Random misfire and hard start 1997 5.7 k1500

[Dlipp_]

Recently did a LT4 hot cam, with all the necessary parts etc. Thing fired right up first start, ran fine, no misfires. Fast forward a couple weeks, trying to figure out the hard start after the first start of the day issue.

Replaced trying to find the hard start:
(All GM parts, no junk)
IGM
Ignition Coil
Cap
Rotar
Plug wires
Fuel filter
Coolant temp
Crank sensor
New distributor last year
Plugs only 8ish months old, sat for 4 months with starting it once a week

And now I’m getting a rough idle along, random misfire as well

Fuel pressure reads 50-55 when pump primes, idles at 50, reads 50ish when turned off. Doesn’t go over 60 when cranking.

If I start the truck and give it throttle it’ll stay running, if i turn it off and try to turn it back on without priming the pump it’ll crank crank crank no start. Prime the pump it’ll try and start but stumble its way up, sometimes stall.

I’m hoping the misfire is related to the hard start. ***it’s been doing the hard start before I did the cam***

 

[Schurkey]

Recently did a LT4 hot cam, with all the necessary parts etc.

Did you degree the cam when you installed it, or did you cram it into the block "dot to dot"? What is the cranking compression pressure?

Did you tune the computer to account for the significantly more-aggressive camshaft?

Thing fired right up first start, ran fine, no misfires. Fast forward a couple weeks, trying to figure out the hard start after the first start of the day issue.

Replaced trying to find the hard start:
(All GM parts, no junk)
IGM

What is an IGM?

Ignition Coil
Cap
Rotar
Plug wires
Fuel filter
Coolant temp
Crank sensor
New distributor last year

What is the cam offset/cam-crank sensor alignment?

Plugs only 8ish months old, sat for 4 months with starting it once a week

Pull the plugs, see if they're fouled.

And now I’m getting a rough idle along, random misfire as well

Vortec distributor caps are infamous for problems.

WHICH CYLINDERS are misfiring? What are the misfire counts for each cylinder?

Fuel pressure reads 50-55 when pump primes, idles at 50, reads 50ish when turned off. Doesn’t go over 60 when cranking.

Prime pressure seems low. Poppet injectors or electronic injectors?

Is the pressure gauge accurate? How do you know?

If I start the truck and give it throttle it’ll stay running

But it stalls if you just let it idle? That can't be good.

, if i turn it off and try to turn it back on without priming the pump it’ll crank crank crank no start. Prime the pump it’ll try and start but stumble its way up, sometimes stall.

Again, fuel pressure is low. Not horribly low, especially with the electronic "upgraded" injector spider. More of a problem if you have the old poppet-style injectors.

I’m hoping the misfire is related to the hard start. ***it’s been doing the hard start before I did the cam***

Should have fixed the hard starting before you made things more complicated with a non-stock cam.

 

[Dlipp_]

Did you degree the cam when you installed it, or did you cram it into the block "dot to dot"? What is the cranking compression pressure?

Did you tune the computer to account for the significantly more-aggressive camshaft?


What is an IGM?


What is the cam offset/cam-crank sensor alignment?


Pull the plugs, see if they're fouled.


Vortec distributor caps are infamous for problems.

WHICH CYLINDERS are misfiring? What are the misfire counts for each cylinder?


Prime pressure seems low. Poppet injectors or electronic injectors?

Is the pressure gauge accurate? How do you know?


But it stalls if you just let it idle? That can't be good.


Again, fuel pressure is low. Not horribly low, especially with the electronic "upgraded" injector spider. More of a problem if you have the old poppet-style injectors.


Should have fixed the hard starting before you made things more complicated with a non-stock cam.

Didn’t mean IGM meant ICM,

Lined it up dot to dot

The computer has a tune from Black bear specifically for everything I did to it, rear o2 delete and EGR delete as well

Plugs aren’t that bad

Not sure about cam offset

Im not sure which cylinders are misfiring, scan tool can’t see that

Pressure gauge was literally brand new before I used it

If It idles it will idle and run fine but with a misfire, runs down the road fine, a little down on power. Just stumbles to start and get up to RPM. Once idling it’s good.

I was hoping the new MPFI injectors that I did, would have fixed the hard start.