95 S10 Blazer 4.3 Vortec W vin~ Miss/Idle Issue~ PLEASE HELP


cherokee83
11-16-2009, 07:21 PM
Bought the vehicle from Craigslist in August. Test drove first, everything was great except minor "miss" at idle, squeaking ball joints and engine would not reach operating temp. (Also discovered after filling the fuel tank completly the first time that there was a minor leak just before my rear drivers tire.) Drove this vehicle several hours from home and back with no problem (other than fuel economy had never been great). Finally replaced thermostat 9 days ago, engine now reaches proper operating tempature but..... let the fun begin! Two days after the new thermostat I started it about 20 mins before leaving for work, as I always do. Got in it, drove 5 miles down the road to find that it was idling very erratically and running poorly, especially when slowing down or stopping. Immediately returned home, where it never died but once shut off would not restart. On my way home the check engine light came on-later discovering the code was a Random Misfire. Replaced the Fuel Pressure Regulator, as my husband discovered that the side of the intake that the regulator was on was washed out from fuel and wouldn't hold pressure when key was cycled. Attempted to start with no avail, but would now hold pressure. Sprayed it with either, fired right up and ran smooth. Drove to town for test drive which resulted in being towed home. Either wouldn't even restart it after it died the second time. Next day removed and inspected the regulator and reinstalled it, then checked fuel filter, lines and re-checked pressures. Started and let it run for well over half hour, drove it all over town, stopped and filled up fuel tank (still noticed leak) and brought it home with no problems. Started the next morning to "warm up" before leaving for work again, got in it and got to the same 5 mile point before erratic and rough idiling occured yet again. Continued to my destination slowly, with no check engine light this time. We can start vehicle and let run for 20 mins to well over in hour in the driveway no problem. Can even sometimes drive for the better part of an hour and nothing will happen, but everytime at random times once hot it will start to miss, idle rough, and sometimes die. Usually will not immediately restart at this point.

Parts Replaced:
Plugs
Cap and Rotor
Fuel Pressure Regulator

NEW Parts Tried: (And have been returned for their lack of assisting ANY in this matter)
ICM
TPS
Coil (even though old coil sparked fine)
EGR

Tests/Cleaning Attempted and other Ideas we've tried:
Cleaned IAC
Tested MAP Sensor
Tested Fuel Pressure (held within all specs)
All fuel system filters have been checked
Plug Wires are within ohms
Plenty of spark from the plug

On the schedule for tomorrow is testing the o2 sensors. Any help, tips, advice or possible repair options at this point would be MORE than appreciated.

MT-2500
11-17-2009, 08:52 AM
Bought the vehicle from Craigslist in August. Test drove first, everything was great except minor "miss" at idle, squeaking ball joints and engine would not reach operating temp. (Also discovered after filling the fuel tank completly the first time that there was a minor leak just before my rear drivers tire.) Drove this vehicle several hours from home and back with no problem (other than fuel economy had never been great). Finally replaced thermostat 9 days ago, engine now reaches proper operating tempature but..... let the fun begin! Two days after the new thermostat I started it about 20 mins before leaving for work, as I always do. Got in it, drove 5 miles down the road to find that it was idling very erratically and running poorly, especially when slowing down or stopping. Immediately returned home, where it never died but once shut off would not restart. On my way home the check engine light came on-later discovering the code was a Random Misfire. Replaced the Fuel Pressure Regulator, as my husband discovered that the side of the intake that the regulator was on was washed out from fuel and wouldn't hold pressure when key was cycled. Attempted to start with no avail, but would now hold pressure. Sprayed it with either, fired right up and ran smooth. Drove to town for test drive which resulted in being towed home. Either wouldn't even restart it after it died the second time. Next day removed and inspected the regulator and reinstalled it, then checked fuel filter, lines and re-checked pressures. Started and let it run for well over half hour, drove it all over town, stopped and filled up fuel tank (still noticed leak) and brought it home with no problems. Started the next morning to "warm up" before leaving for work again, got in it and got to the same 5 mile point before erratic and rough idiling occured yet again. Continued to my destination slowly, with no check engine light this time. We can start vehicle and let run for 20 mins to well over in hour in the driveway no problem. Can even sometimes drive for the better part of an hour and nothing will happen, but everytime at random times once hot it will start to miss, idle rough, and sometimes die. Usually will not immediately restart at this point.

Parts Replaced:
Plugs
Cap and Rotor
Fuel Pressure Regulator

NEW Parts Tried: (And have been returned for their lack of assisting ANY in this matter)
ICM
TPS
Coil (even though old coil sparked fine)
EGR

Tests/Cleaning Attempted and other Ideas we've tried:
Cleaned IAC
Tested MAP Sensor
Tested Fuel Pressure (held within all specs)
All fuel system filters have been checked
Plug Wires are within ohms
Plenty of spark from the plug

On the schedule for tomorrow is testing the o2 sensors. Any help, tips, advice or possible repair options at this point would be MORE than appreciated.

If a no start and then it will start with a star aid fluid you have a fuel delivery problem.
But go essy on starter fluid unless you want to blow the dip stick threw the hood.
Only use carb spray as a starter aid.
The only true test on a fuel pump is to check the direct fuel pressure from fuel pump.
A quick test is to block off the return line and see if fuel pressure comes up to 75-85 lbs.
But do not run the pump at full pressure very long.
Also when testing fuel pump and pressure you need to tape a gauge to outside windshield or outside mirror and drive it on the road for 20 -30 minutes
until the pump gets has run a while to check for a pump fading out after hot.

Hard to start cold or hot and fuel pressure testing guide lines.
Check cold start fuel pressure.
Check engine running fuel pressure.
Check engine running on the road fuel pressure.
Then shut it off and watch for fast leak down.
Pinch off at rubber part or block off return line and check full pressure.
If pump has full pressure with return line blocked and low pressure without it blocked most usually the fuel pressure regulator is leaking or not holding pressure.
Later V6 and V8 gm engines should have 60-66 fuel pressure.
Cold start should be 64-65 lbs of pressure.
If you do not have full fuel pressure on a cold start the injectors will not squirt fuel.
Do not leave home without it.
Engine running should be 60-66 lbs pressure depending on engine load.
Full pressure with return pinched off should be 75-85 or more.
And if it has a fast leak down after shut off you have a leak in system.
Post back fuel pressure readings.







What are you fuel pressure reading at the time or when no start?
Always retest for codes.
Post back any code no.

cherokee83
11-17-2009, 03:09 PM
As I mentioned above it no longer requires a starting "aid". It will either start or not, without the use of an aid. We tested with a fuel pressure gauge many times and (though I cannot remember the exact numbers now) all were within specs according to our manual. That was how we determined the pressure regulator was bad and replaced it. Now what? Any new ideas not already mentioned?

cherokee83
11-17-2009, 03:11 PM
Also, no new codes.

MT-2500
11-17-2009, 06:02 PM
As I mentioned above it no longer requires a starting "aid". It will either start or not, without the use of an aid. We tested with a fuel pressure gauge many times and (though I cannot remember the exact numbers now) all were within specs according to our manual. That was how we determined the pressure regulator was bad and replaced it. Now what? Any new ideas not already mentioned?
Are you telling us starting aid does not help?
If so then confirm good secandary ignition.
And also.
At the time of no start confirm good fuel pressure.
Specs ar 55/61.
You should see 59 -60 cold cranking.
If fuel pressure is good confirm good hot blue spark to all plugs.

If good fuel pressure and good ignition and and still not start with or witout starting aid you have a very strange problem.
I have never saw one with good fuel pressure and good ign that would not start without the use of starting aid or not set any codes.
Always double check the basic.

Add your comment to this topic!