300tdi Auto Check Engine Light sounds rattly

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terrastudios

New Member
Posts
27
Hi all,

Recently bought a 300tdi Auto 1996 Disco. 1 everything seemed ok with it, but just recently I'll be driving along and the engine sounds nice and smooth when at about 2500 rpms the check engine light flashes on and the engine starts to sound really rattly - its definately down on power when this happens. If I let the revs drop less than 2500 the check engine light goes off, but the engine still remains rattly. Sometimes if I let off the throttle all together and let the engine go back to idle it goes back to the smooth sound and the engine gets power again for a short while until it repeats the above.

I've recently done a fuel filter (not done sediment yet), oil change, oil filter and air filter to it.

Just wanted to add as well theres no black / blue smoke out the back, so the fueling must be ok?

Many thanks in advance!!

Matt.
 
terrastudios said:
I've recently done a fuel filter (not done sediment yet), oil change, oil filter and air filter to it.
Click to expand...

Sounds as if you may have a small air leak introducted after you change the fuel filter.

Also crack off each fuel pipe to the injectors in turn and check that there isn't an air lock somewhere. TDi is usually pretty good at self-bleeding but always best to check if a problem is suspected.
 
andyb66 said:
Sounds as if you may have a small air leak introducted after you change the fuel filter.

Also crack off each fuel pipe to the injectors in turn and check that there isn't an air lock somewhere. TDi is usually pretty good at self-bleeding but always best to check if a problem is suspected.
Click to expand...

So I guess cos theres an air lock one/multiple cylinders will be running lean hence why it goes noisy! I'll do this at the weekend, many thanks.
 
That's the theory but I am not sure it's trapped air, more likely air getting in like Andy first mentioned.

Another thing to check the little pieces of leak off pipe going between the 4 injectors, there should be 3 links in total, are the freyed? cracked? leaking? If any of the previous apply to your's replace them all - just ask any good motor factor for a small length or diesel leak off pipe and cut them to size yourself.

Back to Andys theory. The Bosch injection system is damn good at getting rid of air, and fast, but thats not to say it cannot be at fault.

When you put the new filter on, did you wet the orings with diesel/oil and then tighten up just a nick after the seals bottom out? You may have caused the o-ring to ruffle up and it has created a little gap for air to get in. Did you make sure the old o-rings came out with the old filter? If you have two somewhere (usually the centre ring) you will have a made a spacer thats not letting the other ring seat properly.
 
discomania said:
That's the theory but I am not sure it's trapped air, more likely air getting in like Andy first mentioned.

Another thing to check the little pieces of leak off pipe going between the 4 injectors, there should be 3 links in total, are the freyed? cracked? leaking? If any of the previous apply to your's replace them all - just ask any good motor factor for a small length or diesel leak off pipe and cut them to size yourself.

Back to Andys theory. The Bosch injection system is damn good at getting rid of air, and fast, but thats not to say it cannot be at fault.

When you put the new filter on, did you wet the orings with diesel/oil and then tighten up just a nick after the seals bottom out? You may have caused the o-ring to ruffle up and it has created a little gap for air to get in. Did you make sure the old o-rings came out with the old filter? If you have two somewhere (usually the centre ring) you will have a made a spacer thats not letting the other ring seat properly.
Click to expand...

The thing is it was about 2 months back when I did the fuel filter, this only seems to be a recent problem, although when I think back its not really been used that much since the filter change. Hmmm! From what I recall I unscrewed the original filter, wet the o-ring (only remember doing the outer one?) with oil and then tightened it up. I'll pull it off and check to see how many o-rings are on it! I hope its something stupid like that! :D Noticed your footer, its a Britpart filter I put on (short of cash!) but guess theyll be ok for a few months until I can get a proper one.

Cheers again

Matt
 
Well I removed the diesel filter and checked it over... couldnt see any problem with it, but put it back on and made sure it was nice and tight.

I unplugged the MAF at the same time, took the disco for a spin... guess what! No problem anymore, its smoooth as silk but was a bit down on power (guess the Bosch injector pump has an approximate air flow table in ROM to keep the truck running if the MAF isn't present).

The MAF connectors pretty crap anyway, the heatshrinks been sliced through and looking at the crimps they are all corroded. So for now I've had the connector swimming in switch cleaner, shoved it back into the MAF and still no problem! Well fingers crossed and I'll order a new 4 pin AMP Junior Timer connector from VWP and crimp it on next week.

Cheers for all your help,

Matt.
 
Still got this problem.. the 300tdi is sounding like a tractor pretty much all the time now... it does occasionally go "smooth" (no rattle/knocking) but then it starts rattling again.

I've bled the fuel system using the bleed screw/lift pump - fuel comes out under pressure when i use the lift pump manual arm so guess this shows lift pump is working correctly. Recrimped a new connector on MAF but it makes no difference if the MAF is connected or not. I've also had the fuel filter off and put another new (none-Brit part) one on, checked all the seals and tightened it right up and replaced all the injector leak off pipes (they were cracked).

If I keep my foot on the accelerator for about 15 seconds (regardless of RPM/load etc..) I get a check engine light on. If I take my foot fully off the accelerator at 14 seconds and then immediately push it back in, check engine light stays off. I had to drive to Scotland for work last week so did 400 miles of driving with my foot constantly on and off the accelerator!

Other thing is one of the turbo boost pipes (the elbow after the turbo) split, I've replaced this but found it odd (but probably related to the "tractor" sound) that I wasn't getting black smoke out the back.

Thanks in advance!

Matt
 
Hello Matt... my one and only experience with the 'Check Engine' light was self inflicted. Over the course of a couple of days I had been adjusting the timing to get it running as spot on as I could. All was fine until I advanced it just that bit too much and I ended up with the light on. It would come on at certain rev's (can't remember exactly) and go off if I came off the gas.
Backed off the timing a bit and all was back to normal.
Just thinking it might be something else to look at.
 
Thanks guys.

How easy is it to check the timing?

Paul - what should happen if the MAF is unplugged? I took the vehicle to a local landrover garage and he suggested that the MAF is not needed and is part of the EGR setup, but I'm not so sure, my understanding is the MAF sends back to the ecu the amount of air being sucked through the turbo into to the engine and the ecu alters the fueling based upon this flow rate.
 
I dunno, but if it's running crap with it in, and crap with it unplugged, I'd try a new one. It's my understanding that when a working one is connected the engines run fine and when it 'goes' or is unplugged the engines run crap .. for 300 Tdi values of fine ... ;) Do you have a full egr system on the engine? Is it blanked off? If egr's there and if it's not blanked off I'd have thought the MAF would do something to the engine running if it's not working, or unplugged! Maybe the reason it's not working is why the engine's running ****e ... Just a logical assumption, assuming the egr is fitted and working.

A quick perusal of ebay says a MAF sensor is about £30, so better I think, than a trip to another garage .. unless, of course, it's something else ... :)
 
First thing I did was to blank off the EGR valve, so thats not present anymore.

Aye seen a second hand MAF on ebay for £30 - just hope its working!
 
To be honest I don't know enough about the system, I haven't got an egr on mine and wouldn't know where the MAF is, what it looks like or even if it actually has one!

All I was going on was logic, so it may have thrown you right off the scent.

If the MAF is associated with the egr and the egr isn't there, then logic says the MAF probably doesn't have anything to do with the engine running crap then.

And I wouldn't buy a second hand one off ebay, I'd buy a new one for £30 ....
 
MAFSensor

Dunno if it's specifically for your vehicle, so I'd check if I were you, but that was the first in my search ... ;)
 
I reckon all this talk of air in the system is not hitting the mark.

The Engine check light illumination appears to be linked with the (fly-by-wire) throttle pedal, so I would assume it's an electrical problem/s.

The chap who said the MAF only works with the EGR valve is talking tosh, the EGR valve on an EDC-quipped car doesn't even have an electrical connector, that's only for manuals.

The fact that the performance doesn't change when you disconnect the MAF does suggest a problem, but as this light comes on directly in relation to the throttle usuage suggests to me that it's a faulty throttle potentiometer.
 
Hey

Funnily enough I was just under the dash 5 mins ago looking at the TPS... figure its the large round device thats on top of the throttle pedal?

I cleaned up the terminals on the MAF and looking at the circuit diagram, the MAF has two components inside, a thermister (pins 1 and 4) - presumably for intake air temp measurement and a potentiometer thats connected to a big air "flap" inside the MAF, pin 2 is the top of the potentiometer, 3 is connected to the wiper and 4 is a shared ground between the thermister and the pot.

Now I'd expect that the resistance between pins 2,3 and 4 to change when the "flap" is moved with my finger, however it doesn't which makes me think the potentiometer has failed in the unit. Problem is they seem rather expensive (its not a normal hot wire MAF as per the one Paul posted for ebay) - so will go for a second hand one and hopefully that will solve some of the issues.

I figure I've got at least two faulty sensors... the MAF and the TPS as per your suggestion biglad.

Matt.
 
terrastudios said:
Hey

Funnily enough I was just under the dash 5 mins ago looking at the TPS... figure its the large round device thats on top of the throttle pedal?

I cleaned up the terminals on the MAF and looking at the circuit diagram, the MAF has two components inside, a thermister (pins 1 and 4) - presumably for intake air temp measurement and a potentiometer thats connected to a big air "flap" inside the MAF, pin 2 is the top of the potentiometer, 3 is connected to the wiper and 4 is a shared ground between the thermister and the pot.

Now I'd expect that the resistance between pins 2,3 and 4 to change when the "flap" is moved with my finger, however it doesn't which makes me think the potentiometer has failed in the unit. Problem is they seem rather expensive (its not a normal hot wire MAF as per the one Paul posted for ebay) - so will go for a second hand one and hopefully that will solve some of the issues.

I figure I've got at least two faulty sensors... the MAF and the TPS as per your suggestion biglad.

Matt.
Click to expand...


Hi Matt, don't forget that there is a crank sensor as well, which the ECU uses to set timing.
 
Is there any specifications anywhere to say that the sensors have to be within a certain range?

I guess with the crank sensor I can take out my scope and view the waveform, presume its a VR sensor with x number of teeth on the flywheel (like 60 teeth with 1 missing). I just went out and unplugged crank sensor (blue connector) and the engine barely idles, guess because its trying to run just from the VR sensor on inj #4, so this shows the crank sensor must be working to some degree.

Whilst I was unplugging the blue connector I noticed the two (pictured) pipes that seem to be disconnected... are they meant to be?

04102009078.jpg

04102009079.jpg


Thanks again!

Matt.
 
Last edited:
terrastudios said:
Is there any specifications anywhere to say that the sensors have to be within a certain range?

I guess with the crank sensor I can take out my scope and view the waveform, presume its a VR sensor with x number of teeth on the flywheel (like 60 teeth with 1 missing). I just went out and unplugged crank sensor (blue connector) and the engine barely idles, guess because its trying to run just from the VR sensor on inj #4, so this shows the crank sensor must be working to some degree.

Whilst I was unplugging the blue connector I noticed the two (pictured) pipes that seem to be disconnected... are they meant to be?




Thanks again!

Matt.
Click to expand...

Hi Matt, sounds like the crank sensor is ok, the two open-ended pipes are almost certainly breather pipes for either the gearbox/transfer or the front axle.
 
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