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GMTechBernard, Shop Foreman - GM World Class Tech
Category: Chevy
Satisfied Customers: 2158
Experience:  GM
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Where is the fuel pump relay on a 2002 Chevy Blazer I have

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Where is the fuel pump relay on a 2002 Chevy Blazer? I have had the fuel filter replaced, complete tune up (plugs, wires, cap, button) new mass air flow sensor installed. Car runs fine and has full power, but doesn't want to start. I have read that I should check the fuel pump relay, but I can't find it! Before I have a new fuel pump installed, I would like to have the relay checked.

Usually, when a relay fails, its done. You stated that when you finally did get it to start, it ran good. If the relay failed, it normally would have never started. Anything is possible, but if you want to see if its the relay, just swap it with another relay thats similar to it.

The fuel pump relay is located in the underhood fuse box, and there are typically other relays that are the same, and you can just swap the two and see if that helps!


Good luck and please let me know if you need further assistance!

Customer: replied 7 years ago.

They did switch a couple of those out this weekend and it still wouldn't start. It wouldn't start at all unless you sprayed starter fluid into the carburetor. Once the MAF was replaced, it fired right up without the fluid, so I thought the MAF sensor was the problem. Before we put the new MAF on, I thought that it might be the fuel pressure regulator from some posts I had read where folks had a similar problem to mine, but all the men said no way. The pressure test for the fuel pump was right on target. I'm no mechanic, so what do I know? Do I just bite the bullet and replace the fuel pump?

They said that the pressure test was "right on target" but what actually was the pressure and what did they consider "target"? I often wonder this when I hear statements like this, because these trucks have higher fuel pressures then other vehicles and are VERY senstive to the correct fuel pressure. With the pump running, it should have 60-65 PSI.


I beleive that you probably do need a fuel pump. If the pressure regulator was bad, it would leak fuel into the intake (thus flooding it) and adding starting fluid would only aggrevate the condition, no help it!


If you decide to go with teh pump, make sure they use a GM pump. Its more expensive, but I have seen too many aftermarket pumps fail in a very short time period. Because these engines require so much more fuel pressure, its best to go with a factory pump.

Customer: replied 7 years ago.

When you say "with the pump running" do you mean with the engine idling? When they tested it on Saturday they said the pressure was 54 PSI and that was in the target range. If it only tested at 54 PSI while idling, then it was way off according to the correct target of 60-65 PSI that you provide. I don't understand why it runs so perfectly if the fuel pump is bad. It has never died or stalled on me. Once it's running, it's fine. Plenty of pickup, no problems on stopping and starting. Just that intial fire up. And once it's warm it will crank right back up. Some people have said that if the pressure is strong and the car isn't stalling and/or dying, then the fuel pump is fine. Why would the pump only have a problem at startup? Is this just the beginning of a complete systems failure if I don't replace the pump. Not trying to wear you out, I just really want to understand.

"Running" means Key On, Engine Off. This allows the pump to run for 2 seconds and then it shuts off. This will indicate the maximum fuel pressure your system is putting out. When the engine is running, there is vacuum to the fuel pressure regulator and that will lower the fuel pressure. With the engine off, there is no vacuum and fuel pressure is at its max.
Customer: replied 7 years ago.
One more question...and then I swear I will leave you alone. Have you ever heard of a fuel pump going bad and it only affects the actual start of the engine? That's what giving me pause on this. Other than the erratic starting of the engine, once it's going it runs perfectly. Actually, since the tuneup and new MAF sensor, it runs better than ever. Or is the failure to start just the beginning of the fuel pump issues and I'll end up stranded on the side of the road.

No problem! Ask as many questions as you need, its what we are here for. your not bothering me at all!


Yes, I have heard of fuel pumps cause cold no starts. When an engine is first started, it needs more fuel to help get things going, then if it was just idling. And a cold engine needs even more fuel (like a choke on a carburetor). Also note, that system voltage drops during cranking (which is normal) and pump output is directly related to system voltage. The higher the voltage, the higher the fuel volume/pressure and vice-versa.


So if the pump is weak, a cold start is where it will be most noticable, due to the higher fuel demand and lower system voltage. If you spray some fluid in the intake to get it started, this does two things: Gets the engine running to where it doesn't need all that extra fuel any more and also gets it running well enough the starter is no longer needed, but now the alternator is actually charging, which increases system voltage. With these two things out of the way, the pump can now generate enough fuel to run the engine.


I can't garuntee you 100% that your pump is failed because I'm not there looking at it, but after everything I have heard, I'm pretty sure that will take care of it!


Hope this helps!

GMTechBernard, Shop Foreman - GM World Class Tech
Category: Chevy
Satisfied Customers: 2158
Experience: GM
GMTechBernard and 3 other Chevy Specialists are ready to help you
Customer: replied 7 years ago.

You are awesome! Thanks so much. Now I understand it, and that makes me feel so much better.

Let me know if you have additional questions on the matter! Take care!

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