dyno results and A/F ratio

[Kevin - Blown 95 TA]

OK, well I got no way of knowing what's wrong with your car, if anything, or what gas is in it. If it was here, I would tell you what's wrong, but all I can do is help you understand what might be going on with the plugs and the O2 readings - who knows - maybe they are on the level, but of it makes much sense as far as I can tell.

I looked at some of my earliest log readings from the track when I had 24# injectors and a FMU and my pulsewidths were up to 27ms trying to feed the blower - the FMU kept the stock O2 sensors in the 960 range.

[Craig 94 TA GT]

Wow, 27 ms! I'll bet it was running horribly lean? It can only physically achieve 21 ms max at 5800 right?

I appreciate all the info you've given about gas, plugs and the wideband. I've learned so much. It pays to know about the widebands, especially since I'm going to find another dyno. The $#@$ dyno operator let all cars, except mine, cool before the 3rd run. Everyone picked up 5-9 hp due to this. I also told him to close the cutout on the 3rd run. He did, and the dyno showed -1 hp. He then got out and said, "Hey, your cutout ain't worth $#!!." He had just that attitude all day. Which also makes me think he doesn't know or doesn't care what he's doing. Time for find a more reliable dyno once I get the problem fixed.

[94 formula]

Craig...This is a link to another board look at what this guys dyno showed up. After reading this thread and others like it I'm convinced that not all dynos are created alike and not all dyno operators are either.

http://www.fbody.com/cgi-bin/lt1/read.cgi?msgid=250802

[Kevin - Blown 95 TA]

Wow, 27 ms! I'll bet it was running horribly lean? It can only physically achieve 21 ms max at 5800 right?

No, it was in the 960-970 range on the O2 sensors but you're right about the theoretical opening time of the injector being around 20 ms at 6000 rpm, so go figure? The injectors are probably going static momentarily at high rpm while they're being commanded to push out even more fuel than they possibly can. The reason that it was still rich was the fuel pressure from the FMU which restricts return to the tank and lets the pressure spike to 70 or 80 and gives you the extra fuel flow that you need with the smaller injectors. It's how they can make a supercharger kit work with stock injectors and keep the cost down. Most guys, including me, ditch the FMU for larger injectors, because it's more consistent to tune.

So, you can't trust any one parameter as gospel. You need to look at several data to see what's happenning. And there are some PCM scanner bafflements such as the injector pulswidth and timing discrepancies that got tuners scratching their heads about these EFI engines and their computer systems.

[Joe 1320]

I can tell you from personal experience in this. The dyno confirms some basic things that we've seen as already present. I would bet that until you fix that exhaust leak, you're not going to get the power out of the tune you already have. The problem is that you're not getting a balance on both banks. Formulas don't take into account for that. In a perfect world with perfect equipment, a widewand sensor on each header primary with the ability to tune each cylinder independantly would be the ideal. Since we aren't doing that it's tougher to get a good ballpark tune. In order for that to work properly, there can be no exhaust leaks, no plug and wire issues and no injector/pump issues. Now there are a few other issues that can mess with this too. Internal issues like non uniform cam lobe wear, cylinder pressure loss, and so on that can mess with 02 readings. While some of these will still allow the car to make decent power, it just won't make it's peak performance.

Craig, take a systematic approach for a minute. If the 02 sensors seem to be reading some issue, the first place to look is indeed in the exhaust. Make sure the sensor is fresh #1 and there are no leaks #2. If there are no issues.....

The ignition system. Hot spark consistantly on every plug at all rpms? Can you verify there is no miss? I'm not talking combustion event in the cylinder, I'm talking a verified spark at the plug. If there are no problems.........

The fuel system. do the injectors have uniform flow? Ample fuel pressure? If no problems.....could be something internal. maybe a slight headgasket leak, worn cam lobe, worn cylinder, any number of things.

The point is, an exhaust leak will affect the fuel system. The computer affects the fuel system based in part on exhaust readings. Before you do anything else, go through everything systematically and you'll find it. I'm tellin' ya, trust me on this one.

[fastTa]

You can manipulate the formula for estimated air flow to reflect your actual readings, but just remember you have to also adjust the estimated fuel flow as well, because if not it will adversely skew the outcome. I seriously doubt that you are anything over 14.3ish because you would be having serious problems. Also it is not uncommon for the motor to show lean at idle or show lean spikes after lifting the throttle. Anytime load is removed from the motor, it will usually report leaner than normal.

But also remember that chassis dynos don't accurately replicate a real road driving load on the powertrain. They only place enough load on the rollers to obtain calculations based on that specific known resistance. So you will always run leaner on the street than a a wideband shows on the dyno. They are accurate on the dyno for those conditions, but they don't accurately portray a "real life" driving scenario unfortunately. This isn't good in your case!

Many people believe that maximum horsepower is achieved by adding as much fuel as possible and ultimately resulting in a rich condition, but as you know, this is not entirely true. A motor makes the most power when there is a sufficient amount of fuel to burn all of the oxygen in the CC. If there is more fuel than oxygen to support it, or if the flame extinguishes prematurely, leaving residual oxygen (this also makes me wonder if your ignition system is up to par), the power diminishes. This could also be a reason for your plugs showing white and being lean.

A motor requires the most fuel at peak torque and then needs to be leaned out at peak horsepower. The volumetric efficiency of the engine is the highest at peak torque, since the CC is the fullest with a/f mix, thus it requires the greatest amount of fuel. Most bolt on LT1's that I have had experience with like an AFR of 12.7:1 to 13.0:1 at peak torque, then lean out to 12.9:1 to 13.2:1 at the WOT.

This is what I would do. I would swap MAF's with Steve and see what happens. If everything in the PE tables seems to obey the PCM4less tune better, well then you obviously have a malfunctioning MAF. Is your coil, ICM and opti in good shape as far as you know?

[Craig 94 TA GT]

Joe, I'm with you on that. Tomorrow, I'm going to go to a reputable exhaust shop to get the leak fixed. That way, they'll do it right. I have had nothing but trouble trying to do it myself, especially with SLP's poor workmanship on the inner weld. I spent 2 days trying to drill out their bent "aluminum" junk bolts because I had tightened it down so hard to prevent a leak...and it broke in the flange. At least I got it out, and put a heli-coil on the flange now. The exhaust shop can do the rest.

From there, I'll do some more scans and readings.

Kevin, I wish I could swap with Steve's MAF, but it doesn't exist lol. It's '93, and he always reminds me why he doesn't have one (no Steve, it does not fail frequently lol) . I don't want to just spend $$ on a new MAF to test if this one is going sour, but I guess if there's no other way. I think it's around $150, which isn't tooo bad, I guess.
The coil was replaced about a year ago, it's an MSD blaster coil. ICM was replaced 9/04 because my previous ICM was causing it to stutter and backfire. The opti was replaced and installed 2/04 due to code 16. It seems to be OK still. However, when I changed the wires in the header install (the old ones were junk 7mm), I noticed something in the very bottom passenger's side boot to the opti. The inside of the wire boot seemed to have corrosion. All others were OK. The opti to coil (on the opti side) had a bit of the same, but not as bad as the plug wire. I'm not sure if this is normal, or if something's up?

[Z Ya Later]

Joe, I'm with you on that. Tomorrow, I'm going to go to a reputable exhaust shop to get the leak fixed. That way, they'll do it right. I have had nothing but trouble trying to do it myself, especially with SLP's poor workmanship on the inner weld. I spent 2 days trying to drill out their bent "aluminum" junk bolts because I had tightened it down so hard to prevent a leak...and it broke in the flange. At least I got it out, and put a heli-coil on the flange now. The exhaust shop can do the rest.

From there, I'll do some more scans and readings.

Kevin, I wish I could swap with Steve's MAF, but it doesn't exist lol. It's '93, and he always reminds me why he doesn't have one (no Steve, it does not fail frequently lol) . I don't want to just spend $$ on a new MAF to test if this one is going sour, but I guess if there's no other way. I think it's around $150, which isn't tooo bad, I guess.
The coil was replaced about a year ago, it's an MSD blaster coil. ICM was replaced 9/04 because my previous ICM was causing it to stutter and backfire. The opti was replaced and installed 2/04 due to code 16. It seems to be OK still. However, when I changed the wires in the header install (the old ones were junk 7mm), I noticed something in the very bottom passenger's side boot to the opti. The inside of the wire boot seemed to have corrosion. All others were OK. The opti to coil (on the opti side) had a bit of the same, but not as bad as the plug wire. I'm not sure if this is normal, or if something's up?

Hey, ask any GN owner...they'll tell you how long those stinkin' things last lol. Probably the reason some convert to the LT1 or LS1 MAF.

Worst case, if the Y-pipe is too jacked up, I know they can fab one up that will be good for flow...but it won't be Stainless Steel. You could always call SLP, I'm sure they'll take care of you.

[fastTa]

Kevin, I wish I could swap with Steve's MAF, but it doesn't exist lol. It's '93, and he always reminds me why he doesn't have one (no Steve, it does not fail frequently lol) . I don't want to just spend $$ on a new MAF to test if this one is going sour, but I guess if there's no other way. I think it's around $150, which isn't tooo bad, I guess.

I would do a search on ls1tech and cz28 in the for sale section. A used one can be had for $30-$40. Do you not know anyone locally that would let you temporarily use their MAF?

I think through Jason or Dal, a new MAF is less than $150. Part# 25008308. The majority of your part throttle data looks to be somewhat normal, so I suspect that your MAP sensor is OK.

[Craig 94 TA GT]

WOW! gmpartsdirect: GM LIST: $451.28
OUR PRICE: $225.63

Dal and Jason seem to have a general similar price as partsdirect (without the lame shipping and customer service of course). So I guess the price has increased heavily lately.

I'll have to see the new scans after all the leaks are gone. Then, hopefully, a miracle will happen and we can conclude the MAF is ok.

Steve, there's no way in heck I'm getting a new y-pipe, just as you mentioned. If it can't be fixed for some odd reason, that shows defective workmanship and I should be covered under warranty. Or else....

[fastTa]

WOW! gmpartsdirect: GM LIST: $451.28
OUR PRICE: $225.63

Dal and Jason seem to have a general similar price as partsdirect (without the lame shipping and customer service of course). So I guess the price has increased heavily lately.

See if you can open this link: GM Parts Direct MAF

It showed me a price of $141 plus shipping. So figure roughly $166 with shipping.

But I agree. Let's see what the data says after the exhaust leak is fixed.

[Joe 1320]

Hey, ask any GN owner...they'll tell you how long those stinkin' things last lol. Probably the reason some convert to the LT1 or LS1 MAF.

pssst..... don't tell my car this but, she has the same MAF that was on her when I bought the car in 1990. The secret is keeping the MAF isolated and vibration free. Maybe just a little lucky too. Most get a cold air kit that replaces the bellows with a metal tube. That's where they go wrong. The maf is mounted to the rigid tube and it is now subjected to additional engine vibrations as well as stress from mountings. Often times they literally broke apart. If not, the vibrations combined with heat killed them.

[Z Ya Later]

pssst..... don't tell my car this but, she has the same MAF that was on her when I bought the car in 1990. The secret is keeping the MAF isolated and vibration free. Maybe just a little lucky too. Most get a cold air kit that replaces the bellows with a metal tube. That's where they go wrong. The maf is mounted to the rigid tube and it is now subjected to additional engine vibrations as well as stress from mountings. Often times they literally broke apart. If not, the vibrations combined with heat killed them.

How in the...Huh?!?! Dude, you're freakin' lucky. I think she's on her 4th one right now. So, you're runnin' the stock airbox on yours? I'll shoot you an e-mail when I get home tonight...don't wanna hijack anyone's thread lol

Well Craig, like I said, if it is the Y-pipe, give SLP a call, I'm sure they'll take care of you. I'm assuming we're still going to the shop tomorrow though, at least to check for any leaks?

[Craig 94 TA GT]

Alright, I just don't get this. Out of desperation, I tried once more to fix the leak(s) myself (I hate taking it in anywhere for any reason, just as everyone here does). I seems like I got it super quiet underneath, but I'm not 100% sure if it's still leak free. I did 3 idle scans. BTW, do idle scans even count when looking at BLMs?

Scan one: 141/128 Reset the PCM. Here it seems like 0 change from previous scans

Scan two: 141/122 Here I put a small spacer nut in the throttle body stop screw just to see what would happen if the tp sensor and blades were up a tiny bit. It moved up to 0.64 volts (from ~.5). Then tightened the passenger's side header to y-pipe because I think I can hear a slight leak. The passenger's BLMs went down, but the driver's stayed the same

Scan three: 128/122 Reset the PCM. Removed small spacer in TB screw. TP volts back down to .51. Now why is the driver's side a perfect 128, and the passenger's side low? This doesn't make sense from what I did. A difference of 6 is much better than 13, though.
Or maybe, is reading BLMs at idle worthless?

[Craig 94 TA GT]

See if you can open this link: GM Parts Direct MAF

It showed me a price of $141 plus shipping. So figure roughly $166 with shipping.

But I agree. Let's see what the data says after the exhaust leak is fixed.

Thanks Kev..that's a much more reasonable amount to spend, even just for maintenence...condisering it's almost 12 years old with 110k.

I'll try and post WOT results ASAP with the exhaust leaks fixed, and verified.