Hello,
I have a 2001 Blazer 4 door 4wd with the 4.3L engine. Been having hard starting and back firing while trying to start. Fuel pump and filter replaced in last year. Replaced distributor, rotor, plugs and wires last week. No more back fire but have to hold gas pedal to floor to get to start. Read about leaking fuel pressure regulators. Performed leak down test. Pressure rises to 62 with key on but drops to 0 within 3 minutes. Took plenum ofg tonight to replace FPR. Rear 2 intakes had been washed down by fuel. Also fuel was pooled in low spots. Put on new FPR and get same results on leak down test. Can visually see fuel leaking that I assume is coming from around the FPR. Is it common for leaks to come from around the FPR instead of being bad diaphram? Should I have put oil or grease on the o-ring before installing new FPR? Also I did make sure both old o-rings were removed from old FPR. Could old retaining ring be bad and can new ones be purchased? If I cant get leak to stop is my only options to buy used CPI unit from junk yard because I havent found any place to buy new one. Or fo I have to upgrade to he newer MFPI system? Dont really want to due that $300 uupgrade if I dont have to. Can fuel leak from bottom of unit? I noticed washed off spot on bottom of unit. Any help appreciatted.

 

Backfire through the throttle body while cranking, means the spark plug is firing when the intake valve is open. It's usually caused by crossfire inside the distributor cap. These things are real fussy about the cap & rotor, they need to be AC Delco only.

Fuel pressure leaking down to zero is a problem, the only way to tell for certain what's causing it, requires more testing. The fuel pump needs to be isolated from the engine, and maximum pump output pressure and leakdown must be checked at the fuel filter outlet. Here is a list of the necessary parts to build an adapter: (or you can buy one in a kit for around $400)http://i561.photobucket.com/albums/s...ps5c876ad4.jpg
Disconnect the quick connect fitting at the fuel filter. Connect the adapter to the fuel filter. Connect the fuel pressure tester to the adapter. The fuel line going to the engine is left dangling during the test. With the pump activated, pressure must be 73psi to 108psi. The pressure must remain above 55psi for at least 10 minutes after the pump shuts off. Post your results.

 

I put Delco fuel pump in less than year ago so i hope thats not it. And i can physically see the fuel leaking from around the FPR.

 

Checking fuel pressure and leakdown at the service port, (by the distributor) checks the entire fuel delivery system. If it fails pressure or leakdown, it means that a problem exists. It does NOT tell what or where the problem is. Checking it at the fuel filter will tell if the problem is in the tank or in the plenum. Then we do more tests

 

But what about fuel leaking at FPR? Wash down at back 2 cylinders? Fuel standing in low spots in plenum?

 

Pictures added showing washed out intakes next to FPR and fuel pooled up. Also showing FPR orfice, bottom of CPI unit and new FPR installed.

 

Humor me and check fuel pressure and leakdown at the fuel filter. I think you'll be surprised at the results. Either that, or I will be

The first image, at the extreme rear of the manifold, looks perfectly normal. It's not "washed", it's clean due to no EGR residue. The EGR outlet from the valve is at the extreme front of the plenum, and very little of the EGR gasses make it that far back. Same holds true with the other images, they're all in that same general area.

 

Every post and Youtube video I have read or watched says the clean areas at back of manifold indicates fuel leaking (usually from the FPR) and being sucked into the intakes. I had a definitevisible leak coming from the FPR. I think though it was leaking from around the FPR and not regulator itself because when I installed new FPR there was still a leak. Today I wrapped yellow teflon tape (made for gasoline) around the FPR and reinstalled. Hooked up fuel lines and powered up fuel pump with ignition and there is no longer a leak. Performed leak down test with pressure rising to 62 and then fallibg off to about 40 and holding for 10 min. I know 40 isnt recommended level but its not dropping to 0 like before. So there probably is another leak somewhere but at this point I need to get everything put back together so I can drive vehicle. Curious though if the leak down tedt at fuel filter fails what are the possible problems? Failing fuel pump? Bad check valve? Leaking poppets on CPI? I appreciate your input and maybe if Im still having issues after putting back together I will do the leak down test at fuel filter. But like I said I need to get running again because only vehicle I have. It ran fine before its just the hard starting I was mainly trying to fix.

 

In the first image, the rear of the lower intake is clean aluminum. Moving forward, it changes to black carbon, which is caused by EGR gasses, and that's perfectly normal. If it were fuel washed, it would be a golden, honey color, much like it is directly below the regulator. Sorry, didn't notice that at first. Sounds like you've got the regulator leak fixed, but leakdown to 40psi is excessive, meaning there is still a leak somewhere that you can't see. Could be an internal leak in the regulator, an injector not sealing, a leaky poppet valve, or something in the tank. Checking pressure and leakdown at the filter only checks the pump, the line going to the fuel filter, the filter itself, and the pressure tester. It does not test anything forward of the fuel filter, (lines, internal and external regulator leaks, injectors, poppet valves, spider lines, return line, or the fuel metering block). Fuel pump running, pressure needs to be 73psi to 108psi and it must remain above 55psi for at least 10 minutes. Provided the pump is getting good voltage and ground, and there are no external line leaks between the tank and the tester: if it fails either or both tests, the fuel pump module needs replacement. If both of the tests pass, the leak is forward of the fuel filter, (one or more of the items listed above) and more testing is required to pinpoint the leak.

 

After putting everything back together and testing, it starts up almost instantly now and throtle response and performance are improved. So at this point I dont plan on any more work or diagnosing on it unless other issues appear. If that occurs I will look into performing the other tests you have suggested. Again I appreciate your responses and advice. The only issue now is the water tempature gauge is not working. Only thing I can think of is that the wiring or plug for water tempature sensor was domehow disturbed in the process of working on fuel problem. Can you tell me where the water tempature sensor is located so I can try and diagnose this issue?