Non Start - Ideas please !!

87 lh2.2 turbo 745.
I have a intermittent non start.

Checked AMM
FI relay and Radio suppression-relay both good.
Both Fuel pumps run.
cleaned TB.
Swapped ECUs.
Injectors cleaned.
Good hall senor and power stage.
Checked grounds on inlet manifold.

The car runs fine then at random will not start. No injector pulse. The way to get it to fire is to disconnect the ECU while live and reconnect.
The car will either run fine at that point.
Or run with a miss under 3000rpm, not idle properly(hunt), stall and non start (without a ECU reconnect). This occurs with 2 different ECUs. On restart it can also run fine??

I've tried disconnecting the AMM and ICV still same behaviour.
Could anyone suggest a possible cause.
thanks

Maybe its that 20 amp fuse in the engine bay by the battery? I'm not sure, but i had the same kind of problem and it turns out that the fuse was just loose. Just a suggestion.

No injector pulse? Do the injectors receive 12V (during cranking) while experiencing the no start condition? Yes? Then it has to be the hall sensor, injector relay ecu or wiring. No? Suspect a wiring, ignition switch, ecu or fuel pump relay issue.

No fuse down near the battery?

Varg

Yes the injectors are getting 12v during the condition.
This has me stumped.

Then it has to be the hall sensor, injector relay ecu or wiring

Click to expand...

Hall sensor has been replaced 2 years ago... does the Ignition(EK) unit pulse the ECU to pulse the injectors? can I check that easily.

Would a bad injector cause this?

What confuses me is the ECU reset work around. making me think a relay. I have bridged the injector relay with the same results.

nickm said:

No fuse down near the battery?

Varg

Yes the injectors are getting 12v during the condition.
This has me stumped.


Hall sensor has been replaced 2 years ago... does the Ignition(EK) unit pulse the ECU to pulse the injectors? can I check that easily.

Would a bad injector cause this?

What confuses me is the ECU reset work around. making me think a relay. I have bridged the injector relay with the same results.

Click to expand...

have you considered a failure in the wiring harness?

Yes, guess next step is to trace all the pins of the ECU back to the relevant sensor, component , earth or power source. But if I could pin point the circuit that would be a good start. Apart from continuity I'm interested a to what the ECU pins see as a correct signal. That could tell me what might be happening.

I'm ready to part this car if not fixed

Is your spare ECU a known good unit? Preferably a 9xx part number.
There's a good chance it's a sketchy ground- you might as well go clean up every one you can find. How is the harness, '87 was the last year for bad harnesses.

nickm said:

87 lh2.2 turbo 745.
I have a intermittent non start.
Checked AMM
FI relay and Radio suppression-relay both good.
Both Fuel pumps run.
cleaned TB.
Swapped ECUs.
Injectors cleaned.
Good hall senor and power stage.
Checked grounds on inlet manifold.
The car runs fine then at random will not start. No injector pulse. The way to get it to fire is to disconnect the ECU while live and reconnect.
The car will either run fine at that point.
Or run with a miss under 3000rpm, not idle properly(hunt), stall and non start (without a ECU reconnect). This occurs with 2 different ECUs. On restart it can also run fine??
I've tried disconnecting the AMM and ICV still same behaviour.
Could anyone suggest a possible cause.
thanks

Click to expand...

yanking the ECU *WHILE LIVE* is *NOT* a good plan (And the fact that you've done it w/TWO
ECU's and had the same result means you won't have to do this again)...VOLVO *SPECIFICALLY*
warns against this practice in ALL of their service literature....

check ALL of your *INPUT SIGNALS* with the system LIVE by BACK - PROBING the ECU
connectors (*most* of the Bosch units will have a "window" in the connector that you can stick a
LOGIC PROBE on to see if they are "live" - then use DIGITAL DVOM..."swing needle meters"
will "overload the system" and Are NOT SUITABLE for checking computer "circuitry"

SOMEWHERE you're suffering a nasty ground.. also check the harness from the DIZZY to
the ICU ... there are "SLEEVES" that are meant to be on certain pins in those connectors -
and if they are MISSING it creates a NEVER ENDING SERIES of GHOSTS (see GREEN
BOOK LH2.2)....DAMHIKT!!!

How's your ignition unit? On LH-jet the two components interconnect and share some signals, so it's possible that a wonky ignition system or sensor can mess with fuel.

Another thing to check is your wiring harness. 87 is the last of the "bad years", and faulty insulation can do any manner of things to your signals.

Yep. Logic probe time. I'll go and get one.

Does concern me about the hot swap on the ECUs. Hope I haven't fried their little hamster minds.
It was the only way to get the car moving. Stuck on the side of a very busy road in peak hour.
The car is now in a state of non start so at least it's not intermittent.

The car has a "K" motor and wiring harness is in ok condition no crumbling, thinking it may be the updated one build date late 87. But not saying it is not the problem.

ECUs are 541 lh 2.2. Both ECUs "have" run fine. One unit is chipped.

thanks will post my findings

Oh.. went to re-check, starting normally....
Both ECUs running fine- starting, power down, swap, re start and smotth idle. Did this about 4 times.
So haven't damaged them.
Now need the time to let the car lapse back to non start mode.Hard though as I can't drive it, too risky. So it's hard to induce the fault.

re checked gone to non-start
Fuel pump good both removed and run.

Re-checked injectors with a 12v led.
I am getting a pulse. (road side guy said no pulse from the noid light) So I have fuel and injectors.
Could anyone give me a line of attack?

Hmm when i had this brief issue with my car, it turned out that the 12v line from the battery to the ECU had a break in it and was loose, and fixing that issue fixed the issue with the no start. So maybe you need to check into that?