Mark IV 1.8T engine (Golf, GTI, and Jetta) FAQ
I’m putting this up for those who either refuse to use the search function or are too lazy/inept to navigate this forum. This being said, here are some answers and information for frequently asked questions on the MK IV 1.8T (IT’S A MARK IV not AN M-K IV!!!!!). If you wish there to be a link or information added to this, contact me and I will gladly add it. Some of this info has been taken from other websites, if you have a problem with it, take a long walk off a short pier. Anyways, enjoy
Volkswagen transversely mounted 20 valve turbo 1.8L 4 cylinder motor:
Looks like this:
Engines:
The Mark IV 1.8T comes in 3 different motors for
Engine code:AWD - 99.5 - 2000
Power: 150 hp/155 tq.
Turbo: K03
Boost: 8.7 PSI
Engine code:AWW - 01 - 2000
Power: 150 hp/162 tq.
Turbo: K03s
Boost: 8.7 PSI
Engine code:AWP - 2002.5+
Power: 180 hp/174 tq.
Turbo: K03s
Boost: 11.6 PSI
All MK IV VW cranks are forged
After 300 hp it is recommended to upgrade rods, pistons aren’t required until 400 hp
Replacing spark plugs:
If you go to AutoZone or any of those places, make sure you get the correct plug. A cheap plug will cause misfires and lead to premature coilpack failure.
If your car is stock programmed: NGK BKR6E/6962 or NGK PFR6Q
-Gap these to .032
-Torque down to 22 ft. lb.
If your car is chipped (APR, GIAC, Revo, No-Speed, Unitronic, etc.): NGK BKR7E/4644
-Gap these to .028
-Torque down to 22 ft. lb.
Replacing ignition coils
If your engine is misfiring or you get any of the “P” codes from an auto parts store and they call for misfire in a cylinder, chances are it’s a bad ignition coil (or coilpack as some call them). These are a common part that goes bad on these cars. I recommend changing them out every 40k miles or at least purchasing a set of 4 and keeping them handy. It is also recommended to change all 4 at once.
-AWW/AWP use a push down style
-AWD uses the style of coilpack that bolts into the head (all 3 engine codes have the holes for these in the head)
*If you have AWD engine code with coilpacks that bolt into the head, torque bolts down to 7 ft lb.
*Engine codes AWW and AWD may both use the bolt down coilpack, they are more durable and are less likely to “push up” after use (the push down style seal with vacuum which isn’t reliable)
Idiot’s guide to modifying your 1.8T *NOOBS MUST READ THIS*
Here in chronological order are the steps I heavily recommend following in order to get the best bang for your money with a 1.8T:
1.
CHIP - Get a chip, not the potato kind, the ECU kind. I recommend GIAC or APR but Revo and Unitronics are also very good
2.
DIVERTER VALVE - Once chipped your OEM Diverter Valve will start to fail (yes, even if you have a 710N valve), replace with one of the following: Forge 007, APR R1, or Bailey’s. The APR and Bailey’s are maintenance free, however the forge is designed so you can adjust it to hold more or less boost but requires cleaning twice a year. Call Forge Motorsport and ask them what they recommend for cleaning.
3.
EXHAUST - Now that your car is using more fuel and needs to breathe easier to free up any lost power from the stock setup. There are literally a hundred or more different choices when it comes to exhausts, and the prices vary as much as the brands, really there are only several things to really look for in an exhaust:
-Mandrel bent (very important!!)
-Thick gauged stainless steel (T304)
-At least 2.25” wide
What your choice ultimately boils down to is what sound you like. For comparison, go to youtube and listen to different videos on different exhausts as they’re all different. For a chip setup you’ll want to upgrade the turbo downpipe as well as the “cat-back” exhaust (runs from the catalytic converter back).
4.
INTAKE - A turbo engine is useless unless it can easily suck air in. The factory air box flows well for stock tuning, but for more power, it isn’t very useful. You can go three ways with this and I will explain each below:
Cold air intake (CAI): Don’t bother buying one for a 1.8T. They are useless on turbo motors because the “cold” air it sucks in will just get hot again once it hits the turbo, the job of the intercooler is to cool this hot air down. However if you do buy one, be careful of puddles and standing water as it is possible to hydrolock (suck water into the engine block) your engine with a cold air intake.
-Short ram intake (SRI): The preferred and cheapest of aftermarket intakes. It is usually just a section of tubing from the MAF (Mass Air Flow) sensor that connects to a filter of some sort. A lot of SRI’s come with a heat shield to bring in slightly cooler air than that surrounding the motor.
-“Swiss cheesed” airbox: This is the modification of the stock air box to allow more air flow, usually accompanied by a higher flowing air filter such as a K&N panel filter. To “swiss cheese” your factory airbox, you take a drill and a drill bit and make multiple holes in the bottom half of the air box. The name speaks for itself.
5.
SUSPENSION - With lots of power at your foot, you need to be able to carry it through corners and make the launches stiff to prevent wheel spin. Stock suspension is great for comfort but lacks sportiness and is too tame for hard cornering. There are also several forms of suspension discussed as well:
-Coilovers: This form of suspension gives the user full control over what ride height they want. Unlike lowering springs/shocks/struts, coilovers have the option to adjust what is called the “spring perch,” which is a metal sleeve that the spring sets on. You can either raise (unlikely) or lower the spring perch in order to raise or lower the car. This gives the user the ability to adjust ride height to personal preference. This is typically a more expensive form of suspension, but offers more customization.
-“Cup Kit”: Also referred to as spring/shock combo. This is a combination of lowering springs and aftermarket struts/shocks designed to handle the stress and roughness of shorter lowering springs. Unlike coilovers, a cup kit is rarely height adjustable, although some brands will give you several different heights that you can set your rears at. This is the most practical form of lowering a car but does offer the same level of customization coilovers do.
-Lowering springs: Lowering springs are a shorter, stiffer spring that lowers the car simply by being smaller than a stock spring. This is the cheapest form of lowering a car, but it does have consequences. Depending on the age/condition of your stock shocks/struts, they will go out much quicker with lowering springs because they are not designed to handle the additional stress and different spring rate of aftermarket lowering springs. Typically before a year you will be forced to replace struts/shocks in your car with lowering springs.
*On MK IV’s if you lower the car enough you may run into problems with the front sway bar striking the driveshaft when the spring are fully compressed, depending on what setup you are running this may or may not occur. If it does, you can get an aftermarket front sway bar, cut out the stock front sway bar, or upgrade the sway bar endlinks (rarely works).
These are the basic steps that if you’ve done a little looking around can cost less than 1000 dollars for a huge power gain. The beauty of a 1.8T is how easily it is to make quicker than stock in contrast to the other motors in the VW lineup for the MK IV. Other common modifications that can be done:
-Turbo Inlet Pipe/Induction Pipe (TIP) *Recommended*
-Rear sway bar (RSB) *Recommended*
-Front mount intercooler *Not recommended for stock turbo applications*
-Side mount intercooler (Larger) *Not recommended for stock turbo applications*
-Silicone boost hoses
-Throttle body hose
-Lower intercooler “pancake” hose
-Upper strut tie-bar *Not recommended*
1.8T Issue: BOV (Blow-off Valve) VS. DV (Diverter Valve)
This issue is often brought up in the presence of idiots, however I will discuss it to clear up any smoke that might cloud the understanding of some more intelligent forum members. A VW is not meant to run a BOV! The reason for this is because the ECU is programmed to expect that air that the DV re-circulates back into the intake. A BOV vents this air that is expected out to atmosphere, and when the air that doesn’t exist hits the engine, it burns rich and causes a rich condition in the ECU, which in turns messes the fuel map up partially. Over time this can ruin the entire fuel map and cause many problems. This can all be summed up by a quote from a previous member of this forum that I saved on my computer:
Quote:
The purpose of a diverter valve or bov is to release the pressure spike between the turbo and throttle body. This pressure spike builds when the turbo is still spinning but the throttle body closes. If there were no valve what we would get is compressor surge. Compressor surge is, when broken down to its main component, you turbocharger going from 110,000rpm to 0 in less than a second. This is bad. It's a really good way to ruin a turbo. That's the purpose of the valve.
OK, so now that you know what the valve is for... on to why a bov is bad for a 1.8t.
The engine sucks in air. The MAF measures that air. The ECU sends a certain amount of fuel to the engine based on what the MAF tells it. Because of this anything between the MAF and the cylinder MUST be part of a sealed system. Any leak is excaping metered air. The engine will provide fuel for the air that isn't there anymore and the fuel mixture will be rich.
The dv/bov is after the MAF so any air passing through is has already been measured. We can't have any leaks here. A dv reroutes the air back to the inlet of the turbo, after the MAF and still in the metered air system. Totally acceptable. The BOV lets the air go to atmosphere. That air just escaped the system... but the ECU is going to fuel for it anyway. Boom... hard rich. That's the puff of black smoke from your exhaust when the BOV hits.
Now listen up, because this is the important part that kills motors. Motronic 7 is a complex system. The front O2 sensor from a 1.8t is what all the aftermarket companies use for their widebands. Your car is DAMN good at knowing its own mixture and compensating (it has a WIDE fuel trim range. It will actually compensate over problems and you'll never know it happened). So what happens is every time your BOV goes off and the engine makes a rich condition the ECU logs it and leans out the system just a bit to compensate. You keep doing it over and over and it'll keep leaning itself out to compensate. The problem is it doesn't need to be leaned out, it's only too rich when the bov is open. It's still going to trim the whole fuel map. Now you're too lean under boost, too lean at idle, everywhere.
Lean conditions are dangerous. Lean is when you get detonation, piston damage and outright engine failure.
Tightening it down all the way just makes it hard to open which will cause compressor surge and damage the turbo
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Any other questions feel free to ask, if I missed something let me know. I will delete old comments from this and eventually close the thread. I’ll leave it open for the next month or so to get some feedback. The VR6 and 2.0 Section will arrive soon.
