2002 Blazer, 4DR, 4WD, 6 Cylinder, 4.3 L, V6

Hello, I thought I would post here and hope the experts would have some advice for me. For over a year I have had problems with starting and idling. It is very erratic and doesn’t always happen. Sometimes when I start my car it will fire for a second and not start, other times if it does start the RPM will immediately drop very low and will stall right away or when I put the car into gear. I can keep it running by giving it gas but at this point the engine runs really rough. Strange thing is I can shut the car off start it back up and it runs like nothing is wrong. I would appreciate any advice this forum may have. Things I have changed: Fuel pump, fuel filter, vacuum lines, intake gasket, wires and plugs, pcv valve, cap and rotor, belt, tensioner, and probably a few things I left out(normal tune ups and oil changes). Fuel pressure check says regulator is good, Compression check seems good(highest 186psi lowest 182psi).

 

What is your fuel pressure? Have you tested the fuel pressure when you are having the problem?

 

I agree with Swartlkk,
Did you check the fuel pressure, the 4.3l L35 engine which has the SCFI needs around 55 to 60psi to run without misfireing. The poppet valves on the spider injection system are made to open around 40 to 45psi, unless you have the LU3 engine which is the MPI spider injection.
The regulators are well known to fail and either leak fuel into the plenum area or back into the return in the injector assy.
Check you fuel pressure it should go up to 60psi when your fuel pump is good. And should stay pressurized for awhile around 50psi after the fuel pump is off and engine not running. If the pressure drops right away there is a leak somwhere.
Some signs of leaking fuel pressure regulator is hard to long start conditions, misfiring p300 codes.
You most likely have the L35(SCFI) engine since you have a 2002, it will be listed on the glove box label. I believe they went to the LU3(MPI) engine in 2003. Both are the 4.3l but with different spider injector assy.

 

What he said!
The proper fuel pressure test is: key on to prime, dont crank, PSI number;
then watch pressure leakdown for ten minutes. PSI number, then
report
Make sure no leak at test gauge connection

 

Thank you all for your quick responses, I would be glad to give you some exact numbers if you would like. I did just install a new carter(made in USA) fuel pump last week. My old fuel pump was slightly weak but unfortunately not the problem. When I did the fuel pressure tests it didn’t indicate a problem with the regulator or anything leaking but since my pump was beginning to fail I will invalidate the results and do it again with the new pump. I have not been lucky enough to have the fuel pressure tester on when it acts up. Just for reference, on the old pump static pressure was 60psi, but idle was anywhere from 50 to 55. The needle would flicker rapidly in that area but steady out at higher rpm’s. Also, fuel pressure seemed to drop with higher rpm. That’s what made me change the pump and now all those symptoms are gone. My engine RPO is L35 without an EGR valve. I also forgot to add that my OBD doesn’t throw a single code at me even when I keep it running when it acts up. I should be able to post some number by around 6:00pm EST 7 at the latest. Thanks again.

 

Good. Cannot overstate the importance of that combined test.
If you're used to fuel rail systems* as I was when I got here, it seems a little odd, but I've figured it out and seen by example just how important the static pressure / leakdown test it. Running pressure means squat in comparison.
* all you need to check the FPR is to disconnect the manifold vacuum tube and see if there's fuel in it.

 

It is possible to have 50 to 55psi at idle with a bad regulator. A good fuel pump can give you pressure when it running.
You want to be sure the pressure doesn't drop rapidly after it is primed and engine is off. (key on(no start) than off) It should hold for aleast 10 minutes droping very very slowly.

 

There may not be fuel in the vacuum tube if the regulator is leaking back into the return inside the spider injector assy.
If fuel was leaking into the intake plenum the engine could backfire and than there would be fuel inside the vac tube. The backfire could also melt the nylon tubes on the spider injector assy. Also, the inside of the plenum and intake would be clean and not black.
Rule it out using the pressure leakdown test.

 

Did a fuel pressure test again. Initial static reading was 61psi and 59psi after ten minutes.

 

Okay, great numbers, you have that out of the way.
Now when engine is warm, disconnect the Maf and test drive. If the MAF is dirty or malfunctioning, the car should drive better.

Next up.. remove and clean the EGR valve. Install new screened gasket.
Clean throttle plate and IAC thoroughly