I have a 92 f250 with the 351w auto and it has some mods, gt40 heads/ cam to match, 5.0 tune up, headers and 2" dual exhaust, this was done about 5 yrs/ 30K ago
The problem occured last week. this all happened within 2 miles,
I filled up and when I restarted it the amp gauge clicked and quit, then I put it in gear and it died, hmmm, started right back up put it in gear again it died, started it back up idled it up and took off, ( engine light was no longer coming on , read below), did this at the couple of stop lights and i parked it for about 15 min. then I went to leave and the oil and temp gauge no longer were working dont know if the gas gauge quit as it is still at full.
1) dies at idle in gear/ idles rough out of gear
2) amp gauge quit and the oil pressure and temp gauge are either stuck or quit
once up to speed itll run ok but below 1000 rpm it stumbles
the engine light which always came at idle and over 1200rpm is no longer lighting up
the speedo, odometer and i think fuel gauge ( just filled it up) work fine


this truck only get drove on the weekends and in nice weather but it has sat outside it whole life, so moisture in the wiring could be at play
Any thoughts on what to check and how to before i tear into the beast.
thanks

 

It's always a good idea to pull codes first, with engine off first then while running at operating temp. I suggest reporting back those findings. If your like me, it's easy to think what could be causing the issue, but when it comes down to it, you have to diagnose the problem and work to eliminate possibilities.

After you pull the codes, I would eliminate spark or fuel issues, even though it looks like an electric issue. You need to determine what's being affected. Verify fuel pressure, then vacuum. If you don't have the gauges to check, I'd suggest you grab them now, they'll help you eliminate possibility rather than throwing parts at the issue. Next I'd pull the SPOUT and check timing, if it runs any better (I.E. doesnt die) with SPOUT out, that tells you something. Would remove the PCM and open it up to look for bad capacitors.

-Glaser67

 

thanks Glaser for the qwick reply
Lots of stuff to look at but it all makes good sense for sure
Ill have to pickup a fuel pressure gauge this week, as i have the rest.

 

There is a lot going on here that you may want to detail out a bit.

Followed by;

So,

You have been driving for 5 years with your check engine light on? Did you ever read codes to determine what the cause was?

So, you have pretty much lost any gauge indications from your engine? All these systems are independent of the EFI system. Have you checked fuses? The first indication, (the amp gauge) is particularly confusing. The gauge "clicked and quit"? Is this the factory gauge? As far as I know, all 92 and later F150's were equipped with a voltmeter, not an ammeter.

So, I suspect you may have some issues with modified parts of your vehicle. The check engine light may well have been from a missing, or malfunctioning O2 sensor. The ammeter may be an add on and the wiring has failed, leaving parts of your vehicle without power. As these all are non factory issues, only you can provide the info needed. Myself and anyone else will just be guessing.

None of this points to a PCM issue as your title suggests.

 

The engine light is from the O2 sensor not being close enough, when the made the exhaust they placed it to far back i figured, I forgot to mention when above 3k rpm it went out again.
It runs like a scalded dog and gets 15-17mpg for the last 5 yrs so i never messed with it,
One thing i forgot too,the is not shifting correctly either, I manually shifted it to get home.

So ya im getting nothing from the engine, Ill check the fuses, and the volt ( sorry use to my tractors) gauge still clicks a couple of times when I started it the other day, weird eh?

first Ill check fuses, then wiring harness make sure its OK, then go from there
with all thats going on all at once thats what made me think of the pcm

 

I have had one of the connectors on the back of the instrument cluster back out on it's own before. Cold all the gauges worked, when it warmed up up a few went dead. Very consistent, that was the weird part. When I started to pull the cluster the connector near the center of the truck fell out on it's own.

 

well i think i found the root cause of the problem.
I checked all the fuses and they are good and the correct ones. So i fired it up and since the volt gauge quit I tested the volt output of the alt. its a constant 15v no matter if its idling or at 3500rpm.
I'll pull it and take it to my guy and have him test it and replace it, then dump the codes. and go from there.
I'm thinking it spiked and took everything out. I know it should of took fuses out if that's what happened.
The alt has been acting strange lately as in never charging consistently, had it tested in january and it check good too.
I'm hoping it didn't take any of the trans sensors out, if it did then its decision time on the fate of it.

 

Did you measure your alternator output at the alternator stud, or at the battery terminals? Is there a difference between the readings at both points? If so, check you primary alternator wire. There are fusible links at the starter solenoid where everything ties into the battery +, possibly you have blown the one to the alternator.

Also, you likely have the dreaded 2G alternator which is famous for connector failures. If that is what has happened, you will find out soon enough when you remove the alternator. If you are replacing the alternator, the 3G upgrade is highly recommended.

 

I only checked at the battery, but at best it should read only 13v iif the fuse is bad, but i will check fuse and output at the link.
and what do you mean by by 2g and 3g?
Its the original alt so i guess it gave its all.
this truck only has 103k and that's because I had to drive to work for a little over a yr. and put 25k on it.

 

If you can measure 15 V at the battery, you are cooking your battery!

Before you get too alarmed though, try another meter. Sometimes our measurements are in error.

Terms like 2g and 3g refer to new generations of the same product. Actually, I really hate the term, but it is in common usage so.......

Best description may be a link to this commonly discussed topic. There are others, but try this one.

https://www.ford-trucks.com/forums/882243-3g-alternator-install-with-pictures.html

 

the meter is good, and reading correctly, I have only driven it home and that was just a couple of miles since it happened so I'm hoping no harm done to the battery

i did some searching on the swap seems straight forward enough, but with all the issues it has and they all seems connected to the alt, i am hesitant to change it up until i get it figured out.

i dislike working on wiring and this cold weather isn't helping, and wouldn't ya know it a guy called today and said his tractor is down and needs me to come get it and me with no truck!

 

Well I finally got the alt, and i did upgrade to the 3g, then to my guy that clocked it for me. I went to the junk yard on sunday to pickup anothe gauge cluster and also picked up a couple of wiring harnesses for the alt. I took one off a 2001 f250 lightduty with the megafuse (175 amp with the holder) for 7 bucks. This is a direct swap, no need to cut and splice.
On to the dash now and hope the trans sensors are still good.
here is a diagram for a 3G its for a early mustang but the harness i picked up is the same and the 2g for wiring placement reference

 

Good job on the 3G conversion. Did it solve that 15V battery problem?

 

The problem is still there, now its only a constant 14v.
I switched out the instrument cluster and the V gauge is doing the same thing, itll twitch when you first start it and then nothing.
although the oil pressure gauge works in it but not the fuel gauge, i reinstalled the original, it still doing it.
I've gone thru the manual and there are no fuses I can tell control the alt/ fuel / oil / temp gauge, and my chiltons wiring diagram only shows the wiring for the volt gauge not the oil/gas/temp.

 

If you have the same Chilton's manual that I have, it's dwg # 10, p. 12-61.

There is a red/yellow wire to pos. 13 on the plug. It has power from fuse #17 and powers all those circuits. Check fuse #17 and check for voltage on this wire with the ignition on.