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Have managed to get the ECM to yield its fault codes :

14 - Ignition no. 1 signal

15 - Ignition no. 2 signal

27 - Sub-oxygen sensor signal (on left bank)

Anyone able to suggest what I should be swapping out for 14 and 15 ?

TIA

Justin

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I am guessing that you have an LS400 post 1994 build year that is cranking but not firing?

The fact that you have no signal to both ignition amplifiers would suggest a common component.

The device used to tell the ECU what position the engine is in at any given time (so it can provide the spark to each cylinder at the correct time) is the crankshaft sensor so I would 1st check this item and its associated wiring, it is not uncommon for these to fail or the wiring be damaged by the nearby sepentine belt if not correctly dressed.

The other fault code probably has no relation to the above fault but may indicate the oxygen sensor is past its sell by date.

Also bear in mind although useful in helping to diagnose problems fault codes can sometimes be misleading and a little detective work and a multimeter are sometimes the better option.

With modern cars today's mechanic needs to be an electronics engineer as well, I knew one day that old oscilloscope of mine would come in useful again!

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I am guessing that you have an LS400 post 1994 build year that is cranking but not firing?

It's a 96, but has OBD1. It does (or did) fire when cold, and it might even run for a mile or two.

The fact that you have no signal to both ignition amplifiers would suggest a common component.

Crank Position sensor was my initial thought. Got in the car last Tuesday, and the tacho needle was shooting about all over the place when cranking. Prior to that (from the Friday before), the engine would fire and run fine, apart from a periodic short hesitation, where the revs would drop, as though the engine was starved of fuel for a split second. It would only do this on LPG, not on petrol. Basically; it got progressively worse last week; to a point where it was seriously mis-firing on petrol by the Thursday. Bizarrely; the mis-firing was more pronounced when reversing. Whatever the problem is; it's something that has deteriorated, rather than just failed.

The other fault code probably has no relation to the above fault but may indicate the oxygen sensor is past its sell by date.

That was my conclusion; not a show-stopper.

Also bear in mind although useful in helping to diagnose problems, fault codes can sometimes be misleading and a little detective work and a multimeter are sometimes the better option.

Agreed. I paid the $15, and downloaded the engine section from the 94 Repair manual (plus a load of other PDFs).

Manual suggests that the ECM isn't receiving an ignition acknowledgement (IGF) from either Ignitor, and that the problem lies with the ECM, Ignitors, or the wiring inbetween. Can't believe that BOTH ignitors would act up. So I'm thinking Crank sensor, or less likely (hopefully) the ECM. Have the upper/lower resistance limits for the crank sensor, so will measure that tonight, and report back.

Thanks for the reply

Justin

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Just bear in mind that when cold the CPS may read OK so even if the resistance readings are within spec when cold it may as you suggest be failing when warmed up which is not uncommon on other cars.

Keep us posted.

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Just bear in mind that when cold the CPS may read OK so even if the resistance readings are within spec when cold it may as you suggest be failing when warmed up which is not uncommon on other cars.

Keep us posted.

Good point.

I'll measure the resistance when I get home from work, and if it's within limits, I'll (try) and warm the engine up to temperature, or to the point where it's spluttering and misfiring, and take another reading.

I'm hoping it's the CPS, as that is an easy fix, and I've got an option on one for £25 inc delivery

Will report back

Justin

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I am guessing that you have an LS400 post 1994 build year that is cranking but not firing?

It's a 96, but has OBD1. It does (or did) fire when cold, and it might even run for a mile or two.

The fact that you have no signal to both ignition amplifiers would suggest a common component.

Crank Position sensor was my initial thought. Got in the car last Tuesday, and the tacho needle was shooting about all over the place when cranking. Prior to that (from the Friday before), the engine would fire and run fine, apart from a periodic short hesitation, where the revs would drop, as though the engine was starved of fuel for a split second. It would only do this on LPG, not on petrol. Basically; it got progressively worse last week; to a point where it was seriously mis-firing on petrol by the Thursday. Bizarrely; the mis-firing was more pronounced when reversing. Whatever the problem is; it's something that has deteriorated, rather than just failed.

The other fault code probably has no relation to the above fault but may indicate the oxygen sensor is past its sell by date.

Just a thought, bad engine earth

That was my conclusion; not a show-stopper.

Also bear in mind although useful in helping to diagnose problems, fault codes can sometimes be misleading and a little detective work and a multimeter are sometimes the better option.

Agreed. I paid the $15, and downloaded the engine section from the 94 Repair manual (plus a load of other PDFs).

Manual suggests that the ECM isn't receiving an ignition acknowledgement (IGF) from either Ignitor, and that the problem lies with the ECM, Ignitors, or the wiring inbetween. Can't believe that BOTH ignitors would act up. So I'm thinking Crank sensor, or less likely (hopefully) the ECM. Have the upper/lower resistance limits for the crank sensor, so will measure that tonight, and report back.

Thanks for the reply

Justin

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An update :

Cleared fault codes, and tried to run engine. Engine did actually run for about 5 seconds at 3-4000 revs, before dying. Which suggests to me that the engine is mechanically sound, and the problem lies elsewhere.

Checked fault codes again : 27 only. 14 (IGF-1) and 15 (IGF-2) have not returned.

Removed ECM, and took the lid off. I then re-connected E10 plug to ECM, and measured resistance (at the PCB) across pins :

5 and 6 (Crank sensor)

10 and 11 (#1 Cam sensor)

16 and 17 (#2 Cam sensor)

All were returning resistance in the 900 Ohm range (again using 2 multi-meters), which tells me that at least the wiring is good to all three sensors.

I don't believe my problem to be compression.

I don't believe my problem to be fuel; it fails to start on both LPG and petrol.

Can't believe that both ignition circuits (ignitors / coils / dizzys) would fail at the same time.

So I'm left thinking that it's either the Crank Position sensor acting up (I did experience the rev-counter needle bouncing around all over the place); or it's the ECM.

....or I'm missing something.

Really would welcome some advice; as I need to be mobile by Monday (Mother's Birthday).

TIA

Justin

P.S : Engine ECM is a "89661-50310"

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The old way of determining whether there was a fuel problem was to spray so ether/easy start into the air intake whilst some one cranks the engine if it runs albeit erratically on this stuff it would suggest a fueling problem. Take obvious precautions if using this stuff especially if it blows back.

The CPS as you mention could be the prime suspect and to check the output would require a 'scope to see the output waveform during cranking (If you are local to me you are welcome to borrow mine)another one is to give the thing a "tap" with the wood handle of a hammer which sometimes kicks the thing into life or to be completely sure the only other way is to replace it with a new one.

Finally is the timing belt in good order? Is the timing correct? a worn belt may have jumped a few teeth on the sprockets.

Just one more thing(I sound like Columbo now) the MAF sensors are a known problem you can disconnect it and the engine will still run but the EML will illuminate until reconnected.

I hope you get it sorted.

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This happened after you replaced plugs/ leads/ dizzy arms/ caps? It was running ok before?

You put all the old bits back and still had the problem?

If the above is correct, it's a very big coincidence the crank sensor has failed, unless it got disturbed/ bumped.

I had a badly earthed crank sensor once on a Scorpio, engine stuttered for a few days , then died. AA man sorted it, fault was in the AA database, reseated sensor, all sorted

Clutching at straws here, how about a bad engine earth, causes all sorts of mayhem. Test with jump lead from batt neg to engine.

Get a second head under the bonnet, looking for anything disturbed

good luck

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This happened after you replaced plugs/ leads/ dizzy arms/ caps? It was running ok before?

You put all the old bits back and still had the problem?

If the above is correct, it's a very big coincidence the crank sensor has failed, unless it got disturbed/ bumped.

I had a badly earthed crank sensor once on a Scorpio, engine stuttered for a few days , then died. AA man sorted it, fault was in the AA database, reseated sensor, all sorted

Clutching at straws here, how about a bad engine earth, causes all sorts of mayhem. Test with jump lead from batt neg to engine.

Get a second head under the bonnet, looking for anything disturbed

good luck

Sorry, think I got my posts mixed up...

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Finally is the timing belt in good order? Is the timing correct? a worn belt may have jumped a few teeth on the sprockets.

Belt was done 3 or 4 years ago. Don't really do a lot of mileage.

Pretty sure the belt is fine; besides; it wouldn't have run fine at 3500rpm for 4 or 5 seconds.

My fault is one of degradation; started off as a momentary hesitation, and got steadily worse. Engine occasionally will fire and run for a brief period.

Will check the engine earth though

Thanks

Justin

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Swapped out the Engine ECM and Crank Sensor; no difference :-(

So it's back to the multi-meter and schematics, in tomorrow's hot sun.

Getting hacked off with it now, if I'm honest.

Am I right in thinking that it is the crank sensor that governs the rev-counter ?

Something is causing the rev-counter needle to occasionally shoot up and down randomly.

Justin

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Am I right in thinking that it is the crank sensor that governs the rev-counter ?

Something is causing the rev-counter needle to occasionally shoot up and down randomly.

Answering my own question.....it's #1 igniter which drives the rev-counter.

SO; tomorrow; I will check the earths for all the ignition components, and if they check out fine; I'm inclined to say #1 igniter is acting up.

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Engine runs !!

I swapped the ignitors round (they both have the same part #)

Ignitor #1 (now Ignitor #2) was failing to provide a clean RPM signal.

My Ignition wiring colours correspond to the 1996 wiring diagram. However; at the ECM (34 pin connector), my wiring is as follows :

12 : IGF1 : yellow-green

24 : IGT2 : yellow

25 : IGT1 : black-red

26 : IGF2 : yellow-black

In the two 1996 wiring diagrams; it shows IGT1 as black-red to pin 24, and IGT2 as yellow to pin 25.

It would appear that my car defies convention; especially as I have to refer to the 1994 repair manual to look up OBD1 fault-codes

Justin

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