Help with lightly modified L31-R

[davkenrem]

Hello all, looking for some help. I have a 97 Chevy K1500 Suburban w/ a 6" lift. This summer I installed a L31-R crate engine. It has been modified with Chevrolet Performance Hydraulic Roller Camshafts 12677151 (Duration at .050 in. 215/223, Lift .473/.473), Doug Thorley Tri-Y Headers and the upgraded MPFI Spider.
I just had a new exhaust installed with 2 - 2-1/2" highflow Catalytic Converters into a 2-1/2" Y-Pipe into 3" Turbo Muffler and 3" Tail Pipe.
It's running on the stock computer badly. and throwing the following codes:
Current Fault Log
------------------
P0101: Mass or Volume Air Flow Circuit Range/Performance Problem
P0300: Random/Multiple Cylinder Misfire Detected
Pending Fault Log
------------------
P0108: Manifold Absolute Pressure/Barometric Pressure Circuit High Input
P0134: O2 Sensor Circuit No Activity Detected (Bank 1 Sensor 1)
P0154: O2 Sensor Circuit No Activity Detected (Bank 2 Sensor 1)
So, I knew the changes would be allot for the stock tune but it runs pretty badly with a misfire and very poor idle.
I have everything to do the 411 Swap, but thought it might be wiser to get it running on the stock computer before making the big change to the 411.
Maybe that was not the best choice.
For some reason the muffler shop did not plug in my new 02 sensors and only installed the 2 front ones stating "the back 2 don't tell the computer anything."
Once it stops snowing I'll get under there and plug in the front 2 sensor and hopefully that will clear at least 2 codes.
So my question you guys who have much more experience with this than I:
Will the stock computer be able to handle the changes and increased air flow of the engine, or should I send out my 411 PCM and get a tune on it based on the changes I've made?
This my first attempted at a mild upgrade of a modern engine, have much more exp with carbed engines.
Thanks in advance for the help.

 

[davkenrem]

More info
Things replaced with new build:
distributor
AC Delco cap & rotor
Ignition module
crank sensor
cam sensor
ac delco plugs
Summit 8mm wires
new MPFI Spider`
Also Cam Retard set to .02 at 11-1200 rpm

 

[L31MaxExpress]

I would get the O2 sensors connected. Also check for vacuum leaks. That cam should make about 16 in/hg @ 700 rpm. Both the MAP and MAF codes you are seeing can possibly be from a massive vacuum leak. I would verify that you got the spider correctly positioned in the upper plenum. Often times they are nearly impossible to get seated and when they are not seated cause a big vacuum leak. Might not be a bad idea to smoke test the intake manifold and associated plumbing if you have access to the equipment. I have run a 218/218 cammed 305 on a stock 350 tune for startup and cam break in. Did not run perfectly but it did not set either of those codes you are seeing.

 

[davkenrem]

I would get the O2 sensors connected. Also check for vacuum leaks. That cam should make about 16 in/hg @ 700 rpm. Both the MAP and MAF codes you are seeing can possibly be from a massive vacuum leak. I would verify that you got the spider correctly positioned in the upper plenum. Often times they are nearly impossible to get seated and when they are not seated cause a big vacuum leak. Might not be a bad idea to smoke test the intake manifold and associated plumbing if you have access to the equipment. I have run a 218/218 cammed 305 on a stock 350 tune for startup and cam break in. Did not run perfectly but it did not set either of those codes you are seeing.

I've been reading posts on several other boards and finding the same things suggested to others experiencing the same problems.

Thanks I will check all of these.

 

[big_mike]

Ummm, they didn't plug in either set of O2 sensors?? That's just ignorant and without the rears tuned out they will pop a code. They are emission monitors basically for the cats. The fronts though send signals to the pcm that effect air/fuel ratios. They will absolutely effect how it runs.

 

[arrg]

Double check all of your plugs, plug wires, and and all the connections for everything ignition related. The misfire code doesn't usually set unless there is an actual misfire. A misfire will send raw fuel out the exhaust and those new cats will melt in short order. Glowing chunks of cat substrate coming out of the exhaust is never fun.

 

[davkenrem]

Double check all of your plugs, plug wires, and and all the connections for everything ignition related. The misfire code doesn't usually set unless there is an actual misfire. A misfire will send raw fuel out the exhaust and those new cats will melt in short order. Glowing chunks of cat substrate coming out of the exhaust is never fun.

Thanks will check that out

 

[L31MaxExpress]

Double check all of your plugs, plug wires, and and all the connections for everything ignition related. The misfire code doesn't usually set unless there is an actual misfire. A misfire will send raw fuel out the exhaust and those new cats will melt in short order. Glowing chunks of cat substrate coming out of the exhaust is never fun.

I have not put a cam in a L31 yet aside from a stock cam that did not trigger P0300 codes. LT1 F-car cam, LT4 Corvette cam, Marine 395' aka Ramjet/HT383 cam have all triggered misfire codes around idle for me.

 

[davkenrem]

I have not put a cam in a L31 yet aside from a stock cam that did not trigger P0300 codes. LT1 F-car cam, LT4 Corvette cam, Marine 395' aka Ramjet/HT383 cam have all triggered misfire codes around idle for me.

Were you able to clear them? Were you running the stock PCM?

 

[L31MaxExpress]

Were you able to clear them? Were you running the stock PCM?

I have gotten the codes on both the stock PCM and the 0411. That being said I can eliminate the code from setting by adjusting the sensitivity of the misfire detection in the tune. Never have found a reason to completely disable the code from setting. P0300 code in itself will not make the engine run bad although if other problems are causing the engine to run poorly it is usually one of the quickest codes to show up.