Hey everyone.


So we have a 740 that will not stay running. Its an 89 740 GL non turbo.


About 2 months ago the speedometer stopped working. Right around that time it started running real rough and stalling out.


Replaced the fuel pump relay, and checked all fuel pump related fuses. Removed the fuel line from the tank in the injector fuel rail and put it in a can. Turned the key to ACC and a little shot of gas (about a double shot or so) would squirt into the can each time the key was turned, plus you could hear the fuel pump priming. So I don't believe its a fuel delivery problem.


Checked for spark and its sparking. Pulled the ECU (Bosch JT 561 pink label, heard those could be problematic) replaced with a used Volvo reman Bosch 561 white label ECU. No change in condition.


Got a used IAC valve from a similar car, swapped it out, no change in condition. Removed wires from radiator temp switch for electric fan. No change in condition. Checked the circuit and the fan does come on, not sure if that is relevant, but thought I'd mention.


Tried messing with OBD port, getting a series of flashes / error codes on the "2" port, which I know conincides with ECU Fuel Management. Haven't been able to determine exactly which code, it just seems to consistently flash. Have to check back on that.


Pulled the vacuum line off the fuel pressure regulator, didn't seem to be leaking any gas out, which someone said suggests the diaphragm there is probably OK.


Waiting on a new MAF from guy who pulled it from a running car. Can't think of what else to check. The car will only start with the throttle to the floor and when it does start it will idle consistently with no missing in the 2500-3000 range, but as soon as you let off the throttle the slightest bit (and sometimes just on its own), it will run for 5-6 seconds and then rumble down below 500 and just cut out.


Frustrating problem - the battery is dead and we have been jumping it. I'm wondering if this could be a dead alternator, as in its getting enough juice from the jump to start it, but then the alternator isn't kicking in so it just dies? I am grasping at straws. But I don't think a bad alternator alone would be throwing the port 2 error codes.

 

without knowing the specific error code anything would be wild guesswork

after a 3 second push of the botton, the LED should blink X times, pause, Y times, pause, Z times, stop. press the button another 3 seconds, and get another X-Y-Z code. when the same code repeats, you've read them all. 1-1-1 is no error.

 

Check the crank position sensor on the rear of the motor.

 

generally a dead CPS results in a motor that won't even start, no spark, no injection.

 

a video might help you read the diagnostics.

if crankshaft position sensor is dead it might not start but what if It just has a flaky signal?

shot in the dark but try unplugging the MAF sensor and starting it , see if that makes a difference or if it is worse and also check the connector for green terminals. I had issues , cleaned those terminals and it made a huge difference.

Maybe the ignition control module has some intermittent issue? i think its above the drivers feet. I don't know if you have enough info to warrant replacing that unless you happen to have spare parts. it "could be" a lot of things like a bad trace on the board causing intermittents - maybe.

check your engine grounds. alternator ground.

look for a relay on the water bottle , If that goes flakey it can kill the engine.

look near the distributor for a little fuse holder, two red wires and a white plastic cap thing.. open it and see if it's all corroded, clean it up. if that fuse is intermittent it can cause issues.

check your fuse box , if they are corroded, get some new fuses, unhook the battery, pull them all and clean up the holders and then replace them all. - it's a weak spot. check fuses with a meter, sometimes the ends of the fuses break off from the wires but appear ok until you remove them to see the fuse wire is actually broken.

You should have around 12 volts when off, around 14 volts when running check at battery with a volt meter. if you don't have a higher voltage when it is running suspect charging system.

if the battery is dead or almost dead you might be running in sort of a brown out condition. I'd try a better battery and rule that out because you shouldn't have to keep jumping it , that battery might just not be able to hold any charge.

If you put it on a charger on the battery overnight, it should be able to hold enough charge to not die after leaving the lights on for 1/2 hr for example. if it won't do that you are asking for frustration.

make sure the battery has good connections , clean the posts and clamps. If you stick the clamps in a little jar of water with baking soda one at a time for a while it'll help clean them then brush or use some sandpaper on the surfaces.

if the water in the battery gets low this can cause the battery to die but often at that point refilling wont; make it a good battery again. but you can check the water levels and add some distilled water if it's not completely shot.

don't get baking soda in the battery. but you can wash the outside of the case down with water and baking soda just to kill any acid around the outside of the battery to prevent rust. I sometimes soak a towel in it and then let it dry and then put that under the battery so if any acid spills it neutralizes it rather than starting rust.

 

740's have blade fuses, corroded fuses is mostly a 240 thing with the old ceramic bullet fuses.

 

a air leak in the intake path between the MAF and the engine can cause it to stall at idle and only run if you keep it fairly open. check all the plastic and rubber stuff in the air path, including the rubber hoses to the idle air control under the intake manifold.

 

You are right.I have had so many of both I start getting confused ;-)

its a bit hard to get to the terminals in a 740