So I bought this 87 s10 blazer 2.8l v6 about 2 months ago thinking that i could fix it up and make it my dream car. when i drove it home its was perfect. the guy warned me that it was really stubborn. so the next day it wouldn't start. I took it to the shop and they changed the fuel pump. long story short. It starts all the time but misses on idle and if i press the gas it will backfire and cut off. so far i have replaced:
Iac valve
coolant temp valve
Fuel pump
fuel filter
egr valve
egr solenoid
cap and rotor
coil
ported vac switch
a couple of vacuum cables
and im changing the map sensor tomorrow. Any suggestions would be greatly appreciated thank you

 

Check the fuel pump relay, almost willing to bet the whole cause of your problems was that $15 part

 

how do i check it. or should i just change it? Ive been trying to replace the least expensive ones first so that'll work. so ill check that, change the map sensor, and then if neither of those work. the distributor

 

Swap it with one beside it and see if it runs any better. Easiest way to test a relay is with a multimeter and 9 volt battery.

Blindly replacing parts hoping you find the problems gets costly real fast. Unless it was throwing codes for the sensors you replaced that all was a waste of money.

The o2 will sometimes start to go out long before it throws a code but it has a suggested service mileage to be swapped anyways. The map also sometimes acts up, good to have a spare just to test with and swap if needed. The tps has to be set with a multimeter on our year model and sometimes it can get knocked off a tiny bit.

 

I had this same problem with my same year Blazer same engine. It actually came out to be the gap was too close on the spark plugs causing a premature spark before the valve's were closed causing a pop out of the Throttle body. Hope I can be of help. The gap on mine were .28 to .35 when I checked them and then corrected to .45 and no problems after that. I changed hundreds of dollars of equipment before I decided to check the gap and bam.

The reason why I didnt check the gap in the first place was that it had ran fine when I installed the new spark plugs, but shortly after it had started to run bad. Therefore I ruled them out, but at lack of anything better to muster up I dedcided to check the gap and that was it.

 

Okay so I've taking it to one shop it was there for 1.5 weeks. Then I took it to another one and they said in all there 30 years they've never seen anything like this. Sooooo. I'll take your guys' advice and check/change what u all suggested but after that back to replacing parts blindly. They check all the grounding and its all fine. But he said he thinks its something electrical. Honestly the mechanic at the shop sounded like he wanted to quit working on cars. Lol but I have faith in her.

 

so today i replaced the fuel relay and gaped some new ac delco plugs. installed plugs and checked firing order. still backfiring out of the throttle body.

 

I can't think of what its called , I think maybe a ignition module but I maybe wrong it's under the distributor cap and rotor , where the wires go into the distributor , I had the same thing happen to my Z 24 .

 

ignition module
That was gonna be my next suggestion if the relay wasn't it, trying to go from easiest/cheapest to more $$/complex.

A parts store will offer to check it but get a new on. I hate replacing parts that might not be bad but I've had too many of them "tested" and say they were good but I replaced it anyways and fix the problem. Even if its not it you can save the good one for later.

Had it happen once to me (happened to be my blazer) but the pick-up in the dizzy went bad. Drove me nuts for a week trying to figure it out. Off a whim I swapped out the dizzy with a spare I had and it ran right. Finally figured out what it was exactly when I was converting the old dizzy to an oil primer for my 3.4.

 

Yes I have had them test ok and still be bad to , they don't cost to much , but get a good one . when mine went on the z24 I was going down a long hill and all of a sudden BANG , super loud came out my exhaust , the car shut off and I had a friend tow me home . I started it in my shop and revved it right up and Bang so loud it felt like it blew out my ear drums , it blew the muffler up to the size of a 5 gallon pale .