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No Start - Possibly Fuel Pump???

3K views 18 replies 3 participants last post by  speeddemon31176 
#1 ·
I have been gone from the forums for a long time but need some help.

I have a late 99.5 7.3.

I was driving home Sunday night and the truck started running rough/ no power even if I mashed the go pedal. I pulled over and the truck shut off and would not start again.

I still get the Wait to Start light but what seems to be no power to the fuel pump. The fuel pump does not hum or make any noises while the key is on.

I checked the two leads at the pump to see if it was getting any power while the key was on and I do not.

What could some of the other problems be?

I checked all the fuses under the dash and under the hood. They are all good. I swapped all the relays with one another as well and still no luck.

Any info would be greatly appreciated.
 
#2 ·
Just happened to another member. His pcm was bad.
 
#4 ·
No code will come up. It is a burned circuit on the board that doesn't allow the pcm to complete the ground circuit.
 
#6 ·
One thing you could check that I forgot about is the inertia switch. It is in the pass side kick panel below the glovebox. Push down on the red button. There is a small access hole there for your finger to fit in. Sorry I forgot about it.
 
#8 ·
I checked the inertia switch and it was fine.

I removed the pos and neg wires from the fuel pump and I get 6.6V with the key on. When I connect the wires back to the pump, I get nothing. I'm assuming that means the pump is bad?

I called around to the local dealers and a new pump is $440. I remember them being much cheaper for some reason.
 
#9 ·
6.6 volts is no where near enough voltage to run the pump. You should be seeing battery voltage at the pump. How are you testing voltage with the pump connected? You should test it two ways. First test across the positive and negative posts at the pump and then from the positive post on the pump and a chassis ground such as the frame and see if you get two different readings.
 
#10 ·
I tested it the two ways you listed and I get nothing. I only get the 6.6v when I remove the two wires from the pump. There is also an electrical quick connect near the pump. When I check those two pins, I get 6.6V as well.

I thought about running wires directly from the battery to the pump with a toggle switch just to check the pump but the 6.6V had me concerned. I assumed the pump should get 12V but was not sure.
 
#11 ·
That is the fastest, best way to test the pump itself. If you have a spare battery or a charger you can make up some quick pigtails and test the pump. You have a problem in your wiring somewhere. Take your kick panel off on the pass side and test for power there as well. If you have 6.6v there as well You will have to go back to the relay and test the output wire to the inertia switch for power. Basically keep tracing it back till you find the problem. One good place to look would be under the rocker moldings in the harness from water intrusion. Also check the connector for the wiring harness on the driver side frame up near the inner fender.
 
#13 ·
He said he already did that in his first post. Stated he checked all fuses and swapped all relays around ending up in the same situation.
 
#15 ·
Eh, easy to miss in a couple of pages. I forget who the other member is that just had this same issue and we narrowed it down to the pcm. I hope this member gets lucky enough to just have a corroded wire along the way. One of the best tools you can buy for diagnosing these types of problems is the Power Probe III. I can supply 15A at up to IIRC 36v. It does continuity. It reads voltage as well. It is lighted. You can create a ground with it as well. Comes with something like 60ft of cable and two power adapters and a nice hard case. The best 100 bucks I ever spent.
 
#16 ·
Ended up being the fuel pump. I'm still not sure why I was only getting 6.6V when the pump was not working. With the new pump hooked up, I was getting 12.7V at the connections.

I replaced it with one of the aftermarket Airtex pumps. It is a direct replacement other than being shorter than the factory pump. Total cost of the pump with a 20% discount I found online was $131 with tax.

I can tell the difference in how the truck runs with the new pump.

Thanks for your help.
 
#17 ·
Glad you got it fixed and thanks for the follow up. That is odd that the voltage was off with the bad pump. Internal short?
 
#18 ·
I have no idea why the voltage was so low with the bad pump. I ended up running two wires directly to the pump to check it and it got hot fast.

On a side note, it took awhile to get the truck started after the new pump install. I'm assuming it was the air in the lines. I bled the fuel bowl and it seemed to solve the no start problem.

I'm hoping the new Airtex pump has some decent life to it. I got almost 10 years out of the factory pump but did not want to pay the $425 price tag from ford for a factory pump. The good part is that it only took me about 10 minutes to take the old pump out and put the new one in. The hardest part was getting the old pump out of the bracket and the new one back in.
 
#19 ·
If it got hot fast then it was shorting out internally. Yeah air in the lines will cause starting issues. Airtex pump should last a while.
 
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