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2001 Blazer Low fuel pressure at test port but not at filter


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MarineGrunt
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Jul 1, 2021, 9:43 PM

Post #1 of 26 (390 views)
2001 Blazer Low fuel pressure at test port but not at filter Sign In

2001 Chevy Blazer 4.3L 180k

Hey guys. Hope all is well. I'm working on our daughter's friend's Blazer. I need some help troubleshooting the fuel pressure. At the test port I was only getting about 40 psi so it's obviously low. I figured it had to be the fuel pump. I planned on replacing it so installed a new filter first. I then checked fuel pressure there and I got 90 psi. It leaked down to 70 psi after 10 minutes. Although, one time I turned the key and it only went to 20. Turned the key off and it shot back up to 90. I hooked the line back up, went to the test port again, and got 60 psi. I decided to start it and it started right up. Shut it down, cycled key twice, and it was back at 45. It drops to 30 in about 5 minutes. When the gauge was dropping I tried priming the pump and made a quick sound but didn't prime. A few minutes later it was priming again. Most of the times I primed it it seemed to prime okay just with low pressure at the test port.

I think I tested so much I'm confusing myself. Can I assume it's just a weak fuel pump or is it something in the plenum? Fuel pressure regulator? Spider lines?

Let me know if you want me to start testing all over again since the Blazer would've sat all night. Plus, I was kinda all over the place with my previous testing. It was basically testing 40 psi at test port 99% of the time and psi dropped 10-15 psi. At filter it was 90 psi with 15 psi drop in 10 minutes. Since they're both dropping about 15 psi would that also point to the pump even tho it's in spec?

Thanks in advance!


Tom Greenleaf
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Jul 1, 2021, 11:42 PM

Post #2 of 26 (381 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Hello MG! This is better than an Elvis Sighting seeing you back!

To the problem: Check that gauge OMG can read 90 and 40 rule out the tester being messed up.

Spider (so called) was (haven't even seen one of these in ages already) was common TMK once! Do whole thing and never have a leaky problem again if so.

Does it behave like leaking raw fuel into engine - smoke when you do get it going or odor out tail-pipe?

For the moment just tossing out some ideas for a 20 year old 4.3 what weak links were common.

Great to see you around, you still hold the record for the most involved thread on a transfer case as I recall with some shaft that rubbed a hole thru the side?

Tom



Hammer Time
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Jul 2, 2021, 4:18 AM

Post #3 of 26 (373 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In


Quote
I decided to start it and it started right up. Shut it down, cycled key twice, and it was back at 45. It drops to 30 in about 5 minutes. When the gauge was dropping I tried priming the pump and made a quick sound but didn't prime. A few minutes later it was priming again. Most of the times I primed it it seemed to prime okay just with low pressure at the test port.


I would probably start out making sure the pump is always receiving 12v. You may have a connection issue somewhere in the circuit. They have a known problem with the connector right at the tank.

Maybe run battery power directly to the tank or at least monitor the voltage arriving at the pump.

The leaking down issue could be something else. The regulator could be bypassing the pressure or just leaking into the intake. If it's leaking into the intake. the fuel will show up in the cylinder or the crankcase. You can check for bypassing by pinching off the return line and looking for a spike in pressure.



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MarineGrunt
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Jul 2, 2021, 6:23 AM

Post #4 of 26 (362 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Hi Tom. Hope you're doing well. It's not smoking or anything when it did start. I'm not sure about the raw fuel smell but I don't think so. I tried 3 different gauges and all read the same.

I think the record thread was the rear end I installed in my Sierra. Although, I did have the pump rub issue with the t-case too.


MarineGrunt
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Jul 2, 2021, 6:33 AM

Post #5 of 26 (360 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Thanks HT. Can I supply power to the pump by jumping slots where the relay is or do I want to go directly to the wire underneath?

As far as pinching the line. Can I assume the vinyl can hold up to being punched? Should I use some of those vice grips with the long jaws and use a piece of garden hose or something as a softener?


Hammer Time
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Jul 2, 2021, 6:38 AM

Post #6 of 26 (358 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

You can jump it at the relay but then you won't be testing any of the wiring going back, only from the relay forward.

There should be some sections of rubber line somewhere that you can pinch. I think there may be one right at the firewall, at the back of the engine. I have pinched the plastic before but it's not a great idea.



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Tom Greenleaf
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Jul 2, 2021, 6:55 AM

Post #7 of 26 (352 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

On pinching for tests rubber or whatever: Be ready to replace that section with correct grade of hose heading into hopeless weekend for parts I'm sure, Tom


Hammer Time
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Jul 2, 2021, 7:30 AM

Post #8 of 26 (350 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Pinching rubber won't be a problem and pinching plastic hasn't been in the past but avoid it if possible. It's pretty old.

These hoses a crimped to the metal lines so don't start using hose clamps on the high pressure line.



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MarineGrunt
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Jul 2, 2021, 9:23 AM

Post #9 of 26 (337 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I just started messing with it. Decided to check pressure again. I can hear the fuel pump priming for 2-3 seconds but there's no pressure at the test port. Can I assume it's the pump? I'm still going to check for power tho. Just thought I'd add that little bit of info.


Hammer Time
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Jul 2, 2021, 9:30 AM

Post #10 of 26 (335 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

No, that probably mean the lines and filter have siphoned back into the tank. Do it a second time and see if it pops up. Even if it is siphoning back, that would still mean a bad pump.



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MarineGrunt
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Jul 2, 2021, 9:44 AM

Post #11 of 26 (327 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I turner the key on and off multiple times, heard the pump prime every time, but still not getting pressure.

When you said to check power do I want to do that directly at the pump? Go ahead and drop the gas tank?


Hammer Time
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Jul 2, 2021, 9:49 AM

Post #12 of 26 (325 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I'm not sure how that one is set up but if you have access to wire after the main connector, that would be the ideal place. You have to just use judgement on getting as close to the tank as possible.

You could try jumping out the relay socket. You might get lucky and find the problem.



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MarineGrunt
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Jul 2, 2021, 10:13 AM

Post #13 of 26 (321 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

When I jump the relay the pump runs but still not getting pressure. Just so you know battery is fully charged.


Hammer Time
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Jul 2, 2021, 10:16 AM

Post #14 of 26 (319 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

OK, that still leave everything from the relay back as untested.



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MarineGrunt
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Jul 2, 2021, 11:11 AM

Post #15 of 26 (307 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I checked the gray wire in the bundle of wires right before it goes over the front of the gas tank with a multimeter. I got power for 2-3 seconds with key on and again when key is turned off.

Thanks for the help HT. I'm not very good at the electrical side of things. Definitely better than I use to be thanks to this forum.


Hammer Time
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Jul 2, 2021, 11:20 AM

Post #16 of 26 (305 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Did you get a full 12v?
Did the pressure come up?

If you had full 12v but didn't get full pressure, you probably have a bad pump. When you take it out look it over inside for any broken hoses inside.



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MarineGrunt
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Jul 2, 2021, 11:51 AM

Post #17 of 26 (293 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Not quite 12v but got up to 11.5v with key on. When key was turned off it got to 11.78. Still no fuel pressure.


Hammer Time
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Jul 2, 2021, 11:53 AM

Post #18 of 26 (291 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Did you ever pinch off the return to see the pressure?



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MarineGrunt
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Jul 2, 2021, 2:46 PM

Post #19 of 26 (274 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I forgot to pinch the return line but gonna do that now. I see two steel lines running into the upper intake that are all steel. There's another, I think, that wraps around the back of the distributor, turns to a plastic line with a green cap, and then to some sensor or something. Is that the return line or is it one if the two steel going to the top of the upper intake?


Hammer Time
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Jul 2, 2021, 2:57 PM

Post #20 of 26 (272 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

No,no, no. Not the one with the green cap. That is an EVAP line.

It will be one of the steel lines going into the manifold, the smaller of the two. If you follow the lines back I think you will find short sections of rubber on both lines.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



MarineGrunt
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Jul 2, 2021, 3:09 PM

Post #21 of 26 (267 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

And that's why I always wait until I hear back from you.

There is definitely a smaller line. It's the one without the test port which makes sense.


MarineGrunt
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Jul 2, 2021, 3:46 PM

Post #22 of 26 (259 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I didn't see any rubber hose so just carefully pinched the vinyl back above the fuel pump. Fuel lines look pretty new so it held up fine. It didn't cause a fuel pressure spike.


Hammer Time
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Jul 2, 2021, 3:49 PM

Post #23 of 26 (257 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

OK, it's really starting to sound like a bad pump. I hope you replaced the whole assembly when you did that pump.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



MarineGrunt
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Jul 2, 2021, 3:58 PM

Post #24 of 26 (253 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

I haven't replaced the pump in the Blazer yet. When you say "whole assembly) are you talking about the sending unit too?


Hammer Time
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Jul 2, 2021, 4:06 PM

Post #25 of 26 (249 views)
Re: 2001 Blazer Low fuel pressure at test port but not at filter Sign In

Most come with the sender but that's not what I'm concerned about. Some places sell just the electric pump itself and you have to take the assembly apart to change it.

This



as opposed to this





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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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