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[Herb Williams]

Hi, I'm a newbie, and I need help!

I'm the lucky owner of a V reg Omega 2.5 V6, who's not feeling particularly lucky at the moment.

The car stalled several times about 3 weeks ago, with the engine management light (EML) coming on indicating there was an engine management fault, and eventually I had to have Green Flag tow it home for me. I arranged for a mobile mechanic (from a credible firm) to come out, and he did a diagnostic check of the ECU and the fault code it came up with was for a faulty crankshaft position sensor.

A week later he came back with a new crank sensor, and replaced the faulty one, and dah! dah! ... the car still wouldn't start.

So, suspecting the problem was with the idle control valve, he took this out, cleaned it (and cleaned all the associated piping), put the ICV back in, reconnected all the pipework and dah! dah! ... again the car still wouldn't start. The guy eventually spent over 5 hours trying to solve the problem but to no avail (fortunately he only charged me for the time spent in fitting the crank sensor).

The strange thing was though that with the ICV fully connected the car wouldn't start at all; but when the rubber hose which connects to the other end of the ICV was disconnected temporarily then the car started and the engine ran. Reconnected the hose - car won't start; disconnected the hose, car starts OK.

We wondered whether the ICV itself was damaged and was therefore the real cause of the problem, and so a few days later I bought a brand new (and expensive!) Idle Control Valve, fitted it myself (because it's quite simple) and dah! dah! ... the car still wouldn't start, unless the bottom hose was disconnected. Fortunately I got a refund on the ICV!

So, having trawled through the various Forum posts here (I must say this is an excellent forum) but to no avail (though learning a heck of a lot about my car that I never knew before) I guess I'm near wits end.

I don't want to call a mechanic out again until I have a better idea what the problem might be. The previous mechanic suggested it could also be an air leak (hopefully not though - but if so, how do you test for it?) and I've seen other hints of what the problem might be from other posts I've read here (e.g. blocked Small Breather Jet? Butterfly Valve problem? Restricted airflow caused by some other blockage?).

Any helpful suggestions / answers would be gratefully appreciated.

Also, I need to check that this has no connection with the running of the SAI (Secondary Air Injection) valve, since the mechanic noticed there was a kink / narrowing of one of the hoses connected to the SAI valve (the hose connecting at the side nearest to the battery) on the bend of the pipe (someone at some stage in the past had, I think, replaced the original Vauxhall Part hose with a generic one - the original is no longer available I think - but whereas the bends on the original were fortified, the replacement has no such stiffening), and I am concerned that there is restricted air flow here (but not sure what impact if any that might have).

My apologies for the length of my "virgin" post, but I wanted to include as much details as possible because I know how hard it is to answer queries if facts are missing.

Herb W

[RobG]

First thing to do is the paperclip test and see what codes you might have.http://www.omegaowners.com/forum/YaBB.pl?num=1189022687
As for the SAI pump, disconnect the bloody thing.

[jonathanh]

i bet it is still the crank sensor....  code 19 perhaps

[tmx]

yeah id put a wager on it being the cranksensor!!

was it a genuine sesnor fitted? the Aftermarket ones particually Fuelparts Do have Quality issues!

[Herb Williams]

I'll check with the mechanic as to the genuineness of the part he fitted, though I do know he got it from a parts dealer.

Excuse my ignorance here, but I would really like to know what the crank sensor (and the crankshaft) actually does?

Herb W

[Entwood]

I'll check with the mechanic as to the genuineness of the part he fitted, though I do know he got it from a parts dealer.

Excuse my ignorance here, but I would really like to know what the crank sensor (and the crankshaft) actually does?

Herb W

One of the experts will pass by and give a full lecture on crankshaft sensor .. but in essence ... as the car has no distributor like the old ones had ... the "system" needs to know exactly where the pistons are in order to know when to fire a spark, and to which cylinder to fire said spark at !!

The crankshaft is driven by the pistons to transfer the power to the drive train. The position of the pistons is therefore directly linked to the rotation of the crankshaft, so it can be used as a very accurate reference to the piston position, and as such to the timing of the spark.

The very clever ECU uses the piston position (from the crank sensor) and a whole load of other information to determine when to "fire" the spark.

Thats the simple explanation ...  ( I do simple well .. )

[RobG]

 Used on engines with distributorless ignition systems, the crankshaft  sensor serves essentially the same purpose as the ignition pickup and trigger wheel in an electronic distributor. It generates a signal that the ECU needs to determine the position of the crankshaft and the number-one cylinder. This information is necessary to control ignition timing and the operation of the fuel injectors. The signal from the crank sensor also tells the ECU how fast the engine is running  so ignition timing can be advanced or retarded as needed.

There are two basic types of crankshaft sensors: magnetic and Hall effect. The magnetic type uses a magnet to sense notches in the crankshaft or harmonic balancer. As the notch passes underneath, it causes a change in the magnetic field that produces an alternating current signal.

The frequency of the signal gives the ECU the information it needs to control timing. The Hall effect type of crank sensor uses notches or shutter blades on the crank, cam gear or balancer to disrupt a magnetic field in the Hall effect sensor window. This causes the sensor to switch on and off, producing a digital signal that the ECU reads to determine crank position and speed.

 If a crank  sensor fails, the engine will die. The engine may, however, still crank but it won’t start. Most problems can be traced to faults in the sensor’s wiring harness. A disruption of the sensor supply voltage (Hall effect types), ground or return circuits can cause a loss of the all-important timing signal.

[tmx]

The omegas cranksensor usually failes because the wire gets frazzled on a very very hot exhaust manifold!

it really is a very very easy job todo on the miggy its as easy as an oil change imho! if your lucky you can get to the wire with out removing the scuttle

[Herb Williams]

Thanks everyone for all these replies. Very helpful indeed. One thing that's not clear - if the crank sensor is still at fault then how come the engine can start if the hose is removed from the bottom end of the idle control valve (see my initial post), but fails to start if the hose is left attached? Thx. Herb

[tmx]

ICV has its own error codes and the engine still runs with out it so it doesnt really do a great deal

the cranksensor sometimes works and sometimes doesnt! usually works when the cars cooled down

[Herb Williams]

Thanks TMX. The problem is happening when the car is cooled down. Take the hose off and the car starts. Turn engine off straight away (before it heats up) and then put hose back on and engine won't start.

I'm going to do the paperclip test when I get chance tomorrow or weds. If there's no fault code coming up for the crank sensor does that completely rule out a crank sensor problem (for example, an issue with the wiring as someone pointed out above)? Herb

[tmx]

yes if the crank sensor is playing up then a code is stored sam for the IACV too

tried starting it with the iacv disconnected and the throttle slightly open?

[Herb Williams]

OK. I did the paperclip test today and it's coming up with two fault codes:

57 - Idle Air Control Voltage Low

74 - Mass Air Flow Sensor Voltage Low

Any suggestions as to how these "faults" might be causing the problems I highlighted above? For example "wire gets frazzled on a very very hot exhaust manifold"?

Thx.

Herb

[Herb Williams]

Just realised I made a mistake. the codes were right but I put down the wrong description for code 74.

Should have been:

57 - Idle Air Control Voltage Low

74 - Mass Air Flow Sensor Voltage High

Herb