Need advice on a TT408 tune problem..

[Redline Motorsports]

I have been playing with the EFI Live for a couple months and are starting to get the hang of the tuning process...at least on a NA motor! :shock:

I have a friends car in the shop that is a F-body that has a 408 motor with twin turbos. The problem I am having is that as soon as the motor hits 4400 rpm's it just lay's over and drops off in power all the way to 6500. On the dyno it feels like the load has been turned up.

As a novice I am trying to get a good handle on a tune for this car. Someone had tuned the car before in which it ran worse then what I have gotten it to run. I think I have gone through all the basics and feel that I am either missing something stupid or I am WAY out in left field!

I started with a stock 99 bin and worked through every table. I have been told that the MAF may be the problem and the scaling could be off. The guy had a ZO6 MAF in which the scaling was incorrect. I loaded a stock ZO6 scale and no changes. I also checked to make sure that the PCM was not taking timing away for some odd reason and don't see it happening. There is also no KR and the WOT timing is a solid 21 degrees. The A/F is still quite rich but it should still not drop off in power as bad as it is. I have seen plenty of 10:1 AF that still spun up. The AF was 10.5:1.

On the dyno the car is pulling 7-8 psi of boost, all the way through the pull. I am looking for some direction as to what I should be looking for with a boosted application. So far it has been a hell of a learning experience and I have learned a ton. Now I want to get it running strong.

Any direction would be appreciated!

Howard

[Delco]

I have been playing with the EFI Live for a couple months and are starting to get the hang of the tuning process...at least on a NA motor! :shock:

I have a friends car in the shop that is a F-body that has a 408 motor with twin turbos. The problem I am having is that as soon as the motor hits 4400 rpm's it just lay's over and drops off in power all the way to 6500. On the dyno it feels like the load has been turned up.

As a novice I am trying to get a good handle on a tune for this car. Someone had tuned the car before in which it ran worse then what I have gotten it to run. I think I have gone through all the basics and feel that I am either missing something stupid or I am WAY out in left field!

I started with a stock 99 bin and worked through every table. I have been told that the MAF may be the problem and the scaling could be off. The guy had a ZO6 MAF in which the scaling was incorrect. I loaded a stock ZO6 scale and no changes. I also checked to make sure that the PCM was not taking timing away for some odd reason and don't see it happening. There is also no KR and the WOT timing is a solid 21 degrees. The A/F is still quite rich but it should still not drop off in power as bad as it is. I have seen plenty of 10:1 AF that still spun up. The AF was 10.5:1.

On the dyno the car is pulling 7-8 psi of boost, all the way through the pull. I am looking for some direction as to what I should be looking for with a boosted application. So far it has been a hell of a learning experience and I have learned a ton. Now I want to get it running strong.

Any direction would be appreciated!

Howard

21 deg timing :shock: a good stocker will not like that much timing , has this motor been seriously decompressed ?

Pull some timing out and lots of fuel , aim to get it to the 12:1 region as a starting point with min timing , something with 8 psi should see you in the 10-15 deg timing area on stock compression.

[MCG]

One thing that I've found when tuning boosted vehicles is that people underestimate the required seat pressure on springs. If you cut the seat pressure close to what the camshaft required, the extra push from the boost may possibly be opening them up.

I know that I can immediately tell when it is happening. As boost starts to come on, the car just lays down, somewhere around 4500 rpm as you describe and it almost feels like it is hitting a rev limiter without the noise.

I'd be willing to bet what you are describing is a valve spring issue. What springs did you install?

Also, when this occurs, the A/F ratio is exactly as you describe. You can't seem to get it to budge no matter what you do to the commanded fuel curves. It all seems to fit with what you are seeing.

[Redline Motorsports]

I started the timing out at 17 degrees and kept stepping it up. The motor picked up some good power with the timing increase and no KR. I have been suspecting valve float but here is the argument; the motor has less ten 1200 miles on it. The heads where specifically setup for a high boost application (15+). The first 500 miles the guy had front mounted twins and now its a custom rear mount setup, same motor. If the valves should have floated the first time around but didn't and they car pulled to 6500 all day long. I think I need to bump the valve spring theory down a notch and check some other things out first even though it is acting as such.

I just started a new file using a stock A4 file. I changed the VE table at 400-1200 rpm for the camshaft. I left the rest stock.

Changed the IFR table for the correct injector size.
Changed the usual, cat protection, abuse, engine torque, rev limiter and idle settings as needed.

I used a 02' ZO6 MAF calibration as he is using a stock 85mm MAF.
I was told that another approach to deal with the boost was to change the C6101 ETC predicted air flow table by adding 200 % to the entire table.

I haven't got a chance to upload these changes to see whats up. Any other feedback would be appreciated!

Thanks

Howard

[joecar]

Howard,
When you get a chance, please post the following (pictures' worth 1000's words):
a. images of logged data (charts),
b. images of changed tables.

Also, I thought the predicted airlflow table was used only for setting a DTC if actual airflow was too far away from this table...

[hpcubed]

Isn't ~4.5K where the maf usually maxes out (@8lbs) and the PCM dumps a bunch of fuel in? Are you sure the afr is straight all through the run? What is the maf reading at 4.4K?

[joecar]

hpcubed, good point; is the MAF restricting airflow above 4500...?

[Redline Motorsports]

hp,

The AF is going pig rich! 10:0-10.5 at that spot. I am still trying to get a grip on the MAFS operational parameters. As a matter of fact, the motor is pulling 8 lbs of boost when this is happening. Heres the thing though; I believe when this is happening, I have had the MAF disabled..... I assume that if the FLASHSCAN is not ready MAF that it is inop.

If the MAF is going to be a problem with the boost, shouldn't I focus on tuning in SD?

[turbolou]

A suggestion would be to run a tighter plug gap. I have seen many times on the boosted engines I work on tightening the gaps have resolved issues like this. The cars that I'm reffering to are Buick grand nationals. I
would imagine that the principles are simular. Platinum plugs also don't seem to work well with boosted applications. Just a thought.

[Redline Motorsports]

I agree with the plat. plugs not being used...which are not. I believe the problems are more tuning related and I must not having something configured properly. I have already got burned, as a newbee, in forgeting one minor tweak in a table that caused all kinds of headaches :lol:

The MAF sounds like it is the first thing I need to rule out. If I just unplug the MAF won't the car be forced into SD? If not what other parameters can I disable or adjust to take the MAF out of the picture. This motor will be running upwards of 15+ lbs and if the MAF is crying over 8, may it should go.

The power drop off is right between 4400-4500 all the way to redline.

[joecar]

...If I just unplug the MAF won't the car be forced into SD? If not what other parameters can I disable or adjust to take the MAF out of the picture.
This thread http://www.efilive.com/forum/viewtopic.php?t=1737&start=0 contains the following info:


Maybe this will help in getting people started...

Once I got the wideband hooked up, these are the changes I made to go SD.


...
Engine Diagnostics.MAF
{C2901} MAF High Frequency Fail 1, changed from "13500.000000" to "0.000000".
...

[Black LS1 T/A]

A suggestion would be to run a tighter plug gap. I have seen many times on the boosted engines I work on tightening the gaps have resolved issues like this. The cars that I'm reffering to are Buick grand nationals. I
would imagine that the principles are simular. Platinum plugs also don't seem to work well with boosted applications. Just a thought.

I definitely co-sign here.

I go to a colder, COPPER plug and gap the plugs on my supercharged engine down to about .035, sometimes as low as .032. This seems to work well for me.

[Black LS1 T/A]

...Changed the IFR table for the correct injector size.
Changed the usual, cat protection, abuse, engine torque, rev limiter and idle settings as needed.

Howard

Use any calculations for injector size only as a guide to a first stab. It will truly vary from setup to setup. Try to dial the IFR table in by monitoring LTFT's for near zero, perhaps slightly negative LTFT's. (I know some people argue the legitimacy of this, but it really has helped me target A/F more consistently.

Also, eliminate the CAT's (physically) as a problem. They clog easily under boost conditions. Check that.

[Black LS1 T/A]

As far as the MAF is concerned, pegging it won't keep you from making more power and a fairly predicatble A/F ratio.

In this dyno graph, I only had a single pump and 42# injectors (now have dual intank pumps and 55# injectors). At 8 ~ 10 PSI of boost, my MAF maxes out around 4800 RPMs with the stock MAF and around 5400 or so with a bigger, extended MAF.

http://www.blackls1ta.com/images/per_rpms.gif

I took my foot out of it at about 6500 RPM's. It had already run way too lean!

For a boosted application, I believe in targeting richest at peak torque and starting to lean, becoming leanest (targeting between 11.7 to 12.2) at peak horsepower, depending on how safe or aggressive I want to be. Some people run richer than that.

Also, I found, when SC'd, ensuring there is ample fuel, even running quite rich, delivers more power than trying to lean it out of the rich condition. So not only is richer safer for the boosted engine, but potentially could net more HP as well. (Not just my experience, though not scientific and tested across all applications, either, of course. :) )

[BigTex]

.... with a bigger, extended MAF.

Are you taling about the GM 85mm MAF from the Z06 or truck applications?

[Black LS1 T/A]

.... with a bigger, extended MAF.

Are you taling about the GM 85mm MAF from the Z06 or truck applications?

A custom 85mm MAF under research. I can't discuss it beyond that. No need anyway... Far as I know, they ended up not doing anything with it for the LS1... it was great and gave me about 5000 or 6000 more RPM of room, but still not enough to go all the way. It was a great try, though. :)

Edit:
Mean to say 500 to 600 RPM's ;)
Instead of pegging at about 4800, it pegs about 5300~5400.

[hpcubed]

hp,

The AF is going pig rich! 10:0-10.5 at that spot. I am still trying to get a grip on the MAFS operational parameters. As a matter of fact, the motor is pulling 8 lbs of boost when this is happening. Heres the thing though; I believe when this is happening, I have had the MAF disabled..... I assume that if the FLASHSCAN is not ready MAF that it is inop.

If the MAF is going to be a problem with the boost, shouldn't I focus on tuning in SD?

If you want to do this tune totally right then put a 2 bar map in and start down the speed density road. There is a little bit of a write up on this forum. You will need to half the tables that reference map etc. That will take quite a bit of time and tuning. The other option is to leave the maf operational and tune with the PE table. You need to compensate when the maf maxes with the PE table. Tune the car to go into PE mode as soon as you start making boost. Do not disconnect the maf if you are not going to run a 2 bar map and tune accordingly, that would be very hazardous.

[Redline Motorsports]

...Changed the IFR table for the correct injector size.
Changed the usual, cat protection, abuse, engine torque, rev limiter and idle settings as needed.

Howard

Use any calculations for injector size only as a guide to a first stab. It will truly vary from setup to setup. Try to dial the IFR table in by monitoring LTFT's for near zero, perhaps slightly negative LTFT's. (I know some people argue the legitimacy of this, but it really has helped me target A/F more consistently.

Also, eliminate the CAT's (physically) as a problem. They clog easily under boost conditions. Check that.

Thanks everyone for the responses. The cats are not on the car. Its a TT rear mount setup.

I am not sure which parameter I have touched but I do NOT get a MAF reading when scanning. Can I assume at that point that the MAF is not contributing to PCM control and that the PCM is functioning in SD?

I guess I'll check out the plug situation as I am taking it for granted that the guy has them setup right. It just seems like no matter what I changed in programming that it stills drops off a ton of power at that rpm. Maybe it is blowing out the spark....

Question I have is; if the car is in SD that how do you tell the PCM to allow for the increase for boost?

[QUICKSILVER2002]

Question I have is; if the car is in SD that how do you tell the PCM to allow for the increase for boost?

First off, you can't tune a boosted car in SD without a 2bar map sensor. The stock map sensor only goes up to 105kpa ~0psi of boost. You would have no control of the tune in boost with this setup (beyond adding fuel with RPM... You would be much better off with a MAF, since it can read boost up to a certain point.

Now, with a 2bar map you can tune the car with the VE table up to ~14psi.

[Redline Motorsports]

What is the part # for the 2 BAR? This guy swapped the LS6 intake for an LS2 with a 90mm TB since last year and the same time the turbos moved to the rear. He could have left the stock one in and I'm chasing my ass in other directions! How high will the Flashcan read under the MAP gauge? If you install a 2 BAR will it read the actual KPA or is it limited?

[Redline Motorsports]

I think I may be on to something.............I believe that the car has a stock 1 bar MAP. If so; if we where to max it out, would it cause the symptoms as noted? Also if we replace it with a true 2 BAR, how do you properly configure the software to read it?

The guy has the car back and is confirming the MAP that's in the car.

[MN C5]

I think I may be on to something.............I believe that the car has a stock 1 bar MAP. If so; if we where to max it out, would it cause the symptoms as noted? Also if we replace it with a true 2 BAR, how do you properly configure the software to read it?

The guy has the car back and is confirming the MAP that's in the car.

I used a GM 2Bar MAP part #213-1631 AC Delco #12580698 GM# snapped right in and it fired right up with the first tune I tried. Basically you'll have to establish 1/2 values for tables using MAP. It only takes 30 minutes or so to get a base tune setup for the 2bar. Then using Auto Tune it won't take long to wrap it up.

[Redline Motorsports]

I just spoke to the guy that owns the car and he has confirmed that the MAP in the car is a stock 1 BAR that came with the LS2 intake. Good news a guess.

Once we installed a 2 BAR is there any parameters that need to be changed to let the PCM know that it has a MAP with twice the range? Or, according to the way you stated "establish 1/2 values" do I just look at the existing header and assume it is half?

Does it sound logical to say that since we now know that the MAP was being maxed that this was a large tuning issue and was causing this scenerio?

The other question I asked was about the FS dashboard; I noticed duing loggings on the dyno that the MAP would read 105 (which I believe is the max MAP reading out of a stock MAP sensor) will this read a higher KPA with the new 2 BAR MAP sensor?