Have a 94' S-10 Blazer. Had an issue with fuel delivery, changed the fuel pump, then the injectors. Ran fine for a day. Then while driving. developed a miss. Almost like a burnt wire. Changed the plugs and wires. Cap and rotor...... Changed the control module also. Now i get a shake at idle only, when i rev it up it disappears. Adjusted the timing while running, didn't make the shake go away. Any suggestions?????
94' 4.3 Vortec
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Check out www.s10forum.com there is alot of info about 4.3 vortec's.
I appreciate the post, but i went there and it seems to be all modifications. I'm wondering if this could be a timing chain, but im a little confused as why it would seem to have all the power at higher rpm's. this really has me stumped. actually drove it last night and it has almost no power on take off. loses almost everything when its in gear. any suggestions please !
it may have something to do with the fuel filter. if anything has happened with the gas tank recently some crud may have broken loose and is floating its way through the line, or the filter may be clogged up. ive seen that happen where at idle it runs rough but once up to speed it doesnt seem to drag, but at idle its starving for that fuel.
Although there is a lot of information about mods on that site, I am surprised there wasn't anything to help.
I do know that a lot of the early Vortec 4.3's have fuel problems.
When you say that you changed injectors, did you change the main CPI unit itself.? They are known to fail as does the pressure regulator. Also there are numerous problems with the EGR valves. They tend to stick open because of carbon and they can cause idle problems.
If you had a fuel filter restriction problem it would tend to be under load, when more fuel is required.
My guess would be the regulator. Do you have any kind of repair manual that gives the test procedures to check the fuel system.?
I do know that a lot of the early Vortec 4.3's have fuel problems.
When you say that you changed injectors, did you change the main CPI unit itself.? They are known to fail as does the pressure regulator. Also there are numerous problems with the EGR valves. They tend to stick open because of carbon and they can cause idle problems.
If you had a fuel filter restriction problem it would tend to be under load, when more fuel is required.
My guess would be the regulator. Do you have any kind of repair manual that gives the test procedures to check the fuel system.?
the pressure regulator was changed also, i have about 60 lbs of pressure at start up and it drops to about 55 at idle, when i rev the rpms, it jumps back to about 60, the same pressure is when in gear or in neutral. could this possibly be the throttle positioning sensor or timing chain???
I just went through this with my sisters 95 4.3 Blazer, poor idle no power and bad mileage.
I started with a complete tune up, plugs, wires, cap and rotor, and fuel filter. All parts were way overdue.
The fuel pressure was on the low side and it would not hold any pressure when the pump shut off. Next was to replace the CPI and regulator assembly. While the upper intake was off I also cleaned the EGR and installed a new gasket. The fuel pressure was still on the low side but it did hold pressure when the engine was shut off. While testing and about 5 min after restarting it just quit, I could not get fuel pressure above 30 psi. Next was to replace the fuel pump, now it is running better than it had in years and she is happy as can be.
It sounds as though you have done pretty much the same as I.
I was able to smooth hers out with the repairs I did, If you are not getting any codes I would check the vacuum lines, EGR valve and the IAC valve.
If i remember correctly the throttle position sensor should read .45v at idle to approx 5v at WOT, all sensors will vary so your readings may not match exactly. (I would need to look that up to be sure.)
As for the timing gears and chain, Get someone to watch the rotor in the distributor while you turn the engine first one direction then reverse the rotation. What you are looking for is the lag time that it takes the rotor to change directions, it should be minimal, the longer it takes to reverse = wear in gear and chain set.
Hope something here helps.
I started with a complete tune up, plugs, wires, cap and rotor, and fuel filter. All parts were way overdue.
The fuel pressure was on the low side and it would not hold any pressure when the pump shut off. Next was to replace the CPI and regulator assembly. While the upper intake was off I also cleaned the EGR and installed a new gasket. The fuel pressure was still on the low side but it did hold pressure when the engine was shut off. While testing and about 5 min after restarting it just quit, I could not get fuel pressure above 30 psi. Next was to replace the fuel pump, now it is running better than it had in years and she is happy as can be.
It sounds as though you have done pretty much the same as I.
I was able to smooth hers out with the repairs I did, If you are not getting any codes I would check the vacuum lines, EGR valve and the IAC valve.
If i remember correctly the throttle position sensor should read .45v at idle to approx 5v at WOT, all sensors will vary so your readings may not match exactly. (I would need to look that up to be sure.)
As for the timing gears and chain, Get someone to watch the rotor in the distributor while you turn the engine first one direction then reverse the rotation. What you are looking for is the lag time that it takes the rotor to change directions, it should be minimal, the longer it takes to reverse = wear in gear and chain set.
Hope something here helps.
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