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Subject bad fuel injectors, how to check?

Subject bad fuel injectors, how to check?

Postby SpinDoctor15 [OP] » Jul 14 2012, 8:04pm

Hi all,

Over the last 6 months, my '99 Sierra with 5.3L has become increasingly hard to start. Essentially, I crank it over and it will crank for at least 10 seconds without catching. I release the switch and try starting again, and it roars to life! This pretty much happens every time. Crank it once, nothing; second crank and it starts strong as ever.

Additionally, when it is running, I've been told that it's "not running quite right" and seems to "have a lope to it." I asked an Auto Shop to look into it recently, and the owner told me that he's had 2-3 GM vehicles from this era in the shop recently: a common problem with them was a bad set of injectors. He mentioned the term spider injectors, and that those vehicles (a Suburban and other truck) needed them replaced.

Is this something easy enough for the home-mechanic to check and/or replace? If not the injectors, what are other good candidate causes to try? Thanks!
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Subject bad fuel injectors, how to check?

Postby benz604 » Jul 14 2012, 8:30pm

Sounds more like your fuel pump is losing pressure when shut off, they are notorious for doing this and basically it just primes the lines with your first crank over, the lines are supposed to stay primed because this is a returnless system, your pump may work great but it's most likely on it's way out, simple fuel pressure check will confirm this, lots of posts about this on here
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Re: Subject bad fuel injectors, how to check?

Postby LGSONE » Jul 14 2012, 10:07pm

Try this, on your first start just turn the key to on for 10 sec and then start, see if it starts up. That should be enough time to bring the fuel up to pressure. If it starts you might have a leak in the fuel system allowing it to lose pressure when off. Hence the long crank time. You might want to get a reading off the fuel system pressure when off, if it is dropping off you have a leak or a fuel pump going out. My old Jeep had the same problem, a little O rings would leak and do the same thing. I ended up just sitting there for a couple seconds before I started it..

Just my two cents

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Re: Subject bad fuel injectors, how to check?

Postby zacharyh687 » Jul 14 2012, 10:30pm

Check the fuel pressure regulator. While the truck is off pull the vacuum line off and see if gas comes out of the vacuum line. If gas comes out replace the fuel pressure regulator. This is a common problem on almost all newer gm vehicles 96+. The spider injectors are in the older 96+ 4.3, 5.0, 5.7L motors not the 99+ 4.8, 5.3, 6.0
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Re: Subject bad fuel injectors, how to check?

Postby SpinDoctor15 [OP] » Jul 15 2012, 2:45am

Thanks for these replies!

I have definitely tried letting the fuel-pump run for 5-10 seconds before cranking the 1st time, I can hear it running so I know it's fine. I can stand outside the truck and hear a slight hissing from somewhere near the gas tank. It slowly decreases in sound over a 1-2 minute period. My guess it that it has lost pressure.

Additionally, the tech that checked it out said that he's getting a high electrical current spike from the fuel pump-sender unit. I knew it was a problem, as the fuel-gauge reads "untrue" whenever I fill the tank: it tells me I have no fuel. After about 50 miles, it finally settles back in to the right reading.

Which vacuum line would I pull to check the fuel pressure regulator? Anyone have a picture of this? I'm kind of a newb with the whole vacuum system and fuel lines... Thanks!
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Re: Subject bad fuel injectors, how to check?

Postby zacharyh687 » Jul 15 2012, 4:48am

The fuel pressure regulator is on the drivers side of the engine and towards the front of the motor on top but just below the engine cover.
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Re: Subject bad fuel injectors, how to check?

Postby SpinDoctor15 [OP] » Jul 15 2012, 2:50pm

zacharyh687 wrote:The fuel pressure regulator is on the drivers side of the engine and towards the front of the motor on top but just below the engine cover.


Excellent, I'll look at this ASAP.
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Re: Subject bad fuel injectors, how to check?

Postby Lee's07 » Jul 16 2012, 4:03pm

I can tell you from experience that just because the fuel pump is running, doen't mean that it is fine. On my 07 5.3 I would have to crank the engine for a while everytime because I lost pressure when it shut off. I replaced the fuel pump module, and it starts perfect everytime. I know my fuel system is a bit different than yours but if your fuel pressure regulator turns out to be fine, then Im guessing it is your fuel pump.
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Re: Subject bad fuel injectors, how to check?

Postby SpinDoctor15 [OP] » Jul 17 2012, 2:05am

zacharyh687 wrote:Check the fuel pressure regulator. While the truck is off pull the vacuum line off and see if gas comes out of the vacuum line. If gas comes out replace the fuel pressure regulator. This is a common problem on almost all newer gm vehicles 96+. The spider injectors are in the older 96+ 4.3, 5.0, 5.7L motors not the 99+ 4.8, 5.3, 6.0


So... I followed instructions in my Chilton manual for how to check the fuel-pressure regulator. I disconnected negative battery terminal, bled the fuel pressure (of which there was none), and pulled the retaining clip. Then I wiggled the cap off and both heard a slight bubble/gurgle of fuel and saw some come out. A couple quick questions on this, since I'm a fuel system newbie:

- How long do I have to wait for the spilt fuel to evaporate? It looked like it was pretty much gone after a few minutes, but I do need to use the truck tomorrow morning! So I hope it will be ready then...
- Did I pull the right line to check for fuel leaking through? Or should I have checked another 'vacuum line'?
- The Chilton manual suggested replacing and lightly oiling the o-rings. Should I do this? I have some air-tool oil that I could use...

As for the fuel pump, I know for a fact that both the sending unit is ruined (giving electrical current spikes according to the auto shop tech) and that there is a definite hissing sound that decreases with time (as I mentioned earlier). Could this require a fuel-pump replacement? If so, is this something I can do on my own? Thanks again!
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Re: Subject bad fuel injectors, how to check?

Postby Lee's07 » Jul 17 2012, 2:32am

I am not really fermiliar with the fuel pressure regulator because my truck doesn't have one. If you do end up replacing your fuel pump, it's really not that hard to do. You either have to take your bed off, or drop your fuel tank. When I replaced mine, I dropped my gas tank, and pulled out the old fuel pump module, and put in the new one. The hardest part was getting the tank back on the truck, especially when you're doing it By your self.
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