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95 blazer fuel pressure issue...

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Old 10-18-2007, 05:06 PM   #1
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95 blazer fuel pressure issue...

okay, did some more checking today on the truck. i am having hard time starting it. have to spray starting fluid into the intake tube 90% of time to get it to start.

hooked up a fuel pressure test guage. this is what i saw.

truck had sat some time...maybe 15 minutes since last start... (by the way...when i hooked up guage..there was no pressure in port)

first key on, shot up to 50's then edged up to 60's...cranked and fired. shut it off...then the crazy stuff began...

key on, almost like a pulsing thrrough the fuel pressure guage hose. i could feel it pulsing pressure on the line as i was holding it...guage would jump and pulse too...anywhere from 40-60;;;..jumping. obviously...no start.

key on...this time....no pressure showing. try again, nothing. let sit maybe a minute... would do the pulsing thing again and not quite get to 60's. then would bleed off.

basically repeat this scenario across the board.

i am thinking it is the fuel pump.

had checked the spider fuel supply lines in intake.....didn't see any signs of leaking anywhere, same goes for regulator side. i noticed small amount of fluid pooling on intake bolts on regulator side...but it looked mainly to be just oil.

so, fuel pump you think???
Old 11-10-2007, 09:43 PM   #2
neex
 
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Re: 95 blazer fuel pressure issue...

Try dropping your tank and pulling the fuel pump. If it's an OEM pump assy, it will have a little orange/red rubber valve body on the intake line on the pump itself. I believe this ellusive part is called a 'pulsator'. I have seen at least 2 scenarios where all that needs to be done is to pull out the pulsator and replace it with 2 hose clamps and some hose (maybe 4-6" of hose). It seems that the inner 'bladder' of this valve/dampening 'pulsator' tears which feeds pressurized fuel back to the tank rather than to the injectors/spider poppets.

If you haven't pulled the intake plenum to be certain nothing is leaking underneath the spider, you should do it right away. I pulled out the spider and looked over it with a finetoothed comb when I had pressure issues on my 95. It turns out that I had 3 issues: 1) nut kit was needed (leak was a pinhole under the rubber seal so it was almost impossible to see/detect), fuel pressure regulator was leaking so I replaced it separately with a Help! part (it was dead easy to do), lastly, I had the damaged pulsator in the fuel pump delivery line off the pump. I ended up getting a new spider, new pump, replaced the shraeder valve on the test port, etc. No issues now except for the damn false reading of the gauge.

Do yourself a favour and get a fuel pressure tester. If you don't already have one it makes it very hard to tell if you've nailed the gremlin or not. These poppet fuel delivery systems are very fussy on fuel pressure. I belive if memory serves, you should be holding above 56-58psi for 10min or so to show a good working fuel system. You can also use a digital scope on your fuel pump output to check for worn components in the pump and you can also check the amp draw to see if it's on it's way (I think anything over 9-10A could be suspect for failure).

I've also heard that pulling your fuel filter and pouring the contents through a coffee filter will give you a good idea of the fuel pump condition. If it's full of brass/metal filings, it's likely been overheated by being run dry too many times and failure may be just around the corner.

I hope this helps. It took me a long time to nail down my problems. If you need any help with this, please email me. I'm sure someone will tell you to 'SEARCH' but I've been down the same road and it's a PITA.

Thanks.
Andrew.



Quote: Originally Posted by Spl170s
okay, did some more checking today on the truck. i am having hard time starting it. have to spray starting fluid into the intake tube 90% of time to get it to start.

hooked up a fuel pressure test guage. this is what i saw.

truck had sat some time...maybe 15 minutes since last start... (by the way...when i hooked up guage..there was no pressure in port)

first key on, shot up to 50's then edged up to 60's...cranked and fired. shut it off...then the crazy stuff began...

key on, almost like a pulsing thrrough the fuel pressure guage hose. i could feel it pulsing pressure on the line as i was holding it...guage would jump and pulse too...anywhere from 40-60;;;..jumping. obviously...no start.

key on...this time....no pressure showing. try again, nothing. let sit maybe a minute... would do the pulsing thing again and not quite get to 60's. then would bleed off.

basically repeat this scenario across the board.

i am thinking it is the fuel pump.

had checked the spider fuel supply lines in intake.....didn't see any signs of leaking anywhere, same goes for regulator side. i noticed small amount of fluid pooling on intake bolts on regulator side...but it looked mainly to be just oil.

so, fuel pump you think???
Old 11-10-2007, 09:48 PM   #3
neex
 
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Re: 95 blazer fuel pressure issue...

Sorry long day... I saw that you tested the system pressure already. Based on your findings, two schools of thought:

1) replace the pulsator with a piece of hose and retest
2) you spent the time dropping the tank so replace the pump with a new one
(funny thing is that all replacement pumps use hose instead of a pulsator - except maybe true OEM).

Good luck.
Andrew.
Old 11-12-2007, 04:37 PM   #4
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Re: 95 blazer fuel pressure issue...

This sounds like the CPI unit to me. I had a similar issue a couple years back in my 95 blazer.

After replacing the fuel pump, fuel filter, TPS, cap/rotor/plugs/wires/filter/etc.etc.etc. I finally pulled the top half of the intake manifold to find a leaky CPI unit. I replaced the nut kit and the CPI. It turns out that I also needed to spend $100 at Chevy on the damn wire harness that plugs into the CPI since that rotted out.

However the truck was back to normal.
Old 11-19-2007, 10:03 AM   #5
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Re: 95 blazer fuel pressure issue...

hadn't been on in awhile. i dropped tank and replaced the pump itself. looked over the pulsator, almost replaced it...but left it on...not know i should have pulled it at the time. i also had one of the rollover valves busted...that explained my gas smell around the truck.

since i replaced the pump, all is good....back to a good running truck now.

thanks!
Old 11-18-2010, 11:07 PM   #6
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Re: 95 blazer fuel pressure issue...

Quote: Originally Posted by neex
Try dropping your tank and pulling the fuel pump. If it's an OEM pump assy, it will have a little orange/red rubber valve body on the intake line on the pump itself. I believe this ellusive part is called a 'pulsator'. I have seen at least 2 scenarios where all that needs to be done is to pull out the pulsator and replace it with 2 hose clamps and some hose (maybe 4-6" of hose). It seems that the inner 'bladder' of this valve/dampening 'pulsator' tears which feeds pressurized fuel back to the tank rather than to the injectors/spider poppets.

If you haven't pulled the intake plenum to be certain nothing is leaking underneath the spider, you should do it right away. I pulled out the spider and looked over it with a finetoothed comb when I had pressure issues on my 95. It turns out that I had 3 issues: 1) nut kit was needed (leak was a pinhole under the rubber seal so it was almost impossible to see/detect), fuel pressure regulator was leaking so I replaced it separately with a Help! part (it was dead easy to do), lastly, I had the damaged pulsator in the fuel pump delivery line off the pump. I ended up getting a new spider, new pump, replaced the shraeder valve on the test port, etc. No issues now except for the damn false reading of the gauge.

Do yourself a favour and get a fuel pressure tester. If you don't already have one it makes it very hard to tell if you've nailed the gremlin or not. These poppet fuel delivery systems are very fussy on fuel pressure. I belive if memory serves, you should be holding above 56-58psi for 10min or so to show a good working fuel system. You can also use a digital scope on your fuel pump output to check for worn components in the pump and you can also check the amp draw to see if it's on it's way (I think anything over 9-10A could be suspect for failure).

I've also heard that pulling your fuel filter and pouring the contents through a coffee filter will give you a good idea of the fuel pump condition. If it's full of brass/metal filings, it's likely been overheated by being run dry too many times and failure may be just around the corner.

I hope this helps. It took me a long time to nail down my problems. If you need any help with this, please email me. I'm sure someone will tell you to 'SEARCH' but I've been down the same road and it's a PITA.

Thanks.
Andrew.
I am not sure how this works, So I just replaced the Spider Injectors and I am still loosing Pressure after shutting off the engine, I will check the Shraeder valve to see if its hung up and get back to you.

Thanks
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