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Old 09-06-2013, 12:18 PM   #1
THEMCGUIRE
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Starting / running problems with 1988 K5

Had another thread called "88 K5 will not start...need help " and we got it running.

Now however, after running for about 1/2 hour it just died. If I run power to the fuel pump relay bypass the fuel pump runs.

When NOT using the bypass the fuel pump will not run, and the radio is dead, the horn does not work, tail lights and head lights don't work

but the reverse, break, and turn signals do work..

Battery is good. Checked all fuses and they are all fine. Checked all connections to the ECM and they are in place. This is a new ECM btw.

The check engine lite, which is always on, is now off. And jumping ports 1 and 2 using a paper clip on the code test block does not function. Not even a code 12.

Tested voltage at the 3 connections to the MAP and I have zero volts at all three electrical inputs.

Stumped... any advise appreciated....
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Old 09-07-2013, 06:12 AM   #2
mrschaeferpants
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You just do a visual on the fuses? I always touch them with a multimeter to verify continuity. That's a lot of things not to work.

If the fuses are good, then I'd stick the prongs of the multimeter into the panel, check for voltage. If no voltage I'd check on the incomming power wire to the panel. If certain things on the panel have power, and certain things don't. I'd assume the fuse panel has some kind of issue.

For the fuel pump, when you bypassed, you hooked an external source of wire to it? Directly from your battery or some other means?
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Old 09-07-2013, 07:05 AM   #3
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Thanks for the response..

I went from the battery to the red bypass on the relay. Fuel pump ran when I did that.

ok will do a closer examination of the fuse box.
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Old 09-07-2013, 08:51 AM
Posted in reply to THEMCGUIRE's post starting "Thanks for the response.. I went..."
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1) Does the engine crank over, but not start?

2) No SES when key is in the "ON" position right?

If the SES light does not come on.... I know this is gonna sound crazy, but we need to check a few things on the No SES side before we jump too far into the fuel electrical system.

I have the Manual with troubleshooting chart in front of me... The answer to the 2 questions above will help me narrow down the options

Yak

Last edited by crazedyak; 09-07-2013 at 09:14 AM.
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Old 09-07-2013, 09:07 AM
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NO SES LIGHT

---DOES THE ENGINE START-- YES

1) Ignition Off
2) Disconnect ECM connectors
3) Ignition On
4) Probe circuit 419 (brown/white) wire with test light to ground
5) Does the SES light come on?

If Yes
1) Faulty ECM connection or faulty ECM

If No
1) check fuse
2) faulty SES bulb
3) Open in circuit 419
4) Circuit 419 shorted to voltage
5) Open Ignition feed to bulb



DOES THE ENGINE START -- NO

--- Is the continuous battery fuse and ECM fuse OK?

NO
1) Locate and correct Short to Ground in circuit that had a blown fuse.

--- Is the continuous battery fuse and ECM fuse OK?

YES
1) Ignition Off
2) Disconnect ECM connectors
3) Ignition On
4) Probe Circuit 340 (orange) and circuit 439 (pink/black) with test light to ground
5) Is the light "On" on both circuits?

YES
1) Faulty ECM grounds or faulty ECM

NO
1) Repair open in Circuit that did not light the test light.


Do that check to clear your No SES light first... if the fuel pump issue still exists after that We'll tackle it. I had a similar issue, and found that a ground in the 419 circuit leading to the ECM which caused the ECM to just shut down everything fuel related. This may be your problem, but before we jump into the fuel system side we need to clear the SES issue first... they're likely the same issue.
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Old 09-07-2013, 04:03 PM
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THEMCGUIRE
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Had to look up SES on the web. Duh. ok Service engine soon light.

The engine will turn over. Have not tried to start when bypassing the fuel pump relay yet.

I will check all this Monday and get back to you. Thanks for the detailed troubleshooting guide.

( The wife does not allow me to work on this on Sunday)
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Old 09-08-2013, 06:47 AM
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No worries. Take you time. Don't try to get the engine running with the fuel pump bypassed. The fact that the engine turns over is enough to say yes/no to that troubleshooting chart.


Just so you know I had a very similar issue recently. Engine would turn-over, but not start. Never heard the fuel pump prime, assumed bad fuel pump but decided to check voltage at fuel pump and discovered NO 12VDC at the fuel pump. Scratched my head as I checked the entire power wire from the pump to the ECM. Then I realized I did not have a SES light at all. So I started checking power voltage at the ECM connector voltages and signals. I found a ground issue in the ECM. When I fixed that all of a sudden my SES Light problem was fixed and my fuel pump issue was solved too.

The ECM is the "brain" and if any signal going into the ECM is messed up then other problems will pop up that make you think something else is the culprit.
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Old 09-08-2013, 07:42 AM
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ok.

Taking a look at the following wiring diagrams I do not see the circuits you refer to:

http://coloradok5.com/forums/showthread.php?t=302678

These are all A, B, C or D and then a number.

What wiring diagram are you referring to to get your numbers ? 419 340 and 439 ?

================================================== ===========

Looking more I find that Connection A5 is brown/ white and labeled on master diagram as "Systems Check Light" Is this the one you mean ?
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Old 09-08-2013, 09:40 AM
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In the middle of that schematic you see the Fuel Pump Relay Circuit... The SES Lamp, pink/black 430 on the left and brown/white 419 on the right of the lamp.

The schematic and troubleshooting guide I am using is off the Original Chevrolet 1987 Light Truck Fuel, Driveability and Emissions Service Manual. This manual cover Fuel Injected Gas Engines to include the 1988 C/K Model.
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Old 09-08-2013, 10:50 AM
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THEMCGUIRE
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results

The wife went to her mom's. So I went out to try this.

Results:

Jumped test light from Brown/White (A5) to battery negative. Test light comes on and the SES lit dimly.

Jumped A5 to to A12 (labeled ground). SES Lights brightly.

Your instructions say:

---DOES THE ENGINE START-- YES

1) Ignition Off
2) Disconnect ECM connectors
3) Ignition On
4) Probe circuit 419 (brown/white) wire with test light to ground
5) Does the SES light come on?

If Yes
1) Faulty ECM connection or faulty ECM

What do you mean by Faulty ECM connection ?

How do I know if it's a connection or the ECM ? This ECM is only a few weeks old fyi.

Could I have fried the ECM when the fuel pump power line shorted out, I did not have line in snugly and it laid against the exaust pipe and melted and blew the ECM B fuse.

AND the Horn, headlights, and radio don't work and I do not see any connection from them to the ECM...
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