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Gotchas & Tips - C20LET
These cars are reasonably well designed, but they certainly aren't perfect. There are a few cases where the unwary could be caught out. Even pros can be left scratching their heads if they are not familiar with these particular issues.
Motronic2.7 is a sophisticated piece of software, but it has also earned it's nickname - moronic.
The CTS issue is one example.
Looking at the list of trouble codes, one would expect codes 14 or 15 when the CTS starts misbehaving. Like any decent engine management system, Motronic is expected to monitor the values sent by any sensor, occasionally comparing them with those of other sensors for consistency. If the values are found to be out-of-bounds or inconsistent, then the management system is expected to ignore the output of that sensor, display the appropriate fault, and use a fixed (or learned) value to get you home - a limp mode
Well, for some reason this doesn't necessarily happen with the CTS. It can give out rubbish and the Moronic will accept it as gospel. Not only will it not display a fault, but it will act on the garbage output of the sensor. This can create some weird fuelling conditions, occasionally running extremely lean, irrespective of engine revs or boost. The engine starts up fine, but when it warms up the ECU starts listening to the CTS output, and suddenly everything goes downhill. The engine doesn't respond properly, it overheats, and it will eventually stall.
An AFR gauge will indicate the faulty fuelling, but other than that there is no indication of what's wrong. Some people might try and rev it hard to 'clear up' the cylinders. This will not have a happy ending.
The sensor itself is cheap and widely available (£10-20 depending on where you buy it). It's next to the thermostat, so it can be changed in 5-10 minutes (the airpipe has to be removed and the sensor swap has to be quick to minimise the coolant loss).
This is the main source of aggro and bad publicity for these cars.
Left unattended, it appears to be made out of butter and die suddenly and with no warning.
Vauxhall asks for several thousands of pounds to provide a new one, and there is a whole industry dedicated to fixing them.
I suspect that there is a design fault in that the temp sensors within the boxes do not react quickly enough to avoid damage. Earlier models have a digital (on/off) disposable sensor, later models have an analog sensor - but the principle is the same: when the tx box fluid reaches a certain temperature (around 160C), the ECU is supposed to automatically disengage the box to protect it from overheating damage.
Somehow, this doesn't always happen soon enough - perhaps the 'trigger point' has been set too high. Once the dreaded '4x4' fault lights up, the damage has been done. Very expensive it is, too.
Here is a brief description of how the viscous system works in this design
This is an LET txbox clutch plate that has sustained overheating damage.
Some of the lining has gone (suspended in the black fluid most likely)
The only way to prevent this from happening is to follow the 3 golden rules of the tx box:
- Change the tx box fluid every couple of years. Use only Vaux#90443530 or a fully synthetic gear oil 75w90.
- Change the accumulator bulb every 5 years or 50K miles. If yours has no white ring at the top you may have to change it immediately!
- Rotate the tyres (back to front) every 3-4K miles, ensuring that all tread depths are always within 2mm. Keeping them well within 1mm is much better. If you have to run the car with different tyres (i.e. after a flat) always pull out fuse 19 to disengage the 4x4. On the same lines, doing handbrake turns is the stupidest thing one can do with this car (forcing the rear wheels to stop while the front ones are spinning)
If these three rules are adhered to, the tx box should live forever.
If not, then the tx box is like a ticking bomb.
If you're suddenly feeling nervous, here's a quick tx box oil change
Also it's good to verify that your accumulator has not expired, even if it has been recently fittted. Below is an extract from the definitive site on the subject. It also supplies all these parts at decent prices:
There are currently cases of OPEL & GM Accumulator bulbs being supplied which are close the the end of their shelf life. If you have changed your bulb recently or are unsure of its age then in most cases the age of an Accumulator Bulb can be determined. Unfortunately there is no way of determining how long the bulb has been in service, but a bulb older than 16 years would be out of date. It is very important to ensure proper operation of the Accumulator as it's failure may result in premature transfer box failure.
The shelf life of an unused accumulator is ten years.
The operational life of an accumulator bulb is the sooner of 54000 miles or six years. i.e. after it has been taken from the shelf.
To check either an in service bulb, or inspect a potential purchase over the counter, you will need to do the following inspection:
There should be two rows of stamped codes on the bulb.
There is usually a group of five digits on the bottom row and to the extreme right.
Read the first two digits of the group of five, this is the year of manufacture.
e.g. - 94312 was a bulb manufactured in 1994
WARNING: To read the characters on the vehicle, you may need to make use of a mirror and/or release the whole assembly from the bulkhead bracket (Two 13mm bolts)### SAFETY WARNING ###
ON NO ACCOUNT ATTEMPT TO REMOVE, OR LOOSEN, THE ACCUMULATOR WITHOUT DE-PRESSURISING THE SYSTEM - The pressure stored is in the region of 800 psi.
This animation from 'how stuff works' shows that there are no parts to wear out. Click on the button a couple of times to see an exploded view:
All faults are due to overheating - different rotational speeds between front and rear axles and/or inadequate lubrication. Here is how the Vaux/Opel transfer box works inside
If you're curious as to what exactly lives in that mysterious tx box, click here! (local copy here, here and here)
Here's more on how various AWD (All Wheel Drive) systems work from the excellent Difflock webzine
(local copies here: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 4x4 Glossary)
Some enthusiasts have nothing better to do with their time, and instead of maintaining the transfer box, they prefer to amputate or even ditch it. Some even talk about RWD conversions.
This guy actually did it:
Here's another one.
Looks neat:
There are two issues here, that could lead to catastrophic failures
1st/reverse gear recognition switches
Sometimes boost is kept very low by the ECU for no apparent reason. There may even be a TPS fault code, when the TPS is perfectly fine. Check the 1st and/or reverse gear recognition switches. It's easy and could save you a lot of trouble
It's a common gripe of owners of older Calibras. Thinking that the bulbs are faulty, they change them only to find that they're still hopeless. Unfortunately, it's not the brightness of the bulbs at fault. The whole 'innovative, slim and sleek' design ages badly. Plus - the build quality could be better. There's still some hope, though!
1. The wiring is substandard, it loses a couple of volts by the time it gets to the bulbs. Do NOT use megawatt bulbs, the wiring won't take it, and the heat produced might kill everything in there!
2. The reflectors may be gone. Try opening them up to clean them VERY carefully. They're only a few microns thick, so chip out easily.
3. The exterior may be chipped. Try polishing with Brasso, it removes the outer 'rough' layer and the lights appear brighter afterwards.
4. Spray all connectors with a contact cleaner, it will help reduce the voltage drops.
Look under an LET and will most probably leak oil from the sump. Changing the sump is not a pleasant task either, as the exhaust has to come out, the oil feed for the turbo has to move out of the way and a pan bolt is really well hidden in a recess (changing that bolt to an Allen one saves much trouble later on, when putting it back)
If you use the Vaux-recommended gaskets, you'll get two rubberised cork items, that need to have the baffle plate sandwiched between them. So looking from above, it should be block -> cork gasket -> baffle plate -> cork gasket -> sump. All these have to be aligned correctly before they're bolted back. Not easy without having the car lifted high up, and you quickly find out you run out of hands, trying to align all these holes. Using grease to keep the gaskets from moving is a bad idea, because it will leak later. So are we doomed?
Nope - just use the baffle plate from the 8v part # 90528632. It comes complete with rubber gaskets (proper ones) attached from the factory. Dead easy to fit, no leaks afterwards. The 8v sump bolts (Vaux # 90531211) are M6x13 instead of M6x22 of the 16v sump. These are a bit on the short side. It's best to use M6x20, or at least use the longer 16V bolts with a 2mm spacer to make up the difference.
Remember to clean the threads with a tap,you don't want them to bottom out prematurely - either the gasket won't be tight enough, or something might crack.
The baffle plate from the 8v is left, the 16v on the right. Notice how the 8v has the rubber gasket fitted from the factory.
Also note the detail that may need bending back so it doesn't touch any of the reciprocating parts (it should clear them, but you never know...)
Pic courtesy of MIGWeb
Now you know.
The basic idea behind this tip was courtesy of Tim at the Churchhill Garage at Orpington
An alternative (or additional!) way to eliminate sump leaks is by using Loctite 518. It's not just Vauxhalls that mark their territory with oil leaks, EVOs do it too...
Help! My car is suddenly gone slow - The engine mgt light is on, and it goes like crap! Is this the famous limp-mode? What now?
Well, below are the ECU's get you home values until you get it fixed.
Oxygen sensor circuit 450 mV Coolant temperature sensor 40 °C Knock sensor circuit Ignition timing is retarded b 8.5° Throttle valve sensor malfunction Throttle angle 30° Intake air temperature sensor 20 °C Hot wire mass air flow meter Replacement characteristic curve, dependent on engine speed and throttle valve angle. As we can see the ECU errs on the safe side, so it will run rather rich. Prolonged operation under these values will kill the catalyst and fill the inside of the engine with carbon deposits. It's only meant to help you avoid the tow truck!
Don't know how to read the fault codes? Here is a link from the excellent site of Topbuzz
(Local copy here)Another tip: if you blow a boost hose (it does happen when you fiddle with boost pressures and intercooler pipes) the car will most probably stop dead. The Moronic sees strange air quantities that don't tally with anything else and goes belly up. Too stupid to go into limp mode, too upset to sort itself out.
But don't despair, you can put it out of its misery: switch off the engine, and just unplug the Air Mass Meter: this will tell the ECU that something's really wrong with the AMM and it will use the replacement curve and get you home.
There's power steering oil dripping all around the reservoir. I've checked the level and it's fine - what's going on here?
The fluid level can only be checked when the pressure accumulator (black bulbous thing next to the firewall) is full. Very few mechanics know this, and even those who do tend to forget (although it's clearly written on the label of the reservoir!)
With ignition ON (but engine not running), operate the brake approximately 20 times until fluid level does not rise any more, then check fluid level.
With hot fluid (80°C), fluid level at the upper mark (1).
With cold fluid (20°C), fluid level at the lower mark (2).
It sits on the top left part of the intake manifold, covered by the plastic 'turbo' cover. It's meant to alter the FPR vacuum so that the fuelling is correct when starting the engine while it's very hot (it bypasses the throttle vacuum, effectively increasing fuel pressure by 0.6 bar).
But that's meant to happen at 120C coolant temperature. Now who in their right minds would let their engine run until the temp exceeds 110C, is beyond me. Trying to start this engine at 120C is madness, begging the Gods to warp the head. You should let it cool down to below 100C first.On older engines this valve can malfunction, affecting the FPR vacuum when it's not supposed to, creating fuelling problems that are hard to isolate.
The solution is to isolate it from the vacuum loop, so it can do no harm:
Both front and side-facing vacuum connectors can be left undone. The electric plug can stay connected, so the ECU doesn't register a fault.
Everything else stays connected to the vacuum Tee lines, but the HSV is left out in the cold.
Job done.
According to Vauxhall (and their maintenance schedule) the F28 gearbox oil can live forever and a day.
Yet another gotcha, if it's not changed occasionally the feeling will become sloppy, crunchy and a quote for a reconditioned gearbox might not make your day. It's not rocket science to do this job, either. You just need a couple of litres (officially 1.9lt, but you never know) of a good synthetic 75w90 and identify the three plugs involved. My favourite is Mobilube1.
There ya go, Bob's your father's brother...
If the hydraulic tappets are noisy despite them being renewed and despite the frequent oil changes, then maybe the oil pressure is lower than it should be. If you haven't got a gauge installed, either go and fit one, or have it checked at a garage.
A common reason for oil pressure to be low is the oil pump spring getting weak. Below is the oil pump dismantled (you won't need to dismantle it, but it makes identification easier)
Note the oil filter base at the lower left corner. The spring is on the right side, behind that bolt.
Here is the oil pump spring that might need refreshing. Tricky job as there is an engine mount in the vicinity, and aircon cars also have the aircon compressor blocking access.
(pics courtesy of Topbuzz)
It happens quite often to older cars. Usually the ECU is blamed, or the amal valve. This can be easily checked by disconnecting the hose behind the actuator. I know of several people who had been advised by 'tuners' and 'experts' to change turbos/looms/ECUs/sensors etc, when the problem all along was simply a weak actuator!
The actuator itself is a simple device - just a diaphragm and a spring holding the wastegate shut. But remember that the 'chamber' of the actuator is often filled with hot pressurised air. This air is non-intercooled, taken straight from the compressor, and redirected via the amal valve. How long do you think it can take the constant pulsing and the heat? After 2-3 years of hard use the actuator may be shot. It will still show maximum boost on the gauge, but it won't be able to hold it properly.
That's an easy horsepower mod, if there ever was one! Here's how to check your existing actuator using just a footpump.
Aslo be aware of the Uprated Actuator fallacy
Another problem might be oil contamination within the boost hoses. Older engines breathe a lot of oil mist (as we've seen above) The oily area around the dump valve is a give-away. Naturally the boost pipes and the intercooler will be internally insulated with a thin oil film (not good for heat transfer). What most people don't know is that the narrow boost/vacuum hoses are also drenched in this oil mist, and if the car had been smoking badly for a while, then all these hoses resemble the arteries of a chain-smoker.
Some quick investigation will reveal that some of these hoses are vital - the ECU boost signal being the most important. The hoses to and from the amal valve are also users of this dirty air-mist mixture, and so is the inside of the actuator. Food for thought.
Throttle Position Sensor - it's missing and stuttering. It's faulty, isn't it?
Before you start interfering with something that might be perfectly well, try measuring it first. It's only a potentiometer, ie a resistor that changes value depending on the throttle valve position. Set your multimeter for a few KOhms. Undo the TPS plug, and there are three lugs underneath, lets call them 1,2,3 from top to bottom.
You might need someone else to move the throttle, if you cannot secure the multimeter leads to the lugs. But it's certainly DIY, you can open the throttle with the right hand.
Between lugs 1 and 3 you should measure from around 5KOhms to 2.3KOhms (first is for closed throttle, last for fully open)
Between lugs 2 and 3 it should range from 2K to 4.8K (again closed to fully open throttle)Some other models have different values as follows: (thanks for Paul Dale for the info)
Pins 1 & 3 1.87k - 0.8k Closed - Open
Pins 2 & 3 1.02k - 2.4k Closed - Open.
Make sure that the values change smoothly as you slowly open the throttle, especially at the low openings. If the readings jump suddenly (without your MM leads slipping off) then the TPS is faulty.
If the readings are smooth, then it's probably fine.
Aircon LETs and ignition leads
Aircon cars have the coil much closer to the distributor - however the leads are the same length. This can lead to spark leaks, especialy if the king lead has to be close to metal parts, pipes, even the bonnet. On cars running high boost this might be an issue.
Most people run Magnecor leads for peace of mind - here's how to shorten the king lead
I've lost 6th gear and reverse! Help!
Most probably your gearchange has gone out of alignment. It is a bit involved to fix it, but it's doable. Here's how
If you've heard that you can read the fault codes without an expensive special Vauxhall fault reader, then you're right. With just a paperclip you can the two pins on the diagnostic plug (near the bulkhead) and read the flashing ECU codes in the cabin. Here is the list of all codes rehosted from Topbuzz's excellent site
In any case, this Motronic 2.7 diagram might come handy:
Hall sensor/TPS one of the sensors Wiring fault at ECU Throttle body all gummed up.
Immobiliser won't allow power to the fuel pump
It happens often enough to warrant special attention. Sometimes it manifests itself as just reluctance to start, other times it could be intermittent cutouts during full throttle. A kick at the driver's panel might fix it, but this guy claims to have found a permanent fix. I haven't tried it myself, but I guess it's worth a shot if the relay starts to play tricks.
If you're thinking of buying a turbo, here is a basic guide of what to check (local copy here)
Adding Oil Pressure or Oil Temp gauges
Keeping an eye on oil is essential for a healthy engine. You don't want to boost the car while the oil is still cold, and certainly not while it's too hot. Oil pressure gauges came standard with most late turbos, but many people want to retro-fit one. Here is a useful guide, local copy ofcourse since forum threads are notorious for their short lifespans.
....on to Resources