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  #1 (permalink)  
Old 07-04-2011
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Join Date: Jul 2011
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Default F115 HP Fuel Pump Problem

I have a F115 that will not start. The ECU is not grounding the fuel pump connection. The fuel pump works when wired straight to 12vdc. Motor will start if pump is running.

According to the manual, there should be two electrical connections to hook up a test light to review codes. I can only find the blue/white wire. The red/black does not appear to be there. There is a red/black in the test socket but I can't figure out how to see if there are any trouble codes.

Any help would be appreciated. Thanks!
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Old 07-13-2011
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That wire should be there but if it is a fuel problem then that wont activate any codes.
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Old 07-16-2011
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Thanks for the feedback. I believe I found the problem. I am able to get the engine to run by removing the harness from the fuel pump and straight wiring 12 VDC to the pump.

There is +12v on the harness but the ECU won't ground the other side. I was trying to wire in a test light and haven't been able to make it work properly. If I connect the light to the red/black in the test port and the blue/white test connection, the light will burn about three seconds at key-on and then go out. It will briefly come on during starting. It will not flash the "heartbeat" or trouble codes (if any).

While troubleshooting, I found that if I push in on the center of the ECU, the fuel pump will ground and come on. I was able to repeat this several times and even made a device that would keep pressure on the ECU long enough to run the engine.

After reading numerous posts, I began taking temperature on the ISC. It's hard to be sure if I'm gettting a temp from the same spot every time but it appears that the ISC is approching 190-200 degrees F.

Rodbolt17 stated in several posts that this could be due to the ISC sticking and would lead to damage to the ECU.

I ordered and received a new ISC and ECU. I tried to test the old ISC but was unable to verify any movement. Before removal, I could hear it clicking on key-off, but not everytime.

After installation of the new ISC and ECU, I want to make sure that I don't toast either one again... I started the engine and was taking temps on the ISC and when it got around 160 I shut the motor down. I don't know if 160 is normal but I'm a little gun shy at this point.

Also, before removing the old ECU I tried to verify voltages, particularly the 5 volt reference. The only place I can find it is in the test port. I may have to order the test harness' to test the other sensors. Anyway, I can only get 4.32 volts on the white/black wire at the test port. I get 12.6 to 13.5 on the red/black at the test port.

I get the same reading after installing the new ECU.

Prior to this issue, I replace all four fuel injectors and did the service on the VST, cleaned the HP fuel pump screen/filter, replaced the idle speed control filter, LP fuel filter, ignition coils and plugs.

Any guidance would be much appreciated.

Thanks! Lightfoot
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Old 07-21-2011
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Join Date: Jul 2011
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Does anyone have a "normal" temperature for the ISC solenoid valve? Or suggestions on where to test for the 5 VDC other than the test socket? Could a sensor be causing the .68 +/- voltage drop from 5 volts or should I even be worried about this?

Again, thanks for any and all input.

Lightfoot
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Old 07-22-2011
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I recently took my 2006 F115 in for some work. A fairly knowledgeable mechanic said that the isc does get "hot" normally. How hot is hot, I am not sure. He had also replaced a users ecu because of an isc overheat issue. Maybe someone with better knowledge can shed some light on the "hot" issue.
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Old 07-22-2011
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Thank you for your input. This is a great forum.

I work with digital control hvac systems and we have some valves that are driven by solenoid actuators. They also get pretty warm when energized, but they basically only operate in one direction and have to hold at various points/voltages.

I'm assuming that the ISC is similar and if it is driven to a point and held there by the magnetic field, there will be heat generated. If it is driven both open and closed, it may generate more than the above mentioned actuators.

Like you, I just don't know how much is too much...

Since I just replaced it, I hope that it is okay to operate and it won't damage my new ECU. I'm still worried about the 5 volt part of the circuit.

Thanks again!

Lightfoot
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Old 07-23-2011
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Join Date: Jan 2011
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I've checked temps on the F225 idle speed controllers and normal operating temps are in the 160-170F range. When they are bad from an ECU problem they get around 200F. I havent' had problems with the F150 models yet so I don't have exact readings for you. Use these temps only as a guide.
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Old 07-23-2011
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Thanks Seahorse5!

That confirms the temp I got after replacement. Hopefully everything is okay. I'm going to take the boat out this weekend and will update later on how it operates.

Lightfoot
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Old 07-25-2011
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I took the boat out Saturday and I didn't have any problems related to the HP fuel pump or the ECU. Granted, I didn't stray too far from the hill but I was pleased that it ran solid and didn't leave me stranded.

Lightfoot
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