2009 Z06, LS7 AI 280 heads, RPM B3 cam, BTR springs, factory intake and TB, Halltech 103 CAI, LG Headers, Dewitts rad, and Fluidine 2 pass oil cooler,

The engine has 3000 miles on the upgrades in a different car. I purchased it, installed it in my car, had it tuned.

The problem: Under load, the engine hesitates as if it has a bad plug or plug wire. as the rpms increase, the hesitation goes away and strong power comes on. I changed plugs to a known good set. The problem persists. The plug wires are new. I didn't swap any plug wires.

When at the track, exiting a turn in third gear at a certain rpm, I get this hesitation. as the car speeds up the bad plug (hypothetical) starts working. Then the car has great power.

I can prevent the hesitation by downshifting into second before getting back on the throttle. The rpm is higher in the lower gear. It sort of reminds me of clearing out a rich running engine, then it runs good until it loads up again.

I have heard of a bent push rod causing this and the tune may cause it.

Please help me find this hesitation. I think it has to do with the cam and how its tuned

 

What car did this engine come out of, if not from same model car, what was done to match it to your engine control module? Yes, the tune on it now is definitely a suspect in this problem.

 

The car is an 09 z06. the engine was removed from a 2007 z06. I'm not sure what the tuner did to match the two.

It doesn't like to idle at 750 smoothly. Had to idle it at 800. Seems to load up at 750. I think its loading up some at 800 as well. I took it back to the tuner to idle it down because it sounded like it wasn't letting the sweet sound of a good cam be heard. I heard the engine idle on a video before I bought it. It doesn't sound that nice in my car. But it makes great power 593 rwhp 525 torque.

Every once in a while it will hunt for its idle it will hold at 1800 rpm and slowly lower to 800.

All of these characteristics are all on the track as its only used on the track.
When I start it, it will run quite rough for 30 seconds or so. If I rev it a bit it smooths out. Some times it wont start unless I give it gas just as it fires
Thanks

 

While it can be caused by something else, your problems are identical to those that would be experienced after installing a larger aftermarket cam and not properly tuning for it.

 

RPM has agreed to look at my tune file to see if anything jumps out at them. I'm taking the tuner for a ride on Friday to log some data. He has some thoughts about it as well. He thinks there may not be enough timing and maybe fuel as well, in the rpm range where the hesitation is.

 

Sounds to me like it is a lean hesitation in that RPM range. Could be transient fueling, VE, or PE issues. Tuner should be able to see what is happening in a scan. 800 rpm is a touch low for a cam of that size, IMO. It would be happier at 900, but like you said, it doesn't sound as nice. I'd still bump it up, and live with the less lively exhaust note.

No issues with that engine being an 07 installed in your 09, as all LS7 engines are the same.

 

If you ruled out spark, it is probably the tune.

Last thing to do on spark it to swap coils. See if you can find a set to borrow and see if it changes anything.

 

I did consider that. Also, felt of them trying to see if one might have been hotter or cooler than the rest. Not a good test as the hesitation is intermittent. I'll know better Friday when we go for a ride with HPTuners hooked up

 

What is VE and PE. Learning as we go.

 

VE is short for Volumetric Efficiency, and PE is Power Enrichment.

There are VE tables in the calibration that help to determine the fueling requirements for the engine, based on how much air it moves at a given RPM, manifold pressure, and temperature. It is used in conjunction with the MAF sensor. When you change the cam, it changes how efficient the engine is at a given RPM. Some speeds, it will be more efficient, and others will be less than stock. These tables need to match what the new cam requires, or you can have rich or lean areas, which lead to hesitation or flat spots in the RPM range.

PE controls Wide Open Throttle fueling. When you're at part throttle, the PCM is in a feedback loop with the oxygen sensors. They report back what the A/F ratio is, and the PCM corrects it, if needed. When in PE mode, the O2 sensors are ignored, and there is no feedback loop. If the A/F ratio is off, nothing can be done automatically, and the engine is forced to run at what it is. The PE tables need to properly match your new cam's fueling requirements, or you can end up with hesitation or flat spots.

A log of the area giving you issues should show what is going on. If you are heavy on the throttle where the issue is occurring, you may need a wideband attached, so you can see what the A/F ratio is. You may be able to see that spot in the tune, when comparing it with the logs. It could just be an area that wasn't properly "smoothed". Long story short, your tuner should be able to pretty easily identify and remedy the issue.