I'm looking for help finding the correct part number for the ECU on a 1994 Non Turbo Volvo 940. This is located behind the floor right side kick/foot panel on the passenger side. (All it takes is a screw driver one allen wrench to remove the rail cover near it to remove the cover.)

It appears that someone had replaced this previously and based upon my problems, I'm "guessing" they put in the incorrect one? Or the incorrect one for my car. (I know this is NOT the original based upon the writing in magic marker indicating part numbers and year etc. which appears it was purchased used from a salvage.) From what I'm finding there is more than one part number for this ECU for this car.

Another question is... "Why would anyone replace this part to begin with?" Do they really ever go bad?

This would make sense since there are two type known "types" Regina and more commonly I believe is the Bosch. My car is the Bosch.

(If you can help, great!!! I am also thinking that I may have call the dealer for a possible VIN number match to correct ECU.)

Based upon all the recent parts I've replaced and maintenance items I chose to get current, I would say my problem is unique. The car is a 1994 Vehicle, so I chose to bring up as many maintenance items current to eliminate them as possibilities. Most were cheap, some not so much, but still all in all, inexpensive because I did it myself. See the thread below for more info.

https://volvoforums.com/forum/volvo-...problem-66069/

Below is just to elaborate and perhaps help others suspecting a ECT problem.

In short, once I replaced the ECT (Engine Coolant Temperature Sensor) or sometimes referred to as the Fuel Temperature Sensor (near the rear of the engine on the drivers side) the car became hard to start.

I found by trial and error that if I unplugged the AMM (Air Mass Meter) the car would start no problem, but run very rich based upon the smell. Once warmed up, I plug back in the AMM and it runs great!

I just put the old/original ECT back in the car as a test and found that the car starts but idles rough at first while pumping the gas to keep it running. It also smooths out when warm BUT seems to run a bit "sluggish" with poor fuel economy compared to when I put in the new ECT.

The measurements on the old ECT were 3.64K Ohms when room temp and the new one measured 2.68K Ohms. When placed both in hot water the new one went to lower ohms than the old one. (Sorry I didn't have the exact temp of the water. All I know is both Sensors in the same temp water the new one went to about 500 Oms while the old one went to about 900 Ohms based upon memory.) The water of course was not boiling and probably not as warm as the engine coolant so this would make sense.

Below is what I found about the measurements in Ohms for the ECT and as you can see below the new ECT seems to fall into the specs more so than the original.

940
With LH Fuel Injection
14 (-10) ............................ 8260-10,560
68 (20) ............................... 2280-2720
176 (80) ................................ 290-364

I think I'm approaching the conclusion soon, I would like to post the solution if anyone is interested?

 

I have a '92 245 which is impossible to start when cold. Not bad if temp is >60 or so. When it starts, it runs rough for 30sec or more and then seems to do fine. Is definitely rich, so I'm going to check for a cold start injector over-run, if this engine has it. About the only way to start it on a cold day is to hold the throttle @ 75% and then it's not too bad, else, it won't start.

Would love to hear what fixed your problem.

I think there's a control system aspect to it as it seems to suddenly start running better after running for a few minutes - as if the ECU switches something on/off.

Been going on for awhile (time wise, not that much use) but haven't done much as I haven't had many clues.

Thanks for sharing.
Chris

 

When the engine is cold, the Engine Control Unit runs in open loop mode - meaning it doesn't use feedback from the oxygen sensor to determine the fuel/air mixture. It simply uses a programmed amount of fuel the throttle position. After the engine warms to a predefined temperature, the ECU switches to closed loop mode - meaning it uses feedback from the oxygen sensor to adjust the fuel/air mixture to the optimimum ratio for emissions and economy. The signal from the coolant temperature sensor is what the ECU uses to transition from closed to open loop mode. Disconnecting the AMM will also cause the ECU to run in open loop mode.

From your measurements, your new temperature coolant sensor is within specs so I would put it in there and debug from that point. Check to make sure that the throttle body is clean and the throttle position sensor is working properly (you should here a click when the throttle closes entirely). Sometimes the throttle body on these gets gunked up and keeps the throttle butterfly valve from closing entirely and keeps the idle circuit from kicking in.

I assume when you try to start it cold that you don't have your foot on the accelerator.

 

With the old fuel/engine temp sensor (ECT) installed it starts okay. So this tells me that at the higher resistance of 3.6k of this sensor apposed to the new one, at 2.6K the car starts right up. It seems to run rich though. With the (ECT) installed I can only start the car by disconnecting the AMM until it warms up.

I've cleaned the throttle body, and double checked after reading your response that it does "click" indicating the flap is closing completely It's really an interesting yet frustrating problem.

Interesting note... There are two wires connected to the ECT. One of the wires go to the ECU and the other leads to what I think is called the Injection Module located inside the car, above the passenger side feet. With the ECU module unplugged, I measured like 5 ohms from one side of the ECU to the Engine Temp Sensor (ECT) On the other side of the ECT, a white striped wire to the Injection Module measured like 1.2 ohms. Now common sense would tell me that these should be much closer to zero ohms. So, the next step was for me to cut the wire before the module connector and measure it.

Quite the challenge indeed.