1996 k1500. NO RUN!!!

**RAV52202** · 06-20-2012, 11:10 AM

Ok so I thought i had the problem fixed. Guess I just fixed one of the problems. I have a new fuel pump and fuel filter in it now also. I have the harness ripped out and im going to check all the wires and plugins on it. Had a friend hook up his computer to it and found nothing that would make the truck not run. SO that is where i am at now on this thing. Any thoughts from anyone is welcome.

**RallySTX** · 06-20-2012, 12:04 PM

So it cranks but will not start? Pull a spark plug, reinstall the wire to the plug, lay it on the engine where it will ground out, and crank. If you see spark, you have ignition, if you don't, you don't.
Brian L.

**RAV52202** · 06-22-2012, 05:36 AM

Originally Posted by RallySTX

So it cranks but will not start? Pull a spark plug, reinstall the wire to the plug, lay it on the engine where it will ground out, and crank. If you see spark, you have ignition, if you don't, you don't.
Brian L.

I do have fire because when i put a little gas in the throttle body it will fire right up.

**RAV52202** · 06-22-2012, 05:39 AM

I think my computer is toast. I need to find some one that know how to computer controls the injector system. I have traced all wires to the main plug in on top of the intake. All wires are good. checked with meter. The one main wire ,The pink wire has 12v power or better. But the other different colored wires also have power. I thought that the pink wire was to power the injectors and the other wires were ground wires controlled by the computer.

**MrShorty** · 06-22-2012, 08:34 AM

The one main wire ,The pink wire has 12v power or better. But the other different colored wires also have power. I thought that the pink wire was to power the injectors and the other wires were ground wires controlled by the computer.

This is correct, and it would be normal to show 12 V (assuming the negative/common lead of your meter is to ground in both cases) on all those wires. So, I don't see anything in this test that indicates a problem.

We are so used to thinking of hot side switched DC circuits, that sometimes ground side switched circuits confuse us. I'm not good enough to explain why this is normal very well, but I'll try. Maybe, using the water analogy, if you think of this circuit as a hose with a partial kink (injector) in it and a valve on the exit end. With the valve (ground side switch) closed, water bleeding past the kink builds up pressure (voltage) upstream of the closed valve. You will measure the same pressure (voltage) whether you measure the pressure upstream of the kink or downstream of the kink. Once the valve is opened, the pressure downstream of the kink drops, but the pressure upstream of the kink remains high.

If you are trying to determine if the computer is telling the injectors to fire, you will need (assuming your meter is not fast enough to detect/show the brief switch closure) an oscilloscope or a noid light or other gadget that can see and show the brief change in voltage when the switch is closed.

**RallySTX** · 06-22-2012, 08:45 AM

You still need to check the pressure so you know if the injectors have enough to work. Bad pumps get sold all the time. It's not like they are all bad, but it happens. Check and clean all grounds with a wire brush. Are you getting any codes from the ECM? So it still cranks but wont start unless you dump gas down it's throat? Have you tried changing the throttle position while cranking?
Brian L.

**RAV52202** · 06-22-2012, 11:23 AM

Originally Posted by RallySTX

You still need to check the pressure so you know if the injectors have enough to work. Bad pumps get sold all the time. It's not like they are all bad, but it happens. Check and clean all grounds with a wire brush. Are you getting any codes from the ECM? So it still cranks but wont start unless you dump gas down it's throat? Have you tried changing the throttle position while cranking?
Brian L.

I have cleaned all grounds and put some new one as well. I get no codes. I have tried changing the throttle position. I tried putting it to the floor and then turning the key on and also other positions as well. Nothing make a difference. I was thinking maybe the temp sensor was messed up and making it think it was really cold or something like that. I did have a guy with a really nice computer to check the truck and he said that nothing was showing up. He said It should run.

**RAV52202** · 06-22-2012, 11:31 AM

Originally Posted by MrShorty

If you are trying to determine if the computer is telling the injectors to fire, you will need (assuming your meter is not fast enough to detect/show the brief switch closure) an oscilloscope or a noid light or other gadget that can see and show the brief change in voltage when the switch is closed.

My meter is designed for working on automotive. I do believe it should be able to detect the drop in voltage. I have paid good money for it. I could be wrong but im pretty sure that it will do what i want it to. I have been wrong many times before though!

Thanks again to All that have responded to helping me out with this problem. and keep sending the questions through and i will answer them for you.

**RAV52202** · 07-05-2012, 05:55 AM

Ok so After messing with this thing for a while. and tracing every wire. I talked to some people. The computer is junk. something is burnt in it. It kicked a Security code and wont let the injectors fire. SO now I need a new computer. found one on ebay for $100. All programmed to my vin number. Thats my findings. I can say all the wires in the truck are great.

**MrShorty** · 07-05-2012, 10:16 AM

Let us know if the new computer fixes the issue.

While you are at it, since diagnosis can be most of the battle, how did you determine that the computer had triggered a security code and that this required a computer replacement? When I've heard of cases where the security system disables the engine, it usually just needs some kind of reset procedure done to reset the security system.