Lake Effect Posted August 25, 2016 Report Share Posted August 25, 2016 First post here, but not a total newb to wrenching on cars. Son-in-law brought me his new to him 97 Deville, that his mechanic couldn't repair a P300 (random misfire) and P307 (confirmed cylinder 7 misfire) issue that is keeping him from getting the car tagged. I repeated the original work, and did some more. Fresh plugs and wires, replace the coil associated with cylinder 7 because of a corroded terminal, and repaired several vacuum leaks. When I had the throttlebody and the spacer block (EGR port) out to clean them I noticed liquid inside the intake manifold, in the valleys. I'm assuming it is coolant, it's the right shade of green, and I learned the car does "lose" coolant when it's hot out. I know that the intake manifold doesn't have any coolant running through it (nylon 66), and there shouldn't be any coolant on the other side of the intake manifold gasket, so how is it getting into the manifold? Looking at the plugs, #7 looks unhealthy, maybe a bit oily, but definitely darker than it's supposed to be. Cylinder 2 (opposite corner) looks correct with the insulator a nice light brown. All the others have very clean, very bright white insulators. I'm suspecting coolant is getting into the manifold, occasionally fouling the cylinder 7 plug at idle, and the other cylinders are receiving a regular steam cleaning, except for Cylinder 2, which is getting no coolant. The northstar engine runs great, the miss appears to be at idle. The mechanic indicated that he had the injectors out and cleaned. The EGR tube is clear, the port at the TB spacer had a bit of buildup, but it wasn't blocked. It appears that the throttle body has coolant running through it, what are the chances of the coolant in the manifold coming from there? Quote Link to comment Share on other sites More sharing options...
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