7427 install, first impressions

[gregs78cam]

I don't have TP in front of me right now, but I thought there was a bunch of stall saver stuff in the '7427. You might look into those as well. I know that in my '98 Grand Am with the 5 speed it is not easy to stall the engine because the IAC, and fueling helps to prevent it, i.e stall saver. You should be able to ease out of the clutch with out giving it any go pedal without stalling. If it was happening when you add pedal, then yes the AE was needing some tweaking.

[JeepsAndGuns]

Yea the stall saver is working as far as I know. If I put it in first (this is a wide raito trans, aka granny gear 1st) I can let out on the clutch without touching the gas. But first is not normally used in normal driving, you pull out in 2nd. But in first the iac will open so as to keep the rpms up/keep it from stalling. In 2nd it would do that too, but it just always had that dip in rpm's. It just needed a little extra shot of fuel. I have noticed the 7427 pcm has way better iac logic than the old 7747. The iac even seems to work faster.
I dont think I have ever actually looked at any of the stall saver paramiters. I may check them out next time I have the laptop on.

[EagleMark]

It has more IAC logic and ever thing else because it has a bigger chip. The IAC is faster because 7747 is 160 Baud rate and 7427 is 8192 Baud rate. 160 Baud is like ever 1.2 seconds and 8192 Baud is so many times a second I forget?

Stall saver on 7747 I had to turn off for a an Off Roaders who wanted complete control of low RPM driving during rock crawling, they would lug and engine and it would rev up because stall saver kicked in, same guy new engine with 8192 baud system on new engine in same rock crawler said he wanted it turned off and I said to try it first, I had already drove it, lugged engine trying to stall with no rev up issue... no need to turn off it works so much faster he can not notice it working. Actually he said is was much easier to crawl because the engine had a rock solid steady RPM at idle and very low RPM he had to do less to operate engine driving and spends more time looking at and planning obsticles driving... although the engine needed a tune do to non stock engine build like cam headers etc... all I did was fuel and spark... there is so much that does not need to be touched on the newer 8192 baud TBI systems.

Next time I work on his truck I am going to look at the AE difference you found that fixed your issue, seems to be something that would improve this type of driving...

[JeepsAndGuns]

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.

[one92rs]

not to add a pointless post to this thread. but i posted needing info on a 746 to 427 swap in my camaro and a 60e swap from the 700. i cannot tune it myself so i will get a chip. but i needed to know all the info in this thread. now i will be watching closely how all this goes. also can someone in here tell me where to get new plugs for the 4127 ecm.

[dave w]

not to add a pointless post to this thread. but i posted needing info on a 746 to 427 swap in my camaro and a 60e swap from the 700. i cannot tune it myself so i will get a chip. but i needed to know all the info in this thread. now i will be watching closely how all this goes. also can someone in here tell me where to get new plugs for the 4127 ecm.

Mouser Electronics is where I get my ECM connectors from.

http://www.mouser.com/Search/Product...ey829-12110115

http://www.mouser.com/Search/Product...ey829-12110113

dave w

[one92rs]

thank you very much. i will get those ordered.

[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.

[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?