Changed motor from 4.1 to 4.5 but not ecu

[johnnya]

I have changed the motor in my 87 Fleetwood from a 4.1 to a 4.5. Should I have changed the ecu to a 4.5 ecu or not? It works fine but tries to stall for about the first two minutes after starting.

[maydog]

Sounds like maybe the ecu is having calibration issues after going closed loop. The proper ECU may cure the problem.

[Scotty]

I have changed the motor in my 87 Fleetwood from a 4.1 to a 4.5. Should I have changed the ecu to a 4.5 ecu or not? It works fine but tries to stall for about the first two minutes after starting.

This is one I want to follow. Someone else is having a similar problem to this.. Logan had an idea that may be useful to you. Here is the link:

http://caddyinfo.ipbhost.com/index.php?showtopic=5616

[Ed Hall]

Someone else swapped from a 4.1 to 4.5 in the other forum. Refer to

Click Here!!!!!!!!!!1

[KevinW]

I don't have the manuals to make a comparison; I would guess that the ECM pinouts are quite similar, if not the same, between 1987 and 1988 (most of the changes were internal to the engine and in the calibration). A 1988 ECM should be quite inexpensive at a wrecker; assuming it works and the injector capacity is similar, it should run a lot better with a factory 4.5 calibration.

[bobnsue2]

Sounds like maybe the ecu is having calibration issues after going closed loop. The proper ECU may cure the problem.

Hi,

Hi,

The comment about closed loop is backwards.

When it is first started it is in open loop. Only using a few of the sensors for fuel mixture. After it warms up it goes into closed loop which is when the computer uses all the sensors and adjusts the mixture using Oxy sensors etc.

On my 91, open loops only uses the MAP sensor and coolant temp to adjust the mixture.

This is according to the shop manual.

Bob B

[maydog]

No my statement is not backwards,

Open Loop Definition: "A mode of operation in a computerized engine management system that occurs after a cold start. During open loop, the computer provides a fixed air/fuel ratio that is richer than normal to improve cold derivability until the engine warms up. "

Closed Loop Definition: "The basic principle of electronic engine management in which input from an oxygen sensor allows the engine control computer to determine and maintain a nearly perfect air-fuel ratio. To enter closed loop operation, the oxygen sensor must be producing a voltage signal and the engine must have reached a certain operating temperature. "

When the car is cold the engine is supplying a richer mixture to the engine. Since the displacement is larger, this mixture is probably fine for the engine. As the 02 sensors heat up the engine will lean out the mixture for ideal conditions for a 4.1 not a 4.5 displacement.

Open loop is kind of a generic "safe mode" that should work under a variety of conditions. Closed loop is more specific to operating conditions and is only applies when all the sensors are within the correct range. Just because more sensors are operating does not mean that the engine, in this case, will run better.

Until you can find a replacement ecu or higher pressure FPR, you may find the car drives better if you disconnect the 02 sensors. This should leave it in open loop, but the gas mileage may suffer.

[johnnya]

Hey;

Thanks a lot guys I have checked the links and am getting some where with it. I will try the o2 sensor disconnection soon.

Whom new so many people would know about this.

Johnnya