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Going to Shoot My Poor 4.3

DirtyDave

By DirtyDave
in Ask A GM Technician

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DirtyDave Enthusiast

DirtyDave

Posted
Posted

I have a problem. There's a S&W 500S on my kitchen table and a 4.3 in my garage that is driving me nuts.

 

I'll try to give you as much info as I possibly can. I have a 1998 GMC Sonoma 4x4 with a 4.3 and a five-speed. It has a hollowed out cat and a Dynomax cat-back exhaust system. It's got 100,300 miles on it.

 

I'm having a couple of problems. Well, let me step back a little. Last Sunday night I went out the garage to start my truck to go to the store. It cranked but wouldn't start. I could hear the pump coming on and the engine was cranking as it should have been. I stuck a screwdriver in the coil wire and the spark was orange in color and not really snapping. I replaced the coil the next night and the truck started right up and it ran great all week. Sweet, right? Not so much.

 

Yesterday morning (something about Sundays...) I went to breakfast and the d**n thing wouldn't start. Same condition. It cranked like hell, I could hear the pump, no start. Fortunately, I had gone with some friends. We ran some errands, came back and the thing started right up. This time though, the idle was a little screwy. It would idle above 1000rpm, which it never does when it's warm. If I "blipped" the throttle, it would settle right down to ~600 rpm. The truck was surging and back firing occasionally. But, if I put it to the floor, the thing would take right off and leave two black marks, as I'm accustomed too.

 

Here's what I've done: last fall I replaced the plugs with AC Delco platinums, the cap, rotor, plug wires and fuel filter. I replaced the coil last week. Today I installed a new ingnition module. The truck started and ran, but it still had the high idle and it felt almost as though it was missing under part throttle. There was no backfiring or popping, but it definitely was not running well. Again, if I gave it the floorboard, it ran like a champ.

 

I was worried about fuel pressure, but after the no start, I pulled the plugs out and they were pretty soaked with fuel (I had cranked it several times), so I'm guessing I've got enough pressure to open the injectors. I know these things need at least 52 psi or so. I don't think it's bad gas because I've bought gas since the problem started.

 

Any suggestions? I need this thing to remain the dead solid, reliable truck that it has been for its first 100,000 miles. Thanks for your help.

ryank1 Enthusiast

ryank1

Posted
Posted

Pull the dipstick and smell the oil, if it smells of gas you probably have a leaking fuel pressure regulator. if you pull the top of the intake and one side is clean its the regualtor. From GM you have to buy the whole injector assem, but I have heard that the aftermarket now sells just the regulator.

DirtyDave Enthusiast

DirtyDave

Posted
  • Author
Posted

GM sells just the regulator now, too (and for less than aftermarket!). I purchased one and will install it tonight. I'll let everyone know how it turns out.

DirtyDave Enthusiast

DirtyDave

Posted
  • Author
Posted

Fuel pressure regulator seems to have taken care of it. I had to buy a plenum gasket kit.

 

It still idles a little high and has a slight stumble around 2000 rpm under light load. I'm guessing this is a TPS issue though.

 

So, all is well and I don't have to but a 400 grain round through my block.

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