97 Expedition stalling, then theft light blinking

Discussion in '1st Gen - 1997 - 2002' started by PO'dexpd'nowner, Jun 17, 2012.

  1. PO'dexpd'nowner

    PO'dexpd'nowner Well-Known Member

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    First of all, I apologize to anyone who's mad about me making this thread. I read for 4 hours and there are so many possiblities I don't know where to start.

    The truck drives great, runs great...while unloaded. I use it to pull my mowers. About 2 months ago it started jerking and then stalling. Check engine light begins flashing, then it dies. After dieing it won't start again until a lengthy period of time...2+ hrs or so. While trying to start it, the theft light keeps blinking.

    Took it to the dealer who said it needed 2 new upstream O2 sensors, a DPFE sensor and hoses, and a new PCM...for agrand total of $1657!!!!!! I replaced both O2 sensors and get this....still throwing a code for it. Replaced the DPFE and hoses. Got a used PCM off ebay. I was VERY nervous but still took it out on a 40 minute test drive in the city and highway...no issues. I hooked the trailer up and didn't make it 1/4 mile from my house before it threw a code. Pulled over and scanned it...O2 sensors. Cleared it and drove on. Made it about 2 hours into the day with 30+ bales of straw and the SOB starting stalling on the interstate. Waited 3 hours and it would never start. Two hours later I went back and drove it about a mile,...enough to get off the parkway and then it died again. Towed it to my moms where it sits now.

    Where to start? Why no issues when it's unloaded? Do I need a new PCM? The used one I got shows the EXACT same issues as my original. What are the odds of that? What else could it be? I understand it could be the fuel pump which is making it starve for gas and then stalling but why would the theft light come on IMMEDIATELY after stalling? This has happened 4-5 times now and I'm scared as hell to hook a 16 ft trailer with 2 mowers up to it. Two weeks ago I got stuck on an uphill curve and had to wait for a good Samaritan to pull the whole rig up a hill. Scary place to be that's for sure.

    Thanx for any help guys. I really don't want to fork over $827.29 plus tax for a new PCM if I don't have to.
     
  2. Captain Morgan

    Captain Morgan Full Access Members

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    Oh man I feel your pain, I got stranded like that once blocking traffic during rush hour and caused a bottleneck because a shop left me void of clutch fluid.

    Where to start? That's the $2 question.

    There's a thread recently about having a mechanic who is an individual shop owner with a mega diag machine decode the errors logged in the ECU\PCM etc. I think - Screw the dealerships and find some guy who relies on reputation and repeat business.

    It could be something as simple as an 02 sensor wiring problem such a short or intermittent loose connection, where you will get (false) random and repeat catastrophic errors recorded.

    My gut would be to find someone who is willing to go over this top down instead of selling you a shotgun replacement fix for another grand.
     
  3. PO'dexpd'nowner

    PO'dexpd'nowner Well-Known Member

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    The first shop that I had it towed to simply admitted they didn't know what the hell was wrong with it. It was sending a code V1147 SCP Network (forgot to mention that. did search on that code on here and found nothing), whatever that means, and they thought it was the key chip losing their signal to the transponder. If that were the case, it wouldn't start at all. I'm ruling out key/transponder issues for that very reason.

    BTW: that uphill curve was an old country road and a school bus had to go through a ditch to get around me.

    Your idea about someone checking it top to bottom sounds great. I know a guy who tuned my truck and tunes other GM's but when I asked him to look at this, I never got any answer back from him. Around here, besides him, I doubt I'd find anyone else. There is a guy who specializes in electrical work on vehicles. You think it's electrical? Although he's good at it, I've heard some bad stories about his work and his prices.

    I have got to get this thing running......DEPENDABLY running though. I can't worry about getting stranded every day when I'm out hauling equipment.
     
  4. Captain Morgan

    Captain Morgan Full Access Members

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    Basically that code said that his diagnostic machine had a problem communicating with your ECU.

    I found some diagrams for you and the rest of us Gen 1 owners in case it comes in handy.

    Know what your situations have in common? Running about 2 hours.

    Check the 30 amp maxi fuse under the hood and the mini 5 amp fuse for the PCM. Make sure that the fuses and relays both have good clean spades and reseat them.

    I see a PCM Power Diode listed in the diagram, I would replace that too.


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    Interior Fuse Box

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    Instrument panel

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    Last edited: Jun 18, 2012
  5. PO'dexpd'nowner

    PO'dexpd'nowner Well-Known Member

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    Thanks a lot Captain!!!!!!!!! I'll try to get some of these fuses checked out this week.

    Got one question left though: You mentioned the 2 hour issue. If it were a fuse issue, wouldn't it be immediate? I mean, if the fuse is blown, wouldn't something not work right from the start?
     
  6. hovocop

    hovocop Full Access Members

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    the fuse idea is great!!!!!! Keep in mind not to pour money into a pit
     
  7. Captain Morgan

    Captain Morgan Full Access Members

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    What I was inferring is that maybe by running for 2 hours, something warms up enough to not function. When a mechanical\electrical connection gets iffy, the current through that area causes more heat, which causes more oxidation, which causes more heat etc etc. You will see the metal turn dark and\or look pitted.

    In a Molex plug, the female insert is just a tiny piece of rolled tin. I've seen those get so bad the Nylon melted and burned.

    Maybe one of the sockets for a current bearing connection is bad after all these years. Yes typically a fuse will just blow, but it is still a current path and relies on the integrity of the connection. If some of the current is converted in to heat through the resistance of a poor connection, it could make the whole connection intermittent and prevent the fuse from blowing, instead it's more like a slow BBQ. This would be true for the relay connection too.

    Good luck, solving intermittent issues is no fun, you have to be part Sherlock Holmes and part mechanic.

    I think a lot of inspection is due and probably better on your dime than at the shop. Keep some really fine sandpaper or something to clean those connections handy as you go through them.
     
  8. PO'dexpd'nowner

    PO'dexpd'nowner Well-Known Member

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    Thanx again Captain!! I DESPISE electrical issues. If it's mechanical, you can see what went wrong. You can't see squat what's going on behind the wire/relay coverings and I'm no electrician. I've toyed with the idea of buying a circuit tester for a few years but wouldn't have the first clue to know how to use it.

    After all is said and done, how the hell will I know if it's fixed besides actually driving it for 2+ hrs and risk getting stranded again? I let it idle for an hour in the driveway while I mowed my yard and it never threw a code. Let it idle for 2 hours or must I actually drive it? I've already got $500 in this fix with tow bill, my shop, dealership diagnostic, and then me replacing the O2 and DPFE sensors. The pit mentioned above is real for me...it has 242k on it, 112k on motor and tranny.
     
  9. Captain Morgan

    Captain Morgan Full Access Members

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    You don't actually need a cicuit tester to pull a fuse or relay and inspect the spaces, just something to scrape with and put it back in the right location one at a time.

    If it looks tarnished or charred, replace it, if not, give it a scrape anyway and reseat it. It's tedious monkey work, but could pay off.

    Running it till it reproduces the problem only works if you have a plan to diagnose the issue while it is happening, such as measuring the voltage at the relays and fuses etc.

    Have you had this vehicle the whole time? The reaosn I ask, is sometimes we are unaware of hack jobs that former owners did. Can you identify any modifications or add-ons?

    Oh, and clean all of your ground connections when you get the chance. At the battery and at the frame.
     
  10. PO'dexpd'nowner

    PO'dexpd'nowner Well-Known Member

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    It's bone stock, had it for about 8 years now. Previous owner was a doctor who followed the maintenance schedule pretty well, definitely not the type of guy who would actually get his hands dirty and try to fix it himself.

    As for diagnosing it when it happens, I tried it the other day. "No link" shows up on my Actron scanner. I'm guessing that's what the shop machine meant when it says "code v1147 SCP Network". Once it's in Theft mode, the OBDII port is useless. If you're talking about testing relays when it happens, I guess I can give it a shot. That part when you mentioned it getting warmer and then resistance builds up sounds about right though.
     

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