missfires

[truckdoc64]

have 1999 ck 1500 that miss fires on cylinder @ 2 and # 8
have replaced
the injector spider
cap ,rotor
distor
plugs
wires
coil
crank sensor
on snap-on scaner missfire diag is # 2 & 8

[MT-2500]

How many missfire per cylinder?
Can you feel engine miss under load?
Good Ac delco plugs and and rotor?
What is the camshaft retard redings?
Is fuel pressure up to par?
Good even compression on all cylinders?
Any add on air filters or cold air intakes?

MAF sensor good and clean?

[truckdoc64]

had 2 cylinders missing the count was 800 befor cleared
new ac plugs
had 175 compression
56 to 65 psi fuel psi
tried another cap and miss fire went away it was between #2 & 8
thanks for the reply and help

[MT-2500]

You are welcome.
Miss fire gone is good.
But that fuel pressure is off.
And be sure to check and or set camshaft retard.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.