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It depends on the cause and the mileage on the car.

If you're on, like, 120,000 miles or less then there is likely another cause that has damaged the Cat's. I haven't had to dig into this issue much, but burning a lot of oil seems to be one cause.

If you're on more than 200,000 miles, then it could just be old age.
 

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Discussion Starter · #42 ·
It depends on the cause and the mileage on the car.

If you're on, like, 120,000 miles or less then there is likely another cause that has damaged the Cat's. I haven't had to dig into this issue much, but burning a lot of oil seems to be one cause.

If you're on more than 200,000 miles, then it could just be old age.
currently its on 161,000 I guess that is probably about right then, I did have an issue where it was burning about a litre of oil per 1000 miles. That may well have killed them off
 

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Discussion Starter · #43 ·
NZ00Z3
Sorry to keep asking you questions but it keeps bugging me, if the cat is blocked why does the misfire go away one the car is warmed up ? is it down to the fact that the pressure builds up so much that it forces its way through ?
 

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Here is a cold start fuel trim profile. The fuel trims are made rich by the DME to add in starting a cold engine. Lets call it 5% cold start enrichment.

Your engine is running rich. With the extra 5% cold start enrichment, the fuel trims become too rich and this causes mis-fires. As the engine warms up, the DME removes the cold start enrichment and the fuel trims come back into the range that does not cause mis-fires.

I've just published a lot on my data logging reading secrets. Have a read. How To Read OBD2 Engine Diagnostic Logs

Rectangle Slope Font Parallel Plot
 

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Discussion Starter · #45 ·
Here is a cold start fuel trim profile. The fuel trims are made rich by the DME to add in starting a cold engine. Lets call it 5% cold start enrichment.

Your engine is running rich. With the extra 5% cold start enrichment, the fuel trims become too rich and this causes mis-fires. As the engine warms up, the DME removes the cold start enrichment and the fuel trims come back into the range that does not cause mis-fires.

I've just published a lot on my data logging reading secrets. Have a read. How To Read OBD2 Engine Diagnostic Logs

View attachment 949620
Thanks for explaining that - a bit like a "choke" on older carburetor stuff - I forgot it would run rich for the start up.

I'll have a read of your thread

Many thanks for your help.

I'll update you once iv done a cold start with the o2's pulled out
 

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Discussion Starter · #46 ·
I decided to check my fuel pressure today - got a pressure gauge from work - car primes to 50psi - however after 10/15 mins had dropped down to 30psi, from what I gather this is to do with the check valve (built into the fuel pump on these I think) - other thing i thought would be worth checking is the fuel injectors for leaks

after this I thought I would check the running pressure this came up at 55psi consistently - is this over pressured ? i read spec is 50psi - will that 5 make a huge difference ?
 

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All engines except the S54 and the M56

  • Fuel pressure 3.5 +/- 0.2 bar or 50.76 +/- 2.9 PSI
  • Residual fuel pressure after 20 minutes - Fuel pressure >3 bar or >43.51 PSI
Testing is done with key in position 2 and the engine off.

Don't think the extra 1 PSI is going to be a problem. Likely gauge error anyway.

Too much pressure would cause rich fuel trims. Is that what you have?
 

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Discussion Starter · #48 ·
yes it was pulling like 8% fuelling when you did the graphs for me
I think we narrowed it down to cats - I haven't taken the o2 sensors out yet to check this for back pressure due to driving to work every day so will done this weekend job.

one of the techs at work said it would be a good idea to rule out fuelling as a potential issue and handed me a gauge so though might as well
 

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OK, Your in the UK, so you'll be running E10 as standard fuel or E5 if you're getting Shell VPower. Fuel makes a difference in the acceptable range for total fuel trims.

Below is a table I put together recently. If you are on E10, then -8% rich total fuel trims are outside of both the "Normal Running" and "Problems to find" ranges.

Your -8% + 4.5% E10 lean off-set = -12.5% rich total fuel trim. Would 1 or 2 PSI too much fuel pressure cause this amount of rich condition?
The +/- 2.9PSI margin in the fuel pressure test = +/- 5.7% of the 50.76PSI target pressure. 55 PSI is 8.4% too much pressure. It's getting close (2/3) to the -12.5% rich trims.

The DME is pulling fuel to lean out the mixture to the correct level. The Cat's are seeing a corrected exhaust flow and not a rich exhaust flow. The Post-Cat O2 sensors are showing lean blocked Cat problems. I can't see how the extra fuel pressure is causing the Post-Cat signals as any impact has already been removed by the DME pulling fuel?

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Discussion Starter · #50 ·
Ok thanks that makes sense - of course the o2's are only going to see the effect after the fuel is being removed by the computer. anyway I think I need to man up and accept that the cat will be the likely cause of the rich running. I will try to confirm at the weekend

With the fuel pressure continuously dropping after the ignition is turned off I think it was down to 30psi after 10/15 minutes, Do you think injector could leak this much in that time or is the check valve the likely culprit ?

I was under the impression it would drop slightly then settle as you mentioned to about 40ish psi ?
 

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The Fuel can only escape in two directions:
  • Through the injectors. You would need multiple injectors spread over both banks to drop the fuel pressure and also dripple when running to produce your rich fuel trims. If you are worried about this. Pull the injector rail out of the manifold. With all injectors installed correctly into the rail, prime the rail with fuel pressure by turning the key to position 2. Watch for dripples/sprays from the injectors.
  • Through the non return valve back to the tank. It is is not causing a hard to start condition, then live with it. Otherwise, change the fuel pump to get a new non-return valve.
 

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Discussion Starter · #52 ·
The Fuel can only escape in two directions:
  • Through the injectors. You would need multiple injectors spread over both banks to drop the fuel pressure and also dripple when running to produce your rich fuel trims. If you are worried about this. Pull the injector rail out of the manifold. With all injectors installed correctly into the rail, prime the rail with fuel pressure by turning the key to position 2. Watch for dripples/sprays from the injectors.
  • Through the non return valve back to the tank. It is is not causing a hard to start condition, then live with it. Otherwise, change the fuel pump to get a new non-return valve.
Checked injectors today the don't seem to be leaking,

I did pull both pre cat o2s before starting - car ran okay there was a slight misfire every few seconds - is this just due to the fact the computer has no data from the precats to go off ?
puts me off cattless headers a bit as it sounded horrendous
 

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Discussion Starter · #53 · (Edited)
Hi guys. Just did an exhaust back pressure test at the pre cat o2's not even half a psi at idle and maybe 1psi or just over at 2500 rpm
Same on both banks

I did notice it was misfiring I assume because no o2's were plugged in after disconnecting the maf the missfire stopped but I'm sure that's because it has no data from the o2s to go off
 

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That's a good result. Cat's are expensive to change. One item eliminated.

The Bank 2 post-cat sensor must be flat lined due to a bad sensor.

Can you please run a cold start log and post the log. I want to check your Pre-Cat O2's

  • Cold start. Key in position 2, don’t start the engine. Connect the logger, then start the engine. Run the log for 5 minutes. Don’t rev the engine, just let it idle.
 

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Discussion Starter · #55 ·
That's a good result. Cat's are expensive to change. One item eliminated.

The Bank 2 post-cat sensor must be flat lined due to a bad sensor.

Can you please run a cold start log and post the log. I want to check your Pre-Cat O2's

  • Cold start. Key in position 2, don’t start the engine. Connect the logger, then start the engine. Run the log for 5 minutes. Don’t rev the engine, just let it idle.
Okay that's a relief. Just been out in the car so I will let it sit for a few hours and post a log this evening.
 

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Discussion Starter · #56 ·

Here is a 5 min cold start ( car was left for about 4 hours(dosnt normally miss fire unless left for about 7ish hours or more) might have to leave over night and try again let me know if this is any good

I did notice the fuel trims were pretty much zero on the cold start however after about 30 mins of driving they are now back at -7 for bank 1 and -8 for bank 2
 

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any ideas why the Maf was reporting loads of air initially ?
15g/s is not uncommon for a dead cold start.

I'm having a hard time coming up with a probable cause to your problem. Changing the MAF is the next best guess and it's a guess. See the bottom of this post.

15 April cold start.
  • Engine at 44C when started, so not totally cold.
  • The SAP is not commanded to operate.
  • Engine running on E10, so 0.75V is normal max O2 voltage. The Pre-Cat O2's are switching higher, which indicates a rich mixture.
  • Fuel Trims charts shows the typical cold start profile with it running rich, expect it is offset richer than expected for E10 fuel.
  • Pre-Cat O2 sensors are heating during fuel status 1, open loop. They heat rich. This is typical of a partly hot, cold start, where the SAP does not operate. Remember that the fuel trims during open loop are just the last recorded LTFT and do not represent the mixture, so the O2's are your only clue.
  • Everything is saying that you have a rich mixture, which is your problem.

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16 April cold start
  • Engine at 16C, so it's a true cold start.
  • SAP is not commanded on. Does it have a SAP?
  • The Pre-Cat O2's heat and trend lean. This is typical for an Engine without a SAP (reference engine is a M54B30/MS43 without SAP from factory).
  • Remember this engine has new Pre-Cat O2's.
  • On going to closed loop, the DME goes straight to fuel status 8 (not 2 for closed loop). 8 = Pre-Cat O2 sensor fault. The sensors are new, so, it is assumed that they are telling truth and the DME is reacting to the large difference in their signals and that they are not switching.
  • Bank 1 O2 sensor flat lines to near 0V indicating a very lean condition.
  • Bank 2 O2 sensor shoots above 0.9V indicating a very rich condition. Then over nearly 50 seconds, it trends down then drops to around 0.05V indicating a very lean condition.
  • The fuel trims start at the last recorded LTFT during open loop. This is very rich. Remember that this does not represent the mixture at that time.
  • On switching to fuel status 8, the fuel trims drop back to 0% almost immediately. Researching old logs, shows that depending on the DME, when the fuel system goes to status 8, the fuel trims either trends to the last recorded LTFT or to 0%. So, that Fuel trim activity is normal.
  • What is not known is how the DME controls the mixture during fuel status 8? It is assumed that the DME:
    • Has a set of tables that it uses.
    • These tables have no mixture adjustment, as the pre-Cat O2's are ignored
    • So, with a tank of E10, is the 4.5% E10 lean offset enough to suppress the Pre-Cat O2's to a flat line very lean level? I'm guessing yes.



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The mystery. What causes?
  • Rich trims on both banks with working Pre-Cat O2's at hot idle and cruise?
  • Both banks to be rich with Pre-Cat O2's working correctly on partly warm cold start?
  • Bank 1 to be very lean on cold start?
  • Bank 2 to be very rich on cold start, then over 50 seconds become very lean?

I would normally say that the Pre-Car O2's are the problem, but they are new?
The MAF has been checked and it's not causing rich conditions. If anything it's under reporting which causes lean conditions, so it could contribute to the very lean cold start condition.
Fuel pressure has been check and it's good.
Cat's have been check with back pressure test and they are good.

What has not been done?
  • The MAF has not been changed. Considering the misfires only happen a cold start, the very lean mixture at cold start and that the MAF is under reporting at idle, make this the next step.
  • Smoke test to check for vacuum leaks. Only lean at cold start which could be a vacuum leak, but rich the rest of the time, which could be another cause.
  • DME removed and connectors checked for contaminates (oil, coolant). Oil contamination in the 3rd connector counting back from the firewall has been know to cause rich conditions.
  • Flashed the DME with the latest version of software for the car's spec. This removes the possibilities of a custom tune or a corrupted tune.
  • Unplug the MAF and run the 3 standard logs. This test should only be done after a smoke test and all vacuum leaks fixed. There is a known expect result with only the DME and pre-cat O2's in play. With the new Pre-Cat O2's, this test would be looking at the DME.
Time Invested
Surprisingly, it's taken me 4 hours today to spreadsheet 2 logs, research other logs and write up this post. It's been a brain tester.
 

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Discussion Starter · #59 ·
Thanks NZ00Z3 I really appreciate your help.

That post has laid it out nice and clearly for all to understand the process of checking these faults.

No Sap on this car. I'm not sure if we got them in the uk I had a 2004 330ci before which did not have one either.

I'm starting to wonder if there are 2 problems here, maybe a vaccum leak that I missed to cause the cold start missfire, Maybe somthing else is causing the running rich.

The thing that is bugging me at the minute is the o2 pilot mod.

Now i was scrolling through the forum yesterday and saw someone mention oil consumption and o2 pilot mod.
Lightbulb went off in my head,
For the first 4 months on ownership this car drank oil at a rate of somewhere between half to 1 litre of oil per 1000 miles.

I came across 50s kids video on the o2 pilot mod and decided I would give it a try as I was fed up of going through a liter of oil on a fortnightly basis.

Now once I installed the vaccume line I have noticed pretty much zero consumption I think I topped it up once in the past 9 months -with the exception of an oil change.

I do however recall that the missfire started to happen around about this time. At this point in the UK we were getting some negative temps in the morning so I put it down to this for a few days not thinking anything of it.

I have been racking my brain trying to remeber if the miss fire happend at the same time as the mod or if it was after/ just a coincidence.

I hooked up the line to the "exhaust flap" port - quotations because my original exhaust did not have a flap and there was a cap over the port. I am now thinking this port has to increase/decrease in vaccum to function the flap in the exhaust so this vaccum would also apply to the ccv now. Should I have used the larger port in the back of the manifold instead ?

Is there any possible way this could be a cause - I will remove it anyway today just to clarify that this is or is not the problem.

My thinking is if a vaccume leak causes a lean right ?
Could a gain in vaccume not push it in the opposite direction and cause a rich condition ?

Could this be there rich running issue and the cold start be somthing else ?

Sorry for the long post
In hindsight putting I installed o2 pilot mod oil ,consumption now none would have sufficed
 

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I've seen other cases where the O2 pilot mod has caused rich fuel trims.

Is the root cause of your oil consumption problem carboned up oil control rings on the pistons or a faulty CCV?

How would adding extra vacuum to the CCV stop oil bypassing the carboned up oil control rings? There have been a couple of recent threads on soaking the pistons or running cleaner through the fuel to clean the carbon deposits off the pistons etc. Do some research.

If the CCV oil return tube is blocked, or the dipstick tube section of the oil return is blocked, the returning oil would have nowhere to go, so it's off up the CCV system to the inlet manifold. How would the O2 pilot mod fix this. @Sapote and @The_Fixer what is your experience with the O2 piolet mod?
 
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