Z71 GMC new fuel pump still wont crank

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Z71 GMC new fuel pump still wont crank

Unread post by hardonthagas » Mon Jun 22, 2015 5:11 am

I have a 98 gmc z71 the truck was running good got to the lake and killed it and it never cranked again. Fuel pump would not run so I replaced fuel pump brand new put it in and the pump came on now I have plenty of fuel to the pressure relese valve and still won't crank. I replaced throttle poss Sen the map Sen and it still won't crank it's getting fire and it will run if I pour gas in it at the throttle body and will stay running till it runs dry anyone have any idea what is wrong.


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Re: Z71 GMC new fuel pump still wont crank

Unread post by carriedi » Mon Jun 22, 2015 9:47 pm

ok, cranks means turns over. cranking, turnover, is when the starter engages the engine and rotates the crankshaft. What you have is: the engine cranks but doesn't start.

if the engine runs with adding fuel manually then you only have to look at fuel pressure and injector pulse. fuel pressure should be 60-66 psi. a new fuel pump should give you that if everything else is good. Now, what about your injector pulse? That's the computer sending the signal for the injector to open and let fuel into the engine. to check the injector pulse is a little tough since your injector are not easy to get at. you will have to check the wiring that goes to the injectors. All the injectors have a battery voltage power wire that is pink. That battery voltage comes from the ECM1 fuse (20A) in the underhood fuse box. If you have battery voltage from the pink wire then that's good. T fire the injectors the computer grounds the circuit.
Injector1 black
Injector2 light green/black
Injector3 pink/black
Injector4 light blue/black
Injector5 black/white
Injector6 yellow/black
Injector7 red/black
Injector8 dark blue/black

you need to know how to check for the computer ground signal. A logic probe or an LED test light, some kind of lighting device that will use less current that the injector, in series with the injector being tested.

No injector pulse but the battery power side stays up at battery voltage, you may have a passlock problem where the antitheft turns off the injectors. What is your security light doing? Would have to scan the passlock for codes and/or look at the resistance/voltage coming back from the key.

No injector pulse but the battery voltage side goes down below battery voltage by a few volts or more, you could have a shorted injector that will rob the power from all the other injectors.
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Re: Z71 GMC new fuel pump still wont crank

Unread post by hardonthagas » Tue Jun 23, 2015 2:39 pm

Ok will try that boy that sounds like a job and the securtity light goes off after about 3 seconds and truck has no codes at all

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