Hello,

I'm new to this forum and I just want to thank everyone in advance for your help. I have a 1985 240 that will turn but not start. This problem first arose as a hard to start issue with having to crank the car a lot to get it going. Once running it would occasionally start to stall but would pick back up if I let off the gas and then gave it more gas. Now, when it was trying to stall if I held on the gas it wouldn't completely stall out but it would back fire and black smoke would come out the back. After a few months of having this issue and driving it only short distances the car completely died on me and I had to have it towed home. When I try to start it the engine turns but won't catch.

Through the help of these forums I've done the following in trying to trace down the problem:
-Replaced the in-tank hose on the in-tank fuel pump.
-Verified that fuel is getting to the engine and the injectors are working.
-Timing belt is in good shape and properly installed.
-Replaced distributor cap and rotor.
-Confirmed spark plugs are not igniting.

That last bullet point is where I find myself stuck. Before I replaced the cap I had spark on the #1 cylinder but not #2 and I had spark from the Coil. After replacing the cap and rotor I retested and had a much stronger spark on both. I stopped there and never tested 3 and 4 because I thought everything was good but the car still won't start. When retesting I wasn't even able to get a spark directly from the coil.

This is wehre I find myself stuck I'm not sure the best route to take from here. My thoughts are that it may be a bad coil, ecu, or hall sensor. I do think the hall sensor may be alright because I had the distributor fully out and when I spun it with the ignition on It would trigger the injectors but still not produce a spark.

Well, there's my problem I apologize if it was to long but I wanted to give as many details as possible.

 

Part 4 -1988 Volvo 740 No Start Diagnostic Case Study.

 

when you crank the engine , does the tach needle bounce?
If not you have either a bad Power Stage or a bad Hall sensor. I would be inclined to think Hall sensor (if no spark, or a bad connector wire from the distributor to computer)

 

an 85 240 doesn't have a power stage, it has a chrysler ICU which drives the coil directly.

an 85 is right in the middle of the worst of the 'biodegradable wiring harness' era. unless the engine harnesses have been replaced all bets are off, you can chase your tail all day trying to debug problems caused by bad wiring.

 

The wiring the to the hall effect sensor should be checked if not the hall effect sensor itself.

 

Thanks for all the reply's everyone!

Since I first made the post I've done some more testing. I've jumped the connector to the hall sensor to test if the sensor was bad and I still didn't have any sparks. I also tested the voltage and resistance at the ICU and it tested alright. According to the books (Volvo Green Book for Ignition up to year '85 and "Volvo Problem Solver" by RNG) this would point to a bad ICU but with these not failing often I'm still hesitant to believe that's the problem.

I'm not sure if the wiring harness has ever been replaced and I don't have a lot of money to buy a new harness. Is there any easy way to test the wiring between the hall sensor and the ICU?

 

new harnesses for older volvos are for the most part unobtanium. the primary (injection) harness for our 87 is no longer sold and everyone is out of stock.

I'm assuming your car has the 'chrysler' ICU mounted behind the right headlight, this has a 9 or 12 pin rectangular connector on the face, and a vacuum funnel thing on the side of the bottom.... that connector is VERY funky, do NOT unplug it unless you absolutely have to, and then pull it *straight* out, don't rock it. I had to use a small pointy tool to tighten the pin sockets on our 87 with the same setup, and I put a whole lot of silicone grease around the outside of the connector, and deoxit on all the connectors.