Help tuning M42 turbo w/ BEGI LC-1 and stock ECU

[bradnic]

Hi everyone

I bought a 91 318is M42 this summer that came with a Greddy TD04H-15G turbo, BEGI and 24# mustang injectors on it.  Using the stock ECU and hope to keep it that way.  I don't plan to exceed 6-8# of boost, so no stage 2/3, no large exhaust, no ARP studs etc.

I've taken it most of the way now to the point where it idle's well, pulls well, doesn't stall or overheat.  so great progress. Here's what I've done to the motor so far

- new CHRA as the old one was fried documented here
- LC-1 installed and O2 relay bridged per this install guide
- still pending is an oil pan swap as the PO welded in the return line tap too low in the pan.  car leaks oil constantly as a result.  new pan's already ordered.
- installed an LC-1 and fuel pressure gauge for the BEGI.  A basic AFR tune has been done by adjusting the AFM
- installed a custom 2.5" downpipe with magnaflow cat and muffler.  

Still using the integral wastegate+actuator that came with the turbo. I do have a kinugawa wastegate actuator with 5 springs, but have not installed it yet as i want the base tuning done first






Here's the present status
- idle fuel pressure is 45PSI
- AFM adjusted to 14.5 AFR
- car is idling at 800-900 RPM, but with vibration.  car stalled constantly before the AFM adjustment.  turned out per the LC-1 that it was set way lean.

Here's what the LC-1's reporting now when under load
- steady speed an RPM, no boost: 8-9 (very rich)
- boosted, accelerating: 18-22 (way lean)
- return to idle (like at a stop light):  goes lean 18-22, then settles back to 14.7 after 10-15 seconds
- LC-1 goes 'off line' when you take your foot off the gas (like it's maxed lean), then starts displaying readings again if you step on the pedal

Based on these readings I draw the following conclusions so far, but need advice from more experienced folks here

1) since the car's going rich off boost, I'm tempted to lean the AFM out
2) hopefully the idle will respond to the leaned out AFM setting and adjust back to stoich/14.7
3) for on boost the only thing I can do is mess with the needle valve on the BEGI

If (3) doesn't work then I will either increase fuel pressure at idle past 45 PSI or look into getting new fuel injectors.  I really don't know the condition of the mustang injectors as PO installed them and I haven't pulled or cleaned them myself.

Any/all advice sincerely appreciated

[bmwman91]

Hi bradnic,

Your fuel mixture issues are somewhat the result of trying to tune everything by messing with the AFM. It will cause an offset at all readings, meaning that if you tweak it to run rich to make up for more air coming in under boost, it will also be reporting more air flow at idle. My advice is to return it to its original position since it will at least be giving accurate readings then.

Most people that do turbo fuel tuning without a custom chip or stand-alone ECU seem to do it with a mix of larger injectors and an adjustable rising-rate fuel pressure regulator (ARRFPR). With the stock chip in there, the only way to get a good mixture when not under boost (idle & cruising) is to leave the stock injectors in there since it is mapped for those. If you have an ARRFPR in there, you should be able to set it so that it will keep increasing the fuel pressure as the intake manifold pressure goes above atmospheric. Although the stock FPR is a rising-rate one, I think that it maxes out when the manifold pressure is at atmospheric (14.7PSIA).

I have been told by the guys over at Metric Mechanic that the stock 19# injectors are good for ~205HP with stock fuel pressure. I am running 24# ones on my Rally 2100 engine now, but those also came with a custom chip. Anyway, assuming that your stock engine was making ~140BHP, at 8PSI you should be making around 216BHP with an ideal tune. You could try using stock injectors and then using an ARRFPR to set the max pressure to around 48 or 50PSI. That should really help the AFR under no boost, and hopefully get things leaned out a little better under boost.

How did things run before you messed with the AFM? Generally, you never want to mess with that.

[bmwconnect]

Hi bradnic,

Your fuel mixture issues are somewhat the result of trying to tune everything by messing with the AFM. It will cause an offset at all readings, meaning that if you tweak it to run rich to make up for more air coming in under boost, it will also be reporting more air flow at idle. My advice is to return it to its original position since it will at least be giving accurate readings then.

Most people that do turbo fuel tuning without a custom chip or stand-alone ECU seem to do it with a mix of larger injectors and an adjustable rising-rate fuel pressure regulator (ARRFPR). With the stock chip in there, the only way to get a good mixture when not under boost (idle & cruising) is to leave the stock injectors in there since it is mapped for those. If you have an ARRFPR in there, you should be able to set it so that it will keep increasing the fuel pressure as the intake manifold pressure goes above atmospheric. Although the stock FPR is a rising-rate one, I think that it maxes out when the manifold pressure is at atmospheric (14.7PSIA).

I have been told by the guys over at Metric Mechanic that the stock 19# injectors are good for ~205HP with stock fuel pressure. I am running 24# ones on my Rally 2100 engine now, but those also came with a custom chip. Anyway, assuming that your stock engine was making ~140BHP, at 8PSI you should be making around 216BHP with an ideal tune. You could try using stock injectors and then using an ARRFPR to set the max pressure to around 48 or 50PSI. That should really help the AFR under no boost, and hopefully get things leaned out a little better under boost.

How did things run before you messed with the AFM? Generally, you never want to mess with that.

The only thing I can add here is if you plan to run a RRFPR you should do a fuel line upgrade as they will be seeing a 100psi. I know from first hand experience what will happen to the stock lines and have a fire extinguisher handy if you don't upgrade. good luck!

[bmwman91]

Yikes! 100PSI seems way too high...at that point one should invest in a custom tune and bigger injectors! I do agree though, that one should replace all of the fuel lines before a project like this since 20 year old rubber seems like a time bomb.

The stock FPR is a rising rate unit. It just doesn't rise any more once the intake manifold pressure is about at atmospheric as far as I am aware.

[bradnic]

hey guys  thanks for the posts!!  lost track of the thread as I had some other stuff going on on e30tech.
will definitely replace the rubber fuel lines based on this feedback

current situation:

LC-1 installed
BEGi adjusted to 45psi with signal vacuum off
AFM tuned for 14.5 or so idle AFR
runs rich on accel (9-11 or so)
overheating on idle if you let the car sit still too long
check engine light now on steadily.
stomp test shows 1222 error, which I've read is probably related to a vacuum leak

I'm also still dealing with an oil return line leak too (PO tapped the pan too low - see 1st post).  
i have a replacement pan but need to be clear on what the fix needs to be - just higher?  
or - as I read somewhere but can't find now - a 2nd return through the oil sensor?)

[bradnic]

Hi bradnic,

Your fuel mixture issues are somewhat the result of trying to tune everything by messing with the AFM. It will cause an offset at all readings, meaning that if you tweak it to run rich to make up for more air coming in under boost, it will also be reporting more air flow at idle. My advice is to return it to its original position since it will at least be giving accurate readings then.

I'm leaning your way on this (no pun intended).  with the initial setting the LC-1 was reading way lean at idle though.  how do I reconcile this lean LC-1 reading, especially when the PO told me they messed with the AFM (see below)?  I have to believe what I'm seeing there right?

Most people that do turbo fuel tuning without a custom chip or stand-alone ECU seem to do it with a mix of larger injectors and an adjustable rising-rate fuel pressure regulator (ARRFPR).

that seems to be exactly what the PO did here.  He also told me he'd used a wideband O2 sensor to tune the AFM.

With the stock chip in there, the only way to get a good mixture when not under boost (idle & cruising) is to leave the stock injectors in there since it is mapped for those.

conversely, since my injectors have been swapped and I'm using the factory ECU, if the AFM's adjusted back to its original position It'll run rich at idle right?

If you have an ARRFPR in there, you should be able to set it so that it will keep increasing the fuel pressure as the intake manifold pressure goes above atmospheric.

yup that's my understanding.  I pulled the signal vacuum on the BEGI at idle and adjusted it to 45psi fuel pressure.  I then have been trying to tweak the needle valve to adjust the rising rate under boost.  Hasn't been working very well.

Although the stock FPR is a rising-rate one, I think that it maxes out when the manifold pressure is at atmospheric (14.7PSIA).

hence the BEGI..

I have been told by the guys over at Metric Mechanic that the stock 19# injectors are good for ~205HP with stock fuel pressure.

good to know!!!  Given the experience so far, this is a strong argument to just put stock injectors back in.

I am running 24# ones on my Rally 2100 engine now, but those also came with a custom chip. Anyway, assuming that your stock engine was making ~140BHP, at 8PSI you should be making around 216BHP with an ideal tune. You could try using stock injectors and then using an ARRFPR to set the max pressure to around 48 or 50PSI. That should really help the AFR under no boost, and hopefully get things leaned out a little better under boost.

Sold.

How did things run before you messed with the AFM? Generally, you never want to mess with that.

it never idled worth a damn.  there were lots of problems to sort through though including the charge piping, oil return leak, fried CHRA...  it's been an exercise in patience to sort through all this.

definitely going back to stock injectors and starting the tuning over from scratch.

[bradnic]

I have been told by the guys over at Metric Mechanic that the stock 19# injectors are good for ~205HP with stock fuel pressure.

.... assuming that your stock engine was making ~140BHP, at 8PSI you should be making around 216BHP with an ideal tune.

.... You could try using stock injectors and then using an ARRFPR to set the max pressure to around 48 or 50PSI. That should really help the AFR under no boost, and hopefully get things leaned out a little better under boost.

good to know!!!  Given the experience so far, this is a strong argument to just put stock injectors back in.

good M42 fuel injector info here that backs up bmwman91's comments

EDIT:   It turns out the car came with stock injectors after all, contrary to what the PO said.  I rebuilt and reinstalled them.

[mr ilia]

overheating on idle if you let the car sit still too long

fan shroud would help. It will pull the heat away from the radiator.

Not turbo related, but it looks like your a/c belt is not tight enough (post 1, pic 3)

[bradnic]

Not turbo related, but it looks like your a/c belt is not tight enough (post 1, pic 3)

yes car came that way.  started working on the a/c last summer but not done yet.  leaving it that way til the tune is stable.

as to the overheating, i found a crack and steam leak in the bleed screw hole on top of the radiator.  jb welded it.  also topped off coolant and bled the system.  temp seems to be ok now