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Cranks but won't start. No RPM signal, no check engine light

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Cranks but won't start. No RPM signal, no check engine light

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  #1  
Old 03-19-2018, 02:43 PM
Sam1980
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Angry Cranks but won't start. No RPM signal, no check engine light

Hello everyone,

I have 1998 F150 XLT with 4.6 liter engine. I was having intermittent problem starting and a lot of stalling. I suspected a bad fuel pump because the truck acted like it is starving for fuel, so I replaced it, but that did not fix the problem. I could not hear the pump running, so I took it back out and checked it outside of the truck and it works fine. I put it back on and the truck started just fine, then as soon as I put it in gear, it died and won't start back up. It keeps cranking, but won't start.

I noticed that the Tachometer is not moving at all while cranking. I also noticed that the check engine light does not come on when I turn the key on engine off. Other lights come on fine (ABS, Airbag, ...etc)
I also noticed that the fuel pump does not prime anymore so I jumped the fuel pump relay with a wire and I can hear the pump running. I also checked if there is gas pressing the schrader valve, and there is plenty of gas.

I tried starting the truck after jumping both relays (EEC power relay and fuel pump relay). I wanted to eliminate a bad relay, but nothing has changed. I tried swapping the relays with the horn relay and all relays tested good.

What else could it be?

I am thinking next thing to do is to check for a bad CPS, bad computer, or? and how do I test for these?

Thanks for the help guys!
 
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  #2  
Old 03-19-2018, 02:51 PM
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Old 03-19-2018, 03:10 PM
Sam1980
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Is there a way to check if the PCM is bad without buying a new one?
 
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Old 03-19-2018, 03:12 PM
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Bluegrass 7 has a very good reputation on FTE.Bluegrass 7 has a very good reputation on FTE.Bluegrass 7 has a very good reputation on FTE.Bluegrass 7 has a very good reputation on FTE.
When key is turned ON, this checks out all the dash indicators.
If your sure the CEL and some others do not light, there is a power failure to the computer.
In the engine bay fuse box is the PCM relay. Swap it with one of the others. Be sure all the fuses are fully seated.
If the computer does not get power, the fuel pump will not run nor would you see the Tack move..
These are the symptoms your describing.
Good luck.
 
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Old 03-19-2018, 03:24 PM
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Is this the right relay? The one in the top EEC power relay?
 
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Old 03-19-2018, 03:25 PM
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You could also try resetting the computer. Disconnect the battery clamps, touch them together for 10 minutes to empty the capacitors, then reconnect. Just a thought. When in doubt, reboot...
 
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Old 03-19-2018, 04:05 PM
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I swapped the EEC relay with the horn relay which works fine, and still cranks, but won't start. The pump still does not prime. I disconnected the terminals and touched them to reset the computer. I will go try to start again in 10 minutes and see if that helps. Thanks guys!
 
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Old 03-19-2018, 04:39 PM
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Originally Posted by Sam1980 View Post
I swapped the EEC relay with the horn relay which works fine, and still cranks, but won't start.!
After swapping relays, if the CEL doesn't light at KOEO, how can it start?
Did the CEL lamp come on at KOEO?
Did you check fuse #30 in the Junction Box under the IP?
 
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Old 03-19-2018, 04:40 PM
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I reset the computer in two different ways which are essentially the same, but nothing changed. Any thoughts on how to diagnose the computer without having to tow the truck to the dealership? I was thinking about going to the junk yard and buying a computer from there, but there is a chance that the computers in the junk yard do not work.

Thanks,
 
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Old 03-19-2018, 04:50 PM
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I am pretty sure I've seen some members on here unplug their PCM connector, ensure the connectors are good, plug it back in, and sometimes it was just a bad connection. Just a thought.
 
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Old 03-19-2018, 04:58 PM
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Originally Posted by pdqford View Post
After swapping relays, if the CEL doesn't light at KOEO, how can it start?
Did the CEL lamp come on at KOEO?
Did you check fuse #30 in the Junction Box under the IP?
The truck still does not start. CEL does not light up with key on engine off, and it does not light up when I try to crank it (key on engine on).
I checked fuse 30 and it is fine. Is this the 30 AMP fuse #30 you are talking about under the dash in this picture?



Thanks,
 
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Old 03-19-2018, 04:59 PM
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Question

Originally Posted by pdqford View Post
After swapping relays, if the CEL doesn't light at KOEO, how can it start?
Did the CEL lamp come on at KOEO?
Did you check fuse #30 in the Junction Box under the IP?
..............................
 
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Old 03-19-2018, 09:15 PM
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By now with no progress you need to begin checking voltages with a voltmeter.
Pull fuse #24 in the engine bay and check for voltage.
It's not uncommon to have a lead/ connector underneath go open.
If ok advance to the relay and on to the computer lead.
Again, the fuel pump will not run unless the computer powers up.
There will be no spark or fuel injection because the computer is not working and engine in not running..
The computer being faulty is the last thing it will ever be.
Good luck.
 
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Old 03-19-2018, 10:30 PM
Sam1980
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Originally Posted by Bluegrass 7 View Post
By now with no progress you need to begin checking voltages with a voltmeter.
Pull fuse #24 in the engine bay and check for voltage.
It's not uncommon to have a lead/ connector underneath go open.
If ok advance to the relay and on to the computer lead.
Again, the fuel pump will not run unless the computer powers up.
There will be no spark or fuel injection because the computer is not working and engine in not running..
The computer being faulty is the last thing it will ever be.
Good luck.
I know how to check for voltage after pulling fuse 24, but for the relay, should I check the voltage between 30 and 87 after I pull the relay or check the control side of the relay?
 
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Old 03-20-2018, 10:40 AM
Lime1GT
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Maybe this will help; Fuse 30/30amp (hot in run or start only) {under left side dash} supplies PCM relay pin 86 to close relay. Fuse 24/30amp (hot at all times) {engine compartment} supplies PCM relay pin 30. When KOEO or Start Postion, PCM relay pull-in closes by voltage applied to pin 86 through ground pin 85, relay pin 30 supplies power to pin 87 to supply power to engine systems.
 
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