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Discussion Starter #1
Help! I’m running out of ideas! Please review my list. And let me know what I’m missing.
Thanks!
Jay


No spark at plugs while cranking”
What I've done so far:
  1. New Battery: 12.47 Volts
  2. Battery while cranking: 11.56 volts
  3. New Coil positive while cranking: 10 volts
  4. Coil negative while cranking 10 Volts
  5. Flywheel sensors: 1000 ohms
  6. Fuse box fuses: cleaned fuses and spring holders with steel wool,
  7. Continuity above fuses to below fuses
  8. Cleaned ignition switch terminals and checked continuity
  9. New distributor cap: checked continuity
  10. Distributer rotates when cranking
  11. New rotor
  12. New starter
  13. New plugs
  14. New plug wires
  15. New rings and liners
  16. New valve job
  17. ECU: have not checked
 

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Good list of things to check. (Assuming this is an L-jetronic Spider.) My only thought is to remove the flywheel sensors for a visual inspection.

I once helped a guy with a crank but no start Spider. When we removed the sensors one of them had a dent in the end that faces the flywheel. It checked OK with the ohm meter but when we replaced it with a used but known-good sensor the engine started right up.

And there have been cases where the threads for the sensor retaining bolt were stripped out leaving the sensor loose/dangling. It checked out OK with the ohm meter but of course it wasn't able to sense anything...
 

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Discussion Starter #3
I did remove the flywheel sensors. They looked good. No dents. I cleaned and replaced.
I am baffled. What else’s can I try?
 

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Even the factory didn't have a way to test the computers. They best they could offer was to test that all the inputs were getting to it correctly. If so, the next step was 'replace computer'. Is the large harness connector securely plugged in to the computer?
 

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You are certain you are chasing no spark? Ignition system and fuel injection system are separated somewhat on Ljet cars. When you say ECU, are you talking about the ignition one? Do you have a spare distributor?
 

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Did this just one day happen? During a drive? After a long period laid up?
Or did it happen after the head job? (let's presume you did not remove the flywheel for anything, and put that back incorrect.

you have checked a lot already, here some further thoughts:

voltage at coil: you say 10v whilst cranking (so obviously it is not pulsing, correct...because if it was, it should spark!)....10v is perhaps too low (not too sure about that one though...)
test voltage at coil + and - but just key on (not cranking)...are you getting full battery voltage now?

are the sensors correctly connected up: lower to grey, upper to black (assuming the connectors near the overflow bottle are factory)...as you did a head job you might have undone them.

is the coil correctly wired up: greens on the plus, everything else (whites, white/blacks, black, maybeeven a yellow as well) all on the negative side.

remove the thinner white from the coil (the tach wire) and try to start now........if the tach wire has a short to ground the car will not start.
and finally
did you put the ecu grounds to the head (the big bundle, passenger side, cyl #4)......or any that might have been under the AAV mounting back, cleaned and tightened up?

I'll keep thinking:)
 

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Try adding a jumpbox to the battery when cranking. Test for pulse at coil neg. with a test light. Report back.
 

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Even the factory didn't have a way to test the computers. They best they could offer was to test that all the inputs were getting to it correctly. If so, the next step was 'replace computer'. Is the large harness connector securely plugged in to the computer?
I would agree here with purchasing another new flywheel sensor. i have been baffled with one of my spiders for this entire season. No start issues resulted in replacing everything you list aboved on your list as well and still a No Start after intermittent driveability. In the end a brand new sensor that was replaced a few months ago, was the culprit as irritating as this was, once replaced with another NEW sensor this car has never started and run better.
 

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I bet there is a 'signal test' one can do with the sensors (not listed in the hiperformance troubleshooting doc)
It certainly is the case for the Motronic 90-94, where I have tested the S4's single sensor at 1.4V AC.

you put a voltmeter set to AC (not DC) on the connector plug and crank the engine...you should see some voltage, a signal (normally an oscilliscope would be used, but Voltmeter set to low AC volts would pick up a signal too)
 

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Discussion Starter #11
Answers to your questions
thanks to all for your suggestions!


You are certain you are chasing no spark?

Yes
Ignition system and fuel injection system are separated somewhat on Ljet cars. When you say ECU, are you talking about the ignition one?
Yes

Do you have a spare distributor?
No

This just one day happen? During a drive? After a long period laid up?
It just happened to quit having ”spark” before I did any of the things on the list above. I would drive it often.

Did not remove flywheel
no

voltage at coil: you say 10v whilst cranking (so obviously it is not pulsing, correct...because if it was, it should spark!)....10v is perhaps too low (not too sure about that one though...)
test voltage at coil + and - but just key on (not cranking)...are you getting full battery voltage now?

Will check.

are the sensors correctly connected up: lower to grey, upper to black (assuming the connectors near the overflow bottle are factory)...as you did a head job you might have undone them.

Will check

is the coil correctly wired up: greens on the plus, everything else (whites, white/blacks, black, maybeeven a yellow as well) all on the negative side.
Will check again

remove the thinner white from the coil (the tach wire) and try to start now........if the tach wire has a short to ground the car will not start.
Will check. The tach needle is very erratic

Did you put the ecu grounds to the head (the big bundle, passenger side, cyl #4)......or any that might have been under the AAV mounting back, cleaned and tightened up?
Yes

Try adding a jumpbox to the battery when cranking. Test for pulse at coil neg. with a test light. Report back.
whats a jump box?
 

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A jump box is one of those hand-held battery jump-start devices. Like jump starting from another car with jumper cables. Fly wheel sensors connected to the wrong chassis plugs? As for the relays under the shelf, sometimes just knocking them with your knuckle when cranking, or removing and cleaning prongs and reinstalling helps. If it ran before the head job, most likely it is something that happened (something that YOU did) during the repair. Good luck! Please report back with the fix.
 

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Discussion Starter #15
Did not start before head job.

Did a spark plug ground test with the coil: It sparked!

Sensors hooked up correctory.
One sensor tested too low on voltage: .08 - .11 volts
Ordered 2 Bosch sensors from Rockauto (Best price)

Hopefully the sensor is the culprit!
 

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If it sparked at the coil, then you must be getting a signal to coil negative. Yes?? Is the problem in the dizzy cap, rotor, secondary wires?
 

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Discussion Starter #17 (Edited)
I'm wondering the same thing. What's the way to test and isolate the problem?
 

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Discussion Starter #19
I'm not clear on what you mean. They way I test them is with an ohm meter.
the below quote came from
How do I test flywheel sensor?

”I would also test the signal (flywheel Sensors), which normally requires an oscilliscope but a DVM set to AC volts works too. But it need to be back on the car!:
multimeter set to Volt AC (not DC!), clip the meter to the same pins, one outer and middle (remember: one of the outer pins reads nothing, the other does, so try both to be sure!!)
Now crank the engine, it should be reading something like 1.4V AC”
 

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the below quote came from
How do I test flywheel sensor?

”I would also test the signal (flywheel Sensors), which normally requires an oscilliscope but a DVM set to AC volts works too. But it need to be back on the car!:
multimeter set to Volt AC (not DC!), clip the meter to the same pins, one outer and middle (remember: one of the outer pins reads nothing, the other does, so try both to be sure!!)
Now crank the engine, it should be reading something like 1.4V AC”
that quote is from me:)
it was in a thread regarding the S4 spider, mis-titled as 'how do I test flywheel sensor' when the car in question actually does not have fly wheel sensors (2) but a single crank pulley sensor (CS), as it was an S4 motronic spider.

But I do stand by the theory that even the S3 flywheel sensors can be tested with AC volts.....the Ohms test tells you the winding inside is OK, that nothing is broken I suppose....the volts signal test (AC volts) tells you if the sensor is outputting a signal...........when the flywheel spins, that little 'nubbins' sweeps across the sensor and causes a signal.....
Only thing I do not know is whether it should be 1.4V AC (like the S4 crank sensor) or a different voltage.


Jay,
so what did the other sensor read (Volts AC)......was it close to 1.4 ?
 
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