Alright, I have stood for this for to long. I have a 99 blazer 4door 4X4 4.3L vortec.
I am getting REALLY BAD gas mileage. 100-130 miles to a tank is NOT right. recently we just replaced the fuel pump because it died on us because I guess it was trying to pump fuel through a completly cloged filter. I made sure that it was assembled correctly and all that good stuff. But what I am begining to realize is everytime that I fill up, when I take off the gas cap its not releasing the presure like every other car that I drive. Also everytime that it has been sitting for a while I guess that the fuel goes down the return line and back into the tank. So everytime that I start it the fuel has to come all the way back through the lines. Its like trying to start it after it runs out of gas, it just keeps turning over and over and finaly after about a minute it will slowly come up to idle speed. I am about to just junk this truck. It has 152,000 miles and I dont have this kind of money to keep it. What can I do to improve my gas mileage? Should I just take it to someone? And will it be expensive?

 

Sounds like you've got a fuel leak in the intake. Have you tested the pressure at the fuel pressure test port on the engine. If you have, what does it do once you turn the key off? If the fuel pressure drops, you have a leak somewhere. The posibilities are the check valve in the fuel pump, a leaking line external to the engine (obvious), leak at the fuel pressure regulator inside the intake, a leaking electronic fuel injector, or a leaking o-ring in the fuel metering body.

 

No I have not tested the pressure test port on the engine. Where would this be located and how would I be able to do this. I am a new blazer owner and pretty much dont know anything about the fuel problems. But I am willing to learn

 

How does the truck run? Feel sluggish? Misfires? Backfires?

The fuel pressure test port is located on the fuel supply line behind the throttlebody slightly to the driver's side of the engine. There will be a small plastic cap that you will need to remove to connect a fuel pressure gauge. A fuel pressure gauge can be picked up for around $30 from your favorite autoparts store. Some stores allow you to rent tools such as this for a returnable deposit.

You will want to connect the fuel pressure gauge to the test port and cycle the ignition. The pressure should rise to 55-60 psi. When you shut off the ignition, the pressure should not drop more than 5psi over 30 minutes.

If you aren't getting the 55-60psi and ruling out a faulty fuel pump, it is possible that the FPR (fuel pressure regulator) has failed. This is more common in the older CPI motors, but can happen in the SCFI motor. To properly diagnose a failed FPR or any internal fuel leak in the injection spider, the upper plenum will need to be removed and the fuel lines reinstalled to pressurize the system. The fuel line connections at the back of the engine will be fun to remove...[&:]!

If the pressure climbs to 55-60psi when the key is on, but drops faster than 5psi in 30minutes, then there is something else amiss with the system. This would lead me to either an external fuel leak (line leak - pretty obvious with an inspection), internal fuel pump check valve leak (unlikely due to new pump), internal engine fuel leak due to leaking electronic injector or leaking o-ring(s) (more likely). The injectors can be checked one at a time with the fuel system pressurized by pulling the poppet nozzle out of the lower intake and inspecting for fuel leaking out of the nozzle. If you see wet areas under the injection spider (mechanics mirrors work great for this), then you mostlikely have a faulty o-ring and a new o-ring kit can be purchased for ~$40 if I remember correctly.

Hope this helps!!

 

Well... Guess what.

My truck died this moring before class. It just wouldn't start. Usually in the moring I have to turn it over a bunch of times to finally get it started. But today it just gave up I guess. And the reason that comes to my mind of why it takes so long to start every morning is because the fuel goes back down into the tank after sitting for long periods of time.

Well I ended up taking the spare car over to school and while I was there I had the AAA guy come over and tow it to my friends shop (the place where I should have taken it before it died!). I get out of class to find out that I had a ruptured or faulty fuel regulator. AND a faulty fuel pump. What really ticks me off is that not more that a MONTH ago, I replaced the fuel pump. Right now I am too busy to to fix and install these things again. I have to much to do and too much to work on. I think that I might just have these done my the mechanic if they give a a reasonable price. Which I hope they do because the owner of the entire shop and I, go up every saturday to go flying. He is the one who taught me how to fly. And him and my grandpa have a real close relationship too. We own cabins right next to eachother up in Utah for the winter, we each fly our own planes up there for vacation.

Well I hope that I can have this done soon. And hopefully this will be the last of my problems for the next six months.

But as of now I am looking for a new car, I cant afford this right now. So its up for sale people.
Chad

 

So, my truck is still acting up. Yesterday morning it wouldnt start either. I tryed just letting the fuel pump cycle by itself a crap load of times and still, nothing. So right before the battery died, I sprayed a bunch of carb choke cleaner through the intake manafold and it started right up. The thing is, I dont have time for this in the morning. There are places that I have to be. But the problem was, that the machanic said that everything would be fine after he replaces the fuel regulator. HE WAS WRONG. And now hew becoming an ignorant bastard and saying that he "is not touching my car, untill I replace the faulty fuel pump". I dont think that it is the fuel pump because I have been beong told that if the car runs ( after getting it started of course) then the fuel pump is supplying enough pressure. And I talked to the fuel pump manufacturer directly and he said that it was eiter a ecternal fuel leak, or... an external fuel leak. But the ignorant mechanic said "he was just a person over the phone, he doesnt know what he was talking about." And continued to blabber on about " I have the hard copies to prove you have a faulty fuel pump, and that hes 100% sure that there is not an external leak". I have trouble beleiving that I dont have an external leak because when I was sitting and letting the fuel pump cycle, I smelt gas. And yes, it was definatly gas. I told him to answer why I smelt that. And he couldnt. I dont understand how a mechanic couldnt fix it the first time especially since they have been open since 1967. I need help you guys. This mecahnic and the fuel pump situation have me bent over a berrel.
Thanks

 

So, What do you guys think? Should I take it back to the guy and get a new fuel pump from the factory? And then have him check the fuel lines for leaks and replace them?

 

I think you aren't telling us everything that has been done with this car... So you had your mechanic friend (or not your friend) replace the fuel pressure regulator. How does the fuel pressure hold now? Have you tested it yourself? If you have not tested it yourself, or do not have the time to, then you pretty much are at the whim of the mechanic and anything that we suggest here will be summarily dismissed by said mechanic because we are "just people on the internet". Just a fair warning to you.

I have to question how they diagnosed both a faulty FPR *and* a faulty fuel pump both at the same time... If the FPR has failed, typically it will dump fuel into the lower intake, flooding out the cylinders as well as pushing raw fuel into the crankcase, diluting the oil. Was this the case? Or did he soak you for a new FPR (or more likely a new SCFI injection spider) and then tell you that the fuel pump is now bad.

Did the original fuel pump come with a warranty?

And yes, it is possible to not have enough fuel pressure to start the engine, but have enough to keep it running. A pump can have more than enough flow capacity, but if it doesn't have enough pressure generation, it won't start a truck. That is why a pressure gauge is necessary to diagnose this problem. And that is the exact reason why I suggested that you test the fuel pressure yourself. If you do not have over 55psi with the engine off, key on, the engine will not start. If the pressure builds up to say 50psi and holds steady even after you turn the key off, then you definitely have a pump problem.

 

I dont think that they found out that the FPR and the fuel pump was faulty at the same time. Because he said that the gas was all pouring into on cyilinder and that was the reason for my accesive fuel consumption (because the FPR was broken). So he replaced the FPR. Then he retested it and said that I had a faulty fuel pump because it was not runing at the right PSI.


So after that, when he put the presure guage on the fuel line while it was running, it was generating about 35-45 PSI. I dont really remember the number exactly, but I know that it was not in the 50s. That, is when he said that I had a faulty fuel pump. But I guess what you can say is that I am trying to avoid getting another on because Autozone has me bent over a berrel.

Because they cant give me my money back so that I can go to the dealer ship and get a GM fuel pump. (what I should have done in the first place). Autozone says that they are sure that they gave me the right one and that they think that is the correct pressure. And all they can do is swap the one that is said to be faulty with another of the same kind. But that is not giveing me a 100% answer that this isn't going to happen again. How do I know that if I get a second fuel pump from Autozone that this time it will work? The warrenty is for a year, but like I said, I can only get one of the same kind from autozone, not my money back.

To me, it feels like the possibilitys of buying one from GM this time and haveing it work correctly is much higher than just going over to Autozone and trying abother time with theirs.

I hope that is more clear, and hopefully points you in a better direction of what is wrong. Let me know what you think.
Thank you for your help
Chad

 

If the pump can only muster 35-45psi and the FPR is doing its job appropriately, then the pump is indeed either the wrong pump or a faulty pump. Take it back to Autozone and make them eat it. They should be able to give you your money back. Even if it is for store credit. Threaten to call the BBB and see where that gets you.

It should be consistently above 50psi under operation (yes even at WOT & 5000RPM) and over 55psi to start. My Bravada with 80k on the clock never dropped below 55psi during operation (I should know I drove around for a week with the hood off and a fuel pressure gauge strapped to the wiper arm).