I have a 1996 GMC suburban 2500 7.4 vortec that has a miss at idle. I have replaced the FPR, spark plugs, wires, Cap, and rotor and its still misses. when I connect my pressure gauge and turn the key on it jumps to around 45psi and holds but when I turn it off it falls back to around 25psi. could it be a faulty FPR or if it was the rubber hose on the fuel pump shouldn't I hear the gas running back in the tank? any help would be greatly appreciated.
96 GMC Suburban Fuel Pressure problem
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Sounds like low pressure, should be between 56 and 62 psi, block off return line, retest...deadhead pressure should be above 70 psi. From what you described, my first two thoughts would be fuel pump or line restriction. Then possible leaky injector...but I would get the pressure where it belongs before I worried about injectors. Blocking the return takes the fpr out of the equation.
Warning... Above 75psi is rough on the regulators...so be ready to kill pump power or release return line...it will build quick if it does actually build. (I'm expecting, it doesn't though)
Where would I block it at? at the engine or on the line its self?
There should be a "soft line" somewhere around the trans bell housing or at the frame rail just below... Use hose crimps or flat pliers (ones without the grooves cut in the jaws) or wrap a rag around the line first (so as not to damage line when crimping it)
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I'm working on a no-start issue on the same 96 k2500/7.4l engine/chassis combo with the same exact fuel pressure readings. i just went through these steps checking my fuel system. from what i've read, if fuel pressure holds with return line crimped, a bad fpr is indicated. however, if fuel pressure still bleeds off, the check valve in your fuel pump has almost certainly gone bad meaning the fuel pump needs replacing. to confirm this, disconnect the fuel line at the filter and install your fuel pressure test gauge in the filter's place and cycle the pump. replace the pump if it still bleeds down. if pressure holds from tank to filter, check for fuel in vacuum line from fpr and stuck or leaking injectors. mine still lost pressure immediately so i replaced the fuel pump. pressure holds better, but still bleeds down 2-3psi/minute, leading me to believe my fpr is bad as well. my burb has always ran a little rough and gotten terrible gas mileage that is commonly fixed by replacing injectors with Bosch 4-hole style so, since replacing the fpr requires removing the upper intake, i plan on swapping in upgraded injectors and a new dizz cap and rotor, if not a complete new distributor at the same time i have the intake out of the way.
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I was having a no start issue in my 99 k2500/7.4. The truck has run rough (sometimes) and had a slight miss on cylinders 5. It has also been hard to start when warm after sitting for 20 minutes or so. I took off my intake and found that I had three leaking injectors, plus those cylinders' spark plugs smelled like they were SOAKED even though it had been about two weeks since I last attempted to start the engine. I took the injectors to Mr. Injector here in Coeur d' Alene and they tested them, my discs are bad so I will be buying a new set of injectors along with fuel rail, clips, fuel pressure regulator and electrical connectors. Guess I should have replaced them back when I did the engine R&R.
One thing that was different with my situation is that the fuel pressure was 52 but bled down within a couple minutes to 20ish.
One other thing was that the FPR was not hooked up to a vacuum line, I can't find where it was connected, and the manuals I have don't really show me what/where it hooks up to.
One thing that was different with my situation is that the fuel pressure was 52 but bled down within a couple minutes to 20ish.
One other thing was that the FPR was not hooked up to a vacuum line, I can't find where it was connected, and the manuals I have don't really show me what/where it hooks up to.
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2,819 Posts
PyRex,
The FPR attaches to full manifold vacuum. Somewhere on that intake manifold or by the throttle plate area you'll see an unused vacuum port with has no hose on it. Make sure it's "full vacuum", ...not "ported" vacuum.
The FPR attaches to full manifold vacuum. Somewhere on that intake manifold or by the throttle plate area you'll see an unused vacuum port with has no hose on it. Make sure it's "full vacuum", ...not "ported" vacuum.
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