Help me diagnose this Passat please
zoombic
11-18-2004, 09:22 AM
Hi folks....my 1st post, and it's a sad one. My brother died a couple of weeks ago and left a half dead 2000 1.8T Passat in the driveway for me to fix. It's got about 56,000 miles on it. I'm a motorcycle mechanic turned mechanical engineer and he was an ASE Master mechanic - now he's gone and I could use some help.
He was on a road trip and it started to lose power above 2-3K rpm. He must've thought that it was the fuel filter because he bought on along the way, but never installed it.
The symptoms: Starts fine and idles smoothly but erratically between 800-1200 rpm when cold. If you rev it it cuts out at about 2-3k rpm - just plain falls on it's face - doesn't matter whether it's under load or not. If shortshifted, it can attain 50+mph, but don't try to accelerate or it'll nose down on you.
The codes stored (descpription from factory bible) before any work was done:
1128 Long term fuel trim multi., bank1 system too lean
300 Random/multiple cylinder misfire detected.
303 Cylinder #3 misfire
304 Cylinder #4 misfire
302 Cylinder #2 misfire
301 Cylinder #1 misfire
1137 Long term fuel trim ADD fuel, bank1 system too rich.
One is a lean code, one is a rich, and I would think that the random misfires are associated with the lean condition indicated.
Findings/Service performed:
Had no idea when last oil change was, so I replaced with Mobil1 as he used to, but checked the level before draining. The oil level was high when initially checked - about 1/4" above full mark on dipstick - I know of the warning of overfilling that may cause catalytic converter damage, and, per the bible, may cause misfire codes to be stored in the ECM. How high does it need to be before it starts puking into the cat? As a fallback test, I'll yank the 1st O2 sensor to see if an exhaust restriction is in place.
Replaced the fuel filter - the original was pretty well plugged. Factory bible states that the filter is designed to last the life of the vehicle (56,000 miles ???) and that if the filter is plugged, then you need to drop the gas tank and clean the pump screen sock. Could've picked up a bad load of fuel. A local tech buddie of his did a fuel pressure test on it and it had approx. 60 psi (4 bar), but I forgot to ask under what conditions - at idle, or when revved to the point of nosedown. I plan to do a "tape the gague to the windshield" test drive this weekend to see more. It may produce required pressure at idle, but on boost delivery it's starving for volume due to a plugged screen in the tank.
The air cleaner wasn't exactly clean so it was replaced.
The secondary air pump (second one in the car - 1st at 20K) had siezed and blown the 40A fuse to the ECM, so he disconnected it until he got an air pump (and from what I've read, the combination valve should be done as it may be the source of the condensate that is fed to the pump and freezes in places like Buffalo). But the disconnect of the air pump did not seem to effect drivability. But now that I think about it, I never really got it real hot - it may very well be the cats aren't lighting off early enough to make the system happy. I plan to take it out on Friday afternoon to get it good and hot and reset the codes on the 'puter.
Vacuum/pressure sensor lines need to be thoroughly checked - If I can actually get my hands and eyes on them.
Any insight that you guys can offer would be greatly appreciated. We've got a very limited budget (no life insurance) but access to lift facilities and old tech friends as needed. I really don't want to have to drop this thing at the dealer to diagnose, but I'm running out of time and energy!!!!!!
He was on a road trip and it started to lose power above 2-3K rpm. He must've thought that it was the fuel filter because he bought on along the way, but never installed it.
The symptoms: Starts fine and idles smoothly but erratically between 800-1200 rpm when cold. If you rev it it cuts out at about 2-3k rpm - just plain falls on it's face - doesn't matter whether it's under load or not. If shortshifted, it can attain 50+mph, but don't try to accelerate or it'll nose down on you.
The codes stored (descpription from factory bible) before any work was done:
1128 Long term fuel trim multi., bank1 system too lean
300 Random/multiple cylinder misfire detected.
303 Cylinder #3 misfire
304 Cylinder #4 misfire
302 Cylinder #2 misfire
301 Cylinder #1 misfire
1137 Long term fuel trim ADD fuel, bank1 system too rich.
One is a lean code, one is a rich, and I would think that the random misfires are associated with the lean condition indicated.
Findings/Service performed:
Had no idea when last oil change was, so I replaced with Mobil1 as he used to, but checked the level before draining. The oil level was high when initially checked - about 1/4" above full mark on dipstick - I know of the warning of overfilling that may cause catalytic converter damage, and, per the bible, may cause misfire codes to be stored in the ECM. How high does it need to be before it starts puking into the cat? As a fallback test, I'll yank the 1st O2 sensor to see if an exhaust restriction is in place.
Replaced the fuel filter - the original was pretty well plugged. Factory bible states that the filter is designed to last the life of the vehicle (56,000 miles ???) and that if the filter is plugged, then you need to drop the gas tank and clean the pump screen sock. Could've picked up a bad load of fuel. A local tech buddie of his did a fuel pressure test on it and it had approx. 60 psi (4 bar), but I forgot to ask under what conditions - at idle, or when revved to the point of nosedown. I plan to do a "tape the gague to the windshield" test drive this weekend to see more. It may produce required pressure at idle, but on boost delivery it's starving for volume due to a plugged screen in the tank.
The air cleaner wasn't exactly clean so it was replaced.
The secondary air pump (second one in the car - 1st at 20K) had siezed and blown the 40A fuse to the ECM, so he disconnected it until he got an air pump (and from what I've read, the combination valve should be done as it may be the source of the condensate that is fed to the pump and freezes in places like Buffalo). But the disconnect of the air pump did not seem to effect drivability. But now that I think about it, I never really got it real hot - it may very well be the cats aren't lighting off early enough to make the system happy. I plan to take it out on Friday afternoon to get it good and hot and reset the codes on the 'puter.
Vacuum/pressure sensor lines need to be thoroughly checked - If I can actually get my hands and eyes on them.
Any insight that you guys can offer would be greatly appreciated. We've got a very limited budget (no life insurance) but access to lift facilities and old tech friends as needed. I really don't want to have to drop this thing at the dealer to diagnose, but I'm running out of time and energy!!!!!!
boschmann
11-18-2004, 04:27 PM
It's not as common on the 1.8's as the 2.0, but your symptoms sound like the MAF is out of calibration. To diagnose properly you ned to look at certain datastream measuring blocks with a scanner (VAG or simulator preffered).
zoombic
11-24-2004, 02:02 PM
It was the MAF sensor and it was replaced under warranty. Also had them do the secondary air pump while it was there. If I hadn't known that the MAFS was covered under extended warranty, they probably would've charged me for it.
Thanks again - you guys are great!
Thanks again - you guys are great!
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