Disco 1 auto Throttle problem

[Derek Martin]

I'll be about this all this weekend, so if you need any help locating it, I think I posted my telephone number earlier, so give me call.

Derek.

[sotal]

Thanks Derek - not sure if I'll get time or not this weekend but if I get stuck I'll give you a bell

I'm guessing you've had no ill effects from unplugging the ECU??

[Guy H]

do you want a voltage reading at that point or resistance.

voltage - when it's running ok & when the engine check light is on

[Derek Martin]

voltage - when it's running ok & when the engine check light is on

Guy. I already posted the voltage on mine with and without the CEL light on. As I said before I used a digital multimeter, and could not see any variation in the voltage other than the expected change with throttle movement i.e. no sudden drop or increase at the problem position. I have an older needle type multimeter I could use, but I don't have access to an oscilloscope etc.

Derek.

[Derek Martin]

Thanks Derek - not sure if I'll get time or not this weekend but if I get stuck I'll give you a bell

I'm guessing you've had no ill effects from unplugging the ECU??

No, its actually pretty easy to get it out, but a little fiddly. I remove the cover from above the pedals (3 plastic push in fixings), then remove the plug for the laptop used to read the ecu etc, and get the cover out of the way (i've left mine off at the moment to allow me to get the ecu and wiring etc easily). Then remove the plastic panel by the A column to the right of the accelerator pedal(two plastic fixings), get that out of the way. The ECU is located to behind and above the where the panel was. The connector has a retaining clip, you just pull that down, then pull the plug down at the end facing you, the far end is hooked under clip, and will release when you have got the plug a fair way down. The ecu is held in position by two plastic nuts at the end nearest you, these are 10mm, I used a long socket and turned it by hand to remove them, the ecu can then be removed by pulling it off the two threads, and sliding it down to release a catch at the rear, (its not fixed there, just pushed over another pin that fits in a slot on the rear of the ecu. To get access to the wiring, I removed the single screw on the plug to remove th eouter casing, and I could then reach the pins, I then pushed the plug into the ecu and could read the voltages with the engine running.

I never tried to reproduce the problem with the engine running in drive but not moving, as I could do it with the car moving, I assumed it would be the same , I'll give it a go over the weekend.

Derek.

[Guy H]

Guy. I already posted the voltage on mine with and without the CEL light on. As I said before I used a digital multimeter, and could not see any variation in the voltage other than the expected change with throttle movement i.e. no sudden drop or increase at the problem position. I have an older needle type multimeter I could use, but I don't have access to an oscilloscope etc.

Derek.

Ok, found the readings, but we need to take them as I wrote in my previous emails - between the sensor leads and the ground that the ECU uses for those sensors, not just any pin nor across the sensor, as that's not how the ECU looks at the signal. The ECU will have several grounds, you need to use the right one.

Thing is, when the engine check light is on the ECU is complaining that something to do with the TPS is out of limits compared to what it thinks it should be showing. I think that's quite important - the error code posted was TPS faulty compared to .... whatever it was. Now the only items it can be comparing the pedal position to that make any sense are the TPS the fuel quantity sensor in the pump and the MAF sensor. But the fact that changing the TPS has changed the fault would point to that being the most likely culprit. You can always have a check for voltage between 13 & 38 as well whilst you are in there

We need readings when the light is off below the problem, when the light is on, and then again 'above' the problem. One of the readings I asked for will not be 'in line' with the others. Then we can go from there.

We also need all the readings from the same vehicle using the same meter in the same weather conditions etc.

If those readings don't show anything, then we may need to look at the sensor in the pump, but that's a little more complicated to measure and may well be beyond a cheapy multimeter.

BTW The logged fault codes should have given this information (sensor voltage leading to fault condition) - it's all stored.

[Derek Martin]

Ok, found the readings, but we need to take them as I wrote in my previous emails - between the sensor leads and the ground that the ECU uses for those sensors, not just any pin nor across the sensor, as that's not how the ECU looks at the signal. The ECU will have several grounds, you need to use the right one.

Thing is, when the engine check light is on the ECU is complaining that something to do with the TPS is out of limits compared to what it thinks it should be showing. I think that's quite important - the error code posted was TPS faulty compared to .... whatever it was. Now the only items it can be comparing the pedal position to that make any sense are the TPS the fuel quantity sensor in the pump and the MAF sensor. But the fact that changing the TPS has changed the fault would point to that being the most likely culprit. You can always have a check for voltage between 13 & 38 as well whilst you are in there

We need readings when the light is off below the problem, when the light is on, and then again 'above' the problem. One of the readings I asked for will not be 'in line' with the others. Then we can go from there.

We also need all the readings from the same vehicle using the same meter in the same weather conditions etc.

If those readings don't show anything, then we may need to look at the sensor in the pump, but that's a little more complicated to measure and may well be beyond a cheapy multimeter.

BTW The logged fault codes should have given this information (sensor voltage leading to fault condition) - it's all stored.

I've been so many 'it could be this or that' scenarios that I've lost count, at one time I thought it might be the Air Mass Sensor. I found that at one stage disconnecting that appeared to make the problem go away for short a time (maybe a day or so). Disconnecting the plug didn't put the CEL light on at all, I have read somewhere that the ECU uses a default calculation if that sensor goes u/s?. I found after a few tests that it did not necessarily always cure the problem, so I gave up on that line of solution, until I send it into the Bosch specialist. The only other alternative is the replace bits and see it goes away solution, which could be very expensive for a car not worth that much anyway, that's why I bought the replacement ECU when I saw it at a reasonable price.

I'll try and have another go at reading the voltages etc on the pins you mentioned.

Thanks for the advice, all help gratefully received!

Derek.

[sotal]

Ok I've just pulled the ECU out and removed the outer plug as Derek described to give it some testing. I've got my results but they don't seem the same as Dereks (not sur eif that's good or not)

I started off with pin 37 and 13.

The engine was quite cold to start with

On idle it showed 0.44v

1000rpm = 0.67v

1500rpm = 0.74v

2000rpm = 0.80v

2500rpm = 0.85v]

The problem never occured, so I took it for a drive to warm it up as when I'd tested it Neatral before it was after a journey, when I returned the temp needle was just under half (about the max it ever gets to)

2nd Results at normal temp:

1000rpm = 0.65v

1500rpm = 0.70v

2000rpm = 0.80v

CEL came on and voltage went to 0.5v - also you can here a relay click when the light comes on and click when it goes off, I think the realy is inside the ECU but not 100% sure

2500rpm = 0.83v

With the ignition on but the engine not running the range goes from 0.44 - 1.8v and kickdown goes to 2.37v

Next was pin 33, quite boring results but quite interesting effect happened.

Basically it read 4.95v just about all the time, it did vary slightly between 4.93 - 4.97 but that was probably more down to the cheap multimeter.

The interesting part to it was that when I connected the multimeter to these pins I wanted to see the range with the engine not running, as I got to the point on the pedal the relay clicked in the ECU, I started it up and rev'd it but the revs wouldn't rise it just idled. When I got to the approx place on the pedal where it occurs the CEL came on and the relay clicked - I could repeat this every time perfectly with no problems (although I was starting to worry as I couldn't rev her anymore!) I pulled the probes out and it started to rev fine again, I put the probes back and it wouldn't rev, I found that just removing the probe on pin 33 made it rev again. I then switched it off, removed the probes, unplugged and reseated the connecter and tried again, it now rev'd fine with the probes in place. I then took the readings of 4.95 all the way up, the CEL light came on and the voltage remained at 4.95.

I then went on to pin 25 - interesting this one, but I couldn't get the CEL light to come on, anyway the results were:

Range with ignition on but engine not running = 0.48 - 5.99(on kickdown)

idle = 0.48

1000rpm = 0.48

1500rpm = 0.48

1750rpm = 0.49

2000rpm = 0.50

2100rpm = 5.91

As you can see the CEL didn't occur but at the approx point where it does occur the voltage shot up.

I've just remembered you wanted the voltage between pin 13 and the negative terminal so I'll go and get that one after my lunch, anything you can tell so far?

*UPDATE*

Just measured the voltage between pin 13 and the battery negative terminal - it gave a reading of 0.17v. I did the same test between the battery negative and the engine block and that gave 0v

Is the 0.17 significant enough to be a problem?

[Derek Martin]

I took my voltages between pins 33 and 37, so that may explain the difference?.

I would have thought the drop in voltage when the problem occurs is interesting, and may suggest the TPS is at fault?. I still have my original TPS, so if you want to try it, let me know, we could just plug it in under the bonnet., and move it by hand.

I went out to look at mine again, this morning, but found it wasn't starting very well, so I ended up replacing a couple of Glow plugs, beam ends hadn't got any unfortunately, so had to get them elsewhere, very convenient having a part supplier only up the road!

I remembered that Guy mentioned the MAF, the car was having the problem as normal, I removed the connector on the MAF, and the engine revved without problem, I put the connector back on, and the engine has been fine for the rest of the day. This is what happened before when I removed the connector, but I showed my wife what to do, and she said it stopped curing the problem after a few days.

I'll try and repeat your tests in the week, and post the results.

Glad you thought you could hear the click when the light comes on, I found it difficult to be sure, maybe there is a miniature relay in the ECU, I was'nt convinced it wasn't one of the other relays by the ECU.

[sotal]

There was definatley a click from a relay - mine was quite loud, at the point where it wouldn't rev, it clicked everytime I pressed the pedal and the CEL came on, that's when I tried to locate it, I couldn't really tell where the noise was coming from but I held the ECU and I was fairly sure I could feel it.

I've just been to Leek and back and as you reported after fiddling with it's been fine, I can now no longer make the CEL come on at will, and it hasn't done it all (it had now got to the stage where it did it atleast 10 times per journey)

So it does look like disturbing something seems to sort of fix it, I'll see how long it is until it happens again, slightly annoying in a way as I know I haven't fixed it but now I can't replicate the fault, it also seems to have sorted my glow plug issue where it wouldn't start when the engine was warm and I use glow plugs.

Who knows - could be a dodgy wire somewhere - or maybe the power cycle to the ecu does something??? Hopefully Guy can shed some light on it?

[Guy H]

Very good 'n' thorough write up

I then switched it off, removed the probes, unplugged and reseated the connecter and tried again, it now rev'd fine with the probes in place.

Think you may have just fixed it there. It would make absolute sense BUT let's see what happens.

That pin is a nominal 5v feed to the TPS & idle switch sensors (maybe others)

This was also happening at the point that the idle 'switch' in the TPS changes so the load on the pin changes.

Now there's something not quite right there, the nominal voltage from gnd to +ve is 4.95v yet there is 4.99v coming out of the idle switch???? can't confirm as can't look at the diagrams at the moment

I'll try and get time to have a poke around mine tomorrow and compare. but that does look weird

All the other readings (apart from the TPS voltage dying) look ok the 0.17v is fine (ECUs have several different 'grounds' for different jobs)

I would pop down your nearest Maplins or RS or electronics shop and get some contact cleaner, pop the ECU plug off give it a good spray & the ECU socket and reseat it a couple of times.

The relay may be an off-idle or load relay ??? activated by the idle switch.

be interesting if it starts in the morning

[Derek Martin]

................

The relay may be an off-idle or load relay ??? activated by the idle switch.

When I heard the click on my car I had a look at my haynes manual at what relays were in the driver footwell below the ECU. and one of them is the Engine load control relay, the wiring diagram shows this as being to conected to the +ve battery terminal via fuse, then 2 supplies one going to the going to the ecu pin 15, and the other to ECU pins 16, 17, EGR, Fuel pump, fuel injector assembly, and data link conector. Does this just control the power to all these parts?, i.e. turns them on when the ignition is on?, if so why would it click at approx 2000 rpm? .

I couldn't be certain which relay it was, at the time I was operating the pedal by hand, a keeping the probes on the relevant pins, and the ECU got in the way of me putting my ear ot hand against the relays!.

Derek.

[sotal]

Well it did start this morning, the starter was a little slow but it fired straight up, I won't assume that's fixed yet though.

I've used it a couple of times today and it still hasn't prodcued the fault and I can't make the fault occur as I could before.

I've got to say it looks like a dodgy connection espically as Dereks fixes it's for a couple of days each time he has a play with it and mine has fixed itself for now.

When the relay clicks the voltage on one of those pins (pin 25) shoots up - or atleast around that point (can't remember hearing it but the engine was reving louder then)

So I presume the relay clicks and it increases the power - not sure why though? Anyone know what pin 25 does and why the voltage shoots up just over 2000 rpm?

[Arned]

This weekend I cleaned the battery bodywork/chassis connections. The –Ve cable from the battery connects to the bodywork just behind the battery and then continues to the chassis where it is bolted onto and terminates. Under the same nut as for the bodywork connection are also two lugs with each two thin wires wich disappear into the cabling loom going from there towards the motor just under the injection pump. The motor now behaves even worse, multiple throttle positions were the CEM light comes on and the motor runs very irregular. To be continued ……

[sotal]

Well mine started up fine again this morning and I still can't produce the fault with the TPS. Not convinced it's fixed but so far so good.

[Guy H]

The motor now behaves even worse, multiple throttle positions were the CEM light comes on and the motor runs very irregular. To be continued ……

Try unplugging the ECU, spraying contact cleaner in there, then plugiing it in and out a couple of time and see if that helps.

Otherwise you'll need to do the same multimeter tests that sotal did and post the results.

[Guy H]

Well it did start this morning, the starter was a little slow but it fired straight up, I won't assume that's fixed yet though.

I've used it a couple of times today and it still hasn't prodcued the fault and I can't make the fault occur as I could before.

I've got to say it looks like a dodgy connection espically as Dereks fixes it's for a couple of days each time he has a play with it and mine has fixed itself for now.

When the relay clicks the voltage on one of those pins (pin 25) shoots up - or atleast around that point (can't remember hearing it but the engine was reving louder then)

So I presume the relay clicks and it increases the power - not sure why though? Anyone know what pin 25 does and why the voltage shoots up just over 2000 rpm?

Pin 25 is the TPS idle switch, so yes that's what it should do.

The clicking is not the load relay - that relay seems to power the ECU, it would seem that the ECU has the ability to shutdown its own power!!?

If you are interested in tracking down the clicking, you could have a look at pin 6 - red lead on pin 16 or 17, black on 6

Good luck

[sotal]

Go on... You'll have to explain the TPS idle switch for me! Why would the idle switch kick in at 2000ish RPM?

[Derek Martin]

Go on... You'll have to explain the TPS idle switch for me! Why would the idle switch kick in at 2000ish RPM?

I was wondering why the TPS would need to have an idle switch, is it just on/off when the pedal is pressed or not pressed?, i.e. it would signal the ECU to put the engine into idle mode rather than read the pedal position from other circuit?.

Derek.

[Arned]

Last night I removed the multipole connector from the ECU and put it back a few times and can now NOT reproduce the very rough, irregular, throttle position dependant running of the engine. I used the car today and everything seems fine. It is hard to believe that all this could be due to bad contacts. The ECU is in the passenger compartment, not even under the bonnet where one could imagine having much more harsh environmental conditions leading to bad connections.

I will keep the forum informed how long it will last to run correctly.

I seriously start to believe that the manufacturers create more trouble than good with all these sensitive electronics in the cars especially when I think back to my first Discovery 200TDi in 1990 were the only electronics in the car was the radio and most problems were relatively easy to fix.

[sotal]

Well the Disco has started perfectly every morning since sorting this - not sure if it's coincidence or not? It was very cold this morning though and it started straight up.

So that's the good news - the bad news is that the check engine light came back on my way to work today 1st as I left my street, twice on the way down the bank, then the worst bit was going up the bank at the end on my way to work, it's a very steep bank which goes round a sharp bend so would be a very bad place to brake down! As I got about half way up the bank the disco started to slow down, I checked the dash and the CEL had come on and the revs had backed off to their safe value of 1200rpm, I tried reving and backing off but reving didn't do anything, backing off slowed down even more, so I kept my foot about half way down and the revs stayed at 1200rpm and it struggled up the hill, as it levelled out I tried to speed up but it still wasn't having any, a few seconds later the CEL went off and it returned to normal and I drove into work and parked up.

The only thing different is that my low fuel light popped on this morning, would that be related?

[Derek Martin]

The only thing different is that my low fuel light popped on this morning, would that be related?

I have never had the CEL staying on like that, I have thought that the best thing that could happen would be a total failure of whatever is causing it, at least I might stand a chance of finding it!. (not very helpful at the time of the breakdown I know). Seems similar to ours in that messing with the cables etc causes it to run ok for a while, then back to the normal problem.

If the CEL problem is repeatable again, try pulling the connector from the MAF, my wife say our has run with no problem since I pulled the connector last Saturday, rev'd the engine (problem went away) and reconnected it again, how long for though?.

[sotal]

Well I had to go out this morning in the Disco so I was dreading it breaking down, but it's not been too bad, I've done about 60 miles since but mostly just going through stoke-on-trent so no real speeds, I filled up with a bit of fuel on my way which probably helped - I think I was probably unfortunate enough to pull a bit of crud up with it being low on fuel.

I didn't experience the CEL light again at all during the 60 miles but I did have a fuel related problem I think. I was on a 60 road, and the old couple in front were doing 40, it was a nice clear road so I put my foot down, I got level at about 50 and it started to struggle I ended up having to slow down and go back behind he turned off not long later so I put my foot down again to test it and got to about 55 before it started to struggle (this is on the flat).

I then had to mostly do town driving which is fine and it was pulling well and it's as quick as ever pulling out of junctions etc.

Towards the end of the 60 miles I got back to a road I could speed up a bit on, and took it up to 70 on a slight downhill, but then it coming back along that road a few minutes later so slightly up hill it would only go to 60 ish before it started to struggle.

I've just come back up the hill I really struggled on this morning and it was fine.

I've bought a filter set, so I'll change the fuel filter and the air filter. Just wondering if the fuel was a little frozen/waxed this morning or something and it's dragged some up?

[Derek Martin]

I've bought a filter set, so I'll change the fuel filter and the air filter. Just wondering if the fuel was a little frozen/waxed this morning or something and it's dragged some up?

I suppose the engine temperature gauge is ok?, I use my Disco to tow a caravan, and on a return trip from Cornwall had a very bad time with the engine overheating. I eventually traced it to the radiator (most of the vanes on the grill side of the side had collapsed), every time I went up a hill the engine overheated very rapidly, and the power dropped off to the point where I was doing 20 mph uphill on the Motorway (everybody else was very pleased with me!). as soon as I reached a flat or downhill section, the power picked up again as the temperature dropped. I think the ECU has an overheating mode, where it just drops the throttle setting off, making it impossible for you to go any faster. Once I changed the rad, the temperature never changes.

Still no problem with the throttle since I unplugged/plugged the MAF connector, it will be back though!

Derek.

[sotal]

Temp is fine, infact most of the time it hadn't even started to register on the guage, it does get to it's normal position but isn't going any higher, sometimes it just sort of hesitates, other times the CEL comes on. Just got to manage for tomorrow then it'll be off the road for a couple of weeks, beam ends are going to get a lift pump in for me for the new year - just hope it's not an electrical fault!