A mate of mine bought a S4 a while ago.
He took it over to my place to show it off, and we went for a ride. I immediately noticed it wasn't boosting at all (Limp home, mech boost only).
It did not run right at idle either, and he says it sometimes gives a puff of black smoke on cold-starts. After a change of N75 and a re-routing (back to stock) of the vacuum hoses, it would boost, but cut at 1.3 bar. Something weird is going on with the tacho aswell.
So, symptoms were:
- Poor Idle, sometimes stops at lights (low idle speed of 600 rpm)
- Cuts at boost. Fuel cut.
- Sometimes "stutters" at constant speeds. When this happens the tacho will jump all over the place (3k-6k rpm). Warm engine.
- Throws codes on N71.
I only had the time to check his MAF-connector, which looked fine, and do a visual check for boost leaks. We also noticed he had some kind of tuning-chips in the ECU. Changed ECU for a known good one.
Since then he has gone mental and changed parts like a mad-man, with different results.
-N71 - No change.
-MAF- No change
-Fuel pump- No change
-Fuel filter-
-Coils-
-G4+G28- - This one made the car run smooth. It baffled me when he told me. It ran 100% for about half his test-run. Then it started to cut on load like before. After this trip the car supposedly smelled a bit weird on the inside (burnt), and the battery 12v+ cable was very hot. (cant say if this is relevant or not).
I'm getting the car over to my place later to see what I can find out. I'm thinking first to check for boost leaks. But maybe the timing is off, or the pins on the flywheel are dirty or something, making the G4 and G28 relevant?
Did I miss something obvious?
He took it over to my place to show it off, and we went for a ride. I immediately noticed it wasn't boosting at all (Limp home, mech boost only).
It did not run right at idle either, and he says it sometimes gives a puff of black smoke on cold-starts. After a change of N75 and a re-routing (back to stock) of the vacuum hoses, it would boost, but cut at 1.3 bar. Something weird is going on with the tacho aswell.
So, symptoms were:
- Poor Idle, sometimes stops at lights (low idle speed of 600 rpm)
- Cuts at boost. Fuel cut.
- Sometimes "stutters" at constant speeds. When this happens the tacho will jump all over the place (3k-6k rpm). Warm engine.
- Throws codes on N71.
I only had the time to check his MAF-connector, which looked fine, and do a visual check for boost leaks. We also noticed he had some kind of tuning-chips in the ECU. Changed ECU for a known good one.
Since then he has gone mental and changed parts like a mad-man, with different results.
-N71 - No change.
-MAF- No change
-Fuel pump- No change
-Fuel filter-
-Coils-
-G4+G28- - This one made the car run smooth. It baffled me when he told me. It ran 100% for about half his test-run. Then it started to cut on load like before. After this trip the car supposedly smelled a bit weird on the inside (burnt), and the battery 12v+ cable was very hot. (cant say if this is relevant or not).
I'm getting the car over to my place later to see what I can find out. I'm thinking first to check for boost leaks. But maybe the timing is off, or the pins on the flywheel are dirty or something, making the G4 and G28 relevant?
Did I miss something obvious?
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