I have a 1995 4.3 Blazer , pulled the engine due to leaking core plugs and replaced a ton of other stuff while in there.

Now 100 miles after getting it back together she has a misfire at idle. While driving it the other day P0305 came up and then the ses started flashing. Dropped it off at my brothers for the night and when i came and got it the misfire was mild again and no flashing ses.

So I now have a mild misfire at idle, I can feel it and here it from the tailpipe. Truck seems to run good otherwise and have not drove it much to see if the p0305 comes back.

Tested fuel pressure and it is around 53 psi Key on Engine off and seems to hold the pressure no problem. Swapped the old plug wire for cyliner 5 back on and no change.

No visible vacuum leaks. truck only has 93k on it and was very well taken care of, I have not done a compression test yet, but with the low miles I am expecting it to pass.

What am I missing?

I have a pocket scanner to Pull codes with and it works fine. I have a ELM 327 BT I use with an app on my phone, but for some reason it wont communicate with the blazer so i cant get data such as misfire counts.


Update:

I drove a bit and the misfire came back full force including flashing ses.
Swapped plugs and wires around and the mis has stayed at cylinder 5.
I checked cylinder 5 for spark and has plenty of spark.
If i pull the plug wire while it is running I do not get any change in RPM or engine sound,which tells me that cylinder is not hitting at all right now.

I guess that leaves me with compression and or the poppett valve sticking on the new spider unit? will update after compression test.


Update 2:
tested sompression on #1 and #5 both around 130-135.

Should I suspect the spider unit? it is a remanned delco unit, possible ithas a problem in the poppett?

 

Anyone have any input?

 

Your ELM scanner is an OBDII system. That started in 96+ vehicles.

Yes I would suspect the injector of that cylinder.

 

The spider unit was just purchased in may so I have a warranty replacement coming, figured mine as well since no cost to swap it out.

I have an OBD2 connector in the truck, but I dont think it is actually obd 2, works with and Obd2 scanner to pull codes at least.

 

Bastard year. I believe they call it OBD1.5

 

Just an Update to this, I replaced the spider unit and the problem has been resolved. I had a 100 miles on the first replacement one and it started causing a misfire in cylinder 5. Unfortunately there was no easy way to test just the injection unit, after everything else tested good process of elimination lead me to replace it, and it was under warranty so it did not cost me anything.