D2 V8 Intermittent starting

Hi All. Considering I only really post here when I've got problems, I'm amazed that I've not been around here for quite a while.

I've just started getting a problem with my 2001 D2 V8 which is duel fuel.

It's got an intermittent fault where from time to time it's just not starting. The symptom is the starter motor turns over sweetly but the engine just don't fire. No warning lights. The frequency seems to be increasing. This is not statistically proven but, the problem started on a very hot day and mostly seems to recur on hot days. (yeah, I'll be OK soon, I guess

The only engine fault code was :

NANOCOM - MOTRP38.APP - MOTRONIC fault file
PXXXX = PERMANENT VOLTAGE SUPPLY
FAULT DRIVE CYCLE A
OCCURED 1 TIMES
SIGNAL TOO LOW
FAULT IS NOT CURRENTLY PRESENT
FAULT DETERMINED AS PERSISTENT
FAULT DOES NOT CAUSE THE
MIL LAMP ACTIVATION

I cleared this a week ago and it hasn't come back.

I should mention that, if the beast does choose to start then it runs smooth as anything on both petrol and gas. And, so far, once it's started it has kept running.

Manual diagnosis I've done is to :
Try both keys to try to rule out immobiliser problems. (either works or doesn't work the same on both keys, depending what mood the engine is in).
Check for a spark. Took a few goes because the first time I tried this the engine started. Then, bingo, when the engine doesn't fire there's no spark.

So I guess I have an intermittent electrical fault on the ignition system? But, as I've got no fault codes I'm going to have to work through the electrics manually. The Disco is way more complicated than my '94 Golf. What's the best route of attack? In particular, is there smart way for me to test the Motronics ECU and the (Prins) LPG ECU? Are there any special circuits related to starting? And, although I'm aware that this is all in the engine bay, which is always pretty warm, are there any components that might be heat-sensitive?

Or, does this sound like one of the common V8 faults? (Search only showed up an aussie thread from 2008 which got no replies).

Otherwise, I'm in for a slow trawl through the LT/HT wiring. Ugh.

Any ideas, please?

TIA!

I'd be looking at camshaft or crankshaft sensors first, plus the obvious ones like main fusebox connections etc.

'Signal Too Low' suggests a pickup problem.

Peter

Thanks Peter. I can look for wear and tear, of course, but is there a test I can do to prove they're working? They're not cheap parts to just swap out, even at ebay prices.

In the meantime I've been looking at the nanocom manuals. They're not exactly explicit but, I'm hoping I can disable the immobiliser temporarily. And I'll check for BCU fault codes as that seems to control the alarm/immobiliser (as well as checking if that engine code has come back).

Mike

Pity you're so far away, I've got a spare pair of sensors I could lend you to try.

Peter

Thanks v much for the offer. Yeah, it's a pity; even if I get the beast to start I don't know that I'd trust it to drive that far at the moment. There's plenty of land rovers around here but that doesn't seem to be reflected by activity on this forum. Had the same problem when I needed a nanocom a while back.

Where are you exactly?

My sister is coming up Monday and will be going back Monday night to East Grinstead, might be able to drop some bits off to you?

Peter

I dunno much about the later V8's but maybe check your coil packs? In the alternative, look in the Range Rover section and see if there are similar problems with the P38 which I think uses the same engine and management system for some variants. HTH

Peter. I'm in Sutton, so East Grinstead's wouldn't have been too far at all. But, I was away for the long weekend, I fear I've missed the boat. Thanks much for the offer all the same.

Kev, yeah, coil's breaking down seemed to fit with an intermittent/deteriorating nature of the problem. But then, you could say the same for the crank position sensor. I need to get my head straight and work out a logical sequence to eliminate things.

My earlier searches were across all the boards not just the V8. But I take your point, this could easily be computers and ancillaries rather than the lump itself.

There are four coils in two packs, unless all four have failed, it wouldn't cause the issue.

I used to live in Wallington, went to school in Sutton before the family moved to Crawley.

Peter

Ha ha, it is a small world, I actually live in Wallington, just said Sutton because I thought nobody would know where Wallington was

(Sorry for the delay in replying, I've been changing isp most of the week so wasn't online).

And I haven't had a chance to start looking at the disco yet, with everything else going on. Might have a crack at it this afternoon as it's supposed to be sunny. :cool2:

Four coils!? I'd seen coil packs, plural, in the RAVE and assumed there might be one per bank. Four seems like over-engineering. Thanks for the pointer though, I'd now presume a failing coil would just cause rough running.

Lost-spark ignition, one coil feeds a plug at each end of the HT side, so every time you fire a plug, another plug on the exhaust cycle fires as well.

The coils are behind the engine and in pairs on the Thor engine, one 3-way connector and four plug leads each. They are pretty reliable.

We lived just below Wallington Green, in Caledon Road, earlier we were in Park Road, just after the war.

Peter

Didn't get to do much yesterday but did check all the ecu fault codes. The fault I first posted hasn't come back. The only other is an intermittent open circuit on the drivers airbag (which may be from when I had the steering wheel off a while back).

I read in RAVE:

If the engine is
not running when the CKP sensor fails, the vehicle will crank but will be unlikely to start, and no fault code will be
generated. In this instance the MIL lamp will remain illuminated and the tachometer will fail to read

Click to expand...

So, on mine, the MIL goes out after the initial self-test but, as the engine is cranking I don't see any movement on the tacho. Not sure if the revs are too low at that point to register on the instrument but the needles doesn't even twitch. I'll eyeball the CKP next, and try to get a multimeter to measure if I'm getting any output. Seems it should generate 0<v<6 AC. It might take a few days to get round to it, need to recharge the battery for one thing.

Caledon Rd is a stone's throw away, I'm just off park lane.

Interesting about the ignition system firing in the exhaust cycle, I'd not heard of that before. (not that my knowledge of car engines is terribly extensive).

Mike