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Discussion Starter #1
Hey i was wondering if i could get some idea from you guys about my 4.3 blazer. basically it has just started cutting off and bucking while under load at about 40mph. my mom drives this truck most of the time so I really need to get it back to normal. It currently has 117k on it and it has had a rough life. I have replaced the fuel filter, swapped out the dizzy with a known good unit and replaced all plugs and wires. I think ive narrowed it down as not a fuel or ignition issue. I just got done pulling the valve covers to see if i could get the cam to show that it is bad but it looks to be doing its job correctly. My next thought is a cam or crank sensor, but before i go through all that does anyone have any idea's that could point me in the right direction?

Thanks in advance
 

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One common problem on those is the oil pressure switch, which is located on the block right behind the intake manifold. The fuel pump relay is grounded through that switch, so the theory is if your oil pressure drops too low, it will cut fuel and shut the motor off. However if the switch is being intermittent, it could still cause it to die even if the oil pressure is good.
 

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Any codes? A bad 02 sensor, or a dirty MAF could be the culprit, but those should throw codes. Check your TPS too (set your multi-meter to mili-amps and make sure your reading is consistent from closed to wide-open). A vacuum leak can also cause bucking/surging. So can a clogged or leaking fuel injector.
 

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it's a chevy ???????????????? :):tongue::D
 

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it's a chevy ???????????????? :):tongue::D
i totally agree with this one... it is the only bowtie we have ever owned :( ill check the oil pressure sensor and its obd1 with no codes... also since its a chevy it has no maf and the injectors would cause a constant issue. I do have a degree in this crap but man when it gets to you it gets to you... ya know!?

thanks for all the input guys i really appreciate it.
 

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Did you change the distributor or just the distributor cap. I have heard many times of the gear wearing out and causing multiple misifires/ random misfires while driving. They will run ok when sitting still. There is no MAF on a 90 s10. It uses a map sensor. Getting codes like cjhudson says is definitely going to help point you in the right direction. You can run codes yourself on that thing with a jumper wire. I think you jumper between the A and B terminals on the ALDL connector under the dash.

http://www.troublecodes.net/GM/

-Rob
 

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Discussion Starter #7
yeah checked for codes first thing and the distributor was a fresh reman unit that i tested it with. i am leaning towards a cam or crank sensor or like mike said the oil pressure switch.
 

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these are the reasons i have intentionally avoided contact with , and learning about the newer cars till now irregardless of make . i will not touch anything the wife buys anymore as i swear they got a sensor or something plugged into everything including you . something goes wrong they can be such a pain in the arse to diagnose due to all the little sensors , electronic gizmo's etc. to someone like myself . still though it , your blazers 4.3 , is just a 305 with two cylinders lopped off i wouldn't think it'd be too hard to figure out . the trucks i drive at work , now mostly 8-9 ton , and every once in a blue moon a semi still , have the same arrangement as was mentioned before with the oil pressure switch . it will not let the truck run at speed if it's low , and if it does it will run like crap to keep you from damaging it . most of the time it'll just flat shutdown . i thnk the gm's around this time were using a crank sensor also . i bought a gmc dirt cheap as a beater a few years ago { 1500 for an extended cab slt 1/2 ton with all the goodies , 5.7 and mags and heated leather } and it had 2 issues it wasn't starting , and when it did it wouldn't stay running . crank sensor was bad , and the check ball in the fuel pump went bad letting all the fuel drain back down and the pump eventually burned itself up i geuss . replaced both drove it for a while and sold it to finance one of the old ford trucks that seem to litter my property .....:D
 

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There is no cam or crank sensor on this thing. The closest thing to either one of those is the pickup coil in the distributor. If you had a fuel pressure gauge you could actually see if pressure was dropping off when it runs bad. I have also seen crappy old TBI units that were clogged with small pieces of corrosion or rust and had to get cleaned and resealed. Good luck man!
-Rob
 

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A fuel injector isn't necessarily going to cause a constant problem, but if the car is TBI you should be able to rev the motor in neutral and observe the spray pattern, while watching for leaks or drips. Running with a fuel pressure gauge to see what the fuel pressure is doing where the engine starts to f-up, is a good idea too. How is the idle? I've seen a leaky EGR valve cause bucking and surging, but it's usually under light load and causes a rough idle too.
 

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Discussion Starter #11
im going to borrow a fuel pressure gauge and tape it to the windshield tomorrow once i get the valve covers back on it. Ill let you know how it goes.
 
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