hey everyone, i have a 97 ss with a lt4 conversion, hot cam, headers, throttle body, ported maf, and high flow cats.

while i am driving at highway speeds in 5th or 6th the car starts chugging almost feels like its dropping one or two cylinders, also it's popping out of the exhaust, if you floor it it smoothes out, it only seems to do it under load below 2500rpm,
also it seems to run rich at idle, i hooked my scanner up to it tonight and i have
2 codes for o2 sensors, bank 1 sensor 1 low activity and bank 1 sensor 2 high voltage, the long and short term fuel trims are at like 25% at idle and seem to go down with accel (in nuetral haven't tried while driving), i have noticed it runs alot better when cold i.e. throttle response and tourqe.

i found a small header leak on cyl7 tonight do you think this could be causing these problems, or could it be an o2 sensor shorted/bad.

it doesnt seem to be in the ignition system, i just replaced the plugs with ac delcos (factory recommended heat range), is this a decent plug or should use the ngk's that were in it before

thanks,
doug

 

You don't downshift at all? Why are you flooring it at 2500 RPMs in fifth or sixth?

since you have headers and a hot cam your engine would probably like higher RPMs like 4k-6k ideally

 

Weird... I've been having this same problem with my '94 Impala w/ LT4 conversion. Mine happens from 1500-2100 RPM. And it's only noticible when the torque converter is locked up.

I suspect my fuel tables aren't set up correctly. I bought a mail-order tune, but those can only be so close. I've spent a lot of time datalogging and driving, and adjusting the VE tables. Seems like its getting better.

 

The exhaust leak will cause the O2 sensors to see more air in the exhaust.Making the PCM dump more fuel,hence a rich condition.It will foul the O2s....Fix the leaks and change your O2 sensors. Felpro header gasket #1406 works great,

 

Plug wires
Coil wire
Opti rotor loose
Plugs

 

Id definately go through the ignition system. Burnt and arcing wires have both given me the same symptoms that youre describing.

 

hey guys thanks for all the input, i am getting ready to order new wires opti cap and rotor and coil from msd, also replacing both front o2's and header gaskets.

do you think i should keep the ac delcos or replace them with ngk's

thanks

doug

 

Many people have had problems with the AC/Delco platinum plugs losing the little platinum pucks off one or both electrodes. Plugs don't fire very well with a gap of 0.075-0.100". I'd choose the NGK's.

The Bank 1/Sensor 1 low activity code almost certainly indicates a faulty O2 sensor, most likely contaminated. The Bank 1/Sensor 2 code may be a result of the problems with Sensor 1, and the leak in the exhaust system. But the after-cat sensor doesn't affect the way the engine runs, only the pre-cat sensor controls the A/F.

 

I will add that I've already replaced my wires, plugs, distributor, coil without any resolution to this problem. The only thing that has improved it is tuning the VE tables (they were too rich).

What is very strange is I get split BLMs (rich left side, lean right side) under this specific operating condition. Other conditions, when the car runs properly, the O2 sensors generally match from side to side. Also interestingly, leaning the VE tables has not caused the right side to get any leaner. Maybe I have a bad O2 sensor, but I don't get any trouble codes, and they seem to agree under other conditions. Very weird problem.

I bring all this up because I was sure this problem I experienced was related to the ignition system, so I sunk close to $600 in replacing parts that were operating correctly. I won't complain because I have an extra opti now, etc. But I wish I would have spent more time looking closely at the VE tables before I started replacing everything under the hood.

Good luck, let me know how it goes.

 

You should use VEMaster to get the VE tables right. Also, do a search for 'split blms'; you'll find the information you need.

 

Leaking/sticking injector that won't shut off all the way? You could swap them all left to right sides and see if the problem changes sides.

 

i have been thinking i had one or more bad injectors since the pcm is trying to lean out bank 1, but wouldn't it start hard or seem like it's flooded when you first start the car from the injector leaking the excess fuel pressure without engine running.
mine starts great and sounds good on hot and cold starts, i don't seem to have a problem until i get up to about 55-75 mph in fifth or sixth gear. after it starts running bad it doesn't stop until it cools off for a couple hours.
i was told the car has a tune from madz28 and thats when it started running rich. maybe there was a mistake made while tuning the pcm??.
i am going to upgrade to msd ignition and replace the o2s since i do have a code for them anyways. i will post the results when i get to money for the parts.

doug