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96 suburban fuel pressure/pump issue?

8K views 40 replies 17 participants last post by  AJ Hall 
#1 ·
96 burban 350 motor.

went outside this morning. cranked multiple different times would not fire.
not even a sputter.

shot it with starting fluid and it fired right up for 10 seconds then died. figured pump went out. so i pushed it into garage tonight and now its starting for 10 seconds on its own revving up then starting to sputter. then revving up then sputtering and stalling again.

so my question is what actually is a part of the fuel system on this truck. is there a pressure regulator? i already changed the filter last month when i was getting some stalling issues and found a broken ground strap which seemed to be my problem at the time.

I dont want to pull the tank and pump unless i know thats the problem.

anyone around pinckney have a fuel pressure tester I can use tomorrow?
 
#9 · (Edited)
I do believe pressure should be between 60-66 psi...FWIW My wifes pump on her 4.3 went bad (Same FI system) hers was showing about the same 55psi at idle but as soon as I gave it gas it would die, few starts later and it would not start at all. New fuel pump shows 65psi with key on and 61 when running at idle...runs perfect now! 99% sure yours is bad without even looking at it! Very common problem on Chevy trucks in the mid 90's early 2,000's! PS: Another common problem is the connector so if you get a new pump make sure it comes with a new connector and use it. Solder it and use shrink tube, don't rush it with butt connectors and duct tape :teehee:
 
#13 ·
200k. on truck. no idea if its ever been changed. have only had it for a year.

I put guage on it. turned on ignition. went to 55psi. turned off ignition. let it sit 5 minutes and it went down to 45psi. after 15 minutes it was at 40psi. and after 30 min it was at 35psi.
 
#14 ·
nothing to do with this thread just fuel related

yay i had the joy of changing my 165,000 mile fuel filter in my 95 tahoe today


it had a slow loss of power for the past 6 months( i figured it was the converter or fuel pump) i procrastinated until it wouldnt pull out into traffic safely or hit highway speeds.
all good now!
 
#16 ·
pinch off the return line and try it again...if it holds pressure then, the regulator is the problem...if it still leaks, the problem is either a leaking injector or the pump.

to check for a leaking injector, unbolt and lift up the fual rail with the injectors still installed in the rail..make sure anything removed is reinstalled, and then pressurize the system again and watch for any drips coming from the injectors...if you are having a hard time seeing the injectors drip, put a paper towel directly under the injectors and watch that



have you checked the flow rate of the pump yet? not sure what the spec is, but shouldnt be too hard to find...you can have pressure without having enough flow, and it will appear to bleed down slightly...I would suggest checking that first.
 
#17 ·
im going to work on it again hopefully tonight when i get some time. but driving it around today the only issues im having are at low throttle driving. if im giving it 1/4 throttle to keep at 45mph it has a slight chugging feeling. if i give it just a touch more gas it goes smooth again. i can stand on the throttle and its got all the power in the world. it only chugs when its given very little throttle.
 
#21 ·
yes, you can test them with a multimeter, measuring the voltage at the center wire, but it probably wont catch the problem if it is falling out around the center of the throttles stroke (which is common), the sample rate of a multimeter is way too slow..technically, you need a lab scope to test this correctly...I'd let you use mine, but the internal rechargable battery has failed yet again, and I'm still looking for alternatives to the original replacement
 
#22 ·
The fuel pressure spec is 60-66psi. The injector resistace should be between 11.8 and 12.6 ohms. My two cents, put a fuel pump in and a new fuel filter while your at it. 55psi is to low for it to run right. If was much lower, I don't think it would even run. The only exception would be on a big block truck, the fuel pressure spec is lower.
 
#23 ·
well it finally stranded me today on I-75 in flint. drove fine from ann arbor all the way to grand blanc. then starting cutting out at 75mph. from 2500 rpm down to zero for about 10 seconds. then it would launch and take off again for about a minute and then repeat. after about 5 minutes of that it finally just stopped. fuel pump tomorrow night.

TPS did nothing. does the computer need to be reset to see the new TPS sensor? just wondering of it could of still been the problem but i didnt finish it right.
 
#24 ·
This is from GM service manual.


The numbers below refer to the step numbers on the diagnostic table.

2.

Wrap a shop towel around the fuel pressure connection to absorb any small amount of fuel leakage that may occur when installing the fuel pressure gauge. Turn ON the ignition, the fuel pressure should be 415-455 kPa (60-66 psi) for the Central SFI and 385-430 kPa (56-62 psi) for the SFI. This pressure is controlled by a spring pressure within the regulator assembly.
4.

The fuel pressure that continues to fall is caused by one of the following items:
• The in-tank fuel pump check valve not holding.
• A partially disconnected fuel pulse dampener (pulsator).
• The fuel pressure regulator valve leaking.
• A central SFI injector and poppet valve leaking.
• An SFI injector is leaking

5.

When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel pressure regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will very somewhat depending on the barometric pressure; however, the pressure idling should be less indicating the pressure regulator control.
16.

The fuel pressure less than 415 kPa (60 psi) for Central SFI or 385 kPa (56 psi) for SFI, falls into the following 3 areas:
• A regulated pressure but less than 415 kPa (60 psi) for Central SFI or 385 kPa (56 psi) for SFI. Amount of fuel to injector OK, but pressure is too low. System will run lean and may set a DTC. Also, hard starting cold and overall poor performance or may not start at all. Refer to Engine Cranks But Does Not Run
• A restricted flow causing pressure drop -- Normally, a vehicle with a fuel pressure of less than 300 kPa (44 psi) at idle is undrivable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop running as the pressure begins to drop rapidly. This is most likely caused by a restricted fuel line or plugged filter.
• A leaking or contaminated pressure regulator valve or seat interface may not allow the regulated pressure to be achieved. Refer to .

22.

Notice: DO NOT allow the fuel pressure to exceed 517 kPa (75 psi). Excessive pressure may damage the fuel system.

Restricting the fuel return line allows the fuel pressure to build above regulated pressure. With the battery voltage applied to the fuel pump test terminal, the pressure should rise above 455 kPa (66 psi) for Central SFI 430 kPa (62 psi) for SFI, as the valve in the return line is partially closed.
 
#26 ·
Sounds more like the TPS or IAC than the fuel pump, the TPS throttle position sensor tells the engine how much gas to give it depending on how far the throttle is pushed down, and the IAC, idle air control motor is what makes the engine idle at the right temp, either one of them going bad will cause it to not start and to start when started, since it over revs then stalls then it's more likley the IAC
 
#32 ·
My 94 2500

my 94 2500 is doing the same thing and there is so many possibilitys i don't know were to begin at idle if it runs for 5 minutes it willl stall out and sometimes ill get a puddle of fuel on the ground. driving i have no acceleration unless i hit passing gear truck has a 5.7 with 249,xxx miles. when i bought it they guy said he had just put a tune up on it and i ran fine it sat for a month while he was in jail and when i opened the hood i noticed the spark plug wire are mismatched theres some big ones on it. When its running it smells real rich and i go through about $10 to go 15 miles i think im start with new wires and plugs and check for a ground strap pm me and let me know what fixes yours and maybe itle fix mine :usa:
 
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