94 F-body LT1 solving problems/tune

[NomakeWan]

Yes, I'm not sure LT1's ever had an EGR circuit that was active, however, all other ecm's have quite a few separate "tables" when the EGR is active. Or I should say, when the ecm thinks the egr is active.

I read all the time where people block their egr and wonder why they have a part throttle lean and knock issue. IF THE COMPUTER THINKS THE EGR IS OPEN IT PULLS FUEL AND ADDS TIMING!!! These are tuneable events and corrections. Changing a cam/exhaust/heads etc drastically alters the egr qualities.

Some egr's are basically on or off, other later ones are pulse width modulated and there are even more fuel tables and spark tables to work with that.

By comparing the 1996 LT1 tables (which had an EGR) with the 1996 LT4 tables (which did not), we can see how the LT1's PCM handles EGR events.

The obvious differences are the EGR-related error codes. Easy enough to disable, but only gets rid of the MIL. The LT4 sets the enable temperatures high to disable EGR but otherwise leaves the settings within sane ranges (Min MAP 22.2 kPa, Min RPM 900, Max RPM 2300, Enable Speed 8 MPH, Disable Speed 6 MPH...Enable Coolant Temp 151.25C). EGR Spark Advance is set to between 0.0 and 1.0 (odd they didn't just zero out the table). Those are the only differences between the two calibrations with regards to EGR operation.

It would appear that merely making sure that the EGR enable values are out of a sane range is enough to disable all EGR-related changes. GM certainly seemed to think so.

[yoheer]

Well if it is so, then i've disabled it correctly.
What about CAT?

[LeMarky Dissod]

What about CAT?

Asked & Answered.

GM uses the following values for vehicles that were never equipped with catalytic converters:

Min Coolant Temp for CAT Protect = 150°C
CAT OverTemp Threshold (Low Baro) = 1065°C
CAT OverTemp Threshold (Mid Baro) = 1065°C
CAT OverTemp Threshold (High Baro) = 1065°C
CAT OverTemp Air Fuel Ratio = 12.2 AFR

(Although I'd raise the CAT OverTemp Air Fuel Ratio to 14.7 AFR without any fear.)

[In-Tech]

Until you've personally calibrated your spark & fuel tables so that your LTFTs are all between 123 & 133 (123 is slightly better), leave the O2 sensors working.

Yes to the 123, most stock cal's are like this!!! The engine will always respond better with the slightly richer mixture while the computer attempts to remove fuel rather than add.

[In-Tech]

By comparing the 1996 LT1 tables (which had an EGR) with the 1996 LT4 tables (which did not), we can see how the LT1's PCM handles EGR events.

The obvious differences are...Forget about any kind of static ratio pertaining to a dynamic environment. Enable Coolant Temp 151.25C). EGR Spark Advance is set to between 0.0 and 1.0 (odd they didn't just zero out the table). Those are the only differences between the two calibrations with regards to EGR operation.

edited above

[yoheer]

Asked & Answered.

Oh that is clear. I'm talking about back pressure, so O2s can read different parameters without CAT. Any issue or just disabling cat protection(already done) and that's it?
I mostly ask about fuel and timing modifications.

[NomakeWan]

Oh that is clear. I'm talking about back pressure, so O2s can read different parameters without CAT. Any issue or just disabling cat protection(already done) and that's it?
I mostly ask about fuel and timing modifications.

Should be totally fine. The O2 sensors care about what's in front of them, not what's behind them.

[yoheer]

I know, that f-body and y-body engines are the same. 92-94 vette and 93-93 fbody. Same cam and all other stuff is the same. (Correct me if not)
Just headers and intake differs a little bit. And 2 knock sensors instead of 1
So is it good idea to take vette calibration and move all timing and fuel tables to my pcm? Tables differ a little bit. I compared em.
What do you think about it?

[NomakeWan]

Won't hurt anything. The only difference between the two engines is that the Camaros all had 2-bolt mains and the Corvettes had 4-bolt mains. All the other differences were external to the engine (intake design, exhaust design, accessory mounting).

[yoheer]

What about better intake and headers in vette?
Will modifying theese tables take effect in fbody?
And only 1 knock sensor. Detonation?

[NomakeWan]

What about better intake and headers in vette?
Will modifying theese tables take effect in fbody?
And only 1 knock sensor. Detonation?

Changing the exhaust and intake will cause changes in how air flows into and out of the engine. Engines are at their core just air pumps, after all. Much of these changes can be accounted for by the closed loop O2 sensor feedback system. You would have to make much more extreme changes to fall out of the range of what the PCM can account for, which changes to intake and exhaust won't do. If you disabled closed-loop feedback or you just want to adjust the tables yourself, then get a wideband O2 sensor and get to doing your own tuning. There's no magic bullet. But if the question is just "will I blow up my engine if I use the Corvette tables," the answer is no.

No, reducing the knock sensors from 2 to 1 won't cause detonation. On the 94-95 $EE PCMs, whether you have one sensor or two there's only actually one channel being used on the PCM end (the 96-97 PCM used two channels). What's important with regards to the knock feedback system is not the number of sensors, but is rather the calibration stored on the knock module inserted into the PCM. This module is what takes the output from the knock sensor(s) and filters it to tell the PCM when knock is occuring. Making changes to the acoustic profile for your engine will cause this knock feedback system to malfunction, but it's not the fault of the sensor. It's the knock module.

Unfortunately, short of designing your own knock module, you're not going to be able to get around this. Once you start doing custom work in your engine bay, it's best to just disable the knock feedback system entirely and rely on proper tuning, or run an external knock feedback system if you're paranoid.

[yoheer]

Thank you for such detailed answer.
Do you mean that if I have any loud perfomance muffler even with stock headers then i'd better disable knock sensors? Because of false knock.

[LeMarky Dissod]

GM used a different knock module when they upgraded the valvetrain on the '96 & '97 LT4.
The Impala SS Forum's collective experience has shown that using roller rockers and/or headers could cause 'false knock'.
The LT4 Knock Module has been out of production for many years now.

You should be fine with your loud mufflers, though.

[yoheer]

I've made mods to my bin. Lots of vette tables and parameters applied
Here is short log with PE mode and 100% TPS.
Seems to be very lean. Knocks detected. Can anyboby take a look and say what should I move to?

[NomakeWan]

Thank you for such detailed answer.
Do you mean that if I have any loud perfomance muffler even with stock headers then i'd better disable knock sensors? Because of false knock.

Not necessarily. I can't tell you what's going to change the acoustic parameters of your engine, but generally a muffler on the other side of the car isn't going to be what does it. It'll be changes related to the engine bay, or what's immediately nearby the engine bay. Things directly attached to the engine. What you can do is lower the timing on your engine to a point where it won't knock and then test. If you can make the knock reliably appear and disappear by messing with the timing, then it's probably real. If on the other hand you get knock with unusually low timing and/or in parts of the map that have no real load or RPM, it's probably false knock.

And as said, there's no way to fix this in the tune. It's not handled by the tune--it's handled by a physical component, the knock module. So if you find out you have false knock, you either have to make your own knock module tuned to your specific setup's acoustic parameters, or just disable the knock feedback system.

I've made mods to my bin. Lots of vette tables and parameters applied
Here is short log with PE mode and 100% TPS.
Seems to be very lean. Knocks detected. Can anyboby take a look and say what should I move to?

I had a look at your log. The "knock" at 1500 RPM and 40 MAP is probably not real. That's very low load and RPM. There are specks around 4000 RPM, but those could be false too, depending. The fueling at PE looks fine. The closed-loop fueling looks like it wants more fuel, sure, but your log is also pretty darn short, and you don't really cover the whole range without going into PE, so this 'lean' normal operation appears to be well within normal values. The O2 feedback system can handle deviations this small without any issue.