I have a 96 Blazer with the throttle body on top with the black two piece intake manifold.

Sometimes is starts right up. Other times, typically after driving somewhere and letting the car sit for a few hours, it'll need to crank for up to 10 seconds before starting. Just when I'm about to give up, it'll start. Once started, it runs great. No code or dashboard lights.

I put a fuel pressure gauge on it today. When I turn the key on, engine off, the fuel pump kicks in and pressure rises quickly to 58. The fuel pump stays on for a second or two, then stops, and the pressure drops to 0. If I then crank the starter, the pressure rises back to 58 and the engine starts within a few seconds. I haven't been able to replicate a very long crank time yet.

My question is, what is the correct behavior for the fuel pressure with KOEF? Is what I described above normal?

Thanks!

 

To properly check fuel pressure try turning the key to KOEO (key on engine off) to get the pump to turn on for ~2 seconds. Do it a couple of times to build the pressure up. 58 is pretty close to what blazer's usually run at. Roughly around 60 is the ideal, if I remember correctly.

The rough start I would more likely associate to a spark problem.

 

if it drops to 0 its either the valve in the pump,or spider. i bet its the pump ONLY BUY ac delco or delphi pumps unless u like doing them 5 times a month lol.(no seriously,the crap you get aftermarket sucks! ive replaced 40000000 of em. ac delco/delphi? 0)

 

Delphi is pretty good. About the only brand I would consider besides ACDelco. I would put money on the pump over the spider. A way to see if the spider is leaking fuel down is to see if the oil smells like it has some gas in it. No gas, spider is good.

Definitely stay away from aftermarket fuel pumps!! They're junk.

 

yep! on 2nd gens the spiders (injector assemblies in the manifold) dont go bad often unlike the 92-95 models which had a different design. short and sweet,blazers hate fuel pumps, and lower intake manifolds.

ive kinda learned to go ac delco only. i like delphi but im starting to see more failure rates on delphi lately. /sadface.

 

Thanks everyone. So the consensus is that its the fuel pump? The pump runs for a few seconds KOEO and then stops. When it stops, fuel pressure drops to maybe 5 PSI then to 0. That pump is expensive so I wish there was a way to tell.

I've read about this being caused by the fuel pressure regulator? I'm wondering if I should pull the upper intake manifold and check it out?

Little more info, the engine is a transplant from another 96 Blazer. I bought this Blazer with a seized engine and found a great used replacement. I did all new gaskets, including both manifold gaskets before putting the replacement in. While I had the intake manifolds apart, I tool the fuel pressure regulator off thinking one of the o-rings in the manifold gasket kit was for it but none fit so I put the regulator back on.

I do smell fuel occasionally, just the faintest whiff, but I cannot find a leak anywhere. I sometimes smell it while driving with the drivers window down. I don't seem to smell it on idle. Its really hard to pinpoint.

 

If you want to pull the intake you can. But like i said they dont fail nearly as often as the older ones do. pull the intake,if there is any fuel sitting in the lower intake,you found the issue. If not,id pull the pump. If you look on rockauto.com or amazon its ALOT more cheaper then locallly. if you let us know if yours is 2wd/4wd/2door or 4 door. i can get you the part # for the pump.

 

Thanks. (I'm not getting email notifications for some reason so I have to keep seeing if someone replied).

Its a 96 4x4 4-door.

Is the "check valve" I've read about part of the fuel pump? I've read that if its not working, the engine off fuel pressure won't hold.

 

ok you can either get the delphi one (oem) for 165.79+shipping. part #
DELPHI Part # FG0030


or delco (go with this one to be 100% safe)
ACDELCO Part # MU1735
186.79 + shipping.

these are complete units. fuel pump and sending unit for the gauge.
you can look on amazon as well,might be cheaper maybe not. rockautos pretty hard to beat. the check valve is part of the pump. it allows pressure in,but none to leak back into the pump.

 

Your pressure is too low and leakdown is excessive. Key on, engine off, fuel pump running, pressure must be 60psi to 66psi, and it must remain above 55psi for at least 10 minutes after the pump shuts off. Yes, the check valve is part of the pump, not serviced seperately.

Your results indicate that there is a problem with fuel delivery, but it does NOT tell what, or where, the problem is. The next step in diagnosis requires you to do a little "creative plumbing" with the pressure tester. The tester must be connected to the pump pressure output line. This is done at the fuel filter. All pressure and flow must dead end at the tester, (no fuel allowed to the engine). Key on, engine off, fuel pump running, pressure must be 73psi to 108psi and it must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails one or both parts of the test, the pump needs replacement. If it passes both parts of the test, the problem is inside the plenum.

FYI: Delphi and AC Delco pumps are exactly the same, they come off the same assembly line, just a different box.