Help finding possible Vacuum leak...

[Titansilber]

I have been getting fuel trim adaptation cel's for a little while and I think I have narrowed it down to a possible vacuum leak. The cel's are triggered at idle where my STFT are the most negative. Thus, I am running very rich at idle. My vacuum/boost gauge registers roughly -12 at idle, -16 to -18 under engine load off throttle. Should be (-) 18-20 right?

I am trying to check all vac lines, but maybe I am missing something. all clamps seem to be tight, oil breather cups seem ok, icv hose seems ok. I shot some carb cleaner around possible suspect areas and didn't notice a throttle bounce. Any suggestions?

[NickG]

A vacuum leak will allow unmetered air into the system, causing the trims to go POSITIVE to keep up with the extra air. Unfortunately, the STFT value that you see isn't all that helpful. What you need to see is the additive adaption value that the DME is using. That can only be read with a BMW specific diagnostic tool (not a generic OBD2 scantool). That value will tell you what is really going on with the fueling at idle.

[Titansilber]

Thanks for the quick reply. As for the additive adaption value that the DME is using, do you mean the long term fuel trim? What then, do the fuel trim values mean on the scantool, if the DME uses different values?

Just based on the scantool, my:
LTFT's are -5.5 (B1) & -8.6 (B2)
STFT's are -22.6 (B1) & -19.5 (B2) @ idle

Being that my vac reading on my boost gauge is so low, does that still suggest a vacuum leak?

Assuming that I am indeed running rich, what else could cause that? Especially at idle....

[NickG]

Thanks for the quick reply. As for the additive adaption value that the DME is using, do you mean the long term fuel trim?

No, the LTFT is something different (called multiplicative adaption in BMW-lingo).

What then, do the fuel trim values mean on the scantool, if the DME uses different values?

The OBD2 protocol doesn't allow you to see ALL of the adaption values, that's all. You can only see SOME of them.

Just based on the scantool, my:
LTFT's are -5.5 (B1) & -8.6 (B2)
STFT's are -22.6 (B1) & -19.5 (B2) @ idle

Values that negative means the fueling is too rich, and the ECU is trying to remove fuel to bring it back to stoich.

Being that my vac reading on my boost gauge is so low, does that still suggest a vacuum leak?

Yes, it could.

Assuming that I am indeed running rich, what else could cause that? Especially at idle....

A sticky lifter or a leaking (non-closing) valve. Did you overrev the engine recently? Or did the previous owner overrev it?

[Titansilber]

Yes, being to rich was my conclusion as well. Sounds kind of funny, but I guess I could two problems causing both lean (vac leak) and rich (valve/lifter) conditions.

I have no knowledge of an overrev. Other than hitting the rev limiter a few times on acceleration I don't I have dropped a wrong gear to overrev. How might I diagnose "A sticky lifter or a leaking (non-closing) valve"? I have noticed a slight ticking noise twice, but both times my oil level was kind of low. After adding oil, no more noise...

Could it be an injector problem? With my stage 1 kit I only have 24 lb/hr injectors. I believe this rating as at 2.5 bar though, so I am guessing I am closer to 28.8 at 3.5 bar....

BTW, my car seems to perform well and idles smooth (without the stalling/bouncing idle problems a usual vac leak would cause). I just get that CEL, which worrys me, plus I can't pass DEQ (smog) with it.....

[paul e]

Do you Hear anything reminiscent of a leak? Ive heard variously Moo Cow moans, and Snakes Hissing, all having a party under hood at various times. Those are often dead give aways.. Just make sure to corral them before the Snakes kill the Cows, and leave Meadow Muffins all in your Engine Bay!

[Titansilber]

Nope, no farm animal sounds :

At least none that I can hear over the engine/sc noise. That is really the problem, no tell-tale signs such as noise or shakey idle. Once or twice in traffic the idle has bobbed up and down for a few seconds is all I can remember. Plus the vacuum reading at idle....

[paul e]

>>Thus, I am running very rich at idle. My vacuum/boost gauge registers roughly -12 at idle, -16 to -18 under engine load off throttle. Should be (-) 18-20 right?<<

Is the only sign that leads you to think youve a vacuum leak the -12 vacuum reading at idle? That would have me concerned also.. I think 17-21 inches is considered 'normal'. I read about 19 at idle, for instance. Are you saying your reading just 12" at idle?

[Titansilber]

Well until NickG posted I was sure that a vacuum leak could contribute to my rich condition. I got this impression after searching a bunch of threads along with talking to Marco.... Plus my vacuum reading at idle which is pegged at 12. Any other problems that could cause this?

[Titansilber]

I found this a minute ago.

"The fuel pressure regulator vac line leaking would make it run rich at idle and not so rich at WOT"

Could this be the culprit, or maybe the fpr itself?


(http://forums.bimmerforums.com/forum...ight=rich+idle)

[paul e]

>>Plus my vacuum reading at idle which is pegged at 12<<

Wouldnt the usual causes of such a low vacuum reading be just as oftern searched for inside the engine, as well as looking for vacuum leaks? Imagine a small cut in a hose, or a leak at a vacuum hose clamp. Under vacuum, ie, at idle for instance, extra air will be pulled from outside the hose or leaky clamp into the engine, contributing to a lean tendency. The ECUs response will be to Jack UP the fuel with greater Positive LTFT values. The result, once you go Open Loop, will be to add those relatively postitive values to your wot maps, leading to added richness. But the cause of the 12" vacuum is what needs to be found, as you know. Good luck, and let us know what the cause was.

[Titansilber]

Yes, that makes sense Paul... So maybe I have more than one problem. A vacuum leak, plus some other problem causing my richness a idle. Man, this stuff is so difficult to diagnose. Thanks for your guys' help so far....

[NickG]

I found this a minute ago.

"The fuel pressure regulator vac line leaking would make it run rich at idle and not so rich at WOT"

Could this be the culprit, or maybe the fpr itself?


(http://forums.bimmerforums.com/forum...ight=rich+idle)

Yes, that's very possible. A vacuum leak on that line would cause the gauge to show less vacuum. If it's such a large leak that the FPR can't get an accurate signal, then it will increase the fuel pressure causing the mixture to go extra rich.

[Titansilber]

After paying really close attention to my boost gauge I noticed that at cold start idle for maybe 30 sec the boost gauge is 7 psi vacuum and then jumps up to 12 psi vacuum from then on at idle. Anyone know why this could be?

BTW, I am planning to do a really thorough inspection, by taking apart all the sc discharge tubes and TB. I am not looking forward to this as I have done it before and reassembling everything is like doing a rubix cube. :

Should I be able to get the ICV out without messing with the intake manifold? Is this a standard sized hose if it needs replacing? What about fpr hose? The tough thing is that this is my daily driver, so it can't be out of commision for too long, plus trips to the parts store for hoses, etc are a bit tricky....

[DocWyte]

Damn, that's not alot of vacuum. When I was at sea level I'd see 18-19 inches of vacuum at cold start, going to 20-21 inches once warm. Once the motor warms up, things seal up a bit better, hence more vacuum when warm.

Even up here at 5000 ft above sea level I still see 17 inches of vacuum.

You either have one heck of a leak, or a failing motor...

[BenzTech]

Check your map/baro sensor

[slvr98 M]

Can you tell me what you have, SC or TC. And if so which name brand and type setup.

[Armo95]

Can you tell me what you have, SC or TC. And if so which name brand and type setup.

"Blown M3" so I'm assuming he's supercharged...

[Titansilber]

Yeah here is some information:

1997 M3
RMS kit with Vortech V1 SC
6" crank/3.60" sc pulleys
24 lb/hr injectors (not sure at what bar, maybe flowing 28.8 at 3.5 bar)
No aftercooler, but stage II RMS software
ECU not solder socketed for easy chip swap (checked last night)

Oh and BTW, when I said below that at cold start the vacuum is at 7 in hg then it settles at 12 in hg at idle, it does not do that gradually over 30 sec. I turn on the car and starts idling (vac @ 7), then at some point, all the sudden, it jumps to 12, as if a switch is turned. The idle smooths out slightly at that moment as well. I know both 7 and 12 is too low either way. Also, I did notice that my boost gauge reads 3 psi when the car is off. Does that make sense?

[Titansilber]

Found out part of my problem, kind of dumb, but my boost gauge was faulty. I put a new one in there and I am running 20 in hg at idle, right on the money. 7 psi at 6500, seems about right for my stage I rms kit.

I am getting some 28.8 injectors, as my current Bosch injectors may or may not be compatible with my setup. Hopefully that, or some simple software adjustments will cure my CEL.

[Scho]

Found out part of my problem, kind of dumb, but my boost gauge was faulty. I put a new one in there and I am running 20 in hg at idle, right on the money. 7 psi at 6500, seems about right for my stage I rms kit.

I am getting some 28.8 injectors, as my current Bosch injectors may or may not be compatible with my setup. Hopefully that, or some simple software adjustments will cure my CEL.

Was it an Autometer???

[Titansilber]

You betcha. I have heard that they fail often. My buddy had an extra one, so I am using another autometer for now. Maybe in the future I'll get one VDO or Defi. These look pretty cool and seem to match BMW lighting well:

http://www.defi-shop.com/product/dg/dg_top.html

[Scho]

If you want some really nice gauges, try Spa Technique.

CDOC and bimmerworld sell them.

[ipharaoh]

hello every one, a friend of mine just bought E39 BMW-1999 One Year ago, and her check engine light was flashing last night, she said RPM was slightly increasing and decreasing. No limp mode. she drove the car home, i picked up my x431 lunch diagnostic tool and i came with errors codes (Mixtures adaptation long term Bank1) - (Mixture adaptation long term bank2) anyway, i did some testing for (additive bank1) And (additive bank2)
and this was the figure values.
------------------------------------------------------------------
Mixture adaptation -0.51ms long term (additive) Bank1
Mixture adaptation -0.56ms long term (additive) bank2
Short term ( -2.10% Multiplicative) bank1
Short term ( -1.09% multiplicative) bank2
Throttle position. IDLING
O2 sensor signal 0.078 V B1 sensor 1
O2 sensor signal 0.732 V B1 sensor 2
O2 sensor signal 0.156 V B2 sensor 1
O2 sensor signal 0.737 V B2 sensor 2
------------------------------------
Power supply. 14.07 V
Coolant Temp. 92.44 C
Air mass sensor. 10.50 Kg/h
Intake air temp. 45.2 C
------------------------------------
i don't know if these values is correct according to the BMW specifications.????
she also said her car using more fuel than before.?
any help please please.
sorry for my bad English language.