Unexplained power limit during hard acceleration

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
As of August, I'm the proud owner of my first TDI - a 96 Passat wagon. I'm very pleased with the car but it has one odd problem under hard acceleration.

In normal unhurried driving I'm always upshifting probably well before 3000 RPM. But if I push it hard coming up an on-ramp it will frequently "hit the wall" somewhere between 3000 and 3500 RPM. It will be accelerating nicely and then all of a sudden it refuses to get any faster. It won't lose any RPM, but it acts very much like a governor kicks in. The sudden capping of RPM can be pretty abrupt sometimes.

Doesn't happen all the time but a lot of the time. Seems to be most prone when pushed the hardest. If I work it up a little slower I can get to 4000 RPM with no hiccups and I've never tried to push it higher.

The previous (original) owner reported a probably related problem with occasional power loss with the cruise on at high speed. He would disengage the cruise and the clutch and let the RPM down momentarily and then stomp on it and it would recover and he'd re-engage the clutch/cruise. I think I had this happen to me once on a long hill at 70+mph. But the acceleration problem is very frequent. When I hit the wall I just upshift and it is fine in the next gear. Previous owner had a lot of basic things checked and even replaced the wastegate solenoid but never figured anything out.

My first thoughts have been around the turbo end of things as well. Is there some kind of overboost protection that maybe the sensor is a little too sensitive and opens the wastegate a bit early? While we're on the subject - is there a popular (and relatively inexpensive) manifold pressure gage that can be installed. I'm just generally curious to know how much boost is going on and when.

Otherwise the car is still going strong at 215K miles. Can't argue with a car that can take a family of 4 and all their junk on a road trip and get 46-47mpg. Still runing dino-diesel but plan to start using B20 soon. Just used PowerService fuel additive the last two tankfuls (1000mi+ each!) with no improvement other than apparently cleaning out some soot which showed up as a light spot on the garage floor under the exhaust pipe which was wiped up and has not reappeared.

Thanks for whatever help anyone can offer to figure this one out.

Mark
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
When was the fuel filter last changed? Might be due.

Also - any smoke when this happens? Clogged intake will limit your upper-rpm power. Clogged air filter would also. Make sure intake is clean.

Another possibility is the nozzles. At 215K, they are a bit tired. Poor spray pattern may influence this.
 

gt

Veteran Member
Joined
Mar 14, 2001
Location
Sedalia,MO. USA
hits wall

Do a output test with VAG-COM & check for bad wastegate valve on firewall. If it doesn't click it is either weak or bad. It can also be MAF sensor. Unhook & drive if it revs up past 3500 it is a bad MAF. Check all vac. lines & hose going to brake booster. gt Wastegate solenoid is on right frt fender, with red, blue vac. lines. How many miles????
 
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deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
filters and wastegate are all fairly new

Thanks for the replys so far. I checked the records from the previous owner. The fuel filter is barely a year old (about 20K miles) and the air filter only two months older. I'd have a hard time believing that either filter could cause such a sudden cut-off of power. You'd think it'd be a general loss of top-end.

The wastegate solenoid was replaced about 3 years ago. I'll check into these other things when I get a chance.

Anybody in northeast TN area have VAG-COM that I could check things with?

Per my original post, the car has 215,000 miles.

The one reply mentions injector wear. Is there a recommend replacement mileage?

Mark
 

paramedick

TDIClub Enthusiast, Vendor
Joined
Jul 29, 2001
Location
Versailles, Kentucky
TDI
2015 Audi Q5 TDI, 2000 New Beetle
The fuel filter change interval is every 20K. In any case, it's due.

Wastegate changeover valve (N75) is probably OK, but no guarantees. Most likely culprit is the need for all new vacuum lines. I recommend silicone, and preserve the color coding.

Nozzles are recommended for change at 100K miles. Replace them with a good set of Kermatdi/Bosio nozzles. Great quality. I stock the Kerma nozzles for installation.

If you care to jaunt up to see me, I can help you with your car. Lots of TN/NC folks do.

If you really want a boost gauge, some good prices at 42 draft designs. Google for website.
 
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jollyGreenGiant

Veteran Member
Joined
Feb 3, 2003
Location
MA
TDI
03 Golf TDI GLS ( my 5th TDI ), 03 Eurovan GLS - VR6 :(
Agree with everything above especially the new injector nozzles.

The injection pump pressure regulator might have something to do with the power loss as well...

Just so we're clear, it's not going into limp mode when this happens, correct?
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
jollyGreenGiant said:
Agree with everything above especially the new injector nozzles.

The injection pump pressure regulator might have something to do with the power loss as well...

Just so we're clear, it's not going into limp mode when this happens, correct?
How do I know it's going into "limp" mode? It all of a sudden just refuses to accelerate any further. A few times I've held the gas (fuel?) pedal down and it will maintain RPM, but just won't gain any more. Most of the time I know I've hit whatever it is and go ahead an upshift and it is fine after that.

This is not a "loss" of power, but a "limit" of power.
 

jollyGreenGiant

Veteran Member
Joined
Feb 3, 2003
Location
MA
TDI
03 Golf TDI GLS ( my 5th TDI ), 03 Eurovan GLS - VR6 :(
Limp mode is when the car is driving fine until the ECM determines the actual boost is outside of the acceptable window of requested boost. In an effort to save the turbo from an early demise from overboosting the ECM cuts back all its maps to a safe level to ensure the turbo won't overboost anymore. This is what's called limp mode. Once you hit limp mode, the power won't be restored until you shut the engine off and restart. This is also accompanied with a 00575 code and a MIL light usually.

If it's a lack of power just above certain RPM's with adequate power at all times under that RPM window you aren't having the limp mode issue...
 

jollyGreenGiant

Veteran Member
Joined
Feb 3, 2003
Location
MA
TDI
03 Golf TDI GLS ( my 5th TDI ), 03 Eurovan GLS - VR6 :(
Have you taken a look down the intake manifold lately?
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
jollyGreenGiant said:
Limp mode is when the car is driving fine until the ECM determines the actual boost is outside of the acceptable window of requested boost. In an effort to save the turbo from an early demise from overboosting the ECM cuts back all its maps to a safe level to ensure the turbo won't overboost anymore. This is what's called limp mode. Once you hit limp mode, the power won't be restored until you shut the engine off and restart. This is also accompanied with a 00575 code and a MIL light usually.

If it's a lack of power just above certain RPM's with adequate power at all times under that RPM window you aren't having the limp mode issue...
Thanks for the elaboration - I'm definitely not hitting "limp" mode. As soon as I back off on the power (while upshifting) it recovers just fine and will continue up the on-ramp and cruise at 70+. Never have check engine light or had to shut the car off.

I'll be checking vacuum lines and replacing the air and fuel filters etc. May run some biodiesel through to help loosen some crud before changing the fuel filter (just tanked up so gotta run 1000 miles first!). Also will plan on new injector nozzles sometime soon.
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
jollyGreenGiant said:
Have you taken a look down the intake manifold lately?
Only thing I've done to the car so far is change the oil (used about half a quart in 5000 miles which I assume is reasonable at 215K). What exactly would I be looking for when peering down the intake, aside from general cleanliness?
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
Update: Intake manifold is GUNKY!

jollyGreenGiant said:
Have you taken a look down the intake manifold lately?
OK, last night I had time to poke around a little. Pulled the intercooler air return line from the intake manifold and peered in with a worklight. You can't see in very far. But from what I could see, there are definitely some areas of significant buildup, though no huge blockages.

This AM, an e-mail reply from the original owner confirmed that the intake has never been removed. So at 215K miles, I'd say it's time, and the most likely suspect. The car DOES smoke a bit when you really stomp on it, which agrees with a restricted air condition. I probably won't have time to do the job until between Christmas and New Years, but will followup with the results when I get it done.

Also discovered, between rereading the TDIclub FAQ and in poking around that the car is just old enough (8/96) to have the infamous supplementary fuel injector on the exhaust. A while back my wife and I had to drive separately to something and I followed her home and noticed a little blob of smoke every time she pulled out from a stop sign, even though the car was fully warmed up. So that may explain that!

Thanks everyone for your help so far!

Mark
 

jollyGreenGiant

Veteran Member
Joined
Feb 3, 2003
Location
MA
TDI
03 Golf TDI GLS ( my 5th TDI ), 03 Eurovan GLS - VR6 :(
When you end up connecting a VAG-COM to it, make sure to check the ECM number field, it'll tell you if it's a GQ suffix ECU or not, if it is then you have the recall performed already. The recall didn't remove the injectors, it just put in an ECU that doesn't choose to use them.

The smoke puffs you speak off could be unrelated to the supplementary injectors.
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
jollyGreenGiant said:
When you end up connecting a VAG-COM to it, make sure to check the ECM number field, it'll tell you if it's a GQ suffix ECU or not, if it is then you have the recall performed already. The recall didn't remove the injectors, it just put in an ECU that doesn't choose to use them.

The smoke puffs you speak off could be unrelated to the supplementary injectors.
Thanks for the extra info. I doubt my car has the updated ECU, but will confirm when the occasion arises to use VAG-COM. Were there any improvements in the updated ECU or did it just remove control of the supplementary injector?

The FAQ (section 7e, first paragraph) says that the service bulletin calls for a new ECM and if necessary, replacing injectorS (plural - apparently engine injectors, not the extra exhaust injector). Then it mentions "this failure" but does not say what the exact failure was, or what determined if injectorS replacement was necessary.

The second paragraph then speaks of smoke when pulling away from a stop as being at least a related problem and only then brings the supplementary injector into the picture. Then talks about VW having a hard time to get early cars to pass emissions and thus the "expensive replacement components listed above" (apparently refering to new ECM and injectorS in the first paragraph).

Anyhow, if there is an improved ECU or engine injector for my car I'd like to know about it. Maybe somebody can shed more light on this and get the FAQ clarified.

Will see if smoke puffs quit when I disable the injector! Certainly could be other things too, but that sure clicked when I read that section of the FAQ.
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
Update 2: A little better after just diddling with it.

Had to go out on some errands this afternoon and played with it some where the road situation allowed. Had a harder time making it act up - got it up to 4000 a couple times pushing it pretty hard. Seems like it never happens in second but will in 3rd. 3rd is a pretty big jump from 2nd and 2nd is pretty low and hard to work the engine real hard as far as total power needed.

Finally had a long, fairly steep hill on a back road and pulled out easy in first and got into second like I'd be when turning onto an onramp. Then punched it and got 4000 in second OK. Third capped at about 3250 and I had plenty of hill left, so let it back down near 2000, I think, and punched it again. Got to about 3500 this time. Let it off and punched it a third time and got it to 3750. Hitting whatever the limit it is was a little gentler than earlier times too.

Don't know how just fooling around removing the air pipe from the intake manifold and putting it back would help any. I wiped a little oily stuff out of the intake opening and the connecting hose, but thats all I did. Only other difference is that I left off the big plastic engine cover until I can clean the manifold. Also, when I was messing with the air filter box, I found one of the 4 clips undone so they're all now clipped.

But the problem is still there, just not quite as bad, so we'll see what a good intake cleaning will do when I have time.
 
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jollyGreenGiant

Veteran Member
Joined
Feb 3, 2003
Location
MA
TDI
03 Golf TDI GLS ( my 5th TDI ), 03 Eurovan GLS - VR6 :(
Don't foget about a set of new injector nozzles. I guarantee that they'll be a welcome addition, they may entirely fix the issue based on how bad the old ones were. At 215K on the ones in there now, I would do this ASAP as engine damage ( rings, pistons, excessive soot buildup->bearings, etc ) can occur just from running old nozzles too long.

Typically these symptoms are a combination of things that just slowly happen over time... You're on the right track though.
 

le_kid

Veteran Member
Joined
Apr 5, 2004
Location
Mullaloo, Australia
TDI
Landcruiser HDJ100R (it's a turbo direct injection...)
deezulmark said:
Thanks for the elaboration - I'm definitely not hitting "limp" mode. As soon as I back off on the power (while upshifting) it recovers just fine and will continue up the on-ramp and cruise at 70+. Never have check engine light or had to shut the car off.
If you have the BK ECU, then you don't have to switch off the engine to quit limp mode, only raise right foot for a second!
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
Limp mode

le_kid said:
If you have the BK ECU, then you don't have to switch off the engine to quit limp mode, only raise right foot for a second!
Interesting! Thanks for the info.

OK, how do I know what version of the ECU I have (without VAG COM)? The car has an 8/96 build date and I'm pretty sure the original ECU. I'm still doubtful that I'm hitting limp mode. The check engine light never comes on and it will continue to pull at the RPM it tops off at. Power/RPM hits a limit, but there is no sudden loss at the limit. It will still be pulling up a steep hill at 3500RPM in 3rd gear - just can't get it to 4000. I'll have to run that hill a couple times more and work it up with a little less than full pedal.

Hoping to get new fuel and air filters this week. Then clean the intake manifold after Christmas.
 
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Black_Brodie

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Joined
Jul 28, 2006
Location
Ontario, Canada
TDI
1998 Jetta
I beleive that I was/am experiencing the same problem as you. I found that the car will come out of safe mode when you turn off the ignition and restart the car, though the CEL may still be on.

The code I got scanned off my car indicated a blockage in the intake, which I believe would be in the EGR, though I have not checked yet.
 

quantum_tdi

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Joined
Sep 14, 2004
Location
Seattle, WA
TDI
R320 CDI, '96 B4V (for sale)
le_kid said:
If you have the BK ECU, then you don't have to switch off the engine to quit limp mode, only raise right foot for a second!
I was just going to say that is my experience with limp mode... I'm having the same problem as well. It literally feels like it hits a wall. I cleaned the intake to be sure, but it looks like I'm going to have to dig further on this too.

Keep the information flowing, I'm soaking it up even if others aren't!

cheers,
Kyle
 

fastvicar

Veteran Member
Joined
Aug 11, 2003
Location
Lancaster, PA, USA
TDI
1996 Passat, Indian Red
deezulmark said:
OK, how do I know what version of the ECU I have (without VAG COM)?
The ECU should have a sticker on it that will tell you whether it's a GQ or BK. The ECU is buried on the firewall of the passenger's side. It will take you 10-15 minutes to pull it out the first time. Two minutes any time after that.
 

jjasperson

Well-known member
Joined
Oct 30, 2006
Location
Temple, NH
TDI
2004 Jetta GLS PD
Overboost?

Well, not that I'm an expert on this, but it sounds like you're hitting an overboost condition. You've mentioned a number of times that if feels like it hits a wall, which sounds to me like your turbo has been disabled by the ECU. I have a similar problem with my '04 PD when driving way past the speed limit, but if I bury my foot into it for too long in 5th gear, it'll overboost. It definitely will continue to run, but it's got no juice past 3500-4000 rpm and DOES NOT pull at all.:(

As le kid stated earlier, if you have the BK (I don't know this for a fact) ECU, then you'll hit limp mode without ever knowing it...at least not without a VAG-COM.

However, with all that stated, it sounds like your car could definitely use some maintenance with respect to new nozzles, intake cleaning, IC cleaning, etc.

Good luck!!!:)
 

auto

Active member
Joined
Oct 6, 2006
Location
NJ
TDI
jetta
I have a 96 passat that was running fine.Going to work today I noticed a major loss of power problem that wasen't there the last time I drove the car.I read through this post and tried to get a trouble shooting game plane together.What would be the most common problem for a instant loss of power like this.
 

paramedick

TDIClub Enthusiast, Vendor
Joined
Jul 29, 2001
Location
Versailles, Kentucky
TDI
2015 Audi Q5 TDI, 2000 New Beetle
auto said:
I have a 96 passat that was running fine.Going to work today I noticed a major loss of power problem that wasen't there the last time I drove the car.I read through this post and tried to get a trouble shooting game plane together.What would be the most common problem for a instant loss of power like this.
Vacuum tubings, N75, fuel filter
 

deezulmark

Veteran Member
Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
Fuel and air filters help a little...

Well I only had time to replace the fuel and air filter over Christmas break. NAPA is usually pretty good, but their computer had the wrong number and gave me the wrong fuel filter. Gave the Bosch number to Autozone and they came up with right one, but had to order it in. Called the VW dealer and not only was it in stock, it was about 50 cents cheaper.

Had fun getting the car to run with the new filter. Had pre-filled the filter as much as I could, but after it was in the car and it wasn't wanting to run, I found I could get more fuel in the filter and finally it ran.

The power limit seemed a little less with the new filters, but not much better. I did discover along the way though, that when it hits the wall, all you have to do is lift your foot a little and then push it back to the floor and it will recover and make it to 4000 RPM. Once or twice, if I left my foot in it, it would continue to accelerate, but just more slowly after hitting the sudden drop off of power.

Seems like it will always make 4000 RPM in 2nd. Will now usually get to 3500 in 3rd and often a little higher. 4th gear it has more trouble, but haven't tried it much because at 4000 RPM in 4th, it's going way faster than I ever really want to be going!

Next step - cleaning the intake! (see next post)
 

deezulmark

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Joined
Jul 18, 2006
Location
Elizabethton, TN
TDI
96 Passat Wagon
The dirty deed is done!

Well over the weekend I finally got to the intake manifold. The FAQ spells out the procedure very well and I had no major difficulty.

The previous (original) owner confirmed that it had never been done and after 217K miles, I figured it'd be pretty bad. Well it wasn't nearly as bad as the photos in a number of related threads. In fact the upper end wasn't bad at all. The individual ports going into the head were the worst - but probably only 5% blocked. Even so, it was still amazing how much gunk I got out though - fully filled an 8 ounce tomoto sauce can.

I also rinsed out the intercooler per the adjacent procedure in the FAQ. Before filling it with diesel (since I didn't have Kero handy) I pulled the hose off the bottom and had a couple ounces of oil run out. I think I will do this everytime I change the oil from now on (yes I did see the mods for the CCV). Then when I tried to fill it, I had fuel come running down the outside of the pipe and thus discovered the reason I've lately been finding a few drops of oil under that corner of the car. The section of pipe that drops down to the intercooler (next to the battery) had a hole, about 3/16" or bigger! So all the oily air coming through the turbo has been blowing out there and the oil has been running down and dripping. Not to mention costing me some boost. So I epoxied the hole shut and wrapped it with electrical tape. But there's a lot of erosion on the outside of the pipe, so will be calling the dealer this week to see about a new one.

Got it all back together and went for a test drive. After seeing how little real blockage there was, I was not surprised to find only subtle improvements. And overall the car had been driving pretty well, so how much better could it actually get?

Seems like it MIGHT be a little peppier just general driving. Hard to say - a very subtle thing. Off the line full tilt, it doesn't seem to pull any more strongly above 3000, but now when going up my test hill, it will usually pull close to 4000 RPM in 3rd gear if not all the way to 4000. Still has a little trouble making it to 4000 in 4th gear, but I don't expect to be needing to do that very often! So the extra airflow has obviously helped a bit.

Of course peak HP is less than 4000, so why push it further than about 3700 anyhow?

At this point I don't really have any complaints, but am still curious why it has this power limit. It's a lot better than it used to be, but it's still there. Any other things I can check?

Next step is new injectors.

Thanks again to the many that responded about this issue.

Mark
 
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