E36 Turbo, questions about scaling for larger injectors

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Revdperformance
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Joined: Tue Aug 30, 2022 9:50 pm

E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

Hey guys,

so just a quick question here.

I have a bmw 325is here, automatic. Weve set it up with a turbo, with very low boost. 6 psi. Small ebay t4 size.

i have 36lb bosch injectors replacing the stock ones.

So, i have come up with a correction factor of 0.44. 16/36= 0.44

0.44 x 43478= 19323

So, that gets me my constant. It runs very rich on start up, and as such have been reading i need to scale all of the load axis of the tables to the same 0.44 factor? So does that mean i make the numbers in the load axis smaller? I can take care of most of this, i just need to understand what scaling needs to take place

Should i be able to use a stock maf curve? i have the maf pre turbo, with a bend between the maf and turbo. Ive extended the wiring as the turbo is low mount, and far from original position

Thanks in advance.

Evan, Rev'D performance
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

Have a look at this post which includes tunes you can download to see firsthand how to account for 24lb injectors: viewtopic.php?f=33&t=110

Apply the same principal to your injectors and everything should work as expected. Also take note in the post that this scaling factor is just a starting point. You'll need to adjust the scaling as necessary to get it perfect.
Revdperformance
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

Absolutely, i realize it will take some working. ill check that out right now

So, just to be clear, if i use the factory maf, even tho its in front of a turbo, it should still meter the air the same way (makes sense, just want to be clear)

So, ANY table with engine load (ms) basically needs to be scaled if im thinking correctly.
Revdperformance
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

yep, i see what youve done. exactly what i figured. Each load axis was more or less (some different by a small amount, im assuming this was tweaking) changed by selecting the axis in full and multiplying it by the correction factor used on the injection.

So, using a stock maf calibration, and scaling all of this, as youve said, i should be able to start it and have it behave.

Since there is no target lambda that i can see, i assume i tune the WOT and PT tables to get whatever i want for afr?

thanks guys, appreciate it
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

As the post states, EVERY axis which is engine load and EVERY parameter which is engine load itself needs to be scaled by whatever you scaled the injector constant. Don't "tweak" the individual axis values. Instead, "tweak" the value you've scaled everything by until you're happy with global A/F ratio. Once you're happy, then don't touch the injector constant or any of the load axes/parameters again. Only make further tweaks to the fuel tables (main part of the map, not the axes).

Otherwise, your understanding is correct! Be careful because you may max out the stock MAF, even if you have it installed in a "draw through" configuration.
Revdperformance
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

Okay, i think ive got it

i will likely upgrade to the maf youve mentioned in another thread, and use that calibration

So, question on this one, what occurs when i max the maf out, just hit 5v and it defaults to alpha n? Or will it just continue to use the last value of load in the calibration? just want to know what im dealing with. (=

thanks again
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

It will continue to use the last value of the MAF calibration curve regardless of how much airflow is passing through the sensor. This is obviously not a good situation because the DME will think the airflow is constant and will calculate engine load accordingly. The fuel it thinks the engine needs will also become constant when in reality airflow continues to increase. This will lead to a lean situation eventually.
Revdperformance
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

yeah that seems to be the usual failure mode. Definitely not ideal.

Ive been using my obd2 scanner to watch the maf voltage and its been around 4.8v ish.. hopefully it stays there (=
Revdperformance
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Joined: Tue Aug 30, 2022 9:50 pm

Struggling with scaling, 36lb injectors, turbo, maf on turbo inlet

Post by Revdperformance »

Hey guys,

I need a bit of help here, im struggling to make this car behave.

Its an e36 with 36lb bosch injectors, small turbo, intercooler, using stock maf, and basically stock everything else.

Ive scaled the injector constant by 0.44 (16 divided by 36) as well as every other load axis of every table as you advised.

With that scaling, i start the car, and its 10:1 afr, when it warms up its a bit better but not by much.

I remove fuel from the idle fuel table, and tweak the coolant based tables to get it pretty decent.

It will be sitting, idling at 14.7:1. Ill do some part throttle, maybe a pull to see whats up, and all of the sudden itll be 18:1 afr and struggling at idle. The temperatures are remaining pretty constant (around 91c for coolant temp). Could it be one of the undefined load based tables at the bottom playing up? Im just not sure what to do. Ill also have the afr pretty good. etc and then the next day start the car and its 10:1 afr again......

thanks in advance

Evan. Rev'D Performance.
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

Moved this post along with the others you asked regarding the same question to keep everything consolidated.

If it runs really rich on startup, have you tried tweaking your scalar to globally reduce fuel everywhere? Again, this simple division is just a starting point because you're assuming your injectors are flowing exactly 36lb/hr. Have you flow-tested your exact stock injectors and your exact new injectors to confirm actual numbers? If not, you'll have to iterate on this scalar until you get closer to stoichiometric.

When we made the post about 24lb injectors and provided those tunes, we didn't have to touch anything other than the scaling everywhere once we landed on the correct factor. Granted, if we were going further with that tune, we would have spent more time dialing in specific tables, but we didn't have to for general driveability. If it's this rich always, then this suggests you need to pretend your injectors are 37lb or 38lb (this new scalar will further reduce the value of the injector constant). You could even estimate what the next attempt should be because A/F ratio is a linear relationship with the injector constant. In other words, if you need to remove 10% fuel to get back to stoichiometric, try making your scalar 10% smaller and rescale everything with that. Once you get closer to stoichiometric, then you can stop playing with the scalar and focus on just tuning the maps/curves/parameters.
Revdperformance
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

Hey,

Okay, so i should be able to scale my injector constant, as a start by lets say .5 just to overshoot my previous scaling of .44 that ran rich. I should then be able to scale ALL other load based maps by .5 and see how it runs. If its still rich, reduce by say another 10% on injector constant and AGAIN all other maps load side same way. Then see how it runs.

Also, any idea why its sitting stoich and happy, and then all the sudden rich again? I keep getting o2 codes, and once in awhile, a MAF code. Assuming the o2 codes are because its having to over correct to get the fueling back to 1 lambda.

thanks!
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

Exactly this process! Most likely it's in closed loop when it's running stoichiometric. This means it's using mainly just the O2 sensor to adjust fuel. As soon as you force the DME out of closed loop, then it will revert to the parameters instead. You could confirm this theory by forcing it into open loop temporarily via the tune. This could help you while you're tweaking the scalar.
Revdperformance
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Joined: Tue Aug 30, 2022 9:50 pm

Re: E36 Turbo, questions about scaling for larger injectors

Post by Revdperformance »

Okay! so it seems to be a mechanical issue with the car. I wonder if you could help trouble shoot, or know common issues that could cause this.

This morning i tried using the 46 lb scaling map, with an injector constant of 16300 or whatever. Fired it up, instantly buried the afr to 10 afr and richer.

SO,i tried like 10000 injector constant, still rich. to get stoich i had to be at 9000 ish for injector constant. And then it would lean out when i tried to give it a full rev out.

So, i put stock injectors in, put stock chip on ecu, ran it. 10 afr at idle still. stock 16 lb green injectors.

maf voltage is 1.6volts ish, does that seem close for idle? Ive also smoke tested, no leaks that i can see.

No codes being thrown.....im very lost at this point.

edit: Also ive tried disconnecting maf to put it into alpha N, just to eliminate maf placement being a factor. Its still 10:1 afr or more on idle.

Ideas? HELP!

Thanks in advance guys.
Renovelo
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Re: E36 Turbo, questions about scaling for larger injectors

Post by Renovelo »

Sorry, we don't tinker with OBD1 cars much these days. We sold our E36 M3 shop car a while ago when we started getting serious with OBD2 tuning. You might try reaching out to the popular OBD1 BMW forums for more help sorting any mechanical issues.

However, your test with the stock tune, stock injectors, and stock MAF is pretty revealing of an underlying issue. It's obviously best to get this sorted before you do any tuning. Otherwise, you'll waste a ton of time chasing what you think is a tuning issue as you've experienced first-hand.
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