'97 Passat TDI Build
 

I think I have enough posts now to post up pictures.

To recap; I have had this Passat TDI wagon since about '07. I bought it with 224k miles on it. It was a daily driver for about 5 years until I replaced it with a crown vic when I switched jobs, had a shorter commute, gas was cheaper, and I got fed up with fixing all the broken sh.t on the passat.

The B4 Passat chassis and vehicle is infamous for its poor design of simple, but numerous plastic parts failing requiring constant upkeep. Have four working windows and doors is a rarity in these cars. The 1.9 L TDI drivetrain is great though. I did put a 0.685 to 1 5th gear in when my original 5th gear went toast on a low tranny oil situation after I bought the car. It does have a performance chip from a reputable vendor from the TDI Forum and 0.205 nozzles (110 hp). It has great power, but I never hit the 50 mpg mark as others did but I knew its potential.

I kept the Passat, just incase gas/diesel took another huge jump and I had to commute long distances again. It sat next to my house for years, and was fired up about every other month.
It had diesel stabilizer in it. Well the inevitable happened in 2022, gas through the roof and I had a 42 mile round trip commute.

I parked the crown vic and fired up the Passat, which still ran, but was moldy inside, and had two broken rear doors that wouldn't open. Only two front windows worked.

My previous best tank when I commuted and vacationed was 42 mpg. I drove from 70-75 mph and normal driving.

Once I started commuting, I needed new tires for sure, had cracked sidewalls and tread on two. I slowed down to 65 mph max, did my gas mileage and got 45.7 mpg. Best ever. Now, I have a 26 gallon tank, but I am refilling every 8 to 10 gallons or so, so I don't have to wait so long to determine if aero mods help or not. My tank is vented so to get 26 gallons in, you have to fill it until you see the diesel in the neck, otherwise it first shuts off at 21 gallons.

https://forums.tdiclub.com/index.php...-1-jpg.148228/

I joined and starting reading through this forum and wanted to do the aeromods, but not go too crazy. I originally kept this car, because it is rare, TDI passat wagons were made in Germany, so only about 1,000 or so were imported. They didn't sell well in US. I thought this car would increase in value, but it never really did since they were lemons and being a mechanic or mechanically inclined was mandatory for owning one.
So, I have no problems with modifying it, as least it will be getting used and saving me money.

First- Roof rack delete and passenger mirror delete. The car had four antennas or bases, original owner was an archeologist and had 3 or 4 GPS antennas. These cause drag.

https://forums.tdiclub.com/index.php...-4-jpg.148230/

Next, I bought a Scan Gauge II. Now I knew where my poor gas mileage was coming from. Me.

Next mod was rear wheel skirts.
These were made using metal sheet rock corners, which are cut to curve into the wheel opening. They form the frame to bolt the skirt covers to.

https://forums.tdiclub.com/index.php...-1-jpg.148787/

Then I taped the curved frames with gorilla tape to hold the arch, then screwed to the inside wheel arch. Then the covers are cut out of coroplast then screwed to the metal corner frame. These are very secure. I use a piece of sheet rock corner on the bottom folded over both sides of the coroplast, which is bent so the tire doesn't rub. When screwed on, its very secure, no flopping. The bottom edge is held to the wheel well by hooks so the whole thing will swing down if the side screws are removed.

https://forums.tdiclub.com/index.php...03-jpg.148458/

Not sure why none of my pictures will post?

PM the mods?

Rear skirt

https://ecomodder.com/forum/attachme...7&d=1658445870

https://ecomodder.com/forum/attachme...8&d=1658445895

https://ecomodder.com/forum/attachme...9&d=1658445913

Skirts added
 

The paint don't match, but it is better than white coroplast. They are very stable though and don't rub, but tire clearance is only about 1/2". I need some pizza pan covers :).

https://ecomodder.com/forum/attachme...0&d=1658446145

https://ecomodder.com/forum/attachme...1&d=1658446168

Does it have EGR?

For a moment I thought you were reducing th opening of the front wheel well.

I probably will reduce the openings on the front wheels, they are large. I will try to find some 1/8" ABS sheet for the front wheels since its stiffer and more durable.

If I have the time this summer, I was going to repaint the entire car and will paint match the skirts. They will look much better.

Rear Diffuser
 

My next mod was to start the rear diffuser. I will be having a full undertray of coroplast but I need to transition the undertray to the rear diffuser so I had to add a support bar. The bar was aligned so the undertray will curve up and hit the diffuser. Should provide a bit of downforce too :).

https://ecomodder.com/forum/attachme...1&d=1658509989

The muffler is going away but that will be another step.

So the steps are:

1. support bar to screw the diffuser and undertray to.
2. Passenger side diffuser in plastic
3. Remove two mufflers (one is a resonator I believe). Make a new 2" cat back exhaust and install.
4. Driver side diffuser out of sheet metal, with exhaust terminating at surface.
5. Make undertray for the rear bumper at both sides of the diffuse to get rid of the parachute, I have now.

Diffuser part 2
 

So I built a diffuser out of an old Sears rooftop carrier. It was plastic and had a curve I could use, and it was going in the trash anyway. I did build some strakes, mostly for support. These are riveted on to provide strength. Looks a little like tuner bling but they add a bunch of strength and kept a good curve in it for transition.

https://ecomodder.com/forum/attachme...1&d=1658510441
https://ecomodder.com/forum/attachme...1&d=1658510441

I had to cut the rear bumper, which bothered me at first, but it was a parachute really. I cut nothing but plastic, so its integrity is not compromised.

https://ecomodder.com/forum/attachme...1&d=1658510441

The bumper is cut flush to the steel support beam. The diffuser angle is a little steep, probably 15 degrees or so, but I can flatten it by adding a fill in piece at the bumper. I will do some tuff testing once the full undertray is in to determine the proper angle.

Diffuser Part 3.
 

Now that the plastic side of the diffuser is in, time to remove the two mufflers, build a cat back exhaust, then install, then finish the driver side of the diffuser.

I was able to reuse some of the stock bends. The stock pipe was 2" od and stainless and cleaned up nice. I bought a 2" 90 degree bend, and 2 - 18" straight pipe. Welded, then painted with high heat paint.

https://ecomodder.com/forum/attachme...1&d=1658510915

Then install with some clamps. I do have a slight rub problem. More on that later.

https://ecomodder.com/forum/attachme...1&d=1658510974

Then finished the driver side diffuser in sheet metal and installed. Then the two bumper undertray pieces and then spray bomb in green.

https://ecomodder.com/forum/attachme...1&d=1658511059

I left the tailpipe exit protrude long, since the diffuser angle will probably change and the end of the diffuser will be lowered. I wanted to have the exhaust exit near flush to the diffuser surface, as this should be the lowest pressure area. I am trying to get a few thermal efficiency bumps on the motor. The TDI motor is not any louder at all with both mufflers removed and I probably shed 40 to 50 lbs. I have read that reducing back pressure is bad for mpg in a TDI and I have heard that it is good for mpg in a TDI. I am going to find out.

I will do a future write up on how each of these mods effected my mpg and drivability. I record my every day commute each way trip mpg. I drive it the same every day at the same mph, so I can see what the mods I do, do to mph.

So far, I found that with the catback, my driving in cruise mode boost pressure is higher than before, like 16 - 17 psi (absolute) versus the 15.5 to 16 psi before. That is the opposite of what I wanted to accomplish.

But, the mpg going up hill went up 10-15%, so the lack of back pressure helped the turbo to spool more efficiently, it appears. So long hills that I used to get 30 mpg going up at 55 mph, I am not getting 35 mpg or so. My level cruising mpg seems the same. But my one-way trip mpg went up consistently 2 mpg each way. Some of this could be because the diffuser and bumper undertray is now finished.

Of course I left the catalytic converter on. Removing it is illegal. I do have a bad tail pipe rattle, where it is hitting the subframe brace. Sounds like somebody is hammer drilling concrete inside the car, at idle. Goes away when in gear on the motor. I need to fix that, it sucks.

Turbo diesels don't like back pressure.
Do you know if there is an EGR system?

I have a working EGR.

It is not possible to turn off the EGR with a VAG-COM nor should it be turned off. The working EGR system should not decrease the gas mileage.

In a diesel it will usually hurt fuel economy.
Only time EGR helps fuel economy for sure is in very cold climates.
Don't have to delete anything, just make a sheet metal gasket with no hole for the exhaust to flow through. It's all there and still "working" as far as the ecu is concerned.
EGR on diesels is known for increasing tail pipe soot, decreasing fuel economy and decreasing horsepower.
With this mod you can try it and if fuel economy goes down you can easily undo it. Also I have heard of 1.9t intake manifolds becoming horribly clogged with diesel soot.

On a gasoline engine the EGR being disabled usually decreases fuel milage. It does not effect peak power because the EGR closes at around 1/2 throttle.

Also does it have a cold air intake or intercooler?

Now there is a hacker mindset. :thumbup:

I don't disagree with anything you say, but removing (or modifying) working emissions equipment from motor vehicles that travel on public roads is a Federal crime in the US, and they are cracking down on it. If I did do something like that I would not post about it on a public forum, doing so could get the forum in trouble.

Now, I will say that when my Passat is not driven on a public road, the EGR is turned down to the minimum using the VAG-COM so that soot is not clogging up my intake manifold :thumbup:.

Yes, it does have a factree intercooler.
I did a lower grill block but left a smoothed entrance hole for that.

Yes, these intake manifolds become horribly clogged, like over 75% of the passage clogged and up to 50% of the intake ports in the head. Mine was that way when cleaned at 230k miles, probably for the first time cleaned

I murdered all my emissions equipment on certain vehicles a long time ago.
Here crackheads have been stealing catalytic converters, most of the people who have their converters stolen just have a pipe welded in its place so it don't happen again.

Something strange diesel engines do is over time they produce less NOx, where gasoline engines produce more. So if the EGR was blocked now, the engine could very well be making less NOx then when it was new. The break even point between gas vs diesel NOx back then in the 1990s was something like 50,000 miles.

Stupid maintenance
 

Didn't get to work on my undertray this weekend.
Too busy doing this:

https://ecomodder.com/forum/attachme...1&d=1658778276

to get to here;

https://ecomodder.com/forum/attachme...1&d=1658778338

To remove and replace the stupid aluminum and plastic heater core and fix the dreaded blender door missing foam. This is the Achilles heal of the Passat B4. The heater core will fail, and its a 10 hour repair job at the dealer. I will be a little over that in hours.

At least now I will have heat this winter, and have a new stereo wired up.

Wow you went deep.

On the VW Vortex forum, somebody joked but its true:

"They put the heater core on the assembly line, then built the car around it."

The mechanics I used to employ said the New Beetle has the same problem compared to the Jetta.

That sounds like how a lot of cars are built.

Heater Core replacement wrapped up
 

Got interior buttoned up, but then the heater fan wouldn't work :(. So back apart to troubleshoot. There was a single power wire connector that wasn\'t hooked up. After 3 hours wasted, all good. Put in a "new" JVC bluetooth unit and redid the wiring. So, I have at least 3 working speakers now. Upgrade from 1 working speaker and sometimes 2.

https://ecomodder.com/forum/attachme...1&d=1659374781

Wheel Bearing Replacement
 

My front driver's wheel bearing was going out. Too much wheel play.
So I ordered new front wheel bearings, new ball joints, rotors, a new sway bar end, and new front brakes.

This was a tough job. Every single bolt was frozen on and my impact which goes to 300 ft lbs, wouldn't budge but one. The caliper frame bolts were almost impossible to get off. I could not get the tie rod end out of the spindle (completely frozen on), so I spray painted the tie rod threads (to keep track of where it was so I didn't have to get a new alignment) then just backed off the tie rod end off the tie rod to get the spindle off.

I got the spindle off and hammered off the hub. Of course the wheel bearing split apart and left the race on the hub :mad::mad: and ball bearings rolling all over the shop floor. So I had to cut the race mostly off, since I don't have the factree $300 tool to do this. Then hit it with heat and since the race is cut super thin here, it either breaks or expands enough to come off easily.

https://ecomodder.com/forum/attachme...1&d=1659375089

It cleaned up nice, but the scoring on the hub, means I should have replaced it. Too late now.

https://ecomodder.com/forum/attachme...1&d=1659375108

I pressed in the new bearing easy enough, and pressed the hub into the bearing.

Now install. New rotors. Now, where are the brake pads I ordered? Rock Auto stiffed me on these :mad::mad::mad:
So, leave old pads on. Didn't need to use the brakes much anyway, I coast now.

All done.

https://ecomodder.com/forum/attachme...1&d=1659375407

The driver's side took over 6 hours to replace. The passenger side, just over 3 hours. Learning curve.. Of course it was 93 - 95 degrees out the whole time I was doing this.

Of course you may ask, why the spindle had to come completely off the car? Just remove the hub with a puller and press the bearing off and on with the spindle in place like most front wheel drive cars. I have the bearing press tools to do this.

On the Passat, there is a big spring C clip on both sides of the spindle on either side of the bearing. It would be impossible, (or close to impossible) to get this C clip off the inside of the spindle with the spindle on, even if the front axle was pulled. If I had a lift, I might have been able to see this and get it off. There is not really enough meat on the bearing to use a bearing press that clears the C clip, so pressing this off through the back side of the spindle would not be possible without destroying the C clip.

With the spindle off the car, both C clips are removed and the bearing can be pressed out and on from either side. These C clips were thick and a total PIA to get off. I broke my C clip pliers doing this, they couldn't handle the force required.

Yeah I moved up to a 3/4 drive impact.
It breaks them loose or breaks them off.

Undertray 85% complete
 

With the maintenance done, I could now install the undertray. This will be in four sections.

Previously, I had installed some "framing" for the coroplast to screw to. It was framed on 48" centers and held away from the exhaust and moving components. The undertray will not cover the cat, but will cover the exhaust. I will install a diverter in the tunnel to deflect air from going down the exhaust pipe tunnel. The framing is steel firring framing pieces. They are straight and easily take sharp screws.

https://ecomodder.com/forum/attachme...1&d=1659454514

https://ecomodder.com/forum/attachme...1&d=1659454514

The four sections of undertray are:
From diffuser to the rear side of the sub frame,
from the nose to the front side of the sub frame,
then the sub frame cover (two pieces- one on either side of the cat.

I took the undertray 4\' by 8\' corroplast and sandwiched some metal sheet rock corner beading on both edges. Now I can screw the sides of the undertray to the framing and there is no danger of it pulling out of the coroplast.

Finished rear piece tied up under the diffuser. Attached to the metal support bar I previously installed.

https://ecomodder.com/forum/attachme...1&d=1659454756

and the front undertray tied to the bottom of the bumper neatly. The seam taped with Gorilla tape.

https://ecomodder.com/forum/attachme...1&d=1659454756

Now I can remove my hokey air dam made with 6" lawn edging. It would scrape.

https://ecomodder.com/forum/attachme...1&d=1659454756

It's a good write-up that might be helped with a detail illustration of the corner beading. What overlaps what?

The coroplast flutes run the length of the car?

The sheet rock metal corner is folded over the edge of the coroplast and pinched/hammered flat. Like I did on the skirts, see the skirt bottom edge. Then this metal edge is screwed to the framing. I will take another picture under the car when I get home.


https://ecomodder.com/forum/attachme...1&d=1659457501

https://ecomodder.com/forum/attachme...1&d=1659457788


I used some contact cement on the edge too, but not really needed. When the metal wrapped edge is screwed to the framing it tightly grips the coroplast and can't pull out or pull the screw head through the coroplast.

The rest of the undertray is screwed to the framing with 1/2" truss head sharp pointed screws.

Next Mod-Strakes
 

My next mod is to add 4"-6" strakes between the rear tires and the diffuser to clean up the air going through the diffuser. I may extend it to curve close to the front of the rear tire to block some flow to the tire.


something like this:

https://ecomodder.com/forum/attachme...1&d=1659478483

I will re-use the 6" lawn edging I removed from the air dam, I have to find a good way to attach it to the coroplast. I probably will have to remove the undertray to put a steel stud reinforcement strip to hold the strakes in. The coroplast is curved and the lawn edging doesn't curve well in that direction. I will try the heat gun and stretching the bottom edge. The exhaust tip is rattling on the metal diffuser opening and I will bend the metal up.

The center strakes are really for structural support to keep the curved surface and are not doing anything with the air flow. I probably will cut those flush.

But first I have to figure out what is rattling and scraping while driving. It gets louder as I go faster, so it has to be the wheel. Sounds like right rear wheel. Doesn't look like the skirt is rubbing.




Unfortunately I did not refill my tank and get my gas mileage before my heater core job. Didn't occur to me that I would lose my odometer reading when I unhooked my battery and removed the instrument panel. Rats, I had at least 650 miles on the odometer, probably closer to 700 miles.

And double rats that my blend door for the heater is hanging up and I still have some heat on in the car while driving. There is no way in hell I am pulling the dash apart again. I may just bypass the heater core until it gets cold out, then hook it back up when it gets cold.

Looking through the last page got me fantasizing about A-B-A-B testing of that air dam.

One series of tests to see the effect of the stock, dirty underside, and another to see the effect with/without the air dam when you have the undertray.

Air dams give most of what you would get with a full belly pan but with about 10% of the work, materials and hassle.

nice! thanks for sharing!

More undertray photos
 

The edge of the coroplast with the sheet rock corner support on the left, screwed to the framing strip on the right. Viewed from upside down.


https://ecomodder.com/forum/attachme...1&d=1659635254


Here is the undertray deflector that diverts flow back out of the exhaust tunnel, viewed upside down, see below.

The deflector goes around the exhaust pipe and is to keep air from going under the undertray via the exhaust tunnel. The main flow through the radiator will make it through the tunnel around the cat where it will hit the deflector about 1' past the cat. The deflector is held together by gorilla tape but that won't last too long. I will make a duplicate shield in sheet metal to replace it when this one fails.

https://ecomodder.com/forum/attachme...1&d=1659635336

There is a slight exhaust leak where my cat back exhaust attaches to the factree exhaust pipe. It is only a slip on U bolt connection. I need to fix the small leak as I can smell diesel exhaust fumes slightly now, when stopped at lights. Must be exhaust fumes trapped under the undertay. No smell when driving though.


So far I have seen a 13% bump in trip gas mileage with the installation of the undertray on my commute. Some of this bump is probably from the new front wheel bearings (one was bad), and some may be from the improvement of the undertray to the diffuser. The diffuser was installed first, which kind of traps air until the undertray is installed. I also have new rotors, the old ones were warped which may have caused some drag.

There is no doubt that I can coast farther with the undertray, and my terminal velocity of hills has increased where I need to use brakes now in a few places where I never needed to before. It accelerates much faster coasting on hills. Also after disconnecting my battery to do the heater core, when battery hooked back up, my idle fuel usage went from 0.16 gph to 0.12 gph, so 33% less fuel used now when coasting. I must of cleared some code. It got rid of an excessive vibration at idle.

I had a Passat once. A B5.5

Every time I looked at it, I wanted to beat it with a baseball bat.

It was the worst car I have ever known - it made me hate Germany.

Strangely, the one [and only] time it drove right and didn't give me any problems is the day I finally took it to the junkyard.

Been there, agree 100%. I parked mine for over 7 years after getting another vehicle. I had no intentions of driving it again or selling it whole for next to nothing, but was keeping it for the TDI 1Z drivetrain only for a swap, like into a Caddy pickup, or maybe a Jetta TDI A3. It was on my bucket list.

I only started driving it again recently when it was costing me towards $100/week to drive my Crown Vic. My passat has only two working doors and no windows that work correctly. The driver's window won't go up all the way and slips on stripped gears, one window is unhooked from the motor (since it is shorted to stay down) and slides down when the wedges come loose, Passenger front window is cocked at the top and protrudes out of the track an inch at the top, and passenger rear window won't come up if lowered all the way and only works off the door switch.

My cruise control doesn't work, and my heat is currently stuck 25% on. My a/c isn't working and most of the plastic interior pieces are cracked or has a broken piece out of it. Until recently I only had one working speaker and no heat and a leaking heater core. The stock head lights completely suck and are down right dangerous without auxillary lights. My first gear synchro is about gone, and my second gear is starting to grind. The brakes suck though, and no ABS. Parts are expensive as new Audi parts and there is no longer a supply of Passats at the junkyard, they have all been crushed. Not many older Passats left on the road, the owners have given up on them.

If you lower your expectations, it isn't too bad as a commuter. It actually handles really well and feels stable at speed, and has a ton of cargo room for hauling sh.t. If you don't care about your interior or working accessories, doors, or windows it makes a good dog hauler or muddy bike hauler.

Lol! I had a bunch of similar stories with my Passat, too. 😁

The first was a CEL that no one could fix. I took it to the VW dealer, the mechanic came out, said "this is a Passat."
I said yep.
He said "nope."
"What do you mean, 'nope'?
He said, "Every Passat between [years] gets a CEL and no one can figure out why. Scrap it and buy a Toyota."
He wouldn't work on them!

Timing belt tensioner gave out on I-40, miles between cities, in a snow storm. $400 to get it back home. Found out the valves got crushed and piston heads scored.

The alarm system would randomly close all windows and lock the car (the tire dealership was pissed when this happened to them, with keys in the ignition).

Or, usually sometime in the night, the alarm system would disarm itself, unlock the doors and lower all the windows. I come out the next morning and everything is opened up.

The rust underneath!!

I held onto it for about two years after buying another car ('08 Dodge Caliber R/T) because I was thinking of converting it [somehow] to all electric. But my hatred for it got me to just junk it.

🔥🤬

Now there is a car with a sense of humor.

A B A B A testing results Air Dam versus full undertray with diffuser
 

Some A B A B A B A B A Testing results with the full undertray and no air dam.
compared to A B A B A B A B A B results with the air dam and diffuser only.

-Using Scan Gauge II trip, no fill up yet.
-Using my GPS speedometer my car is showing about 3% off (speedometer reads high) so Scan Gauge II is probably reading 3% high. Not calibrated yet
-A = ride to work 20.8 miles.
-B = ride home from work 20.8 miles. 1,400' elevation gain 1,500' elevation drop (100' net elevation drop) to work, 100' net el' gain home.
-Drives are 57- 60 mph on interstate (speed limit of 60 mph), and 45-50 mph in 45 speed limit. About 2/3 of the commute is interstate and 1/3 at 45 - 50 speed limit.
-Coast in neutral with engine on, as much as possible. About 1.5 miles of trip is 30 mph speed limit and steep.

At least 3 miles of entire trip is just coasting.

With air dam and diffuser;

To work (trip mpg)..............Home (trip mpg)
67.9 .................................64.3
71.7..................................67.7 3 mile shortened trip
66.9..................................62.2 3 mile shortened trip
68.2..................................64.2
68.3..................................69.4

With Full Undertray tied to diffuser
78.2....................................77.4 To work from gas station to work only
81.7....................................76.1
83.7....................................78.6
82.5....................................79.4
81.8....................................79.5
85.3...................................... - New all time high trip this morning :)

I can easily see the difference driving and coasting. I can reach 75 mpg on flat road at 60 mph and I can coast way farther now. I am getting 35 mpg on the big hills that I used to struggle to get 32 mpg on. I can now link several shorter coasts into one long coast.

I did install new front wheel bearings the same time as I installed the undertray so that does skew the data a little.