Major misfire

At idle it misses on 1, 3, and 5, and when in the throttle it misses on 2, 4, and 6. This problem started overnight, first thing it broke the starter bolts off and push started it to find a P0300 misfire. It has gotten progressively worse since it started 5 years ago.

Replaced:
plugs, wires, cap, rotor, coil
ecm, egr, injector spider,
fuel pump, fuel filter, fuel pressure regulator,
upper intake plentum, camshaft sensor,
crank sensor, all 4 o2 sensors, MAF,
MAP, TPS, and starter ring.

Fuel pressure is holding at 55psi, getting spark on all cyl. at all times. Runs rich with white smoke and burns nose hair. I'm out of ideas, so any help would be amazing.

Running Rich with white smoke!
Check your coolant level, and look for coolant in oil.
Is the coolant reservoir tank contaminated with oil?
These are symptoms of a bad Inake, or head gaskets

No coolant leaks, rebuilt the motor was the last thing I did. Oh yeah, and I put in a NEW wiring harness. I have replaced everything external at one point or another with new or known working used parts. The only things I havn't replaced or not completely sure of is the camshaft, distributor housing and shaft, and the balance thing under the intake.

What year and engine and engine code?
Any check engine lights or other codes?

1996 S-10 4.3 vortec "X" vin (plastic intake plentum)

Had a P0300, P0301-P0306, all four o2 sensor codes for running rich, maf code. Thats all I remember right now, got the batt on trickle charger now. Will have to grab a scanner later to see if they're still there.

Try spraying some carburetor cleaner around the intake. If the motor smooths out that is where your leak would be located.

Fuel pressure is low.
Run a full fuel pressure check.
You should see 62-64 lbs engine running.

I replaced the fuel pump and filter, had the lines out for inspection and blew them out with air and checked for kinks (none). 55 psi was found at engine not running. rigged up an old fuel pressure regulator to a fuel pressure gauge at the spider and got the same reading. gone through a case of carb cleaner since it started to check for leaks to no avail.

I replaced the fuel pump and filter, had the lines out for inspection and blew them out with air and checked for kinks (none). 55 psi was found at engine not running. rigged up an old fuel pressure regulator to a fuel pressure gauge at the spider and got the same reading. gone through a case of carb cleaner since it started to check for leaks to no avail.

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.

Fuel pressure readings:

At fuel pump w/return line blocked: 110psi
At Check valve...
With ign. on: 63.5psi
With return blocked: 65psi
With engine running: 60-62psi
Cannot test driving fuel pressure, no power to get over 5 mph. and not legal.
No leak down found at any time during testing. Pressure was held for 5 min. plus for each test. (enough time to have a smoke)

Some pressure regulators can be adjusted try raising pressure slightly,as not all gauges are completely accurate and are off 5 to 10 percent.

with these issues you have I would look at the spark plugs . any white tips on those plugs ? If so I suspect a coolant leak in the cylinder[s] this would explain the starter bolts breaking. this is because you can't compress a liquid..

compression test the cylinders using the proper method for a complete result.

Spark plugs look like new. The starter bolts broke off six times total with one starter being broke in half due to the engine kicking backwards. I thought it was a timing issue but it is computer controlled and a timing light conformed timing is correct. The timing chain is also new along with new gears.

Spark plugs look like new. The starter bolts broke off six times total with one starter being broke in half due to the engine kicking backwards. I thought it was a timing issue but it is computer controlled and a timing light conformed timing is correct. The timing chain is also new along with new gears.
Check the plug wires with a wiring diagram this will cause a rough running engine.

Spark plugs look like new.

runs rich,white smoke out the exhaust, missfires , and you expect me to believe the plugs look new ?

take a good color picture of those plugs and mark what cylinder they came out of then post here ..

The spark plugs look new because they only have about 30 min. on them. Under a magnifying glass I can see that they have a slight discoloration, a light white or yellow color. Will be able to post pics thurs. or fri.

Have you checked the distributor driven gear? If the distributor is not centered in the intake manifold hole, it will wear the teeth on one side of the gear down. Have you checked camshaft retard? Did you do a crankshaft position sensor relearn after you replaced it? (must be done) GM dealer issue shop manual warns not to exceed 75psi when restricting the return line. If you restricted the return line and had a pressure reading of 110psi, it would be a small miracle if the fuel pressure regulator is still good.

The dist. Gear is good, no abnormal wear. Camshaft retard, it's been a while
, if I remember correctly it was advanced about 20 or 30'. Didn't do a comp relearn on the crank sensor. 110 psi was at the pump with no return line restriction.

Camshaft retard must be zero degrees plus or minus 2 degrees. Rotating the distributor is how it's adjusted. The lock ring on the distributor base will allow slight movement to adjust camshaft retard. The only way to check and adjust it is with a capable scan tool dialed in to camshaft retard. The cheapie $400 jobbies that the auto parts stores use for retrieving codes will not access the data.

Any time the crankshaft position sensor is moved in its mount, or replaced, the relearn MUST be performed. Again, only a capable scan tool can command the ECM to perform the relearn. The crankshaft position sensor and the camshaft position sensor, (in the distributor) work together to monitor engine misfire. That's all the camshaft position sensor does, it has nothing to do with ignition, or ignition timing.

Timing is now at "0", and the crank sensor has been taken care of by the local chevy dealer. There is still no change in the miss.
Would a complete ecm reflash have any effect? I replaced the ecm out of a known running truck. I can't think of anything other than replacing the entire wiring harness. Thanks for your help so far.

Timing is now at "0", and the crank sensor has been taken care of by the local chevy dealer. There is still no change in the miss.
Would a complete ecm reflash have any effect? I replaced the ecm out of a known running truck. I can't think of anything other than replacing the entire wiring harness. Thanks for your help so far.
Did you match the numbers on the ecm?

It matched by year, make, model, and engine. The only difference was it was for an automatic tranny.

Running Rich with white smoke!
Check your coolant level, and look for coolant in oil.
Is the coolant reservoir tank contaminated with oil?
These are symptoms of a bad Inake, or head gaskets


I have to agree. When a vehicle is running to rich it will blow black smoke, not white. The only thing I have ever seen cause white smoke is a leaking head gasket. Just because you rebuilt the engine does not mean you do not have a leaking head gasket. How many engines have you rebuilt?? I know guys that have rebuilt 100's of engines and still jacked something up at one time or another and had to go back and redo their work. Maybe i am wrong but what else will cause white smoke??? :runaround:

I've rebuilt too many to count and more head jobs than I want to remember. Do you think I should Magnaflux the heads? I cant see any cracks but I don't know if there is small cracks or even if that small of a crack would cause that big of an issue. White smoke can be caused by burning coolant or burning oil. Burning coolant can come from a cracked intake or intake gasket leaking into the cyl via open valves or a buster head gasket. Same thing goes for burning oil, exept it can also come from bad rings. Now, the question is, What would make an engine go from running like a top to missing on all six cyl from one start to the next?

Napa sells a test kit for combustion gas in the anti freeze cheaper than pulling the head.