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Poor Idle, Loss of Power, Stutter

 
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Old 04-18-2019, 09:16 AM
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Exclamation Poor Idle, Loss of Power, Stutter

Hi everyone, this is my first post so bear with me. I have a 94 F150 XLT, 5.0 V8, 2x4. The truck starts fine, but the idle RPMs fluctuate. When it is up to normal operating temp. it starts to almost die then the RPMs go up. It has died twice in the past couple days while driving. I wait a couple min. than it starts right back up. It also has a lot of hesitation when driving in low speeds. You push on the gas, but nothing happens until it is almost all the way down, then it downshifts really hard and works fine. It does this off and on. the engine light comes on and off also. Some times when it I hesitating I can hear and feel a knock either from transmission or engine. So far I have replaced the following parts (EGR Vacuum Solenoid, Throttle position sensor, Idle air control valve, new thermostat and engine temp sensor. I have cleaned the throttle body and flushed the coolant system). I did check the EGR system with a multymeter and charged the vacuum solenoid to activate the EGR. It all seams to be working fine. I did notice during my check of the EGR system that the ground wire to the EGR Vacuum solenoid is reading 2.5 volts when unplugged. Should it not be at 0? Any thoughts on what could be causing this or what to check next? Thanks in advance.
 
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Old 04-18-2019, 09:58 AM
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The first thing I would do is to see if you have any codes stored in the ECU. After that, I would clean the IAC valve.
 
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Old 04-18-2019, 10:13 AM
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I have tried getting codes, but when I plug the reader in it says there are no codes. I bought an OBD one code reader just for this. I think it is because the check engine light only comes on while driving. When I parked the car the light goes off. The idle air control valve is brand new. That was the first thing I changed. I have also pulled the computer and checked the capacitors to see if they were all intact and all looked brand new.
 
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Old 04-18-2019, 11:03 AM
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I want to question the Keep Alive Memory of your computer then, especially if it is not communicating with the code reader. Pull the ECM and give it a visual.
 
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Old 04-18-2019, 11:10 AM
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I agree with the above. Non communication with the computer generally means it's toast. Pull the computer and look for blown/leaking/corroded capacitors. All the symptoms you describe can be indicators the computer is toast.

If you are handy with a soldering iron many times you can repair it yourself, but then there may be other problems that are not so readily apparent to just a visual check.
 
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Old 04-18-2019, 11:11 AM
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If the Check Engine Light (CEL) came on when driving it will have a stored code. If the code reader "says there are no codes" that means it is not communicating with the computer. If the Key On Engine Off (KOEO) tests pass the code reader will display Code 111 System Pass. If there are no codes stored in Continuous Memory the code reader will display Code 111 System Pass. If you ran the Key On Engine Running (KOER) tests and everything passed the code reader will display Code 111 System Pass. Anything less means the code reader is not communicating to the computer or the computer is seriously compromised.

Clean the data link connector pins with contact cleaner or if they are really corroded use a small finger nail file to clean them. Once the pins are clean use the code reader again.
 
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Old 04-18-2019, 12:23 PM
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Thanks for all the responses. I will try what was mentioned and see what happens.
 
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Old 04-18-2019, 01:02 PM
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Non-Motorcraft IAC valves are crap in my experience.
 
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Old 04-19-2019, 11:21 AM
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OK, so I pulled the ECM, Open it up and it looks brand new. All the capacitors are connected nothing is leaking, there are no burn marks, on both sides. I put it back together plugged it in and my code reader is still not communicating with the computer. I also tried the paper clip method to verify that it was in my code reader and even with that I cannot get the check engine light to flash whatever codes are stored. All the capacitors are connected nothing is leaking, there are no burn marks, on both sides. I put it back together plugged it in and my code reader is still not communicating with the computer. I also tried the paper clip method to verify that it was in my code reader and even with that I cannot get the check engine light to flash whatever codes are stored. Any suggestions on where to send my ECM to have it checked out further?
 
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Old 04-19-2019, 11:46 AM
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Electrolytic capacitors on the board are 25+ years old. They might look OK but that doesn't mean anything. If they show visible leakage they are always bad but the problem there is bad caps don't necessarily leak. In fact they usually don't. Any piece of equipment with 25 year electrolytics should have them replaced as routine maintenance no way around it.
 
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Old 04-19-2019, 01:41 PM
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Clean the data link connector pins with contact cleaner or if they are really corroded use a small finger nail file to clean them. That's cheaper than tossing in a "rebuilt" PCM for no reason. Eliminate that as a cause for your no code issue. Then move onto the bigger ticket items.
 
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Old 04-19-2019, 03:34 PM
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Originally Posted by rpupo View Post
Hi everyone, this is my first post so bear with me. I have a 94 F150 XLT, 5.0 V8, 2x4. The truck starts fine, but the idle RPMs fluctuate. When it is up to normal operating temp. it starts to almost die then the RPMs go up. It has died twice in the past couple days while driving. I wait a couple min. than it starts right back up. It also has a lot of hesitation when driving in low speeds. You push on the gas, but nothing happens until it is almost all the way down, then it downshifts really hard and works fine. It does this off and on. the engine light comes on and off also. Some times when it I hesitating I can hear and feel a knock either from transmission or engine. So far I have replaced the following parts (EGR Vacuum Solenoid, Throttle position sensor, Idle air control valve, new thermostat and engine temp sensor. I have cleaned the throttle body and flushed the coolant system). I did check the EGR system with a multymeter and charged the vacuum solenoid to activate the EGR. It all seams to be working fine. I did notice during my check of the EGR system that the ground wire to the EGR Vacuum solenoid is reading 2.5 volts when unplugged. Should it not be at 0? Any thoughts on what could be causing this or what to check next? Thanks in advance.
my 94 f150 5.0 is doing the same thing. let me know if you find the issue.
 
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Old 04-22-2019, 03:28 PM
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OK, so I have tried all the suggestions with no success. Does anybody know anywhere I can send the computer to have it checked or anything else I can check?
 
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Old 04-23-2019, 10:25 AM
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rla2005 will not steer you wrong. You may be able to find a computer at a u-pull-it from a truck with the same options that will let you check the theory. Any used ones are likely to be bad aswell. Find my thread and check the pin connections for the computer grounds as ZombieF150 directed me to do. 60/40/20/16 are the pins, guessing by memory.
 
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Old 04-23-2019, 10:28 AM
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Originally Posted by Gary Brewer View Post
my 94 f150 5.0 is doing the same thing. let me know if you find the issue.
Visual of your computer is a pretty cheap / cost effective check.
 

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