Codes and a bunch of new parts

[E30SCragtop]

This question (or similar) has been asked many times I know and I've read many of the past threads about this without finding a specific solution. I'm trying to avoid paying for the dealer computer scan but I may have to.

Car: 2000 740i
Codes: p0174, p1161, I did have a p0150 but after clearing codes that never came back. (I live with a scan tool in the passenger seat)
The Symptoms: CEL, rough idle (when warm not cold start), fine above 1500 rpm, stinky exhaust but no smoke, back driver O2 was majorly black with carbon when I removed to replace it.
What I've done so far: New MAF sensor and all four O2 sensors have been replaced. Did a spray test for a vacuum leak and can't find one.

I got the same or similar codes about 2 months ago. I first replaced the MAF...no change. Then I replaced the pre-cat O2's and it started running fine. Ran fine for about 6 weeks then the codes returned. Just replaced post-cat O2's and no change.

I've read about the OSV issue but I was under the impression that I would see smoke. The exhaust does smell horrible though. It seems my options are cat replacement or OSV replacement unless I should check something else. It may seem I'm throwing parts at the problem but all the ones I have replaced were well past due but I'm done replacing things until I know what it really is.

Anyway, I'm open to suggestions and appreciate feedback.

[Ruskii]

When you say stinky exhaust - what kind of stink? Fuel, oil? If fuel, check plugs and coils. If oil, could be the OSV on the back of the intake.

[E30SCragtop]

When you say stinky exhaust - what kind of stink? Fuel, oil? If fuel, check plugs and coils. If oil, could be the OSV on the back of the intake.

It smells sulfur like. Not oil. Maybe fuel

[drinkingsnake]

Hy,
Sulfur stink is THE smell for a catalyst issue...;-)

With ratling noise on idle at cold start

Try to change them , perhaps...

Regards,
Chris from france

[NordmanMg]

Well, sounds like clogged or shattered cats, might need "new" headers (since they are one peace with cats)

[740iSport303]

Well, sounds like clogged or shattered cats, might need "new" headers (since they are one peace with cats)

If he is lucky it isn't the pre-cat in the header, but the primary just before the rear O2 sensor and resonator.

[E30SCragtop]

Sounds like the best option at this point is to have a mechanic look at it. What's the damage typically for new cats?

[Ruskii]

Any updates?

[E30SCragtop]

It was still kicking out O2 codes and my mechanic confirmed. I went to switch the two fronts to see if the problem followed the "bad one" and discovered a coolant leak. It appears that the coolant got onto the connector and shorted out the new O2 sensor. I replaced it and the code went away as well as the shaking and bad smelling exhaust but then three days later it returned. I don't have the O2 codes but still getting a P0174 (too lean).

I traced the coolant leak to the water pump and replaced it.

I just replaced the MAF too. So either it went bad or I have a vacuum leak somewhere. I've checked for it with no luck. May have to pay for a smoke test. My mechanic said it could be the MAF already going bad when I told him I bought the one that you remove from the sleeve and replace just the sensor instead of the whole thing.

Oddly enough the rough idle and sulfur smelling exhaust happens once the car is warmed up. On cold start it is fine.

[Ruskii]

I would try and hook up an OBDII scanner and try to read live data. It's interesting that the car is running fine when cold vs. when warmed up, so it may still relate to O2 sensors. Per my understanding, when car is cold, it's running on open-loop system, without taking reading from O2 sensors. Once it warms up, it starts to adjust fuel trims based on O2 data = closed-loop.

Were the replacement parts good quality or aftermarket?

[E30SCragtop]

Were the replacement parts good quality or aftermarket?

Yes, Bosch.

[E30SCragtop]

The saga continues and I'm totally confused. I continually get a P0174 code (System Too Lean) and often I will get a P1161 code (Fuel Trim Additive Bank 2 High). Once I clear the codes the car runs smooth again but only for a short time. On one occasion I got a P0145 code (O2 Sensor Circuit Slow Response). As mentioned I have replaced all O2 sensors and the pre-cat (upstream) bank 2 sensor twice. All parts are Bosch.

Could this be a injector?

[asianvenom]

Lean code is almost always related to vacuum leak.

[Ruskii]

Lean code is almost always related to vacuum leak.

Also check MAF.

I recently did TC guides, valley pan, intake, and all associated seals and still got P0174 code. Cleaned the MAF and my LTFTs were still in high teens and occasionally bank 2 would reach 20%. Replaced the MAF with the VW one and now my bank 2 LTFT is around -1%.

My bank 1 O2 might need to be replaced since now it's reading -7% (used to read 15% with the old MAF).

[E30SCragtop]

So I broke down and took it to my mechanic who confirmed that there are no vacuum leaks. He suggested it might be cats and also recommended a compression test.

How do you confirm if a cat is bad?

[koole39]

If it is just p0174 then it is bank2 only. These are cylinders 4,5,6 in the back. Did your mechanic check the fuel pressure? When was the fuel filter changed? I had this same issue just p0174, no other code and it turned out to be fouled injectors. Cleaning them up and a new fuel filter (mine was original) fixed the issue.

[E30SCragtop]

If it is just p0174 then it is bank2 only. These are cylinders 4,5,6 in the back. Did your mechanic check the fuel pressure? When was the fuel filter changed? I had this same issue just p0174, no other code and it turned out to be fouled injectors. Cleaning them up and a new fuel filter (mine was original) fixed the issue.

He did not check fuel pressure. FYI, I’m also getting P1161 as well.

While the exhaust smell would seem to point to the cats, there are no cat codes and when I clear the codes it runs smooth again for a short period. No nocking noise. No hesitation on take-off.

[E30SCragtop]

This thing just keeps getting weirder and harder to figure out. I have been getting a whole variety of different codes now. The latest is P0152 which is High Voltage on O2 Sensor. This is the new one that I have replaced twice. Inspected it this weekend and it had moisture around it so as a precaution I cleaned it up and made sure it stayed dry. Also checked the wiring to make sure there were no shorts or breaks and from what I can see it looks good.

Getting hesitation on take-off now which I never had before.

On two occasions it posted a P0492 (Secondary Air Injections System, Insufficient Flow) but that went away. I've also intermittently had P0159 (O2 Sensor Circuit Slow response) pop up.

The one that comes up the most is P0174 System Too lean

Is this plugs? Coils? injector? How do I figure this out?

[Ruskii]

Can you check your live data? Most of OBDII scanners should have that feature. Check your LTFTs for both banks. As I have mentioned previously, I had similar issue with P0174 code and it ended up being MAF.

Also see how the voltage fluctuates for the O2 sensors. If you had O2 replaced, maybe a fuse is shot or DME connector got coolant from Tstat and is causing electrical gremlins.