2000 blazer 2wd 4dr LS 177,000
fuel pump failed - replace
new fuel filter
water leak rear intake - replace upper/lower gaskets fel-pro gaskets
ran good for a month or so
started getting p300 ( high speed misfire) driving 30 miles at 75 miles per hour
idle good, good pick up - just the high speed misfire

replace dist rotor and cap advance auto parts aluminum shaft
timing marks on cranshaft and dist rotor pointing to #6
if I connect a timing light to #1 plug - were should the timing mark be at idle? at 2000 rpm 3000 rpm
replace spark plugs (autolite - may made a mistake here)

smooth idle till it warm ups - rough as hell
get above 2000 rpm runs good - driving 30 miles at 75 miles per hour no misfires

Starts right up cold or hot ( rough idle till 2000 rpm )


gas mileage is not good - was getting 20 to 23 miles per gallion


Having a hard time nailing this thing down -- getting personal now

thanks

James

 

How old are the plug wires? Sounds like you may have some arcing going on here.

Also the brand of cap and rotor used is questionable....may get carbon arcing inside cap.

Keep after it...you will find it.

 

Is temp sensor reporting correct engine temp? Is it storing any error codes?

 

good suggestions -- the temp sensor has been replace --- the one btw #3 and #5 really no change --- oil pressure is good 60 highway , 30 idle --- gas gauage solid no extra movement -- no other codes --- once in awhile p300 (great) not much help thinking to pull the plugs see if I can get any idea what is going on

may be on to something -- someone posted that they file out the bolt hole on the dist to get a little adjustmust --- thinking may have some timing chain wear did help but still have the problem rough idle and low speed misfire (below 2000 rpm)

 

Did you set the CMP Retard and do a CASE Relearn after replacing the distributor (which I think you replaced the distributor since you noted the "aluminum shaft", but without any punctuation, it is difficult to follow along with what you replaced )? CMP Retard is set by moving the distributor in it's bore through the LIM. There is enough room to allow for ~15 degrees of timing change and the CMP Retard value displayed on an enhanced data scan tool should be set to zero. A CASE Relearn should be performed after any major timing component is replaced (timing set, distributor, CMP sensor, CKP sensor, cam, etc).

What brand were the cap & rotor? Fuel pump? Reason I ask is because we have seen it time and time again that aftermarket caps, rotors, & fuel pumps do not meet the OEM requirements. You've replaced the part and have since taken it off your list of potential sources for the failure, but in reality, the fault likely still exists. It is amazing how much money people will pour into a problem having already done the general tune up only to find that the $20 cap & rotor set either partially cured or, as is in some cases, didn't change the symptoms.

And a little side note. The question asked was "is the temp sensor reporting the correct temp" and the response was "the temp sensor has been replaced". It may sound trivial to some, but there is a definite difference between the question and the response. The fact that a sensor was replaced has no bearing on the question which is why I have labeled that statement as a response and not an answer.

 

I agree about using OEM fuel pumps. I too tried the economical route on my K-5 Blazer, failed miserably. Thank goodness it was an 87 and I was able to change it without dropping that darn tank.
I'm not so lucky with my 99 Trailblazer. I have to replace the fuel pump and am NOT looking forward to dropping the tank. I've already bought the Delphi pump, now I just have to figure out how to drain the darn fuel.

 

when I replace the pump - had a full tank of gas --remove needle value from test connection connected 1/4 nose , removed the fuse for the pump and jumper the pins needed to keep running - got all the fuel out
don't remember the pins I jumper at the moment

 

took a pictre of the temp -- this is after approx 15 miles --- when things are running right 2200 rpm 75 miles per hour going down the tollroad
if you donot have to stop things are great

use craftsman infrared thermometer to check the temp 165 degress F when I got home - looks like the temp is correct

working on part list and who made the parts

 

Thanks everyone for the feedback.

Had some time and a nice day and wanted to check everything that I had done before.

1. Pull dist verify that no arching. Everything in great shape.
2. Changing plugs autolite platinum #3 ceramic was crack in two places
3. Check each plug wire for cracks and archiing check ohms readings

Runs great now yeeehaaa!

Things left to do:
1. Replace plugs wires
2. Set CMP Retard
3. do a CASE Relearn

My code reader does not do this.

Looking for code reading software to set CMP retart and do a case relearn , anybody have any suggestions


Thanks again to everyone
Have a great day

James