I need some help. I have a 99 250 psd six speed with 240,000 miles. Yesterday, the truck wouldnt crank over BUT the "wait to start" light would come on. I started by checking out all the fuses, key out of ingnition, with an ohm meter. I then realized it was the clutch safety switch, fixed that problem. However, now the "wait to start" light wont come on but it cranks. No fuses are blown. No control voltage to glow plugs. No electronic fuel pump voltage. I think its the pcm.
Make sure its not a blown fuse or power loss to the PCM before replacing the PCM. I can't remeber the fuse that poweers the PCM but I think it is under the hood. I got my newer PCM from car-parts.com for $75 delivered.
My "new" one came from a junkyard, contrary to what Ford will tell you most of them are interchangeable. If you want to be really sure everything stays the same then get your calibration code off your old computer and get another one with the same 4 digit code. I believe that any computer in the same family would work though. I got a used computer from an 01 and put in my early 99 and it works fine. I know the automatics can’t use a manual computer but I ‘think’ the manuals can use either.
On my early 99 the fuse that effected the wait to start light was micro fuse #30 located under the dash, it was a 30 amp. It was the same fuse on the fuel bowl heater that was blowing the fuse. Good luck
To update: I do have the early 99 psd. I have previously unplugged the fuel bowl heater, and the fuse isnt blown. On both sides of the #30 fuse there are 12 volts. So, unless there is a break in the line between fuse and pcm, i guess it would be safe to say i need a new pcm.
i believe i would do more diag before replacing the pcm, few and far between the pcm goes , bad , half of them that get replaced are replaced on a guess and really dont need it , so what im getting at , just make sure first, no wait to start light means no power to the pcm, dig a little deeper
Well, when you "fixed" the clutch safety problem, you seemed to create the next problem. Interesting. I'd look at that circuit there some more...the clutch thing, I mean. Make sure you didn't cross something up in your first fix. Just double check.
Is there anybody close enough to you to try a PCM swap with to satisfy your curiosity on the PCM before you commit to hunting one down?
First of all thank you everyone for the help and ideas.
Second of all i found the problem. It was the pcm relay diode within the fuse panel in the engine bay. I hope this is the real problem, not just patching a bigger problem.
everything is fine with the pcm now since i replaced the diode. Costs 3.59$ from ford.
The truck seems to be running better then it has in the past two weeks since i blew the 30amp pcm fuse because the fuel heater. So i think it has been a problem since then.
Man I love those cheap fixes, sometimes it pays to spend more time digging into things. That Scuffy is pretty sharp. Heck I didn’t even know it had a diode that worked in conjunction with the computer power fuse. I’ll have to remember this one.
i learned a long time ago that the pcm doesnt give any problems, like i said before , i think alot of them get replaced only on a guess and not actual diag , the fuel heater shorted probably overloaded th diode on his , the diode keeps power from surging into the pcm to eliminate pcm problems , but can be blown just like a fuse
man i just ordered a pcm from the dealer for 450 dollars. it was supposed to be here in two days as of last monday and it still aint here apparently it's nationwide back order and coming from canada i never even knew that it had a diode where is that the fuse box under the hood i've never heard of it either
the diode is located, in my early 99, all the way forward, towards the headlights, in the engine compartment fuse panel. Its small and black the size of a afd fuse(i think thats what its called), with the diode symbol on it. I tested it with an ohm meter. The new one or a good one should read unlimited in one direction, and 5-10 ohms in the other direction.
I found it in my ford manual, under the fuse panel section.
I dont have a camera at school, but i can get a picture up thursday if needed. Let me know.
i should be able to figure it out if not i'll let you know thanks for the info
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