Hi guys. I been lurking here for a couple months. Great forum and you guys really know your stuff.

I recently bought a 90 F350 4x4 with a 7.3 and E4OD. I love this truck but the transmission is driving me nuts. I have researched and read all the info I could find on this board and have tried all the usual fixes. Nothing works. Sorry this is getting long but I figure a brief history will help you guys help me. I bought the truck from the guy that bought it new. It has had a pipeline weldors bed on it since new. I didnt need that so I bought it without the bed with intentions of putting a plain flatbed on it. Well we weren't in a hurry to swap the beds so I drove it like that for about a month trying to figure out the transmission problem with no luck. We got around to swapping the beds last weekend and after we set the flat bed on I drove it to my place about 8 miles to hook up all the light wires. The wiring on the old bed was a rats nest so I just cut em back to good wires and started from there. While the wires were cut it shifts like a brand new truck and performed flawlessly so I thought I had found the problem. I bought new lights and wires an rewired the new bed. Now the transmission is back to it's old tricks. Shifts all kinds of crazy. Torque conv in and out, in and out. I pulled to the side of the road and unplugged the wires again, bam, the trans shifts like a new truck again. Plug em back up and bam, it goes to crap again. I don't get it. The lights are working perfectly. Anybody got any ideas?

Again, sorry for the long winded first post.

 

galute,
Welcome to FTE and the IDI diesel forum.

The brake lights send a signal to the torque converter to unlock.

I would look at your grounds for the bed lights or a bare wire causing the brake light circuit to backfeed.

Trailer wiring sockets are also a good place for this to happen if you have the battery wire to charge the breakaway battery with a 6 or 7 pin connector.

 

Bingo, its most likely in the break light wiring. Might be a good idea to get a haynes manual for the wiring diagrams or head down to a ford dealer and they should be happy to give you a scan of the wiring for the transmission.

The other option is to simply disable the break light signal that goes to the PCM. One less thing to go wrong that way. The aftermarket computer in my truck only uses MLPS, TPS and VSS signals. The OEM computer will use all of that plus break lights and engine RPM (may be others as well to help complicate things).

 

You don't suppose he is also having trouble with the vss wiring? It's back there too, and goes to the rearend, so maybe it's getting mixed up somehow with the rear light wires.

 

Thanks guys for the suggestions. I double checked the wiring to the lights. There are no trailer light plugs installed yet. The only thing hooked up at this point is, left and right signals (which works the brake lights) and tail light.The light is the rubber mounted type and grounded with a wire directly to the truck frame. I even unhooked all the lights but the left side, just the signal/brake and tail light and that is enough to cause the transmission to go nuts. It even does it if the lights are not turned on. Just hook up the wires is all it takes. I did notice one glitch tho that I havent figured out yet. When I connected the back up light it backfeeds thru the tail light (all in one unit). I can see no reason for it, the ground is good.

 

what do you mean the backup lamp back feeds through it

 

Perhaps backfeed was not the proper term. When I hook up the tail light wire with the lights on, the tail light lights up. When I hook up the back up light with the tail lights off it lights both bulbs, back up and tail light. The only common wire they share is the internal ground inside the light assembly. It lights both bulbs brightly, the taillight bulb is not dim like it would be if the back up light was drawing a ground thru it. I left the backup lights disconnected and taped up before I drove the truck as I didn't want that causing problems. Is it possible that that circuit not being complete and working properly is causing my shifting problems? I dont see how it could cause when I had all the wires cut the trans shifts perfectly. But then again, I'm not sure.

Thanks you very much for everyone's help.

 

I have seen guys hook up a "brake light" wire to the system.
You don't do that as the turn signal/tailight IS the brake light.
You may already know not to do this but I've sen it done and it really screws with your tail light wiring.
Usually it's done while wiring up a trailer plug though. The guy sees 'brake" and he runs a wire from the brake light to the trailer brake position on the plug.
You made no mention of doing this but I thought I'd throw it out as a possibility. Working at my Dad's shop when I was younger I saw this more than once.

 

Thanks Dodge/cummins, I thought of that too, but, it's not the case. As of right now there are only two wires from the truck harness hooked up. Left turn and tail light (left side only). The lights are working properly. I unhooked everything else trying to eliminate the problem. The only other wire hooked up is an internal ground wire from the light that is hooked directly to the trucks frame.

With those wires hooked up, I cruise down some county roads at about 25 mph. The shift from 1st to 2nd takes too long then hard shifts to 2nd, the 2nd to 3rd shift is the same. As soon as it shift to 3rd the torqe locks up then immediatley unlocks, then its a constant, lock, unlock, lock, unlock and it will keep doing it as long as I hold that speed. At this point the tail lights are off and the brake light is steady off. I can apply light brake pedal just enough to make the brake light come steady on and the torque will unlock and stay that way as long as I hold the brake pedal. I can unplug the two wires that are hooked to the light and the transmission will shift like a brand new truck. I wonder if the ground from the light to the frame is somehow confusing the computer? I think I will go see if there is a ground wire supplied in the harness for the lights and hook the light ground to that if there is. Maybe the hot wires supplying juice to the lights without the ground side hooked up is what is confusing the computer. I cant see how that could happen but who knows, computers can be picky like that.

 

its possible that someone replaced the transmission range sensor and when they installed the new style sensor they did not move the pins to the correct position when they installed the new hardshell connector because the reverse light circuit goes through the TR sensor

 

Thanks ford trans tech. I will check that next when I have time to mess with it again.

I didnt have much time to mess with it yesterday but I did find two problems and corrected them. I don't know if that helped yet cause I didn't have time to test drive it.

The first problem I found was that the wire harness that was supplied with the new light kit was not wired up right. The ground wire was actually hooked to the tail light pin in the plug at the light. Not sure how it kept from blowing a fuse but it didn't and they worked. I noticed this when I turned the tail light and turn signal on at the same time. They both blinked. When I checked them one at a time they worked properly.

Second problem I found. When I first got truck I took it to the transmission shop that recently rebuilt the trans and had them check the voltage at the FIPL. They said it was in spec and not the problem. So I assumed it was good. Yesterday I decided to check it for myself and I found the readings to be .5 volts throttle closed to 3.5 volts WOT. I adjusted it to 1.1 volts throttle closed to 4.2 volts WOT. I guess it's true what they say, if ya want something done right, do it yourself.

 

Amen to that. I hope you found the problem, galute.

 

Well I finally finished up the wiring today. The lights work great now. Wish I could say the same for the transmission. No such luck. Still doing the same thing. I did notice it shifts better when it's cold but gets worse as it warms up. Adjusting the FPLS seemed to make it prolong the shifts more and it did tame the torque kicking in and out some, but it's still pretty bad. I noticed the speedometer doing some funny stuff today. I picked up a speed sensor at the parts store, the parts guy said it was in the rear diff. Changed it out but it made no difference. Is there another speed sensor in the trans?

 

I had a prob with my trans locking up in revese I had it rebuilt and it still did that and kicked in and out of gear it turned out to be the wiring from the sensor in the rear dif about 2 ft back the wire was broke in the harness.

 

I had same problem for years off and on. I think I found the bad wire when I was swapping to a ZF5 and doing a 2" lift. A wire was pinched along the frame. My question is do you have cruise control, because you said it worked fine when you had your foot on the brake pedal. The cruise control unlocks T/C when you apply the brakes, maybe there is something wrong in the C/C circuit. My speedometer would go crazy too. Hope this might help.