Help with eng miss ALH TDI

boomstriker

Member
Joined
Apr 23, 2012
Location
Washington MO
TDI
00 jetta TDI
Got a 99.5 MT tdi with 250k on the clock. Fuel filter came apart sent trash into my pump. Tore down pump cleaned and inspected. Everything all OK. Did the same with injectors. Cleaned hard lines, hoses and entire fuel system. Engine now has a miss at #4 with pronounced shake at idle. Checked #4 injector again being sure there were no pluged nozzles or any debris. All was clean and clear. Back on it still has a miss at 4. If compression was low on one cylinder I would hear it in cranking so I did compression check which confirmed what I already knew. Compression is strong and even across the board. I removed and inspected pump again paying close attention to plunger and head. No damage. Reinstalled, still has miss at #4. Removed the upgrade 10 mm head and put the original MT back on along with all four original nozzles. Still a miss at #4. I purchased two low mile used injectors on eBay, a factory Bosch and an aftermarket brand both manual trans. Neither made any difference in #4 hole.
Yes I'm sure the compression is good on # 4 I've checked it. I also went through the head only two months before this happened. New lifters and valves and I double checked since, nothing wrong there.
I'm also sure the miss is at #4. It throws a P0304 and by cracking the lines open.
One thing though, it's not a dead miss. It smooths out above 2K RPM (no load) and when cracking #4 at idle it does make a slight difference but fuel squirts just as strong as the other 3. While driving theres a noticeable shake in taller gears and lower RPMs. It does REV out strong and pulls hard at higher RPMs under boost.
I cleaned the fuel delivery valves but did not replace them. It doesn't act like a check valve so I'm not exactly sure what they do. Could a bad one cause this weak cylinder?
Getting real tired of messing with this POS
Any help would be appreciated
Thanks in advance!
 

Dhawk12

Veteran Member
Joined
May 21, 2018
Location
Langley, Canada
TDI
2002 ALH 5 spd
I don't know much about the fuel system on ALH cars, but have you checked the IQ with VCDS? It is possible that when taking the pump apart you inadvertently changed it mechanically. My car had a similar, although milder, issue of rough running at idle that felt like a misfire and would cause the car to shake (no codes were thrown for misfire) because the iq was set too low (~1). I adjusted it up as far as I could with the software (~3) and now the rough idle is gone.
 

boomstriker

Member
Joined
Apr 23, 2012
Location
Washington MO
TDI
00 jetta TDI
Thanks for reply!
The injection pump is not able to supply more or less fuel to any one cylinder either mechanically or electrically, only all four simultaneously and equally. This is why the injectors' fuel flow s/b calibrated to each other to 'balance' them as a matched set for a very smooth idle.
I'm familiar with the rough, loping, erratic idle associated with overfueling. The hammer mod will cure that.
This is a miss. Its a very even, rhythmic, shake which changes frequency with rpm.
 
Top