I have a 350 in my Blazer. It's been gone over a few months ago, New wires, plugs, cap and rotor. When I start it in the moring Cold, it runs fine. But after 5 minutes and the engine is all warmed up it develops this miss, few times a minute, but it's there, In idle it's there or in drive, it's there ! I can't figure it out, What am I missing ?

 

What year engine? Carb or fuel injection setup?

 

Just some ideas,
You might want to check for vacuum leaks around intake gaskets or between intake and carb/throttle body.
Also could be valve adjustment a little tight and tightens up more when engine gets hot.

 

It's a 1988 TBI fuel injection and the only mod i did was put a Edlebrock 3704 TBI intake manifold.

 

Could be a bad O2 sensor.
When the engine is first started it is in "open loop" and running off other tables in the ECM. But once the engine warms up it flips to "closed loop" and uses the O2 sensors to monitor fueling.


You can try getting the truck warm, then disconnecting the O2 sensor and see if it runs better. when you disconnect the sensor it should set the Service Engine Soon light and force the ECM into open loop.

 

It Has a new OYX2 sensor. But I'm going to put a new set of AC Delco professional Rapidfire plugs in it. It's gotten to the point you can stand by the Magnaflow exhaust by the quarter panel and hear to pop pop pop and it just about every second. That makes me think it in the secondary wiring and I have gone backwards and examined the plug wires and brackets and holder and can't find a single problem.

I have a brand new AC Delco wires, ( lifetime warranty) and it has a MSD 40K volt coil and cap and rotor. The only place where the exhaust close to the wires in at the 90 degree boot at the plug connection. So I made some asbestos "booties" and have them fit over each wire connection. The #2 is the worst as the plug wire boot is like 3/8 of an inch from the super hot cast iron manifold. Tried 2 different sets of "Shorty Headers" but none will fit this engine bay. In the first picture, you can see the black frame sitting 4 inches from the heads ?

 

is this a fresh swap? or has this problem developed after you have been driving this truck?

 

It has been there for awhile, but it's getting worse with time.

 

OK, I ask because I was wondering if something could be hooked up wrong. But if it was running fine and this suddenly happened i doubt something is hooked up wrong.
For example, I had a dumb moment on my recent swap. I accidentally hooked my left and right bank O2 up backwards. as soon as my blazer got warm it would start missing bad. but being OBD2 I was able to hook up my scanner and see that at that moment one bank was going lean and the other bank was going rich and I knew instantly what I did wrong.




Are you able to get a fuel pressure measurement?
Also when its missing like this are you able to see how the TBI injectors are spraying? Is it a good pattern or does it seem weak?

 

ignition module?


When you turn it off and restart when hot. How is that?