7.3 Intermitent lose of power at hwy speeds - Ford Powerstroke Diesel Forum
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post #1 of 17 Old 07-26-2017, 01:45 AM Thread Starter
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Exclamation 7.3 Intermitent lose of power at hwy speeds

Hi, I've taken my truck to a diesel mechanic and they seem to NOT understand my problem.

At first I had a No Start While Hot condition. Faulty CPS was ruled out by installing new Ford OEM one right after it died suddenly on the hwy. When a Faulty CPS code was scanned I told the shop that and suggested maybe bad CPS pigtail. They changed pigtail and had same problem. The truck was brought to the shop and ran until it died suddenly. Air was blown on the IPR cooling it and then they were able to start the truck while hot. However, road tests showed good power and acceleration until it hit 100 km/hr and then dead throttle pedal. They tested fuel pump and it fell within specs so the shop said they needed to replace the HPOP for $2200. I road tested it and was experiencing intermittent lack of throttle response at city driving speeds.

After paying $331 for CPS pigtail replacement and diagnosis and $961 for IPR replacement I couldn't afford the $2200 for HPOP replacement.
I ordered a HPOP from DieselPartsCanada out of Edmonton, Alberta for $964 and replaced my HPOP. Now I experience an intermittent lose of throttle response at speeds above 72 km. About every 4-5 km, I would get no throttle response while travelling 80 km down the road until the truck slowed down to 66 km then the engine would respond as if it just got fuel and I could press the accelerator down to get back up to posted speed.

Before giving quote for HPOP replacement the shop had tested IDM for voltage (14) and did a buzz test to determine if injectors were working. They said they got good sound from all cylinders on the buzz test. They also tested the fuel pump and said it fell within specs.

The truck starts cold and hot. It sounds like it should. I've test driven it at speeds in between 66 km and 72 km whereupon it runs rough until either I lower the speed to below 65 km or increase speed above 72 km. I can drive at speeds lower than 65 without problems (??), but driving at speeds above 72 km after a few km I lose throttle response.

Even though instrument testing of IDM was ok, I'm thinking faulty IDM. At this point its either the IDM or the fuel pump.
I am going to order a new IDM. Is this what I need? Any help would be appreciated.
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post #2 of 17 Old 07-26-2017, 02:46 AM
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Throttle position system... They are known problems.. that would be my next step... How many miles are on your truck?


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post #3 of 17 Old 07-26-2017, 11:14 AM Thread Starter
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Just spoke with shop diesel technician and that is what he is suggesting. These guys are the go to diesel mechanics in my small town of 7000+ residents. I have 431,000 km on this truck. The tech said there is a sensor on / near the foot pedal that I can order for $104 plus tax.

He also suggested cracked oil line pickup from low pressure oil side may be causing this problem with low oil pressure send to the HPOP and to run front end up ramps to test that.

From all their experience in powerstrokes this the first time they seen / heard this "Ghost" symptom. So instead of replacing IDM or the Fuel pump and cleaning in tank fuel filters I may as well order that sensor. I don't have a lack of fuel symptom at 1/4 tank, but then again current tank is just above 1/2 full.

I'm going to try and see if I get rough running in a lower gear (1 or 2) at approximately the same throttle position.
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post #4 of 17 Old 07-26-2017, 12:13 PM
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+1 for TPS
I used a lot of compressed air and WD-40 on my buddies and its been trouble free for over 1yr
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post #5 of 17 Old 07-26-2017, 02:36 PM
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Glad it's the tps


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post #6 of 17 Old 07-28-2017, 06:35 AM Thread Starter
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I have replaced the TPS and it has NOT solved the problem. I still lose throttle response at in each gear at a certain speed and every 4 km above 72 km.

I lose throttle response: 1st gear at 28 km and 1700 rpm; 2nd gear 38 km and 1400 - 1600 rpm, 3rd gear at 68 - 71 km it runs rough. Above 72 km I lose throttle response every 4 km - doesn't matter which speed from 77 km all the way up to 130 km.

I'm at a loss, what next?

It's a 1999 F350 Lariat Crewcab with 8 ft box and 7.3 powerstroke, basically stock with AutoPage RS-455 remote car starter, BD Turbo Mount Engine Exhaust Brake, BD X-Monitor.

... and has 431,000 km on it

Last edited by Ford CeLaVie; 07-28-2017 at 06:40 AM. Reason: to add vehicle information
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post #7 of 17 Old 07-28-2017, 06:35 AM
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U replaced the entire assembly?


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post #8 of 17 Old 07-28-2017, 07:07 AM Thread Starter
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I replaced the Throttle Position Sensor with a new one.

Removed wire pigtail, unscrewed two screws and put new TPS back on making sure it aligned with the slot, then took a test drive.

I now understand what you mean - "replace entire assembly". No, I just replaced the sensor, however I noticed from another site the slot position of the pedal is vital.

In order to put in new TPS and align it with the pedal mechanism, I had to tilt the TPS up and forward, then pull it back down to align the screws to their respective holes.

Obvious from reading information from another site this changes the voltage signal of the TPS. Any thoughts? replace pedal assembly or try to fix current pedal ?

Last edited by Ford CeLaVie; 07-28-2017 at 08:02 AM. Reason: add more information
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post #9 of 17 Old 07-28-2017, 06:38 PM Thread Starter
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I took pedal assembly out and put TPS in. It is very close tolerance to NOT have TPS spring to be at rest without it being turned in any such way by installing it. And lack of throttle response is same as old TPS.

The recovery of throttle response is very RPM based. For example: If travelling at 85 km/hr and I lose throttle response, if I hit the brake and drop RPM to about 1200, I regain throttle response at 80 km/hr. ????? If travelling at 80 km/hr and drop rpm to 1200 I regain throttle response at 74 km/hr
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post #10 of 17 Old 07-28-2017, 06:40 PM
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Fuel delivery?


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