low power alh tdi. none of the normal issues but still low power

Ok. I use this term alot. "Its not my first day" I love working on tdis, own several myself and have seen so many different things cause a low power situation but this one has me stumped.

Either myself or one of the shops it went to before it was brought to us has installed the following in an attempt to fix the issue:

There are no codes.

All vacuum lines tested, verified they are going to the right place and in good condition.

swapped in a new maf. Both old and new the readings drop to 280 as rpms rise for actual maf reading no matter what requested maf readings are. I am sure this is part of the issue but I have checked all the inlet piping, charge piping, intercooler, etc and have not found any leaks or obstruction. We also swapped on a downpipe with the cat removed just to make sure we didnt have a clogged cat.

The turbo was replaced because we could barely spin the impeller on the inlet side however that made no change even though the only code stored was a underboost code which has not returned but the car is still low on power.

I put in egr block off plates to eliminate a possible bleed off in the egr system.

I swapped in a known good N75 solenoid. Logging vagcom the duty cycle will stay at 24.7% even under WOT instead of cycling up to 70ish % and tapering off from there. If you unplug the maf duty cycle rises but not very quickly and it reaches requested boost but still no power. Lots of black smoke with maf unplugged and none plugged in. I swapped in a brand new maf and same results both plugged in and unplugged.

I have checked the air filter, air filter housing and "snorkel" for obstruction.

The fuel filter was replaced within the past few months according to the customer and looks brand new from the outside and the filter media inside is very clean.

The intake manifold was cleaned about 6mos ago and doesnt appear to have any substantial buildup. I very thin light coating of carbon on the inside but nothing that would cause a restriction

I had a spare immo defeated ecu for a personal project that I installed and still no change.

At this point the issue seems to revolve around a restriction limiting airflow at the maf which in turn is causing the ecu not to change n75 duty cycle and is making for a very slow car.

If anyone can shed some light on what I am overlooking or has a suggestion for a mvb I have not mentioned to look at please chime in.

Ive been working on tdis for years and this one has me stumped like no other so please feel free to say "hey stupid you forgot to check______! so I can fix this car and wear my dunce cap with pride for a few days.


Cheers.

67 views and not one opinion or suggestion. Does any body see something I am overlooking?

long shot but....are you sure no one stuffed a rag into air intake some where that was forgotten?
Did you verify complete timming by setting crank tdc, pinning ip and installing cam lock, especially cam?

Pull the valve cover and inspect the cam and valvetrain components for wear.

N75 wires? Or maybe that little white one-way vacuum valve?

Run logs for requested versus actual fuel and boost. I suspect there's an obstruction that you've not yet identified (anti shudder valve, down pipe gasket, intercooler, something) but low fueling from a failing pump would cause this symptom, too.

An obstruction is what I keep coming back to. Injection pump is basically brand new from a reliable source. The car feels like it has a rag in the intake so next step is to check there and look at the valvetrain. If this is a worn lobe situation like a BRM cam I will be shocked. I have personally only had one bad ALH cam but we've had months where we did 3 brm cam replacements. I will report back once I get a chance to dig deeper.

well damnit. no obstructions anywhere. none. nada. zip yet still no power. The only thing I can't figure out now is why the n75 duty cycle goes straight to 24.7% when you hit the throttle. Its the reading I see on all of the alh cars we have at the shop at idle and when you let off throttle but this one will not move off 24.7% at all. I think the turbo is the restriction as the vnt is being commanded to run bare minimum pressure. I swapped in a map sensor with no change.

check that your anti-shudder valve stays fully open when running. Mine had a faulty solenoid and was closing a little bit, choking out the airflow causing low power - no codes.

Do you have proper voltage at the MAF connector?


Pin 2: 12v
Pin 3: 5v
Pin 5: Ground (1.5 Ohms or less to ground)

I know i currently have a check engine light on for my fuel cutoff solenoid, and it has really low power above 2,000 rpm.

I just did a few more vagcom logs. Car will make boost, n75 duty cycle will move with the maf unplugged. With the maf plugged in I get no boost and a 16683 boost pressure regulation negative deviation. Also whether the maf is plugged in or not I get little to no black smoke. I feel I need to dig into the fuel level sender unit in the tank and see if a fuel line has collapsed or clogged. I have already inspected and drained the fuel filter which looks brand new(filter media inside is still white, fuel that came out is clear. I may put a new one in just for peace of mind. if any of this sparks an idea or you have seen the same symptoms please feel free to chime in.

Gerich@apex-tuning said:

I just did a few more vagcom logs. Car will make boost, n75 duty cycle will move with the maf unplugged. With the maf plugged in I get no boost and a 16683 boost pressure regulation negative deviation. Also whether the maf is plugged in or not I get little to no black smoke. I feel I need to dig into the fuel level sender unit in the tank and see if a fuel line has collapsed or clogged. I have already inspected and drained the fuel filter which looks brand new(filter media inside is still white, fuel that came out is clear. I may put a new one in just for peace of mind. if any of this sparks an idea or you have seen the same symptoms please feel free to chime in.

Click to expand...

If you are getting no boost with the MAF plugged in I would suspect some sort of a MAF problem. If you have VAGCOM/VCDS I would suggest you log MAF and MAP requested and actual during a run up the gears. My suspicion is that your MAF is underreporting and you will see that in the logs. When the MAF is unplugged the ECU will assume a default figure for the missing data and from your description I assume the default is greater than what your MAF is reading.

Dave

http://wiki.ross-tech.com/wiki/index.php/16683/P0299/000665
has some good ideas.
Also, like you said, restricted air flow. Check the snow screen (air box inlet), air filter

I had a simular problem on a ATD engine..

Low on power, so replaced all filters, stat and the temp sensor..

Nothing worked..

Took the battery leads off to do something, put then back and hey presto i had power again..

Must have reset the ECU..

I understand that the maf readings are in part the issue but I have tested both a new Bosch maf aswell as one off my brothers 2002 alh tdi. Same readings with all 3 mafs. the n75 solenoid duty cycle and the maf readings correlate and both remain lower than expected. I thought maybe the n75 was stuck at 24.7% because the actuator was frozen but when i run basic settings for boost control the duty cycle goes from 0-100% no problem and the actuator moves smoothly thru its range of motion.

The car drives like it has a massive air restriction or isnt getting enough fuel but I have checked from the snow screen in the airbox, the inlet pipe past the maf, the charge pipe from the turbo to the intercooler, the intercooler to the asv, blocked off the egr, pulled and cleaned the intake manifold, replaced the turbo, and installed a test pipe with no cat. I have found no restrictions in any of these items. The vacuum hoses to the egr and n75 solenoids have been replaced and triple checked for proper routing. The injection pump was replaced with a reman unit from Bora Parts. The injector nozzles were sent to a local diesel injection shop and are in good working order. I have checked for proper voltage and ground at the connector to the maf and n75 solenoid. I swapped in a known good MAP sensor just for good measure. no dice there. I have driven the car and looked at every measuring block that could have anything to do with anything about low power and the n75 duty cycle is the only reading I cant explain why it does what it does. I have disconnected the battery a few times and even done a cap discharge. I swapped in a spare ecu and all the same readings on all the same sensors. Is there anything I should look at that I have overlooked?

I know you sent the nozzles and had them checked...but my '03 TDI Wagon had huge power lag issues and lots of smoke until I replaced nozzles with 520's. I have a Stage 1 tune and an EGR delete, but it's stock other than that. Installed new nozzles and the car came to life, very little smoke and increased fuel economy. Replacing nozzles is fairly cheap compared to what's already been done. Mine felt like someone was pinching the fuel hose and the car just would hit a wall at just under 3000rpm.

My two cents.

Its not wise to throw parts at it when you see an obvious issue, the maf! Fix that obvious issue before throwing injectors etc at it. Even without turbo you should be getting 480 mg/s maf at 1 bar map (atmospheric). Man, I should be a troubleshooter consultant, I face the same iffy diagnosis in the electrical field lol.

The n75 will stay low, trying to increase airflow but maf stuck at 280.

So swapping mafs no go. Does the maf value even change a bit? If not, I say the maf wiring may have a gnd or open OR ecu itself is dead where it senses maf input.

Also check the anti shudder valve (by egr) is fully open and can move freely.

If maf numbers change some with boost,
then look for intake clogging or cam/valves timing.

Also if the maf readings do change, another possible issue could be that the egr is stuck open. Easy to check: pop off the rubber 90, with flashlight and mirror look and see if the shaft is full down (covering the hole). Its also a quick way to check clogging, but not a conclusive way.

I have swapped both the ecu and maf with known good components. I dont think the injectors are the issue. The maf readings fluctuate from 440 at idle but drop and flatline at 280mg/str at wot up to 4000rpm and with that reading the n75 duty cycle sticks at 24.7% all the way up. If I unplug the maf the ecu shows 550 and still feels very low on power but the ecu will slowly creep duty cycle up to 40-50% and meet the ecu's requested boost. With the maf plugged in this never happens and i get the boost negative deviation code. So I can get the boost eventually but there is no fuel to go with it. Even with the maf unplugged there still really isnt an excessive amount of smoke and the car stiil feels very slow. Again no fuel. So if the injection pump is good, the injectors have been checked, the fuel pickup screen has been checked along with the fuel filter what have I overlooked. i guess i am going to check the fuel line itself for pinches under the car and blast some compressed air from the line at the fuel fitting tank to the fuel filter inlet. Maybe there is some schmegma stuck in the line? All the wiring to the maf has been checked and as far as i can tell everything has proper voltage, ground and continuity.

You mentioned blocking off the EGR. Have you replaced the N18 with a new/known good one or blocked off all of it's vac lines? Just wondering if you have a vac leak by way of the N18 itself?

Weird, it shouldnt drop to 280 at higher rpm.... It seems like a clogged intake if you put a block off for egr.
At idle you should get 480, not 440 (wo egr on).

Good point nw, with vac gauge check vac at the main line from vac pump.. Id say look for 22 in hg min
Then w vac gauge, t into line that feeds n75.... Then plug the vac that feeds the n18, test again... do same for vac ball line and the asv solenoid.
Hopefully its just a leak but the maf readings make me think its the intake clogged.

Ever find out the issue!!!??? I'm having the exact same problem with mine. With the original maf the reading will be around 4ish and then upon acceleration it drops down to about 280mg! With a different maf from a friend I get good results but then no fuel, it surges and gets mad. Does t throw any codes. So with my original sensor, I watch my MAP reading drop. If I let off the throttle it go's back up. Im just installing a boost gauge now. everything is good to go minus whatever the F is causing this

Check your egr... if the valve spring is weak it can open under high exhaust manifold pressure and lower maf readings... (exhaust gas displaces fresh air)

Removed egr and asv, no cat while I'm troubleshooting. Swapped injectors, actuator starts to move between 3-5 and hits stop right about 18 hg. Pulled actuator off and got some soot out of the weep hole, but holds vacuum great. The lever on the turbo moves easily with arm off. All new hoses routed correctly, even intentionally hooked em up different ways to try. N18 doesn't seem to make a difference. New fuel filter. Basically everything the OP had done I've done. I pulled sender out of tan and drilled out the check valve.. I'm getting frustrated

MAF wire connectors have been known to cause flaky behavior. Not sure how one goes about eliminating them as a problem source (other than wire in new connectors), but some have managed to get better behavior by cleaning and applying dialectic grease.

Worth a shot while waiting on an answer from the Mother Ship...

The guy I bought it from had it greased pretty good, I actually cleaned most of it off so there's a normal amount yet. I had to run and get a tap to finish boost gauge install and was searching for chafeed wires for a while beforehand. See what happens I guess

Without egr or asv to limit fresh air through maf, you should never go much lower than maf 400 or so on our 1.9 L (unless you're at pikes peak lol).

Definitely weird... check your grounds?

Yeah I checked all the wiring out, whatever they wrap wires in is a real sticky pain! I think I'm going to adjust the wiper arm in the QA and hopefully eliminate the shudder. I can deal with slow for now but that drives me nuts

Check the grounds below battery and ground strap engine to frame.

Try to reseat the ecu connections.

I think it's electrical because you see both maf and map drop weirdly. If you can log group 10 which has maf and map, I can calculate whether it's really correlated or wildly wrong. (ex: 500mbar map would be around 240 maf -- 480 maf for 1000mbar -sea level on 1.9 tdi.)