dtfastbear

Good advice. We'll definitely be monitoring voltage in HPtuners and also will be monitoring fuel pressure at the rail to make sure it isn't something so simple as the fuel pump not keeping up (Walbro 255).

orion4096

iTrader: (5)

There might be something with the coil packs. I dyno'ed my ls6 today and had no problems with my coil packs. These were the same ones that were missing on your car. I checked over the dwell settings in your old tune and they are identical to mine. There were coil changes across different years so maybe:

- make sure you have ls1/fbody coils
- check back over the coil pins and wiring if you haven't already done so

dtfastbear

That's good advice. I've occasionally got sporadic misfire codes, and I'm 100% convinced they weren't from plugs/wires. Either I or the previous owner could have pinched one of those wires to the coil pack plugs when swapping the motor.

I'll go through them tonite while installing my V8R brakes! Even if the car won't go very well, it will stop like a champ. ;-)

Did you get your car all back together yet?

Cheers,

Dean

orion4096

iTrader: (5)

The car is back together and made 368/373 hp/tq at the wheels yesterday. The ls6 cam is nice and quiet. Break-in was a 30 mile drive to the alignment shop to fix my toe and 20 mile drive to the dyno.

joecar

Maybe check that your battery is ok (doesn't have an intermittent shorting cell).

dtfastbear

*sigh* The saga continues. New 36lb injectors, MAF removed, nice straightened intake and a speed density tune. EXACT same behavior - big 40+ HP dip between 5200 and 5800.

Fuel pressure is fine. Voltage is fine. Pulled apart, resoldered and cleaned up the metal contact on all grounds. Tried a new crank sensor. Replaced MAP sensor. Tried an entirely new PCM. EXACT same behavior, every pull on the dyno.

One thing we didn't try but I feel is a real stretch, is alter the exhaust system in some way. I have Sandersen shorty headers back to the diff the they come together to a single tube, 90 degree bend to a smallish Borla muffler then a 90 out to the end. Is it remotely possible that there's some sort of resonance that's causing incredible back pressure and causing such an abrupt power dip just in the tight rpm range?

The only other thing we can think of is "something in the wiring harness", but I don't even know what. We tested the resistance an continuity in the coil pack harnesses - everything was fine.

Don't really know where to go from here. Will drop the muffler off and do a session on the track (until they black flag me for sound) just to rule that out...

Thoughts or suggestions appreciated. Please talk me off the ledge, 'cause I'm getting awfully close to putting this damn thing on Craigslist! ;-)

Cheers,

Dean

rob69zombie

iTrader: (7)

Holy crap! Mine is doing the EXACT same thing. It stumbles from 5k-5.5k rpms and them comes back into power. I have LT's, ORY, LM1, ls6 intake, and a 25% u/d. I noticed it stumbling a couple of months ago. I took it to Mayhem motorsports where my dyno looks EXACTLY like yours. We did 15 pulls and it stumbled 12 of those times. I put a Walbro 255 in it, changed the plugs, wires, and the coils on the dyno, and nothing fixed it. I also changed my MAF with no difference. It's still at Mayhem where they are further troubleshooting. Wish us both luck!

rob69zombie

iTrader: (7)

Also, we measured the fuel pressure on the rail and it was 58lbs and when it stumbled, the pressure stumbles with it; not that the fuel is causing the stumble but it correlates with it. IDK what the hell to do next.

dtfastbear

Misery loves company.

It certainly sounds like if one of us finds a cause/solution, we'll both be in the clear, as our symptoms seem to be identical. We also put a fuel pressure gauge on the rail and saw the exact same thing you did. Steady 58psi and then a flutter along with the breakup, but it certainly appeared to be a result, not cause, of the stumble.

My tune was also scratching his head and thinks the problem could be "in the harness". My car is a conversion, and I'm using a Painless wiring harness. Sounds like your car probably has a stock GM harness in it?

Please keep posting hear as you try things, even if they don't work.

My next steps are to try a track session with the exhaust system significantly altered (remove muffler) and we're also going to trace back and ohm-out every fuel and ignition wire in the harness to see if we can find anything suspicious.

Good luck!

Dean

rob69zombie

iTrader: (7)

Thanks Dean. Yes, mine is the factory 2000 SS harness. I'm referring Mayhem to this thread so they can see all you did as well. Thanks man.

dtfastbear

Do you know what your plugs are gapped at? Mine are brand new NGK TR55V's gapped to 0.054" I had the exact same behavior with platinum tipped NGK TR55's where I wasn't careful on the gap.

Thanks for including the Mayhem guys. With more eyes on this collaborating, I hope we can get to resolution faster. We're assembling a list of things to try and may get on the dyno tomorrow:

- remove muffler (possible resonance/back pressure)
- try different coil packs
- try plugs gapped to 0.032"

I'll update this list with more tests as we brainstorm this afternoon.

Cheers,

Dean

rob69zombie

iTrader: (7)

My TR5's are gapped at .035. I have the most free-flowing exhaust you can have with a y-pipe but maybe there's something to it.

orion4096

iTrader: (5)

Completely random thoughts:

• gaskets - maybe the exhaust gasket is broken. Do you even have an exhaust gasket on the sanderson headers?
• intake gaskets/seals, intake torqued properly, no random junk stuck in it, not pinching the knock sensor wiring
• knock sensors torqued properly and working right? I assume these would show up as KR and timing drop in the scan
• tb functioning properly
• does this only happen on a 4th gear pull?

Is it at Synergy? If so, I can bring some random parts to try tomorrow.

dtfastbear

Thanks for the thoughts, Mike. Any and all ideas will at least help lead us in new directions, as I have this sinking feeling that we're not yet close to sneaking up on the problem with the current lines of investigation...

- I do have exhaust gaskets. They are in good shape - this has been happening since day one with the car, and we've had the headers on and off many times. Standing right by the engine during dyno pulls, I think we'd see/hear/smell an exhaust leak. Nothing there, IMHO.

- Intake - again, it's been on and off of the car several times on two different engines, so I don't believe it is a torque or "random stuff in it" issue. I put new gaskets on it when we swapped motors, and this problem has persisted across both of them.

- Knock sensors is an interesting path to pursue. Rick did say yesterday when he first started running the car that it seemed "sensitive" to knock and asked about the gas that's in the car (it's 91 pump gas). Wonder if I should put 100 in at Infineon and see if that has any effect? I'd think Rick would very easily be able to see on HPTuners if KR was the real cause of this, though... I did move the knock sensors and associated wires over from the previous motor, so that is definitely a possibility. I honestly can't remember if I was careful in torquing them...

- No idea on the throttle body. Since we're doing all WOT pulls, not sure how a problem would manifest itself there. Any specific ideas that made you list that?

- I think Rick was only doing 4th gear pulls on the dyno, but on the track I absolutely have the issue in 3rd, 4th and 5th.

One thing we have NOT tried (and I'll put on the list for dyno testing) is part throttle pulls to see if this is really load related or rpm related. I think it isn't a coincidence that this happens at the torque peak. If it is load versus rpm related, that might lead us in different directions for investigation.

The car isn't at Synergy now, Mike. I had it there yesterday and Rick was super helpful and motivated to find the issue, but we really just ran out of time as he squeezed me in and had other committed work he had to do in the afternoon. We are probably going to run the car on a dynapac at Works at Infineon tomorrow if we have a long enough list of things to try to make it worthwhile.

Cheers,

Dean

Schwanke Engines

iTrader: (1)

It looks like it might be going into CAT overtemp or Piston Protect mode. Log the commanded A/F ratio and see what is going on. In the good dyno runs, your A/F ratio is going from 14.5-13.9, lean if you ask me, but might just be the sensor. In your bad runs, you are starting at 12.3 and ending at, well pig rich.

My guess is you are going into one of those two modes and it is dumping fuel and causing a rich misfire.

dtfastbear

Thanks for the input! CAT overtemp mode - this is a race-only car and has no cats (assuming that CAT overtemp mode refers to catalytic converters, right?) Could they have been improperly deleted in the PCM?

Is Piston Protect mode based on knock or something else? Wouldn't that show up as a DTC code or show up on HPTuners? I don't know - I'm asking...

As for the AF, the "good" runs were before we adjusted anything, and we agree it was too lean. The tuner made some changes to richen it. The bad runs are after this change was made. There were bad runs when the car was leaner, too, I just didn't take pictures of those traces...

I appreciate all the input guys. I know it's difficult to diagnose without complete data!

Any thoughts on what could cause the car to go into either of those protect modes?

Cheers,

Dean

orion4096

iTrader: (5)

I'm sure Rick disabled COT protection.

More random ideas:

• You have an aftermarket starter. The CAS is right next to the starter. I wonder if something is happening there under load. I'll have to check if hptuners has a tooth logger/cas output.
• If we can figure out how to disconnect my AN fuel rail adapter we can try my intake, throttle body, and intake piping. Or maybe I can just unbolt my fuel rails from the intake and bring everything else.

joecar

Has COTP been disabled for certain...?

joecar

Has valve float been ruled out...?

dtfastbear

Not "for sure", but I trust that Rick would have done this. Worth verifying, though.

As for valve float, my motor is a bone-stock LS1. This problem has persisted without change over my initial used, high mileage motor, a brand new GM crate motor and now (a long story) the new motor with the heads from the old motor. I find it almost impossible to believe that a stock LS1 would have valve float like this at 5200 rpms...

Cheers,

Dean