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96 s10 Blazer not getting gas


goat2789
09-03-2007, 07:54 PM
this is a wierd problem. today engine wont start, no codes, put fuel pressure guage on and turned key on, heard pump, 50 lbs pressure. pulled plug had spark but plug dry so poured some gas down throttle body and started car, runs fine,when throttle opened up it hesitates and sometimes backfires through throttle body, been fighting this problem for awhile, car ran fine yesturday. has had p0442 evap emission code in past and when you take fuel cap off it has pressure in tank. replaced fuel cap did not help. any suggestions
thanks

blazee
09-03-2007, 08:02 PM
Your fuel pressure is too low.You need 60+ for trouble free starting. 55-60 gives hard starting. Less than 55 and it won't start on it's own.

Start by making sure that your battery is fully charged, then check fuel pressure. If it's still low check it at the fuel filter.

goat2789
09-03-2007, 08:47 PM
thanks, will check, what about the pressure in the tank when you remove the cap

TomB985
09-03-2007, 09:11 PM
You're confusing the fuel system with the EVAP system. The evaporative emissions system sucks out fuel vapor from the tank and burns it in the combustion chamber. This system is irrelivent when troubleshooting a hard starting problem, unless you are looking for a vacuum leak.

As Blazee said, your fuel pressure is too low, sounds like a fuel pump or a pressure regulator....

goat2789
09-04-2007, 10:37 PM
how can i test to see if its a regulator or pump,

Chris Stewart
09-05-2007, 07:34 AM
Right here.

http://www.automotiveforums.com/vbulletin/showthread.php?t=747235

blazee
09-05-2007, 11:51 AM
how can i test to see if its a regulator or pump,That was the purpose of checking the pressure at the fuel filter.

MT-2500
09-05-2007, 12:34 PM
What engine and engine code?

blazee
09-05-2007, 07:52 PM
What engine and engine code?They're all VIN W Vortec 4.3 CSFI.

goat2789
09-05-2007, 09:54 PM
thanks, missed that part, will check at filter

blazee
09-06-2007, 05:44 AM
thanks, missed that part, will check at filterI'd recommend replacing the filter while you're there. If it hasn't been changed in a while, it's probably due, and could also be restricting the fuel a little. If it turns out that your pump is bad, you'll need to replace the filter anyway.

goat2789
09-06-2007, 06:16 PM
thanks, already replaced fuel filter, i have enother question, from what i see the fuel regulator is in the cmdi unit under the intake so the port to check fuel pressure and the fuel filter are before the regulator. It looks like checking the filter or port should give same pressure unless the fuel line is kinked. am i write or wrong in this statement?

blazee
09-06-2007, 06:27 PM
When you check pressure at the service port, you are merely "T"ing your gauge into the line. Doing this lets you see the pressure in the line, but doesn't tell you where the problem is if the pressure is low. While checking at the service port, the regulator is still working and allowing fuel to return to the tank, in which case you don't know if the regulator is sending too much fuel back to the tank and causing low pressure, or if the pump isn't supplying enough fuel pressure to begin with.

When you check at the filter, on the other hand, you are disconnecting the rest of the fuel system, and hooking directly to the line, in this case you eliminate the regulator, injectors, and return line. While checking at the filter, if the pressure is still low, you know that the problem is in the tank. If the pressure is good at the filter then you know the problem is further up, and part of the system that you eliminated, in which case it could be the regulator, a line, or injectors leaking.

Just to prepare you..... the regulators on the CSFI engines rarely fail, and low pressure conditions are nearly always caused by a faulty pump or electrical connector at the pump.

old_master
09-06-2007, 06:37 PM
You are correct. There is only one place to check fuel pressure without using other special test equipment. The test port is between the fuel filter and the injector. The regulator is after the injector. Restricting the fuel return line should cause the fuel pressure to increase. It should rise to 75psi. Do not allow pressure to rise above 75psi or permanant damage can occur to the fuel pressure regulator. If the fuel pump cannot build 75psi when restricting the return line, and fuel pressure remains above 50psi after the pump shuts off, the fuel pump needs replacement.

goat2789
09-06-2007, 07:21 PM
thank you for the explanation, it makes sense to me now.

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