98 TDI excessive smoke

alanack

Member
Joined
May 10, 2022
Location
Rhode Island
TDI
1998 Jetta
First post here....

So i bought this car in October 2021 because the price of fuel was killing me in my long owned and beloved 12v Cummins diesel Rams.... i commute 90 miles a day. Its 1998 Jetta AHU 5 speed

Anyways the car smokes like a friggen freight train..... since i got it. Normal throttle its grey-ish smoke, heavy on the foot its dumps out black smoke like an old mack dump truck.... car is a baby, has just over 150,000 miles on it.

When i bought it the PO replaced the pvc system, turbo, rad, some sensors.... and I further went through it, new vacuum lines, change over valve, glow plugs+ harness full timing belt service with WP, coolant& thermostat everything. Just changed the fuel filter with a filled with liquid moly diesel purge.

Timing verified using my scan tool a few times, ive put over 10,000 miles on the car and it doesnt seem to burn any oil, oil analysis reveals a slight fuel dilution (0.5% and sootly oil) poor combustion?
Other than smoke the car runs great, starts in single digits with ease, and has consecutively given me 48-52mpg US gal.... What gives?

On a side note i bought another one a 98 tdi that the engine was blown, so i had that swaped to a 1z by a reputable VW guy. because the original ahu dropped a valve... that car will not smoke no matter what you do, slight haze of idle on a cold start, but barely.
Im no stranger to diesels but this car has me stumped!
Thanks!
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Smoke is usually a fueling related problem. You're going to want to check that

A) your quantity injection value is within standard value range
B) Your turbo is actually providing full boost and your piping hasn't sprung a leak (usually this throws a code for an underboost condition)
C) Your injectors are not worn, clogged or outright failed. They could also be the incorrect injectors for the car, but unless the car is obviously modded I would not suspect that off the bat.
D) The boost sensing line to the ECU is good and not frayed or broken (also can - but doesn't always - throw a code.)

Since the car seems to run, I wouldn't suspect the injection pump. However there are a couple other sensors that also control fueling, including the coolant temp sensor and the fuel temp sensor on the inside of the pump, which I also wouldn't suspect.

All of these have been covered in extensive detail in other threads. I recommend searching the forum for the various procedures to check.
 

alanack

Member
Joined
May 10, 2022
Location
Rhode Island
TDI
1998 Jetta
I had a temp boost installed and the car would build about 12psi quick... every single vacuum line has been replaced. I swapped ECMs temporarily to see if there was a tune on it, no dice there. Coolant temp sensor was replaced when i did the glow plugs.

What is correct injection quantity? I do not have a vag com, but a friend with access to one.


Now im familiar with old diesels, mechanical injectors like these usually have a nozzle, an small indexing piece, spring and a shim. What is there to fail? I've seen the nozzles wear the holes out to a larger size on old diesel engines with literally 400,000 miles. Mines a baby with only 150 on it.

Something wack is going on that im missing, that fuel iq has my interest though
 

garciapiano

Veteran Member
Joined
Feb 12, 2018
Location
Southern California
TDI
1997 Jetta TDI (1Z)
Injection quantity and timing would be the first thing to check. If the timing belt was installed but the calibration was not set, the car could have the incorrect injection timing which can cause smoking.
 

alanack

Member
Joined
May 10, 2022
Location
Rhode Island
TDI
1998 Jetta
Timing is currently set at *57, target value according to my snap-on scanner, well within the limits....

Also the car smoked before i replaced the belt, so that leads me to believe its not a timing issues. Im thinking iq or injectors
 

Rig

Veteran Member
Joined
Apr 14, 2010
Location
New Mexico
TDI
1998 Jetta TDI, 210k miles
Yes, i would agree on the injectors, after everything you described.
 

burpod

teh stallionz!!1
Joined
Nov 27, 2004
Location
cape cod, ma
TDI
82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
take a log with VCDS - 011 + 001 + 004 all together, just make sure to keep pedal planted in a few various positions/rpms for a good 5 seconds each time. since logging 3 channels at once sample rate is low
 

alanack

Member
Joined
May 10, 2022
Location
Rhode Island
TDI
1998 Jetta
I have an AHU on the floor in my garage that has a messed up valve/ lifter im going to pull the injectors out of that and try and swap it....

Hopefully it didnt drop a valve and smash the tip off
 

burpod

teh stallionz!!1
Joined
Nov 27, 2004
Location
cape cod, ma
TDI
82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
next time car is hot, also check 001 + 004 and see what IQ and pump voltage shows at idle as well as actual timing.
 
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