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Blown pressure relief valve

After replacing the fuel pump, the dealer attempted to start the car, causing a backfire and blown pressure relief valve. Is there some way he should have evaluated the fuel/air mixture before trying to start and avoiding having to replace the pressure relief valve?

Offhand, I’d say no. Are you referring to the fuel pressure regulator?
What are the circumstances behind this fuel pump replacement? Quit, running poorly, CEL on, towed in, or what?

What year model is the car? Was it a throttle body injector?

There is no fuel pressure regulator. Car is 96 Seville.Quit running suddenly. Pressure relief valve is supplied to prevent backfire from blowing the intake manifold. I have questioned how GM could design an engine which would “automatically” backfire after new fuel pump installed, resulting in improper fuel/air mixture. Seems to me GM should provide some kind of diagnostic test to make sure fuel/air mixture was ok before trying to restart engine after new fuel pump installed. Thanks and please reply.

96 Seville. I believe it has a throttle body injector.

It is difficult for those of us here to get on board with you when there is a difficulty with the nomenclature of the parts involved. The 96 Seville had a fuel pressure regulator. And the most likely part that could be described as a backfire prevention valve is the PCV valve. I can assure you that there is a plethora of automotive wisdom available on this and similar forums but a meeting of the minds will be necessary to gain any headway in your efforts to access that wisdom. Good luck.

I suspect Rod is correct in his guesses about what parts you were alluding to. I too thought of the PCV valve. Actually, “backfire check valve” would probably have been a better name for it originally, because it’s function was to prevent against backfires lighting up the crankcase gasses while still allowing the air inlet to draw in crankcase vapors.

To answer your question, no, there is no way he could have evalusted the mixture before trying to start the vehicle. After a fuel pump replacement the pump has to push the air ut of the line and there’ll simply be irregularities until the line becomes filled with pure fuel. Stuff happens.

As far as I know, every fuel injected car has a pressure regulator including this Cadillac.

Both the pump and regulator are aged so my theory would be this. My theory would be that an aged regulator diaphragm gave up after the new pump was installed. This allowed raw gas to flood into the intake manifold and away she goes when the spark is applied to a flooded engine. Just a guess on my part.

There is a fuel pressure regulator if the engine is fuel injected. Here’s what can happen if the fuel pressure regulator leaks on a GM engine of this vintage.

This GM engine has a wasted spark ignition system. This means one coil fires two cylinders at the same time. One cylinder has the fuel/air charge with the valves closed and the spark occurs to fire that cylinder. The other cylinders don’t have a fuel charge and the intake valves are open so there’s no ignition in those cylinders. Thus the name Wasted Spark Ignition. If the diaphram in the fuel pressure regulator has a leak, the fuel can enter the intake manifold via the vacuum hose. The fuel then can enter cylinders where the wasted spark should occur where the intake valves are open. And if that happens, the fuel is ignited while the intake valves are open and the backfire blows the intake manifold.

I’ve seen many plastic intake runners blown apart on GM engines all due to a faulty fuel pressure regulator.


Thanks all you guys. I am a carburetor type. Not very familiar with fuel injection and assorted accessories such as fuel pressure regulators and pcv valves. I appreciate all your comments. I will just have to find the bread to pay for replacement of that valve and the head gasket–more than 300 bucks! After $900 to replace the fuel pump and filter. Hurts.

“As far as I know, every fuel injected car has a pressure regulator…”

Actually, the newer returnless systems don’t have the fuel pressure regulator that you are used to. They have a fuel pressure sensor about where the fuel pressure regulator would have been. It senses fuel pressure relative to intake manifold vacuum. The PCM reads the pressure and then commands the fuel pump to run slower or faster to regulate the pressure. (The commands are usually sent to a module that controls the power to the fuel pump to accomplish this.)
So, they do have regulated fuel pressure, but the returnless systems don’t have a single specific component that is the fuel pressure regulator.