Low power - MAP/EGR testing

[gavin0268]

Hi there

I've got an Passat 1.9 TDi, 02 plate, AVF engine.

It's lost power from the turbo (or at least feels like it's in limp mode) - the only fault coming up is 17552 - Mass Air Flow Sensor (G70): Open or Short to Ground (intermittent), but the first thing I changed was the MAF! Previously got a coolant temperature sensor code, that's been replaced and the code's cleared.

From my post on the Passat board folk have suggested replacing the MAP sensor or EGR valve, but I was just wondering if there are any checks on these I can do through VAG-COM before replacing? Also maybe how to check that the MAF is OK that was fitted (was VW part)

Thanks for any ideas, the local garage are pretty hopeless at fault diagnosis!

Cheers

Gav

[gavin0268]

Hi again folks

Fair does - I spent the last few lunch hours trawling through the site, and got a lot of ideas - sorry for being lazy! Most answers are here if you know where to look

I've run the measuring blocks test which displays the MAF values, and EGR Duty Cycle (sorry, can't remember which one, just closed VAG-COM down). When driving the EGR sticks at 4.8% - is this an indication that the valve is shot, or does it reflect some other problem? If the EGR, is it a replacement job or is it worth removing it and giving it a good clean?

Thanks again

Gav

[saabsalltheway!]

hi
the measuring block group you used would be 044
they did have a problem with maf sensors readings should be around 180 to 350 i think
wouldnt hurt to take egr valve out and clean it
what vag com do you have as the latest will give you a guide to what the readings should be
hth paul

[gavin0268]

Hi Paul

Thanks for that

I'd changed the MAF first, and that made no difference - the readings look within the range though not sure how having a duff EGR would affect those readings.

Its VAG-COM release 4.09, so it does give indicative ranges - I think it said 35-50 or similar. So well out at 4.8! I was just wondering whether that indicates that the EGR is completely kaput or whether it was worth giving it a clean. I'd have thought it would have given some sort of variable reading if it needed a clean but I'm not sure how it works!

Cheers

Gav

[saabsalltheway!]

hi
egr exhaust gas recirculation valve
so if egr is stuck open no matter how wide it will recirculate thus engine will not draw air through maf
turbo will not spool up enough so loss of power
check and clean egr or if its broken you need to fit a new one
hth paul

[gavin0268]

hi
Sorry for long time to reply, can only work on the car on dry weekends!

OK, to summarise, I'vev replaced the MAF, coolant temperature sensor and most recently the EGR, with little effect on the performance. Have also tried putting the old MAF back in with no difference.

Have replaced all the vacuum hoses I can think of, checked the 3" hoses and they appear OK. The VNT mechanism is moving up and down as the car is turned on and off.

I've logged these measuring blocks - basically the MAF and EGR values seem to be static - MAF at 539, EGR at 4.8%. Second last reading (bold) is 3000 rpm in 3rd gear.

Any suggestions what to try next? MAP looks OK from the readings. N75 valve perhaps?

Thanks for all the help so far

Cheers

Gavin


Group A: '003

Time Engine speed MAF (specified) MAF (actual) EGR duty cycle
790-870 230-310 210-350 40-75%
/min mg/str mg/str %
0.76 1239 360 539 4.8
1.96 1113 545 539 4.8
3.16 903 810 539 4.8
4.36 882 585 539 4.8
5.56 1302 610 539 4.8
6.75 1722 755 539 4.8
7.95 2121 800 539 4.8
9.16 2520 785 539 4.8
10.36 2184 245 539 4.8
11.56 1869 850 539 4.8
12.76 2037 850 539 4.8
13.96 2184 850 539 4.8
15.15 2331 850 539 4.8
16.34 2478 850 539 4.8
17.54 2667 850 539 4.8
18.74 2835 850 539 4.8
19.94 2982 850 539 4.8
21.15 3150 830 539 4.8
22.34 3255 415 539 4.8
23.54 3213 395 539 4.8
24.74 3129 380 539 4.8
25.94 3024 365 539 4.8
27.14 2961 390 539 4.8
28.34 3024 705 539 4.8
29.54 3213 775 539 4.8

Group B: '010

Time MAF Atmos. pressure sensor Intake air press. Throttle
900-1250 2100-2600 100%
mg/str mbar %
0.01 539 969 1006.2 0
1.16 539 969 1088.1 27.8
2.36 539 969 1216.8 34.5
3.56 539 969 1240.2 0
4.76 539 969 1123.2 32.5
5.96 539 969 1380.6 42
7.15 539 969 1907.1 56.1
8.36 539 969 2351.7 60.4
9.56 539 969 2164.5 59.2
10.76 539 969 1240.2 34.1
11.96 539 969 1883.7 75.7
13.16 539 969 2234.7 78.8
14.36 539 969 2316.6 76.1
15.54 539 969 2398.5 79.2
16.74 539 969 2410.2 82.4
17.94 539 969 2340 83.1
19.15 539 969 2234.7 83.1
20.34 539 969 2269.8 82
21.54 539 969 2211.3 63.5
22.74 539 969 1298.7 29.4
23.94 539 969 1275.3 29
25.15 539 969 1263.6 27.8
26.34 539 969 1275.3 28.2
27.54 539 969 1357.2 39.2
28.74 539 969 1708.2 55.7

Group C: '011



Time Engine speed Spec. intake press. Actual intake press. D.cycleMAP 2850-3150 2200-2400 2100-2600 35-80 %
/min mbar %
0.37 819 1050.6 1006.2 19.9
1.56 1134 1244.4 1134.9 19.9
2.76 1134 1366.8 1251.9 19.9
3.96 819 1060.8 1146.6 19.9
5.16 1176 1264.8 1193.4 19.9
6.36 1596 1662.6 1532.7 33.5
7.55 1995 2111.4 2070.9 41.8
8.75 2394 2091 2340 61
9.96 2667 1081.2 1907.1 47
11.16 1827 2203.2 1415.7 26.3
12.36 1974 2264.4 2035.8 33.1
13.56 2142 2295 2281.5 44.6
14.75 2268 2315.4 2340 47
15.94 2436 2335.8 2421.9 53.4
17.14 2604 2346 2410.2 57.4
18.34 2793 2346 2281.5 55
19.54 2940 2346 2246.4 55.4
20.74 3087 2346 2293.2 57.4
21.94 3255 1407.6 1836.9 72.5
23.15 3213 1224 1275.3 52.2
24.34 3150 1224 1287 51.8
25.54 3066 1213.8 1263.6 51
26.74 2982 1213.8 1263.6 50.6
27.95 2982 1417.8 1509.3 61.4
29.14 3129 1836 1930.5 67.3

[martin1810]

You can cancel out the effect of the egr by making sure it is closed and then pulling off the vacuum pipe and plugging it. (air tight). Have you done another code read. A faulty N75 valve usually gives a code. Long shot but have you checked the air pipe from the n75 valve that runs to the air filter. It looks like a vacuum pipe but is actually an air bleed pipe and must not be pinched or blocked.

[gavin0268]

Hi martin

Thanks for response

No new codes - just a MAF short to ground which has always been there - the local mechanic said to ignore this and I read on the Ross-tech instructions that these aren't a problem

How do I make sure the EGR is closed - do you mean the big shut off flap in the middle, i.e. hold that closed then plug the top? It is a new EGR so I'm interested to know what this will do (not being cheeky!) - won't it just kill the engine?

Will check that air bleed pipe for pinching, but don't think it was obvious as the EGR pipe runs alongside.

Have tried the online VW database (ensa?) but couldn't find my way aorund it to find any troubleshooting info - hopeless design!

Cheers

Gav

[gavin0268]

Hi again

I was getting confused between the N75 and the EGR control valve - they have almost exactly the same part number, and that's what I searched for on Google. Anyway, changed the EGR control valve, and no change ( I think I replaced that N75 pipe when I replaced all the other vacuum pipes, when it all started.

Think I'll have to give in and take it in to the garage. Problem is none of the local ones are that great, and I'm worried they'll just replace the turbo.

Would seized vanes through a code? The oil level was (just) below min when the problem started

To crown it all the exhaust just split in two on my T4!!!

Cheers

Gav

[martin1810]

A turbo fault should show as a fault code, usually a high pressure fault because the vanes stick at that point. IF you have a MAP sensor fault, which measures turbo pressure, a turbo fault might not show. The turbo actuator moving doesn't mean the vanes are free. If you are up for it, you could take off the turbo and give it a clean. The turbo could always be seized due to a lack of oil at some point....Lets's hope not.