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I bought a 2000 beetle with what seems to he a awp motor (317cc injectors, ko3s turbo & vvt). The car still has the original APH ECU. Every now and then the car will stumble on deceleration under load ( ac on and turning the steering wheel). I verified all timing Mark's, no vacuums leaks and no ECU codes. Would the APH ecu have trouble keeping up with the larger injectors and require me to get a tune? Any advise would be greatly appreciated.
 

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I’m not a parts swap expert on the mark iv vw’s but there was definitely some changes. Not only in parts but the ecu and wiring, to handle the added vvt and i believe the wideband bank 1 sensor 1, 02 sensor, that was upgraded with the AWP engine code. For example if you have the earlier 1.8t’s and you want to run a stage 2 or or higher through unitronic, you were required to upgrade the later ecu and wide band adapter harness, sensor.

All of this assumes, you have different parts; THAT, would need to be confirmed to rectify the situation and confirm, what parts should be installed, to make everything work correctly.

It sounds like you inherited; someone elseÂ’s project and need to figure out the puzzle if what they did to the car.!
 

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Your detective work; could really be easier, if you could contact the previous owner or shop, that did the swap. Otherwise, you are going to have to play sherlock holmes and confirm the identity/part#/compatibility of all the parts currently installed, that are crucial, to make the car run correctly. So, it sounds like you have your work cut out for you.

As to your poor running engine and drivability problems; on a stock, fully compatible parts car, a poor running 1.8t can have a whole list of possible reasons, things aren’t running correctly. Most drivability issues; come down to fuel delivery, ignition system and turbo/boost control issues.

As to what is causing the current problem and if you have incompatible parts thrown together; is a open question.

To start troubleshooting things; it would be nice, to square away any parts incompatibility problems first and then, go from there. Otherwise you might be chasing your tail and fall into a dark hole, of confusion!

These 1.8T's can be somewhat of a challenge to diagnose/tune in stock form but various parts thrown together, adds a whole ‘nother level of complexity to the mix.

Tell us more about the history of the car and whether or not, you can discuss the swap done with the previous owner or shop, that actually did the work. These VW's are like lego’s; the parts can be put together but that doesn’t always mean, it can run right with incompatible parts, attempting to work together. Thanks.
 

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Discussion Starter #4
Thanks for the thorough response!

The previous owner did not have any knowledge of the swap. I bought it with a blown headgasket. In addition to rebuilding the head, all the sensors including maf and 02 where purchased for the year and model of the car (APH). Vacuum lines and PCV valves where also replaced. The wiring harness and ECU are still APH so compatibility issues minus the unplugged vvt should be resolved. I ordered a vag cable and downloaded unisettings and vag-lite so I can get more visibility and some degree of tuning. My last resort was calling apr and getting a tune to match the combo.
 

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Yeah, you would have to call APR and see what they offer; I don't know, if they do custom tunes? Again, the lack of a ecu and wideband upstream 02 sensor; that are specific to a 1.8T AWP engine, how this could affect it working correctly, is still a open question? From reading Unitronic's website; when going beyond stage 2 on the earlier non AWP ecu's; they require you to upgrade the ecu to a AWP spec one and add a adapter harness, so you can use a wideband upstream 02 sensor, that is a AWP spec one. Again, more research and possibly discussing this with Unitronic, APR or other tuner; might help you figure out, what is the best solution for you.

Let's just assume; everything currently installed in the car is compatible. I would check for trouble codes and that might give us, some clues, as to the cause of your current drivability issues.

Considering, the type of repairs done recently (head gasket); I would start with baseline testing things, like compression (confirm head gasket repair) and fuel pressure, those, could then be ruled out as major issues. After that, looking at fuel trims; could indicate, the current state of tune, the car is in (+or- 10% is considered in the "normal" range). Fuel trims, can pinpoint; possible vacuum leaks or fuel delivery problems; read more here:

Fuel Trim Info - Ross-Tech Wiki

Starting with the basics like compression and fuel pressure; is a good place to start, as we have had people "chase their tails" or get sucked into a "black hole" of trying to fix "symptoms" of a greater problem and start throwing tons of parts, at a issue. Then, after spending a bunch of money on replacing parts that are actually "good"; they find out, they have low compression, a bad fuel pump or other major problems, that they overlooked and the "shotgun" or "parts cannon" troubleshooting technique, didn't work.

Again, successful troubleshooting; is about going through a process of elimination, testing, observing, making change and testing again, after changes are made. The most effective route; is a process of elimination and eventually, you find the problem.

You might start with a fresh scan of the car and let us know; what trouble codes, you find and we can go from there. Thanks! :)

PS: you might post to other sites; in the 1.8T section and see, if others, who have done swaps similar to yours, have to say about compatibility issues. (e.g. VWVORTEX: 1.8T engine forum, call tuners tech support/sales reps, etc).
 

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This is a late contribution to this thread but I will lend some input in case there are still questions on this subject.

The 286cc size of the original APH engine injector, 317cc is about an 11% increase, the ECU should be able to handle this difference, however, the questions would be more to the following:

1. Can the MAF housing flow enough air to match the extra fuel.

2. Is the stock FPR pressure being used or has that pressure been reduced to accommodate the slightly larger injectors.

Since you state that no codes are present, some changes would have been necessary to account for an AWP engine with VVT, some wiring changes might be required for this.

Although there are differences, on a basic level all MKIV 1.8t engines are the same, any of the related ECU's will interchange with some electrical and/or mapping adjustments.

On the other hand an APH ECU will not be looking for the VVT in an AWP engine that is so equipped because the APH engine did not have VVT, that being said, there probably would not be a related code for this reason.

If you do in fact have an AWP engine with VVT, you might think about upgrading to an AWP ECU that can deal with the VVT etc., some wiring changes might be necessary in order to accomplish this, check with Unitronic.

FYI, the APH ECU is wideband, the big difference between the APH and AWP wideband is, the AWP has much greater processing capabilities, this is why tuners require the AWP ECU upgrade when a real Big Turbo tune is being done.
 

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Ok I just bought a 01 beattle 1.8 turbo sport , is it a APH engine or a AWP engine my first beattle and turbo so sorry if this question seems odd thanks vic
 

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That is a break year, however, it is likely an AWP engine.

You will want verify this by looking on the front of the cylinder head, probably on the passenger side, or check with the dealer.
 
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