Hello all, I’m a new member to the forum and I’m in need of some help with my recently purchased 1995 XLT F150 5.0 automatic rwd. I bought the truck with a check engine light. Codes that came back are 558, 565 and 332. All my research led me to think I had a vacuum link in the truck. I’m no mechanic by any means but try my best to do all my own work on my vehicles. I figured probably a broken line or egr issues and could fix myself. I tried to trace the leak with a vacuum pump but essentially realized I wasn’t getting any vacuum from the main vacuum line of the block. I’m assuming pcm is not grounding and therefore no vacuum. I went to junkyard and pulled exact same pcm model my truck has code “JAB1” on it just like the original pcm. Once I installed no more check engine light. However now I’ve lost overdrive. I’ve tried to hit the switch on my gear selector but it doesn’t turn “on.” The “off” for the overdrive light stays illuminated and never shifts into 4th. I did not have this issue with my original pcm and have just gone down a new rabbit hole of what can be going on. Is the junkyard pcm faulty as well? Is the OD issue a pcm symptom as well or do I have a new problem? Sorry for the long rant but any tips or info you guys might have is greatly appreciated.

 

How did you test the “no vacuum” to the EGR? You will not have vacuum to the EGR valve at idle. It will only open under certain conditions when driving.

What about the rest of the numbers on the PCM? Are the same engineering numbers on both parts?

 

Swap back your other pcm, that will tell you if it’s a new issue.

 

I watched a YouTube video of somebody showing how to diagnose your egr and vacuum system. The video showed if you have a vacuum pump on the line to the egr at half throttle on a warm engine I “should” see vacuum pressure build at least a little bit. I had a warm engine and tested for vacuum pressure at multiple different rpm ranges and gauge never moved.

Yes, I also verified the part number I believe? I read in another forum to verify the 126A50 and matched them

 

I will swap back to original pcm today and see what happens. The fact that the check engine light went away on the junkyard pcm does confirm my suspicions of the original pcm being bad though right?

 

Update!
So I swapped back to my original pcm and OD is not an issue now. I can hit OD switch on gear selector and it functions on and off no problem but check engine light is back on. So I’m guessing junkyard pcm is no good as well and need to order another or repair one of the 2 I have. I’ve opened up my pcm as well to see if there is anything wrong. I’ve read the capacitors can go bad and leak but both pcm seems to look just fine. No corrosion on the board or anything broken. Is it possible the pcm isn’t the cause of my vacuum leak?

 

I don't know but my 95 5.8 does not have the capacitors that leak like the older versions. I do have a California truck w/MAF and E4OD

 

That makes sense. Im honestly getting to the point where I’m ready to let the CEL be and just drive the truck as is but I’m worried about damaging anything else with the truck

 

CEL light on means codes are present. Have you read codes? Post your results.

 

Yes I have the codes that are present are 558, 565 and 332.
Code 558 EGR vacuum regulator solenoid did not respond.

Code 565 Canister Purge Solenoid Circuit Fault

Code 332 EGR did not open during test. The EGR is activated by the pcm switching vacuum to the solenoid from what I read.

I also replaced EGR position sensor and EGR vacuum solenoid and neither resolved issue.

 

What type of EGR do you have? There is the simple version that just measures if it is on or off. Then there is the more sophisticated version that has a sensor that actually measures the lift of the valve [I believe that's what it does]. The more sophisticated versions came on the California models. At least, that is what I got.

Knowing what type you have could change how you are going to diagnose it.

 

Interesting that makes sense. I do have a California truck as well. It was bought from SoCal. I might be diagnosing the EGR system incorrectly then. I had not read anything on the 2 different EGR systems. Do you know what I would need to be diagnosing differently?

 

Just so you understand, I am not a Ford guy and probably never will. I work on high end German cars and I have owned my 95 Ford since 97. That is my limited experience with the Ford products.

There is a type of EGR that Ford uses and it measures the pressure difference of the EGR flow when it's on. That is what I got [95 5.8L CA]. You might have it to. If there is flow [and the right amount] across the EGR vale, the computer will be happy and not turn on the light. If there is no flow or the wrong flow, the computer gets mad and turns on the light and probably changes the ignition timing. The flow is determined by the transducer and it determines using the pressure drop measured at the large vacuum lines attached to the transducer.

I believe the older systems just assumed the EGR valve is working if all the EGR electrical connections are made. It does not know if the exhaust is actually flowing into the intake manifold or not. Easier to bypass for those that like to do that thing.

Here are a couple pictures of my EGR valve.


EGR Pressure transducer

EGR Valve

 

I just wanted to update everyone because it was driving me insane not being able to figure this out. I went to the junkyard this weekend because I couldn’t shake the feeling I just found a bad pcm. I found another pcm matching my part numbers and no more CEL and I have my OverDrive back in my truck. Thanks for everyone’s input.

 

Thanks for reporting back. All too often threads get started and there is no official ending. Good for you that you found a computer at a junkyard.