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92 5.8L troubleshooting PCM or something else?

 
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Old 05-09-2019, 08:13 PM
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92 5.8L troubleshooting PCM or something else?

Help. I think I have changed too many variables to know where to start.

1. My initial failure seemed to be related to the burnt PCM. The truck would barely start, would not idle at all and would barely move forward at all when in gear and almost stall, but would freely rev. while in park or neutral. It did not matter which fuel tank was selected, the selected fuel pump would run continuously with the key on and engine off. I was unable to get my never used before Code reader to read anything at all or get codes using a paper clip, CEL light came on at the time all this started. Preexisting issues were the front tank would fill the rear tank and the front tanks sending unit did not work.



2. While working with AutoZone to replace my Cardone computer which was under warranty, I installed 2 used fuel pumps with sending units, a used 3G alt which I rebuilt, tested each ground pin to the PCM harness for continuity, and removed the relay/fuse box and that attached harness to rust convert and paint the support bracket. I installed a 3” body lift, which caused me in turn to also separate the two harness that run down the fender well, I think one is brakes and turn signal lights and the other is for the fuel pumps. The trucks bed was completely removed and reinstalled to get to the fuel pumps from above. Removed the surface rusted but year old brake booster and painted it. New PCM installed, CEL was out, and truck seemed to idle fine on each tank several times checking back and forth between the tanks.



3. Today I tried to use the AutoZone loan-a-tool gauge before planning to return it just to check the fuel pressure on each pump. I got a little mad because it seems to be missing a piece which would depress the Schrader valve to allow fuel and pressure to reach the gauge. While getting ready to go for a bit of a test drive I started it on the front tank, saw that my brake lights were on and shut it off. The CEL self-checked and went out after starting up. For the brake lights, I remembered to release the parking brake and then topped off the brake fluid which was low. (I had also disconnected sensor and reconnected while removing the relay/fuse box.) Turned key on and brake lights and CEL self-checked, then all turned off when I started the truck.



4. Started the truck up to let it warm for a test drive. It high idled like I expected for a bit using the front tank then kicked down to normal. As I got in to leave it flipped it to the rear tank and it started idling poorly and rather low. Flipped to front and it got normal, revved it a few times and it acted fine on the front. Flipped back to the rear and still choppy, if I revved it up a little lively it started to stall and miss immediately. If I gently apply a little throttle it revs smoothly as far as you like but stalls if you hit it any harder. To start trouble shooting I tried a little test drive.



5. Test driving on the front seems pretty normal save for Item 6 and 7.



6. Each time I tried to use or switch the rear (on side streets) it would get choppy/miss/try to stall. Lightly applying throttle, I can get to about 10mph before it gets weird.



7. Right turn signal was used to get on a main road, then while coasting to pull off, it seems to work rather normally. I did notice while driving home that the truck immediately seems to down shift as soon as the right turn signal starts clicking. Checked overdrive button function which the turn signal off and it seemed fine. Under steady throttle at 55 mph it downshifts when right turn signal is turned on. Both front and rear right turn signals blink along with my LED strip. Head lights and taillights for each side seem normal too.



8. Left turn signals do not blink. The arrow just stays green. Neither the corner or taillight flash. I noticed my LED brake strip just stays red on the left side.



9. Codes. No CEL came on while driving; it does illuminate with the key on then turn off when starting. I still cannot get the code scanner to talk to my truck in key on engine off. I couldn’t get it to show the symbol for data connection or the triangle for scanning after hitting hold/test. If I attempt a Key on engine running test, it does show the triangle and then if you hit memory it shows the 8 for 8 cylinders. If you try to the key on engine off and hit memory after it shows 70. It showed 70 before with the old PCM. I did not attempt a manual CEL test with a paper clip because the sun set and dinner got cold.

 
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Old 05-10-2019, 06:05 AM
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Fast update for #8. Checked this morning to see if emergency flashers worked. All lights blinked except for the rear divers side so it might be the bulb or a ground. I think when trouble shooting 1 I swapped a relay with the fuel pump relay that had the same markings. I probably will not be able to check my manual until Monday to verify the function of the second relay but I think it was right next to it in the fuse box. Also asking my wife to grab the round turn signal flasher relay out her 93 ranger this weekend while i am gone.
 
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Old 05-10-2019, 06:23 AM
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Sounds like a bad check or shutter valve in the front FDM.
 
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Old 05-10-2019, 07:10 AM
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That sucks. So I am really not confident getting out of this without two new ones at this point. I plan on asking a guy at work if I can test my code reader on his truck next week to verify it functions. Each tank had the inline check valve installed outside of the tank, I think it was the for TSP part, I left them in place. So a back check in the front will cause the engine to stall or miss when the rear is in use? After I return the fuel pressure test guage, I may get one from a different parts store in hopes it will have all the piece.
 
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Old 05-10-2019, 08:56 AM
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Are spectra fuel pumps as bad some reviews make them out to be? I am not a fan of crimping a positive 12v and ground wire to be near each other inside the tank.
 
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Old 05-10-2019, 09:01 AM
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Originally Posted by CamoF-250 View Post
So a back check in the front will cause the engine to stall or miss when the rear is in use?
It can but it could also be a week pump in the rear tank.
But most likely the front shuttle valve.
This is why if you take it to a dealer they will just replace both front and back FDM to make sure they get the right one and do not have a call back.

By the way the fuel pump relay is OK with either one selected and getting fuel pressure (running OK).
 
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Old 05-10-2019, 09:13 AM
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Seems to be running OK except for the downshifting when I turn on the right turn signal. I pulled and replaced both pumps from a 94 5.0 which had been T-boned. I swapped each FDM on to the original hangers. If i can find the guy at work, I am going to try to test my code reader on his truck. The first time I tried to use it was with the burnt PCM. Looking at pictures of schrader valve adapter online, it seems the loan-a-tool adapter was missing its internal pieces. So are spectra ones that bad? Also do the turn signals function independently from the PCM, can I isolate these issues as unrelated? My past experience told me that fords have the dash light flash really quickly when one bulb was burnt out, not stay on.
 
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Old 05-10-2019, 10:21 PM
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Switched flasher relays, the motorcraft original for flashers flashes front light slowly, swapped bulbs in rear lights and problem moved, one bulb is bad. Will not be back until Sunday evening. Is it safe to jack up drivers side of bed with a body lift installed? Just loosen nuts on passenger side and drop tail light harness on drivers after disconnecting fuel tank nozzles?
 
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Old 05-11-2019, 08:29 PM
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double up on heat shrink on each crimp, buddy has spectra fuel pump in his 3-4 yrs now
 
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Old 05-13-2019, 11:01 AM
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I like that idea, so I will redo any crimp connections for inside the tank with heat shrink. i will probably overkill it with heat shrink on top of the water resistant heat shrink crimp connectors I already use. If the spectra's fail, then they fail, at least I will have a pig tail and cap that will be much easier to remove and install with another FDM in the future.

I tried testing my code reader on a strangers truck in the parking lot this morning at work. I explained to him that I wasn't able to get it to read anything from my truck and he was more than happy to help as he told me all about his 93 which he has owned since new. It did not work on a KOEO test for him either. No triangle or square appeared and the batteries are new. I am going to try to pass it to a friend to test on his truck this evening, I did just notice two of the male pins were loose and pushed in a little bit. I carefully pulled them back out and they seemed to snap into place. I do not know where to start by contacting AMAZON or Inovva, it is the 3145 model, if it will not read his truck. I have probably had it for about 8 months and April 4th 2019 was the first time I had attempted to use it which was on a burnt/failed computer. It is possible but, I think, not likely I received a "dud" computer from Cardone. I tested the code reader this morning and am giving it to my friend to test without the extension cable to take out a variable. I am a little upset there are not any screws in this code reader to aide in disassembly. I am likely to break it trying to pull it apart to check the connections to the male pins.
 
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Old 05-13-2019, 05:38 PM
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I have the same problem with my Innova code reader for the past few months. It's only about 2 years old, maybe they just don't last long? Mine eventually will work but takes several tries.
 
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Old 05-13-2019, 05:59 PM
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Clean the pins on the diagnostic link with contact cleaner or if they are really corroded use a small fingernail file to clean them up.
 
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Old 05-14-2019, 04:47 AM
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I meant to do a paper clip test with my male to male wire I keep in the glove box yesterday evening but got caught doing honey-do's for a little honey. Looking at Amazon reviews of the code reader, i guess that is more or less a common problem with them.
 
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Old 05-16-2019, 10:26 AM
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Just to update anyone following. Fuel pumps installed and new bulbs installed. Engine throttles freely on both tanks. I would like to get some help tightening the body lift bed bolts back down before test driving. Might even cruise to work in it a little bit with painters tape around my tail lights as I am need to start wet sanding for the next endeavor. Does anyone know if the Harbor Freight Fuel Pressure Test kit has the fittings for the schrader valve? I had one in my hand at the store but put it down because I could not find anything on the box that gave me confidence it would have the right fittings.
 
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Old 05-16-2019, 08:04 PM
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if you are talking about the $20, one that one piece(in blue circle) looks like the Innova piece, but it dont list ford, it lists Lincoln, see if they will let you open before you buy/leave

 

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