1994 850 T5 with no spark at coming from the coil.

CFL850T · Post by **CFL850T** » 29 Dec 2023, 16:34

Hello!

I have a crank no start condition. I used an inline spark plug tester to determine I had no spark. I then performed the following test from Volvo tips:

Turn ignition off. Connect ignition coil connector. Turn ignition on. Disconnect coil wire from distributor cap. Hold end of coil wire about 3-5 mm from ground. Operate starter and check for spark. If spark is present, go to next step. If spark is not present, replace ignition coil and retest.

No spark between the coil and the ground, and I tried 3 different working coil modules.

I also used a test like to verify that power was going from the wire harness to the module, checking pin 3.

My sources for trouble shooting: are the Haines manual and this http://www.volvotips.com/index.php/850- ... ce-manual/

The problem started after unplugging the wire from the coil to the distributor to remove the airbox. I was routing a vacuum line through the conduit that goes into the cabin to instal a boost gauge.

In addition to swapping the coils I also tried replacing the crank and camshaft sensors as I had extras, I did this before verifying there was no spark from the coil.

Post by **scot850** » 30 Dec 2023, 10:44

Check how you have the cam sensor and crank sensor wires routed. It is possible to route them too close to the distributor that will kill the signals.

Have you tried locking and unlocking the driver's door lock a couple of times in case you have tripped the immobiliser?

Neil.

CFL850T · Post by **CFL850T** » 31 Dec 2023, 10:06

So my question. If I know I'm not getting spark at the coil, could the cam or crank sensors still be to blame? I thought that those would only be part of the equation once spark made it to the distributor from the coil.

Post by **erikv11** » 31 Dec 2023, 10:21

I would be suspicious of the coil wire at this point. Check for continuity with a voltmeter and carefully check that the connectors are right on the ends. Better yet swap it if you have an extra one.

Try locking/unlocking the car doors with the key fob, it could be the immobilizer.

Yes, a bad crank sensor will cause no spark at the coil. I thought (less sure) a bad cam sensor will be no pulse to the injectors but not no spark.

CFL850T · Post by **CFL850T** » 31 Dec 2023, 11:46

So I was suspicious of the cable as well. Just tried a spare and got the same issue. I'm not sure if the 94 has an immobilizer, as there is no fuse for one in the fuse box where it would usually be on later models. When you remove the bottom portion of the steering column there is no collar like you see on later models. I did try the unlock/lock trick though. I also tried two spare crank and cam sensors that I confirmed have previously worked. Harness is receiving correct voltage as well. Very confused as things were fine a week ago. Any other tests I could perform? Would it be possible to hook the coil terminals directly to the battery bypassing the module or to perform a similar test?

Post by **abscate** » 01 Jan 2024, 04:46

The coil produces spark by being turned off rapidly by the module so a direct connection won’t work to run the car. Trying multiple coils has pretty much ruled out the coil as bad, it looks like the ECu is not sending the trigger signal to the module , causing the no start

A wiring fault is most likely

CFL850T · Post by **CFL850T** » 01 Jan 2024, 12:46

abscate wrote: ↑01 Jan 2024, 04:46 The coil produces spark by being turned off rapidly by the module so a direct connection won’t work to run the car. Trying multiple coils has pretty much ruled out the coil as bad, it looks like the ECu is not sending the trigger signal to the module , causing the no start

A wiring fault is most likely

Any way for me to test this? Would It be enough for me to remove the ecu and check for continuity at the pins and if so any idea where I could find a diagram that would show me which one heads to the ignition coil? Thank you!

Post by **erikv11** » 01 Jan 2024, 23:18

Remove and re-seat the ECU is certainly worth a try.

Does your car have three computers in the ECU/TCU box, or only two?

CFL850T · Post by **CFL850T** » 02 Jan 2024, 07:57

Only two so I think it is the 4.3. I found this amazing eco wiring diagram. Plan is to check continuity between the wire at the ignition coil connecter to the pin on the ECU box. Does that sound like the right idea? https://ibb.co/jbwxQMb

Post by **scot850** » 02 Jan 2024, 10:32

While you have not updated if you have tried the manual locking and un-locking of the driver's door lock with the key (if the immobilizer has been tripped it can kill starting), this will reset the system.

Have you been having any issues with the ignition or transmission locks?

Neil.