Bad dyno run

[Craig 94 TA GT]

I just had a couple baseline pulls and found out that there's something wrong with the T/A. Here's the dyno graph:



Notice it flucuating a whole lot at 4500+ and just gets worse. The overall numbers are very disappointing as well. The whole thing seems to die at 5000+.

I'm thinking could this be the alternator? My voltage has been showing pretty low lately, and when I turn the fan switch on, the voltage dips into the yellow. The only other thing I could think of is the coil, but I doubt that's the problem. I just had a new opti, new plugs/wires, new fuel system (pump, filter, regulator, injectors) put in. Thanks in advance.

[KnightFire]

Actually the first thing that came to mind when I saw the graph was a bad coil...LT1s are VERY picky in the upper RPMs about how much spark they get. However, with your symptoms your probably right on the mark...I would have your alternator load tested, most places will do it for free. See if that or the coil is the culprit. At least you found out about it NOW, instead of late at night in the middle of nowhere...gotta look at the bright side broh.

What mods do you have?



KnightFire

[Craig 94 TA GT]

Thanks for the reply Knightfire...
I will have it load tested ASAP. Hopefully that's the problem, as I can easily replace it.

I could have had one more dyno run but we just agreed to quit because it would be beating a dead horse. He did give me a discount on the next time I get her dynoed...so at least I can test it again once the alternator is replaced.

My mods aren't much... the main things for hp: Borla catback, Moroso CAI, 75 mm MBA MAF ends.
The other mods include 160* thermostat, SLP fan switch, TB coolant bypass, LT4 KM, Vortech intake elbow, 2200-2400 stall converter, rebuilt and strengthened 4L60E, 1LE DS, suspension stuff, poly mounts, etc.

How much power do you think I lost considering I had this problem?

***edit***
I forgot to mention...I also have the intake manifold leak. I'm not sure if that would make the dyno chart, or at least contribute, to it flucuating so much and dying at a certain RPMs.

[Injuneer]

Low system voltage also screws up the fuel system... the pump will slow down, the injectors will slow down. That would show up as a "lean", and the A/F ratio does start to rise on the blue line after 5,400RPM. But it looks like it holds the A/F ratio (typical "too rich" LT1 stock tune - 11.7:1).

But it looks like its losing spark when the curve takes the nose dive, and then recovers. Sometimes the hill and valleys get covered up, depending on how much "smoothing" they set the dyno plotting program for. It might be a case of them having very little smooting applied at all, and all the warts and scabs showing up all too clearly.

Does the voltmeter go into the red only at idle? When you are cranking 4,000rpm, the capacity should be a lot higher than at idle.

Have the valve springs ever been replaced? How many miles on the engine?

[Craig 94 TA GT]

Thanks Fred for the great info... the motor has just under 105k and the valve springs are original. I was planning on putting 1.6 RRs with LT4 valve springs, but I needed to wait a bit to shell out extra $$ for the valve covers (for clearance).

I believe they set the smoothing to "5", but I'm not sure what the value represents. The guy who was overseeing the dyno said that the curve isn't right, and there's something majorly wrong - way too much flucuation and the motor dying at certain RPMs. He dynos a lot of Camaros/Firebirds, so I am suspecting that the valleys aren't normal. Also, during the second run, the motor heavily stumbled at ~5400 RPM. Not sure if it was a miss, but it's almost like it died then quickly came back to life. I kept on the throttle until ~5800 RPM. Steve93Z (who was there) and the overseer said that they said popping when I was revving up - and definitely heard the huge miss.

The alternator dips into near-yellow only at idle...when it's fully warmed up. When the fan switch is on, the needle dips definitely into the yellow. When the revs come up (say 2000 RPM), the voltage does go up, but not THAT much (maybe just under the 13 volt mark). However, when the motor is cold and warming up, it holds at just a bit over 13. Doesn't make sense condering when it's warm and at 1500, the voltage is less than when cold at 900. I didn't notice the voltage when at WOT on the dyno though.

[Injuneer]

When you first start the engine, the voltage regulator pushes the system voltage up to recharge the battery from the load used to start the engine. You might see 14 or 15 volts. 13 sounds low for a cold start. As the battery "recharges", the voltage regulator pulls the system voltage down to a "normal" level. But it shouldn't allow the voltage to drop into the yellow, unless you have an extremely low idle and a lot of heavy loads like a big stereo.

A smoothing of 5 is the right value. It means the valleys you see are very real, because even with the smoothing, they aren't covered up. I'd guess ignition breakdown. The reason it seems to go slightly lean on the blue line at 5,400rpm is all the oxygen from the unberned combustion chamber contents.

[fastTa]

It does sound like a major culprit in your scenario is low system voltage. What wires/plugs and gap? Stock fuel pump replacement?

The pulse width of the injectors can unfortunately be adversely affected by the PCM not getting proper juice. A load test would help to diagnose that.

Using a 17% drivetrain loss correction factor (which is about normal for a 4L60E), you are making an estimated 308 flywheel hp. While this isn't really too far off, I suspect you should be seeing about 15-25 more hp given your mods.

BTW did you mention to the dyno operator that your MAF had modified ends?

Do you ever see any blue/white smoke from the exhaust? It is possible given your mileage that you are getting a slight amount of blowby which can rob you of some hp and could even contribute to the apparent "leaning condition" at about 5400 rpm due to the additional oil present in the cylinder.

If you are getting blowby through the oil ring pack, the greater the piston speed and overall speed of the rotating assembly the more the oil blowby is exaggerated.

BTW did you do your pull in 3rd?

Let us know!

[Craig 94 TA GT]

Thanks for the info on the alternator...so it looks like it is getting weak. When the voltage is in the yellow, I am not using any accessory except for the fan switch. The stereo is stock too. The idle is normal, about 600 RPM.

The plugs/wires were replaced 500 miles ago, and are Delco Platinums, correctly gapped to .050 and the wires are Supermas? 7 mm. I didn't have a choice in choosing those because of the sugar in the tank incident. Previously, I had good NGK TR55s with Spiro Pro 8 mm wires...and they were just thrown out by the moron mechanic.
The fuel pump was a stock replacement, as the insurance wouldn't be happy to give any aftermarket parts (and they weren't even happy about the MAF ends I have).
I didn't mention to the operator that I had MAF ends, but they're red MBA ones, so it's hard not to see 'em. I don't know if he knew though....BTW, what would he do if I told him about them?

I haven't seen any blue/white smoke the from exhaust. The only thing is a bit of black smoke came out when I punched it on the dyno. I don't think I'm getting blowby, but you never know...

And the pull was done in 3rd gear. I wish I had punched it sooner as the computer started picking up the RPMs at 3600.

Also, it seems to start break down at 4900, but why did the RPMs read on the dyno seem to go haywire at 5400 RPM (and stop reading hp in the first pull)? I punched it all the way to 5800 RPM...both times. So is this the largest sign that the problem is the iginition? His RPM reader wire was hooked up to wire #3...so is it possible that it's breaking down so much that the computer doesn't know what to do anymore?

I really appreciate your guys' help!

[Craig 94 TA GT]

I don't know how much it will help diagnostics, but here's the speed chart of the hp vs mph.


The "missing" seems more drastic here and really shows the hp numbers flucuating as the speed goes up.