I have a 96 Blazer 4*4 with the 4.3 engine. I've been having a hard time getting it to start. Once it does start it runs rough for maybe 10 seconds then smooths right out. I have no acceleration issues, no rough idle other then the initial 10 seconds, fuel psi is at 60-65, 1 psi bleed off in 20 minutes. It has a new distributor cap and rotor, plugs, wires and coil. When starting the first attempt it will sputter but not catch, second attempt nothing but cranking, third attempt it usually starts right up but lately it has.taken longer. I have tried to start with the maf, intake temp and coolant temp sensors unplugged. I have a blue driver scanner and have no codes showing up. Fuel pump is not even 2 years old (not that that means anything these days). Issue started in the spring and got worse over time. Any help would be greatly appreciated.

 

Welcome to the forum, lets get you fixed up.

I don't like stabbing with guesses using the parts cannon, I prefer a methodical diagnostic approach. Others see it differently. As I am sure you know, this can be a lot of things. Ignition, fuel pressure, fuel injectors, timing, mechanical problems, sensor problems, module issues, wiring/connectors. Since you have no codes you need to be ready to check spark and fuel pressure while cranking and not starting to see if that's the problem. After that checking all sensor values in live data to see if they all make sense. Then it would be on to the other areas. Let me know if I can help. These may be of use:

https://blazerforum.com/forum/2nd-ge...rticle-103750/

https://blazerforum.com/forum/2nd-ge...72/#post732722


George

 

USing the blue driver scanner all the sensors appear to be working not sure what the numbers are supposed to be though. My timing advance for cylinder 1 on the scanner says -20 when idle and up to -40 when going down the road. Not sure if that is normal. Though it idles good and runs good going down the road with no hesitations. I'm like you don't want to just throw parts at it and hope for the best. I have checked fuel pressure but not spark as I will need to get a tester.

 

The important thing for timing is cmp retard which needs to be within -2 to +2. The computer controls timing advance and is not adjustable. You need to double check fuel pressure when it runs crappy in case you have some injector problems when firing for instance. Sensors in live data:

ECT should read ambient with engine cold and around 195F with engine hot
MAP or baro should read ambient with KOnEOff
TPS should be smooth and follow the gas pedal through its range from around zero to 5V, KOnEoff
O2 sensors should be switching between around 0.15V and 0.85V at a frequency of around 1-3 hertz at idle
MAF sensor should be reading around 6-7 g/s at idle but the definitive test is a screen capture at the full throttle 1-2 gear shift
IAT is ambient at KOnEoff
Fuel trims are <+/-10 each bank ST+LT

Report back on FP, ignition and sensors

George

 

O2 sensors

 

Maf, map, intake temp, coolant temp and timing to cylinder 1

 

Can your set up graph the O2 sensors, that is more useful. Here is an example:




It looks like you sent the O2 data twice.

George

 

Also, the truck has to be really warmed up for the post cat O2 sensor to make any sense.

George