98 TDI No power, no boost, becoming dangerous

[OldSchoolFresh]

Well my 98 Jetta TDI has been really underwhelming lately. It seems that in December that the power output has been decreasing gradually. Now in January my car doesn't want to rev past 2000 when cold and not over ~2600 when at normal operating temperature, as well boost pressure seems to top out at about 5 psi. When idling and I rev it a bit it seems to sputter or misfire at about 2000 rpm, but idles perfectly. I checked with my VAG com and boost pressure is definitely low. I suspected the N75 valve so I replaced that with a new one but still no change at all, and wasn't the N75 supposed to click all the time when the engine is running, it's silent for me.

It's gotten to the point where I can out accelerate a semi trailer or a city bus so it's getting hazardous now. Any help would be great. Oh and the air filter is clean, the fuel filter has about 10,000 kms on it and I always fill up with V-Power diesel. The car starts fine in cold temperatures without being plugged in but just no performance at all.

 

[PaPa Bulldog]

Well my 98 Jetta TDI has been really underwhelming lately. It seems that in December that the power output has been decreasing gradually. Now in January my car doesn't want to rev past 2000 when cold and not over ~2600 when at normal operating temperature, as well boost pressure seems to top out at about 5 psi. When idling and I rev it a bit it seems to sputter or misfire at about 2000 rpm, but idles perfectly. I checked with my VAG com and boost pressure is definitely low. I suspected the N75 valve so I replaced that with a new one but still no change at all, and wasn't the N75 supposed to click all the time when the engine is running, it's silent for me.

It's gotten to the point where I can out accelerate a semi trailer or a city bus so it's getting hazardous now. Any help would be great. Oh and the air filter is clean, the fuel filter has about 10,000 kms on it and I always fill up with V-Power diesel. The car starts fine in cold temperatures without being plugged in but just no performance at all.

OldSchool, sounds exactly like the problems I was experiencing a few months ago. I opened up the hood, and replaced every vacuum line possible. Two to the turbo, the ECM line, the one going to the EGR, the other one coming off the N75 Solenoid, the brake booster, etc...etc...I didn't use pretty silicone hose like posted about in the forums, but if I had to do it again I would. If you want to go that route do some searching here, and you will find it. Do you have access to VAG Com? oops just saw you did my bad! I wasn't so lucky. Is your check engine light on? When I had these issues I had a " Charge pressure deviation " code, so I knew my turbo wasn't getting full boost. I could push the car up to a bit, and then SLAM!!! the power would stop, and it would go into limp mode. I could cycle the key on and off, and it would refresh the ECM, power was suddenly back!!! Yeah, but annoying to have to do that.

I lifted the car, and rigged an air nozzle up to the blue turbo hose. I verified that the waste gate actuator rod moved. As I was applying air to the blue hose I heard a POP!!!, and that must have been the release of oil, and crap from the diaphragm. That did it for me. You may have more constrictions in the intake system.There is always pulling your intake to see how much soot is built up. And then you can have a buddy with VAGcom change the duty cycle of your EGR Valve, so that you wont ever have to clean it again

Anyhow hope this helps it sounds exactly like my situation. I think you will benefit greatly by changing vacuum lines, and verifying that your wastegate rod moves freely. If it doesn't apply penetrant oil, and go out for a beat while getting the turbo hot. That may free things up.

I hopefully can get my car back tomorrow. Waiting on parts...The shifter lever that sits under my clutch cables stripped out, and cause the Jetta not to engage gears. I could get it to budge in 3rd but not always. Hopefully (fingers crossed ) I get the parts tomorrow. I need a reverse switch too, and that's on order. Does anyone know if these are common wear items???

On another note how's the weather in Calgary???



Cheers,



Bart

 

[OldSchoolFresh]

I'm thinking that it may be a vacuum hose, but right now I'm going to replace the one going to the car computer as I heard that was a common source for problems. I think I will set the computer with my VAGcom so I won't have to clean the intake, but I've had the car nearly five years and this is a first time problem for me. Hopefully it's a simple fix, but I don't really have the time to diagnose problems since I'm going to university, so if I can't mend it... well it might be time to let the car go, the body is rusting incredibly fast anyways

Oh and I'm in Edmonton now, so the weather is similar just about ten degrees colder

 

[Canadian_Grizzly]

Replace the short one inside the computer...known problem, quick and cheap.

 

[PaPa Bulldog]

I'm thinking that it may be a vacuum hose, but right now I'm going to replace the one going to the car computer as I heard that was a common source for problems. I think I will set the computer with my VAGcom so I won't have to clean the intake, but I've had the car nearly five years and this is a first time problem for me. Hopefully it's a simple fix, but I don't really have the time to diagnose problems since I'm going to university, so if I can't mend it... well it might be time to let the car go, the body is rusting incredibly fast anyways

Oh and I'm in Edmonton now, so the weather is similar just about ten degrees colder

All in all it took me only about two hours to replace all lines, and to verify rod movement. replace all lines you will be happy you did, and power will be back. It's really not a time lagger job.

 

[OldSchoolFresh]

Well I did replace the one that goes to the computer and still no change. As for changing all the hoses did you have access to a shop? Is it necessary to hoist up the car? Are the hoses all the same size?

 

[TonyJetta]

All the same ID hose. No need to hoise up the car. You may need to contort a little and use a mirror, just because access is tight.

Are you getting any codes?

Tony

 

[OldSchoolFresh]

I did get a "MAF implausible signal" code other than that no. I did disconnect the battery waited and reconnected, no change at all.

 

[Nevada_TDI]

Did you reset the code, and drive it and get the code again? I ask because MAF implausible signal, could mean a bad MAF, or an EGR that is not opening. Have you started the car, unplugged the MAF, and driven it to see of it acts the same? Just an idea...

 

[OldSchoolFresh]

I did reset the code and it does come back, take a little for it to come back though it's not immediate.

I haven't tried unplugging it and driving it like that yet. Should I notice an increase in power, since I don't think it can get much worse? I thought the Peirburg MAF was pretty reliable, but I do guess it can still fail.

 

[OldSchoolFresh]

Well small update, I did unplug the MAF and drove around like that for a while and power did increase but I noticed that it was sputtering more around 2000 rpm and it became more violent the more I pushed down on the accelerator. There's a bit of black smoke coming out as well. It can rev higher without the MAF plugged in, to maybe about 3000 and there is more boost pressure ~8psi on full load, but the backfire/sputtering sounds sure aren't comforting. I have to get to changing the vacuum lines when it's not -10000 outside. I see the red and blue hoses reach way back, how do I get in there, I pretty much need another elbow!

 

[TonyJetta]

I see the red and blue hoses reach way back, how do I get in there, I pretty much need another elbow!

Only the 2 hoses on the turbo are hard to get at. Sometimes, it's easier to take the turbo inlet off.

Tony

 

[lekolite]

If you unplugged the maf and performance improved then you have your answer. Your maf has bit it. Especially since your car already told you the maf is dead, twice. Replace, then troubleshoot other issues.

 

[OldSchoolFresh]

Would a malfunctioning MAF cause the stuttering/backfire like problems? I'll make a visual inspection and log some data with my VAGcom.

 

[PaPa Bulldog]

Only the 2 hoses on the turbo are hard to get at. Sometimes, it's easier to take the turbo inlet off.

Tony

That's not necessary! They really aren't too far down the firewall. I have access to a shop, but you could use ramps even to raise the vehicle. Unless the lines have been replaced due to the age of the vehicle I would replace all lines!!! Take time to do the job right (2hrs max), and you will be paid for your efforts!

 

[tdidieselbobny]

You said you replaced vacuum hose TO computer-did you take the ecu out,take cover off,and replace the short hose INSIDE the computer? Also-are all the hoses connected correctly? Was the intake manifold ever cleaned? How many miles are on car?

 

[OldSchoolFresh]

Oh there's another inside the computer, I didn't know that! I guess I'll have to check that out as well while I replace all the other lines. If this fixes my problem it'll save me from buying a new MAF, besides I already have the tubing. I'm sure the hoses are correctl installed, the intake manifold was never cleaned and there's nearly 387 000 kms on it. I did do a quick visual inspection of the intake and while there was some gunk, nothing too major.


Edit: Is the hose inside the computer the same inner diameter?

 

[tdidieselbobny]

I believe it is-Rocketchip did mine when he put the chip in 3 years ago.I think it's only about an inch long,but you need to be careful when sliding it off not to break the nipples that they slide over.

 

[Canadian_Grizzly]

Oh there's another inside the computer, I didn't know that!

I told you in post #4

 

[OldSchoolFresh]

I told you in post #4

Oops I should read over the posts more carefully. Is my face red!

I did do some logging with my VAGcom and the MAF requested was 850 when floored but the actual never broke 400 I believe, I will graph it and post it soon. While I don't know if there was actually more power with the MAF unplugged I could hit 110 kmph. While with the MAF plugged in I could only get to 80 kmph so there is a large difference. It also revved higher with it unplugged.

Could a bad MAF also be responsible for the stuttering/backfiring?

Thanks to everyone so far for all their help!

 

[TonyJetta]

I would replace the hose in the ECU, before going after the MAF. If the ECU won't let the turbo build boost, the MAF won't see the increase in airflow!

Tony

 

[OldSchoolFresh]

Both excellent ideas, and a lot cheaper than a new MAF. I know that the signal isn't flat lined at 550, so the MAF could be dirty and it's worth trying to clean it. It's just reading WAY below 550 (but still a variable signal!) so maybe the engine is cutting back on fuel so no power. But there is a huge increase in black some with the MAF unplugged.

Of course I'll crack open the computer and replace that hose was well.

But I still am concerned about the stuttering/backfiring, any ideas?

Oh and I removed the snow screen and the filter is clean.

 

[TonyJetta]

Of course I'll crack open the computer and replace that hose was well.

But I still am concerned about the stuttering/backfiring, any ideas?

One step at a time. Replace the hose, then lets see what the issues are.

Tony

 

[OldSchoolFresh]

Cracked open the computer, hose was pristine, no signs of leaks, did a quick test by blowing into it Now I broke down and purchased a Pierburg MAF, ugg almost $200. I'm starting to run out of ideas.