truck won't start

[the_goat]

Alright, a few days ago my truck hesitated then stalled while I was driving. Since then it won't start. It turns over and will run for a second if I pour gas into the TBI. My fuel pump wasn't getting any power. I ran the hot wire off of the fuel pump to the battery and it works but it still won't start.
What do you think?
Also it appears that the hot wire off of the fuel pump goes into a 3 wire connector that goes into the back of the distributor. Is this correct?

[the_goat]

there are 4 wires coming out of the coil, 2 red and 2 white. Where do these go? One of the red wires isn't attached to anything. Could this be the problem?

[the_goat]

any ideas?

[wibilly]

sorry i can't help my friend, that is exactly why i drive these old trucks because they don't have all that electronic bs ttt for you

[rick0312]

do you have an hei setup? if so, make sure that the BAT wire is plugged into the HEI.

[rick0312]

sorry, if it runs for a second then the BAT wire is connected.......hows the fuel pressure?

[89 crew]

What exactly are we working on?

[the_goat]

It's a 70 blazer with the TBI from an 89 2500. The PO did the swap so I don't know to much about it.

[89 crew]

Where the fuel pump doesn't run without a jumper wire I would start with the power problem. First look for a fuel pump relay. test for power going in and out (you will need help for out) where after you jump the pump it still won't give gas check the inline filter. Those are the 2 most common problems a tbi system has. If the filter is plugged you will soon be needing a pump. If the relay doesn't have incomming power from the factory a 89 was fused. That could have been removed, or changed so you will have to track wires.

[the_goat]

Alright, with power from the battery the fuel pump turns on but the truck still doesn't run. Would it be smart to disconnect the fuel line and see if it's pumping gas? I'm still thinking that it's the fuel pump because it runs when I pour gas in the intake but quickly stalls when that gas is gone. Where does the fuel injectors get their power, any relation to where the fuel pump gets it's power? It seems weird to me that two different things would stop working on my truck at the same time without being related.
I hope this makes sense

[Boog]

The fuel pump can run but still not create enough fuel pressure to start the truck. You need to check the fuel pressure before the inline filter. TB engines need about 11 to 13 pounds of pressure to run right. 9 pounds or less and it might not start. Pump on my 97 shut down while driving like I turned off the key and it would not restart. Once home I found the pump still ran but only produced 16 lb and it would not start. The Vortecs require a lot more pressure than the TBI engines but you get the idea.

[89 crew]

When you turn the key on the fuel pump is suppose to run for approx 3 seconds, then stop and wait for a signal from the distributer. Depending on how it is wired there can also be a oil pressure cut out. This is a simplified version of what happens but it should give you an idea of what is suppose to go on. If you want you can break the fuel line open but I'm going to expect you will have fuel when you hear the pump run. Without the jumper wire to the pump, does the pump run for the first 3 seconds? If so then I'm going to bet there is a loss of signal from the distributer to ecm, or ecm to fuel pump relay.

[89 crew]

Is there any spray from the injectors when you try cranking?

[the_goat]

Without the jumper the pump doesn't turn on at all. I'll check right now to see if it's spraying fuel.
Thanks guys.

[the_goat]

I changed the fuel filter just in case and there is no spray form the fuel injectors when it's cranking. Could this be do to fuel pressure? Where do they get their power? What's the easiest way to check the fuel pressure?
Thanks again.

[neonlarry]

T into the fuel line after the fuel pump with a fuel pressure gauge. Not knowing how the PO set your system up its hard to be more specfic.

[the_goat]

Does it matter where in the line I put it? is something that I get get from a local parts store?
Thanks

[89 crew]

I don't know about all parts stores, but Oreilly does have what you need to test pressure. The injectors get the signal from the ecm to let the fuel through. THIS DOESN'T mean the ecm is bad! A loss of signal can cause the same problem. check the wires! check the pressure. If the pressure is low replace pump, filter, and relay. If the signal isn't getting to the ecm fix the wires. The other remote possibility is the tbi isn't letting fuel in to the injectors. For that one try tapping on the back side of the tbi as someone else cranks the engine.

[the_goat]

Thank you, I'll check all of that today. I really apreciate it.

[463]

i wonder if the P/O or the conversion artist put in the diagnostic port in the cab and a bulb to serve as a check eng light so that with a scan tool you can trace problems in one direction if it's a computer related. this will be the odc 1 computer to run this setup. to test the injectors you use a volt meter and prob the hot pin on the tbi injector for a 12 dc key in the run pos. you may have a burnt wire or ground off/not grounding , blowen fuse in truck wiring or fuse box. water in the fuel pull off filter and drain fuel into a clear container let it sit and then look to see if it's dirt or h2o. test the hot wire to the pump(key switched to the run pos the pump hot wire needs 12v if the relay is working on for 2 sec) fuel psi should be 15 lbs.

[the_goat]

Where should I look for the fuel pump relay? I took the harness apart and I can follow the wire from the fuel pump to the ecm but that's it. I can't see it going from the fuse box, it doesn't go to the distributor.

[463]

Originally Posted by the_goat

Where should I look for the fuel pump relay? I took the harness apart and I can follow the wire from the fuel pump to the ecm but that's it. I can't see it going from the fuse box, it doesn't go to the distributor.

the relay is got to be between the ecm and the pump as the ecm will not have enough amps by it's self to run the fuel pump ( if this did happen the ecm will be cooked ). thats some of the rats nests you find when you have an opportunity to to work on a project such as this. Lets fix this #1 the truck should have a hot wire with a 20 amp fuse going to the relay plug spot 4 . #2 ecm wires out of ecm colors are as follow's 2 orn wires should go to the down stream side of the red 20amp fuse from the battery juction block and into spot 4 at the relay plug . #3 wire color is grn/wht and it goes to spot 5 on the relay connector hot control side of the relay plug spot 5. emc wht wire to relay spot 2 this is the ground wire and also grounds to the engine block. spot 1 on the relay plug is hot (12vdc) color gry to the pump in the tank and back to the ecm (ecm see this as the fuel punp signal or a voltage monitor) and the fuel pump/oil pressure switch on the engine. that switch has a tan wire for the indicator light and a orn wire leading back to the orn wire 12dc from the ecm. the hot wire at the pump should be a grey wire if they were useing a stock gm wire code. so from your ecm wire trace the wire back to fined the relay and plug. - GM has a noted problem of the relay plug shorting due to the fuel pump drawing higher the normal amps caused by 1 to low of a fuel level repeatedly as the fuel is the cooler for the pump. 2 a worn out pump, 3 a pump trying to pump fuel though a restricted fuel filter plug or bad injector. this will the cause this relay plug to fail.

[the_goat]

I really appreciate the help. Let me read over it a few more times and try to digest this info.
I think one of the problems I'm having is that the fuse box is stock from 1970 and the pump is an aftermarket inline type pump. So far I've seen that the negative ground wire is green and the hot wire is gray with a white stripe.

[red71cheyenne]

If its an inline, frame mount type pump, that may be your problem right there. I know the one on my TPI only made it a year before it gave up. I had it too far from the tank though. Check all the wiring for the relay though. If the pump doesn't run when you first turn on the key(you should hear it), it may be the pump or the relay or wiring. Good luck!