1991 Turbo ignition problems

[balto8]

Hello

Have read almost every old topic but couldn't find a situation like mine here.

My clutch was on it's last days so It had to be replaced.

I went the hard way, dismounted the subchasis and I think I did a good job. The old one was on it's knees. Also replaced the gearbor rearmount that was all broken and the reason I think why I had a shacking car. Also renewed the bearings seals, gear change bar and other minor jobs. Put it all back together with extreme care.

Now I have no ignition.

Things checked this far.:
1 Start motor turns and flywheel turns aswell
2. Battery recharged overnight and in good condition
3 I get a nice spark on the plugs.
4 Fuel pump working fine.
5 triple checked every cable and earth around: all in place.

So it seems to me like something is jamming the fuel injection.

I just bought a new flywheel impulse sensor to try and replace. This will be done next weekend.

Any other ideas of where to look at?

Please help!

[balto8]

On the 4th every single cable follow to check integrity found this sensor on the gearbox lower side of the engine. It's a bolt that screws in the engine. Volvo part 3435172. Replaced it, but still no ignition. What does this sensor do?

Still waiting for the replacement for the flywheel sensor, it's the 3 cable one.

What is the way to proceed to access injection relay and Ecu?

Any comments appreciated

[balto8]

So...

Replaced the flywheel sensor for an original Volvo part. Still no ignition. And increasing electrical gremnlins

Right before replacement of the flywheel sensor, whe turning the key I had the normal "check" on the infocenter. Showed range, the oil temp and back to the selected position info.
Now I hace a blinking "check - check - check" three times then shows range. Then again "check" blinks three more times and shows oil temp. Thenh goes to the selected position info.

No diagnose box on mine.

All my work this far.

Replaced clutch
Replaced rotten rear gearbox mount.
New fuel filter.

Have nice spark on plugs
Have fuel at very good pressure up the the injection ramp. Have not taken out injectors to see if I have fuel spray. Beyond my skills.
Start motor and flywheel turning as intended on ignition.

Any tip at all??? The car is right now at a Volvo, but I'm quite afraid of the incoming bill as they keep spendig hours on the damm engine.

[Robou]

You claim getting a nice spark on the plugs, on the other hand having no ignition.
This is quite confusing, if you found out about the "nice spark" by manipulating the coil while connected to the ignition module you may very well have blown it by the sparks you invoked. If so, also a transistor in the ignition ECU may have suffered.

[balto8]

I checked having spark on the spark plugs by taking out each lead, connecting a new spark plug to the lead and then make a pal turn the key to ignition while I hold the spark plug end to the engine to have ground. I can see a bright, consistent spark.

Has anyone had a faulty injection relay?
Are ECUs prone to fall if you have a lowish voltage battery? (Let's say all the clutch replacement, rear gearbox mount finding process and reassembling took me 3 weeks)

Thanks

[balto8]

The battery was disconnected during all the clutch work and reconnected again prior to try and start the car.

[Robou]

Even more confusing, there should not be a spark when just turning on the ignition. Under certain conditions this might ignite the mixture and start the engine spontaneously.

A simple explanation: The coil has two connections, one is permanently connected to +12V when the ignition is switched on, the other is connected to ground about 6 milliseconds before a spark is due. Then upon release the spark occurs. This is accomplished by a power transistor in the ignition module which is switched by a transistor in the ECU. The ECU does not activate this circuit at power on, it needs some time to boot and then waits for the pulses from the flywheel sensor.

There are sophisticated checks to find out if this all is working well, but a oscilloscope is needed. Best you can do is to begin by checking if both the coil connections carry +12V. If not, the ignition module is at fault because the switching transistor is shorted. Anyway, exchange the ignition module and the ECU. Not just the ECU, because the 300V or so occurring at a switching coil may well have damaged it when the module is out of order.

As usual there are lots of other possibilities for this failure to occur, like bad grounding of module and/or ECU, but looking at your resume the above seems most likely.

The ECUs need at least 10V for proper action. This is why sometimes the motor will start at releasing the starter motor, at that split second the voltage rises.

[balto8]

Sorry for my poor explanation, I only have spark when I turn the key, not with the key on "contact" position. The car is at Volvo and being tested. I'll pass them this information but we still think that something is blocking fuel injection... Still to be found

Thanks a lot

[balto8]

Got it!

The cable going to the injectors had a faulty connection. Refitted and started at once.

So it was the injectors blocked.

Hope this might be useful to someone sometime.

Cheers

[doingitsideways]

Ah yes.

I read this thread earlier and though I was sure I had a similar problem once.

I eventually found a break in the wiring to the injectors at the end of the fuel rail.

Glad you're sorted