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88 K5 will not start...need help.

Having trouble with understanding the wiring diagram. But to me the diagram looks like the output from "E" at the relay runs directly back to the fuel pump.

So my plan to splice E after it exits the relay and splice it to the pump seems ok to do?

or does it go to the oil pressure switch FIRST. It is really tight where the oil switch is (that is new as well btw). Do you think that the "E" wire goes to the oil pressure switch or not ?

I would not want to bypass that switch on an engine that has not run for over 5 years.

1227747-$42-5.gif
 
Look at the oil pressure switch in diagram. It is redundant and you don't need it at all. It only keeps engine running if relay fails when engine is running.

ok sending power to the red wire "aka "C"". I checked for power at "E" and have 12v +. Then I checked at fuel pump assembly purple wire. also 12v + but pump does not operate.

This is crazy. when I apply 12v to purple directly from battery the pump "wirrs".
Click to expand...
You have a break in purple wire from relay to pump.
 
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Sorry to be so redundant but what I am getting from you is that it is ok to run a new line from the "E" on the relay to the purple wire on the fuel pump assembly.

Correct ?
 
at least temporarily, to verify where the fail point is...
 
Sounded like you already had power there? But somewhere from purple on relay to purple at fuel pump has failed. Chase the wire from relay to tank and find break.
 
ok 1st thing in the AM I have been at it all day I am old and it is so hot...

Hate chasing things at my age LOL Will report back tomorrow.

Thanks to you both, Eagle and royken for your help and especially your patience.
 
Don't "splice" into anything. You will just cause more problems, or potential for more problems down the road. It's ok to jumper things temproarily, cutting wires is almost universally a no-go, which is what I hear when someone says "splice".
 
by splice I mean: scrape away the covering of the wire to bare metal so I can tape the new line without severing the old. Then if I decide to use the new line I cut, and make new connection using solder and shrink tubing.
 
Got a helper today. So I did the following using the new relay - FYI they all result in NO START:

1. Tested voltage at relay. With key on I have 12v at power IN connection i.e. "A".

2. When turning the key I have 12v for about 2 sec at the output side of the relay. "E"

3. I tested the other end of "E" at the fuel pump assembly and have 12v for 2 sec.

To me the means that the existing wire is OK!

4. When turning key and holding the relay in hand can feel the click and 2 sec later another click.

5. Connected 12v to red wire at relay. I have 12v at the fuel pump assembly.

6. Connected new 14 gauge wire (temporary splice) from "E" to the fuel pump assembly. I have 12v at the fuel pump assembly.

7. I have tested the ground from fuel pump assembly to frame using continuity. Result is .000 on the meter.


Following resulted in fuel flow and start.

a. Connected power from battery to fuel pump assembly.


So if I am getting 12v to the fuel pump assembly via the existing wire and the new wire why doesn't it run the fuel pump and start ?

Been reading and wondering if the cause is a lack of a engine start signal or an engine running signal?

I have been unable to find what creates these signals.

Am I correct that while I have the initial 12v at the pump, that voltage stops after 2 sec and without the appropriate start or running signal voltage to the pump is cut off ?

What tells the ecm about these signals ?
 
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On the ECM pin B2, see if it gets power during the 2 second prime when key is on? If not fix it, look at diagram. If it does? Replace ECM...

If you have a known good working 1227747 ECM just plug it in with your chip and try.
 
THEMCGUIRE said:
by splice I mean: scrape away the covering of the wire to bare metal so I can tape the new line without severing the old. Then if I decide to use the new line I cut, and make new connection using solder and shrink tubing.
Click to expand...

Yeah, thats a bad idea. But its your truck do as you wish.

The ECM "knows" the engine is cranking from the ignition module. Easiest test (although not authoritative, usually accurate) is to check for injector pulse while the engine is cranking. No pulse=ECM doesn't know the engine is cranking (so something with the ignition circuit; pickup coil, module, etc.), or there is something wrong with the ECM or fuel injector wires.
 
When I hard wire the battery to the fuel pump the truck will start and it will run, but I did note that the fuel from the injectors are big drops, not a fine mist or spray.

So does this mean that fuel is being forced out of the injectors and the injectors are not actually pulsing ?

And if that is the case does that mean it is running without the ECM being involved ? sort of by passing the ecm ?
 
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Check for injector pulse. You are bypassing the ECM's control of fuel pump, so the injector pulse wouldn't be needed to run the fuel pump. Since it won't run off the relay, but the relay is good, sounds to me like the ECM isn't turning on the pump for whatever reason. Injector pulse is the only way to easily check if it is trying to do so or not.

Did you check for 12V across the relay with the engine cranking? That would tell you if the ECM is trying to run the pump too.
 
get a noid light..... or at least check the grd side of the injector leads for pulse, as they are grd fired..
 
have a problem spending 25 bucks on a tester that I will just use once. But I did a volt test on injector electrical when cranking. Zero on 1 side 1.3 v on the other.

Tomorrow will test pick up coil. thinking if coil is dead it will not tell ecm engine is rotating

Will report back after test..

thanks all.
 
your not looking for voltage thru the injector wire.. as I said, your looking for a grd pulse.. a test light stuck in the neg side and clamped to your hot bat post... look for the flash...
 
Or a 194 bulb with the leads straightened and wires soldered to them. Diagnosis is a hell of a lot cheaper than guessing.

You can't test injector pulse with a digital multimeter.
 
I have 12v at B2 for 2 sec during starting. So ordered a new ecm.

Ryoken, yes it's 10 bucks but it is also 11.80 shipping. for 25 bucks I can get a set at auto zone. But going to wait on that till I get the new ecm tomorrow. and try the 194 bulb that Dyeager is suggesting. :))
 
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