7427 install, first impressions

[dave w]

I was suggesting useing a TCC brake switch (cheap) to a NOS corvette part (expensive), it's just a switch... $75?

Ok, I get it. Apples and Oranges.

TH400 Kick Down switch is used on '427 PCM conversion to kick down a TH400 like the old 1228747 ECM did. The '427 PCM can't send "ground / battery negative" to the TH400 kick down relay like the old 1228747 ECM did.

TCC Brake Switch to DFCO? Not sure I understand how a TCC Brake Switch helps DFCO? I think I understand DFCO, hit the brakes then the DFCO programming happens.

dave w

dave w

[EagleMark]

TCC Brake Switch to DFCO? Not sure I understand how a TCC Brake Switch helps DFCO? I think I understand DFCO, hit the brakes then the DFCO programming happens.

dave w

dave w

I'm not sure how that became part of this discussion? He was talking of DFCO and we hijacked then it got combined? No coralation between switches and DFCO...

[JeepsAndGuns]

The bin we started with BMHK when checked on CalData was superceded to BPRJ a bin no one has...

Brake switch was just a sugestion to daves commnet, it was a hijack of your thread, your right it's to disengage TCC.

So is the BHDC spoken about, a newer manual trans bin?

[EagleMark]

Mixed info? CalData says it's manual. greg78cam said and read it to be from auto, Read last post here:
http://www.gearhead-efi.com/Fuel-Inj...=4789#post4789

[1project2many]

I thought the brake switch was just for the TCC?
I disabled DFCO below 20mph, its not really needed at speeds slower than that, and like mentioned above, had very bad parking lot manners. The way I have it set now, it pretty much comes on anytime I let off the gas, and works great! I dont really see the need for the brake switch, unless theres more to it.

GM went to a lot of work to make vehicles coast when you let off the gas. Overrunning clutches in the auto trans allow the engine to idle down without slowing the vehicle down and vehicles with TCC are designed to release the TCC when the throttle is closed. The whole point is to save fuel by allowing you to coast down hills or to ease off the throttle when it's not needed. With your settings there's no way to do this. Brake switch input would allow a way to engage DFCO only when the vehicle is being slowed. And with a manual trans or an auto with the shifter in a lower range, you'd have engine braking to help slow the truck.

[EagleMark]

TH400 Kick Down switch is used on '427 PCM conversion to kick down a TH400 like the old 1228747 ECM did. The '427 PCM can't send "ground / battery negative" to the TH400 kick down relay like the old 1228747 ECM did.

dave w

Do you have any wiring info on this to 1228747? We are trying to figure if 1227747 can be swapped in it's place...

[dave w]

Do you have any wiring info on this to 1228747? We are trying to figure if 1227747 can be swapped in it's place...

So I'm wanting to make sure I understand the question. You need the '8747 TH400 Kickdown Relay Wiring schematic? You are swapping out an '8747 and installing a '7747? I have schematics on my home computer, but I'm at work now. Later this evening I should be able to post back the '8747 TH400 Kickdown Relay Wiring. The parameters for the '8747 TH400 Kickdown Relay are different than the '7747 TCC lock / unlock parameters. I think if I were to swap out an '8747 and install a '7747, I would install a TH400 gas pedal kickdown switch to send ground to the TH400 Kickdown Relay.

dave w

[EagleMark]

Yes I'd like to have them as I don't know how it works and would like too!

Thanks for the info! So same switch in trans would work triggered elsewhere? Right?

[woody80z28]

Well did some more tweaking today and had some good results, so I figured I would just go ahead and keep adding to this thread.

I touched on this a little bit when I got my vss working and dfco started working. When it would come out of dfco, it would jolt the engine when it cut the fuel back on. Basicly it would be like you just lightly bliped the throttle. At first it wasnt annoying, but it kept on untill it did! After a little while it became VERY annoying. Would do it at about 1500 rpm, and I had not gotten to the point when I downshit. (remember, I am running a manual trans)
Well I find this parameter in scalers under "AE parameters" called "post DFCO AE pulse" with the discription that it provides a AE pulse when exiting dfco if no tps increase. I thought that kinda odd. Why would it want to add more fuel when kicking the fuel back on if the throttle did not get re opened. I did drop it straight to zero right away, I took it in steps. The jolt got lighter the lower I went untill i eventually set it to zero. Now it simply cut the fuel back on post dfco, but didnt add any extra AE. The jolt was a lot less that it was, but there was still a jolt (like you bliped the throttle) when it turned the fuel back on.
Now just to keep from confusion, there is still a parameter for a AE pule when exiting dfco if you DO open the throttle. I forgot exactly where it is. But that one makes sense. Your in dfco slowing down and then need to accel again (like slowing down for another car making a turn, then you take off again) I left that setting stock, as it does just fine if I hit the gas again when in dfco.
Now back to the jolt when it kicks the fuel back on. I thought about it and where it kicks it back on at 1500 rpm, it would be nicer if it did it at a lower rpm. I did a little more carefull looking at all the avalable parameters in my xdf, and found something I thought would be usefull. Its under tables and is under dfco parameters and is labeled " minimum dfco rpm vs. temp. In a nutshell its basicly what I was looking for! Its what rpm it cuts the fuel back on post dfco, and it splits it up into diffrent tepatures. I changed it to 1000 rpm for most closed loop temps, and a little highr for colder temps. Saved it, burnt a chip and took it for a drive. Sucess! I now no longer have the jolt when in dfco, because now it doesnt cut the fuel back on while I am still slowing down! It now does the jolt/blip when I push in the clutch to downshift. I watched the rpms and it doesnt drop lower than it should, the fuel cutting back on catches it, and it still does that blip. I now like it, because its like your bliping the throttle in between downshifts. I actually can kinda time it just right and use that blip when double clutching and not even have to touch the throttle. Kinda a added bonus...lol
BUT not all was well. Because I lowered the min rpm, I now made it to where if I was at parking lot/driveway speeds, it will go into dfco! Say like you pull out, drive a few yards while still in first gear and let off again, it went into dfco real quick and then the jolt of cutting the fuel back on, made a interesting combanation, and not a good one. It was like hitting the brakes and the gas real quick.
So some more digging around in the xdf, I find the parameters in scalers under "dfco parameters" and found the two parameters "minimum MPH to enter dfco" and "MPH to disable dfco"
The first one was set to 10 mph. I doubled it to 20 mph. I figured there was no need to go into dfco under 20. I then changed the disable dfco from 7 mph to 15 mph. That way, I have to be going 20 mph or faster for dfco to come on, and under 15mph, dfco is completely disabled.
Saved, burnt a chip and test drive. I now have full sucess! I now have no more jolt when slowing down, have a nice blip in the throttle between downshifts I can use when double clutching (that was completely unexpected, and just kinda a added bonus side effect), and no more dfco at too slow of a speed.

Hopefully all these little updates may help another manual trans 7427 user one day.

Interesting. I'll be playing with this as well.

[dave w]

Yes I'd like to have them as I don't know how it works and would like too!

Thanks for the info! So same switch in trans would work triggered elsewhere? Right?

The attached wiring schematic shows both the TH400 Kickdown Relay and the TCC wiring. Pin A7 on the '8747 is wired as either AT Kickdown / Shift Light (manual trans). Pin A7 on the '7747 is wired as either TCC / Shift Light (manual trans).

The pictures below shows a TH400 accelerator / gas pedal mounted kickdown switch. I would image most any junkyard that specializes in light truck would have a TH400 accelerator / gas pedal mounted kickdown switch.

The wiring is very basic. Remove Pin A7 from the '8747 and connect the wire from Pin A7 to one (does not matter which one) of the termianls on the TH400 accelerator / gas pedal mounted kickdown swich. The other terminal of the TH400 accelerator / gas pedal mounted kickdown swich is wired to Battery Negative. Adjust the TH400 accelerator / gas pedal mounted kickdown switch as outlined in a GM service manual. Sometimes a thick rubber hose needs to be installed on the tan plastic plunger of the TH400 accelerator / gas pedal mounted kickdown switch to get the kickdown where you like it.

dave w

[JeepsAndGuns]

GM went to a lot of work to make vehicles coast when you let off the gas. Overrunning clutches in the auto trans allow the engine to idle down without slowing the vehicle down and vehicles with TCC are designed to release the TCC when the throttle is closed. The whole point is to save fuel by allowing you to coast down hills or to ease off the throttle when it's not needed. With your settings there's no way to do this. Brake switch input would allow a way to engage DFCO only when the vehicle is being slowed. And with a manual trans or an auto with the shifter in a lower range, you'd have engine braking to help slow the truck.

I guess some of it comes down to personal prefrence. I like mine just the way it is. When I let off the gas, I want it to slow down. If I didnt want to slow down I wouldnt have let completely off the gas. If I want to coast without it being in dfco, then I will just shift into neautral.

Interesting. I'll be playing with this as well.

I am still verry happy with the changes I have made. Cant think of anything to do with dfco I would change right now. I have gotten good at using the blip it does when cutting the fuel back on, when double clutching while downshifting.

[1project2many]

I'm not telling you to make a change. I asked if you were interested in a modified approach. One of the downsides to DFCO enabled with nearly every decrease in load or throttle angle is an offsetting AE pulse or rich VE table to make up the difference when you resume speed. This can end up using a lot of unnecessary fuel. Like pumping the gas over and over on an old carby engine. Using a brake switch input is one way to ensure DFCO isn't active if all you're doing is letting off the gas for a short time, for example when changing lanes on the highway or turning a corner in traffic.

Out of curiousity, what's your final drive ratio and what size tires are you running?

[JeepsAndGuns]

No clue on final drive ratio. But I have a wide ratio T-18 4 speed (granny gear first gear) so 4th is 1:1, axle gear ratio is factory at 3.54, and I am running 31X10.50's.

[EagleMark]

I'm not telling you to make a change. I asked if you were interested in a modified approach. One of the downsides to DFCO enabled with nearly every decrease in load or throttle angle is an offsetting AE pulse or rich VE table to make up the difference when you resume speed. This can end up using a lot of unnecessary fuel. Like pumping the gas over and over on an old carby engine. Using a brake switch input is one way to ensure DFCO isn't active if all you're doing is letting off the gas for a short time, for example when changing lanes on the highway or turning a corner in traffic.

Out of curiousity, what's your final drive ratio and what size tires are you running?

I always wondered why DFCO was such a small window. Maybe this is where Decel Enleanment comes in?

No clue on final drive ratio. But I have a wide ratio T-18 4 speed (granny gear first gear) so 4th is 1:1, axle gear ratio is factory at 3.54, and I am running 31X10.50's.

That should be a real good higway cruiser!

I had Wide ratio (granny low) on a Scout and the granny low was great off road. But made it a 3 speed on street driving. On a street only Scout I had I put in a close ratio trans and got to use all 4 gears. 4th was still 1 to 1 ratio.

[woody80z28]

I'm still getting used to the gearing on my 1-ton 5spd. I rarely use 1st and the gear splits are huge! (5.61 / 3.44 / 1.71 / 1.00 / 0.73) Can't exactly speed shift in it either...the syncros need a little time to line up those heavy gears.