Low mpg question

I know this has been probably been covered numerous times before but I've been trying to trace down a low MPG issue. 2003 ALH 5 speed bone stock Jetta. I got the car 2 years ago with 152k miles on it which the previous owner just replaced the timing belt, tensioner, water pump, egr valve and cleaned the intake. I had a friend with vag-com check timing last year and was spot on. I always consistently got around anywhere from 48-53mpg depending how many highway miles I drove, mainly back roads. Last fall around 180k miles I started getting an over-boost code so I bought a kit from IDparts and replaced the MAF, N75 valve, waste gate actuator and all vacuum lines with silicone hoses from another site. Turned out to be the waste gate actuator diaphragm was dried out. After replacement car ran great and could actually hear the turbo whistle again.

Car now has 185k on it but around 183k miles I noticed a loss in power, a slight haze of smoke during take off, slightly rougher startup when weather was cold with slight white smoke and also a loss in mpg, last 4 tanks have only been ~37mpg and two of those were 90% highway doing 60-65mph where before I would avg 52-53 doing that speed. I haven't changed my driving style at all. I swapped MAF sensors with my old but good one and no change, just to try. I unplugged MAF and it made the car more sluggish. I also disconnected the waste gate actuator and it feels like it moves freely, full movement too. Removed the egr valve and other than a slight film the intake and all looks to be in good shape. I replaced the air filter and fuel filter ~700 miles ago just to be safe as well.

I currently live 5 hrs from said friend who has vag-com as I'm in the navy so I don't have access anymore. Anywhere else to start looking other than hooking the car up and seeing what is going on? Maybe injectors starting to get wore out? It was kinda like a instant change in the loss of power, car was running fine and wife took the car and said it felt slower than normal. No CELs either. Thanks for any input or help.

Also forgot to mention I checked all wheels and none of the calipers are hanging up/dragging. Was one of the first things I checked and just checked again today.

I have used a Scangauge II on my Jettas for years. I picked up a new-to-me Jetta earlier this year. My Scangauge II reported the engine temp was only reaching 173F. That was not full operating temp, and I had a sluggish car and lower MPG. The thermostat was bad, but the temp needle showed full temp on the gauges. I replaced it with a new one from the dealer (Yes, get it from the VW dealer). My car runs much better (like it should) and gets over 50MPG routinely. Temp now reports 193F.

Be sure the check the coolant temperature sensor as well. Better yet, just replace it to be sure.

Report back with your results....

I actually did just replace the coolant temp sensor last fall along with 4 glow plugs and wiring harness. I guess the best thing would be to find someone in the local area with vag-com to get a reading of what is actually going on. I'm located in Groton, CT now.

yeahkkyle said:

I actually did just replace the coolant temp sensor last fall along with 4 glow plugs and wiring harness. I guess the best thing would be to find someone in the local area with vag-com to get a reading of what is actually going on. I'm located in Groton, CT now.

Click to expand...

I got 2 from the local parts store and both seem to last only a few years and the temp would read low for the ECU but the gauge OK.
I have to install one in mine again when I get a chance.

I'm meeting up with a local guy who has VCDS and plan to pull some data off the car on Saturday to get some more info and see what is actually going on with the car. I found on Malone Tunings website how to do datalogging with VCDS and just wanted to make sure that will be enough data to maybe diagnose my issue.

https://malonetuning.com/assets/files/vagcom_logging_guide.pdf

This is the website that I was reading and for 03 alh they recommend measuring blocks 001, 003, 004, 008, and 011. Doing them one at a time as well.

Is there any other blocks that might be helpful to log or look at to get some more info that might point me in the direction of my issue? Thanks for any input.

How is performance?

I'd look to verify you're getting good vacuum out of the vacuum pump. Might need to trace from there.

A bad thermostat is something I'd check for.

BTW - It's a "turbo actuator" (rather than a "waste gate actuator").

Car is low on power, not like when it goes into limp mode but definitely feels slower. From like 2-3k rpm just doesn't seem like it has as much power. I'm going to check the temperature with vcds Saturday before I start throwing more parts at it. I know the temperature could be low even if the instrument gauge reads 190, which it does but I can't see it being off that far causing a 13-14mpg drop in mileage.

Timing, vacuum, sticky veins, look for the second two AZ nd check timing when you get the vcds.

The veins seem to be moving freely and I just replaced the actuator. I will have to hook a gauge up and check the vacuum.

Check vacuum, n75 swap with n18 and check adjustment of the actuator to rule those things out first.

Shot in the dark- was the actuator adjusted to just open at 3.5 to 5.0 "hg?
First check to make with VCDS- Stored Codes.
Thermostat seems O.K.
Oilhammer has broke down all the dumb stuff for us

Yes when I installed the new actuator last fall I hooked up a vacuum gauge, used a hand pump and adjusted the rod so it moved between 3.5 and 5". After the install of new N75, turbo actuator and new MAF the car ran normal. Those were just installed to fix the limp mode from over boost code. Hopefully Saturday I get some data that points to the issue.

Check the actuator again - I have seen them installed and work fine only for the locknut to come loose and cause boost issues a month or two later.

https://log.malonetuning.com/chart/33254#H8KLCADCpsKkfFkCA23DjMOLCsKAIBDChcOhd8KZwrVCF8OoZcOEw4VUwoMNwpjChk5QPX0pBC1awp7Dr8KHYwxMcR05wpB2KcOuWwbDlVhVw5DDh8OEFz1TwoHCo0AJwoXCoBTCnGd9ajw4w5fClsOYLVJDJsO5woRWQcO7w4PDnT/Dty/Doy4xb8KewqV+DMOWw57Do8OwwrDCn8KhAAAA
https://log.malonetuning.com/chart/33257#H8KLCADDusKkfFkCA03Di0EKwoQwDMKFw6HCu2TDncKAwrrCmMOLwpQuwqrChhrDkEbDkig6wqcfwqswwrh8w5/Do8O3HgZZesOOwoRJZVsLwrgmwrjCisKzKH/DqcKaDhJlw5JoBMOPwpN3UkMTPDAeXMKLwqfCicOjwojDp8KfQDlNdifChcOsdXQOw5rCm8OjZlLDlsKZwq1qw7sJw6EHd8Ojw4LClsKNAAAA
https://log.malonetuning.com/chart/33258#H8KLCAAawqV8WQIDbcOLSw7CgzAMRcORwr14HEtkw4JmUAYBwqzDlBLCjSPDhyDDisOqw4tHwq0YMHzDp8Opdh0Mw7LDrjkTJsKVwrlUcE1wB07CosK8w5E+HSTDisKkw5EIwq4nL8KkwoYmwrhiXMO5KMKuJsKOI37DvgTDisOpZWdSw4luw4d+w7kHw7Y/wo7Cs0ktE8ObwqltCF/DpcKMbMORwqQAAAA=
https://log.malonetuning.com/chart/33255#H8KLCAA5wqV8WQIDbcKLQQ7CgzAMBMO/w6JzLDUcw7oZwpRDWsKsYAliw6QYRMO7w7oSUBEHwo47wrPDk8K2w7DClsOxw4XCmTDCqcOMUwHDtwjCrsOCQcKUwr/CtE0HwokyaTTCgsODw6TChcOUw5AEV8KMK8OXw6JoYsOXw6HDp0TCoMKcesObwpNCdhHCm8OyN8OYw5/Do8Omwo/Do2xSwqbCgW0/P0PDuAHCtUXDiT3CuwAAAA==
https://log.malonetuning.com/chart/33256#H8KLCABiwqV8WQIDTcOLQQrChDAMwoXDocK7ZMOdwoDCusKYw4vClC7CqsKGGsOQRsOSKDrCpx/CqzDCuHzDn8Ojw7ceBll6w47ChEllWwvCuCbCuMKKwrMof8OpwpoOEmXDkmgEw4/Ck3dSQxM8MB5cwovCp8KJw6PCiMOnwp9AOU12J8KFw6x1dA7DmsKbw6NmUsOWwpnCrWrDuwnDoQd3w6PDgsKWwo0AAAA=

Got a chance to meet up with a local guy with vcds. The above post is from blocks 001, 003, 004, 008, 011. Before doing the logs I checked block 010 and outside pressure is exactly 1bar which makes sense since I am at sea level. MAF sensor seems to be all over the place but maybe I'm not reading correctly. Any advice based on the data? Thanks.

I also checked the timing again while we had vcds hooked up and the timing is just slightly above the blue line.

What was the IQ and timing could probably be advanced a touch more.
I find that actuator adjustment takes a bit more than just setting the low end.
Adjust, log, adjust, log, fine tune then log some more.
Timing is a little easier, however, need vcds to get it all together and set right.

After talking to someone at Malone they said everything looks normal and with a dramatic decrease in mpg he would guess towards nozzles but would expect drivability problems long before that. So I decided to do a compression check as well just to check the numbers. When I pulled the glow plugs I noticed No.4 cylinder plug had a lot more carbon buildup than the other 3 cylinders. Attached are the 4 glow plugs, left one being cylinder No.4 and then the compression numbers. All numbers seem good.

MAF ain't right. Not going to be responsible for the big FE hit, but it's just not delivering. Should see it spike over 1,000 (I seem to recall my cars hitting 1,200 or so, though briefly). BUT, theres's also the EGR to consider in this mix.

I'd have liked to see Group 013.