C4ProjectCar

I'm tuning my 1990 Corvette. It uses the $8D mask with a 1227727 ECM.

I recently discovered that my O2 sensor was fouled, so I pulled my #1 plug, and it was fouled as well. I've noticed it smells really rich when I start it, so I think startup enrichment is a little too high and/or PE is a little too rich. Consequently, I'm decreasing startup enrichment now, and I'm getting a wideband to dial in PE.

I went to decrease startup enrichment, but I realized there are two tables that could potentially be used to tune this: "Open loop %change to AFR vs temp" and "Startup enrichment vs temp." It seems like the latter would be the one to change, but for my own education I'd like to figure out the need for the open loop table.

AFAIK, the car is in open loop in three scenarios: when it first starts up, when it is in power enrichment mode, and when it is in limp home mode. Since PE has its own AFR table, and startup seems to have its own AFR table, I guess the open loop table is solely for limp home purposes?

RBob

iTrader: (1)

Need the table addresses to know which ones you are referring too. Folks that create the ECU/XDF files use different and various names for them.

No ECM tables or parameters are used in limp mode. The ECM is running from the redundant fuel device (RFD). Which is calibrated by the CALPAK resistors on the MEMCAL. The PROM calibration plays no part in limp mode.

RBob.

C4ProjectCar

Sorry about that, RBob. "Startup enrichment vs temp" = 0x431, and "Open loop % change to AFR vs temp" = 0x45E.

By the way, thanks for all the time you've invested in this forum. I'd wager a good chunk of what I know about $8D is from reading your old posts on the subject. Might be easy to forget about that stuff you wrote so long ago, but just know it's still helping people!

RBob

iTrader: (1)

"Startup enrichment vs temp" = 0x431

This is really an after start enrichment. Comes into affect once the engine is running and is decayed out over time. Quick on a warm engine, likely a couple of minutes on a cold engine. Its purpose is to help prevent stalling right after the engine is started.

There is also an after start spark adder.

"Open loop % change to AFR vs temp" = 0x45E

This table is in use whenever in open loop (except when highway mode is active?). It usually uses the engine coolant temperature, but it can be MAT based. It changes the commanded AFR from the base AFR table based on engine temperature.

Good to know, thanks.

RBob.

C4ProjectCar

Many thanks, RBob. And from what I recall of what you've written on other threads, whether I need to increase or decrease the numbers in that table to reduce enrichment depends on my particular XDF?


One other thing while I have you: I've realized my stock injectors are maxed out, so I'm looking at upgrading to some 36lb Accel injectors to meet my current need and give myself some growing room. I'm concerned about idle quality though.
With my current 22lb injectors, I'm seeing pulsewidths of around 2ms at idle, so I calculate that would translate to roughly (ignoring complicated injector dynamics) 2*22/36 = 1.22ms with the 36lb injectors.

The datasheet for the injectors I'm considering specifies 1.38ms as the minimum linear pulsewidth, which would put my idle pulsewidth in nonlinear territory. Apparently the 1227727/1227730 ECM can operate in single-fire mode, but a thread on Gearhead-EFI cites you saying it only goes into single fire for pulsewidths less than 0.85ms.
Unless I'm missing something, this would leave it in double-fire at idle.
Is it possible to increase that maximum pulsewidth for single-fire? Or do you think driveability would even be affected by the nonlinearity there?

From the document at Gearhead-EFI:

Orr89RocZ

iTrader: (20)

Not familiar with accel but i had 36 lb bosch injectors in my 305 car with 730 $8D. Worked fine.

Wideband will help alot in your start up tuning. Open loop afr vs temp is handy for cold start. Generally colder engine wants to be richer to run right. As it warms you can target stoich. Not uncommon to see high 12 low 13’s afr when very cold. Depending on combo. If plug is warm enough it shouldnt foul.
I like to disable closed loop and tune the car to stoich or so across all idle and part throttle ranges before enabling closed loop and dialing in BLM

GeneralDisorder

iTrader: (1)

Do you have any issues with lean hot-soaked starts though? It seems that the point on the open loop enrichments in the stock tune is to get the engine setup for closed loop (of course) so it's suitably rich to ensure these hot restarts don't go lean before the closed loop timers and O2 heaters are ready, etc.

GD

Orr89RocZ

iTrader: (20)

i know i had the restart lean out issue when it went into closed loop for a few seconds or so, with my 383 but never did figure it out. It run fine in open or closed normally but on restarts when warm it would go lean for abit and nearly shut off before everything got warmed up and ready again. I dont know.
If i disabled closed loop it was fine. So it must have been closed loop timers for o2 ready etc. even tho it was a heated o2.

GeneralDisorder

iTrader: (1)

Yeah - that's essentially what happens - the open loop enrichment goes away when it enters closed loop and it goes crazy lean before the O2 can compensate. Sometimes to the point of nearly stalling. That's a sign in my experience than it wanted to wait longer before going into closed loop because it was still lean from the heat soak. Being I'm running a stand-alone (which I run in open loop for tuning), I see the effect as if you zeroed out those open loop enrichment tables. So to clean that up I had to create another table that takes care of the enrichment based on coolant temp and run time.

GD

Orr89RocZ

iTrader: (20)

It definitely seemed like it wanted to wait longer but the reason for it i did not figure out. I should have tried lengthening the o2 timers for closed loop. But i believe i could be running fine after a long drive, shut down and restart immediately and still see the lean out. So it wasnt heat soak since it didnt have time to heat soak. If i remember right that is, it was back in 08. But i do know i could stop for a few min at a gas station and go to restart and would see the issue. So maybe some heat soak, but the mat isnt really used on maf 6e i dont think.
Havent seen the issue on other milder combos i have done so not sure what the deal was

GeneralDisorder

iTrader: (1)

Yes I have experienced that also - where you stop for a relatively short time in hot weather and when you restart it's just crazy lean. But this only lasts for a short time then the fuel trims will stabilize and go back to a normal level again. I definitely ran into this with the EBL as it wanted a IAT that was actually accurate but finding a place for an IAT that won't heat soak is problematic. So even with the EBL I had to use it's "hot restart enrichment" feature to richen it up on a hot start before it went back into closed loop.

The MAT isn't used by $6E except for emissions control activation you're right about that. So it's not a sensor heat soak issue. Fuel/rail/injector temperature is my current most likely candidate. I'm thinking I'll get those glass fiber bolts and insulating washers...... give that a shot anyway.

GD

Orr89RocZ

iTrader: (20)

That was a stealth ram car with aftermarket fuel system but i guess it could have still gotten hot. I just disabled closed loop and been happy ever since. On the turbo cars with victor efi the rails are even more isolated than tpi or stealth ram, so its possible they got less soak. But its a return style system so even if rails and that gas inside the rails got hot, few seconds of pump run would wash that hot fuel out with tank fuel that should be lower in temp. Idk. It is interesting tho. I never had the issue with several other cars i tuned.

84Elky

The post originally here should have been in this thread:
https://www.thirdgen.org/forums/diy-...open-loop.html

Apologies, but have no idea how it got here.

GeneralDisorder

iTrader: (1)

Ok so I guess then the question becomes - what about my setup would cause this level of enleanment on a hot restart?

If we accept that this is not a problem at all with the factory hardware, then really that doesn't leave much for a cause of the lean hot restarts other than the Bosch III injectors themselves maybe? My setup is basically stock 1986 TPI. The engine has 1.6 roller tip rockers, headers, Bosch III 24lb injectors, and an adjustable FPR hat on the TPI regulator.

Any suggests on what to test next to determine a cause?

GD

Dominic Sorresso

As an FYI guys, I experience the same “lean out” w my LT-5 on hot restart as u r describing. And the LT-5 uses 8 21# injectors. Currently using FICs but ACCELS exhibited same issue previously. I do believe as Orr has suggested that it simply seems that startup enrichment needs to remain longer before handing fueling over to “running” state.

Orr89RocZ

iTrader: (20)

Even my big block running holley hp needs some kind of initial enrichment post cranking to fire and run. I had all the cranking and startup afterstart enrichment at basically 0% added. It runs perfect at op temp but shut down and try restart, even adjusting the cranking fuel til you got an attempt to fire, it wouldnt catch. It needed abit of afterstart enrichment to get to run. Then decay out quickly.

It just seems like a necessary thing but i cant explain why lol

84Elky

This discussion assumes the Startup enrichment is sufficient and there is a need to delay the decay (elimination) of that enrichment. Will approach this using $8d references, but other masks likely similar.

There are 2 elements to Startup Decay:
1. The delay before decay begins, which is based on a number of injector firings
2. The amount of decay after the delay which is applied every 12.5ms

To increase the delay before enrichment decay begins, INCREASE the number of injections in the Table at 0x441=Startup Enrichment Decay Delay .vs. Startup Coolant. This generally takes longer to occur than the actual decay below because injector firings are RPM dependent.

To reduce the rate of decay (startup enrichment remains longer), REDUCE the values in 0x44F=Startup Enrichment Delay Amount .vs. Startup Coolant at the temp(s) of concern. This value cause decay to occur very quickly unless the values are small (reduction is applied every 12.5ms) .

Either or both of the above will ensure startup enrichment remains for a longer period avoiding a lean condition immediately after startup.

HTH, Elky

RBob

iTrader: (1)

The chambers are colder on a hot restart then what the CTS & MAT are telling the ECM.

RBob.

Orr89RocZ

iTrader: (20)

that is my thought as well. Just requires alittle extra fuel to heat up before running off base map

Dominic Sorresso

So is the idea to treat the CTS and MAT temps w a fractional factor ie the fueling would be more like what it is at lower values of each?

RBob

iTrader: (1)

That could be done. GM enriches the AFR by changing the commanded AFR.

RBob.

Dominic Sorresso

RBob,

So this suggests Startup Enrichment is managed as an O/L function then. Forgive me if I am stating the obvious.

RBob

iTrader: (1)

It is actually after-start enrichment, but yes, it is in open loop during this time.

RBob.

C4ProjectCar

Now that I have a wideband, I'm finally revisiting this. I've datalogged a few cold starts, and I'm starting to slowly inch up 0x41F (Open Loop AFR % Change at Idle). Once I get idle nailed down, I'll start looking at AFRs elsewhere, and I'll probably need to shift some of the enrichment from 0x41F to 0x45D (universal open loop AFR change).

I'm doing two cold starts per tune change, because it needs to learn new BLMs with a new tune before I can get a true warmup log (I think?). I've just taken my first log after increasing 0x41F 10%, and it has definitely helped. Where my first start with the previous tune showed a median of 1.31 lambda before closed loop, the new log has it at 1.16. That's remarkably close to a 10% reduction - didn't expect it to correlate that well.

However, target AFR from the datastream doesn't seem to echo this change. Over 40.5 seconds, it rises from 0.74 to 1.01 where it stays until it hits closed loop and drops back down to 1.00. This is consistent with other logs. (Sometimes its max is 1.00, but curiously it always takes 40.5 seconds to get there.) Does target AFR reflect startup enrichment but not open loop enrichment?

GeneralDisorder

iTrader: (1)

That's about an 11 AFR for cold start..... fairly typical. Even much more modern cars are easily in the 10's for cold start (choke) enrichment.

My standalone, which uses a sophisticated engine modeling mode, handles cold start enrichment, warmup enrichment, etc without the use of separate tables (unless you want/need them, or tune in "traditional" mode where they are typically required) - it's all just handled by the engine modeling - as long as the model is setup accurately and the fuel table is tuned properly, it just works all on it's own..... Startup AFR is typically about 11.5 to 12.5, tapering to target AFR - which I have set to 14.2 in the idle area - fairly large cam with only 12 in/Hg at idle wants a bit richer than stoich.

GD