Issues after rebuild, N/A S5.
09-29-11, 12:59 PM
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Issues after rebuild, N/A S5.
Recently finished rebuilding my second motor, I was really hoping this one was going to just start up and go, but you know how it goes. I've tried a few different things but so far nothing. 
Hopefully this weekend I'll have plenty of time to find the culprit. Here's the video and then I'll provide as much info as I can. I'd just like to see if you guys have any suggestions of what it could be.
http://www.youtube.com/watch?v=BCo7U42ySrQ
The car starts right up every time. If I don't give it throttle it dies right away. If I give it partial throttle and try to keep the rpms steady it stumbles, misfires, backfires, etc. (as seen in the video.) If I continue to pulse the throttle it sounds like a normal running car. I cleaned the plugs and stabbed the CAS a bunch of times. I really don't think the problem is ignition. I think it's running lean, huge vacuum leak or fuel delivery issue. I'm worried that perhaps an apex seal spring is out of place or something! Very unnerving.
The exhaust gets dull red hot, I think one of the rotors isn't getting enough fuel. Today I pulled the UIM off and checked all my vacuum lines, everything looked proper. I didn't pull out the primary injectors yet but I did check the wiring to them, looked fine. I also haven't tried the starter fluid method yet, one thing I hope to try this weekend. At first I drove it down the driveway and back hoping it just hadn't settled in or something. Didn't drive it more than a few minutes, don't want to risk damage. I noticed this; engine braking is smooth, partial throttle it stumbles and bucks badly, steady throttle it runs smooth, full throttle it feels at a lack of power with a slight stumble. What's it sound like to you guys?
Hopefully this weekend I'll have plenty of time to find the culprit. Here's the video and then I'll provide as much info as I can. I'd just like to see if you guys have any suggestions of what it could be.http://www.youtube.com/watch?v=BCo7U42ySrQ
The car starts right up every time. If I don't give it throttle it dies right away. If I give it partial throttle and try to keep the rpms steady it stumbles, misfires, backfires, etc. (as seen in the video.) If I continue to pulse the throttle it sounds like a normal running car. I cleaned the plugs and stabbed the CAS a bunch of times. I really don't think the problem is ignition. I think it's running lean, huge vacuum leak or fuel delivery issue. I'm worried that perhaps an apex seal spring is out of place or something! Very unnerving.
The exhaust gets dull red hot, I think one of the rotors isn't getting enough fuel. Today I pulled the UIM off and checked all my vacuum lines, everything looked proper. I didn't pull out the primary injectors yet but I did check the wiring to them, looked fine. I also haven't tried the starter fluid method yet, one thing I hope to try this weekend. At first I drove it down the driveway and back hoping it just hadn't settled in or something. Didn't drive it more than a few minutes, don't want to risk damage. I noticed this; engine braking is smooth, partial throttle it stumbles and bucks badly, steady throttle it runs smooth, full throttle it feels at a lack of power with a slight stumble. What's it sound like to you guys?
09-30-11, 02:15 AM
#2
Free bumpp.
Would also like to know. Having all the same issues except I don't have his full throttle issue. 1500mi on a rebuilt s4 t2 with new apex seals.
Fwiw I had all my injectors rebuilt and flowed and it got rid of SOME of my backfires but that was all. Still stumbles on partial trottle ect. Even have a dead zone at ~1800 to 2500.
Hope you figure it out. I'm outta ideas lol
Would also like to know. Having all the same issues except I don't have his full throttle issue. 1500mi on a rebuilt s4 t2 with new apex seals.
Fwiw I had all my injectors rebuilt and flowed and it got rid of SOME of my backfires but that was all. Still stumbles on partial trottle ect. Even have a dead zone at ~1800 to 2500.
Hope you figure it out. I'm outta ideas lol
10-07-11, 01:02 PM
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Check to be sure you have the vacuum lines in the backside of the dynamic chamber snug an in place my 7 sounded like this and the large line that goes into it was popped off.
10-18-11, 05:13 PM
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When I sprayed the starting fluid I found a ton of vacuum leaks. All the hoses were just dried and old. I replaced them thinking that had to be it. It still runs the same! I reused the middle intake manifold gasket during the rebuild, in the process of replacing that now. I'm really bummed, I hope I get it done before winter! Thanks for the suggestions. I don't think it's the TPS because it worked before the rebuild and the throttle doesn't cut or anything, it feels like it's a huge vacuum leak or a fuel issue. Does it sound anything like bad compression? It runs smooth on throttle so I figured it couldn't be that. I guess my next step could be to do a compression test.
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