I need help with ECU Problems! Here is how I got into trouble.
1. Diagnosed a bad fuel Injector.
2. Installed an injector with the wrong coil resistance. The car has 16 ohm injectors and I installed a 4 ohm injector.
3. Car wouldn't run!
4.Installed the 4 ohm injector- car wouldn't run.
4a. Found that the injectors put out way to much fuel!
5. Decided i'd blown the ECU with too small a load on the output transistor.
6. Removed the ECU and checked the output transistor to the fuel injectors. checked OK.
7. Tried the ECU in another car.Wouldn't work! Too much fuel out of the injectors.
8. Got another 0280 000 951 from the wrecking yard-$75.
9. Plugged in the ECU. Same results.I should have checked the ECU in the other car before plugging it into the symptomatic car.
10. Checked all the ECU inputs per the Bently Manual. All Ok except the temp input read 2000 ohms which was high- should have been 1000 ohms. don't believe that should have been a problem.Also the engine speed voltage was 6.5 volts when cranking -not 8volts minimum.

Dare I plug in another ECU from the wrecking yard? After I check it in a known good car!!
Could the first one from the wrecking yard have been bad?
Would the local Volvo dealer have a machine to check the ECU inputs?
Suggestions solicited!!
Thanks,
Art

If you have another 240 available that is a LH 2.4 check your ECU's to see if they are good. Then check to see if you have spark and fuel.
Dan

This is awfully complicated and I can't be sure of helping you out, but I can say 951 ECU failures are very rare (I've seen one or two out of ~100), so pretty unlikely you got a dud from the yard, but possible. I doubt you wrecked an ECU with a fuel injector. Do you have a bent pin at the ECU connector? Bad fuel system fuse or relay? I would go back to basic, simple 240 stuff on this one.

Agreed. Seems really weird to me, as it must to Art.

I tried some creative reading between the lines to come up with this. I'm hoping Art will post back and set me straight:

1. Diagnosed a bad fuel Injector.
It was running, but only on 3. Pulled plug on #4 injector, no change. Swapped #4 and #3, still misses, but now pulling #4 injector cable makes it die, pulling #3 injector plug offers no change.
2. Installed an injector with the wrong coil resistance. The car has 16 ohm injectors and I installed a 4 ohm injector.
Got an injector out of my turbo 700. Swapped in place of the clogged one.
3. Car wouldn't run!
only the turbo injector is opening now?
4.Installed the 4 ohm injector- car wouldn't run.
???
4a. Found that the injectors put out way to much fuel!
Pulled spark plug and found cylinder awash in fuel
5. Decided i'd blown the ECU with too small a load on the output transistor.
Expect to find short emitter-collector, holding all injectors open constantly
6. Removed the ECU and checked the output transistor to the fuel injectors. checked OK.
measured resistance pin 17 to 18 - open circuit with positive probe to 18.
7. Tried the ECU in another car.Wouldn't work! Too much fuel out of the injectors.
Other car also a 240?
8. Got another 0280 000 951 from the wrecking yard-$75.
T402 also looks not shorted? What unlikely coincidence could this be?
9. Plugged in the ECU. Same results.I should have checked the ECU in the other car before plugging it into the symptomatic car.
If it is a 240...
10. Checked all the ECU inputs per the Bently Manual. All Ok except the temp input read 2000 ohms which was high- should have been 1000 ohms. don't believe that should have been a problem.Also the engine speed voltage was 6.5 volts when cranking -not 8volts minimum.
agreed the temp reading is gonna be a swag, and if you condemn it, the reading better be an order of magnitude off to agree with the symptoms. The "engine speed voltage" is a 12V rectangular wave some tech writer found made his DVM show 8V.
--
Art Benstein near Baltimore

Police were called to a day care where a three-year-old was resisting a rest.

Art Benstein near Baltimore Here is some further info.
1. No 1 injector was diagnosed by removing spark plug wire with no change in idle(still rough) remove injector plug(still rough).Check compression on No 1 (160psi). Plug sparking. conclusion =fuel injector.
4. Perhaps.
4a. Pulled fuel rail, disconnect coil, crank engine--very high fuel flow from injectors.
6. Opened ECU and checked transistor with an in-line transistor checker. checked OK
7. Other car same year 240. Smelled lots of fuel when cranking.
8.Haven't checked the output transistor yet in the 2nd ECU. Will use the ohm meter between 17 and 18 this time-- good info(method)
9. Same year 240.

I'll try the wrecking yard ECU in the other 240, but expect the same results.
I don't want the input to the ECU to blow another ECU, if that's what has been doing it.I'll try the next ECU in the running 240 first this time!
Keep the suggestions coming!
Art

You certainly have an uncommon situation. The LH2.4 ECU seems well protected against input malfunctions. It is supposed to run a rich, limp-home mixture based on rpm in the event of way out of range sensor readings- about 5mS at idle, not a flooding mix, and I haven't seen any reports (ever) of permanent damage resulting from anything short of prolonged reverse polarity (backward jumpstarting); for example, the AMM input is protected by 5.6K series at the pin. Even nearby exhaust system welding - only rumors and speculation. Maybe you've found a new way to destroy them?

Maybe you could pick up a noid light for the convenience. Should be an auto parts store item, I'd think. You'd see if the ECU did anything like open the injectors at key on. If not, then you could use the diagnostic output test before actually cranking. Careful it doesn't fill the crankcase with fuel and wash down the cylinder walls.

In any event, it sounds like you have a good plan to get to the bottom of it, and a not-too-costly source of parts. Testing the parts first in the other car is a good idea in hindsight, but I don't think anyone would have known to do that. I hope you pin down the answer for us all.

Here are some "normal" readings I made quite some time ago. Upper trace is the ignition derived "engine speed" signal you were looking at on pin 1. Lower trace at injectors. Still about 5mS, just a whole lot more squirts during cold cranking. The 951 does not use the 5th injector your 90 has.



Cranking - using light bulb for load instead of injectors (don't wanna flood or start)



Running at idle


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Art Benstein near Baltimore

Hello,


You said that the fuel flow was very high, this is indicative of a hardware malfunction (I'm sure this is old news.)

Your ECU's air meter sensor input may be being countermanded by intermittent voltage transients that are not evident during poke and probe diagnostics. You should ensure that the power supply for the AMM is not being fed into the computer input by failure or defect.


Goatman

Hi Art,

4a. Found that the injectors put out way to much fuel!

How are you determining the injectors are putting out too much fuel?
--
Art Benstein near Baltimore

Dijon vu: the same mustard as before.

It's a 240!
Art