random misfiring at idle & low-load operation

[phuz]

just got my blazer back from the shop and noticed it has a slight misfire especially noticable at cold idle and low-load operations. i am not taking it back there to have them fix it because they have done enough, and i want to make sure it gets done right. the vehicle sat for several months so i thought maybe the gas gummed up, so i put some techron concentrate in, and no improvement yet. surprisingly, it does NOT misfire under moderate-full acceleration.
i forget what this symptom means, but could it be the fuel pressure regulator?
if so, what is the best source to get one?

thanks!

matt

[Fractured1]

I would start the engine on a very dark night and look for arcing at the plug wires and cap..also may want to take the cap off and look for carbon tracks, moister, or a possoble crack...good luck

[BlazerLT]

Originally Posted by phuz

just got my blazer back from the shop and noticed it has a slight misfire especially noticable at cold idle and low-load operations. i am not taking it back there to have them fix it because they have done enough, and i want to make sure it gets done right. the vehicle sat for several months so i thought maybe the gas gummed up, so i put some techron concentrate in, and no improvement yet. surprisingly, it does NOT misfire under moderate-full acceleration.
i forget what this symptom means, but could it be the fuel pressure regulator?
if so, what is the best source to get one?

thanks!

matt

Please tell us all information, we can't read your mind.

Year, engine? What was done at the shop?

[phuz]

its amazing how i forget to leave out detail...sorry

1995 blazer LS 4x4
my engine was under warranty from having it replaced awhile ago, and when i got it back it had very low oil pressure. so i took it back and they replaced the bearings, etc. they didnt even touch the top part of the engine, but somehow i have terrible misfire now.

in fact, i just took it out to get air in the tires and twice when i came to a stop, it stalled out.

[BlazerLT]

Was it running rough before it stalled out? Or did it just die completely with no warning.

Does it run really rough at idle, but then seem to run better when accelerating?

[phuz]

it was running smooth and the rpms dropped as i came to the stop and it just died. however, at idle lately, it has been running smooth. it seems to do it the most between 5%-25% throttle. anything over that it smooths out.

[BlazerLT]

Is the CPI injector new in it?

[phuz]

no, its not new

[BlazerLT]

Remove the top vortec name plate. Then remove the round IMTV valve underneath it and look down into the hole with a flashlight and look for washed spots that will be a golden color and note any strong gas smell or pools of fuel.

[phuz]

well, on thursday i am going to pull off the whole plenom and replace the fuel press. regulator. i am also going to replace the cap and rotor. i had this problem on the original motor and replaced the fuel press. regulator and it worked fine. i just dont understand how the engine ran fine before i took it back to have the bearings replaced and now it misfires. it shouldnt be any different if they didnt touch anything up top. and i highly DOUBT that the gas got gummed up causing a problem. if anyone can think of anything else that COULD have caused this phenomenom, let me know, otherwise i will post results following the test-drive after i replace these parts. thanks guys!!

[BlazerLT]

Check fuel pressure before you start aimlessly throwing parts at it.

[mrfirebird]

my kids 94 does the same thing, even after we replaced the plugs,points cap,button, wires. keep us imformed on what you find.,
maybe coil haven't looked at that yet,but i noticed some red rusty coloring around the coil and mounting bracket.

[phuz]

ok...put the new pressure regulator in last nite and it appeared to run fine on the 45 min. drive back to my place. i took it out today for a test drive and let me give you a better idea of the symptoms for a better diagnosis:

1. after the car is started and it sits and idles for a few minutes, it hesitates and stalls out.

2. at idle speed it runs smooth, but if i open throttle and bring the rpms up to anything over 1000 and hold it there, it starts to misfire on atleast one cylinder (possibly 2). when i rev it, it is smooth, but once i try to hold it at a certain rpm, it sputters.

3. if i have the car in park after starting it, foot on the brake, and go to put it in drive or reverse, it will sometimes stall out before im able to move.

[BlazerLT]

Replace the injector, not just the regulator.

[phuz]

what is the cheapest source for a CPI?