G60 Drivability Tech Tips

I also edited the text a bit to increase readability. My additions are surrounded by [ ].

Jan

Tech Tips

by Chris Lagattuta, Autowerkstat
 

My name is Chris Lagattuta and I've worked at ND as a technician for the last ten years or so, and now started my own business. Over the years, I've had the great pleasure of encountering some great technical mind bogglers as well as repair a lot of problems that other people had trouble with. When you see the same cars come in the door day after day, you start to see patterns.

I read a lot of your postings when I get home from work and often think I can help out with the solution, except I never have time to write. So, I wanted to dump a whole lotta stuff I accumulated over the years in hopes it can solve some driveability problems for you. 

G60

Driveability- on Corrado g60 the TSB concerning the flat ground strap that goes from the coil to the right rear nut on the valve cover-move the vc end to the top of the throttle body because it acts like a knife and abrades into the two hot wires of the fuel rail power supply wires (no thermal protection) and causes fire up to the fuse box. 

Most of the G60s Electronic Control Module grounds terminate at stud above left coolant flange on cyl head (4 wires-brown, brn with black tracer). [Jan: I only found 3 wires]. I usually remove ring term ends, solder on four longer wires and run directly to battery neg post. [Jan: Actually, a better solution is to run a 12-10 AWG wire from the battery negative to the that stud. When I did what Chris recommended, it actually made the situation WORSE and it also made my oil temp reading totally flackey. The problem was that parts of the engine had spurrious currents causing false grounds reference voltages. Once I ran a wire to the head, all worked well again. As usual, ALWAYS solder everything. NOTE 2: See also Chris' rebuttle below].

One large ground for ECM is also at bolt on clamp-clean it shiny bright and tighten. Any undue resistance or corrosion from the wires causes overly rich mixture and problematic idle. {I have not been able to locate this ground as yet].

Overly rich mixture (black smoke, no power) also usually caused by these three things: 

1. broken signal wire on harness side of o2 sensor plug behind engine on right rear mount [Jan: Yep, had both the ground wire and the signal wire break. You can extract the metal connectors, buy new ones, and splice in a new wire. The metal connectors come out through the rear, by pressing their sides together and pushing a third mini-screwdriver in the middle].

1. bad nt. sensor (blue, front of engine)

[Jan]: The values of this sensor must be roughly, Bentely pp 24.250-2:
10 C = 3000 - 4000 Ohm
20 C = 2000 - 2800 Ohm (this is typical room temp)
80 C = 300 - 400 Ohm
100C = 170 - 220 Ohm (this is typical operating temp)
2. bad o2 sensor. 

You need a four gas analyzer to determine if co.% is problem and also to see if what you are repairing fixes the problem. The signal wire is purple and goes to the black wire from the probe. It breaks from bad front mounts causing undue strain on harness or old age and heat. Ntc sensor can fail from an overheated car or just no reason at all. O2 sensor failure isn't that common but contamination from using too much K & N oil and not letting it dry thoroughly, silicone spray or goop, or letting the car run with a bad miss or too rich too long can do it. 

[Note. The CO Potentiometer value must be between 0 and 2000 Ohm. The CO should be set at 7%. See Bentley on procedure on how to check. Jan]

Also check the two vac hoses behind the throttle body. One goes back to the firewall and the the ecm-it is the signal for the map sensor (it controls fuel delivery for load). A gaping hole in this hose causes rich mixture because ecm thinks atmosphere pressure is manifold pressure. 

Incidentally, don't replace your o2 sensor unless you are sure it has a problem- its really expensive and they normally last at least 75-100k miles for the heated variety. Also, this component is covered (as well as your cat) under your federal emissions warranty for 6yrs or 60k and 7yr and 70k miles! 

Idle problems are usually related to incorrect mixture and idle screw adjustments and it really does help to have it on the scope to set these properly. However, some quick checks: replace small o-ring on the idle screw-they almost always leak and allow false air to enter the engine unmetered.

Never disconnect idle stabilizer two wire connector with the car running or the key on. Reason: you can short the driver end stage of the ECM and ruin it. To quick check, disconnect ntc [Blue temp sensor] and see if the idle changes- usually, if it does, it is working. The idle can go up or down depending on where mixture is and a whole lot of other things, but generally it should go up. Also, the unit should hum when held in your hand with the key on and the engine off. I never had much luck cleaning them-usually replacing them is best. 

[Note, the ISV resistance should be between 2 and 10 Ohms. Jan]

When your car feels like it is only as fast as a rabbit-look down by the battery at the intercooler pipe-if you press your finger into the plastic you will find a hole where boost can escape. [Note: Snake a PVC tube from the battery drain to past the intercooler tubes, if your battery has one. That will also reduce the chance of corrosions. Jan]

Check the vac hose to fuel press regulator and on cars with microswitches instead of tps [Throttle Position Sensors] at throttle-remove plug and check resistance of switches. I usually change them if the resistance is higher than one ohm closed and anything other than "open" when pulled off throttle. Too much resistances here causes the ECM to think the car is off throttle and changes the timing and signal to the stabilizer, thus affecting idle.
 

Chris Lagattuta

Hard Starting a Corrado G60

by Jan Vandenbrande
 

This is a common problem with the Corrado G60s, and I went through the above diagnostics without finding a solution. There is a TSB out on this that recommends cutting a wire to the ECU. I don't like cutting wires, so I never did that.

However, about a year later, I finally resolved the problem. 

The symptoms of a "hard starting" G60 is that you start the car, and it sputters a bit, then dies. Usually after the 3rd start of so the car will run, but will stall out when driven. Over time, the hard starting got worse. First I needed two tries, then three, and so on. Only when the car is warmed up, will it drive normally. Once car cools down again, the problem re-occurs. Needles to say, this was driving me crazy. 

The solution was extremely simple...fuel filter. After I installed the supposedly "unservicable" fuel filter during the 120 000 miles service, the car finally starts up the first time and keeps on running. I change the fuel filter, which is near the passenger right wheel, every 60 000 miles, but you may need to do it more frequently. You'll need to get a new set of hose clamps, but the rest is trivial.

If that and the above does not solve your problem you may want to check out the corrado-club archives. There is one under "Fixing a Bad G60 Idle" that mentions a bad ECU frame ground contact.

I found another strange one to check for. I noticed that my 90 G60 had more cold starting problems with the coolant below Max. than at Max.  It's a bit of a mistery as to why this is, but it may have something to do with bad grounds and possibly the Blue coolant sensor not contacting the fluid. Weird.

Go figure.

by Chris Lagattuta, Autowerkstat
 

The repair regarding the pcm grounds located at the coolant stud pose a serious problem. You stated that a better method of repairing the problem is to simply run a wire from the negative post of the battery to the stud. You also stated that when you cut the ground wires and repaired them as I suggested that your car actually ran worse and your oil temp readings went wacko. The reason for this is simple. Obviously, if the bad ground was your original problem, regrounding them at the battery negative post would have made the car run better. This can only mean that by attempting to repair the problem, you caused another one (it ran worse). What probably happened is what I see all the time, the wire is in a difficult to solder location and the wires themselves are tarnished and don?t solder very well. I often have difficulty performing this and use additional flux paste and make sure to cut the wiring back a few inches to expose cleaner copper wire.

You may have induced an open in the ground, or a highly resistant one from a cold solder joint. To remedy the situation, you ran another wire to the original stud and the car ran normal, or the way it did before the repair. The whole problem with the ground is twofold. Over time, the crimp and the ring terminal corrode and coolant works its way to the threads in the stud. These conditions combine to cause high resistance in the ground feedback. Running a new wire and clamping it on top the old terminals to bring a better ground is a temporary fix at best. Better still, and I failed to go into detail on this in my earlier article, is the initial voltage drop test of the battery cables. Simply checking resistance with a dvom doesn?t reveal problems. You have to replicate the conditions that the circuit is failing , and that is under a load. Hot engine compartment temps, age, corrosion, and vibration all affect the circuit under load. If the battery neg cable is performing within specifications, then simply resoldering new pcm ground terminals at the stud would seem a logical step. However, in the real world of diagnostics, technicians must perform a repair that is quick, precise and within budget constraints. This is the reason for legnthening the wires and running them to the negative post. You do away with the posibility of a bad neg battery cable and you aren?t providing a shunt to ground with a wire jumper. Down the road, if your negative cable fails, consumers such as the starter, alternator, headlites will seek the path of least resistance. Your jumper will now be under more load that it was intended, and you may end up with lots of other problems. Ideally, I would check and replace the ground cable and relocate the pcm grounds to the battery negative post. I suspect that your oil temp readings fluctuated because of bad engine ground to begin with. 

At this moment, the only wiring diagram in front of me is a digifantII and I believe the schematic issimilar for the g60. There are three main grounds, two of which terminate at the studs. Pins #19 and #6 go to the above mentioned stud. The third is the one I mentioned in the tech tips article that terminates at the negative clamp from the factory. It should be the ground for the ignition control module located inside the control unit on a corrado. The remaining two grounds that you find on that stud don?t go the pcm, but I include them for good measure. Why leave yourself open to more trouble if you know that the ground point isnt suitable.

I also remembered reading something about spurrious currents causing false ground reference voltages. Simply, spurrious currents aren?t usually a problem with modern integrated voltage regulated alternators. 

Volkswagen does rely on grounds and 12v reference voltages, particularly with oxygen sensor and tps circuits and one does affect the other. Most often than not, checking the charging system and performing voltage drop tests on the alternator harness, starter cable and ground cable will root out 90% of all VW starting , charging, and grounding problems. The remaining 10% is found with sweat and tears, pulling, tugging and testing pins, connections, and components.

This is how to perform a voltage drop test on a battery negative cable using the largest consumer..the starter. First, use a high quality, high impedance digital / volt/ ohmeter. Set the selector switch to measure volts on lowest setting, preferably one volt or one to ten volts. Connect black to neg clamp and red to the terminal end of the cable. Disable the ignition so the car wont start when cranking, such as pulling off the power wire to terminal 15 of the coil or removing and grounding the coil wire from the distributor cap. Crank the the engine for 3-4 seconds and note the highest reading. All technical references point out that anything above .2 volt is excessive, but I have found that even brand new cables will achieve this amount. I choose to condemn a neg cable with any reading above .4volts. This test can be performed on any circuit to check relays and ground paths. The only time I?ll use an ohm test is when I am checking the resistance between a pin from the pcm to a component. At that time, I make sure the engine has been run hot, and I jiggle and wiggle all loose parts of the harness. I also check the insides of the terminal blades and the condition of the crimp. If all looks good, I conclude with a healthy shot of high quality contact spray and an application of Stabilant 22. This material acts like solder when applied to mating terminals and works on any connection EXCEPT the oxygen sensor terminals. 

I have to comment on checking plug wires, tps , and coils with an ohmeter. If I had a dollar for every bad plug wire that checked out within specs with an ohmeter, I would be rich. Simply put, the factory gives these specs only for reference. We see plugwires all the time that are almost new that fail. The reason is that they were abraded, nicked, or simply routed improperly. Other times, the wires failed because the owner installed good wires on a cheap quality cap and rotor, or forgot to properly torque the plugs. All these examples provide secondary ignition voltages that range in the 40-50,000 volt range a chance to seek a shorter path to ground and arc or short. Remember that these voltages cannot occur at idle but only during load. That?s why a scope pattern will reveal minor glitches and a meter cant. I can recall a pattern and analyze where the voltage has fallen off and start from there. Whenever the wires come off for service, I recommend taking a moment to notice for corrosion on the inside of the insulators and removing the coil terminal to check for arcing. Always make sure to use the provided wire seperators when possible and try not to let the wires touch coolant hoses or other good ground sources. Checking ignition coils with ohm readings has proven fruitless every time we try. I have had at least four vws come in this year with intermittant power failures, or no starts. After concluding that there is no spark and verifying that everything is working except the coil, we check the coil against the ohm values given by vw. They check out every time. Only by substituting a know good coil can I confirm that the other has failed. By the way, the ones I am referring to are the small square coils with the attached igniter and heatsink. Go figure, you wonder why my hair is falling out so early!

You mentioned checking and adjusting the co% to seven percent. I think you mean seven tenths percent. Actually, digifant II specs changed a few years ago to %1.20 percent measured before the cat. There is just no way to adjust the co on a corrado at home. You must have the car checked on an analyzer after replacing the oxygen sensor or repairing any part of the fuel system that will affect closed loop conditions.

This is my personal troubleshooting flow chart or series of checks on any driveability:
 

1. NO STARTS- think basics, basics, basics?what is missing from the essential five components? Compression, timing, spark, fuel , and air. Focus on owner?s last remarks about the car and take them into consideration as a starting point. Hesitated and died? Check fuel first, then spark. See if pump runs during crank, check coil wire for spark. Pump runs and wire sparks? Install plug tester in end of wire and verify spark reaching plug and that its hot enough to fire. If no, check cap, rotor and wires. Why isnt secondary reaching plugs? No pump, then check for voltage at pump. Make sure distributor rotor is turning to see if cambelt intact. Remove plugs, check for fouling or fuel in cylinders, etc??Verify and confirm that each of the five components required are satisfactory before jumping to the next.
   
   
2. HESITATION UNDER LOAD- almost always a fuel or spark related problem. I start by confirming complaint and identifying severity of problem. Hestition that is harsh usually points to interruption of secondary ignition such as firing voltage shorting to ground in wires, cap, rotor., or even bad pickup coil in distributor. The latter will be noticeable with ignition failure without tach needle dropping with the problem. The tach gets it signal from the coil and if you watch it close, it can help you deduce the culprit. Ignition switches in corrados are problematic with a telltale symptom. If you go to "crank" but have to really turn hard and it catches at the point the key feels like its going to break, its probably the driver at the end of the tumbler that is worn and bent. Repair by replacing the ignition switch and the tumbler section with key. Lots of starters got replaced because of that one. Early 90?s g60s with the main pump under the car with the filter have transfer pumps. Check it by running battery power to the terminals and listening for the hum. In doubt, replace it. Running low on fuel is number one killer of fuel pumps. They are cooled and lubricated by cold fuel. Low fuel levels cause cavitation and the inner workings of the pump get destroyed. In my opinion, if you are going to keep your car for a long time and you have over 100k miles, the main pump is going to die sooner or later. All the hard driving and harsh underhood conditions of a supercharged corrado rapidly deteriorate the epoxies and windings of delicate parts like coils, idle air valves and particularly idle switches. Throw in oil and grease reactions with rubber and plastics and you are asking for trouble. Hestitation caused by transfer pump is abrupt and momentary. It feels like your engine is dragging and then catches its breath. Ignition problems feel like you just turned the key on and off real quick. They can be scary and recurr at a moments notice or not for several weeks. Pay attention to your fuel level if something happens, the tach needle, and if all the idiot lights quit at the same moment the car did. Try to trace the problem backwards from the symptoms. Did it occur on an onramp under load, with air conditioner on, or cruising down the freeway? Determine what your engine would be needing at that moment, loaded or not, and try to work from there. Back in the garage, check your basics and try not to think computers or chips. This is almost NEVER the problem with a g60. The only computers I have seen fail were ones that got wet or suffered from battery terminals being installed or charged backwards and failed ground cables. They really are built tough.
   
   
3. INTERMITTANT DRIVEABILITY- first and foremost, you have to confirm the problem and recreate it. Don't buy tune up parts and hope it'll go away. Unless your parts are hammered, its not going to fix it. When applicable, check fault memory. Remember that just because a fault reads "fuel adaptation", or " exceeds limits" doesn?t mean oxygen sensor is necessarily the problem. The pcm is only trying to tell you in its simply analog communication that this area of its programming is being affected. Check technical service bulletins and troubleshoot with the factory flow charts. In my experience, most fuel related fault codes are caused by broken wires and vacuum leaks. On corrado g60?s its broken wires at the plug, faulty grounds and bad oxygen sensors. See the other tech notes for details. Find out if any recent work has been performed on the car like a clutch job, or brakes. You would be surprised at how many brake booster hose leaks we have fixed at the grommet to the booster caused fuel codes. They got moved when the engine was moved to remove the tranny. Be a detective and look for clues. Check for white powdery lines that signify an arc near wires or the coil body. Check tps values, but check them at the terminals on the pcm plug so you are reading the signal the pcm is. Wiggle wires with car running and listen for hissing signifying a vac leak. On corrados, check the braided hose to the fuel pressure regulator and two hoses behind the throttle body. If you do find a problem with the oxygen sensor and do any repairs that affect the mixture, take it in to a shop qualified tocheck and adjust the mixture. Most shops have a hard time figuring out VW?s method of adjusting a corrado properly. When the timing, mixture and idle are adjusted properly, your idle should just hover for a second above 1000k rpm and thendrop to about 850 at rest hot. Bouncing around or sticking indicate something isnt working or adjusted right. Bad idle valves aren?t that common but faulty throttle switches are. Learn how tocheck them.