2000 Chevy Blazer fuel filter

What's it doing? What's the symptoms?

Got it. "There isnt really anything that its doing" is going to throw anyone off. You wouldn't be needing help if nothing was wrong. :)

Two things come to mind. First of all, GM had a huge problem with the electrical ground on the fuel tank when they get rusty. Intermittent no-start was the most common complaint but they could also cause stalling while driving. A fix that was much more reliable than the original design was to drill a small hole in the tank's flange outside of the seam weld, and use a self-tapping screw to attach a ground wire. The other end of the wire was attached to the frame or body sheet metal. That only applies to the steel fuel tanks. Newer models use a plastic tank. Don't go drilling any holes in that one! Those already have a separate ground wire. Banging on the metal tank can disturb the two metal straps and cause them to make enough of a connection to get the pump to run. If this is the problem, you will find that the pumps that are removed will run just fine when connected to a battery with jumper wires.

The other thought has to do with repeat pump failures on Chrysler products but it might apply to your vehicle too. Chrysler fuel pumps are extremely quiet compared to other brands of vehicles but it comes at a price. They are built to very close tolerances to make them quiet but the impellers can become clogged from a buildup of microscopic debris in the tank. The typical scenario is you buy a replacement pump from the auto parts store, and it fails within a few weeks. They replace it under warranty and the new one fails in a few weeks. You try a couple of pumps from a different store and the same thing happens. Out of desperation, you buy the entire pump assembly from the dealer and have no more problems. The assumption is the aftermarket pumps are junk. In reality, those pumps are fine, in fact, NAPA is one store I'm aware of that buys their replacement Chrysler pumps from the same supplier that builds the original ones for Chrysler.

What is really happening is that microscopic junk in the tank is getting stuck in the new pumps. By the fourth or fifth pump, all of that stuff has been removed so the next one doesn't get plugged. That next one happens to be from the dealer. What more and more people are finding out is to prevent repeat failures, they are having the tanks steam cleaned by radiator repair shops before installing the new pumps. I don't know where that debris comes from but this is a common enough problem that it is becoming well known.

There are other things that can cause the pump to not run, but your dandy observation, (thank you), that banging on the tank got the pump going really narrows down the list of suspects. If you have a metal tank, the next time the pump doesn't run, use a grounded test light and touch the probe right on the tank. If the test light lights up, the tank has a bad ground. With a bad ground, the pump can't run.

Caradiodoc

Hi there, I hope you got your blazer all figured out. We appreciate your donation and look forward to helping you in the future. Thank you for using.

You probably have the solution staring you in the face. It's not terribly common, but if wiggling / removing the relay got the pump started, there is likely a bad connection on it. We had a GMC truck that was a lemon law buyback and was donated to our school. We used it for troubleshooting exercises and had a lot of trouble with relay sockets. The terminals are nothing to brag about and can't handle much probing with test equipment so we were always repairing or replacing them to keep the truck running.

The next time it won't start, push a little on that relay. If that gets the pump going, use a skinny pick to go beside the terminals in the socket to squeeze them tighter. If corrosion is the problem, the scratching action of removing and reinstalling the relay will often scratch a clean spot for them to make better contact for a while.

Caradiodoc

Did you buy a new relay or a new fuse? The next step is to get it and try to keep it in the non-starting condition. When that happens, use a test light to find if / where the voltage to the pump is being lost. If you have voltage all the way back to the pump's electrical connector but the pump doesn't run, it has to be an intermittent pump motor. I suspect more likely you will find the voltage missing, telling you the pump is not the problem.

Now I'll have to rely on your observations. On Chrysler products, the pump will only run for one second when the ignition switch is turned on. It starts running again whenever there is engine rotation, (cranking or running). That means you must have a helper cranking the engine when measuring for voltage to the pump. I'm pretty sure GM is doing it the same way now. On older systems the pump ran during cranking, then it was switched on again through the oil pressure switch. Either system causes the pump to turn off when the engine stops running. That is a safety feature if the vehicle is in a crash that ruptures a fuel line. The engine won't run without fuel pressure.

Instead of cranking the engine, you can bypass the relay, then if the pump is not running, you can troubleshoot the system. If you knew for sure which two of the four terminals where the switch contacts, you could just remove the relay and connect those two terminals with a stretched out paper clip. I prefer to just pop the cover off the relay and squeeze the contact arm. A rubber band around it works well too. That way you don't have to waste time trying to figure out which terminal is which.

The relay should not be getting hot, ... Warm maybe, but not hot. Heat is generated when current is flowing through resistance, and resistance in that part of the circuit is very undesirable. Resistance is the result of corroded contacts in the relay socket or on the relay terminals, or burned or pitted contacts inside the relay itself. Excessive current will also lead to heat buildup. Excessive current that is not high enough to cause a fuse to blow is usually the result of a dragging pump causing the motor current to go up.

Caradiodoc