Let me start by saying I've had fcs since I've owned a vehicle which is over 10 years. However, I'm stumped on this damn car. My buddy purchased a s4 tII and after fixing everything I could find wrong it still won't quite start on it's own.

I can barely press on the afm flap door, I emphasize BARELY, and the car will start. It won't stay running on it's own and if you touch the throttle it dies/backfires occasionally.

It has good compression
The injectors have been cleaned/flow tested
Fuel filter and pump are replaced.
Fuel pressure checked out to be good when not running (as it's hard to get to start).
Afm tests good and get same condition with another one.
Have spark
Boost sensor is out of spec by .05 volts
Smoke tested and fixed all intake leaks.
Fuel mixture screw is all the way counter clockwise.

Suggestions? Comments? I'm open...

 

I was having a similar problem with my JDM s5 swap into my s4. I was hard to start and would shut off randomly after about a minute or two of running.

Eventually after starting it and running it one time I heard a weird noise which turned into a knock when I tried to start it again.

A problem that seemed like something not so bad turned into a spun bearing and a seized front rotor to the e-shaft.

Not saying this is happening in your case but just a heads up with what happened to mine when I had similar symptoms.

Might be worth having a shop diagnose.

 

Have you tried to jumper the fuel check connector?

 

Yep, jumpered the connector just in case the issue was the ignition switch. No change.

- Chris

 

did you have to install this engine?.harness to the injectors?

 

Styx, the engine was installed by the previous owner (not saying he was a great mechanic, but he wasn't an idiot). I have had the intake manifold off and checked that the right injector wires were to the correct injector based off wire color in the fsm.

The most odd thing is that if I barely touch the afm door it starts and runs fine (sounds smooth, and clean). And if I let it go it dies. If I touch the throttle it dies or backfires then tries to die. If I push the flap slightly more in anticipation of the throttle input I can get it to rev up.

 

Why the mention of the ignition switch? And has the timing been checked?

 

I have came across an ignition switch issue that would allow the car to start then would not keep running after the key wad turned back to the run position. (I noticed b/c the fuel pump power would cut).

I had restabbed the CAS properly. Timing could not be fully set as the car wouldn't idle.

Now; UPDATE.

I pulled off the water temperature connector and inspected it to find the pins were not making full contact with the sensor. I repaired this, and reset the throttle body (butterflies, then tps) and the car will now start and stay running.

For the next issue.

If I barely give it throttle it will rev up slightly (up to around 3k rpm) then start to backfire and smoke. If I try to give it more than slight throttle, it will backfire and smoke.

I am now searching for solutions to this problem (with the search function and in this thread). Thanks for all the input thus far.

- Chris

 

Did you set the TPS after the car was as hot as it can get which is required? G/R wire should read 1 volt w/key to on.

 

Check your Trailing plug wires..they sound backwards.

 

Double checked the trailing wires, they are correct.

The tps was set based on resistance (1k ohm). The thermowax was deleted by the engine installer. The vehicle is also running a rtek 1.7 with rc 750's in the secondaries although I don't imagine this would matter to this point.

After checking tps voltage it was a poor connection between harness and tps.

The car now will free rev and although there is one small hiccup in throttle position I think the car is relatively fixed. The hiccup isn't due to a flat spot in the tps resistor, but that'll get it moving for now. Thanks for the help guys.