I need a Calibration Package Chip for a 1991 Cadillac DeVille with a 4.9 Engine. Also for the same car a Prom that fits on the ECM.

no problem told just hunt. sad no?
other answer is for new car Airbox = air cleaner box.
and is wrong.
3.3L GM V6.
most old cars ECM is in passenger compartment far cooler than near any engine, and back then that was true. (hot ecm have shorted lives)
no it is not at hood air box, 1991,


IT IS PNP. (no programming but has a PROM pack)
ACTUAL 99% SENT IN ARE GOOD. INPUT SENSORS BAD. or output actuators bad or 50 other causes and 20 + tests to find them.

here is the real answer and told at Fixya

The ECM is mounted on the right side of the dash above where the passengers feet would be.
The lower panel will need to be removed to see it.
Here is the service manual procedure to remove it.

1. Turn ignition to "OFF".
2. Disconnect battery ground cable.!!!!!!!!!
3. Remove right hand hush panel.
4. Disconnect connectors from the ECM
5. Remove ECM mounting hardware.
6. Remove ECM from the passenger compartment.
7. Remove ECM access cover.
8. Transfer PROM unit to replacement ECM. Using two fingers, push both retaining clips back away from the PROM. At the same time, grasp it at both ends and lift it up out of the socket. Do not remove the cover of the PROM. Use of unapproved PROM removal methods may cause damage to the PROM or socket.

all this is in the service manual, BUY ONE?

this post is for only 1 engine, or for only one VIN
I can not read your vin
or buy the shop manual and read it
real ones are here, or on CD
buy it? and not work blind again. or mess up easy guessing procedures.

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2380057.m570.l1313&_nkw=1991+Buick+Century+service+manuals&_sacat=0



end

Why ? what are you trying to do ? Replace it with a used one ? Your vehicle PCM has a prom chip inside , just pull it an transfer to the new (used ) PCM / ECM . This chip has the correct running info for your vehicle.

Hook it up to a code reader via OBDII for specifics. Tecnically, there is no reason to flash your ECM unless you are using another ECM from a parts car...for say a 1989 Chevy. This ECM was used on the 1989 S-10 truck with the 2.5L four cylinder, the ’89 Camaro with the 5.0L HO V8 and the ’89 Corvette with the 5.7L Tuned-Port V8 engine. The only difference (aside from the vehicle wiring harness pin population) was the PROM. The PROM contains the calibration software for the ECM. Another reason would be to bypass a security locked ECM like a 2001 Pontiac GT which was notorious for shutting off the fuel pump if the security chip in the key lost connection through switched power.

No , it has a PROM that plugs into the ECM ! The PROM - program read only memory chip . it has the engine operation information programed on it ! The ECM is located in Front seating area, passenger side, under dash, above passenger side of glove compartment cavity, mounted on firewall !

The ecm,the last didget can't be under no more than 2 didgets or over 2 didgets if so the ecm is program for different sensors

ECM = Engine Control Module
ECU = Engine Control Unit

On '96 upper vehicles this is the PCM (Powertrain Control Module), also called CAR COMPUTER.

Good luck.

anything will fit with a bit of gentle persuassion ,now how about a nice small diesel engine with a manual gearbox for a start ,so it has a very high fuel economy

The only thing that it would most likely be (if not the ignition module, the fuel pump, a faulty fuel pump relay if applicable, or a faulty ignition coil pack but only if one coil pack is used, and if more than one coil pack they would all have to be faulty to shut down the engine) is the ECM/ECC, especially since the vehicle shuts down about every 10 minutes, and that is the classical sign of over-heating electronics that act almost normal until the electrical componet becomes too hot and then begins to malfunction.

The ECM (Engine Control Module) or ECC (Engine Control Computer) for those vehicles were not manufactured very well and were prone to failure, and that is why you can purchase a re-manufactured one for only $85.00-$89.00, and the re-manufactured one will not have the stock defects.

If you do purchase an ECM/ECC and if it has a PROM chip (Programable Removable On-board Memory) that must be installed from your old ECM/ECC be very careful when removing and installing the PROM, and the plastic retainers on either end of the PROM will push back away from the PROM and lift the PROM out of the connector on the circuit board. When installing the PROM be sure that the retainers are pushed back and that when the PROM is pushed down into the connector that the retainers lock in the PROM. Not all vehicles will have a PROM and be very careful with the PROM if you do have one to remove and install because it can easily be damaged, and if it is a necessary procedure to change the PROM, then the ECM/ECC that you purchased should come with a detailed diagram and procedure for you to follow so that the PROM is properly installed into the ECM/ECC.

Here are two links that show the price of the ECM/ECC from a major auto part store depending on if the vehicle has a 2.5 liter 4 cylinder engine, or a 3.3 liter V-6 engine.

Link for 2.5 liter engine.
http://www.kragen.com/ProductDetail.aspx?MfrCode=A1C&MfrPartNumber=777748&PartType=248&PTSet=A


Link for 3.3 liter engine.
http://www.kragen.com/ProductDetail.aspx?MfrCode=A1C&MfrPartNumber=778706&PartType=248&PTSet=A

Bad ecm (engine control module) or prom chip issue. Prom is located inside ecm QDM is quad driver module which is electronic portion of ecm. Would replace ecm first remebering that prom chip must be swapped from old box to new.

get new key with newer chip or replace ignition cylinder.