Newbie here with a problem already..I have a 93 S10 Blazer with a 4.3 Vortec, CPI, 4x4,140,000 miles.
It has a miss at speeds between about 40 and 55 mph..Starts great, and runs great but never fails as soon as it reaches 40 to 55 mph it starts missing, slightly at first then gets worse at all speeds, low or high and even at idle..
Things I've replaced so far and didn't make any difference at all.
I clean the EGR valve every Fall, and replace the gasket with a screened gasket. I just checked it and it's clean.
Replaced the oxygen sensor, wasn't getting a code on it but the heater was open.
Replaced the fuel pump about 40,000 miles ago, it was still putting out about 58 lbs. and holding but I replaced it anyway.
Replaced plugs, set gap at 0.35 per book. Replaced wires, cap, and rotor.
Replaced fuel injectors 40,000 miles ago, but decided to replace it again..Bought a re manufactured unit off of Amazon, wouldn't work. They had the pressure regulator set at about 54, I turned it up to 65, worked great.
Replaced nut kit.
Vacuum is between 15 and 20.
Fuel pressure is steady between 58 and 65 and holds for several hours.

Can't understand it. Even when it's cold, starts on first crank, idles great, goes into closed loop within 2 to 3 minutes and runs great as long as you stay under 40, go over that and it starts missing, every time. Never sets a code.

Thanks, appreciate any help I can get.

 

You need to test your coil and ignition module. Sounds like something is failing either hot or under load.

 

sounds like you may have some of the same symptoms as we do. Do you have access to a scanner? Our truck runs strong as long as I keep the TPS under 30% and the ignition advance at least 25 BTDC. TPS voltage is smooth up scale and down scale.
If you have access to a scanner, watch those parameters, see if something strange is happening.

 

My 1992 S10 Models Service Manual by Chevrolet has these setting for spark plugs:

W engine .45
Z " .35

My Chiltons list:

92 W & Z engines .35
93 W & Z Engines .35

I believe your 93 CPI should be set at .45, not .35.

 

Thanks Leeann, that's about the only thing I haven't checked, of course when they're cold they would probably check ok. Right?

No, I don't have access to a scanner. I bought one on Amazon but all it would do on the OBD1 was check the codes. I can do that with a paper clip, so I sent it back. I guess I could advance the timing and see if that helps..

Do you guys know if Auto zone can check that coil and module? And wonder how honest they would be.
Thanks a lot, every little clue helps..

Thanks, JustJerry, we were posting at the same time..

I have the W vin. BTW..Every book I've read on it gives a different setting, some even says .50, I got the .35 reading from the owners manual that was in it when I got it.
I saw on here some place where somebody else was having a problem figuring out which reading was right too. Somebody said they put out a service bulletin changing the original settings, but didn't know what they changed them to.

 

if this truck has the obd1 setup use a paper clip and get the codes that way one u have the codes collected u can get it down to what ever is wrong 1-1-1- 1-1- =code 32 so u get the picture on how to read the code once u get the codes i'd be glad to give u the listing

 

Thanks for your reply..The problem is it never sets a code. We've had so much snow and ice here the past 2 weeks I haven't been able to test drive it. Going to try another coil and see if that stops it, if not I'll try an ignition module. Have to wait til the ice melts. Can't tell if it's missing or from hitting all the bumps.

 

if u buy a new ignition module be ware they can be defective just buy one directly from gm cause autozone one are junk i went through 3 of them on my 88 before just going to gm

 

Just replaced the ignition module, and ignition coil..Didn't make a bit of difference..When I test drive it after every replacement part, seems like it starts missing at about the exact same place every time, about 3 miles from home. I pull out from a stop sign, it starts shifting up, everything is fine til it shifts into high, then it starts missing and keeps missing no matter how fast or slow I go. About the only thing that keeps coming to mind now is "Wonder if it could make it to the shredder" lol

 

Years ago had something similar, finally found out it was the new high dollar spark plug wires. At that time I still had my old ones of which I knew one of them was bad. I bought one new plug wire, put the other 7 old ones back on, problem cured.

Not saying that is you problem, yet something is surely doing it and most likely its in the firing system.