I've previously posted about my truck, and having some transmission issues. I was able to confirm that I was having issues in the electrical components on the truck causing it to not shift in D (speedometer was not reading properly due to bad gears in tailhousing and on speedo cable, speedo cable, gears, and speed sensor on rear diff were all replaced, Transmission now works properly when the truck isn't running weird.. I found some info and ran it 1, 2, and then D and it worked like a charm confirming it shouldn't be the transmission itself being "bad".

Now that I've gotten that going and my transmission is in good shape, I've actually been repairing other bits and seem to be having some other weird issues, and I'd like to see if anyone could help me troubleshoot them, or understand what I need to be looking into to troubleshoot them.

Truck is an 88 f150 XLT super cab body on top of a 90 f250 chassis (3/4 ton 460 EFI e4od 4wd). The cab was off an airforce base and is super clean, the f250 parts idk where it came from, but is in very good shape with almost no rust. The PO told me it was done before he got it, and he didn't know enough to understand how to troubleshoot it. I clearly don't either but am too stubborn to give up and not figure this out. I have been reading everything I can and trying to understand this truck and hit a bit of a wall. I'm going to describe all the weird and I'm hoping that maybe someone can point me at the parts that can cause the problems so I can dig into how to troubleshoot them.

First, I am getting no codes at all from the test port EECIV. I have the digital reader, and the book, and have confirmed I am using them properly and in the correct location. I also cannot seem to get the truck to give me any blink codes by grounding out the proper pin after trying that. I know they would be useful, but am kinda going into this blind without that, and unfortunately I have no clue how to figure out what could be missing there ...

For the weird stuff:
My CEL comes on and stays on while the truck is acting weird, and then it seems that when it warms up it runs like a normal truck, I've got full power, the transmission works properly, and everything is great. I actually drove it in this state 60 miles the other day and had no issues until my rear brakes locked up. I bypassed the RABS temporarily and that has fixed the rear brake issues so I know I ahve a problem there, and my RABS light is on, and staying on as I unplugged the fuse for it to not add other issues into the mix. I am looking for one of these, or possibly rebuilding mine, but it's not part of the overall mix below. Just pertinent to the truck.

When you put the key in and turn it to on without cranking, the fuel pump turns on and doesn't turn off. I read this is the ecm, and thus found 2 blown caps in the ECM. I replaced them and my issue is still exactly the same, so either I botched the ECM repair (I don't think so and am pretty comfortable soldering as I've been working on electronics as a hobby since I was a kid), or it's not the ECM. I don't think it's in the ECM, at least not the capacitor circuit in the ECM.
After letting the truck sit for a week or so the truck seems to "reset" itself, and the first crank the truck will start up and run like normal, but if you turn off the truck and try to crank it a second time it goes back into weird mode.
When the truck is being weird, it audibly blows through the egr circuit. The barrel next to the battery with the open end has air flowing through it, and when it stops acting weird this stops blowing, and doesn't start up again.
If you stop the truck to get gas or whatever and turn it off, it does not want to crank at all, and I have continually cycle the key off and on until the starter "catches" and turns over the engine - I have replaced the start solenoid, but I think maybe a bad ground is causing this or a bad starter, but this isn't causing the CEL and weird issues, just hard crank when warm.
When the truck is running weird, if you give it gas slowly, you can rev it all the way through, but if you put your foot into it hard off idle, it will rev to about 2100 rpm and then just sit there making this weird sound but will not idle higher. The whole time it's running "weird" through any rpm it still doesn't sound smooth and "right" until the truck kicks out of weird mode and runs normally.

As I cannot pull codes, I'm hoping the above symptoms make sense for some part of the truck that maybe controls these bits. When it's in weird mode, I've been all under the hood bumping things with a wrench trying to see if I could knock something loose and make it come out of weird mode, but I can't find anything. I have 2 times been able to shift it through the gears (only 2 of the maybe 100 times I've tried it ...) and have it come out of "weird" when I put it into 1 on the shifter. Maybe weird mode is really just limp mode, I'm not certain, but I can't for the life of me figure out why when it gets hot enough it seems to go away. Heat I would think would cause problems and make it more prone to go into limp mode??? but maybe not, Idk.

To date (if it matters). I've replaced:
speedo cable,
speedo gears
speed sensor on rear diff
replaced fluid in rear diff
replaced the IAC valve (had weird idle issues all the time and this fixed them outside of "weird mode")
replaced both front brake soft lines
rebuilt all 4 corner brakes with new pads and calipers up front, and new shoes, wheel cylinders, springs etc on the back)
replaced the axle seal on the rear floating axles on both sides as they were leaking, also replaced the lip seals on the face of both floating axles behind the shaft face with the bolts on it.

Could this be bad grounds, or something? I do have a black rather thick ground wire hanging down under the truck next to the starter. It doesn't look like there's a place to put it on the starter though. I've run my own ground (an old 12" negative battery cable) from the negative on the battery to the frame. I've checked all the body grounds I can find and they all look proper.

When attempting to google on this, I'm not really getting any traction on what it could be, and I'd hate to replace more parts that are still good as most of the stuff I can buy now seems to be junk compared to the old stuff.

I do have a new fuel filter, and a fuel tester kit. Prior to reading about the ECM keeping the pumps on and killing the pumps, I was thinking weird mode was caused by low fuel pressure, but it seems to be more than that after reading on especially knowing it goes away eventually when the truck warms up.
The PO told me they replaced both fuel filters with whole new assemblies (probably cheapest possible kits ... I'm ok buying decent ones and replacing them, as I intend to take the bed off and replace them both properly if needed. When I got the truck the front fuel pump did work, but stopped making noise about a month ago. The rear one still is audible, and while it seems to not turn itself off like it should after a few seconds, I'm not certain if it's staying on 24/7 after the truck is cranked, you can't hear anything when the truck is running in weird mode as with the miss, it sounds like a really badly tuned cam, and the exhaust is much louder than normal.

Sorry for the wall of text, if anyone can point me at something I can test / try to figure out where to go here I'd appreciate it.

 

The continuous running fuel pumps, continuous CEL during running and getting no codes are classic symptoms of a bad computer. They can and do fail beyond the simple capacitor leaking issue. Also getting the air injection system acting up, not the EGR, is another sign the computer is not functioning properly. You already replaced some components, but are still getting the same symptoms. Verify the computer is getting a good ground on Pins 40 and 60 as well as case ground on Pin 20. If those are good that is another sign the computer is toast.

 

Oh man dude you are awesome, and I super appreciate that response. I at least don't feel so lost on this, and I'm 100% ok with replacing that ECM with another one that has actually been rebuilt and tested (it was gonna be my next step if this yielded nothing useful).

 

I checked and have a great ground on pin 20,40,and 60. I'm gonna order a rebuilt unit off rockauto (the only place I can find one currently lol) and put that in. Hopefully my issues go away after that. Thanks for the input on this, and will update next week when I get it in.

 

i had most of the same issues with my 90 ford and I was at the wrecking yard getting a trans. found out someone had put gear oil in my manual trans. but while I was in the yard I happened upon a brand new toatly updated ecm and it was only 15 dollars. those were the days. got the ecm and the trans for 65 dollars. and put them in my truck. night and day difference. then I did stupid and loaned my truck out. they rear ended someone because they were not paying attention. it was a nice truck and if I can find another I will grab it.

 

Sorry to hear that man, I've been looking for an early 90s era f150 since I got my license. I couldn't afford one back then, and now that I can, I'm trying to bring this one back to life and make it a reliable runner. Honestly the engine when it smooths out is stellar, and the transmission seems to be in pretty good shape now that I've got the electronics on it actually functional.

 

I wanted to say thanks man, I got the new ECM in, installed it in the truck and every single thing that was wrong is now not wrong lol.

The truck shifts like butter, starts right up, and the fuel pump runs for about a half second then turns off. Now that it runs so well, I've found that I have a small miss or stumble in the engine at idle, but I think that's probably related to the ignition system. I'm gonna give it an update as the wires on it right now were installed by the PO and look to be rather puny.

Either way I can now troubleshoot the single few issues remaining, and enjoy the truck.

 

Thanks for the update!