99 blazer 4x4 plugs button and cap are good , new coil, new wires new fuel filter really rough idle and a dead spot around 1000rpm sometimes with back fire? What do I need to check or change next ?

 

Runs good over 1500 rpm

 

these blazers suck on fuel pumps,99% chance its the pump. go to autozone,etc. rent a fuel test kit,if you dont know how to use it just go to a garage etc and play dumb. tell em u think u need a pump to ask them to check pressure. they will for free since it might make em a profit. MUST MUUUUST hit 60 psi and hang above 55lb for 10 min. if pump is a fail buy ONLY ac delco. anything else the car eats it.

 

You didn't mention if it has a check engine light on. If so get the codes read and post them back here.

I am working on an 02 4x4 right now that had similar issues to yours. Check engine light on and lashing, p0300 code. Turned out to be a dead cylinder #3, 0 compression. Bad Intake valve, was bent. New head $240.00 + Gaskets kit $50 + Bolts $10.00 and a day or so of work.

 

Check the plug wire routing. Common mistake to switch 1 & 3 on the cap:

 

Checked pressure 62 with key on through out rpm 52 at idle needle bouncing but never under 50 holds constant 52 slightly above idle .....pressure never drops when shut off? I know you said 55 at a minimum but read a post earlier that said 50 55 but guess ill get a pump....but shouldn't the pressure drop ? When shut off.....wiring is good thank you....haven't checked compression yet...guess that will be this weekend jobs ...any other advice is greatly appreciated ....tried of driving my company's work truck all the time just been crazy *** schedule lately and ain't had time to fix it until this weekend

 

Oh yes it does have the random misfire code....

 

Fuel pressure and leakdown specs are different on CMFI and CSFI systems. Your engine has CSFI.

GM does not publish "engine running" fuel pressure specs for this engine, (they are meaningless). All tests are done with the engine off. On your 1999, in the underhood fuse panel there is a vacant terminal next to the fuel pump relay. With the ignition OFF, and the pressure tester connected, install a jumper wire from battery positive to the fuel pump prime terminal. The fuel pump will run continuously with the jumper wire in place. After the fuel pressure stabilizes on the tester, note the pressure, it must be 60psi to 66psi. Next, remove the jumper wire. Wait 10 minutes and note pressure reading. It must remain above 55psi. Post the results for both parts of the test. If it passes both tests, the fuel delivery system is fine. If it fails one or both parts, there is a problem with the fuel delivery system, and will require further diagnosis to pinpoint the problem.

 

Captain would this also work on a 97 blazer 4.3 I'm not sure where the change over happened from csfi and cmfi

 

The changeover was late 95, (very few 95 CSFI's).

Specs for your 97 are the same as 99, but your 97 does not have the pump prime terminal in the fuse panel. You'll need to cycle the ignition to activate the pump. It will only come on for ~2 seconds and shut off.