Missfire in 97 1500

[primal099]

I have a 97 1500 with the 4.3. I recently had to put a new head gasket in it. When I started it back up the computer says i have a missfire in the #5 cylinder. The truck never overheated and it sounded and ran perfectly fine when I pulled it into the garage to put the head gaskets on. It has all new plugs, cap and wires and I checked the spark, it was fine. The misfire seems to be worse when it is at idle and cold. If there is a loss of horsepower it is not noticable. I pulled the push rods and checked the rockers and springs and found nothing wrong. Could it be a valve spring? I am grasping at straws because i am very lost. What happens if you put a push rod in backwards? I really dont believe that could be the problem but.... Any ideas would be greatly appreaciated. Thanks in advance!

[MT-2500]

Originally Posted by primal099

I have a 97 1500 with the 4.3. I recently had to put a new head gasket in it. When I started it back up the computer says i have a missfire in the #5 cylinder. The truck never overheated and it sounded and ran perfectly fine when I pulled it into the garage to put the head gaskets on. It has all new plugs, cap and wires and I checked the spark, it was fine. The misfire seems to be worse when it is at idle and cold. If there is a loss of horsepower it is not noticable. I pulled the push rods and checked the rockers and springs and found nothing wrong. Could it be a valve spring? I am grasping at straws because i am very lost. What happens if you put a push rod in backwards? I really dont believe that could be the problem but.... Any ideas would be greatly appreaciated. Thanks in advance!

Run a compression test and post back compression readings.
Does it have good spark to no 5 cyl.?
Try switching wires and plug to.

Was the camshaft retard set after head gasket job?
What are the fuel pressure readings?

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.