Hi,

I have a 1985 Cadillac Sedan DeVille that I have done a lot of work to. A couple of years ago, I replaced the stock 4.1 with a 4.9 short block and a heavily modified 4.5 TBI intake [I have a build thread on cadillacforums if anybody wants to see it, not sure about link privs with low post-count]. I'm currently looking into replacing the 440-T4 with a 4T60E and an independent TCU. This forum has been coming up in searches a lot lately, so thought I would sign up. It'* nice to know I'm not the only idiot that sinks time and money into a 80s GM POS.

Welcome to the Forum Eric!
Look at the bright side your probably enjoying the extra power and it'* all in good fun!
I'm sure it did not cost all that much right!
Ya I went a little crazy once on an RWD 81 Cutlass, until the body mounts broke...I decided a body off resto was not in my best interest$.

Wouldn't mind seeing your build, however you will need 10 posts before you can post any links.
I am sure the Admin team will be here to Welcome you as well, and may comment regarding the competing forum link.

welcome to the site. im sure you will find many people here who dont think sinking stupid money into a car thats never going to be worth it is just fine. to me its a hobby like any other, if its something you enjoy who is to say its a dumb move. people have all sorts of hobbies that dont have any return on their money, that seems the same to me.

Just stick around a while, we will get you convinced you should put a truck 4.8 or 5.3 along with the 4l60e would be a good move too. they arent that expensive, you get over 20mpg, 300hp, and dont have to pay for the stand alone tcu.

I bought this car used for a get-around car when I moved back to Calif from extended overseas trip in the mid-90s. Never wrecked it or exploded anything so I kept driving it. It did build up a list of small problems, and a few years ago I had to decide between fixing them all or pushing it off a cliff. Everything was pretty clean, no significant rust, just a lot of small stuff to fix. You don't see these cars around much so I decided to reset the clock and see if I could get another 20 years out of it. Fresh paint, new carpeting, new bushings, springs, air shocks, all new brake parts, a few Fleetwood trim package upgrades, and so on. Still working on this stuff part time, just keep polishing the turd.





Also did a lot of work on the engine during this time, trying to address persistent problems and improve basic performance. However it kept having problems, poor compression, brittle rocker guides that were snapping on short trips, CEL periodically coming on without throwing codes, oil tests showed small amount of coolant that was probably a leak in the intake, just kept fixing small stuff, but the engine profile did not get any better. Old and tired and unreliable, needed to be retired.

The HT4100 originally in this car is infamous for reliability problems and low power, so I didn't want to put another one in. The most common swap is a 4.5 TBI from 87-88 but I really wanted to go beyond that. I found that TBI 305 swaps to 350 were pretty common and only required switching injectors. Math shows that a Cadillac 4.9 is about 300 CI, and less than 2% difference from a Chevy 305. New plan, use a 4.9L short block, with a TBI intake, Chevy 305 injectors, and 4.1 sensors and ignition.

Found a low mileage donor at a salvage yard I had used for rebuilding my Jeep Cherokee and stripped it down to the short block





Acquired a 4.5 TBI intake to replace the 4.9 PFI intake



Had to make some minor adjustments to get the ports matched up







Shaped and rebuilt a 4.5 throttle body





Reassembled with mix of parts to make it all work. 4.1 exhaust had to be retained due to cross-over, delete the stock AIR assembly and vacuum pump, coolant outlets were changed, stuff like that. Mostly bolted up and came together pretty easily.





After some tweaking and fixes, it starts and runs great with lots of power for prowling and passing. It runs a little rich at cold start, but evens out as soon as it goes into closed loop, which could probably be corrected with adjustable FPR. The real problem is that my 440-T4 started slipping in 2nd when cold, and slips most of the time in 3rd when torque lockup is not engaged. I spent a lot of time trying to correct it from the outside--adjustable vacuum modulators, replacement TV cables, fluid treatments, etc--but I am 90% sure that the piston seals are shot. The 440-T4 cannot be serviced in the car so everything has to come back out in order to affect repairs.

At this point I do not want to put another 440-T4 back in, and am exploring options for significant upgrade that is mostly transparent, to go along with the 4.9 TBI upgrade. First option is a 440-T4 from 90 DeVille that is drop-in replacement, it would have some significant improvements over the 85 but it would still be a 440-T4 with weak parts that must be removed for any repairs. Second option is 4T60E from a 92 DeVille with a standalone TCU, should have minimal differences since it was designed to work with the 4.9 in a C-Body (my existing half-shafts may even be compatible because of same chassis) and is a bit more serviceable in the car. Third option is a 4T65e from a 97/98 GM, stronger internals and lots of upgrade options, but the only thing it shares in common with my car are the bolt holes, and I would certainly need to do some wiring and make new shafts, maybe more if I cant find a good match for gearing/stall. I am actively exploring 4T65E pathway now, and Google gives a lot of hits for older posts on this forum, so I am hoping to get some of that knowledge on me.

very interesting, unique. you tuning the car to make that stuff work together?

No programming required. The computer is pretty simple and only looks at rudimentary data values, and generates pretty basic signals in response. As long as you are able to give it the info it expects, and able to use the signals it generates, it all works.

Mechanically the 4.9 is basically the same as the 4.1 just bored and stroked (and a lot of structural improvements), block is similar, crank and cam profiles are basically the same, lots of shared parts and gaskets, so mechanically it moves the same. Lots of little changes like roller rockers instead of flat tappets, structural webbing in the casting, etc. Distributor in the same place with the same lower assembly, but different electronics for the 4.9, reinstall my old distributor and ignition parts and it is all the same again just better.

The central thing is Fuel Injection system that is easy to trick. Basically the butterfly valve on the throttle body only controls how much air enters the system. Then the computer measures the airflow, and applies fuel to match (and lights a spark at the right time). Air temperature and manifold pressure sensors tell the computer air density. It already knows air volume (cylinder displacement), so density tells it how much O2 is present, and then it looks up correct fuel in the table and fires the injectors for the appropriate duration. Chevy TBI injectors use the same fuel pressure and duration, and the only significant difference is the size of the opening, so ~100ms duration on a 5.7L injector flows more than ~100ms duration on a 4.1L injector but otherwise same operation and are interchangeable. Just match the injector to the displacement.

Like I said the only real problem is its a little bubbly at cold start, but once the O2 feedback kicks in the computer is able to tweak the injector pulse duration and it evens right out. 305 is the closest I can get on TBI injector so I'm kind of stuck on that. I could probably put an adjustable FPR in the throttle body to reduce the amount of pressure on the injectors (thereby reducing spray volume), but I need to get transmission sorted before I do any more engine work.

it just seems impressive to me that it runs good at all, that it has enough adjustment. the guys using the 80'* efi stuff and the early tbi dont normally try and modify it because even a cam swap or something will put a tbi 350 out of range of the stock tune. i dont know much about it but maybe someone can tune your chip closed loop seperate from open.

Well I did not change to v6 or supercharger or port injection or put in racing parts, the only thing I changed was displacement and kept everything else the same. Jeep community also does this a lot, taking a stock 4.0 6cyl and stroke it to ~4.7, then go find injectors from another car with the desired pressure * flow to match the increased displacement. In my case the fuel pressure is pretty much the same for GM TBI cars so I only needed to get close on displacement.

At some point I will install an AFR monitor in the exhaust and put an adjustable FPR in the throttle body, then change the fuel pressure to get it so that its not as rich at cold start, but right now it is perfectly fine for the amount of driving I do (not much with the slippage) and I dont need emissions testing in this county so there'* no hurry.

You can see the full thread here if you are interested in the details.

Trans appears to be the same in that its just a handful of simple inputs and outputs that should be easy to fool. The ECU only controls torque lockup but otherwise assumes that the transmission does everything on its own, so all I have to do for seamless integration is feed the ECU some signal data and then let it signal the aftermarket TCU for lockup (it will throw a code if it doesn't control the TCC lockup--per the FSM, it does not monitor the circuit directly and instead looks at RPM drop to see if it succeeded). Should be able to do that with the TCM-2000. Mechanical issues are more challenging at this point.

they are pretty proud of that tcm. in that link i put in your other thread the guy adapted a diesel 4l80 controller to a 4t60e for less than 200. it was more complicated but you seem to like a challenge.

you might consider swapping a whole 3800 series 2/4l60e, its got 5 more Hp than the 4.9, and most get over 30 mpg. and its cheap most all of them go to the yard with good engine/ trans, bad body. my inlaws had a 96 forever that ran and drove perfect but the frame had a bunch of soft spots and cracks and the junk yard maybe gave them 2 or 3 hundred. you see ones like that all the time you could get the whole car and swap everything, have the bad stuff tuned out. couple hundred for that but still cheaper than just the TCM-2000. and once you have converted to obd2 its so much easier to work on and mod. if you get real lucky you can find a wrecked l67, they have 240hp, 280lbft stock and unlimited mods. i dont think a 96-99h body would be too hard to do, similar size and width to the C