Omega Owners Forum
Omega Help Area => Omega General Help => Topic started by: magnul on 20 August 2007, 22:59:46
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A few questions from a newbie:
A few days ago I got fault code 92-camshaft sensor incorrect signal, and the car went into limp home mode. I ordered a replacement from ebay and changed it today.
1) The fault persists. EML lights up a few seconds after start, and the engine still has to be cranked longer than usual to fire. Any ways of testing sensor and/or wireing with a DMM? Can incorrect fitting of the timing belt cause cam sensor fault? The timing belt was of a couple of weeks ago when I had the HG replaced.
2) I have never removed the timing belt cover before, and never seen a cam belt. I was a bit surprised that it wasn't fully tensioned all the way around. There was quite some slack on the exhaust side. Is this normal?
3) After replacing the sensor and starting the engine I noticed a funky smell. Like hot (but not burning) rubber or plastic. Is it possible to do anything wrong when refitting the timing belt cover? I also imagine that I hear some noise from that area. I may just be hysteric, but I'm a bit concerned about that part of the engine :-/
The car is a -95 2L 16V
-Magnus-
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How much slack? Should have reasonable tension all way round. Do not use if it has more slack than this!
Incorrect timing can cause ecu to think cam sensor problem. When cambelt changed, was the tension also changed, or just the belt? If just the belt, do it again properly, with tensioners and rollers.
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Tension didn't appear to be even all way around. Could probably push the belt 1cm without much force on the stretch below the exhaust cam.
Cam belt wasn't changed when HG was changed, since belt, tensioners and rollers were changed a few months ago.
-Magnus-
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I just had another look, and I think that the smell is from the exhaust manifold (small experiment with exhaust repair tape on a small crack) and the noise appears to come from the PS pump.
Assuming that timing belt is OK, how do I test the sensor? Will the AC reference signal be on with just ignition on? Is it possible to remove the connector with the engine running?
I think I'll ask the mechanic who did the HG change if the timing belt has excessive slack. Forgot my Haynes manual while on holiday, so I can't really check anything myself.
-Magnus-
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Nobody knows how to test the sensor and/or wiring?
Perhaps a dumb question; is it possible that a faulty crankshaft sensor cause discrepancy between cam- and crank signal and hence apparent cam sensor fault? The wiring on my crank sensor is in awful condition.
-Magnus-
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Nobody knows how to test the sensor and/or wiring?
The only way to check the signal properly is to use an oscilloscope
to check the waveform it produces. Tech 2 boys will know more than
me, but I would imagine you would need to take it to someone
who owns the equipment as the cost of buying would be prohibitive.
As for the wiring, you'll need to identify the connections on the ECU and
do a continuity check between the Cam sensor and the ECU.
You can do this bit yourself with a conventional multimeter. They're
not expensive and worth their weight in Gold for checking out
electrical problems.
Sorry I couldn't be of more help.
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The wiring on my crank sensor is in awful condition.
Change it now while you can do it at a time and place of your choosing.
It will fail if you leave it.
Not expensive and well within the scope of a 'do-it-yourselfer'.
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If the wiring continuity is OK, sufficiently away from alternator, the cam timing is correct, then it will be the sensor. It seems on of the capacitors fails inside the sensor itself...
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Thanks. I didn't think of such simple things, as I'm not completely aware of the way the sensor works. I can cope with DC, but hate AC;) I have DMM, so I guess it's just a matter of disconnecting the big connector to the ECU and check continuity from pins 2, 4 and 22* to the plug.
I measured resistances in the old sensor (open circuit) and the new one (20ish ohm between left and right pin and short circuit to middle pin).
I ordered a new crank sensor yesterday and will change it when it arrives next week. Just wondered if it could be related, but obviously best to check the simple stuff first.
*According to: http://www.euroscan.hu/files/sim561.pdf
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I've checked the continuity, and it's very good (actually read -0.5ohms, never seen that before).
What's the thing with the modded sensor I've read about? Is the sensor different or just the wiring?
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I've not heard about an actual modded sensor, although that doesn't
mean there isn't one. Someone here will know.
What is important is the modded route of the wiring. 'Spikes' from the
alternator were damaging the the cam sensor, so the cable routing
was modified to route it away from the alternator and it's cabling.
The cable run from my cam sensor runs past the inlet manifold and
round the back of the cylinder head to join up with the ECU.
Don't know if that helps you?
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i believe it is both the sensor and the wiring and connector that have been modded. thats why the new sensors come with a new wiring loom. as grumpy says it's to help protect against "spikes"!!!!! in my opinion get genuine sensor as i bought 2 and neither worked till i bought genuine one.
only bout £45 i can give part number if you want as well!
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I guess your car had the modded sensor fittet from factory as yours is newer than mine? The sensor I bought from ebay has Vaux P/N 90458252. Came without new loom. Sensor looks identical to the old one. Do the P/N match the genuine you bought?
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no mine had un-modded one fitted.i had to fit modded one. no the part number wrong, the genuine modded one p/n is 93171450
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So it's basically a shielding problem then. Find it a bit puzzling, as the problem started as a temperature dependent one (fault only appeared at hot start). Think I should hook it up to a Tech2 and check some livedata before buying any more sensors...
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if it only does it on a warm start i think it's more likely crank sensor, somebody else had same prob think it was grumpy. is it limiting at 4500 rpm???
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In the beginning it was only when warm. After a few days it became permanent. A new crankshaft sensor is on its way from the uk. Dunno if it will sort the problem, but I guess the crankshaft sensor would fail soon anyway, so I'm being a bit proactive.
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I replaced the crank sensor. Didn't solve the problem, although the engine appears to run a bit smoother after the change.
Got a mechanic to check cam belt timing and tension, all in perfect order.
Bought and fitted the modded sensor today, but fault is still there :'(
Any advise on what to do next? I'm getting a bit desperate now.
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hi again,
check that you have made connections good on new wiring loom on modded sensor. and that none are shorting. seems daft but it does happen. try reading codes again and see if you getting same codes. is engine limiting at all???
cheers steve
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I've just re-checked the continuity, and alle the connections from ECU connector to sensor connector are good.
From what I've read this sensor should operate with a high frequency reference signal (100-180kHz) of unknown magnitude. As the modded sensor gave me some points to measure at, I tried to measure AC volts from red/white cable (AC signal from ECU) vs battery negative with a Fluke. The signal was only a few tens of mV. Tried the frequency-mode (not used to working with AC), and the frequency was a few tens of kHz, but basically just noise/background. Don't know whether this signal is within the capabilities of my Fluke, but I'm a bit concerned that the AC-thing in the ECU is broken. I think I can borrow a decent oscilloscope from work, but I'm not quite sure what to measure, and how waveforms should be. My only reference is this page: http://www.picotech.com/auto/cam_ac.htm
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Now I've soldered the sensor into the loom closer to the ECU. EML still on and still in limp home mode. :'(
TB wrote in a related thread:
Unplug crank sensor, see if symptoms are similar....
Other thinks to check - try switching on ign, leaving 20s, then starting. Also, try crank for 5s WOT, then start normally...
Should the crank sensor be disconnected with engine running or before start?
What would I learn from the above tests? I guess cranking at WOT would be to clean out any fuel from leaking injectors, but could that throw up a fault code?
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It is possible that one of the cables to Cam Sensor is earthing and
destroying your Cam sensor signal.
The cam and crank sensors share a common earth, so disconnect the
cam sensor plug to break the earth connection from pin 3 on the
crank and cam sensors to Pin 2 on the ECU.
Now check that there is no connection to Earth on Pins 1 & 2 on the Cam
sensor plug or Pins 4 & 22 on the ECU.
As a final check, check that the earth connection is actually intact by
checking between Pin 3 on the Cam and Crank sensor plugs and Pin 2
on the ECU and Earth.
No guarantee this is the fault, but assuming you haven't fitted a new duff
cam sensor, or the common earth from the crank sensor isn't duff, then
you have to check the wiring again from a different perspective.
'Sparks3ks' will be probably be able to advise better on this approach as
he actually is a 'Sparky'. :)
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Thanks. I think I've done all the things you mention, and could not find any earth errors within the cable harness. I thought I found a problem yesterday when checking all the connections at the ECU connector, as I got continuity between ground pin and crank AC signal pin, but soon realised that it should be a connection there. This connection was in the sensor, not harness (unplugged sensor and rechecked). I'll try to measure resistances on new and old crank sensor and see if they match. The old sensor was changed before it failed.
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This connection was in the sensor
Yes, both Cam and Crank Sensors are connected to Earth due
to capacitors linked within each sensor, but both Earth cables,
from each sensor, also link together to form a single common Earth
to the ECU. Whether this is at the ECU or within the Harness to the
ECU, I don't know.
When you disconnected the Crank Sensor Earth return, you would have
broken the Earth return path from the Crank Sensor, but not the
Cam sensor Earth return.
When you originally started this thread you've been checking for faults on
your Cam Sensor and associated wiring, but now you're talking about
the Crank Sensor wiring. The only common wiring to these 2 sensors
is the Earth return paths on Pins 3 at the Cam and Crank Sensors and
Pin 2 at the ECU. If you had a fault in this circuit I would have thought
that you would have got error codes for the Crank and Cam Sensors.
But you say you're only getting a Cam Sensor code.
When you disconnect the harness at the ECU, and the Cable connectors
at the Cam and Crank sensors, you say you've checked the Harness
between the two and can find no faults.
With the ECU and Cam and Crank sensor plugs disconnected, have you
checked the cabling for faults between the plugs and the sensors?
For instance, are you getting an Earth return on any of the cables, when
you shouldn't do because the Crank and Cam plugs are disconnected and
thus breaking the Earth return circuits?
Sorry if I'm stating the bleeding obvious here, but I don't know what
checks you've carried out.
No offence intended. :)
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Can't blame you for not knowing what I've done during my many hours of fault finding:)
The common earths of the two sensors appear to be at the ECU side of the loom.
The reason why I'm talking about the crank sensor is that browsing all kinds of forums have told me that cam and crank sensors are often related. Now I'm pretty sure that there's nothing wrong with my cam sensor or wireing. The only common wire is, as you say, ground at ECU pin 2. However, I'm wondering whether crank sensor problems appears to be cam sensor problems, as the crank signal is the primary trigger and discrepancy between the two signals can be interpreted by ECU as cam sensor fault. This is why I changed the crank sensor a couple of weeks ago.
With the ECU and Cam and Crank sensor plugs disconnected, have you
checked the cabling for faults between the plugs and the sensors?
For instance, are you getting an Earth return on any of the cables, when
you shouldn't do because the Crank and Cam plugs are disconnected and
thus breaking the Earth return circuits?
Yes. I have checked from ECU plug both with sensors connected and disconnected. Earth and shilding cables are grounded, whereas the others are not when sensor plug is disconnected. To summarise I've performed all tests I can think of on the electrics and found nothing wrong.
I have tried to start the engine by rolling down hill (someone claimed tired starter could cause problems), but to no luck. I have not yet tried to start the engine without aux belt (is it ok to do for a few seconds?) as some have claimed that interference will be caused by ignition system, not alternator.
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Yes. I have checked from ECU plug both with sensors connected and disconnected. Earth and shilding cables are grounded, whereas the others are not when sensor plug is disconnected
If you've checked from the ECU Plug, then the plug would have to have been disconnected
for you to check. If the ECU plug was disconnected then the Earth cable should not have been
grounded.
Or am I misunderstanding what you are saying?
Also, although you probably have if you've done loads of checks, have you actually
checked the cabling between the sensor plug (not the ECU plug) and the sensors
when all plugs are disconnected to isolate each circuit?
As said, you probably have, but you didn't actually state this and I'm just checking.
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With ECU plug off I use ECU connector pin 2 as earth. With ECU connected I use battery negative as earth to check earth connection for both what should be connected to earth and those that shouldn't.
Sorry that I'm not able to make everything clear. I express myself a bit better in Norwegian ;)
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Forgot to add. The reason I'm concerned that you may have an Earth
when you shouldn't, is that although we draw our Electric circuits showing
the flow from +ve to -ve, electons are negatively charged and actually
flow from -ve to +ve. That's why you get some weird results, for instance, when wiring
up tow bars.
No idea if you know all this, you may be an electrical genius for all I know :)
But plenty of folk reading this thread aren't. :)
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I express myself a bit better in Norwegian
And my I say that you express yourself much better in English
than I would ever do, trying to speak Norwegian. ;)
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No idea if you know all this, you may be an electrical genius for all I know
I'm pretty retarded when it comes to electricity, but being and ELECTROchemist I'm pretty used to fault finding at the lab. A bit embarrasing that I don't know more about the electro-part of my profession...
However frustrating this particular fault it, at least I've learned to read wiring diagrams in Hayes the last couple of weeks:)
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hi again.
cam and crank sensor problems are known to be related. i.e one playing up sending wrong signals to ecu makes other behave stupidly. yo've been messing about with oscilloscopes and measuring the resitance when i believe that crank sensor comes with a wiring loom and plug and modded cam sensor comes with a wiring loom as well. now surely for the sake of the say £80 i will cost you for both sensors you might aswell go bythem and fit them. there is obviously a fault with one of them. have you actually changed either??????? from what i can remember of this thread you've changed cam sensor i believe if not change it then change crank sensor. it's ok thinking that its ok but thinking and knowing are two different things. it may look ok and you might get decent resitance but, that when there is no current. cables behave differently when they have a current flowing through them to when they are idle and nothing flowing through them. Change sensors then if still a problem at least you know the sensors are ok and the aren't going to need replacing for quite a while. DON'T FORGET FIT GENUINE MODDED CAM SENSOR, CHEAPO ECRAP ONES DONT TEND TO WORK AS I FOUND OUT!!!
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I have replaced cam sensor twice (first cheapo one from ebay, then genuine modded) and crank sensor once. There's obviously still a chance that I've gotten faulty sensors, but that will still be the chance if I change the once more.
I haven't tested with oscilloscope yet. I will probably take me a few hours to learn its use, and I'm not quite sure what to look for.
I'm still curious about what:
1) Cranking at WOT then start normally
2) Leaving ignition on for 30secs prior to cranking
would tell me.
Leaving ignition on prior to starting improves cold starting. Did that before EML appeared also.
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I'm still curious about what:
1) Cranking at WOT then start normally
Cranking on a Wide Open Throttle
would close off the injectors and clear any flooding from your
engine due to leaky injectors prior to starting normally.
2) Leaving ignition on for 30secs prior to cranking
This would give the fuel pump time to pressurise the fuel rail, prior to starting,
to test for a leaky pressure relief valve.
These 2 tests are more for diagnosing starting faults than your Crank/Cam
sensor faults.
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This was my interpretation of the tests as well, that's why I didn't understand why it was sensor related.
As the car is running on ethanol, it is very sensitive to cold starts (needs heavy enrichment). I'm in the process of increasing the gasoline percentage to check if starting problems persist, but it will take some time as I only drive a few km a day.
When cold starting the car fires briefly and appears to run on less than 4 cylinders. After a couple attempts it starts just fine.
Edit: Is it normal that the fuel rail pressure drops after a few hours with engine off? I've noticed when depressurising the system (for fuel filter change) that there's hardly no pressure when engine has been off for a few hours, whereas the pressure is more than sufficient to squirt in my eyes when engine was running a few minutes earlier..