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P38 diesel warning light - check engine


v8bobber
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Learned friends,

I have a 98 diesel RR P38. I have an ongoing problem, not a major one, but one that is still bothering me all the same!

I have a warning light coming on occasionally. I believe it to be the "check engine" light which looks like the picture of the end of an injector complete with spray pattern.

It comes on when it should with the ignition and then goes out again as it should when the engine starts.

The issue that I have is that the warning light flashes on for a fraction of a second and the engine seems to "die" a little bit, but then runs fine.

It usually happens when changing gear (its a manual) when the revs drop. Also sometimes happens when lifting off sharply but staying in gear. If you rev the engine sometimes and let the revs drop then it also might do it

It seems to only do it when the engine is cold, or at least its certainly worse. If you go on a long run, say more than Ten miles then it will go away.

Anyone got any clues as to this? Anyone know the circumstances in which this warning light should illuminate. I could try and trace the fault back then.

Hope someone can help, as i think it may be getting worse!

Dave

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This topic (intermittant short flash of the engine warning light) has been covered, by myself and AN Other, but on the Blackbox Solutions Rovacom Forum (Owners only).

Assuming you aren't an owner, this will have to wait until tomorrow evening for any other input by me.

You might like to update your profile to say where in the country you are., although it isn't mandatory!

Cheers.

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" the "check engine" light which looks like the picture of the end of an injector complete with spray pattern."

Check Engine is good enough, the Workshop Manual Section 19 Description refers to it as a 'diagnostic lamp'.

WM Section 19 pages 1 to 11 inclusive is recommended reading, to make yourself familiar with the different components and their functions.

ETM Section A6 pages 1 to 4 inclusive is also useful reading, as it generally states against each component if the Diagnostic Lamp is illuminated when the component fails, which helps answer "Anyone know the circumstances in which this warning light should illuminate".

However, as your problem is intermittant, this is only a partial help.

Summarising the points from the Rovacom threads ...

The initial suggestions have to be around 'is the fuel system set-up correctly?'.

Pay close attention to the Timing Modulation : "On a fully warm engine this value should steadily remain between 45% and 55% (at tickover). There should be no erratic fluctuations.".

Do this by manually swinging the pump a fraction, with the engine stopped.

In my view, this change takes preference over the setting by dial gauge, as described in the workshop manual. The dial gauge gets it close, but adjusting to meet the dynamic figures gets it closer.

If this doesn't completely cure it, adjust the tickover upwards : "Idle value: This value should normally be 128 and may be altered to increase or decrease the idle speed, however, moving this value more than two or three in either direction may have undesirable consequences."

One enquirer changed the setting from 128 to 130, and the idle changed from ~750 to ~800 rpm.

There has been a suggestion that a slight defect with the Dual Mass Flywheel affects the output from the Crankshaft Position Sensor, with the resultant erratic output slowing the engine. In my view this is 'not proven' wrt producing the symptoms you are experiencing. Note that the ECU does not output any information which directly shows the CKP output, so a Rovacom etc cannot relay the information to you. To monitor this you will need an oscilloscope / data recorder.

HTH

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I've seen a couple like this,but a while ago now.The timing modulation figures in my experience rarely match on Testbook what LR state and often do fluctuate more than they are supposed to but the engine runs fine.The last issue I saw like this was on an EDC auto 4cyl disco which put the cel on and went into limp home.On that car the pump was worn out and the advance solenoid could not do its job properly.

Before anything else I would scope the crank sensor as they are prone to damage from bits of clutch plate/flywheel that come apart.Remember that the speed signal from the needle lift sensor is lost when the engine slows down during gearchanges,(the engine slows very quickly on a manual car as its not overdriven from the motion of the car like an auto)

A slack timing chain will also have the same effect.Have any codes been read from the car ? EDC codes are usually very accurate.

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I've seen a couple like this,but a while ago now.The timing modulation figures in my experience rarely match on Testbook what LR state and often do fluctuate more than they are supposed to but the engine runs fine.The last issue I saw like this was on an EDC auto 4cyl disco which put the cel on and went into limp home.On that car the pump was worn out and the advance solenoid could not do its job properly.

Before anything else I would scope the crank sensor as they are prone to damage from bits of clutch plate/flywheel that come apart.Remember that the speed signal from the needle lift sensor is lost when the engine slows down during gearchanges,(the engine slows very quickly on a manual car as its not overdriven from the motion of the car like an auto)

A slack timing chain will also have the same effect.Have any codes been read from the car ? EDC codes are usually very accurate.

Thanks for that. What i did forget to mention is that my vehicle also suffers from the engine "wobble" at idle. There is a chance that they may be connected i guess. The warning light has only been showing for the last few months or so. The engine wobble problem has also been mostly fixed by my dealer raising the idle to 800, this has mostly completely cured it, but it still does occur now and again.

The dealer told me that there was a bulletin years and years ago relating to the dual mass flywheel which caused this wobble.

When you say "scope" the crank sensor, what does this mean? Is it worth just buying a new one?

I am interested in what you say about the speed signal from the 4th injector being lost when the engine slows down during gearchange, how on earth did you learn about that? Do you run a garage by any chance?

Unfortunately i don;t know what you mean by EDC codes, i'm still learning about all electronics unfortunately! I think what i need to is to take it to someone who knows these engines and surrounding systems, if i dont sort it soon enough.

Hope i can extract some more info from you!!

Dave

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AllyV8 has perhaps missed this first time around, so perhaps my response will help, although I can't speak for him.

I've looked under Engine, Clutch, and Information, going back to 1994, and have not found a bulletin about the Dual Mass Flywheel, although I suspect not every Technical Notice made it to the RAVE CD, which is what I'm looking at.

'Scoping' the crank sensor means monitoring with an oscilloscope. AllyV8 has the experience, but I think you are looking for variations as much as what the actual value is. Note that (from the reading I recommended earlier) the air gap is critical. Too big and the signal is weak, too close and the sensor is smashed, calling for gearbox removal to clear the remains from the bell housing.

Worth buying a new one? Don't know, I'll leave that to AllyV8.

Signal from the 4th Injector.

Go back to the reading I recommended, this is a 'Start of Injection' signal, so happens once every 720 degrees of crankshaft rotation, against the CKP getting 12 signals during the same time period.

When you release the accelerator, and the engine is being driven by the vehicle, the fuel supply is cut, thus no 'start of injection'. Fuel supply should resume as the engine speed drops, I forget the figure, assume about 1500 rpm.

Yes, he is a professional, so sees many more vehicles than I do, for instance. He is also an enthusiast, otherwise he wouldn't be here, helping us all.

EDC is Electronic Diesel Control, a term coined by Bosch, I think. EDC codes refers to the fault codes the ECU (Electronic Control Unit) puts out. Anyone with experience of Microsoft, or other computing software, will be aware that error codes can have a very approximate relationship with what is 'wrong'. I read AllyV8s comment as saying that his experience is the EDC fault codes are helpful.

It's difficult for anyone to give you recommendations of people to go to if people offering advice don't know where in the country you are.

HTH.

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AllyV8 has perhaps missed this first time around, so perhaps my response will help, although I can't speak for him.

I've looked under Engine, Clutch, and Information, going back to 1994, and have not found a bulletin about the Dual Mass Flywheel, although I suspect not every Technical Notice made it to the RAVE CD, which is what I'm looking at.

'Scoping' the crank sensor means monitoring with an oscilloscope. AllyV8 has the experience, but I think you are looking for variations as much as what the actual value is. Note that (from the reading I recommended earlier) the air gap is critical. Too big and the signal is weak, too close and the sensor is smashed, calling for gearbox removal to clear the remains from the bell housing.

Worth buying a new one? Don't know, I'll leave that to AllyV8.

Signal from the 4th Injector.

Go back to the reading I recommended, this is a 'Start of Injection' signal, so happens once every 720 degrees of crankshaft rotation, against the CKP getting 12 signals during the same time period.

When you release the accelerator, and the engine is being driven by the vehicle, the fuel supply is cut, thus no 'start of injection'. Fuel supply should resume as the engine speed drops, I forget the figure, assume about 1500 rpm.

Yes, he is a professional, so sees many more vehicles than I do, for instance. He is also an enthusiast, otherwise he wouldn't be here, helping us all.

EDC is Electronic Diesel Control, a term coined by Bosch, I think. EDC codes refers to the fault codes the ECU (Electronic Control Unit) puts out. Anyone with experience of Microsoft, or other computing software, will be aware that error codes can have a very approximate relationship with what is 'wrong'. I read AllyV8s comment as saying that his experience is the EDC fault codes are helpful.

It's difficult for anyone to give you recommendations of people to go to if people offering advice don't know where in the country you are.

HTH.

Thanks for that David you saved me loads of typing ! Not much to add except that with any running fault on a petrol or diesel p38 I tend to scope the crank signal as one of the first checks.What I'm looking for is a clean 36-1 waveform with no other gaps or spikes etc to confuse the Ecu.On the petrol ones I scope the cam sensor at the same time as their patterns remain in synch,with the diesel its not so clear cut as the signal from the needle lift sensor is not always present and is a nasty squiggle that moves in relation to the crank signal as the Ecu alters the advance via the solenoid in the bottom of the pump.Also the amount of advance is dependant on air/coolant temp,boost pressure and probably ambient pressure too.From the advance that the Ecu dials in it knows when to expect the start of injection via the needle lift sensor - if this does not happen it will log a fault,put the CEL on and possibly cut power.

One last thing that occured to me was that some "plug in" power boosters will cause this type of issue too,so if your car has one try unplugging it.Sorry to dribble on but you did ask,and for my sins yes I do run a LR garage.

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Thanks for that David you saved me loads of typing ! Not much to add except that with any running fault on a petrol or diesel p38 I tend to scope the crank signal as one of the first checks.What I'm looking for is a clean 36-1 waveform with no other gaps or spikes etc to confuse the Ecu.On the petrol ones I scope the cam sensor at the same time as their patterns remain in synch,with the diesel its not so clear cut as the signal from the needle lift sensor is not always present and is a nasty squiggle that moves in relation to the crank signal as the Ecu alters the advance via the solenoid in the bottom of the pump.Also the amount of advance is dependant on air/coolant temp,boost pressure and probably ambient pressure too.From the advance that the Ecu dials in it knows when to expect the start of injection via the needle lift sensor - if this does not happen it will log a fault,put the CEL on and possibly cut power.

One last thing that occured to me was that some "plug in" power boosters will cause this type of issue too,so if your car has one try unplugging it.Sorry to dribble on but you did ask,and for my sins yes I do run a LR garage..................

Dribble away,

The vehicle does not have a powerbox or similar, its completely standard apart from a K and N filter. I managed to induce this fault again today, not only while changing gear, but when easing off sharply in a third gear at fairly low speed. As previously mentioned, i'm pretty sure that it dissapears completely when the engine is hot. It's worse during the first couple of gearchanges and you get a very minor flicker now and again after that. it seems to persist longer on a cold day and only seemed to happend once on the way back from work today as it was very warm here (relatively!) I have also found in the past that on a cold morning, if i start the engine and let it idle for a minute or so before moving off then the problem, or the persistence of the problem, is reduced.

Have you any idea why this may be? Or would it lead to one problem in particular?

I am in Pembrokeshire and would be willing to drive up to you to get this sorted, except that the engine would be red hot by the time i got there and the problem would have gone away!!

Any further ideas?

Dave

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Unlike AllyV8 I'm a private owner, and 'advice by Forum' is the closest I get to working on someone else's vehicle.

From my reading of different threads, in different forums, and my own experiences, this problem seems centred around the high pressure Fuel Injection Pump, driven off the camshaft and situated above the alternator.

I've seen cures claimed by different actions:

Adjustment, as already described (but you need the equipment (Bosch or Blackbox Solutions)).

Changing the fuel temperature sensor, which is accessible by removing the top cover (although this is more to do with poor warm starting).

Removing this cover and giving eveything a good drenching in spray on brake / carb cleaner.

Changing the pump.

In my own case I changed the top half of the pump, called the HDK unit, while leaving the pump on the engine.

I cannot recommend this course of action, as removing the unit destroys the internal pump calibration, and it's a real hit and miss to get this back anywhere near while on the vehicle.

I assume more accurate recalibration can be done on the specialist test & overhaul bench.

The difference lies in the cost.

My 'used but guaranteed good' unit, with money back gaurantee, cost about £30.

A new unit would have cost about £150 (Trade source, but incl VAT, IIRC).

A new (rebuilt) pump from a diesel specialist will cost around £1,000, probably +VAT and fitting (but do check locally).

Clearly, having the pump changed is the most expensive option, and I would get prices locally so you have a comparison figure. I'm thinking here that gambling £50 to save £200 is not a good bet, gambling £50 to save £1,500 might be more acceptable.

While getting quotes you can also ask the local Diesel Specialists for their opinions, remember the Customer Base for these engines includes BMW 325/525 and Vauxhall Omega cars, so they should have some experience. Given the exchanges in this forum you have some background information.

The problem does get worse, to the point where the engine dies and needs a bump or key restart, so how urgent the repair is depends on how long you can put up with this. Bear in mind that you 'can't' sell the car as it is, so the sooner it's fixed, the more time you have enjoying a car in good condition. It seems daft strugging with a car for months just to save a repair bill, then having to pay anyway, or lose on the sale price. You might as well spend now and have some time to enjoy the result.

I thnk that's as far as I can go, good luck.

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Hello again,

You mention that you changed the HDK unit on the top of your pump? what was it that was wrong with your vehicle?

I still can't work out why this tends to be worse in bad weather and / or when the vehicle is cold. I happened to get a phone call this evening just after I started the RR up this afternoon to leave work, which meant i sat there with the engine running for a few minutes before i set off home. Because of this i didn't get the light flash on at all, even for a moment!

Any ideas as to why this might be?

David you also mention that you got some second hand parts, can I ask where you sourced these as I have a contact in the Local Land Rover dealership and could borrow the associated special tools in order to have the pump tested / repaired

Dave

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