The non existent vac leak

[spyderg0d]

I've been chasing a 27% idle stft and misfire on start up for a while on a yet to be road driven m54b30 on a x3 I purchased a few months ago. I installed New gaskets, hoses, cvv, valve cover, intake hoses and connectors, fuel pump and filter all 4 Bosch 02 sensors. I've checked and replaced a few coil packs and plugs.
Today I went through the entire intake and RTV'd every gasket and matting place to make sure I had 0 vac leaks!
Stillllllll 27% stft that goes 0 or far negative when I rev the engine.

My maf does read around 3gsec when at 700 idle and it does seem to respond correctly when revved.

For the love of all that is holy. Someone tell me what I may have missed! Lol

[MarcoZandrini]

What codes axis the engine computer (DME) throwing? The only way to find all the vacuum leaks is to professionally smoke test the intake manifold.

[R Shaffner]

And for some BMW engines, you need to smoke test the crankcase too.

Many of these CCV systems pull will try to pull a lot of air from the crankcase. A leak there can throw off the mixture at idle. What happens if you pull the dipstick when it's idling? Normally that will change the short-term trim and the idle. And you can feel the negative pressure at the tube opening.

If you don't notice those changes, that might be because you already have a leak into the crankcase somewhere else.

(Once I found a leak using the simple cigar smoke test method. It was from an old shrunken gasket on an upper timing cover of my M62TU.)

If the engine has an oil leak, that's the first place I'd look for air getting in, or smoke coming out.

[spyderg0d]

What codes axis the engine computer (DME) throwing? The only way to find all the vacuum leaks is to professionally smoke test the intake manifold.

It gets misfire code for any and all cylinders while the minute or so at startup, it's different ones everytime I clear codes and retest if not all of them. Those are as far as I get as everything else seems to be alright after it sets for a few seconds and clicks over to closed loop and runs smoothly. I'm running fresh gas with a fuel system cleaner treatment in it and it doesn't seem to making any difference.

I'm 100% there are no vac leaks in the intake.. every spot is sealed. I made sure with rtv.

[jclausen]

It’s probably not a vacuum leak, how old are the spark plugs, coil packs and fuel pump

[spyderg0d]

And for some BMW engines, you need to smoke test the crankcase too.

Many of these CCV systems pull will try to pull a lot of air from the crankcase. A leak there can throw off the mixture at idle. What happens if you pull the dipstick when it's idling? Normally that will change the short-term trim and the idle. And you can feel the negative pressure at the tube opening.

If you don't notice those changes, that might be because you already have a leak into the crankcase somewhere else.

(Once I found a leak using the simple cigar smoke test method. It was from an old shrunken gasket on an upper timing cover of my M62TU.)

If the engine has an oil leak, that's the first place I'd look for air getting in, or smoke coming out.

I haven't noticed any oil leaks at all. But I will inspect closely today.

I will also be doing a solid coolant bleed today as the vehicle came with leaking coolant hoses. *pray the engine doesn't have to be swapped.

[spyderg0d]

And for some BMW engines, you need to smoke test the crankcase too.

Many of these CCV systems pull will try to pull a lot of air from the crankcase. A leak there can throw off the mixture at idle. What happens if you pull the dipstick when it's idling? Normally that will change the short-term trim and the idle. And you can feel the negative pressure at the tube opening.

If you don't notice those changes, that might be because you already have a leak into the crankcase somewhere else.

(Once I found a leak using the simple cigar smoke test method. It was from an old shrunken gasket on an upper timing cover of my M62TU.)

If the engine has an oil leak, that's the first place I'd look for air getting in, or smoke coming out.

I haven't noticed any oil leaks at all. But I will inspect closely today.

I will also be doing a solid coolant bleed today as the vehicle came with leaking coolant hoses. *pray the engine doesn't have to be swapped.

[spyderg0d]

If I take the oil cap off, it does effect idle and will start small misfires until I cover it. Also will check the dipstick tube today.

[R Shaffner]

If I take the oil cap off, it does effect idle and will start small misfires until I cover it. Also will check the dipstick tube today.

That's good news. But if you can't find the cause of the trim issue, I'd still smoke test the intake and crankcase.

[spyderg0d]

I noticed my dipstick isn't exactly snug. It can wiggle alittle bit. I'm gonna put a new one ring on it tm. It can't be the whole 27%, but hopefully it is some of it.

[spyderg0d]

I also ordered a new maf, just incase.

[MarcoZandrini]

There are 2 IIRC o-rings on the dipstick. Replace them and see what happens.

[spyderg0d]

I changed the o ring, to a not perfect fitting one. So I ordered one. I also for giggles unplugged the maf... suddenly my stft went down and misfires disappeared. Not sure if it indicates the maf was bad, but it sure runs better without it. Now my stft roam wherever they want from 15 down to 0. My ltft stay between 23 and 28, fluctuating along with the stft... not sure if the exhaust leaks would cause this, or the possibility of bad converters.

I don't get any white smoke like a it's eating coolant, and just now was the longest its ran for me to partially bleed the cooling system and have it continuously run without overheating. I see cats aren't that expensive, il probably put new cats in anyway. New maf should be in within a few days.

[Muzz258]

Arh the old "Unplug the MAF trick". You have to be careful with that one.

If you have vacuum leaks, the DME runs on internal mixture tables with the MAF unplugged and will mask the vacuum leaks. The internal mixture tables are rich at idle and offset the lean of the vacuum leaks.

The "Unplug the MAF" test is only valid for checking the MAF if and only if you have sorted all problems with the fuel system and vacuum leaks. Basically anything that normally causes a lean condition.

An exhaust leak before the pre-cat O2's will give you lean codes. The leak will not be found with the standard smoke test of the intake.

Blocked Cat symptoms are:
- P0420 or P0430
- High Lean fuel trims at idle followed by high rich fuel trims when at highway speeds
- Hot idle MAF reading is low e.g. 3.0 g/s or less for the M54B30.
- Reduced performance from the engine

[spyderg0d]

Arh the old "Unplug the MAF trick". You have to be careful with that one.

If you have vacuum leaks, the DME runs on internal mixture tables with the MAF unplugged and will mask the vacuum leaks. The internal mixture tables are rich at idle and offset the lean of the vacuum leaks.

The "Unplug the MAF" test is only valid for checking the MAF if and only if you have sorted all problems with the fuel system and vacuum leaks. Basically anything that normally causes a lean condition.

An exhaust leak before the pre-cat O2's will give you lean codes. The leak will not be found with the standard smoke test of the intake.

Blocked Cat symptoms are:
- P0420 or P0430
- High Lean fuel trims at idle followed by high rich fuel trims when at highway speeds
- Hot idle MAF reading is low e.g. 3.0 g/s or less for the M54B30.
- Reduced performance from the engine

I've been through the intake. There's no possibility for vak leak in the intake unless the disa diaphragm is bad.lol. every hose and gasket is new from the valve cover to the intake gasket. Even put on new valve cover and many hoses, boots, cvv system. And every thing that isn't new was checked, good o ringed, AND rtv'd to make sure it didn't leak.


With the symptoms of clogged cat you list, it does bare resemblance. So I can't rule it out until new maf is tested positive results

[MarcoZandrini]

Like I’ve written above, you need to professionally smoke test the intake manifold. Unplugging the MAF masks vacuum leaks.

[spyderg0d]

Tried a used maf today. It reads up in the 5.6g range when at 750rpm. .. which seems high compared to the supposed proper reading around 3.4g at 700. ..

The engine didn't misfire at all when started. But...
The stft are negative 16 and negative 13 while the ltft were both positive 21.

[harrier]

You need a new MAF. That is too low a reading at idle, and you have dealt with the usual suspects. Normally MAF causes high fuel trims at idle and cruise, however.
And the only rtv this engine needs is a tiny amount on the oil pan and valve cover. Everything else should seal without it.

Did you check the SAP hose behind the manifold and the caps on the manifold nipples?

[harrier]

The LTFT/STFT readings you are getting are consistent with adaptations re-adapting. Give it a few days.
BTW, my MAF comment was from the first post.

[spyderg0d]

The LTFT/STFT readings you are getting are consistent with adaptations re-adapting. Give it a few days.
BTW, my MAF comment was from the first post.

I only used rtv as a sure fire check for any intake leaks. I made sure to check the 3 nipple on the back of the intake by the brake booster as I've been through this rodeo before on the family 03 325i. Lol.
Which is also why I'm so sure I font have any intake vacuum leaks.
After letting the new/used maf run on the car for a bit the g/sec do seem to settle around 4.6 to 5.6 when at 700ish rpm, but that said, the reading floats around quite a bit. . I'm not convinced it's proper working condition and still in search of a good one.

I will run and drive the car a bit tomorrow and monitor the fuel trims. It certainly runs smoother with the second maf,. But the stft run to 0 when I rev it now. But, I guess you could be right. I'm just happy it drives at all at this point! As soon as i can get am appointment for the dmv and get plates, it will get a proper smoke test.

[Muzz258]

The 4.6 to 5.6 g/s hot idle MAF reading is really high. Are you getting double digit negative (rich) total fuel trims (SFTF + LTFT) at highway cruise?

[spyderg0d]

The 4.6 to 5.6 g/s hot idle MAF reading is really high. Are you getting double digit negative (rich) total fuel trims (SFTF + LTFT) at highway cruise?

Can't drive highway... waiting for dmv to have an available slot for appointment to get plates.. at idle stft float around negative 20 while ltft are positive 20.

[spyderg0d]

Drove it up and down the driveway about 10 times and the fuel trims all cut in half! Yeeeeee boiiii! If they cancel each other out my ltft will be less than 3%!

[spyderg0d]

Solved. Turned out it was indeed a bad maf. My maf reading at idle roam around a 3.6 to a 4.0 at 700 idle. Not from 3.2 to a 3.6 like the old maf. Which leads me to believe these are the more accurate readings for a proper maf. Double verified with near perfect fuel trims.