Understading ECM and electronic transmission control system???
I'm trying to find information on a late model aerostar's ECM and electronic transmission control system. I'm seriously thinking about swapping out differential gears and possibly making other changes as well. But I don't want to start making changes without thoroughly understanding how this control system works. I'd like to be able to predict what it will do if I drop my rear from 4.10 down to 3.45 or even down to 3.27 etc. Will the transmission shift ok? Will the motor be "off the cam" at those lower rpms? Will everything be entirely screwed up? Can certain simple mods be made to make the trans shift at the proper points again with the taller gears? And I'd also like to try adjusting the cam timing by advancing it a few degrees so that I can shift the torque and powerband downward to a lower max rpm range. But again, don't want to disturb the ECM gods without having a sense if this can be done successfully.
Any thoughts or sources of info greatly appreciated.
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1997 Aerostar Extended 3.0 2WD, 28K miles
I'm trying to find information on a late model aerostar's ECM and electronic transmission control system. I'm seriously thinking about swapping out differential gears and possibly making other changes as well. But I don't want to start making changes without thoroughly understanding how this control system works. I'd like to be able to predict what it will do if I drop my rear from 4.10 down to 3.45 or even down to 3.27 etc. Will the transmission shift ok? Will the motor be "off the cam" at those lower rpms? Will everything be entirely screwed up? Can certain simple mods be made to make the trans shift at the proper points again with the taller gears? And I'd also like to try adjusting the cam timing by advancing it a few degrees so that I can shift the torque and powerband downward to a lower max rpm range. But again, don't want to disturb the ECM gods without having a sense if this can be done successfully.
Any thoughts or sources of info greatly appreciated.
The later models have the EEC V computer chip. This chip as well as the EEC IV before is tunable. However these tuners are not cheap but they are affordable. The later 3L Vulcan engines also had a bit of tuning done from Ford, I believe they upped the HP by 10 on the 97 model, or it could have been the engines that went into the Taurus, not sure.
The transmission will shift at the same RPM's & loads as it did before you change the differential. Only thing is you'll be travelling at higher speeds when it does change gears. This totally depends on what your use of the vehicle is. Will you still tow stuff, highway cruising ,town driving etc. Ford has basically set up the engine /gear ratio for best general usage ,fuel economy etc. There are obviously some compromises there.
Good luck Aeroman,
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Green-96, XLT 2wd, 3L Vulcan, from Ontario, Canada
All original powertrain except alternator & starter motor. 292,000 kms & going strong !
Thanks aeroman. Right now I believe my aerostar is set up to be a people hauler - it's definitely trucklike in it's hauling capacity. It has a 4.10 rear and it's the extended version with seating for 7 or 8 with cargo space too. I think it's configured to haul a LOT of weight right now, especially considering it's a little 3.0 engine. 7 grown American adults + cargo is a load of about 3/4 ton. But for my uses, for the most part I'll only be driving by myself or maybe with one or two other people at most. And cargo will almost always be very minimal (mountain bikes, backpack, camping gear etc). Plus I don't really plan on towing anything substantial. I do plan on getting a light trailer about the size of a pickup truck bed, but don't plan on towing anything really heavy for any real distances. The vast majority of time I wont be towing anything. So my payload requirements are much lower than what the vehicle was originally configured to handle. I'm looking to improve the gas mileage as much as possible, as I see gas going to $6/gallon or so within the next few years, and probably $8/gal or so within 4 years. So in my view even achieving just a few more mpg is worth shooting for. I'd like to get this van to achieve at least 25 mpg, and hopefully closer to 30 mpg if at all possible.
But getting back to the transmission, you say that it will shift at the same rpm points. Isn't there also vacuum actuation on the shifting? Or is it based entirely on engine rpm? Also, even with the 4.10 rear that's in it right now, at highway speeds the engine doesn't seem to be spinning very fast to me. I don't have a tach so I can't tell how quickly it is rotating, but it certainly doesn't seem to spin as fast as my old roadrunner engine and it had a 4.10 rear. So I'm wondering just how far I can go with the gears. Pablo said 3.45 were optimal with the 3.0 and manual shift. Hopefully they'll work as well with an automatic...and maybe I might get away with the 3.27's too?? Hard to say, just wish I knew in more detail how it all ties together so I can make these changes intelligently instead of just trying this and trying that.
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1997 Aerostar Extended 3.0 2WD, 28K miles
Shifting of automatic transmissions have always been regulated by a combination of speed and load. The way those parameters are detected have changed as cars evolved, especially with computers.
If you are able to accelerate gently, then yes, the transmission may shift at the same engine speeds as before. But "gently" is determined by the load on the engine. When you change to a shorter rear end ratio, the load to the engine will increase.
Your Road Runner probably did not have an overdrive transmission, like your Aerostar (and most modern cars today) have, so it will be spinning its engine faster in its top gear at any speed compared to the Aerostar.
The best way to improve the gas mileage of your van may be to change your automatic transmission to a manual. You save a little weight and power loss through the automatic, although the difference decreases when the locking torque converter engages at higher speeds. But the best part of the manual transmission is that you decide when to shift and when to clutch (coast). You also avoid most of the problems with automatic transmissions. Add that to a shorter rear end, and apply judicious driving habits, and you can gain big mileage increases.
One other thing you can do is weight loss; try to remove any excessive weight from the van.
Much beyond these changes will require very costly modifications.
Thanks 96, I'm gonna print that out and have a look at it. XLT I'd love to have a manual transmission, that's what I've wanted all along. But the vehicle I have now only has 28k miles and it has the more modern automatic with locking converter. Seems a waste to take it out now, but I'm definitely considering it anyway. I figure I could probably sell the tranny in it for enough money to buy an old donor machine and a manual shift ECU. I've already taken out the seats to get it lightened up some. And my roadrunner had a 4 speed manual shift, the aerostar has a 4 speed automatic (point being that both have 4 speeds), they also had about the same size tires so I was thinking they'd be roughly proportional in their final drive ratio. But the "hemi box" transmission in my roadrunner probably had a closer ratio than the aerostar's does. But then the aero is designed for hauling, so maybe it's closer than I think? Dunno. Just seems like the aero's motor was loafing along at 55 mph, I was surprised to learn it had a 4.10.
Otherwise I am thinking about tweaking the cam timing as decribed earlier. What do you think about that? It shouldn't be expensive, all it involves is a pretty inexpensive cam degree adjusting adapter. If I advance the timing a bit (maybe 6 degrees?), from what I've read this should make the engine produce more torque and power at the low end, which is pretty much just what it would need with tall gears. I'll probably make other mods like install an electric on demand cooling fan, use synthetic oils etc.
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1997 Aerostar Extended 3.0 2WD, 28K miles
Aero-fan, your Aerostar's 4th gear is an overdrive, unlike your Road Runner's 4th gear, which is just 1:1. This allows the Aero's engine to run at much lower speeds above certain vehicle speeds. So its effective final drive is probably closer to 3.5:1 (I don't remember the overdrive ratio).
Advancing the cam should in theory improve low end torque, but I'm not sure how the engine computer is going to respond to that.
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