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88 K5 Will not run - only 8.48 v at fuel pump!

T

THEMCGUIRE

1/2 ton status
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Jan 15, 2009
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Location
Las Vegas, Nevada
Driving along, truck just died. No fuel at injectors.

I replaced the: fuel pump, fuel sending unit, filter, fuel pump relay, MAS sensor. I shot compressed air through the fuel line from the pump to the filter.

Still will not start, no fuel. Starts with starting fluid.

I am getting 8.48 volts at the white striped tan wire going to the fuel
pump.

Is this enough voltage ? If not, Can I send 12 volts directly from he battery?

If it requires 12 volts any ideas why voltage is low with new relay and pump?
 
There is a fuel pump relay located on the firewall behind the right side of air cleaner.
it has a red wire hanging out of it not connected to anything. Run 12v + from the batt to the red wire. That bypasses the relay, Your fuel pump should run.
Possible that the contacts in the relay are worn and not passing full voltage.

Behind the distributor there is a oil pressure sensor. It is aslo wired in the starter circut. It is a failsafe that will keep the engine running as long as there is oil pressure, if the fuel pump relay fails. Possible that voltage drop may be there.

Also could be a bad dist module or pick up coil as said above.
But the fuel pump should still run if 12v is connected to the relay bypass wire no mater what.
 
Thanks for the advise.

I tried the relay bypass and got 12 volts at the fuel pump. Still no start.

I replaced the Ignition control module also no start

A MAJOR point I forgot to mention is that The engine starts and runs as long as I spray starting fluid.

Also, I had put it out of my mind but:

This is my second new fuel pump. I had the key on when I connected the battery after putting in the first fuel pump. But I did not have any gas in the tank. I heard a loud whine and then nothing. I had fried the pump because it did not have any fuel to lubricate it. This means that the electric to the pump was working.

So I have now ruled out the following:

1. Ignition because it starts and runs with starter fluid.
2. Electrical because I was able to fry the first fuel pump and now have 12v at pump

I do not see or smell gas at the throttle body. Tomorrow, I am going to disconnect the fuel filter and see if it is pumping any gas.

Also, is it a good idea / safe to blow air from the fuel filter to the "carb"?? Will this damage the injectors?

This test would eliminate any issue of cloging - is there a proper way to do this test ?

Any other ideas ?
 
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I tried the relay bypass and got 12 volts at the fuel pump. Still no start.
Click to expand...

If the pump wont run when you power the bypass and you have 12V back at the pump it is either bad or maybe the wires got disconnected in the tank.

If you replace the pump it is best to use only AC delco replacement or genuine Walbro.
many of the rest of the fuel pumps are imported fron china junk.
 
88 K5 still will not start - Could it be a safety switch?

I connected the fuel pump directly to the battery and disconnected the filter. Fuel flows to the filter.

I disconnected the fuel line to the back of the throttle body and shot air through it Air flows - apparently no blockage.

I cannot find a fuel pressure regulator. Fuel line flows from tank directly to throttle body via the filter. Could the fuel pressure regulator be part of the sender unit (Sender unit is new also) I do not have any floors or fenders on the truck right now total rebuild pending so everything is exposed.


Another issue I had forgotten until now ----

This truck was towed by the police for being on the street too long -49 hours. They did not have the key so they disconneced the linkage from the trans. When I had it towed back home the driver reconnected it.

However, I can push this truck forward and back while in park. I do not know why and was putting this off until I got the body back together.

Like I said it will run with starting fluid but not stay running. I thought that if it will start with the starting fluid then it could not be the Park /Newtral safey switch. But could this have been messed up when it was towed?

Any ideas...
 
i dunno if you fixed this yet but you can pinch off the return line to see if its the regulator. only problem with that is the soft parts on the lines are steel braided. and when u jumpered battery voltage into the relay did you get battery voltage at the pump. and did you clean and tighten the bolt on the frame for pump ground? i only ask cauz bad ground or wires can cauz voltage drop resulting in low psi.
 
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I have not worked on it for a few days. Some town inspector came around saying that since the truck was just a bare bones it made my place look like a junk yard. I have a tent as big as a garage but not wide and it is hard to work in it. So I am trying to figure out how to continue "inside" the tent.

I do get 12 v when I bypass the relay. I plan on running a new line from the pos side of the relay. I also want to check the voltage at the injectors. Could it just be a fuse?

I will check all this when I figure out how to work on it and report back.

Thanks to all for your advise.
 
this is gonna be a bad wire or connection... check your grd wire too....
 
ryoken said:
this is gonna be a bad wire or connection... check your grd wire too....
Click to expand...


I second the ground wire. I have had these kind of problems on my 89 k5. I dropped the tank and put it the new pump and found that the wire going to the frame was badly corroded.

Once I fixed that it ran like new. Wish I'd found it before dropping $$$ on a new fuel pump I didn't need.

Oh well....
 
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