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'87 740 Turbo no start

black 940

Member
Joined
Sep 12, 2004
Location
Charlotte, NC
I just rescued a sad 740 Turbo wagon. It ran fine when last attempted to start (friends old car). I am not getting any spark when attempting to start. Where should I start? I have checked all the wiring to the best of my abilities. The wires going to the hall sensor on distributor look a bit suspect. Does anyone have any specs or can lead me in a good direction on this one?
 
Does the tach jump up and down while you try and start it? It's my understanding that if the needle doesn't jump, then the hall isn't sending an rpm signal, which causes a no start. If it's jumping then the sensor is sending signal and it's probably fine. How do the wires look "suspect".

Is the power stage mounted to inner fender wall?
 
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are you getting fuel? Because fuel and spark get their references off the hall sensor, like lh2.4 crank angle sensor AFAIK.
 
Thanks for the replies. I am not sure if I am getting fuel. As for the tach jumping, (honestly I have not paid attention) I don't know.

The wires look suspect as the outer sheething is coming apart it does have the yellow banded updated harness. Can anyone tell me a way to test the wires coming from the hall sensor?

Thanks a ton.
 
I just got back from toying with the car again for a few minutes. The tack only jumps for a split second when the key is switched to on, but none when cranking. Would it be safe to assume that this would have something to do with the hall sensor?
 
On my 745, I had a similar no-start situation. The car went from running to no-start overnight. Turned out to be the crank sensor (on the top of the transmission case, behind the engine block). Easy to replace (one bolt, but don't drop it into the transmission), and if the wiring insulation is frayed, it's time to replace it.
 
Update the blue connector in the middle is getting no voltage and the black on the connector is getting way to much resistance. Where do I go from here, besides rewiring?
 
Update the blue connector in the middle is getting no voltage and the black on the connector is getting way to much resistance. Where do I go from here, besides rewiring?

Test it all again pre-connector and see what sorts of readings you get. If everything is normal then just rewire. If I was in your shoes I'd just snip a good one from the junk yard and rewire that. Aside from that, clean all your grounds and connections everywhere.

Is oil coming from your distributor? Those seals are a common failure and will cause oil to leak all over those wires. Take it all apart and make sure you aren't getting leakage from there.
 
I retested and came up with the same results. I attempted to splice in some wires to do a temp. fix. I am getting the same results 11 v. on red, Blue in the milivolts and Black large ohms.

Is there anyone with some experience with this system that can help me with this?
 
the 740's that have the hall censor are notorious for the little ears breaking off the distributor housing.

best to get another dist from another car and try that only other thing you might try is replacing one of the radio suppression relays they are located on near the coolant tank if you have a 740 non turbo and on the other side next to the power steering reservoir. I had a no start issue and after replacing the relay the car started.
 
Thanks for the responce. Is there a way to test the radio suppression relay? I don't have another 740 laying around unfortunately. As for the ears, they are all fine, I pulled the distributor today and inspected the sensor and cleaned the distributor.
 
you might have some luck by pulling the relay apart gently and maybe cleaning the contacts and hopefully they are not melted in any way these things do get hot.
 
Thanks for the responce. Is there a way to test the radio suppression relay? I don't have another 740 laying around unfortunately. As for the ears, they are all fine, I pulled the distributor today and inspected the sensor and cleaned the distributor.

Testing with a multi-meter? I don't know. The way I've "tested" that relay is by listening for it to click when I turn the key. No click = bad relay. Not the most scientific thing in the world but it's worked for me.
 
n rippe, it clicks when the ignition is armed.

Anyone have a site or can tell me how to test the ignition module, coil. I know the site presented above has a brief overview of how to test the hall sensor but it does not tell you any info. past what the measures are to be. If they are not in spec, then what?


Anyone in Charlotte NC want to help with this?
 
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