VAG-COM Log - Boost Issue 2.5TDi - N75?

AlexGSi2000

Well-Known Member

VCDS Map User

Joined

Feb 14, 2012

Messages

1,467

Reaction score

202

Points

63

Location

Liverpool

• Feb 19, 2012

• #1

Hi,

Some of you may have seen my post a few days ago about surges / loss of boost on my A4 2.5TDi 180.

Basically, if I put my foot down (for example 1500rpm in 4th) I will feel the boost build, then it will drop, build again and drop at certain points throughout the rev-range, usually two to three times.

I have added the vag-com log which was a 4th gear pull - just wondering if anyone can tell if the information given points to a particular problem?

I have a new N75 on order from Audi but would just like to see what you guys think from the log? - Many thanks!

Group A:	'010				Group B:	'011				Group C:	'008
	MAF	Atmo. press	Intake press.	Throttle		Engine speed	Spec. intake press.	Actual intake press	N75 duty cycle	Engine speed	IQ driver	IQ rpm(torque)	IQ MAF(smoke)
TIME	>750		1900-2300	100%	TIME	2900-4000	1900-2300 mbar	1900-2300 mbar	TIME	2800-3500	>50	42-47	>48
STAMP	mg/str	mbar	mbar	%	STAMP	/min	mbar	mbar	%	STAMP	/min	mg/str	mg/str	mg/str
6.74	651.5	1020	1570.8	100	6.1	1694	2121.6	1305.6	80.5	6.42	1670	69.3	43.6	32.9
7.79	773.2	1020	1958.4	100	7.08	1717	2131.8	1693.2	74.6	7.42	1740	69	45.5	40.8
8.87	867.4	1020	2315.4	100	8.15	1810	2162.4	2091	56.4	8.51	1833	68.4	45.5	46.7
9.94	902.8	1020	2468.4	100	9.23	1902	2182.8	2366.4	45	9.59	1949	67.8	45.2	50.8
10.9	706.5	1020	1948.2	100	10.26	2018	2193	2295	49.3	10.58	2042	67.5	45.2	40.2
11.86	726.1	1020	1978.8	100	11.22	2111	2193	1938	56.4	11.54	2134	67.1	45.2	40.8
12.82	792.9	1020	2162.4	100	12.18	2181	2203.2	2019.6	53.3	12.5	2204	66.5	45.2	44.2
13.8	816.4	1020	2305.2	100	13.14	2274	2203.2	2244	45.4	13.47	2297	66.2	45.5	48.6
14.87	726.1	1020	2101.2	100	14.15	2366	2213.4	2274.6	40.2	14.51	2390	65.9	45.5	44.2
15.95	761.4	1020	2162.4	100	15.23	2459	2223.6	2060.4	49.7	15.59	2482	65.6	45.8	43.6
17.01	785	1020	2295	100	16.31	2552	2223.6	2223.6	43.8	16.65	2575	65.3	45.8	46.4
18.02	737.9	1020	2152.2	100	17.34	2645	2233.8	2203.2	46.6	17.69	2668	64.9	45.8	42
19	745.8	1020	2233.8	100	18.34	2738	2233.8	2213.4	44.6	18.68	2761	64.6	46.1	44.2
19.96	741.8	1020	2233.8	100	19.32	2807	2233.8	2223.6	46.2	19.64	2830	64.3	46.1	43.6
20.92	730	1020	2244	100	20.28	2877	2244	2244	44.2	20.6	2900	64	46.1	43.3
21.86	730	1020	2244	100	21.24	2946	2244	2233.8	43.8	21.54	2970	64	46.1	42.7
22.82	730	1020	2254.2	100	22.18	3016	2244	2244	43.4	22.5	3039	63.7	46.1	43
23.82	718.3	1020	2233.8	100	23.14	3086	2244	2244	41.8	23.47	3132	63.4	46.1	42
24.89	714.4	1020	2254.2	100	24.17	3155	2244	2254.2	41	24.53	3178	63.4	46.1	42.4
25.95	702.6	1020	2244	100	25.23	3225	2244	2233.8	41.8	25.59	3248	63.1	46.1	41.4
27.01	702.6	1020	2244	100	26.31	3294	2244	2254.2	39.8	26.65	3318	63.1	46.1	41.7
28.05	694.7	1020	2233.8	100	27.37	3364	2244	2233.8	41	27.73	3364	62.7	45.8	40.8
29.02	694.7	1020	2254.2	100	28.38	3410	2244	2244	40.2	28.7	3434	62.4	45.8	41.1
29.98	682.9	1020	2233.8	100	29.34	3457	2244	2244	40.2	29.66	3480	62.4	45.8	40.8
30.94	679	1020	2254.2	100	30.3	3503	2244	2233.8	40.6	30.62	3526	62.1	45.8	40.8
31.9	682.9	1020	2244	100	31.26	3550	2244	2244	41.4	31.58	3550	62.1	45.5	40.2
32.86	679	1020	2244	100	32.22	3596	2244	2254.2	40.6	32.54	3596	62.1	45.5	40.2
33.91	675.1	1020	2254.2	100	33.2	3619	2254.2	2254.2	40.2	33.55	3642	61.8	45.5	39.8
34.99	671.2	1020	2254.2	100	34.27	3666	2254.2	2254.2	40.6	34.63	3666	61.8	45.2	39.8

 

A

adamss24

Registered User

Joined

Jul 3, 2007

Messages

4,543

Reaction score

421

Points

83

Location

London

• Feb 20, 2012

• #2

Get it to a good mechanic mate, i don't fix cars by reading boost logs but by driving them and checking the components involved. Start with the cheapest fixes first: clean the turbo, a new air/fuel filter, then move on to the next more expensive item. We all try and save a few pennies but in the long run a decent mechanic could save you loads of dead brain cells !

 

N

nice-one-bruv

Registered User

Joined

Jan 10, 2011

Messages

13

Reaction score

0

Points

1

Location

Hemel Hempstead

• Feb 20, 2012

• #3

Hi mate,
ive had the exact same problem with my 2.5tdi, and have changed the n75, thrust sensor, and another 2 others, plus the intercooler and the vacuum pump. the problem is still there and after having it checked it came down to the one thing i didnt want it to be, needs a new turbo

 

A

adamss24

Registered User

Joined

Jul 3, 2007

Messages

4,543

Reaction score

421

Points

83

Location

London

• Feb 20, 2012

• #4

nice-one-bruv said:

Hi mate,
ive had the exact same problem with my 2.5tdi, and have changed the n75, thrust sensor, and another 2 others, plus the intercooler and the vacuum pump. the problem is still there and after having it checked it came down to the one thing i didnt want it to be, needs a new turbo

Click to expand...

Did anyone messed about with the turbo's actuator ? I would love to have a look at your car and run a few tests...

 

AlexGSi2000

Well-Known Member

VCDS Map User

Joined

Feb 14, 2012

Messages

1,467

Reaction score

202

Points

63

Location

Liverpool

• Feb 21, 2012

• #5

Thanks for the advice again adamss - I have posted the log on a few other forums, a few people have said that the MAF looks like its holding things back.
I spent a few hours going over the car last night, all boost and vac pipework is ok with no leaks - Will replace the MAF and N75 towards the end of the week - if that doesnt rectify things then I will be looking into the turbo.

 

marktdisport

Registered User

Joined

Jul 14, 2011

Messages

1,195

Reaction score

15

Points

38

Location

mids

• Feb 21, 2012

• #6

give it a blast with the maf unplugged m8.....