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1998 Chevrolet K1500 Vortec 350 L31 w/MPFI Spider & new camshaf - MISFIRES/P0430
1 year 8 months ago #58043
by 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 random misfires. (see below)
The engine is a fresh rebuild with 5-10K miles, I have added all new wires, IAC, cap, rotor, coil and even the MPVI efi "spider" has been replaced . I have not replaced the plugs yet - but am wondering if the misfires are from the 1) airflow 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 ), or 2) the misfire monitor picking up uneven crankshaft rotation speed from the slightly larger camshaft, or 3) or a vacuum leak on the stock MPFI manifold? Wondering if the CAT code is a simultaneous fault with the misfire, or related - IE the misfire causing the CAT code.
QUESTION: With a vacuum leak what would the fuel trims look like percentage wise?
Seems like this cam is a small step over stock and indeed the truck runs pretty/very 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. The stock cam is really puny.
Any ideas appreciated - thank you
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 random misfires. (see below)
The engine is a fresh rebuild with 5-10K miles, I have added all new wires, IAC, cap, rotor, coil and even the MPVI efi "spider" has been replaced . I have not replaced the plugs yet - but am wondering if the misfires are from the 1) airflow 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 ), or 2) the misfire monitor picking up uneven crankshaft rotation speed from the slightly larger camshaft, or 3) or a vacuum leak on the stock MPFI manifold? Wondering if the CAT code is a simultaneous fault with the misfire, or related - IE the misfire causing the CAT code.
QUESTION: With a vacuum leak what would the fuel trims look like percentage wise?
Seems like this cam is a small step over stock and indeed the truck runs pretty/very 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. The stock cam is really puny.
Any ideas appreciated - thank you
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