Hey all, Im new here and not really tech savvy with the newer vehicles. And i have run into a real WTF..lol. I just bought a 95 chevy blazer 4.3 vortex and my problem is that it has to be jumped to start but runs then.. I've had the alternator tested it's good, got a new battery today. tested the battery it's at about 12.3 and while its running the voltage is at 14.7. Checked and cleaned the positive from the battery all the way to the starter (and cleaned up the connections on the alternator) and negative wire all the way from the battery to the block. When it's running its at a higher idle then it should ( or seems that way to me) but seems alright but seems to have a bit of a miss, there's new plugs and wires and the distributor cap is new to I think so i'm at a bit of a loss.. any ideas?.. maybe in the timing?

 

Its kind of a pain but it may be worth pulling the starter and having it tested as well, then you will have a better idea if its the engine fighting back or not. You should look up starter voltage drop testing on youtube, theres a guy named dan sullivan who has some really good videos on voltage drop testing. You could have a bad contact in the starter solenoid or a bad winding in the starter motor itself, also if you dont have a bunch of money throw around just get another starter from a salvage yard, you can usually get one for cheaper than the core charge on a new one, like 30 bucks.
Your need for being jumped means that your starter circuit is requiring more amps than it should in order to turn the engine, this means that there is either a wire or component in the start circuit with high resistance caused by corrosion or charring or opens in the windings...or the engine is too tight for the starter to turn it, quick check for this one is to try turning the engine by hand with a wrench on the crankshaft pulley.
Another thing i have seen but its rare is the nose cone broke off the end of the starter so the armature had no end support and was laying on the magnets in the starter body which will require tons of amperage to overcome that amount of friction.

 

Thanks for the reply! ok i'll have to give that try, had heard something like that on the starter doing that but hadn't given it much thought. turns it over good so that makes sense that it's drawing to much so there isn't enough to get voltage to the rest of the systems.. Thanks again

 

Maybe i misunderstood your first post, does the engine turn over fine on just its own battery when fully charged but will not actually fire up and run? If thats the case then you may just have a bad ground somewhere and maybe not supplying enough current to the fuel pump, ignition system or computer.

 

My guess would be starter, they use bronze bushing at each end instead of bearings. They start to wear and cause slop in the armature making it angle and jam so it needs extra amps. Depending on what starter is in there now you my need a couple of tricks to get it out. There all here on this board.

 

Well got the battery tested and that's fine.. It turns over on it's own just doesn't start unless you jump it or hook up a battery charger.

 

Wow ok so it spins with battery you have. Then you add more juice and it will light up.
Fuel pump might be getting tired. Do a fuel pressure test. You can get the gage at autozone for a deposit. The connecting point is something that looks like a 38 with a tire vale in the center if it comes up less then 62psi check the black ground wire from the pump to the frame and clean it up. In fact you could do that even before you test the pressure.

 

i'm +2 on the starter bets its draging bad enough it's pulling way too many amps robbing voltage from everything else

 

Yea, have the starter tested for draw while it is in the vehicle, I think autozone does this, or a volt meter with an amp clamp.

 

More than likely it's the fuel pump getting weak. Check fuel pressure, since it's a 95, the pressure must be no less than 54 psi...Injector poppets won't even activate until minimum psi is met. Sometimes giving the battery an extra jump is enough to push fuel psi to be able to start/activate injectors. Specifications are 55-61 on this setup, plus the fuel system is very finicky as well as any vacuum leaks. Simple and basic testing is all that's needed prior to throwing anymore parts at it. Bogging and hesitation upon acceleration are some of the other early symptoms with fuel pump getting weak. Good luck. Let us know how you make out!