'95 Chevy Blazer 4x4 4.3L engine 105K. A while backI posted the same problem. Well I went ahead and installed new plugs Autolite APP25 Platium, Distributor cap, rotor, spark plug wires, Fuel filter, and Fuel Pressure Regulator (part of fuel injection system under Plenum). Also found the EGR valve port almost pluged so I cleaned it out also. Everything ran great for about 500 miles then it started again with hesatation, missing, rough idle. I went out and reved the engine and after a while the idle started to smooth out. Not sure if I want to take into a Chevy dealer. I'm afaird they'll just throw in some spark plugs and say it's all fixed. I've installed two sets of APP25's, the first set only lasted 1k and this set only 500 miles. Could it be that Autolite APP25's foul out easy? Any thoughts. Sorry for any mispellings. Thanks in advance for any suggestions

Also after reading all the feedback on other posts, it seems that most people use AC Delco Double Platinums #1 is that correct? Maybe my problem could be as easy as the Autolite's APP25 won't work well in this engine? Is the AC DP #1 the correct plug for the 4.3L engine?

Forgot to add that the cataylic converter also rattles internally? So I also thinking maybe it could be blocking the exhaust? Any thoughts on this? My concern with replacing it first is that, I heard if your engine is runing to rich that it could damage the cataylic converter? So I didn't want to damage it. Any thoughts on this, or is it okay to install the new one even if the engine is runing rich how long would it take to damage it?

 

There have been many threads on this topic. Any good or even crappy mechanic will tell you to only put AC Delco plugs in especially on a 4.3L motor. I work at aretail/commercialautoparts store and have asked many mechanics at my job and they all say the same thing. They would never put Autolites in a Chevy. They use Champions for Chrysler/Dodge, Ac Delco for GM, Autolites for Ford, and NGKs for Toyota. I would put some Ac delco platinums in and clean everything out again and then see what happens. I would also run a 20 gallon treatment of Chevron Techron Fuel system cleaner with a full tank of gas. If this doesnt solve your issues then you might be looking at a faulty coil pack, distributor, etc.

 

I would run a fuel pressure test, especially paying attention to the pressure drop after the key is off. It is possible you have an internal fuel leak that is causing a rich condition, thereby fouling the plugs. No plug should foul in 500 miles on their own. I think there are other things going on here.

 

Can you please tell me what the pressure should be, and how long should it hold after the inginton is off? Also what do you think about the spark plug brand? I did find the passenger side clean when I opened the plenum, that's why I replaced the pressure regulator. Is there any way to test the injector system for leakswith the plenum top half off? This problem has been a pain the !!!! to say the least. Thanks

 

When you replaced the FPR, did you remove the spider to do so? Did you replace the internal fuel lines (called the 'nut kit') at the same time?

THe fuel pressure should hold at 55-60psi and should not drop more than 10psi over 10 minutes. Typically there will be a drop in line pressure when the pump shuts off as the check valve in the fuel pump closes. There definitely should not be a steady drop in pressure however minute it is. If there is a steady drop, then you have a leak somewhere.

 

First thank you for replying with the pressure info. Also it's just my unprofessional opinion that the spark plugs are fouling out. They just seem darker than normal. Maybe I can pull them again and take a digtal photo and upload it?

I did not have to remove the spider inorder to replace the FPR. The drivers side was not clean like the passenger side under the plenum so I figured the "Nut Kit" was okay?

If I get a fuel pressure gauge and do the test and find the a pressure loss, how would you proceed? After removing the top plenum can I turn on the fuel pump and just look around for leaks? What about taking out the individual injectors? I'm very mechanical but have never dealt with fuel injection systems.

Also you didn't make any suggestions regarding the spark plug type?AC, Autolite, etc.

I do agree with you that I can't belive that even with Autolite APP25 that they should foul out within 500 miles.

Thanks for all your suggestions and procedures, they've been very helpful

 

You can just pull the upper plenum and turn the key on to pressurize the system.

It may also be time to replace the upstream O2 sensor. If you do not find an internal leak or the pressure holds fairly well, that may be the next course of action. I typically won't recommend an O2 change without first looking at the output of the O2 sensor, but that is quite difficult to do without the proper tools (scan tool w/ graphing functions). With 105k miles, if the O2 sensor has not been changed, then it may just be time. The sensor you want to change is the on closest to the engine on the exhaust pipes.

 

'95 Chevy Blazer 4x4 4.3L engine 105K. A while backI posted the same problem. Well I went ahead and installed new plugs Autolite APP25 Platium, Distributor cap, rotor, spark plug wires, Fuel filter, and Fuel Pressure Regulator (aftermarket)(part of fuel injection system under Plenum) I did not find alot of gas laying in the intake manifold area, just replaced incase the pressure regulator maybe bad. Also found the EGR valve port almost pluged so I cleaned it out also. Everything ran great for about 500 miles then it started again with hesatation, missing, rough idle. I went out and reved the engine and after a while the idle started to smooth out. Not sure if I want to take into a Chevy dealer. I'm afaird they'll just throw in some spark plugs and say it's all fixed. I've installed two sets of APP25's, the first set only lasted 1k and this set only 500 miles. Could it be that Autolite APP25's foul out easy? Any thoughts. Also the Cataylic Converter also rattles?

Now it's 12/23/08, I've done everything back 6 months ago. The cpu is OD 1.5. I have not had it checked yet. So after so of your help I install a new GM O2 senser and did the fuel pressure check (50-55PSI was not steady but the needle was jumping around in the 50-55PSI range. I can't remember if it was dropping after shut off, but I would probably say no). So still having the same problem with spark plugs fouling out? It doesn't seem that all of them are as bad as some of the others? All I know is that if I put in a new set it will run for probably 500 to 1K then start missing and ruff idle. Some feedback say that I should only put in the AC Delco spark plugs? I can't beleive that any plug should go bad with in 500 to 1K?

What controls the amount of fuel that is sent to the cylinders?

Thanks in advance for any suggestions

 

The rattle in the cat is not good and could be the cause of the quick plug foul.

When you say that the plugs foul, what do they look like? Can you take some pictures and post them?

When you first start your truck in the morning or when it is just idling, do you see blue smoke come out of the exhaust?

 

First thank you for replying. Well right know it looks like the battery is just to far gone to crank the car. But I was able to do the fuel pressure test again. Even though the car will not crank there wasenough power forthe fuel pressure pump came up to 55-60PSI and after I shut of the weak battery it still was at the same pressure 30 minutes later.

I can't remember about the exhaust color? But I will get back to you after I get the new battery.