Volkswagen Passat Forum banner

1 - 13 of 13 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter #1 (Edited)
Before I'm going to sell the car ('99 B5 APR 2.8 30v 4Motion manual) because of this single reason, I'll try and solve it first.
I get normal city MPG (16 MPG), but highway the best I can manage is around 23 (10L/100km), with super economic driving.

I've swapped out the CTS behind the engine, new spark plugs, new air filter, new fuel filter. The O2 sensors seem to be working though I don't know what would be the correct numbers in the diagnostic and VCDS gives 0 faults in the engine. Engine runs smooth and well.
 

·
Registered
2004 GLS 1.8T
Joined
·
12,135 Posts
The government rated highway MPG for that car - when new, 22 years ago - was only 26. I don't think you're doing so bad!

O2 sensors over 100k can drift off accuracy; might try a new upstream one(s).
 

·
Registered
Joined
·
15 Posts
Discussion Starter #3
My previous 2.8 with 100k km more on the clock got 7L/100km so I'd expect a year newer and a less mileage one to get at least something close to it.
Right now driving home from work, over 50km, the average highway mileage was 21.3mpg (11L/100km).
 

·
Registered
Joined
·
27,352 Posts
I've never heard of a 4Mo V6 gas engine with a manual. Is it a wagon or sedan? My 4Mo V6 wagon (with Tip trans) got similar mpg, but it was at 80mph. At lower speeds it was significantly higher. What is your speed on the highway? The Tip wagon was rated 17/23.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #5 (Edited)
Well I'm from Europe, Estonia to be exact and they sold manual 4Motions/Syncros here. Mine's a sedan and used to be a cop car for 14 years.
We don't really have highways in Estonia, but it's easier to say highway than out of the city every time.
Usually the speed limit everywhere outside of the city is 90 km/h (55mph) so I do around that. On the few 4 lane roads we have where we can go a bit faster, the fuel economy does not change much.
 

·
Registered
Joined
·
27,352 Posts
Most of the 4Mo I have heard of in Europe were TDI. At 55mph, you should get much better mpg and the sedan gets far better mpg at 55mpg than a wagon would. I've seen 28mpg averaging 55mph in my wagon.
I would start with the physical condition of the brakes and bearings. Check for drag and play. Then check the engine, vacuum hoses, O2 sensors (VCDS should list correct range), injectors and exhaust. Scan for fuel trims, both short term and long term (I can't remember the blocks in VCDS).
 

·
Registered
Joined
·
15 Posts
Discussion Starter #7
Over the year I've owned it I've already changed all the bearings, discs and pads.
Recently the exhaust fell off and swapped it out for a better condition one, but that didn't change the mileage. Vacuum hoses seem fine. I don't know how to check the injectors and they've probably been in one place 21 years.
While I've got VCDS, I've got no idea how to use it besides fault codes and live data, but VCDS doesn't have info for live data blocks, for the 2.8 30v.
 

·
Registered
Joined
·
15 Posts
Discussion Starter #9
Both on-board computer and how much I can actually drive with each tank. They're spot on actually to each other.
 

·
Registered
Joined
·
27,352 Posts
This will help you learn more about VCDS, and it does live data for the 2.8 as I have used it. Go into Engine, then measuring blocks. I actually ran through them all to learn how each one worked.

This might help with understanding the fuel trims and O2 readings:
 
  • Like
Reactions: Iowegian

·
Registered
Joined
·
5,373 Posts
If your thermostat is operating incorrectly, and allowing too much coolant to flow to the radiator, then the engine's efficiency would decrease. Cylinders need to be hot to limit heat transfer to the coolant, which is otherwise wasted as hot air from the radiator. Your "gauge" might look normal, but not really represent the proper operating temp.
 

·
Registered
2005 Passat B5 2.8l V-6
Joined
·
17 Posts
My two cents for things to throw at you too is to perhaps look at is fuel delivery/fuel pump. Just had that issue on a non VW car. Gas mileage plummeted before the fuel pump died and I couldn't figure out why. My old '98 B5 2.8L V6 did 19mpg or (much) less in the city and at 65-70mph on the highway it managed over 30mpg - and that was with over 300k miles on the car. I miss that buggy. I now have a '05 2.8L V6 and haven't been able to get it up over 27mpg on the highway at all. This current car most often takes about 5 seconds of cranking for the engine to start. Someone at a nearby VW parts counter said the problem could be the fuel pump near the end of its life or the fuel filter. I changed the filter (as well as the plugs, wires, and coil pack and fixed several broken vacuum lines) but haven't driven the car anywhere yet to test it for MPG or the starting problem. We had to take our vehicles off the road because of covid-19. Can't afford the insurance. Still out of work since March. Good luck.
 

·
Registered
Joined
·
5,373 Posts
This current car most often takes about 5 seconds of cranking for the engine to start. Someone at a nearby VW parts counter said the problem could be the fuel pump near the end of its life or the fuel filter.
When everything is working correctly, that engine should take 0.5 seconds of cranking to start, which is about how long my 3.0 V6 needs the starter motor. That sounds like an engine with a missing sensor signal, so the ECU resorts to a default value for the lost signal to run.

Regarding filters: an old and dirty fuel filter won't affect starting because the fuel flow is so low during cranking. It's at full-throttle, max RPMs where the high flow would cause a troublesome pressure drop.
 
1 - 13 of 13 Posts
Top