Lock Up Converter Vacuum Switch FAIL???

[VAL]

I think I have a gremlin, I traced the wires going through the firewall into th cab, found the brown power wire on the block, checked it with the meter and it gave me 12volts, 30 seconds later I check it again, and theres no power.

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Well it turns out, that my radio fuse blew, its somehow linked to the acc that powers the tcc wiring.

 

[chengny]

I think I have a gremlin, I traced the wires going through the firewall into th cab, found the brown power wire on the block, checked it with the meter and it gave me 12volts, 30 seconds later I check it again, and theres no power

There are 3 sockets in the ACC bank. It appears that you have a spare one available (the second from the top - to the right of the WDO marks). Try plugging the brown lead into that socket.

If the power to the ACC bank is still intermitent (or out), look at the radio fuse. I know it sounds strange, but that's how the ACC bank is powered - via the radio fuse.

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[MadOgre]

Mad-O; I'm am kind of losing track of your exact situation.

The vehicle in question is an 84 pick up, 1/2 ton with 4WD - true?

As for the power plant, you currently have a stock 350 coupled to a 700R4 transmission (RPO = MD8) - right?

The truck's wiring harness/controls are stock, and everything was originally set up for a TH400 transmission driven by a 6.2 liter diesel motor?

And, your objective is to get power (from the stock wiring/control components) down to the 700R4 and energize the internal TCC solenoid - correct?

If I am getting something wrong as described above, let me know. We'll see if we can somehow reconcile the two different set ups (i.e. the gas power plant you have now vs. the wiring and controls that came with the diesel plant).

BTW - I hope I have not given the impression that I am an expert on this subject. Because trust me, I'm not.

Everything I know is only what I have picked up since stumbling across this thread... what - like 3 days ago.

Also, something to be aware of; all the "advice" I post on TCC's comes entirely from what I find while reading schematics and service manuals. I have never even seen a TCC solenoid or a low vacuum switch in my life. All my trucks have been very basic - and they all came from the factory without O2 sensors, catalytic converters, EST/ESC.

As the saying goes - "When it comes to advice, consider the source".

LOL that's ok. I greatly appreciate the help as I don't think I would have ever found those schematics.

And I am definitely learning here too.

I guess I will take it with a grain of salt from now on LOL

Yes everything is correct except the truck was originally equipped with the 700r4 behind the 6.2 diesel from the factory. PO installed the th400 for durability issues.

 

[VAL]

I think I have a gremlin, I traced the wires going through the firewall into th cab, found the brown power wire on the block, checked it with the meter and it gave me 12volts, 30 seconds later I check it again, and theres no power

There are 3 sockets in the ACC bank. It appears that you have a spare one available (the second from the top - to the right of the WDO marks). Try plugging the brown lead into that socket.

If the power to the ACC bank is still intermitent, look at the radio fuse. I know it sounds strange, but that's how the ACC bank is powered - via the radio fuse.

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You are correct Chengny, I put in a new 15 amp fuse, and the acc where the brown power wire to the tcc, and everything is good. I bypassed the vac switch with a toggle switch, I'm thinking I have to bypass the pink/redish connector also. I'm still trying to figure out what that switch it was connected to is, and what was its function. From the diagram its something with the EGR, I think.

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[chengny]

Yeah - from looking at the schematic that yellow wire - the one that goes from the EGR bleed valve solenoid to the 4 prong plug (in which only 3 prongs are installed) - can be eliminated.

That wire has nothing to do with the operation of the TCC solenoid. It just uses the same harness group to enter the transmission. Once inside, it splits off from the other two wires (the ones that supply power to the TCC solenoid). There are two hydraulically operated switches in series at the end of the yellow wire. They are in the ground path - "downstream" - from where the yellow wire enters the transmission.

Apparently, when the switches are both closed, the yellow wire is grounded. That yellow wire is the negative side of the EGR bleed solenoid coil. If power is available to the positive side of the coil and both those switches are closed, the circuit is completed and the EGR bleed valve opens (or closes IDK)

 

[HotRodPC]

Well, looks like you guys are having fun and getting it figured out. I don't have internet currently so I have to limp along with a phone that doesn't have much data to be connected for long.

I was going to say to Val, to recheck the fuses because chances are, when you pulled that 4 prong plug out, as bad of shape as it is, if you did have power there at all, you probably grounded it and blew a fuse. There are pigtails for sale on eBay for $12.XX Free Shipping. Obviously that one needs replaced. Of course going to a DIY junkyard with a pair of wire cutters would be cheaper and quicker if you have one local. And if you got it off a like truck, you could get the matching wire colors too instead of having to figuring out which is which in the connector to make the correct splice. Outta here. Hope back in a day or so.

 

[MadOgre]

Is there a difference in the TCC wiring from 1984 to 1990 on the 700r4 ?

 

[HotRodPC]

Is there a difference in the TCC wiring from 1984 to 1990 on the 700r4 ?

yes there is. 84 is Vac switch operated, 90 is going to be ECM operated.

 

[MadOgre]

Is there a difference in the TCC wiring from 1984 to 1990 on the 700r4 ?

Ok makes sense. I guess I should have asked is there a difference with wiring inside the 700r4 as to how the TCC is actuated. from the 84 to 90 ?
Will the 84 truck wiring actuate the 90 700r4 the same way ?

 

[HotRodPC]

Ok makes sense. I guess I should have asked is there a difference with wiring inside the 700r4 as to how the TCC is actuated. from the 84 to 90 ?
Will the 84 truck wiring actuate the 90 700r4 the same way ?

That part of it should be the same. You're referring to the wiring inside the transmission. So long as the same activation wire is in the same place it'll work and I don't know that there is any difference. Just that some models have different pressure switches but should work all the same no matter how they're triggered, either by Toggle switch, Vac switch or ECM.

 

[MadOgre]

OK. well I still have the pig tail from the 90 burb so I should be all good to go I think. looks from the schematics that chengny posted I should be able to replace the throttle switch with the vacuum switch unless im missing something about all that ?

 

[HotRodPC]

OK. well I still have the pig tail from the 90 burb so I should be all good to go I think. looks from the schematics that chengny posted I should be able to replace the throttle switch with the vacuum switch unless im missing something about all that ?

I'd say it'll be alot easier to go backward in year model to the Vac switch than go forward to ECM. Follow that schematic and should work just fine.

 

[chengny]

At it's most basic, the only thing the TCC system requires to lock up the power train is 12VDC to the solenoid.

The solenoid is internally grounded through the transmission casing. So, if the coil is good and you supply a hot wire to it, the valve will operate.

I have looked at a lot of wiring diagrams over the past couple of days and, while there are many variations of the wiring harness into the transmission, one thing is consistent. The lead that supplies power to the TCC solenoid is always light green.

Take 12 volts from anywhere, run it through a switch and feed the solenoid coil (via the light green wire). When you want overdrive, flip the switch closed and the torque converter will lock up.

 

[HotRodPC]

I agree @chengny. Requires the 12 volts to the solenoid which permission given by any 1 of the pressure switches which is usually just 4th in the later models IIRC.

 

[VAL]

I was looking at this adjustable vac switch,
http://www.jegs.com/i/TCI/890/CMP3766B/10002/-1?parentProductId=748599
I was checking it out, but it doesn't show how you can actually adjust it to work between 1-7lbs of vacuum? Anybody familiar with these? I also need to replace the pressure switch, but there is so many different ones. there's a high gear pressure switch, a 3rd clutch pressure switch and a 4-3 pulse switch. How can I identify which one I have on my 86? I don't see any marking on it.

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