1998 Chevrolet K1500 Vortec 350 - 4L60 trans w/3.73 Gear Tune Q - MISFIRES/P0430 code

[REM]

I have changed the stock camshaft from:

FROM:

STOCK CAM : 191 / 196 414/428 lift on 111 LSA

TO:

203 / 203 450/450 lift on 112 LSA - this camshaft has a lobe off an earlier (203/210 corvette camshaft)

Truck has good drivability right now ( runs good and can lay down rubber when power braking ) except: - 1) sometimes stalls when I put it in gear when it is cold and 2) hunts very occasionally in gear when hot - by hunt I mean a cyclic surging against the brake pedal.

Has been setting catalytic converter efficiency P0430 code and I noticed in the HP Tuners diagnostics - that there seems to be misfires. (see below)

Trying to diagnose the P0430 code and the misfires ( which are probably setting the CAT code), aside from the engine being a fresh rebuild, I have added all new wires, cap, rotor, coil and even the MPVI efi has been replaced . I have not replaced the plugs yet - but am wondering if the misfires are from the airlflow and fuel map being off because of the slightly larger camshaft - IE lower engine vacuum at low rpm throwing off the fuel map. ( IE too rich at idle ).

Timing: with the 9.4 CR and iron heads and regular fuel have not detected any pinging ever.

The intake has a K&N element in the stock housing and the exhaust is a cast iron manifold duals into a large muffler and single outlet from the muffler to a larger tail pipe. This motor was a "heavy half" - 6600GVW so it has the bigger factory exhaust.

Any ideas appreciated - thank you REM777

[2xLS1]

Just about any cam other than stock is going to show misfires because you lost the smooth rotation of the crank reluctor. Desensitize the misfire tables. It's part of tuning for a larger than stock cam. P0420 and P0430 codes are almost always caused by bad cats. Are you sure of that stock 111 LSA spec? Maybe that's the ICL? Everything I can find shows something around 118 LSA.

[REM]

Seems like this cam is a small step over stock and indeed the truck runs pretty good - only stumbles and stalls when cold occasionally ( like a bad IAC valve) and it hunts against the brake in gear occasionally. I also have added 1.6 rockers in addition to the .450 lift on the regrind. I ran a CAM Doctor on the stock cam but misplaced the cam card it generated. But it is very small in lift, duration. ANy thoughts about re-generating the CAT or masking the deterioration ( like additing a fouler cup on top of the downstream O2 sensor? thanks for you ideas

[REM]

https://www.youtube.com/watch?v=vyVnhCIMDnw

[Fast4.7]

Just about any cam other than stock is going to show misfires because you lost the smooth rotation of the crank reluctor. Desensitize the misfire tables. It's part of tuning for a larger than stock cam. P0420 and P0430 codes are almost always caused by bad cats. Are you sure of that stock 111 LSA spec? Maybe that's the ICL? Everything I can find shows something around 118 LSA.

Stock L30/L31 cam is 261/263 @ 0.06, 191/194 @ 0.050, 0.418/0.424, 111 LSA, and 106 ICL (Stock timing set has 5 degrees advance built in although the cam is 111 ICL on a true Zero'd aftermarket set.)

Cat code can be a failing cat or from a real misfire.

My 97 Express van ran for a couple of years with a 96 LT4 cam, 1.6 rockers, shorty headers, factory dual 3" exhaust to the dual 3" in, single 4" out muffler, throttle body lip removed, K&N filter, modified heavily ported MAF with the resistor trick and a S10 converter with no tuning changes and no codes.

[Fast4.7]

Looking at your misfire data 2&4 share the same section of intake gasket. Have you ruled out a vacuum leak? Misfire on bank 2 could be the cause of the P0430 code even if it has yet to hurt the cat.

[Fast4.7]

https://youtu.be/-3N2behNqso

https://youtu.be/_6NUzPdti8M

I only use composite paper intake gaskets on these engines. I refuse to use the stock or updated stock style gaskets. Having had a factory gasket cause a catastrophic engine failure from a broken connecting rod when it hydrolocked at 57K miles as well as the problem solver Felpro gasket disentigrate in 30K miles causing an external coolant leak.

I run Edelbrock 7235 gaskets that are gasgasinch contact cement glued to the cylinder heads. Completely clean the head surface, apply a thin coat on the head, then apply a thin coat to both sides of the gasket. Let it get tacky, then line the gasket up and press it into place. Then lay down the silicone RTV bead on the clean china walls. Once the silicone is tacky, line the intake up, still holding it above the heads, line a couple bolts up so that it drops straight down without sliding. Torque the bolts per the OE pattern at 13 ft/lbs. The 305 in my 99 Tahoe ran for over 100K and was still leak free when I pulled it for the 8.1 swap.

[REM]

Hmmmmm, yes - this was my first thought - IE the misfire causing the rich condition on the cat - this motor is a new motor from the exact catastrophic engine failure you mentioned - a leaking intake gasket causing a very slow coolant leak which during the covid shut down got driven less and the owner ( not me ) started it and broke a rod from a coolant hydraulic lock - broke the rod in 5 pieces and broke the piston into two large pieces - crack right through the pin boss. I used the new and improved MAHLE intake gasket ( was wondering if the manifold was warped from the previous really bad goo gasket - was completely deteriorated from the red coolant) . My intention was to put a new spider in it and if that didnt fix it was going to surface the manifold and put some new gaskets on it. I did put the spider in it to no effect . This motor probably has 5K on it since rebuild..

[Fast4.7]

Hmmmmm, yes - this was my first thought - IE the misfire causing the rich condition on the cat - this motor is a new motor from the exact catastrophic engine failure you mentioned - a leaking intake gasket causing a very slow coolant leak which during the covid shut down got driven less and the owner ( not me ) started it and broke a rod from a coolant hydraulic lock - broke the rod in 5 pieces and broke the piston into two large pieces - crack right through the pin boss. I used the new and improved MAHLE intake gasket ( was wondering if the manifold was warped from the previous really bad goo gasket - was completely deteriorated from the red coolant) . My intention was to put a new spider in it and if that didnt fix it was going to surface the manifold and put some new gaskets on it. I did put the spider in it to no effect . This motor probably has 5K on it since rebuild..

Mine was sitting 2 weeks back in 2004 at 57K. Went to start it and coolant had worked its way into #2 intake port. Rod and piston shattered into what had to be 100 pieces, what was still attached to the crank put a hole in the block, broke the cam and punched holes in the oil pan. I doubt the manifold warped from that but anything is possible.

I had a 305 in my Corvette get rain water down the shot gun scoop in a freak down pour while it was parked outside and thus the tunnel ram that was on it and it bent a "X" casting rod on startup. I felt the misfire in it at about 5,000-6,200 rpm. Checking things #6 had 120 psi compression yet the leak down test was solid. Pulled the head and staring me in the face is a piston twisted in the bore that would only come up to about 0.250" under the deck. The old forged steel rod bent but did not shatter and the forged piston stayed intact. I will never use PM rods again. That 305 survived minus the bent rod and some scuffing on the twisted piston skirt. I ended up putting 1 piston, 1 rod, 1 con rod bearing, and a single piston ring set in that engine and drove it for another 3 years.

[REM]

Actually the powder rods have some impressive specs but nobody knows what the outer limits are - GKN made most of them - the OEMS love them because they come out of the mold perfect requiring no finish machining and all balanced equally ( IE notice no balance pad on these rods) . Howards was selling these - but stopped .. I was amazed at the low speed ( IE on a crank) hydraulic would shatter them like glass .. I said 5 pieces because I didnt think anyone would believe me but it was 7 pieces .. one went through the pan .. didnt broach the block .

ANY thoughts on the fuel trims or other evidence pointing to a lean condition VS a crank speed irregularity tripping the misfire monitor ?

[Fast4.7]

Actually the powder rods have some impressive specs but nobody knows what the outer limits are - GKN made most of them - the OEMS love them because they come out of the mold perfect requiring no finish machining and all balanced equally ( IE notice no balance pad on these rods) . Howards was selling these - but stopped .. I was amazed at the low speed ( IE on a crank) hydraulic would shatter them like glass .. I said 5 pieces because I didnt think anyone would believe me but it was 7 pieces .. one went through the pan .. didnt broach the block .

ANY thoughts on the fuel trims or other evidence pointing to a lean condition VS a crank speed irregularity tripping the misfire monitor ?

What do the fuel trims look like?

I am headed over to my shop later to grab my tuning laptop out of the Express so that I can tune a friends truck. If you post a datalog it would give some more info. I would be looking for unbalanced trims left and right. A few percent is normal, 10-20% is not.

Also you did cross the spider tubes when you installed them? I fought with one that was running poorly once and the owner had incorrectly installed the fuel tubes on the spider. Each pair of tubes cross over each other to get to the correct cylinders.

[REM]

1998 - Chev Truck Vortec startup and drive file-9-3-2022.hpl1998 - Chev Truck Vortec misfires added.hpl1998 - Chev Truck Vortec startup and drive file.hpl

Truck runs the same as the older spider which had like 10-15K miles on it but was replaced because of suspected contamination when the manifold was off because was off for over a year and not really covered

I did not screw up the injector nozzle placement - IE the cross over is correct.

thanks REM777

[Fast4.7]

I finally had a chance to look over your datalog a bit. I would suggest starting with the VE and MAF tables. I do the VE tables first. In the Engine Diagnostic/Airflow tab, set the MAF Frequency Fail High to ZERO then in the Engine Diagnostic DTC tab set P0103 to Mil on 1st Error. That will disable the MAF so that you can tune the VE. You will need to datalog and adjust the Secondary VE table. The Primary table is disabled when the MAF is failed. I setup the histogram table in the scanner to exactly match the VE table. Then I use an Open Office file I wrote to tune adjust the VE table via fuel trim feedback. I hand smooth the VE tables in areas that are not hit in a good datalog session. Then after a few trips and corrections, I copy the appropriate rows from the Secondary VE table to appropriate rows of the Primary table. Then interpolate between each row to get the primary table populated. Once the VEs are in good shape, I re-enable the MAF by reversing the first steps. I then adjust the MAF table using fuel trims and the spreadsheet. After a few logs to help adjust the MAF table values it should be running alot better. I use 1/2 the difference for the spreadsheet adjusted values. If the fuel trims are adding 5%, the spreadsheet will add 2.5% and vice versa. If the PCM is removing 5%, the spreadsheet will remove 2.5%. I like my fuel trims between 0 and -5% and never positive values. If the value is positive, say 10% and you enter power enrichment the PCM will continue to add 10% across the whole RPM range.


Fuel Correction.xls