Surging at WOT, the saga continues

[Fopar]

Well the saga continues (from here: Aluminator/3 valve block guys)

Combo is - 2.9 Gen 3 non-crusher, Nemak 5.0 stroker with about 25-30k miles on it now, fox lake rebuilt and CNC ported heads 60lb injectors, return style fuel system... tuned by me.

Car ran fine for couple years with this setup, took crank pulley off over winter to rebuild and now is down on power with some surges that 'almost' feels like it used to. I corrected the pulley offset and it changed nothing. Brought it to a dyno for some pulls and also to verify the A/Fs on passenger side (my wideband is on drivers side) are still good.

Well the A/Fs are fine so thank god don't have a lean cylinder on my non-monitored side, but graphs say it all, low power and surging wildly. Below is graph and below that is datalog from SCT during the pass, wideband on dyno is passenger side pipe, wideband in SCT is drivers side

Full symptoms:
-Low power overall except "sometimes"
-Airflow maybe slightly less? Hard to judge with the high temps we've been having
-Car idles lower and smoother, almost like there's more load on the engine
-Idle vacuum also lower, about 17.5 inches at 850ish (20ish normally, but also used to idle at like 900-950ish due to single blade TB)
-Idle vacuum does recover to 20 or slightly more with SC belt off
A/Fs at WOT are the same, short terms are right where they used to be

To date:

- I've run a compression test, all cylinders are decent, #1 is down by maybe 10ish psi
- We did a dyno pull with the cap off my catch can and blow-by was negligable
- Re-gapped my TR6s to .028 from .032
- Swapped TR6s for brand new BR7EF gapped at .028
- Swapped MSD coil pack set in the car for spare OEM set
- Swapped BACK to TR6s gapped all the way down to .022 to verify not a spark issue
- Re-aligned crank pulley as described in linked thread above
- Had several different belts on it


0 changes from any of this. The car doesn't break up when it surges, it just feels like someones holding the brakes and letting off randomly, this only happens at WOT. Car runs great, runs as cool as usual, doesn't use a drop of coolant or push any out of the overflow.

Next things to do:
-Maybe refine crank pulley alignment as there is some angular mis-alignment between it and the SC
pulley
-Would like to pull valve covers and make sure no broken springs or popped off rocker arms... is it possible to pull the inlet on a 2.9 non crusher to get the passenger side VC off or do you have to remove the SC?

 

[stang910]

With the info you've given, the wideband reading on livelink is showing 5-6% swings WOT and that's only as fast as the wideband can translate the info, it's possible it's more than that. I also see you reach 96% max injector duty cycle. The reason you don't go over a certain injector duty cycle is because the injector can no longer control the fuel.

Maybe it's not your issue, but this is what stands out at me.

 

[Blackedout]

What maf are you using ?

 

[Fopar]

With the info you've given, the wideband reading on livelink is showing 5-6% swings WOT and that's only as fast as the wideband can translate the info, it's possible it's more than that. I also see you reach 96% max injector duty cycle. The reason you don't go over a certain injector duty cycle is because the injector can no longer control the fuel.

Maybe it's not your issue, but this is what stands out at me.

Those swings are normal... with a JLT in tube setup, also they go over that, wanna see it hit 106%? Again this is new, the setup is not.

 

[Fopar]

What maf are you using ?

SCT BA2600 in JLT tube thing... been like that for years

 

[DSG2003Mach1]

Could it be the clutch on the verge of giving up the ghost?

 

[Fopar]

Could it be the clutch on the verge of giving up the ghost?

Checked RPM vs vehicle speed, no slip. It's an RXT with like 8k miles so should be well within its wheel house

 

[Fopar]

Where's Bob?

 

[01yellercobra]

Where's Bob?

If you're looking for me I've been on the east coast. Just got back this evening after a 39 hour drive. So I'm not the smartest right now.

Can you log the boost? Or am I missing it? I had a similar issue with my Vortech and pretty much did everything you did and it ended up being belt slip.

I think the idle is something different.

 

[Fopar]

If you're looking for me I've been on the east coast. Just got back this evening after a 39 hour drive. So I'm not the smartest right now.

Can you log the boost? Or am I missing it? I had a similar issue with my Vortech and pretty much did everything you did and it ended up being belt slip.

I think the idle is something different.

There he is . Boost is logged in the dyno graph, somewhat steady and linear... still convinced there might be belt slip tho

 

[Fopar]

Anyone have a broken valve spring or lose a rocker arm and get something like this?

 

[Fopar]

Welp, checked the reluctor wheel through the pickup hole, not loose so that's not it.

 

[03' White Snake]

Sub’n… having similar issue but only one blip up top on mine. My voltage drops to low 12’s high 11’s under WOT. Might need to try a new battery. I’m down on boost too. I degreed the cams and lost over 100 hp.

 

[Fopar]

interesting.... sure you degree'd them correctly?

 

[03' White Snake]

interesting.... sure you degree'd them correctly?

I thought so. My tuner suggested to check a few things first, if not I'm pulling the motor back out this winter to investigate the cam timing again.

 

[Fopar]

I thought so. My tuner suggested to check a few things first, if not I'm pulling the motor back out this winter to investigate the cam timing again.

Have you checked compression and compared to before? How much did u move each cam?

 

[DSG2003Mach1]

Sub’n… having similar issue but only one blip up top on mine. My voltage drops to low 12’s high 11’s under WOT. Might need to try a new battery. I’m down on boost too. I degreed the cams and lost over 100 hp.

View attachment 1756925

your alternator is supposed to supply all the power the vehicle needs when running, if voltage is dropping that's where you need to look. I dont know what pumps you're running but my tuner was telling me that with the bigger pumps when you start dropping much into the 12s fuel flow can drop off quickly.

as for the whole deal with the cams I'd do a compression test and see what you have, especially comparing bank to bank

 

[03' White Snake]

Have you checked compression and compared to before? How much did u move each cam?

Motor is healthy, has about 3k miles on it. Compression test on the the list of things to check. Car still made 744 on 19 psi, Problem is it was pullied for 26 psi. Both pulley sets were 6 psi low, so it's not belt slip.

I wish I had accurate degree's from before to now. But now they are degree'd to within 1/4° of the cam card. 110° intake and 114° exhaust.

Sorry to hijack your thread too btw.

your alternator is supposed to supply all the power the vehicle needs when running, if voltage is dropping that's where you need to look. I dont know what pumps you're running but my tuner was telling me that with the bigger pumps when you start dropping much into the 12s fuel flow can drop off quickly.

as for the whole deal with the cams I'd do a compression test and see what you have, especially comparing bank to bank

I was told during WOT, the alternator is supposed to shut off and the car is running strictly from the battery. My battery is in the trunk, I am running 4 ga wire to feed the relay and the pumps. I have 1/0 ga power and ground wires running to the alternator and starter. During normal idling or driving, I'm reading 13.3-14.2 on my gauge.

I am running 2 465 pumps full time.

4 things I changed between last dyno session and this time.

1.) Degree'd the cams. I am 99% confident they are set correctly.
Last time, not so much, I was not using a crank socket with the degree wheel, so not actually sure what how accurate the measurements were.
2.) Ported the Lower Intake. Had it done, did not do this myself.
3.) 0.010 thinner head gaskets.
4.) I installed a new blower gasket, but I did not RTV it to the blower. Not sure if this is where I am loosing the boost or not. I need to smoke the intake and check for leaks.

 

[01yellercobra]

In my experience a loose reluctor wheel won't cause surging. It will however leave a bunch of marks in the tops of your pistons.

I've heard the alternator shutting off thing before, but it doesn't make sense to me. Nothing is controlling the alternator to shut it off. And why would anyone want dropping voltage at the time its most important? Not too mention those running upgraded alternators seeing 13.5+vdc at WOT in logs.

@Fopar, can you record the boost gauge during a hit? Maybe angle it to get the tach in the view?

 

[DSG2003Mach1]

Motor is healthy, has about 3k miles on it. Compression test on the the list of things to check. Car still made 744 on 19 psi, Problem is it was pullied for 26 psi. Both pulley sets were 6 psi low, so it's not belt slip.

I wish I had accurate degree's from before to now. But now they are degree'd to within 1/4° of the cam card. 110° intake and 114° exhaust.

Sorry to hijack your thread too btw.



I was told during WOT, the alternator is supposed to shut off and the car is running strictly from the battery. My battery is in the trunk, I am running 4 ga wire to feed the relay and the pumps. I have 1/0 ga power and ground wires running to the alternator and starter. During normal idling or driving, I'm reading 13.3-14.2 on my gauge.

I am running 2 465 pumps full time.

4 things I changed between last dyno session and this time.

1.) Degree'd the cams. I am 99% confident they are set correctly.
Last time, not so much, I was not using a crank socket with the degree wheel, so not actually sure what how accurate the measurements were.
2.) Ported the Lower Intake. Had it done, did not do this myself.
3.) 0.010 thinner head gaskets.
4.) I installed a new blower gasket, but I did not RTV it to the blower. Not sure if this is where I am loosing the boost or not. I need to smoke the intake and check for leaks.

ac cut off during WOT? yes
Alternator cut off during WOT - never heard that before. Again, my tuner told me to get a new alternator because it was dropping into the mid/high 12s during the pull