Brand New Nozzles; Big MPG Drop

My A4 wagon used to return 48-50 MPG regularly for the first 200K miles, but had dropped off to the 45-46 range over the last 100K. I did a lot of reading and concluded that my original nozzles at 300K were possibly hurting my mileage.

So I decided to spend the money to replace them. Bought a set of Bosio DLC520's from DBW. Installed them and as suggested set the IQ to the high end and set the timing to the upper end of the range (advanced).

Fuel economy on the last (old nozzles) tank was 46 MPG. First tank on the brand new nozzles is 40 MPG. Similar weather, driving/commute, pretty much everything. That seems like a steep and sudden drop with the install of the new nozzles. I will continue to monitor it, but was wondering where I should start looking.

I would check with either vag-com or some other OBD interface tool to see what the coolant temp is.

The thermostats can graduall go bad over time and open at a lower temperature thus a gradual reduction in mileage. I know this isn't directly answering your question of the new nozzles but it's something I would suggest looking at.

but make sure you're not going by the temp gauge on the dash. I've seen some that would show 190 (which is about 87 deg C) on the dash but when using a OBD tool it showed the ECU was reading 73 degrees C.

-J

I had the same thing happen to me unfortunately, I put some Sprint nozzles in and I use to get 650 Miles in a tank with the timing maxed out and adjusting the IQ and everything was great so my car had 185k on it so I thought I would replace the "OLD WORN OUT NOZZLES" and now Ive lost about a good 20-40 miles. Its not as bad as yours but its definitely not great. I thought maybe the stage 3 malone tune would help but nope, its still the same right now. Pretty disappointing. I did not balance them though so maybe that is the trick.

Sleet said:

I would check with either vag-com or some other OBD interface tool to see what the coolant temp is.

The thermostats can gradually go bad over time and open at a lower temperature thus a gradual reduction in mileage. I know this isn't directly answering your question of the new nozzles but it's something I would suggest looking at.

but make sure you're not going by the temp gauge on the dash. I've seen some that would show 190 (which is about 87 deg C) on the dash but when using a OBD tool it showed the ECU was reading 73 degrees C.

-J

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That's what Drivebywire suggested looking at, and it makes sense. I will connect it to VCDS tonight and see what my actual temps are.

98rzvr6 said:

I had the same thing happen to me unfortunately, I put some Sprint nozzles in and I use to get 650 Miles in a tank with the timing maxed out and adjusting the IQ and everything was great so my car had 185k on it so I thought I would replace the "OLD WORN OUT NOZZLES" and now Ive lost about a good 20-40 miles. Its not as bad as yours but its definitely not great. I thought maybe the stage 3 malone tune would help but nope, its still the same right now. Pretty disappointing. I did not balance them though so maybe that is the trick.

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Unfortunately I bought a balanced set of injectors, so I'm hoping I can rule that out. And yes, it is very disappointing. It reminds me of the old saying: "If it ain't broke, don't fix it."

Perhaps your use of the accelerator to drive the smile factor is the result...

I've had, what I thought was the same issue...
I religiously hand calculate every tank, vented till I see fuel in the filler hole.
Was getting 45-46ish pretty much every tank.

I had the original nozzles (340k on them) in my 03 replaced with DLC520's...
Not sure what the IQ and timing are...local guru (Robby) did it.

Mileage actually went down for the next few tanks (42-44ish)...turned out to be a sticking caliper and a faulty thermostat only letting my coolant temp get to 170 max, which on the gauge shows 190.
Some timing these issues were...

Did a full refresh of the front brake system with rebuilt calipers, new rotors and pads.
Replaced thermostat, now stays @ 190-195 range perfectly.

Mileage went up slightly back to my original 45-46ish range, not as much as I was thinking it would.

Now out of the blue the last 5 tanks have all been easy 48-49-50 MPG's...not sure what happened.
This thing has never got this kind of mileage this easily without trying.
Driving exactly the same, 90% highway miles.
I think the new nozzles took some time to break-in honestly, about 5k miles.
Idle sounds a lot more clattery now then it did when the nozzles first got replaced.

I would touch your wheels after driving awhile and see if any are getting hot and check actual coolant temp.
If those are in check, just give the new nozzles some break in time before writing them off.

My car has the OEM stock exhaust, no tune, original VNT-15 turbo if it matters, pretty much the only upgrade is nozzles, fresh N75 and all new vacuum hoses.

I am running 2 sets of DLC 520 nozzles from DBW, a set of PP764 nozzles from DBW, a set of T4 from Boraparts, and 2 sets of titan 520 nozzles.
The best car i have is my 02 jetta wagon running DLC 520 nozzles at about 49 mpg with my spirited driving, followed closely by my 01 bug running PP764 and on its heals my other bug with titan 520 nozzles and another bug running the T4 nozzles. Not far behind at 44 city is my other bug with DLC520 and and my golf with titan 520s.
I am very satisfied with the bosio DLC520 nozzle.
All cars running Malone dyn EGR 2.0 tunes and original VNT15 turbo except for my 02 bug with DLC 520 nozzles which runs a Malone 1.5 tune. T-stat in all replaced to bring temp to spec.

richmondvatdi said:

That's what Drivebywire suggested looking at, and it makes sense. I will connect it to VCDS tonight and see what my actual temps are.

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Use a handheld thermal sensor measured at the Drivers side of the head at the coolant exit point. temp should be 190-193 ideally once warmed up.

Why the drop?

Old injectors mask the inefficiency since they flow less due to age and time and the fueling is reduced enough that the abnormal sensor readings don't figure as heavily into the overall performance of the engine.

Its like an old guy that used to run but with a bad knee, he gets the knee replaced and then realizes his 5 mile run takes the same amount of time or longer... He never realized his shoes were worn out and are now slowing him down where they weren't a factor before.

As soon as you restore the original flow for fuel now the other aspects such as a bad thermostat, bad ECU coolant sensor, leaking vacuum lines, Worn N75, Contaminated MAF, Failed fuel thermostat, etc work against you now that the fueling is restored the efficiency drops since the sensors are now needed to regulate the engines performance.

If you have high miles on a TDI where injectors are needed, maybe a list of other items needs to be reviewed to check the other normal wear items that draw down the efficiency.

For the most part assuming all the sensors are working correctly, most report a 4-6 mpg bump, if not... Time to start looking around and start diagnosing.

VCDS tells me coolant is 90℃ (194℉) so it's off to get myself an infrared temp scanner. I have a spare MAF on the shelf. Assuming temp is OK is it worth swapping it out to see if it helps?

The easiest way to tell if you have a bad MAF is to simply disconnect the current one - if the car runs better - replace it.

scooperhsd said:

The easiest way to tell if you have a bad MAF is to simply disconnect the current one - if the car runs better - replace it.

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Car runs perfectly, so it will not run better unplugged. The only thing that might happen is if it is giving faulty readings it might be causing overconsumption of fuel. Maybe...

Latest tank improved at 46 MPG. Hopefully trending in the right direction. Thanks for all your advice.

Third Tank Improved Again

Third tank improved again. Up to 49 MPG. Nice.

Bet the rings were jamming, with the improved combustion, cylinder sealing is improving and efficiency is going back up.

I see this a lot on engines that are lugged and short shifted, or ones with poor fueling and weak combustion due to nozzle choke.