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Last edited by UrS4boy; 6 August 2012, 14:11.
Reason: Stupidity
RS2'd 93 UrS4 5 spd sedan
94 UrS4 V8 6 spd manual avant
Here are the codes and I see G68 as Vehicle Speed Sensor:
Well that makes no sense. The AAN (and 3B and ABY/ADU) engine speed sensor is the G28. Anytime the codes are read with the engine off, you get a G28 fault code (but it isn't real).
The G42 intake air temp fault is likely real. A bad signal call for the ECU to pull back timing = less boost
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The G61 front knock sensor (for cylinders 1, 2 and 3) is likely real. A faulty knock sensor = ECU pulls the timing back = less boost
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But did you ever confirm that your moisture trap is properly attached and that the boost signal is getting to the MAP in the ECU? (your boost levels = Waste Gate spring pressure):
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A faulty MAP or connection to the MAP will cause no ECU controlled boost:
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Is you Waste Gate Frequency Valve functioning properly? Is it even connected. An unconnected/faulty WGFV will result in only mechanical boost (WG spring pressure only):
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All of the above links were pulled from this diagram by clicking on the labels (all live links):
Well that makes no sense. The AAN (and 3B and ABY/ADU) engine speed sensor is the G28. Anytime the codes are read with the engine off, you get a G28 fault code (but it isn't real).
The G42 intake air temp fault is likely real. A bad signal call for the ECU to pull back timing = less boost
The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
The G61 front knock sensor (for cylinders 1, 2 and 3) is likely real. A faulty knock sensor = ECU pulls the timing back = less boost
The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
But did you ever confirm that your moisture trap is properly attached and that the boost signal is getting to the MAP in the ECU? (your boost levels = Waste Gate spring pressure):
The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
A faulty MAP or connection to the MAP will cause no ECU controlled boost:
The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
Is you Waste Gate Frequency Valve functioning properly? Is it even connected. An unconnected/faulty WGFV will result in only mechanical boost (WG spring pressure only):
The Audi Enthusiast website. Forums for all Audis including A4, S4, A5, S5, A6, S6, allroad, A8, S8, TT, R8, Q5, Q7, 4000, 100, 200, v6, v8, vintage, local forums
I really don't know whats the difference between VEHICLE speed sensor G68 and ENGINE speed sensor G28. On ECU pins I can see G28 but there is no G68 at all?!?!
IAT G42 I solved, it was broken wire, but it didn't solved the problem with boost.
G61 front knock sensor, I put from my other car (URS4), no changes.
I changed all vacuum lines with brand new and check moisture trap off course but I didn't know that there is wrong and right position of moisture trap?!?! So it is possible to put moisture trap on wrong side?
WGFV is good, I tried one from URS4 and tried to initiiate test with Vagcom, it works fine.
I didn't see that type of boost nightmare on complete forum ever
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
1.I really don't know whats the difference between VEHICLE speed sensor G68 and ENGINE speed sensor G28. On ECU pins I can see G28 but there is no G68 at all?!?!
2.IAT G42 I solved, it was broken wire, but it didn't solved the problem with boost.
3.G61 front knock sensor, I put from my other car (URS4), no changes.
4. I changed all vacuum lines with brand new and check moisture trap off course but I didn't know that there is wrong and right position of moisture trap?!?! So it is possible to put moisture trap on wrong side?
5. WGFV is good, I tried one from URS4 and tried to initiiate test with Vagcom, it works fine.
6.I didn't see that type of boost nightmare on complete forum ever
1. G28 engine speed sensor is connected to the ECU to tell the ECU what the RPMs are. Also connected to the instrument cluster tachometer.
G68 = signal to the speedometer = generates the road speed, independent of the G28 RPM signal. G68 is NOT connected to the ECU (which is why it doesn't have anything to do with boost. G68 info here:
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2. You need to pull the red S26 ECU power fuse to clear the codes so the ECU knows that the IAT is good again.
3. Having cleared the codes, the repaired/new G61 knock sensor should make the ECU happy again.
4. Moisture trap - there is no check valve or the such inside. However it is important the inlet and outlet hoses are securely attached to the inlet and outlet nipples and that the moisture trap is not cracked.
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5. WGFV - check the hoses to and from the WGFV for breaks/cracks/loose clamps, etc.
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6. Not the first time people have had a boost problem. It is just very difficult to diagnose correctly the first time remotely. With the help of the forum and the links I have provided, you will find the problem. It will likely be a small one.
7. One thing to consider is a failed G71 MAP sensor inside the ECU.
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Happy hunting. Let us know what you find.
RS2'd 93 UrS4 5 spd sedan
94 UrS4 V8 6 spd manual avant
Also, I have a proof that both knock sensors do not cut boost, disconnected both of them, boost 1 bar. Also I saw in some threads that bad MAF connector can cause low boost, I tried to disconnect MAF, boost is great again, 1 bar
It seems that I can't make URS4 to cut boost, also URquattro to have full boost, whatever I do
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
Also, I have a proof that both knock sensors do not cut boost, disconnected both of them, boost 1 bar. Also I saw in some threads that bad MAF connector can cause low boost, I tried to disconnect MAF, boost is great again, 1 bar It seems that I can't make URS4 to cut boost, also URquattro to have full boost, whatever I do
The G61 and G66 knock sensors will tell the ECU that there is pinging (pinking, pre-detonation) if/when it occurs and the ECU will pull timing and, in turn, decrease boost. No pinging, no signals from the G61 and G66.
The MAF and its connection can cause a wide range of issues when it goes bad. Confusing the ECU and resulting in lower boost is apparently one of them. Check the MAF for dirt/clean, check for broken wires and/or pins out of position in the connector.
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(You need to plug the MAF back in to run properly)
RS2'd 93 UrS4 5 spd sedan
94 UrS4 V8 6 spd manual avant
Hehe, You solved my problem with one free connector I found today, it's connector for G68 Vehicle speed sensor because I don't have it at all, it's URquattro and there is no place in UR differential for it
I disconnected complete ECU during changing IAT cables and knock sensors, so it cleared fault codes. Everything is ok with vacuum lines, as I said all lines are new with new clamps. Also, hoses attached to WGFV are new also with all clamps.
MAP sensor is definitely OK, I tried to change complete ECU between URquattro and URS4, off course, URS4 get 1 bar, URquattro 0.4 bar.
I forgot to mention that today I changed wastegates between UR and URS4, guess what, everything is the same I didn't doubt at all
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
After all combinations, I pulled codes from URquattro and only code I get now is G68 which is definitely not important for boost, because I never had it on my car.
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
I'll check MAF connector with multimeter to see if every wire has a connection, but I doubt that it can be a problem, URS4 works great without MAF
Also, I had one spare MAF and change it on my UR, nothing changed.
Only idea I have now is to change every sensor from URS4 with UR and see what will happened, but as I remember, I had done it in all my tries
Your URS4 goes great without a MAF ? It would go a lot better with a MAF, without it the ECU defaults to a safe map and uses throttle position for ref.
I guess I was/am confused. Now I understand that the boost issue is on the Urq with an AAN conversion. *IF* that is true, how are you reading the boost? On the digital Urq gauge or on an aftermarket analogue gauge? At this point, I suggest installing an analogue gauge to confirm your boost readings since the digital boost gauge might not be compatible with the MAP sensor signal from the AAN ECU.
RS2'd 93 UrS4 5 spd sedan
94 UrS4 V8 6 spd manual avant
Yes, the problem is on UR with AAN engine. Boost is the same on digital gauge and analog gauge, 0.4 bar and car is much slower than earlier when boost was OK, 1.2 bar because some chip I have.
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
OK, just to show a list what I did try in last few months, to have all in one place
Just to mention again that I have one URS4 with AAN engine, the car have no fault codes at all and works great, so I used most of the parts I know that they are correct and in working condition.
1. N75 from URS4, and test it through Vagcom, it clicks
2. Dump valve from URS4
3. Complete ECU from URS4
4. Other spare MAF
5. Changed all vacuum hoses and clamps with brand new
6. Moisture trap from URS4
7. New turbo hose from Maf to turbo
8. Unpluged MFTS
9. Changed TPS
10. Checked all fuses
11. Bought boost leak kit and tested system, no leaks
12. Complete 1.8T coil conversion
13. O2 sensor from URS4
After all of this changes, I used Vagcom and list codes:
IAT sensor G42 I solved, one wire was broken. Knock sensor I used from URS4, and after these changes, there was only one fault code, Vehicle speed sensor G68, but this code is usually for my UR because I don't have this sensor at all and never had it. It goes in front differential on URS4, but this can't be a problem because I didn't have it from the beginning, and car works perfect earlier.
So to continue the list:
14. Both knock sensors from URS4
15. Wastegate from URS4
I REALLY don't have any more ideas what else I can do
Audi URquattro 4.2l, Dodge Charger 7.3l, Golf 4 TDI 4Motion
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