your help is appreciated !!

o2 sensors ok
fuel presure ok
new plugs
mass air ok

misfires like crazy.code 300
worked fine over night , in the morning = problems
random misfires, although #7 was missing most !!
now #2 is acting up.the plugs were replaced 4 months ago.

Thoughts?

Frank

 

Check your plug wires. Make sure they aren't getting burnt by a header primary or cut by one of the pulleys where they wrap around the front of the block. Check the coil wire.

Make sure the wires are on the opti in the correct firing order.

Then when you are absolutely sure it's not the plug wires, check them again.

 

Need details on the engine.... is it totally stock, or mod'd? If mod'd, what are the mods? At what RPM and load conditions does is miss..... idle, cruise/low load, WOT/max load, all of the above? In the "morning", was the humidity high? If so, spray a mist of water on the plug wires in the dark, and look for a light show.

 

The car is all stock !! and well maintained.1996 z28 5.7 man.

new plug wires installed today = no differance
firing order fine
misfires in all conditions ALL the time
fuel filter replaced too

readings say # 7 cyl constantly missing.Swaped plugs = no differance.

Thanks guys!!!

 

Swap injectors on #7.... see if there is a difference.

 

is there a diagram to show how to ?
thank you

 

Blow the dirt out of the holes in the intake manifold that the injectors sit in. Release the clip on the drivers side that holds the two fuel "hard lines". Take the vacuum line off the fuel pressure regulator.

Remove the 4 bolts that hold the fuel rails to the top of the intake manifold. Pull the rails up one side at a time, pulling the 4 injectors out of the intake manifold. When you have the rails/injectors out, turn the key to "on" (do not attempt to start the engine). That pressures the fuel system, and any leaking injectors will be seen dripping.

If there are no drips, press the Schrader valve on the fuel line to relieve the pressure. Have a rag to absorb the gas that runs out. Slide the spring clips that hold the injectors to the fuel rails to the side, on #7 and another injector. Pull those two injectors out of the rail and swap them. Slide the clips back on, and reassemble.

When you pull the injectors out of the intake manifold, and out of the rails, make sure they have the o-rings on them. Before reassembling, lightly coat the o-rings with light oil.

 

Waiting for new injector ( tomorrow AM ),# 5 leaks really bad (streams out ! ) all others appear fine. I'm going to put the new one in # 7 and place #7 old into #5 and then run and scan.

I'll keep fingers crossed.
By the conclusion I'll have a 96 with 2006 parts. LOL.

Thanks

 

Check your oil!!!!!!!!

 

#7 injector moved to #5 ,as #5 was clearly malfuntioning and the new one placed into the #7 cylinder , the car ran smooth. no codes and no misfires.Yeah.

However, once the smoke cleared from the injector lube being burnt out, I have small amount of blue smoke exiting the car. its probably because #5 was just pouring tons of fuel in cylinder and may have scored the cylinder.

During the misfire you could smell lots of gas from the rear.

Odd that #5 injector was bad but misfires reported as #7 ?

Your thoughts ?

 

That's why I said to check the oil. If that was the case, by checking the oil at the recommended intervals, you would have caught that BEFORE it could have "souped" the cylinder.

I see it often occuring that way. Think about the firing order. Sometimes the missfire isn't detected (or reported) until later.

 

Wasn't and old oil problem. the car is extremely well maintained. oil changes are every 2500 -3000 miles even when the oil looks good .Oil changes and some repairs are "right offs" through my business.

Prior to the failure there was no issue re blue smoke.The 1st time the SES light came on ,I had the car flat decked to my buddy's shop ,then the repairs began.

With the firing order , your right 7 is the next, does the computer try to compensate for too much fuel in #5 (perhaps leaning out the rest), and then #7 shows the misfire ?

I just want to say thanks to all for taking the time to help me and my Ride.
Your experience and insight is appreciated.