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Gary
Gary, Chevy Technician
Category: Chevy
Satisfied Customers: 16100
Experience:  15 years GM master tech
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I have a 1996 chevy k1500 Tahoe w/ 350 R code eng. crank

Customer Question

I have a 1996 chevy k1500 Tahoe w/ 350 R code eng. long crank ,hard to start cold. had restricted fuel filter, pressure leaking down. replaced filter and pump(Delphi). after cold soak no start. What I've found is no fuel injector msec. reading on scan tool when won't start. What is odd is if you tip in fuel (I use a squirt bottle into throttle body). will start immediately and run fine good ckp signal and good cmp signal. had iffy signal at cmp when backprobe and wont start, replaced distributor same result, replaced pcm w/ good used. checked voltage at cmp sensor ok. checked for continuity on cmp sensor gnd and cmp sensor signal to pcm tested good. I have a rpm reading on scan tool when no start (crank sensor ok?) just no injector drive, why does tipping in fuel make signal work? If anybody can help pulling my hair out on this one.
Submitted: 3 months ago.
Category: Chevy
Expert:  Roy replied 3 months ago.

hello, my name is ***** ***** I will be glad to assist you. please allow me a couple of minutes to gather some basic info.

Roy

Expert:  Roy replied 3 months ago.

ok, I want to start at the pump.

what is the exact fuel pressure key on engine off and while running???

the fact tht it fired right up with a squirt of fuel indicates the injectors are being commanded on by the pcm. your reading may be wrong on your scan tool.

Roy

Expert:  Roy replied 3 months ago.

are you there

Customer: replied 3 months ago.
60psi koeo, 55 psi koer. replaced first Delphi with a second one and then did spider injector. Installed updated harness end with first pump installation checked pump ground and voltage . had to bump key toward start to get 2sec pulse so replaced ignition switch.
Expert:  Roy replied 3 months ago.

ok, thanks

are there any codes stored???

when you turn off the truck, what did the fuel pressure do??? what was the reading???

Roy

Expert:  Roy replied 3 months ago.

what I am after is too see if the pressure bleeds off and it looses prime

Customer: replied 3 months ago.
no codes, pressure holds for awhile. at the moment hose went bad on my fuel pressure tester. still waiting for my snapon dealer. I thought it was losing prime also. Fuel filter was so restricted never good for pump. when it wont start not getting cmp signal at pcm with lab scope( Intermittent or no signal). when signal ok vehicle starts and runs.
Expert:  Roy replied 3 months ago.

but you get signal when it runs???

the fact that you squirt fuel and it fires indicates a fuel delivery issue

Roy

Customer: replied 3 months ago.
doesn't the pcm use the cmp signal to trigger the injector driver.
Expert:  Roy replied 3 months ago.

crank sensor. I dont think you understand. if you squirt it with fuel, they are getting signal to pulse because it stays running. if it started and died, then we have a injector control issue

Customer: replied 3 months ago.
vehicle is restarting right now I get a cmp signal. don't get a cmp signal when vehicle wont start. I do get ckp signal either time. this has to mean something. I should get a signal when cranking right.
Expert:  Roy replied 3 months ago.

your missing the point.

I am opting out and someone else will be along shortly

Roy

Expert:  Gary replied 3 months ago.

new expert here did you still need help ?

Customer: replied 3 months ago.
sorry roy took a step away got tunnel vision . got fp pressure tester replaced. checked fuel pressure this am . you were right had to cycle key three times to get pressure to 53 psi then when cranking pressure dropped off. had to jumper power to pump at the relay got pressure to 60 psi the vehicle started. sorry for being so difficult, test and retest have to remember that. waiting to see if pressure bleeds down.
Expert:  Gary replied 3 months ago.

my name is ***** ***** am another expert Roy opted out of the question

so key ON engine OFF the PSI with a good fuel pressure gauge is 53 PSI ?

with it jumped and it reading 60 PSI it will still do this ?

if you unplug the TPS and the ECT sensor with both of those unplugged will it still do this ?

Customer: replied 3 months ago.
I've rechecked some things. was not getting enough fuel pressure. went through fuel pressure troubleshooting. the fuel pump relay and controls seem to be operating (powers and grounds test good). I decided to isolate the pressure side of system removed upper fuel line at plenum and connect tester to fuel line at distributor so am reading fuel pressure after fuel filter with no return. thought it should dead head pump and give high pressure reading can only achieve 50 psi ( was trying to test between pump and pressure regulator). jumper relay to run pump longer. still only get 50 psi, can hear pump run has lots of fuel in tank. am I looking at bad new pump?
Expert:  Gary replied 3 months ago.

yes it is more than likely the pump defective

BUT before you change it run a new power and a new good ground to the pump at the connector at the top of the tank if it still has 50 the pump is bad

if the psi is good then the ground or the grey power wire is bad from the relay to the pump

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Customer: replied 3 months ago.
went back and put original injector assy back on with new regulator and replaced 2nd Delphi pump w/ 1st Delphi pump. checked power and ground used a sealed beam headlight to make sure have voltage and amps. nice and bright. checked the fuel lines for pinching or restriction they look good. got vehicle running. this am tried to start took a couple of key cycles pressure there but seems to drop when cranking. started hard. went and put oe parts back on. distributor(replaced cap and rotor)and ignition switch. started hard again. ran it for a few minutes. now when you check koeo pressure a solid 60 psi and holds 55psi when cranked vehicle starts immediately.(like it should). runs good with no codes not running rich. going to let cold soak and see what happens. a restricted return should make pressure go high? a restricted supply would cause a low power like bad fuel filter? It seems like every cold start the system has bled the fuel out and allowed air to enter. Thanks for your time. Mark