I have a 96 4.3 Blazer and I have been trying to diagnose this issue I am having but its not working. I had a trouble code saying my car is running Lean. I know I have an okay MAF sensor and I replaced my fuel pump along with my fuel filter. So I am down to either the Fuel Regulator or Injectors. It keeps running at 50 PSI at a normal Idle when I diagnose it with the fuel pressure gauge and if I am correct, Its suppose to be around 60-65 at normal idle. It will stall or bog out on me when driving in early morning or when the heater/ac is on high. Also when I drive long distances, it will get even worse and the RPMs will skyrocket and the engine sounds like its running really hard and will buck or jerk on me. I checked the OBD but it only said random misfire and lean fuel code around 2 months ago. Now it says nothing. The previous owner before me said that it has a "newer" engine with only 44,000 miles on it but ever since this problem, I highly doubt he told me the truth. I want to fix this issue, it just bugs me, does anyone have any ideas or has gone through something like this?

 

iam kinda goin through the same thing now. getttin a p0171 and p0174 code. been going on for a while. this is a new engine too like 20k replaced pump and regulator had some vaccume leaks fixed them and still had the codes and same drivability issues. i unplugged the mass air flow sensor and it drove a whole lot better pretty much like it should... idk if the sensor is bad or how to check. going to check the fuel filter though been a while since it was changed.

i did have fuel pressure issues but they are all fixed now.

 

Yeah those codes popped up with...I think it was...a P0300 code or something like that indicating a random misfire. So how did you fix the fuel pressure issues? So after you fixed the pump and the vacuum leaks, it was still acting up?

 

well i had a weak pump pressure was low. replaced it and the regulator. it ran fine for a few eeks untill the codes popped up. now pressure is good and it holds good for hours. thats what made me try unplugging the maf. i did that today. and it runs great i gotta figure out if its the sensor though thats actually bad. i had the fuel issues a couple months ago. gonna do fuel filter just cause it needs done anyway..

 

Fuel pressure must be checked with the engine off. GM does not publish any "engine running" specs for the CSFI system. Key on, engine off, fuel pump running: pressure must be 60psi to 66psi and must remain above 55psi for 10 minutes after the pump shuts off. Post your results.

This link will help you: https://blazerforum.com/forum/2nd-ge...agnosis-45941/

 

Oh okay, the master tech at my school said to drive around with it to try to catch it when it drops or bogs out on me. That didn't work since it only does it early in the morning when AC/Heat is blasting for a few or just when the engine is cold. I did the test again this morning. It was at only 53psi with the key to the on position. It didn't go over or under, even after 10 minutes later. I will have to try out the diagnosis next time i get a chance. Thanks.

 

A live data stream from a scanner might help if it is an intermittent issue. It was the only tool that helped me figure out my problems.

 

If all you're getting is 53psi with the key on and the engine off, there's your problem. Gotta be 60psi to 66psi. Check maximum pump output at the filter, should be around 108psi.

 

I have the same problem-P0171 and P0174 codes. No rhyme or reason. One time after 10 drive cycles, the next 1, the next 5, etc... This all started after I had an oil pan leak repaired. The engine was out getting a new gasket set, engine reinstalled and now the codes. Only symptom in the begining was surging when cold-soaked. To date the following has been changed with the problem only getting worse. MAF, IAT, IAC, Fuel Pump, fuel filter, Vapor Canister, 5/8" Vapor Canister Line (kinked), Fuel injectors, and pressure regulator. The EGR was also checked. After all that, it will barely run now. The shop that pulled the engine is getting ready to send it out to a Chevy Dealer to get fixed. They had a "Scan-Man" in and after about 6 hours he gave up. In two of the posts, a prior engine replacement was indicated if I read them right. That could lead to an exhaust leak before the O2 sensors, but they say they have checked that too. Has anyone had any progress yet?

 

Sounds pretty simple, check fuel pressure and leakdown, this link will walk you through it.

https://blazerforum.com/forum/2nd-ge...agnosis-45941/