Guy's & Gal's
I need some advice on my sons 1995 Blazer CPI. We just changed the the fuel pump and a re-man injector spider and seems no matter what we've done it continues to bypass to the return line. I put the old spider in and the same thing happened. I also changed out the fuel pressure regulator with a new one.....same/same. I just put back in the old fuel pump and guess what..........SAME THING!!!! Yeah I know the first response will be......"did you check the fuel pressure?" Well to me if it is by passing down the return line it will NOT have any pressure to speak of. What on earth have I done wrong? Wanted it to have new fuel pump and new-ish spider (re-manufactured) and a new distributor. Before we tore it apart this past weekend it ran horrible....I mean just barely! HELP ME PLEASE!!!

 

Fuel pump dead-head pressure is considerably higher than the 60psi that the regulator maintains to the injection spider. As a result, there will be fuel bypassing back to the tank via the return line almost all of the time. The only time that it wouldn't would be when fuel demand meets or exceeds pump supply which will not happen stock. So... You know what's going to be said already... Get with the program and test before you continue to shotgun your truck to oblivion. Your wallet will thank you.

 

OK...........thank you for that advice. My wallet feels like scrapping it all and getting him another vehicle as that would be cheaper it seems...but since I have a considerable amount wrapped up in this vehicle for my son I want him to be able to enjoy his first truck. (first vehicle period) I just put the old pump back in it this past Saturday so how would that make more pressure than the regulator can maintain? I also put the old spider back in before switching back to the re-man spider since they both did the exact same thing. I work on multi-million dollar military jet aircraft so it's not like I'm a complete moron and have not idea what I'm doing but this one is puzzling to me. If it hadn't been for seeing that my gauge is now broke I would have done the pressure check on Saturday. I guess I have to go rent one.

 

Lets start with what prompted you to replace the pump & spider to begin with? Typically a fuel pressure and leak down test are the first two things done to determine the cause of a fuel related issue. Replacing parts is only done after proper diagnosis.

As far as the operation of the fuel system, the pump supplies fuel to the engine at a higher rate than required to remove the possibility of fuel starvation. The regulator maintains a semi constant pressure at the spider, dumping excess fuel into the return line. Engine off (key-on) or at idle where fuel demand is low will result in a lot of fuel returning to the tank. Engine under load at red-line where demand is at its highest should still result in fuel flow back to the tank, but dramatically less than the previous scenarios.

 

Well..........those parts of unknown reliability were changed to make it much more reliable for my son. Him and his brother are the last of my children (almost 60) so yeah......I want it as reliable as I can get it. Didn't think it would be more of a hindrance then doing good. I see you are an engineer. You must already know that if a company doesn't have confidence in it's suppliers products.......it gets changed even in a multi-million dollar fighter! All the items in the sticky about fuel pressure by Capt. Hook will be followed to ascertain the exact problem.

 

As an engineer, I root cause symptoms to get to the true cause so as to not waste time & money. Hopefully your new parts were Delphi or AC Delco for reliability sake. ;-)

 

Kyle.......they did away with Corrective Action group here. Cost too much I guess. I think the MTE's have a roulette wheel to do their disposition. MR engineering also has a few reliability problems themselves. We are starting to get the one fresh outta college.....I worry about the future of Aviation! 3 years........10 months..........12 day left to go!!!!