Strange tuning problems

Car is a 94Z28 with a fresh D1SC blower. Doing tuning on it right now, and can't get it right at all... The only thing I can get to effect my a/f is the injector sizing. Any changes in any of the other fuel tables does absolutely nothing. To get the car to run in the mid 12's a/f under wot, I had to set the injector sizing to 21 #. That in effect is causing the car to idle at 10.8:1. Above 4500 RPM the motor goes lean and detonates. It's basically doing the exact opposite of what it should be doing. The car has a brand new inline fuel pump... but possibly the intank pump is going out? It's got about 55-60 lbs of fuel pressure at wot. Any thoughts would be appreciated...

Are you working with the MAF calibration table or the PE table or both?

Steve

Are you working with the MAF calibration table or the PE table or both?

Steve

PE Table. MAF table doesn't effect WOT on OBD1 as far as I know...


Chuck

So you are saying that adjusting the PE tables isnt effecting the AFR at WOT? Maybe you arent adjusting them out far enough or in the wrong direction?? I have this excel program that calculates the PE values based on your current PE values and the AFR reading you get using at wideband on the dyno. I havent had a chance to put it to use just yet but I believe it should work great. I found this program on a guys web page.. his name on cz28 is cmillard and I think the link to his site is in his sig so you could try searching for his name.

MAF will certainly effect fueling at WOT. You must be in Closed Loop for the PE table to come into play however. Are you running an open loop program?

So you are saying that adjusting the PE tables isnt effecting the AFR at WOT? Maybe you arent adjusting them out far enough or in the wrong direction?? I have this excel program that calculates the PE values based on your current PE values and the AFR reading you get using at wideband on the dyno. I havent had a chance to put it to use just yet but I believe it should work great. I found this program on a guys web page.. his name on cz28 is cmillard and I think the link to his site is in his sig so you could try searching for his name.

Basically I zero'd out the PE table to start from scratch. I went as high as 5.5 in the 4000 rpm and above range, and that did absolutely nothing. So unless 5.5 is a very small number on LT1 edit, there is something else causing this thing to do what it's doing. I'm still leaning towards fuel pump..


Thanks,
Chuck

MAF will certainly effect fueling at WOT. You must be in Closed Loop for the PE table to come into play however. Are you running an open loop program?

Not unless somebody before me tuned it that way. But I doubt it.


Chuck

PE tables are %change to fuel vs temp and RPM... so assuming you're working the PE vs RPM table as most of us do, you're only making an adjustment of x% above base fueling.

So if the car is lean before going into PE it will continue to be lean and require larger numbers in the PE table to compensate.

For example: my stock table had values as high as 9.8 in the PE vs RPM table, well after installing my headers, the car was lean and adding fuel prior to WOT. I mistakenly locked the BLMs and added 3 more to the PE table making it a total of 12.8 and it made up for the lean condition, I would have had to add even more to get the ratio lower to make up for the increased chance of detonation with a blower.

Now, I'm tuning the MAF table by logging, and making adjustments to the MAF table based on the average fuel trims for each step in the MAF table. That should get my Ltrims (BLMs) close to 0 (128) and then let me reliably tune the PE vs RPM table.

I'd say that getting the Injector constant set right, and adjusting the MAF table will get you MUCH closer to where you want to be at WOT. Shoot for the tune to be a tad rich before going WOT, that way you're better off during WOT runs, and then tune that PE table. Oh, and make sure you're BLMs are not locked during WOT.

Just my opinion here, but this approach seems to be working for me...

I think at WOT before closed loop the PCM might be looking at the VE tables what do you think? cuz I know in open loop the PE table is ignored now LOL, I don't think tunning the MAF table will be any more accurate then the PE table unless there is a sertain area that you can't alter with the PE table then use the MAF to alter that A/F like say between the PE rpms.

Matt.

I think at WOT before closed loop the PCM might be looking at the VE tables what do you think? cuz I know in open loop the PE table is ignored now LOL, I don't think tunning the MAF table will be any more accurate then the PE table unless there is a sertain area that you can't alter with the PE table then use the MAF to alter that A/F like say between the PE rpms.

Matt.

Just to see if it did anything, I leaned the MAF table out by 25% across the board, and it did effect my a/f by about 2 points in closed loop. But open loop it still leaned way out, even with PE values as high as 21.


Chuck

Oops, I just saw that you have a blower. Are you pegging the MAF?? If so, your only solution is to put big, big numbers in the PE table or use an FMU (boost referenced fuel pressure regulator) to add extra fuel.


Steve

Oops, I just saw that you have a blower. Are you pegging the MAF?? If so, your only solution is to put big, big numbers in the PE table or use an FMU (boost referenced fuel pressure regulator) to add extra fuel.


Steve

It's not responding to PE table changes, unless I need to go even bigger than 21... And it's got an FMU that's adding over 15 lbs of fuel pressure. Goes from 45-62 under wot. Something has got to be messed up with this car....


Chuck

Can you post some MAF vs RPM readings on one of your Dyno pulls. Kinda sounds like your MAF might be hosed up. Also make sure that you are really entering PE mode, theres a PE enable vs TPS table (this one's a long shot). Another question, If your injector constant is set to correct #, how are your BLM's at idle and at various cells during cruise? we might be able to narrow down some WOT problems be evaluating part throttle characteristics. My tuning philosophy is:

1) Do Idle 1st
2) Then spend most of my time on driveability, part throttle tuning, and BLM's
3) Only head to the dyno when step 1 and 2 are hunky dory

Steve

Can you post some MAF vs RPM readings on one of your Dyno pulls. Kinda sounds like your MAF might be hosed up. Also make sure that you are really entering PE mode, theres a PE enable vs TPS table (this one's a long shot). Another question, If your injector constant is set to correct #, how are your BLM's at idle and at various cells during cruise? we might be able to narrow down some WOT problems be evaluating part throttle characteristics. My tuning philosophy is:

1) Do Idle 1st
2) Then spend most of my time on driveability, part throttle tuning, and BLM's
3) Only head to the dyno when step 1 and 2 are hunky dory

Steve

Well I own 2 dyno's, so heading to the dyno is only 50 feet away for me :D

Chuck

If I lived in Houston I would become your very best friend in the whole world! :D :D :D :D

If I lived in Houston I would become your very best friend in the whole world! :D :D :D :D

If you could simply tune this car for me you would become my very best friend in the world :D It's a customers car, and I'm at my wits end with it. LT1's are normally pud to tune. But this one is giving me nightmares! :cry: I didn't work on it today though just because it's too frustrating. I might try it again for the last time tomorrow. Thanks for all the help. Appreciate it much.

http://pic2.picturetrail.com/VOL5/758497/3133707/54899139.jpg


Chuck

If I were you I would set the maf tables back to stock. Use them for tuning part throttle blm's if you choose, but I've found that if you get the injector constant right for the injector you're using and the fuel pressure you're running...that the stock maf tables work fairly well.

How much boost are we talking?
What size injector?
Is the fuel pressure regulator a boost referenced unit?
What ratio fmu?
Is an fmu even required with the amount of boost and injector you're running?

There are quite a few things that factor in here...

If I were you I would set the maf tables back to stock. Use them for tuning part throttle blm's if you choose, but I've found that if you get the injector constant right for the injector you're using and the fuel pressure you're running...that the stock maf tables work fairly well.

How much boost are we talking?
What size injector?
Is the fuel pressure regulator a boost referenced unit?
What ratio fmu?
Is an fmu even required with the amount of boost and injector you're running?

There are quite a few things that factor in here...

haha, it's got stock injectors (24#). I bet that's the problem :o

The customer purchased the kit, we only did the install. It's a Procharger D1SC, but has a big pulley. We haven't hooked a boost guage up to it yet, but I assume it's around 7 psi. Couldn't tell you what fmu it has, or what the ratio is. It's got a stock fuel pressure regulator as far as I know..

Thanks for the help Dan. You made the ol light bulb light up :bow:

Chuck

I'd be willing to bet you're out of injector.
Find out what size injector you could go to and be able to get rid of the fmu.
Old technology. It works, but a big injector is the way to go IMHO.

I think at WOT before closed loop the PCM might be looking at the VE tables what do you think? cuz I know in open loop the PE table is ignored now LOL, I don't think tunning the MAF table will be any more accurate then the PE table unless there is a sertain area that you can't alter with the PE table then use the MAF to alter that A/F like say between the PE rpms.

Matt.

the OPEN LOOP vs TEMP vs MAP is the table refered to in WOT mode when in open loop. The VE tables also play a roll in all open and closed loop fueling but the specifics are complicated and not believed by some. And I do not want to start something here. Also since he boosting hes going beyond 100 KPA sooooooo the VE tables are very inccorrect and would be better if he didnt touch them.

I'd be willing to bet you're out of injector.
Find out what size injector you could go to and be able to get rid of the fmu.
Old technology. It works, but a big injector is the way to go IMHO.

Well after a week of replacing parts, we're still in the same boat! Brand new SVO injectors didn't fix it, and a brand new Walbro 255 in tank pump didn't fix it. Fuel pressure goes from 45-60-back down to 45 (which is when it starts to cut out real bad.

Chuck

Well after a week of replacing parts, we're still in the same boat! Brand new SVO injectors didn't fix it, and a brand new Walbro 255 in tank pump didn't fix it. Fuel pressure goes from 45-60-back down to 45 (which is when it starts to cut out real bad.

Starting to sound like you may have some ignition problems as well as the fueling problems that you've taken care of. You already know the biggies I'm sure.

1) Fresh Optispark
2) Fresh Wires
3) Colder Plugs - to avoid blowout
4) Bad MSD box if your using one - I've heard of a lot of problems with MSD's

Also: What kind of Duty Cycle are you seeing right before it starts breaking up now with the larger injectors? What the heck would cause the FP to drop back down to 45? Probably loosing boost when it starts to break up, then mainifold pressure drops, and thus FPR lowers FP. Just thinking out loud here. :)

Good luck.

Steve

Well after a week of replacing parts, we're still in the same boat! Brand new SVO injectors didn't fix it, and a brand new Walbro 255 in tank pump didn't fix it. Fuel pressure goes from 45-60-back down to 45 (which is when it starts to cut out real bad.

Starting to sound like you may have some ignition problems as well as the fueling problems that you've taken care of. You already know the biggies I'm sure.

1) Fresh Optispark
2) Fresh Wires
3) Colder Plugs - to avoid blowout
4) Bad MSD box if your using one - I've heard of a lot of problems with MSD's

Also: What kind of Duty Cycle are you seeing right before it starts breaking up now with the larger injectors? What the heck would cause the FP to drop back down to 45? Probably loosing boost when it starts to break up, then mainifold pressure drops, and thus FPR lowers FP. Just thinking out loud here. :)

Good luck.

Steve