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Simon_CSK

P38 V8 Coil Pack

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Does the bolting of the coil pack to the engine block and inlet manifold provide any earthing for it or is it all done through the wiring loom?

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There will be enough path for the earth to run through the various bolts from the manifold to the block and on to the earth strap, but it may well go via the loom, too.

Have a rummage in RAVE's electrical library to be sure.

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5 hours ago, JohnnoK said:

There will be enough path for the earth to run through the various bolts from the manifold to the block and on to the earth strap, but it may well go via the loom, too.

Have a rummage in RAVE's electrical library to be sure.

 J

Thanks for the reply but my issue was I haven't bolted it in place yet and was wondering if that would weaken the spark. I know I am getting aspark because I have put a plug on a lead outwith the block and have seen it.

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I have no idea what the answer is but wondered if you should make it clear whether you are talking about earthing the LT or the HT side?

As I implied, I know nothing about the P38, but if they have a 'wasted spark' system, then earthing the HT side is not a concern, and the LT side usually earths through the loom...

Hope this helps, and if not then sorry to have wasted your time.  :)

Rog

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Why not simply connect a temporary fly lead from the pack to any earth? You could have done that in less time than to ask the question!

 

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6 hours ago, walace58 said:

Why not simply connect a temporary fly lead from the pack to any earth? You could have done that in less time than to ask the question!

 

Agree if the car was next to me but it is in a workshop 45 mins drive away so just trying to get some ideas as to why the thing will not start.

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Hi SImon,

In the same situation - car stuck in a carpark 80km away. If you have the Motronic P38 then the coil packs do not need to be bolted down for an earth - earth path to collapse the primary is via ECU. 

Which model do you have and what have you done so far - we can compare notes.

Peter - Australia

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On 12/31/2018 at 12:55 PM, walace58 said:

 

 

 

Peter thanks for the reply. 

My car underwent an engine change two years ago in the middle of a very bitter divorce and never got restarted. I couldn't get it running so it got put to the side. Now got time to give it  try and so far I have stripped back the inlet manifolds and refitted them making sure they are secured tightly, filled the fuel tank, pluggd in the computer which is not listing faults. and basically rechecked all the connections. I did put new plug leads on as the old ones were not fitting comfortably.

Am getting to the point where I think it needs to go to someone who knows more than I do. In reality that is anyone 

 

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As I recall from the wiring diagram the coils are fed with 12v from the ignition and the ECU grounds the other side of the LT to energise it, where the HT side grounds I'm not sure but "to the block through the bracket" would not be a major surprise.

If it's not even coughing I'd suspect something basic like crank or cam sensor - if there's no signal from them it doesn't know the engine's turning or which cylinder is due to fire so it'll do nowt.

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16 minutes ago, FridgeFreezer said:

 

If it's not even coughing I'd suspect something basic like crank or cam sensor - if there's no signal from them it doesn't know the engine's turning or which cylinder is due to fire so it'll do nowt.

It is coughing just not firing. Just out of interest how do I check the sensors?

 

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17 hours ago, Simon_CSK said:

It is coughing just not firing. Just out of interest how do I check the sensors?

Depends on the type of sensor - temperature sensors are usually a varying resistance, the crank/cam sensor would likely be variable reluctance (basically, a magnetic coil) or hall effect, very similar to ABS sensors (same idea, different place), airflow meters (ignoring flapper) are a cunning bit of electronics involving a heated wire, lambda sensors are darker magic but either produce a small voltage or change resistance.

However, very few things will stop it from starting at all so it comes back to checking the basics carefully and methodically and not skipping anything because you "know" it's OK. If it has fuel & spark it should make a fair go of starting and running.

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Ignition is the likely cause of a non-starting V8. Pretty sure we had a P38 running with the coil pack unbolted at some point. As Fridge said, the LT side gets its ground through the wiring loom.

If the crank sensor isn't working, I don't think you'd get a spark at all, as the ECU would know when to spark. Cam sensor is not vital, it will run without it,  just used for fine tuning. Lambda isn't needed for starting and even without a MAF it should go to a default mode and start. A bad or unplugged temperature sensor will cause a low reading (high resistance), and overfueling that can prevent it from firing. 

Are you sure the plug leads are in the correct position? Another thing to try is new spark plugs. Sometimes they spark (a little) when out in the open, but lack the strength to ignite the mixture under pressure.

Filip

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Posted (edited)

Have you got access to the electrical troubleshooting manual - don't give up yet.

You have a cranking engine but no firing - that's better than no crank.

Have you read the fuel pressure. There are two 3 pin plugs on each coil pack - ensure that battery voltage exists at pin 2 of connector 52 and 156 - the BeCM grants this via grounding relay 23. BTW your fuse box lid may not show a relay 23 - maybe someone else can explain which is the correct relay - anyhow the important point is getting power at the pins of the coil packs

Insert an inline spark tester - check the quality of the spark. Its is very strong and will jump at large gap.

Carefully inspect all of you wiring loom - looking for rubbed insulation. Any rubber insulation with corrosion will have a large impact on sensor input waveform 

Lastly remove the crank position sensor - check it is not damaged at the tip and that it is about 940 ohms between pins 1 and 2. Aftermarket ones are pretty cheap - buy a replacement and fit it. Be careful and check if there is a spacer or not.

 

Don't worry you will get there eventually.

Ignition coils relay.pdf

Edited by V8 Freak
Combined info from two messages.

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20 hours ago, polycraftman@gmail.com said:

 

Lastly remove the crank position sensor. Be careful and check if there is a spacer or not.

 

 

Ok we have something here. The engine that was fitted has been GEMS, THOR, GEMS and now THOR again. I had to fix the mounting for the sensor into place so there is a possibility that it is positioned incorrectly. So how can I find out if this is the case? Everything else I am pretty sure about.

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You should havetwo large access ports in the bell housing - you access the flex plate bolts from here.

Firstly check these bolts are secure and torqued correctly. Its easy to rotate the engine via the crank pully bolt - especially if you remove a couple of the spark plugs.

Then get a cheap USB endoscope via ebay and check the gap between the tip of the sensor and the flywheel. When I refit mine Ill try and get a photo to post. It should be very close without touching.

If it is not close enough then the waveform on crank will be poor without enough amplitude to be accepted as a valid sigmal by the ECU - my interpretation.

However before you do all this you need to confirm the integrity of the wiring loom for the sensor - is it rubbed/ stretched anywhere. Normally on an engine removal the mechanics stretch this wiring and damage it because it is hidden behind the engine and they dont know its there. It is not until they have stretched the wiring quite a bit do they realise there is still something connected back there.

This can be done by checking the resistance at the correct pins of the ECU where the crank sensor feed and earth reside. Im away from my books - cant check the pinouts. The resistance should be about 950 ohm - howver the only real way to check the CKP is via oscilloscope and check the cranking waveform against a good known one - this will also confirm the gap is correct.

Good luck

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I finally got my car going - How did you go Simon. What transpired is as follows - hopefully this might help someone else.

Finally got the car going - the amplitude of the crank signal was low and the loom was slightly damaged  - although not corroded at all. There must be a threshold at which the ECU rejects the crank signal. Cant find this in any LR documents. Fitted a new crank sensor and after a few revolutions the ECU recalculated piston position and fired up.

Regarding the anomally in the relay illustration - it appears that the electrical troubleshooting manual was updated in 11/2000. RL 2 took the place of the previous RL23. The engine managemnt section still shows RL23 feeding the coils - footer date 11/99. The power supply section displays RL2 as feeding the coils - footer date 11/2000. So they updated one section and not the other.

The key to this fault was no spark yet the 5V reference circuit from the ECU was active - it was active but needed a good valid crank signal to initiate firing of the coils. This is highlighted by the continual illumination of the amber check engine symbol on the message centre whilst cranking.

Thanks to the quality and extensive abilities of the MSV I was able to diagnose the security system and confirm that indeed it was not the culprit. The strange thing was that the car ran beautifully for the 100km drive to my work carpark. When I returned 3 days later I was faced with this problem and no codes to even hint at  a CKP issue.

I am yet to repair the nick in the loomthe loom  - it may be partly responsible if it have some unwanted resistance.

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On 1/8/2019 at 10:33 PM, polycraftman@gmail.com said:

You should havetwo large access ports in the bell housing - you access the flex plate bolts from here.

Firstly check these bolts are secure and torqued correctly. Its easy to rotate the engine via the crank pully bolt - especially if you remove a couple of the spark plugs.

Then get a cheap USB endoscope via ebay and check the gap between the tip of the sensor and the flywheel. When I refit mine Ill try and get a photo to post. It should be very close without touching.

If it is not close enough then the waveform on crank will be poor without enough amplitude to be accepted as a valid sigmal by the ECU - my interpretation.

However before you do all this you need to confirm the integrity of the wiring loom for the sensor - is it rubbed/ stretched anywhere. Normally on an engine removal the mechanics stretch this wiring and damage it because it is hidden behind the engine and they dont know its there. It is not until they have stretched the wiring quite a bit do they realise there is still something connected back there.

This can be done by checking the resistance at the correct pins of the ECU where the crank sensor feed and earth reside. Im away from my books - cant check the pinouts. The resistance should be about 950 ohm - howver the only real way to check the CKP is via oscilloscope and check the cranking waveform against a good known one - this will also confirm the gap is correct.

Good luck

Yes that sounds doable. Have the camera already so when I get a moment I will take a look. In the meantime I have an engine to fit to the Discovery.

 

 

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