Help with lightly modified L31-R

davkenrem · Post by **davkenrem** » Mon Nov 26, 2018 12:40 pm

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 everythhing 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 · Post by **davkenrem** » Mon Nov 26, 2018 6:25 pm

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

orange ss · Post by **orange ss** » Tue Nov 27, 2018 8:52 am

engine will probably run on stock tune, just not very well....misfire codes probably associated with cam, not sure about MAF, check for leaks in intake tube.

97k15004wd · Post by **97k15004wd** » Tue Nov 27, 2018 12:34 pm

probably needs a relearn since the disty was changed.

davkenrem · Post by **davkenrem** » Sat Dec 01, 2018 4:59 pm

After hooking up 02 sensors and fixing 2 wires not fully seated on spark plugs, I'm down to one code P0101 Mass Air Performance. I started looking for vacuum leaks but got rained out. Will tray again tomorrow. Will also look into testing MAP Sensor.

Thanks for the help so far, will report back.

97k15004wd · Post by **97k15004wd** » Sun Dec 02, 2018 5:31 am

davkenrem wrote:After hooking up 02 sensors and fixing 2 wires not fully seated on spark plugs, I'm down to one code P0101 Mass Air Performance. I started looking for vacuum leaks but got rained out. Will tray again tomorrow. Will also look into testing MAP Sensor.

Thanks for the help so far, will report back.

Great work! Sometimes it's aggravating but worth it, to go back over everything just to be sure.

davkenrem · Post by **davkenrem** » Tue Dec 25, 2018 2:46 pm

Ok, finally getting a chance to report back. I did not find any vacuum leaks but the P0101 code is cleared. Took the truck for a short drive today started right up but will not idle well. It drops below 1000rpm. Slight backfire when accelerating and not much power. Cam Retard was at 1.7 at 1100rpm. The PCM Stored P0108 and P1106 both dealing with Manifold Absolute Pressure, but I replaced the MAP sensor a few weeks ago. I guessing the Cam and headers could be confusing the PCM at this point. I also looked at the PIDs for misfire and it was show as misfires on at least 3 cylinders, I can only hear them at idle. they seem to disappear above 1800 rpm. The only other thing I can think of is the Valves are adjusted too tight.

Anyone have any thoughts?

Hog · Post by **Hog** » Fri Feb 22, 2019 1:44 pm

By those codes they hooked up the rear O2 sensors and NOT the fronts. Non functioning front O2 sensors will run like garbage when in closed loop, but should run fine in open loop. After a warm up try a WOT pass as the blackbox switches to OPEN Loop(PE Mode) and doesnt read the O2 sensors at all when at WOT.

peace'
Hog