Im working on a friends 740 Turbo that wouldn't start. I had no information about how it got this way and its been sitting for approx 2 years.
I found initially no spark. I have traced that down to a bad distributor cap. I replaced the cap and rotor with new parts. The battery was also shot so I replaced that.
I found a nice "no start" flow chart on the internet for this particular vehicle that has helped tremendously. Everything was starting to check out ok until i couldn't get the fuel pumps to activate. EM2 on the fuel relay wont close when the key is in "Start". If i manually close EM2 with a screw driver the car starts and runs great (both fuel pumps work fine). How do I get EM2 to close??
Im guessing its tied to the Hall sensor. I need help isolating this problem.
Any ideas, because im running out and ist driving me crazy. Per the flow chart i have proper inputs to the hall sensor.

 

I double checked the inputs to the hall sensor last night. With ignition on I got 10.95v on the red wire. 5v on the blue and 8.0 ohms on the ground. The ground is supposed to be 0ohms. If I turn the ignition off I get 0.3 ohms. Is there a problem with the ground or am I using the multimeter wrong?

 

you can't use an ohm meter on a powered circuit.

 

Ok, so I'm going to take this response: as a yes to my question "am i using the multimeter wrong"

So with the ignition off I'm getting 0.3 ohms, is this correct or am I still using it wrong?

I was anticipating more of a helpful response to my problem....

 

Do you have spark?

 

I don't have any car with a hall sensor here, I don't know what the resistance should be. a hall sensor is sort of a transistor thats sensitive to a magnet, so DC resistance is kind of iffy anyways.

 

The crank sensor on 740 is a hall sensor.

 

Yes, I have spark.

 

just to clarify, thats true up through 1988 (and 1989 turbos) but 1989+ (1990+ turbos) use LH2.4 with the crank position sensor, same as 940's.

the OP has a 1987, so yeah, hall sensor, we established that.



anyways, in answer to his original question... the hall sensor goes to the ICU (ignition control unit) which uses it to generate the spark timing, so if you have spark, then the hall sensor is working. the ICU also sends the timing signal on to the ECU, and the ECU uses it to both turn on the fuel pumps, and to generate the fuel injection timing. when you first turn the ignition on, the fuel pumps may run about 1 second, but not all cars do this. Then when the car is cranked over, they come on and stay on til the engine stops turning, and go out about 1 second later.

 

I was guided to alldatadiy.com for assistance, lots of info. Anyways, I'm going though the fault tracing steps for the ECM. So far I've found one problem; terminal 12 (Constant idle speed system) should show a resistance of infinite, but is registering 6.22 ohms. How do i correct this problem?

 

The fuel pumps do not run when the ignition is first turned on.
So how to i get the signal from the ECU to turn on the fuel pumps??
If i remove the fuel pump relay and put a jumper between #30 and #87/2 the pumps turn on....so the pumps work, i just cant get a signal to the relay.

 

was that AT the ECU, or was that at the plug with it disconnected from the ECU?

pin 12 is, I believe, the full throttle switch, which is fairly unimportant, it should be open (infinite ohms) AT THE PLUG WITH IT UNPLUGGED. the resistance at the ECU side is immaterial. pin 3 is the idle switch, that should be 0 ohms at the unplugged plug, with the throttle at idle, and as soon as you touch the gas pedal should be infinite ohms

note that the pinouts are different on LH2.4 cars, so make sure the guide you're following is specific for LH2.2

 

that suggests a bad relay. have you replaced it with a known good one from another car?

the LH2.2 ECU grounds fuel relay pin 86/2 to turn on the fuel pump relay. this pin is connected to ECU pin 17 via a blue-green wire.

 

I replaced it with a brand new relay, right out of the box.

 

is any of the wiring harness under the hood crunchy? Volvos up to 87 were subject to this, so-called biodegradable wiring.

 

That was at the plug with it disconnected. The diagram I have shows pin 12 as the "constant idle speed" which is a red/white wire. I verified the wire color, it matched the diagram.

 

Ill check this weekend, i do recall seeing a wire that was missing some of the sheath. Ill investigate its function soon.

 

its the inner insulation, the colored coded stuff, that flakes away, leaving corroded naked wires behind. bad juju.

are you talking about pin 12 of the ECU or the ICU? I have the wiring diagrams for the LH2.2 ECU (fuel injection) as used on mid 80s 240s, I do NOT have the wiring diagrams for the same year 740's, only for 1991/1992 740, and all 940.

the ECU are the same between same year 240 and 740, the ICU are NOT, the 87-88 240's used a chrysler ICU


anyways, according to this diagram, which is really hard to read,
http://www.volvowiringdiagrams.com/v...%20Diagram.pdf

if you find the LH2.2 ECU on the B230F block on the left side of page 8, in the middle, pin 12 is wired via a dotted line (for the F non-turbo version) to the full throttle switch, also to test point 220. for the FT turbo version, its not wired except to the test point.

my 1987 LH2.2 Volvo 240 diagram shows more or less the same thing but with different wire colors.

on OTHER ECU's its something else.

 

fwiw, here's the IGNITION greenbook, you have the EZ117K, mated with the LH2.2 fuel injection. this has the theory, troubleshooting, and everything for the various ignition systems, including yours.
http://www.k-jet.org/files/greenbook...incomplete.pdf

 

and THIS wiring diagram, for the contemporaneous 760 Turbo, the LH2.2 and EZ117K pages for the B230FT, they show ECU pin 12 coming from ICU pin 15 (different car, but same ECU and ICU).
http://www.k-jet.org/files/greenbook...g_diagrams.pdf

in fact, that other 'all car' diagram shows the same thing, its just harder to read. In "S6" of that hard-to-read diagram, you'll note that EZ-K ICU 260 pin 15 is a red/black wire to LH ECU 217 pin 12. Near as I can tell, this is the knock control fuel enrichment signal... the ICU senses knock, and tells the ECU to richen it up..