1998 A4 2.8 to 1.8T

[macwithdacheese]

Helloo all,after alot of time i finally have finished my 2.8 30V to 1.8T swap but having issue's to keep it running,what happens is that she stalls if dont give throttle and even there is kinda rough,its an AEB that i had bought from a guy that made it run in front of me in his Mk3 swap,everything has been properly connected using an 1.8T 1998 Passat Harness M/T Harness also have the ECU out of it just incase.
im 100% sure its some electrical problem but where that is a big question mark.
My scanner is able to scan the ECU for the codes prior of starting it(while battery disconnected and swapping ECU) but as soon as i start it and then she stalls the scanner will say failed to communicate,witch happens right away after the 1st start up.
I have another ECU of a 1999 A4 Quattro AEB M/T and it does the same thing.
I checked all my fuses and all of them are good exept found the rear whipper fuse blown but that dosent matther at all.
Connected my 2.8 ECU just for fun and was able to read aswell.
Also Cant access ABS/Air Bag Modules after the swap witch i absolutly need because they are popping out and i need to pass inspection aswell(didnt have them before swapping the engine too)
The car itself its an 1998 A4 M/T Avant that had a 2.8 30V,witch i really didnt like so swapped for the 1.8T witchmore realialbe,easy to work and has way much potential when they properly work.
The 1.8t is bone stock with no upgrades,few sensors are new,some are reused,yes i did a TB adaptation and even tried a 2nd TB,tried 1 brand new temp sensor and one original from the passat, new BKR6EIX as plugs,tried with and without MAF sensor connected,im out of ideas at that point do i need to do some wiring( did check the end of the harness and there is 1 pins in the yellow connector and one in the brown that dosent link up with any pins from the car connectors all the rest seems to be connecting to some pins)
Has any of you went thrue this kind of situation?
Tought this is pretty straightforward swap till this happens
Any help with be gladdy appreciated,wiling to ship you out some food via ubereats to the one that can seriously help me out here(no jokes )
Thanks in advance

Info pulled out of Maestro Scanner on the Passat ECU
Controller part number :8D0907557P
Ecu software number is :1037352103
Ecu hardware number is :0261204258
Vin number is :unknown
Ecu type :256K M3.8/5.9
Engine type :5V 1.8Turbo

Was able to pull few check engine codes : 16946 ,System Voltage too low / 16806 Bank 1 Catalyst Below threshold ( New O2 sensors so maybe from previous car ) / 16500 G62 implausible signal / 18010 Power supply terminal 30 , Voltage Low( im boosting the car everytime to get it started ) & last code is 18021 MIL Control circuit open.

[Blazius]

You are loosing system voltage, either you got some main power lines loose, or your alternator is dead. Check those first.

[macwithdacheese]

You are loosing system voltage, either you got some main power lines loose, or your alternator is dead. Check those first.

Will definetly check into that,thanks for the guidance mate

[LREDb5]

Did you do a throttle body alignment via vagcom?

[macwithdacheese]

Did you do a throttle body alignment via vagcom?

I did with my Vagcom Tools yes.Its wrotten TB Adapt.Ok!
Just also got a new battery but didnt do much as a difference.
rechecked all the plugs aswell.
I dont get why the ECU can be readed with VAGCOM before starting the car and then it dosent communicate no more...
Yesterday actually i was able to start it once,then read the ECU again but then a 2nd start and again no communication.
Everytime it starts it will stall unless i give some gas to it,but even there the response is really not instant.

[Blazius]

If you are absolutely sure your supply is good and stuff, then your CPS is dead, it will cause no start and stall issues. Please make a log using vcds on a measuring group with RPM in it , preferably in one gear pull and you will see if thats the case.

[macwithdacheese]

Ill check both crank and cams one,but why would the communication with the vagcom wont work after starting the car once,would i need to do some programmation maybe?

[macwithdacheese]

So i had the grounds rechecked and cleaned over again just to be sure,also insalled a new battery and had the alternator checked up,changed nothing at all,Wondering why would the CEL,ABS,Air Bag & brake light would be going on then,its for sure not a mechanical problem.
What is this connector in the 3th picture,i can find where do connect this one at all(located on the line that goes for oil switch,near the oil filter/oil cooler)?
Found out that i need a 10amp fuse instead of 15Amp for the injectors will give it a try..
When removed the harness at the scrap it was connected to nothing but maybe it should connect somewhere..

[Blazius]

The stall issue is related to the CPS most likely. As for the rest they are sepearate problem. Connector picture is too out of focus but looks similar to wheel speed sensor connector but it could be many things..

[macwithdacheese]

Well i found out the issuee,was so stupid,had a vacuum leak straight in the intake manifold...
Now at least it can idle,gotta figure out the electronic stuff now tho,i saw that 2 out of 4 connectors that plugs into the car were the ECU box is located yellow connector and brown connector has 1 pins in each connector mismatched witch dosent align with the harness one.
Will check more into details this week,im sure its one of those wires gives some signal to Airbag/abs module since i remember not having those lights in the past and also scanner dosent read shit,but car runs,also when it runs i see the CEL but its dissapears when i turn off the car and cant either scan nothing while the car running.
Anyways its a good progress,btw not Audi related but its still a Euro tho,yesterday my buddy came to see me with this beast that he rented,the car is nuuuttss :O

[Blazius]

Did you move the car at all btw? And yes the chassis connectors are likely likely mismatched.

[macwithdacheese]

hahhahah guess what no even,i think i damaged the pilot bearing while installing it,i hear rattling when pushing clutch fully & also cant enter any gear either,so im most likely to remove everything again just for a pilot bearing,but at least i know it runs tho.

[PZ.]

I had no power to my ECU after the swap on my B5 Passat. There were several connectors that needed to be re-pinned, but I ended up swapping the interior dash harness too. I had the donor car in the garage and I did a manual swap at the same time. I also replaced the heater core, so everything was apart. A few months later, I had a bad ECU relay that caused starting problems when the car was warmed up.

[macwithdacheese]

Well thanks,several even with manual to manual swap?Looks like i most repin 2 connections that pretty much it,could you please PM me some more details on what have you done please.

[PZ.]

Sorry, several wires, but not the whole connector. I did not bother counting once I saw it was more than one. My engine just cranked without it. Instead of re-pinning, I pulled the dash on both cars and swapped the entire dash harness over. I had planned to do that eventually to have OEM wiring and working CC and clutch switches, so I just dove into it.

[macwithdacheese]

okay makes sense i will check into that,kinda to lazy to remove the whole dash thats the thing but if have too ill have to do it.
thanks for the info tho

[PZ.]

No need to do the dash, I just wanted matching wiring since I was also doing a manual swap. The heater inlet was cracked, so it was coming apart anyway.

[macwithdacheese]

No need to do the dash, I just wanted matching wiring since I was also doing a manual swap. The heater inlet was cracked, so it was coming apart anyway.

makes sense,i got info that only the cluster itself will do the job,will definitly need to check into all this