I bought a 95 blazer for 300 bucks and it never ran well. It shakes while idling and is missing like nobodies business. I replaced the leaky fuel pressure regulator, spark plugs, wires, and cap and rotor. I know other people have had this problem and wonder how I can fix it.

 

for 300$ thats what you get these days.It can be alot of things...Fuel issues(pump,etc..),map sensor,the fuel injection system...Did you ckech your cylinder pressure,could be that you motor head is blown!?Maybe others have a good idea of the problem,thats just me.

whats the mileage?

Mart

 

Let's look at the positives here, for $300.00 bucks the engine runs and you say it idles rough. At least it idles, that's a good thing, now we just need to smooth it out. The basic components of running an internal combustion engine require fuel, air, spark and timing. Trouble shoot each category in turn and you'll get her running back to normal (or close to it anyway). She starts and idles, so you are getting fuel. She starts, so that tells me the fuel pump is delivering adequate start pressure (58 - 60psi) and running pressure (mid -50's +/-). Have you changed the fuel filter? Have you changed out the air filter and checked for blockage in the air intake system? Clean the MAF sensor in the air intake tube. Now on to spark, are you sure all the wires are routed to the correct cylinders? Mis-routed wires will cause mis-firing of cylinders. I wouldn't worry about timing at this point since she runs and idles. Eliminate the easy stuff first, then dig into the harder stuff next (checking sensors, etc). Investing in a Haynes manual will be very beneficial, they're cheap and reasonably good for what you'll need to do. Also, you might as well dump some fuel injector cleaner in the gas tank too (won't hurt). Change the oil too, if you haven't done that yet. Check for "milky" oil. Could indicate a blown head gasket. Check coolant level in radiator, flush system and re-fill with fresh stuff. These are all pretty basic low cost first steps. Work through them patiently and the ol' Blazer'll be humming nicely soon. You gotta just have some faith. Keep us posted as you progress.

 

So I have to ask. When you had the fuel pressure regulator replaced, was the 'nut kit' (internal fuel lines) replaced as well? More often than not, when the internal fuel system is disassembled and the 'nut kit' is not replaced, you will still have leaks. This could cause rough running. You could try removing the upper plenum and pressurizing the fuel system to make sure that you aren't leaking somewhere.

Other than that, I would agree that since it starts, you probably are good on fuel pressure, but it never hurts to check. If the fuel filter hasn't been replaced, then that is a definite must.

The EGR valve could also be a culprit of a rough running engine. You'll probably want to pull that off and give it a very thorough cleaning before messing around with the aforementioned troubleshooting steps I have suggested.

You'll also want to go over all of the connections and wiring to the various sensors on the engine to make sure that everything is in order.

Junk, his '95 won't have a MAF...

 

The first thing I did when I bought it was replace the air filter and change the oil. The second thing was to clean the EGR and make sure that was not stuck open.As I stated before the spark plugs all got changed along with a new cap and rotor. All the spark plug wires are on the correct plug and the "nut kit" did not appear to leak when I pressurized the system. I had my friend hook his diagnostic tool up to it and it gave a random misfire code for cylinder 4. I hope this will help narrrow the problem down.

 

The Haynes manual states:

ENGINE MISSES AT IDLE SPEED
1) Spark plugs worn, fouled or not gapped properly
2) Fault in the fuel or electrical systems
3) faulty spark plug wires
4) vacuum leaks at intake or hose connections
5) Uneven or low cylinder compression

ENGINE MISSES THROUGHOUT DRIVING SPEED RANGE
1) fuel filter clogged and/or impurities in fuel system
2) same as 1 above
3) same as 2 above
4) same as 3 above
5) faulty emissions system components
6) same as 5 above
7) weak or faulty ignition system
8) same as 4 above

D'oh...forgot '95's don't have MAF.

Age of vehicle would point me to start looking for potential vacuum leaks. I personally changed out quite a few vacuum lines on my '96 when I bought it used. Most looked fine but if you squeezed them, they showed the telltale hairline cracking that old rubber hoses experience (rubber hoses do dry out over time). Another technique (I think Kyle has mentioned this before) is to run an unlit propane torch along the vacuum lines and intake sealing sufaces while listening for the engine speed to suddenly increase. A sudden increase in speed indicates propane introduced into the combustion chamber, which indicates a vacuum leak. Good Luck.

 

if you get the random misfire code (flashing SES light)

Try the plugs. I have found one too many times that its caused by bad or broken plugs.
Seeing as you have already dont the cap/rotor/wires this rules out broken external plugs, but not internal fouled.

Good luck