on the Scanmaster performance tests, it's running just a little worse than the original 2002 specs for 0-60 etc. But is better than advertised '02 spec for mpg. I couldn't help myself when I discovered that part of the software! Could the VANOS cause any of these symptoms? it's slightly noisy, and the car has over 150k on it with no service record to refer to.

Thanks again for the replies. Gasket should be here tomorrow or Wednesday, I'll report back more then.

Steve

[pyrael]

Well, I replaced the gasket yesterday, been driving it and so far so good. I'm not getting over excited though. That attitude has a tendency to make the Engine Gods mischievous! I'll report back after a few more drive cycles. I looked at the O2 voltages from the last trip, it looks like my cats are failing I may have to use the anti-foulers on it to get through emissions. I just don't have the dough to replace manifolds right now :/

[pyrael]

Ok, I'm officially blaming my wife for this!! (No not really) All was well, Drove her to and from work, checked the codes each trip - not even a pending code. When I picked her up last night, she commented that the light was still out! I swear she jinxed me!! This morning the SES came back on at exactly 50 miles. However, now its the SAP bank 1 and system too lean. I think the lean code may be realted to the MAF because the last time I had that code it was fixed by removing, cleaning the rubber, and reinstalling it properly. I lost the hose clamp to the SAP hose under the airbox and had to remove it to fish out the clamp. So I "think" that may fix the lean again. but I don't know. I AM seeing erratic voltages on the downstream O2 sensor and as I understand it, this is common with failing Cats. Perhaps the cats are "going bad". I can't afford new cats at the moment, I've already put quite a chunk of change into this car. I don't like the idea of doing the non-fowler or Resistor/Capacitor trick because that doesn't solve the issue. But at the same time, I'm desperate. I need this thing inspected ASAP. I'm going to re-seat MAF and see what happens, but I KNOW that wont fix the O2 readings.

So, before I go crazy replacing cats, is it possible the O2 sensors are just shot? What I mean is, what do the graphs normally look like when an O2 sensor starts failing? I'd hate to spend four hours under this car replacing manifold in my driveway just to find out it was really a sensor.

I'm going to have the back pressure checked again as well. Maybe the mis-fires did damage to the cats.

[pyrael]

Update!

I went back through the Vacuum steps again. MAF, Upper and lower intake boots, all the hoses... The I decided to pull the DISA. Well, the DISA visually looked good. Noted that the o ring was kinda flattened. I did the pressure test with my finger over the weep hole, dead. absolutely no hold! tried it a bunch of times and no dice. it's not holding a vacuum at all so that should be here Saturday. Still unsure on the cat/O2 issue, but I'm fixing the vacuum leaks first since I can at the moment. If anyone has any ideas on aftermarket or affordable cat Ideas, I'm all ears!

[jclausen]

Secondary air system has the pump, valve, hose and line, solenoid that allows vacuum to valve and the passage ways on the cylinder head. The oxygen sensors are the sensor that looks for operation of that system, meaning the air being injected on cold start into the exhaust ports hits the oxygen sensors and they register the fault if in they in case there not seeing enough air. On cold start the engine runs on a rich mixture for a short time and the secondary air injects ambient air it in to the rich exhaust mixture to lean it out before hitting the sensor. The engine is usually only cold enough to activate it then the car sits over night. That's it nothing else's effects it air mass, cats etc. the solenoid is the rear of the intake manifold underneath has a line that's goes from that to the valve the line is nylon with rubber hose connecting it. I would check all rubber vacuum hoses, test the valve and the pump, i have never seen e46 with plugged in passages in the head yet. Since the system does not have monitored sensors in it the pre cat oxygen sensors do that. The system works for maybe 4 mins on cold start and that is it.

[pyrael]

Thanks jclausen. I took a break from trying to figure this mess out and took the car off the road for a while. . Cant afford the no inspection tickets.

I'm back at it again now since my VW transmission died on me. (Auto trans, lost 2nd gear). So, I've put the e46 back on the road and will be replacing the O2 sensors tomorrow. The O2 graphing shows that they are not reading properly (the graph stays low for seconds at a time) so I'm assuming they are just tired. I've went back and rechecked every vacuum line under the hood and none are bad. I also removed the solenoid and tested that it operates. As far as all these parts go, all are in proper working order so I'm really hoping this solves it. Basically, I'm assuming that if the o2 sensors arent reading properly, the ECU will think it's not getting the air it expects to see?

I was really not looking forward to driving this car in the winter, I'd rather keep it looking as nice a possible. Oh well.