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View Full Version : engine cuts out when hits boost, help?



Simon69
10-30-2018, 06:17 PM
so I took my lovely a4quattro 1.8t for a ride after i replaced the turbo gasket and the engine just cut the throttle when i hit boost which was at around 4k rpm. CEL shows 02 sensors but thats been on before because cat delete, and codes 17606, 16524, and 17963 pops up. I am chipped for 18 psi and it hits 5-10 and than cuts out which is strange. my n75 isnt hooked up but it worked fine before. i was told the previous owner installed a new blow off valve and i know these cars use diverter valves, but I dont think that matters because I believe the bov is recirculated. so I dont know much about turbo audis so any help is very much appreciated lol

b6Hate4
10-30-2018, 06:29 PM
Pull out your spark plugs and double check the gap, sounds like it may be too large causing the spark to be blown out.

Which turbo gasket did you replace? Exhaust side?

Simon69
10-30-2018, 06:45 PM
Pull out your spark plugs and double check the gap, sounds like it may be too large causing the spark to be blown out.

Which turbo gasket did you replace? Exhaust side?

I replaced the headers side, what should the gap be?

Blazius
10-30-2018, 07:50 PM
I replaced the headers side, what should the gap be?

0.71mm or 0.028 " from what I've read on stock turbo's

Simon69
10-30-2018, 08:55 PM
I checked the plugs they're all gapped to .030-.032 I don't think its a spark problem because it revs to redline with no issues

walky_talky20
10-31-2018, 11:22 AM
A - Is this a 2000 or a 2001? I'm guessing it's a 2000.
B - Is it misfiring, doing a hard fuel cut, or just tapering the throttle? I'm guessing it's doing a hard fuel cut (not misfire).

2 of your codes are for the rear oxygen sensor. Not a big deal.
1 of your codes is for over-boost.

The over-boost is your problem. You have no N75. So upon boosting higher than requested, the ECU is helpless to do anything to bring the boost lower. It has literally zero control of the wastegate. If it was a 2001, it will generally just taper the throttle to keep the boost in check (we're talking limp mode levels of boost here). It's limp mode with no wastegate, but it's pretty smooth. However, you are saying it "cuts out". So I'm guessing you own a 2000 model year which does not have the nifty throttle taper feature. The only thing it can do to protect itself against the onslaught of uncontrollable boost is to shut off the fuel injectors. Hard fuel cut. Right now.

So I'm pretty sure you just have a boost control issue. Reinstall your N75, clear the codes and see if runs better. That is my suggestion. Do note that I'm not a mechanic (see signature). That is just what I would do first if I were asked to address this issue.

Simon69
11-04-2018, 02:43 PM
A - Is this a 2000 or a 2001? I'm guessing it's a 2000.
B - Is it misfiring, doing a hard fuel cut, or just tapering the throttle? I'm guessing it's doing a hard fuel cut (not misfire).

2 of your codes are for the rear oxygen sensor. Not a big deal.
1 of your codes is for over-boost.

The over-boost is your problem. You have no N75. So upon boosting higher than requested, the ECU is helpless to do anything to bring the boost lower. It has literally zero control of the wastegate. If it was a 2001, it will generally just taper the throttle to keep the boost in check (we're talking limp mode levels of boost here). It's limp mode with no wastegate, but it's pretty smooth. However, you are saying it "cuts out". So I'm guessing you own a 2000 model year which does not have the nifty throttle taper feature. The only thing it can do to protect itself against the onslaught of uncontrollable boost is to shut off the fuel injectors. Hard fuel cut. Right now.

So I'm pretty sure you just have a boost control issue. Reinstall your N75, clear the codes and see if runs better. That is my suggestion. Do note that I'm not a mechanic (see signature). That is just what I would do first if I were asked to address this issue.

its a 1999 aeb to word it better the car jerks hard like the throttle goes in and out. Could it be a BOV issue?

nunya
11-04-2018, 09:21 PM
its a 1999 aeb to word it better the car jerks hard like the throttle goes in and out. Could it be a BOV issue?

Its likely boost cut, and/or a vacuum leak. Do a pressure test. Also, get rid of the BOV. Its just a noise machine, doesnt help performance.

--dillon

walky_talky20
11-05-2018, 09:03 AM
An AEB, eh? Yeah, it will definitely do a hard fuel cut when it is trying [desperately] to save the engine from destruction by overboost. That's the only thing it knows how to do.

I didn't realize it could actually set an overboost code due to the AEB having no MAP (boost) sensor at all. It is likely setting this code based solely on the MAF value (airflow) being way too high. That could be from a boost leak (somewhat unlikely as you have no mixture codes) or it could be from the ECU trying to run in low boost mode and your manual boost control obviously not jiving with that.

Think about it: on a stock, or even a chipped AEB - when things get out of hand (say running lean, or sensors are failing or whatever the heck) it will go into "limp mode". This is where it cuts the boost in half (or less) to keep things safe until you fix the junk that's broken. But on your car, it *cannot* cut the boost. And being an AEB, it can't close the throttle plate either - you've got that mechanically held open with your foot. The absolute only thing it can do is a hard fuel cut when things get dangerous. It cannot handle it gracefully. You done bypassed all the safeties, so that's what you get.

I think you have to fix what's known to be broken first: your boost control circuit. Hook up the N75 like it is supposed to be and see how it goes. Without that we can't really tell if it's having overboost problems at full power, or just the inability to run in limp mode when it wants to.

Secondly, you may need to address your rear oxygen sensor. It's not currently giving a code for bad or missing cat. It's giving codes for a sensor that's junk. I think it *should* still run at full power like that, but I'm not certain.

Simon69
11-14-2018, 03:01 PM
An AEB, eh? Yeah, it will definitely do a hard fuel cut when it is trying [desperately] to save the engine from destruction by overboost. That's the only thing it knows how to do.

I didn't realize it could actually set an overboost code due to the AEB having no MAP (boost) sensor at all. It is likely setting this code based solely on the MAF value (airflow) being way too high. That could be from a boost leak (somewhat unlikely as you have no mixture codes) or it could be from the ECU trying to run in low boost mode and your manual boost control obviously not jiving with that.

Think about it: on a stock, or even a chipped AEB - when things get out of hand (say running lean, or sensors are failing or whatever the heck) it will go into "limp mode". This is where it cuts the boost in half (or less) to keep things safe until you fix the junk that's broken. But on your car, it *cannot* cut the boost. And being an AEB, it can't close the throttle plate either - you've got that mechanically held open with your foot. The absolute only thing it can do is a hard fuel cut when things get dangerous. It cannot handle it gracefully. You done bypassed all the safeties, so that's what you get.

I think you have to fix what's known to be broken first: your boost control circuit. Hook up the N75 like it is supposed to be and see how it goes. Without that we can't really tell if it's having overboost problems at full power, or just the inability to run in limp mode when it wants to.

Secondly, you may need to address your rear oxygen sensor. It's not currently giving a code for bad or missing cat. It's giving codes for a sensor that's junk. I think it *should* still run at full power like that, but I'm not certain.

connecting the n75 works but it's only boosting around 4 psi and 10 by redline It's chipped to 18, if I hook up the boost controller and set it to 18 would it affect anything and throw it into limp mode? the car is also running pretty rich I can smell gas in the cabin, the plugs are dry and black, and my fuel mileage is absolute dogshit. it idles from 500-700 rpm and sometimes dies on startup and when it does that I unplug the maf and plug it back in and it works I believe the maf is dirty because I just replaced it but could the richness also be from the 02 sensors? the car is also straight piped from the turbo back so would replacing the 02 sensors even work since it's straight piped and not reading the chemical balance as it would stock?

nunya
11-14-2018, 08:27 PM
connecting the n75 works but it's only boosting around 4 psi and 10 by redline It's chipped to 18, if I hook up the boost controller and set it to 18 would it affect anything and throw it into limp mode? the car is also running pretty rich I can smell gas in the cabin, the plugs are dry and black, and my fuel mileage is absolute dogshit. it idles from 500-700 rpm and sometimes dies on startup and when it does that I unplug the maf and plug it back in and it works I believe the maf is dirty because I just replaced it but could the richness also be from the 02 sensors? the car is also straight piped from the turbo back so would replacing the 02 sensors even work since it's straight piped and not reading the chemical balance as it would stock?

Have you tried a known working n75, properly hosed up?

--dillon

Simon69
11-14-2018, 09:17 PM
Have you tried a known working n75, properly hosed up?

--dillon

not sure, I bought the car with an L fitting in place of where the n75 would be fitted and the n75 was connected to the plug and folded to the side of the inlet pipe

walky_talky20
11-15-2018, 09:33 AM
- When the N75 is connected properly, what codes do you have?
- What does the N75 duty cycle look like?

Simon69
11-15-2018, 10:13 AM
- When the N75 is connected properly, what codes do you have?
- What does the N75 duty cycle look like?

when the n75's connected I only get the 2 02 sensor codes 17606 & 16524. around 3500 - 4000 rpm when boost hits with regular driving or floored it's at 3-5 psi and rises, and by 5000-5500 it'll stay at 10psi

nunya
11-15-2018, 06:59 PM
when the n75's connected I only get the 2 02 sensor codes 17606 & 16524. around 3500 - 4000 rpm when boost hits with regular driving or floored it's at 3-5 psi and rises, and by 5000-5500 it'll stay at 10psi

https://www.google.com/search?q=n75+plumbing&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj0wunN9dfeAhV0GjQIHZUODpUQ_AUIDygC&biw=1373&bih=718

Simon69
11-16-2018, 01:36 PM
https://www.google.com/search?q=n75+plumbing&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj0wunN9dfeAhV0GjQIHZUODpUQ_AUIDygC&biw=1373&bih=718

the n75 is hooked up properly but still running rich and boost is only hitting 10 psi

walky_talky20
11-17-2018, 01:58 PM
What's the duty cycle look like on the N75? And have you tried a different N75 valve?

Simon69
11-21-2018, 05:58 PM
What's the duty cycle look like on the N75? And have you tried a different N75 valve?

I do not know how to check n75 duty. I have a high probability that the n75 is the issue. so when I had the n75 plugged in as it it was hitting boost really slowly and only got up to 5 or 10 sometimes than tapered down to 0 by 5500rpm, it also idled up and down, and sometimes stalled after about a minute of idling. & the car just wasn't running right either. so I got vacuum lines and hooked up the manual boost controller with the n75 only plugged in through the electrical connector, and in place of the n75 was an L fitting going from the compressor and the other going through the mbc and from mbc to wastegate and the inlet part was plugged with a bolt. after that it started idling perfectly, hit boost like it should would go up and hit 15 in second gear than in third it would cut, pop backfire, and jerk a couple times at around 5 psi and than gave me the code 17963. After that I plugged in the n75 with the mbc and it idled fine but it had stalled after about 30 seconds and worked the same as it unplugged but it hit 15 fine in second and in third it oddly didn't jerk as hard but still cut out and backfired rapidly and gave the 17963 code so idk but I think I'll find an n75 and replace it and see how that goes

Simon69
11-27-2018, 02:10 PM
bump? I replaced the n75, fuel filter, cleaned the bov, took the turbo off and checked if the wastegate was stuck and the issue is still present.

Blazius
11-27-2018, 02:11 PM
Logs ?

Simon69
11-27-2018, 03:32 PM
Logs ?

dont have vag

Blazius
11-27-2018, 04:21 PM
Well that is unfortunate my friend, a VCDS replica or something shouldnt break the bank, even VCDS lite or borrow one .Pretty much obligatory if you own a VAG group car. If its not hardware issue related to boost control , then atleast we need logs , what gas u running ?

Simon69
11-27-2018, 05:43 PM
Well that is unfortunate my friend, a VCDS replica or something shouldnt break the bank, even VCDS lite or borrow one .Pretty much obligatory if you own a VAG group car. If its not hardware issue related to boost control , then atleast we need logs , what gas u running ?

the car says 91 on the gas flap, but the previous owner says 93 keeps it cooler so I use a mixture of the two sometimes

walky_talky20
11-28-2018, 04:42 AM
I'll comment on a couple things.

- The N75 will never be the cause of a rough idle or stalling, no matter what it's doing. It's a valve for the wastegate and makes no difference at idle. Unless it's physically leaking air (creating an air leak in the turbo inlet pipe), the rough idle and stalling is something else entirely.
- The fact that plugging in the N75 causes it to run more poorly suggests that it might be having trouble with closed loop operation. Perhaps a faulty oxygen sensor or MAF.
- The AEB is using MAF values to determine "overboost". And you also had a stalling issue. I'm skeptical of the health of the MAF. Maybe log that guy.
- If you continue to have trouble getting this thing to run properly, you should consider that it's trying to run on modified software. Installing a stock ECU and running at stock power (the horror) will greatly simplify the diagnostic process. Once it is running mint again, with zero codes and awesome fuel trims, then you can try the modified software and see what happens.

- just my two cents
- not a mechanic

Blazius
11-28-2018, 09:37 AM
I'll comment on a couple things.

- The N75 will never be the cause of a rough idle or stalling, no matter what it's doing. It's a valve for the wastegate and makes no difference at idle. Unless it's physically leaking air (creating an air leak in the turbo inlet pipe), the rough idle and stalling is something else entirely.
- The fact that plugging in the N75 causes it to run more poorly suggests that it might be having trouble with closed loop operation. Perhaps a faulty oxygen sensor or MAF.
- The AEB is using MAF values to determine "overboost". And you also had a stalling issue. I'm skeptical of the health of the MAF. Maybe log that guy.
- If you continue to have trouble getting this thing to run properly, you should consider that it's trying to run on modified software. Installing a stock ECU and running at stock power (the horror) will greatly simplify the diagnostic process. Once it is running mint again, with zero codes and awesome fuel trims, then you can try the modified software and see what happens.

- just my two cents
- not a mechanic

Yeah agreed. The thing is he just said he doesnt have VCDS, its a must , without logs its a guess game pretty much.

Simon69
11-28-2018, 01:17 PM
I'll comment on a couple things.

- The N75 will never be the cause of a rough idle or stalling, no matter what it's doing. It's a valve for the wastegate and makes no difference at idle. Unless it's physically leaking air (creating an air leak in the turbo inlet pipe), the rough idle and stalling is something else entirely.
- The fact that plugging in the N75 causes it to run more poorly suggests that it might be having trouble with closed loop operation. Perhaps a faulty oxygen sensor or MAF.
- The AEB is using MAF values to determine "overboost". And you also had a stalling issue. I'm skeptical of the health of the MAF. Maybe log that guy.
- If you continue to have trouble getting this thing to run properly, you should consider that it's trying to run on modified software. Installing a stock ECU and running at stock power (the horror) will greatly simplify the diagnostic process. Once it is running mint again, with zero codes and awesome fuel trims, then you can try the modified software and see what happens.

- just my two cents
- not a mechanic

do you think the maf being faulty could be tricking the car & think it's overboosting? or could it be a vaccum leak? because with the maf unplugged the car still stalled. It only stalls when its below 40 degrees.

I'm surprised I can't find anyone else online that has a similar problem that has been resolved.

walky_talky20
11-28-2018, 01:34 PM
Yes, that's possible. Yes, that's also possible.

Temperature related stalling? Maybe coolant or intake temperature sensor.

Blazius
11-28-2018, 01:37 PM
you can test the CTS with multimeter , vacuum leak = soapy water :D

Simon69
12-14-2018, 05:29 PM
update: I cleaned maf sensor, put in new spark plugs with .28 gap instead of .34 and with the n75 plugged in and a boost controller taking over the wastegate, it runs better, hits 15-20 psi fine but sometimes breaks up. however if I'm in 4th or 5th and floor it itll hit 20 than breakup and give me the overboost code & small evap leak code. I was also getting 18010 when it was cold outside and the car would die just after I started it. Now I'm thinking it could be bad coil packs?

Blazius
12-15-2018, 01:24 AM
update: I cleaned maf sensor, put in new spark plugs with .28 gap instead of .34 and with the n75 plugged in and a boost controller taking over the wastegate, it runs better, hits 15-20 psi fine but sometimes breaks up. however if I'm in 4th or 5th and floor it itll hit 20 than breakup and give me the overboost code & small evap leak code. I was also getting 18010 when it was cold outside and the car would die just after I started it. Now I'm thinking it could be bad coil packs?

Fueling okay ? Car wont die from more air , but low fuel or low air.

Simon69
12-15-2018, 09:21 AM
Fueling okay ? Car wont die from more air , but low fuel or low air.

when the car would die it would give the 18010 code which is power supply b+ low voltage. I just put a brand new battery in during november

Blazius
12-15-2018, 10:07 AM
when the car would die it would give the 18010 code which is power supply b+ low voltage. I just put a brand new battery in during november

ahhh I see, then something is not okay with electronic, prolly coils

walky_talky20
12-16-2018, 12:46 PM
Breakup at high boost is often inadequate ignition coil output voltage capability. IE: weak coils. 1.8T's love them some freshy coil packs. There are tools to measure max attainable output voltage.

Secondly, if it is telling you overboost, it could be correct! Maybe 20 is too much boost. In that case, adjust your boost control so it never hits 20.