Disabling ECU fuel trims?

[forcefed86]

Well I'm running a dsmchips stage 3 chip with my 750's. I switched over to e30 fuel and installed an SAFCII. This worked great for WOT, but in closed loop the ECU just trims the fuels back to the preset levels. This makes the car idle to lean. Can I just unplug the 02 sensor and the ECU will go into closed loop? Is there anyway to disable the ECU's control over the fuel trims?

Thanks

 

[->PrOjEcTGS<-]

Yes you could do that... If you really wanted to hack your shit up... It will throw a CEL for O2 sensor. Which in turn will more than likely put you into limp mode.

The best way to force yourself into OPEN loop is to get access to a Eprom Burner and change the code to set the closed loop to open loop crossover point for the TPS to 0%. That way any time you're above 0% on the TPS (all the time) you'll be in open loop where the ECU is ignoring the O2 sensor's signal.

 

[forcefed86]

Yes you could do that... If you really wanted to hack your shit up... It will throw a CEL for O2 sensor. Which in turn will more than likely put you into limp mode.

The best way to force yourself into OPEN loop is to get access to a Eprom Burner and change the code to set the closed loop to open loop crossover point for the TPS to 0%. That way any time you're above 0% on the TPS (all the time) you'll be in open loop where the ECU is ignoring the O2 sensor's signal.

Will forcing the ecu into closed loop with a fault code alter anything else? Timing...etc.?

It seems I can also just max out the ECU's trim ability. MMCD shows 82.2 on my low fuel trim. I've got the SAFCII set at 30% rich at idle. This nets me right at 13.9-14.0. This seems to work, although I haven't had much time or the proper weather to test it much.

Is 82.2 the most the ECU trim can take out?

Appreciate the help.

 

[->PrOjEcTGS<-]

Will forcing the ecu into closed loop with a fault code alter anything else? Timing...etc.?

It seems I can also just max out the ECU's trim ability. MMCD shows 82.2 on my low fuel trim. I've got the SAFCII set at 30% rich at idle. This nets me right at 13.9-14.0. This seems to work, although I haven't had much time or the proper weather to test it much.

Is 82.2 the most the ECU trim can take out?

Appreciate the help.

WTF? With a low fuel trim of 82% this is telling you that the ECU is pulling fuel because you have your SAFC set too rich! +30%!! Try leaning out your idle til the low fuel trim comes back to 100%.

Numbers Greater than 100% = Lean. SAFC Corrective action = Richen it up.
Numbers Less than 100% = Rich. SAFC Corrective action = Lean it out.

Hope that helps.

 

[forcefed86]

WTF? With a low fuel trim of 82% this is telling you that the ECU is pulling fuel because you have your SAFC set too rich! +30%!! Try leaning out your idle til the low fuel trim comes back to 100%.

Numbers Greater than 100% = Lean. SAFC Corrective action = Richen it up.
Numbers Less than 100% = Rich. SAFC Corrective action = Lean it out.

Hope that helps.

Thats correct.

Originally I had the idle set 14% rich. (running e30 on a 91 octane chip). This worked well until the ecu trimmed the mixture lean agian. The chip has always run lean at idle 14.5-15.5. This wasn't a big issue with 91 octane but it is when running e30. So in order to richen the mixture at idle I had to max out the ECU's low-trim. Once I did this I was able to richen up the mixture and see actual changes in the AFR on my WB02.

Problem being I need to run the idle mixture richer than the chip is set for. So currently I'm maxing out the low trim and then adding additional fuel to get me to the 13.9-14.0 AFR range.

make sense?

 

[steve]

The chip has always run lean at idle 14.5-15.5.

The nature of closed loop is that the ECU will track lambda = 1 due to the O2 sensor switching. If you want to run open loop recode the software to not go into closed loop. Disconnecting the O2 sensor will induce a fault and cause it to assume limp mode for that fault.

 

[forcefed86]

The nature of closed loop is that the ECU will track lambda = 1 due to the O2 sensor switching. If you want to run open loop recode the software to not go into closed loop. Disconnecting the O2 sensor will induce a fault and cause it to assume limp mode for that fault.

Will limp mode cause any other changes? Timing etc? I can live with a CEL. And I can lean the car out at cruise with the SAFC.

 

[->PrOjEcTGS<-]

I guess I don't really understand your problem here...

Why do you want to run richer than 14.5-15.5 at idle?

1 lambda is 1 lambda no matter what fuel you are running. And since your WBO2 is set to read gas AFRs, it will read 14.7 at 1 lambda regardless of what fuel you are running.

Example:

Your WBO2 is designed to read lambda the number of unburnt oxygen in the exhaust. 1 = complete combustion. > 1 = Lean < 1 = Rich. Now the amount of fuel needed to reach lambda is different for various fuels.

Fuels with less BTU's per/gal or less energy potential require more fuel to reach lambda. Thus their lambda is of a lower number.

Gasoline = 125,000 btu's per/gal = 14.7 lambda
E85 Ethanol = 90,500 btu's per/gal = 9.8 lambda
Methanol = 62,800 btu's per/gal = 6.5 lambda

AFR = Lambda of fuel x lambda reading

So, if your sensor is setup to read lambda and outputs an AFR that's based off of gasoline but your running a different fuel like methanol, at 14.7 AFR your at 6.5 AFR on meth. But still at 1 lambda.

Get it?

14.7 AFR Gasoline = 9.8 AFR E85 = 6.5 AFR Meth = 1 lambda. But gauge is setup for gasoline so it reads 14.7.

Now, your trying to get it richer than "14.7" or 1 Lambda and your getting 13.9 which equals .945 lambda. How do you get AFR again? Lambda of fuel (14.7) * Lambda Reading (x) = AFR (13.9) Solve for x. 13.9/14.7=.945 lambda. Multiply that by the lambda of the fuel you are running (Methanol's 6.5) and you get an actual "AFR" of 6.14.

Take this a step further... You know how people are always saying that you need roughly 30% more fuel if you run E85. How do they come up with these numbers? Well, BTU's per/gal of gasoline = 125,000 BTU's per/gal of E85 = 90,500. What percentage difference is that? (90,500/125,000)-1 *100= -27.6% less BTU's or "Energy Potential".

Coincidentally, its lambda is also 33.3% less. (9.8/14.7) - 1 * 100= -33.3%

As steve said, the ECU targets Lambda therefore, no matter what fuel you run it will always target it's sweet spot.

Hope this helps. I believe your trying to tune it too rich and your ECU is doing what it was designed to do by attempting to lean it out.


Oooooo... I can take this even one step further... Why is gasoline with ethanol cheaper? It contains less BTU's/gal. As an energy source, it's not worth as much to people. Which is why it will always be porportionally cheaper than straight gasoline. Why do you think it now says "May contain up to 10% ethanol" on the pump now? Yet we still get charged the same amount... Weird... 0_o

 

[Colt4G63 also]

I would have to agree with ->ProGectGS<-, why would you want to alter your target idle AFR?

 

[GooeyGus]

The chip has always run lean at idle 14.5-15.5. This wasn't a big issue with 91 octane but it is when running e30.

Sounds fine to me! You cant really do damage from running lean at idle... the car will just stop running if there is not enough fuel/too much air.

A lot of people get a bit spooked at the idle AFR's because we're all told that running lean is the death of engines. Well, running lean at WOT at peak cylinder pressures = a lot of heat, which can cause damage. Running lean at idle may cause a tiny bit more heat, but at idle this tiny bit of extra heat is negligible. Like I said you could slowly lean out the mixture until the engine died from having no fuel and you still wouldn't be able to do any real damage.

 

[dsmfa9nutter]

Easier way would be to get ostrich and change the trims in the tables or cut the code out entirely.

 

[forcefed86]

I appreciate all the help.

At 14.0 AFR the idle smooths out considerably. The whole car/steering wheel vibrates at idle with the AFR's @ stoich. When I bump the AFR's up a tad to 14.0 the car smooths out considerably. I don't know if this is cam related or the fact that the weather has been down in the teens here lately or what. I just know my idle improves 100% when I go richer than 14.7.

That is the only reason I wish to change it.

 

[JayRolla]

I know it may be out of the question but have you thought of trying e85. It may be close on those injectors but people have made some good power on e85 and 750cc injectors and I think you have it right?

I ran my 16g for over a year on e85, 1000cc, safc, maft and it worked out great. With the chip and safc you should be pretty good.

 

[->PrOjEcTGS<-]

I appreciate all the help.

At 14.0 AFR the idle smooths out considerably. The whole car/steering wheel vibrates at idle with the AFR's @ stoich. When I bump the AFR's up a tad to 14.0 the car smooths out considerably. I don't know if this is cam related or the fact that the weather has been down in the teens here lately or what. I just know my idle improves 100% when I go richer than 14.7.

That is the only reason I wish to change it.

You might be having an issue with what your deadtimes are set to. I'd try to get with someone that has a chip burner and add a little to the numbers. Adding to the deadtime compensation will richen it up and smooth out idle and removing deadtime compensation will lean it out and make a somewhat crappier idle comparatively.

 

[forcefed86]

I know it may be out of the question but have you thought of trying e85. It may be close on those injectors but people have made some good power on e85 and 750cc injectors and I think you have it right?

I ran my 16g for over a year on e85, 1000cc, safc, maft and it worked out great. With the chip and safc you should be pretty good.

It sure is tempting! But.... I think I can max out my current combo and turbo with e30 and meth injection. So it's hard to justify the cost of extra injectors. I'm a little under 70% DC now. But I think making the e85 switch would max out the DC on the 750's quick. Also wouldn't the timing tables be all jacked up if I had to add that much fuel through the SAFC? Although 1000cc injectors on a 750 chip may work out about perfect for e-85. Fine tuning could be accomplished through the SAFC.

Either way, as it sits boost spikes to 30 and settles at 27lbs. Not seeing any knock. So I don't think I'd really see that much of a gain switching over fuels.

I'm also out of work now and don't know if I'll end up in a city with e85.

I wonder if spraying meth pre turbo and post turbo is more efficient than e85 alone? Seems like it might be to me, depending on how much of it you spray.

You might be having an issue with what your deadtimes are set to. I'd try to get with someone that has a chip burner and add a little to the numbers. Adding to the deadtime compensation will richen it up and smooth out idle and removing deadtime compensation will lean it out and make a somewhat crappier idle comparatively.

Couldn't I also accomplish this by lowering the base fp? Then adjusting idle fuel trims to 100 via the SAFC?

 

[JayRolla]

No deadtime wont be affected by the fuel pressure. I do know it took me a few tries to get DT right when I first started tuning e85.

 

[forcefed86]

No deadtime wont be affected by the fuel pressure. I do know it took me a few tries to get DT right when I first started tuning e85.

What did you end up with I'm at 288us with precision 780's. I was thinking of going up to 312uS or even 336uS.

After speaking with keydiver a bit and fine tuning I pretty happy with it now.

The idle is actually alot better. I completely disassembled my FIAV and adjusted/cleaned it and reinstalled it with great success. I think this was part of my problem. Car starts right up cold with no throttle. Works perfectly. Idle is great.


Base FP at 40.

Tuned in an additional 13-15% across the board on the high throttle map. 9% across the board at low throttle map. Except for the first cell in the low throttle map. I had to jack that up to 20% rich to get the L-trim to around 100. It fluctuates now between 98-103. Injector DC peaks out @ around 80%. Not to mention there's another 7.75gph of 100% meth being injected. (actually more at 250psi) So I must be flowing some serious air! Boost spikes to 30 and settles at 26-27.

Also keydiver suggested bringing up base timing and idle with the BC 272's. This helped out alot as well. Set the base timing up to 10* (from 5*) and idle up to 900 (from 850).

I'm only pulling 12 inches of vac as well so I'd bet my cams are a bit off. They are straight up ATM.

Either way I'm stoked, I didn't think a little 16g could pull this hard! CAn't wait to see what this thing traps in the spring.

Are you actually running 32psi throughout the rpm band? Or do you just spike to that momentarily? What kind of timing are you running?