LSJ Boosts Fine for 10-15 Minutes, Then It's a Bucking Bronco Under Boost
 

Hi guys,
Car has been running great ever since I gapped the plugs to 0.032 and eliminated all boost blowout. However, a month or so later I am driving home on the highway and doing some pulls; everything is fine until one pull hits the wall at just 6k rpm. I suspected boost blowout, however, when I got back on the gas under boost lightly, around 3800 rpm, the car started bucking and jerking all the way up the rev range from there. I put the throttle down without coming too far out of vacuum and the engine was able to build RPMs to 5k without any bucking or hesitation.

I do not feel this is boost blowout because I've never had it at this level of RPMS. It feels different too, a much harder abrupt stop of the revs, just like slamming the throttle plate closed. Also, the car starts and runs perfectly each time until a random time duration later it starts being a bucking bronco again.

Plugs and coils appear to be fine.

I am looking for ideas on diagnosing this issue, where should I begin, has anyone experience this?

Thanks kindly

In your description it says you have a canned tune. I'm betting your fueling is off. Do you have a wideband to monitor air/fuel ratio?

Appreciate the reply, the canned tune has been great though. No issues with it for months on months... I wonder if it's an injector. I don't have a wideband, but I guess I need one.

Has your weather recently changed and have you ran it in these conditions before?

It got quite a bit colder, never ran into this issue before, but always drove this tune in the "warm". Could cold weather affect a tune this much? I am doubtful of that..

Doubtful or not it can definitely be a factor depending on how far off your calibration is. Canned tunes are just a starting point as I am sure you have probably heard 100 times already. If you don't have any check engine light codes indicating sensor faults the most likely culprit is your canned tune. Have somebody, that knows what they are looking at, run a data log on your car to see what is going on and then if it is your tune have them make proper adjustments. There is a reason everyone says don't get a canned tune and it is because they are not that good and in some cases garbage. Most likely your car is not the exception.