96 vortec wont start

[89muscletruck]

Hi, my dad's 96 1/2 ton Z71 with 5.7L vortec will not start. And he is looking for opinions on what to look for to try to get it running again.
Apparently one day when he went to drive home from work it just would not start up again, it had been running fine that mourning.
He had thought that it was one of the ignition modules, the one that sits just under the dizzy, he replaced that but still nothing.
I haven't had a chance to personally go a look at it yet, I am going to do this tomorrow, and we thought we would ask you guys to share your wisdom on what the problem might be.
I don't know as much about the problems of the Vortec as most of my experience has been with the TBI's, so any help will be greatly appreciated.
Thanks

[SwampDonkey]

when you turn the key can you hear the fuel pump kick on? my buddys vortec fuel pump randomly quit a few times

[BigBlocksRule]

^ actually a pretty common problem.
Sometimes you can whack the gas tank right in the middle and get the pump to run again for a few minutes.
After it's sat a while and had time to bleed pressure down, put your ear directly against the side of the truck by the tank and listen when someone else turns the key "on" for you. Don't try to start it, just the key "on" and listen to hear the pump.
When it's time to replace it, loosen the bolts on the passenger side to the point where they only have a couple of threads engaged. Pull 'em all out of the driver's side, then tilt the bed up to gain access to the tank. This is a whole lot easier than dropping a dang tank.

[89muscletruck]

I believe that the fuel pump is working.

[speedygonzales]

Fuel pump more than likely. Relieve the pressure at the schrader valve on the fuel rail. Then cycle power 5 or 6 times on and off about 3 seconds each. The hit the schrader valve again to see if there is any pressure. If pressure is at the prescribed 60PSI minimum it should spray like a fire hose.

If pressure checks out, go to the cap and rotor.

[ChevyTech]

Put a fuel pressure gauge on it and see what the fuel pressure gets up to during the 2 second prime cycle with the key on and engine off.

Then watch the pressure and see how much and how fast the pressure falls after the fuel pump stops.

Let us know what you find.

A 96-up Vortec engine should have 60-66 psi. Key on/engine off = book spec 60-66 PSI
Engine running = 58+, pressure should increase when you blip the throttle

[chevyndn]

i know this sounds crazy, it did to me to, but change the battery terminals. my 98 gmc sat for a month because it wouldnt start. i tried jumping it, changed fuel pumps and all sorts of other things to. i talked to a buddy who had a 99 burb and told me to try that. i looked at him like he was stupid to my disbelife it started when i changed the screws on the terminals. i would try that first they only like 5 bucks to change. i know it sounds crazy but try it.

[bwood]

The module he changed is not for the ignition, it was a camshaft position sensor and it will not keep the truck from starting.

Checking the fuel pump as everyone has stated is step #1. The suggestion to check the battery connections also is a good one. These trucks use stacked positive cables and are prone to corrosion between them. The one farthest from the battery powers everything in the truck except the starter, a poor connection can cause a host of PITA issue.

[89muscletruck]

thanks for the replies guys.
Sorry I didn't reply sooner but I have been busy with getting ready for the winter semester. I will pass the info on to Dad, but it may be till the spring melt till he or I get a chance to look at the truck again. As it is sitting in a snowdrift by the grain bins, and I am 2 hours away at university.

[bwood]

Also make sure the crankshaft position sensor is plugged in at the timing cover.

[speedygonzales]

crank sensor won't keep it from starting either.

[89muscletruck]

update:
Dad has been working on it, but it still won't start here is the rundown
It has spark and it turns four times before it sparks again, fuel pump starts and then shuts down once it has pressurized the system, but it seems to have a weak spark, its not too bright.
Any ideas on why it won't catch?

[Boog]

The engine will not startup with low pressure even though the pump cycles on and off. You gotta get that fuel pressure number.

[big_ac2001]

Originally Posted by 89muscletruck

update:
Dad has been working on it, but it still won't start here is the rundown
It has spark and it turns four times before it sparks again, fuel pump starts and then shuts down once it has pressurized the system, but it seems to have a weak spark, its not too bright.
Any ideas on why it won't catch?

My '96 had the same problem a while back. The truck would not start and it had a very weak spark. I changed the distributor cap and rotor and it started and has been running good ever since. Take the cap off and see if there is any corrosion in it or on the rotor.

[spudz]

Originally Posted by speedygonzales

crank sensor won't keep it from starting either.

YES IT WILL.... Just about the only thing that goes wrong with these trucks that make em not run in the most common order are:...... fuel pump, crank sensor, and ignition module that located on a bracket on the passenger side of the intake with a little aluminum heat sink under it. OR the distributer caps are bad about shorting internaly. You need to A: check and verify your fuel pressure. If no guage, spray some starter fluid into intake and see if it trys to start.. If it does, then fuel is your problem.. If nothing then you are going to need a scanner and diagnostic flow chart to correctly diagnose it without just throwing parts at it.... BTW... it will spin a few times before each cyl will spark. If you are looking for a contant spart check it at the coil...

[Jaybird74]

I know this is an older thread but I'm having same problem I think, Quick rundown....

Stopped for fuel the other night, everything was fine till then. After pumping gas wouldn't start, ended up having it towed to my house. Checked all fuses, replaced fuel filter, then pump, it will start if I dump a bit of fuel into throttle body but have no pressure at all, pump is not engaging at all. I'm at a loss

[BarryB]

Originally Posted by Jaybird74

I know this is an older thread but I'm having same problem I think, Quick rundown....

Stopped for fuel the other night, everything was fine till then. After pumping gas wouldn't start, ended up having it towed to my house. Checked all fuses, replaced fuel filter, then pump, it will start if I dump a bit of fuel into throttle body but have no pressure at all, pump is not engaging at all. I'm at a loss

If you replaced pump. You should double check all the connections going to the pump. have you checked the fuel pump relay?

[Jaybird74]

Yea I checked all connections, probably gonna pull it and double check wires in tank after I take a volt meter to it

[Jaybird74]

Was pigtail in tank, fixed!!!

[Ricky381974]

I've working on a 98 Chevy z71 new fuel pump crank senser cam senser ignition module new coil new pcm new ecm new cap and rotor fuel pump pumps up 55 psi no fire out of the coil still

[BigBlocksRule]

Check wiring ground near the thermostat and is the engine grounding strap hooked up?

[Ricky381974]

All three grounds are hooked up the one on the back of passage side of head black with white stripe the one by lower left by the crank senser and the one by the thermostat

[speedygonzales]

Start a new thread instead of bringing back a 5 year old one

[Ricky381974]

Up date put new ignition switch pass lock module. No go test the white wire ignition module to the computer and key off no voltage key on 0.06 volts start jumps to 0.46 volts my other running truck no voltage key on and start