tuning programmable engine management systems

[scarceller]

Originally Posted by psalt

Sal,

I don't know the Euro Carrera chip map, but if they didn't have a cat and the IM240 test, it would be closer to optimum. I think it had higher compression and a different fuel spec. Many of the US 911 road cars were detuned for low octane fuel after the 60's because it is such a knock sensitive design. Copying the factory timing from these models may not be so good if you have a modified engine, twin plugs or good fuel.

Is that 8%-58% load map, total timing or an offset from idle (static) ? I don't understand a $1336 offset, sounds like it belongs on Martha's tax return. Does it say that timing goes negative (-1.4 and -4.2), ATDC, when suddenly accelerating of idle ? I wonder if this is a "burst Knock" or throttle response issue ? I agree that timing changes can do a lot for drivability. Idle timing should be close to TDC, there is really no need for advance at idle on a properly fueled engine and it is bad for cranking. OEM's are now retarding the idle timing after start up to intentionally overheat the exhaust, in an attempt to get the cat up to temperature to meet the hardest part of the emissions test. Not something to copy. For part throttle cruise on a road car, you are just wasting fuel if you do not lean above 14.7 and have a load based advance above the 40's BTDC. There have been some interesting articles about the choices we have made about emissions and how they have increased overall fuel consumption. With a different emission strategy, fuel consumption could be much lower. I am not familar with ECU's with maps that target AFR's. It has to be irrelevent at cold start and during transitions.

That offset is simply the hex location in the chip where the map is located, ignore it. The numbers you see in the tables are real ign advance numbers, if you see a -1.4 for example that's a retard of 1.4ATDC, they really are that simple to read. Now in the real map on the chip they are keep in a digital format that is converted to real value via a formula. Not going into the formula here, but those are the real timing numbers already converted by the formula.

The Euro cars had no cat and where most likely not detuned in anyway, I'll dig a map up and show you soon.

As for going negative timing when accel of idle, yup that's what is says. But keep in mind the 89 cars where 880RPM idle so that says they do backoff some on timing off idle under sudden accel but they would only go -1.4 if the RPMs dropped as low as 800RPM. But you have the right idea they backoff timing under sudden accel at low idle, correct. In the end this area of the map really is not that interesting because how often do you gun the throttle below 1500RPMs?

The real interesting area is that big hump you see in the graph above 2500RPMs, I have played in this area a lot and will tell you it completely changes the car. The throttle response goes flat if you lower that hump and it really comes alive if you make it steeper. I'm simply giving you some ideas to play with in your EFI setup, try them.

[psalt]

The real interesting area is that big hump you see in the graph above 2500RPMs, I have played in this area a lot and will tell you it completely changes the car. The throttle response goes flat if you lower that hump and it really comes alive if you make it steeper.

Sal,

OK, you are interested in the "big hump" (like everyone else). The way I read this map is the steepness of the "big hump" is the rate at which you pull out timing when the throttle opens. I know you said the 8%-58% is not correct, but if it relates to manifold pressure (load) or throttle angle, the timing increase only occurs under 21%, which is light load. I doubt you ever get to 5000 rpm under 20% throttle, unless you are coasting, certainly not under acceleration or top speed. What kind of % are you seeing at 65 mph cruise ? I am used to seeing a 15-20% throttle angle at part throttle cruise, where timing needs to be advanced above the WOT curve. As soon as you step on the pedal (throttle response) the extra timing goes away. Most systems use a 30% throttle position to go open loop, when does the Carrera TPS go open loop ?

[dfink]

OK well now we are getting into some good discussions. Have not seen timing suggestions posted that high they may be out there just never found them.

I don't see why there can't be some sort of suggested range for the new tuner to shoot for. If you have been doing this for a long time you will ignore anything posted here anyhow. This really meant for the new guy with no idea to give some idea of what to shoot for and what is safe. Along with some discussion as to why.

For a couple of earlier questions. The electromotive system can do pretty much anything you want it to do. I can go open loop, closed loop, I can use the ignition to get the idle about anything discussed can be done.

My car has had the wide band checked against two different dyno setups and the ignition has been checked with a timing light. Perhaps I had an entry wrong and I will recheck but the car would not start at 5* I had to go back to 12* and popped right off. I will revisit my idle settings.

The PT advance issue is interesting indeed but needs to be mixed with the A/F ratios under those conditions. I could easily put those advances in my table. Car has been dyno tested and for me a WOT ramp up to 30* works the best. Higher numbers at the lower RPM range resulted in a loss of power and anything over 30 resulted in a loss of power. The twin plug never did ping.

[scarceller]

dfink,

I simply think starting with the 89 maps just makes a lot of sense. I'll post the fuel maps soon. But not that much magic in those, simply the set the low load area (first 3 or 4 rows) to about 14.2AFR then the high load last row to 13.0AFR then the area that matches the 40deg ign advance simple gets about 13.2AFR.

[scarceller]

Originally Posted by psalt

The real interesting area is that big hump you see in the graph above 2500RPMs, I have played in this area a lot and will tell you it completely changes the car. The throttle response goes flat if you lower that hump and it really comes alive if you make it steeper.

Sal,

OK, you are interested in the "big hump" (like everyone else). The way I read this map is the steepness of the "big hump" is the rate at which you pull out timing when the throttle opens. I know you said the 8%-58% is not correct, but if it relates to manifold pressure (load) or throttle angle, the timing increase only occurs under 21%, which is light load. I doubt you ever get to 5000 rpm under 20% throttle, unless you are coasting, certainly not under acceleration or top speed. What kind of % are you seeing at 65 mph cruise ? I am used to seeing a 15-20% throttle angle at part throttle cruise, where timing needs to be advanced above the WOT curve. As soon as you step on the pedal (throttle response) the extra timing goes away. Most systems use a 30% throttle position to go open loop, when does the Carrera TPS go open loop ?

The way to think of the rows in that table is the 8% is when you first transition from closed throttle (very low load) the last row 58% is just before you transition to WOT, my WOT switch kicks in at about 80% open throttle.

I know a little about open-loop in the motronic but my car is a Euro Car and I never run in closed-loop (no O2 feedback). But here is how the motronic gets out of closed-loop:
1) These cars do not have a TPS they simply have 2 simple switches (open or closed) one for idle which closes when the throttle plate returns to idle this switch tells the DME to use the idle maps. The other switch is the WOT switch and it closes when the throttle plate is about 80% open but you can adjust it's close point by rotating it. If this switch closes then we are using the WOT maps. If both switches are open we are using the PT maps, very simple.
2) Then if the WOT switch closes the motronic comes out of closed-loop and stops monitoring O2.
3) If idle switch is closed we are at idle and using idle tables the Motronic always goes into closed-loop here if CHT is in normal range, I won't talk about cold start for time being.
4) Then in PT maps (both switches open) the motronic has some advanced algorithms to determine if closed-loop is appropriate. First under normal cruise and light to moderate loads it's in closed-loop shooting for 14.7AFR. But if the motronic detects accel conditions (like jab on the gas) the code will take you out of closed-loop and really start looking at the PT fuel map which in many cases will drop AFR into the 13s, this is how it achieves accel enrichment. I don't fully understand all the workings of these algorithms because they never interested me since I'm always in open-loop in the Euro engine. But a common misconception is that in PT you are always in closed-loop this is not true! The DME evaluates the AirFlow via the signal from the AirFlowMeter compares this to the given RPMs and comes up with a load factor and if the load is very high and changing rapidly (jab on the gas) it comes out of closed-loop.

With all this said, I would always suggest tuning without monitoring the O2 sensor (open-loop mode). You only bring the O2 back in for fuel economy and really don't do this till you are happy with what you have.

Here's the other misconception: can I run my USA car in open-loop all the time? answer is sort of yes but only if you don't have a CAT. Basically the DME is designed to run either way just fine but in Open Loop your mixture most likely will be to rich and you will damage the CAT other than this issue no harm done running a USA car in open loop mode.

[psalt]

dfink wrote,

My car has had the wide band checked against two different dyno setups and the ignition has been checked with a timing light. Perhaps I had an entry wrong and I will recheck but the car would not start at 5* I had to go back to 12* and popped right off. I will revisit my idle settings.The PT advance issue is interesting indeed but needs to be mixed with the A/F ratios under those conditions. I could easily put those advances in my table. Car has been dyno tested and for me a WOT ramp up to 30* works the best. Higher numbers at the lower RPM range resulted in a loss of power and anything over 30 resulted in a loss of power. The twin plug never did ping.

dfink,

Sounds like you have the WOT maps set up properly. On a road car this is less than 10% of the time and cold start, cold running, warm up, acceleration enrichment, and cruise take a lot of time and trial and error. Cold start can take a long time if your climate changes, but once you learn what changes work and why, it is easier. The Carrera spark map is for a single plug engine and a twin plug map may need to be different. One thing is certain, if 30 BTDC is your best torque WOT timing, your cruise timing will be higher if you are looking for mpg.

[psalt]

Sal,

I was thinking about the big hump and your throttle response comments. I am always interested in the "why" certain adjustments have the results they do. Throttle response is a perception and I have experienced large changes with different manifolds on the same engine with small changes in output, so I understand it is very subjective. It could be that what your are noticing is that without the extra advance of the hump, more of the fuel is burning in the exhaust, doing less work and causing more throttle angle for a given cruise load. When you bring the advance up, more fuel is burnt in the cylinder, more work is done, less throttle angle is needed and when you step on the throttle response is improved. You would need datalogging to see if this was the case.

If you are tuning an ECU with a target AFR table, doesn't it have to be closed loop to make the corrections ? My experience is changing the injector pulsewidth tables open loop, then using closed loop to datalog the correction factors.

[dfink]

Originally Posted by psalt

Sal,

If you are tuning an ECU with a target AFR table, doesn't it have to be closed loop to make the corrections ? My experience is changing the injector pulsewidth tables open loop, then using closed loop to datalog the correction factors.

On my system anyhow and I think most work this way. I can run either open loop or closed loop. Closes loop simply allows the EGO to control the a/f mixture within a set of guidelines I can prescribe. If I stay open loop the computer takes the fuel table, then addes and or subtracts the various other tables to come up with a pulse width for whatever the current point on the map is.
My map is based on RPM for the X factor and Manifold air pressure for the Y factor. The table is 16X16 but the numbers are interpolated at I believe 256 points between each of the 16X16 squares. So rarely will you see the exact target that you have set on a square. In open loop you get whatever output you get, based on how the engine reacts to your specific inputs. In closed loop the EGO table is brought into play. In my case I have given the EGO authority to make corrections to 15% max. In this case the output should be somewhere around the a/f setting you have in the EGO table because the system is making correction to what is happening.
This can be used as a tuning tool especially for the new tuner because the engine will try to stay close to where it should be on a/f and you can use the correction factor to try and get within 5% +- on the correction values this is done by adjusting generally the V/E table.
To avoid having the computer take the engine lean at WOT you can set a cutoff point for the EGO and open loop at either a set rpm or a set MAP actually you set the MAP where the RPM cutoff is allowed. The system then goes open loop and runs just off the fuel maps. In either case the system is ultimately controlled by the fuel map which is the pulse width for anygiven point. The A/F table is only the target for the EGO correction in closed loop.
The stock system has a point at which it also goes open loop for WOT but also has a switch that tells the system the throttle is fully closed and goes to an idle mode. On my other car this switch makes a big difference in how the car idles. I am sure that scarceller could enlighten us more on exactly what this switch does. My electromotive system does not have this feature.

[safe]

Originally Posted by scarceller

The Euro cars had no cat and where most likely not detuned in anyway, I'll dig a map up and show you soon.

I would be really interested in the euro ignition map!

[scarceller]

Originally Posted by psalt

Sal,

I was thinking about the big hump and your throttle response comments. I am always interested in the "why" certain adjustments have the results they do. Throttle response is a perception and I have experienced large changes with different manifolds on the same engine with small changes in output, so I understand it is very subjective. It could be that what your are noticing is that without the extra advance of the hump, more of the fuel is burning in the exhaust, doing less work and causing more throttle angle for a given cruise load. When you bring the advance up, more fuel is burnt in the cylinder, more work is done, less throttle angle is needed and when you step on the throttle response is improved. You would need datalogging to see if this was the case.

If you are tuning an ECU with a target AFR table, doesn't it have to be closed loop to make the corrections ? My experience is changing the injector pulsewidth tables open loop, then using closed loop to datalog the correction factors.

Paul the tuning I do is with the stock motronic and burning new chips, it's very crude. I do have a full WBO2 setup that logs the following:
- AFR
- RPM
- AirFlow via AFM 0-5v signal
- CHT in deg F
- MPH speed

The data logger has matrix analysis ability that lets me then see what's going on in the PT tables, it simply figures out what he AFR is for a given load (cell location) after I look at these results from a run I simply fine tune the AFR map. WOT tuning is much simpler to do by just logging the AFR in a 2nd gear run from 1000RPMs to 6800RPM (my rev limit is also bumped up to 6800). I could never have tuned the PT tables without the matrix analysis mode.

I understand some of the new EFI systems have this real cool ability to monitor the WBO2 AFR and auto tune the map for the target AFR. Way cool, but I just can't do this with the stock motronic.

[scarceller]

So here are the fuel and ign maps for the 86 Euro, the 86 car was not as aggressive in WOT ign as the 89 but at least this is a 86 Euro not detuned for the US market and CATs.

I risk someone getting upset at me for posting these maps but here goes. I simply only wish to share what I know about the stock chips and setup in the hopes of helping others struggling with custom EFI systems. Please do not ask about any custom chips.

Ignition map:


Fuel map:

[scarceller]

Originally Posted by dfink

The stock system has a point at which it also goes open loop for WOT but also has a switch that tells the system the throttle is fully closed and goes to an idle mode. On my other car this switch makes a big difference in how the car idles. I am sure that scarceller could enlighten us more on exactly what this switch does. My electromotive system does not have this feature.

dfink,

If the idle switch does not make contact when the throttle closes the car idles like crap for 2 reasons: It's not running off the idle maps and is simply running off the PT lowest load row (8% row). The second and most important reason is that if the switch does not close the IdleControlValve does not function to maintain idle. That idle microswitch must close for the cars to idle properly.

[scarceller]

Paul,

At 65MPH in 3rd gear I run in the 3000-3500RPM range and I can tell from my AFR that I'm generally running in the lo-load first 3 rows (8, 10, 13%) so long as I'm not going up any steep hill.

If I hit a 10deg or more hill it starts to dig into the center load part of the map and my AFR drops into the 13.7 range.

Also if just cruising along in lo-load 14.2 AFR, I suddenly tip-in on the gas for quick acceleration (but not WOT) I can very quickly tell I'm in the upper half of the map because my AFR snaps quickly to the 13.2 range. I have my fuel map setup so that the first 3 rows (lo-load) keep me at 14.2AFR then the last 2 rows (hi-load) are down in the 13.0 to 13.2AFR and the rest of the rows simply transition me from 14.2 to 13.0 smoothly, slowly getting richer and then riching quickly after center of the load table. So I combine fuel enrichment with more timing on tip-in and this really helps throttle response. I know it's seat of the pants but I also have created maps that don't do this and are simply flat and you really can tell the difference. Not only that I can see the effects via my data logger by simply looking at my 2nd gear 30-60MPH times (Cruising at 30 then tip in to 75% throttle) with each map on the same stretch of road.

[911st]

Great thread!

[psalt]

Sal,

Trying to absorb the Carrera timing maps.... the Euro vs US difference is, +0.8 compression, no cat and 2 or 3 RON higher fuel spec ? The fuel specs in the owners manual and spec book don't seem to agree, was there a different fuel spec ? They both wind up with 26 BTDC max which is knock limited or detuned to me, based on dyno tests of water cooled, hemi headed engines with similar VIA's. I'm sure these engines would continue to make higher output on higher octane or alcohol based fuels out into the mid 30's BTDC.

My point was that at a 65 mph cruise in 5th, that map (big hump) is pulling timing out when you open the throttle to accelerate.

[scarceller]

Paul,

If you look at WOT ign maps over the 84-89 years you see them getting slightly more aggressive over the years which to me indicates the engineers where being very conservative with ign maps at first and then improved them slightly over the years. But even in 89 they still never went much above 26BTDC for WOT.

But you are very correct that power was left on the table and these cars certainly can push WOT ign in the low 30s but you MUST use 93 octane once over 29BTDC or so. I have seen some WOT tuned cars push 32BTDC at WOT but I think you are in detonation danger here especially if your car leans out for some reason. I personally would not push past 30BTDC in a street car. You have to trade off power with engine life and these motors cost $$$.

Now be very careful of your AFRs at WOT and in a up coming post I'll explain something else the Motronic does with AFRs and how the WOT AFR is designed to change based on intake air temp. The same exact chip will produce different AFRs on a 90 deg F humid day vs a 40 deg F dry day. Just think about what you think should happen to AFRs under these conditions? I'll post on this soon as folks have made big mistakes here by assuming the AFR is always the same on all days.

[psalt]

Sal,

The Haltech ECU's use a GM intake air temperature sensor and a correction map to alter the pulsewidth for air temperature correction. I don't think it knows about humidity.

I was thinking more of 105-110 octane ethanol fuel. It seems that cylinder head temp with the air cooled motor is the limitation, as DOHC water cooled hemis make best power out around the 36-40 BTDC range. Some of the early Euro 911's had 38 BTDC for max advance before the unleaded fuel spec came in.

[mppickett]

Really great thread! One of the things we've not touched on very much is the difference dual plugging makes on the timing map. I've heard you should pull a couple of degrees of timing over single plugged maps because of the speed of flame propagation. Any rules of thumbs here?

[dfink]

A couple of things from the last couple of posts.

It is correct that the pulse width is a basically an absolute value. The injector is on for a specific period of time based on what point in the table is active. It is then effected by the various other tables for a total on time for any given point on the map. Air density will effect the final A/F mixture. Most systems I would think have manifold air temperature, some including stock have an altitude sensor, I don't know of a humidity sensor. In practice at least during closed loop operation the EGO correction should compensate for any humidity differences as it measures the output not the input. You would still be subject to the effects once the system went open loop. This is one reason I would like to put a readout on the dash. With the electromotive system you can set an input up with a resostat and dial in up 5% +- correction with the turn of a knob. You can also adjust timing in the same mannor.

Now for the twin plug question. Several posts through out my searches found that 24-25* was the max for a twin plug system. I and others have not found this to be the case. There was about a 6hp loss going from 30* to 24* at WOT 7000rpm. I found that under WOT I got the best results from a rather linear ramp up peeking at around 5000-5500 rpm. Jumping up too soon also caused a loss in the lower to mid ranges. So for my setup 30* appears to be the best. I tried to go to 32* and also experienced a loss of power. I never did get any hint of knocking. This was with a 12.5:1 A/F ratio and 10.5:1 compression ratio.

[scarceller]

Originally Posted by mppickett

Really great thread! One of the things we've not touched on very much is the difference dual plugging makes on the timing map. I've heard you should pull a couple of degrees of timing over single plugged maps because of the speed of flame propagation. Any rules of thumbs here?

First, I don't have much experience with dual plug. But I have looked at the 993 ign maps and they do seem to reflect what you are suggesting.