1993 Buick LeSabre (140,00 miles)
Daughters college transportation vehicle
12/30/08 Upon MN cold driveway starting- a sound like a ‘gunshot’ was heard from under the hood followed by some smoke. Exam revealed fragmented plastic intake manifold and overlying engine decoration. Seems like a backfire that ignited fuel in manifold. New manifold offered online (via A1) suggests that original may be deficient and suspect to corrosion and failure.
Question- is it appropriate to JUST replace the intake manifold with IMPROVED version? Have additional concerns about timing belt, PCV and perhaps other things…?
Return to college: 01/19/09
First, the engine utilizes a timing chain, not a timing belt.
I’ve seen these GM intake manifolds explode before. And usually what happens is the fuel pressure regulator diaphram developes a leak allowing fuel to be pushed into the intake manifold via the regulator vacuum hose, or a fuel injector developes a leak and loads up one of the cylinders with raw gas. The ignition system on this engine is what is called a Wasted Spark Ignition System. This means each coil fires two sparkplugs for two cylinders at one time. Only one sparkplug fires in a cylinder where there’s an air/fuel mixture and the valves are closed for that cylinder. The other sparkplug fires in a cylinder where there should be no air/fuel mixture and the valves are open in that cylinder. Hense the name.
Now if for some reason gas gets into the intake manifold such as from a leaking fuel pressure regulator or in a cylinder with a leaking fuel injector, and this wasted spark occurs in the cylinder where the valves are open, it’s going to ignite the gas in that cylinder from a leaking injector, or ignite the gas sitting in the intake manifold. And when this happens, the intake manifold explodes.
Replace the manifold and then check for a leaking fuel pressure regulator or fuel injector to make sure the new intake manifold doesn’t explode.
Tester