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No Injector Pulse - '91 745T with LH 2.4

CaliMeatWagon

CaliMeatWagon

Cause of Head Scratching
Joined
Jun 29, 2011
Location
Stockton, California
1991 Volvo 740T with LH 2.4

Car was sitting for awhile, started a couple times, then went no start.
Gas was bad, fuel sock corroded, so it got replaced, and the tank and lines got cleaned.
Both pumps are fine, working and pushing fuel. I'm getting spark, and it will briefly run on carb cleaner.
The problem is the injectors are not firing. They are getting battery voltage, but are not pulsing.
I checked Crank Position Sensor and it seems to be fine, with 160ohms of resistance, and when cranking I get a voltage reading from it.
What do I need to test next, and what should the voltage/resistance be?
 
You have spark, which indicates that the CPS is working correctly.
Since the fuel pump relay seems to be working, the other components inline before the injectors are the radio suppression relay and the ballast resistor. Could be as easy as a bad ground.
EDIT: There is a ground point inside the LH inner fender right behind the headlights and it's a bit prone to corrosion, I've had that happen when switching on my high beams switched my engine off and all sorts of weird stuff. The radio suppression relay is in the vicinity of that.
 
white855T said:
Connector on radio suppression relay bad/not making contact. This is what grounds injectors.

Right by or in front of coolant reservoir.
Click to expand...
Fa182 said:
You have spark, which indicates that the CPS is working correctly.
Since the fuel pump relay seems to be working, the other components inline before the injectors are the radio suppression relay and the ballast resistor. Could be as easy as a bad ground.
Click to expand...

Do you two know where the ground is? My AllData subscription expired.
 
white855T said:
Connector on radio suppression relay bad/not making contact. This is what grounds injectors.

Right by or in front of coolant reservoir.
Click to expand...
No. The radio suppression relay supplies power to the injectors. The ECU grounds the injectors. I wouldn't be surprised if the fuel pump relay is bad. That is actually 2 relays in one. One side of it turns on the ECU. Also, check fuse 11. That supplies the ECU.
 
2manyturbos said:
No. The radio suppression relay supplies power to the injectors. The ECU grounds the injectors. I wouldn't be surprised if the fuel pump relay is bad. That is actually 2 relays in one. One side of it turns on the ECU. Also, check fuse 11. That supplies the ECU.
Click to expand...

I don't have an easy means to swap in a spare, is there a way to test the relay. I read on one site about popping off the cover and manually depressing the relays while trying to start it, but I'm not sure about that.
 
2manyturbos said:
The ground plate is on the inner apron right behind the head light, It is a piece of sheet metal bolted to the apron with several male spade connectors sticking out of it for the female ground wires to connect to.
Click to expand...

Okay, found it, unplugged the spades, cleaned them, and the connector, tested to make sure ground was good (complete circuit between it and battery negative terminal), and tried starting it. No go.
 
CaliMeatWagon said:
Fuse is good, so is Fuse 1.
Click to expand...
You're not looking for a blown fuse. The fuses may have a hard scale on the surface of the contacts preventing them from supplying enough power. I bought a non running 1992 940 Turbo that had that exact problem and several non running 240s that had the same issue with the 25A fuse in the engine compartment. It took awhile to figure out. The car was filled with spare parts the owners had tried replacing.
 
2manyturbos said:
You're not looking for a blown fuse. The fuses may have a hard scale on the surface of the contacts preventing them from supplying enough power. I bought a non running 1992 940 Turbo that had that exact problem and several non running 240s that had the same issue with the 25A fuse in the engine compartment. It took awhile to figure out. The car was filled with spare parts the owners had tried replacing.
Click to expand...

Pulling the fuses they look good. I even made sure to clean the contacts with a wire brush and they look brand new.
I'm getting continuity through them as well. Tried cranking it, no start.

Any other test I can run?
 
Check whether you are getting power to the ECU. I don't have a wiring diagram in front of me. You should be able to come up with one online. It is possible your ECU had failed. The early 5XX ECUs were known to be problematic.
 
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