ECU issues
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New User
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ECU issues
I need help from an expert on ECU's. I have a 1990 F150, EFI 300, 6, with 4 speed standard and overdrive. PS, Air and Pwr Brakes. I had the ECU replaced 5 yrs ago for and the mechanic put on a used part, he had in stock...now I have a lot of miss fires, fast idle and other problems that another mechanic said is the ECU, I have had the idle control changed, ERG replaced, Tune up, vac hoses replaced, but now need the replacement for the original ECU but we are having a hard time finding the right ECU. any suggestions on how to find the right one? 
Fleet Mechanic
Joined: Mar 2014
Posts: 1,926
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From: Saskatchewan Canada
Yup. Check for codes.
Is this a case of suspecting the wrong ECU may have been installed 5 years ago? Can you identify what version you now have? Has the truck been running poorly since the ECU change 5 years ago? What were the symptoms and the codes at the time the ECU was changed?
Reason I bring this up is it is far too common to blame the ECU for anything and everything. It is possible that the problem years ago was not the ECU and the original fault remains unrepaired. The scenario that has the mechanic replacing the ECU with a used one he had available, but possibly incorrect for the application greatly increases the chances that this may be the case. If you do have the correct ECU, it is possible that 5 additional years of service have aged the components, (usually some easily replaced capacitors), but outright failures of the ECU are relatively rare and would usually result in a completely inoperative vehicle.
Is this a case of suspecting the wrong ECU may have been installed 5 years ago? Can you identify what version you now have? Has the truck been running poorly since the ECU change 5 years ago? What were the symptoms and the codes at the time the ECU was changed?
Reason I bring this up is it is far too common to blame the ECU for anything and everything. It is possible that the problem years ago was not the ECU and the original fault remains unrepaired. The scenario that has the mechanic replacing the ECU with a used one he had available, but possibly incorrect for the application greatly increases the chances that this may be the case. If you do have the correct ECU, it is possible that 5 additional years of service have aged the components, (usually some easily replaced capacitors), but outright failures of the ECU are relatively rare and would usually result in a completely inoperative vehicle.
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New User
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Thanks for the reply, the truck has run great for 4 yrs, in the last yr it began a fast idle, and we replaced the idle control, no impact. the codes show a idle control issue, but we replaced the new one with a Ford original still no impact. now it has started a "missing and wrong fuel mixture" when it warms up...So my question is how do I determine what is the correct ECU? I can not find the numbers on the used one, they are worn off. I am at square one on knowing the original ECU numbers? I have had a ford dealer look into the VIN and Ford has not been able to tell me the correct original ECU? is there a vendor who would know? Seems Fords does not.
Logistics Pro
Joined: Mar 2005
Posts: 4,698
Likes: 47
From: Mexico, Missouri
There is a Calibration Code on the door jam. It's probably there or worn away. But it will help narrow down the correct PCM.
Now, next question...
Did the mechanic 5 years ago replace the PCM with a USED one from salvage yard OR a Reman PCM?
Next, I would pull it out and open it up and look inside for bad capacitors if it wasn't a Reman PCM, but just an d one laying around.
Now, next question...
Did the mechanic 5 years ago replace the PCM with a USED one from salvage yard OR a Reman PCM?
Next, I would pull it out and open it up and look inside for bad capacitors if it wasn't a Reman PCM, but just an d one laying around.
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New User
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Subford, thanks, Only part of the tag is available, the rest has worn off, I will post what I have, thanks..
As for the older one put on 5 yrs ago, it was one that the mechanic has laying around and he said it was off a "like truck"....it did work for 4 yrs...now a lot of engine problems that is why I want to get an original one back on my truck..
As for the older one put on 5 yrs ago, it was one that the mechanic has laying around and he said it was off a "like truck"....it did work for 4 yrs...now a lot of engine problems that is why I want to get an original one back on my truck..
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Cargo Master
Joined: Mar 2007
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From: Arcadia, Fla
Thanks for the reply, the truck has run great for 4 yrs, in the last yr it began a fast idle, and we replaced the idle control, no impact. the codes show a idle control issue, but we replaced the new one with a Ford original still no impact. now it has started a "missing and wrong fuel mixture" when it warms up........
It may not be ECU problem but a vacuum leak somewhere. I see you replaced all vac hoses in 1st post. Check for a vacuum leak around the intake manifold. With error codes of unable to idle AND improper fuel mixture. I'd look there before changing out he ecu and waste more $$$.
I use a can of carb cleaner and spray around intake manafold gaskets. Once you found a leak, the idle will drop till you stop spraying the cleaner.
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Thanks for the tips on the vac system, we have sprayed everything after we replaced all the hose/tubes. the manifold gaskets were replaced when we did the hoses/tubes. WE have also replaced the idle control twice, one aftermarket now have the Ford Motorcraft original part on. So we have followed a logical step process trying to get the fast idle and fuel mixture issues corrected. We have even replaced the water temp control sensor, to insure we were getting the correct output to ECU there. the ECU is the last step before I put the truck in my burn pit (just kidding)
Subford asked for the numbers on my numbers off the door jam. here is all I have
RO2 cae-6e06-ec
This is all I can find other then the vin number
Thanks for everyone's help
Subford asked for the numbers on my numbers off the door jam. here is all I have
RO2 cae-6e06-ec
This is all I can find other then the vin number
Thanks for everyone's help
Fleet Owner
Joined: Aug 2005
Posts: 23,667
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From: Easton,Ks
Sorry I can not help as there are five different calibration 1990 4.9L trucks that have a calibration number that ends with R02.
I need the center letters and numbers also. So far all I know is "0-???-R02.
If you have the sticker under the hood and you can give me the three letters at the bottom left on the sticker I might be able to do some matches.
In the examples below the letters are "DET" and "DEU".
/
I need the center letters and numbers also. So far all I know is "0-???-R02.
If you have the sticker under the hood and you can give me the three letters at the bottom left on the sticker I might be able to do some matches.
In the examples below the letters are "DET" and "DEU".
/
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