I have recently purchased a 1991 Bronco with a 351cid. It had been sitting up for a year. I replaced the battery, removed fuel tank and cleaned, replaced fuel pump, replaced fuel regulator, replaced plugs, wires, cap and rotor. The truck fired up and I drove it home. It ran fine with no smoking or other problems. About half way home it started acting as though it was starving for fuel, run fine for one minute, running really ruff the next. Well I made it home and started checking things out. Fuel injectors were new(previous owner replaced), all vacuum lines are ok, checked fuel pressure and it is fine. I started pulling plug wires on the distributer and found that while idleing I could remove two wires and the engine did not change, so I checked compression on these two cylinders and did not get any reading. I checked the rest of the cylinders and they all were between 115 and 120 psi. This sounds a little low to me but at least there is some there. The front two cylinders( I believe the #1 and #5 on a ford) have no compression. I have considered rocker arms broke or pushrod bent, or maybe a stuck valve, but it is odd that it would be the same thing break on opposite cylinders. I guess my question is, could it be a problem with the gasket under the intake possibly causeing the loss of compression? Or where should like look to solve the problem. I have not removed the valve covers yet.
Pull the covers and look at the valve train. Could just be a bad coincidence that the front on both sides has a problem
April, 10, 2007 AT 4:06 PM
I pulled the valve covers and cannot find anything wrong with the valves. I had a friend watch the copression gauge while I turned the truck over. He said the copression would go up and down as if it was sucking the compression back out of the gauge. I checked the gauge on 3 other cylinders to make sure it wasn't faulty and it work as it is supposed to. What would be causeing the egine to pull reverse compression? By the way the Engine has a 153000 miles.
April, 10, 2007 AT 4:08 PM
A bent or stuck intake valve. Or pushrod or colapsed lifter!