it's on! (AGAIN!) TDI upgrade in my diesel bay

trev · Posted: Wed Jul 06, 2016 10:41 pm Post subject:

300 mile round trip in the bag! No major issues along the way. I bought a new, genuine Bosch MAP sensor halfway through the trip and it cured the boost issues. Error code associated with it is gone too Happy

Next is to find the missing horsepower. I think there is still a boost leak or something that's causing a lack of power. It still doesn't feel like 110BHP should.

Driving around in 4th on the B-roads is fine, the engine is right in the power band/boost range at 50-60MPH. Shift up to fifth before 60MPH and it drops below the power band/boost range and actually slows down. Shift into fifth at 65MPH and it spools up and pulls. Touched 80MPH briefly but TBH, I'm not comfortable driving a bay on stock suspension, stock brakes, stock van tyres etc at that speed.

Kai · Posted: Sat Jul 09, 2016 11:14 pm Post subject:

Hi Trev,

That's exactly what mine feels like. Got worse after fitting the 18's as it's geared up even more then when it was on the 16's. So now I just stick to 4th gear at 55mph. Admittedly my karmann has worse aerodynamics then a bay and well that's loads more. If I go for 5th my speed is creeping no up over 60mph but the throttle is almost flat out, forget about anything surface that isn't level as I just start going backwards.

I was talking to a mate who suggested he knew a company that would regear my Passat box. In hindsight I wish I'd just swapped the engine now. But it's not that inbarable. Just have to drive slower.
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Think......

Don't sleep and drive!!!

Wilfred · Darth Admin Joined: 13 Nov 2013 Posts: 366

I think you should be able to get more out of it.

My cruisin speed is 110- kph (70mph). Then I drive in 4th, because I have really big wheels at the back. I can speed up though, en get into 5th while driving over 120-130 kph (80 mph), but it is just not comfortable. Nothing regarding the engine but just too much wind noise and knowing I still have stock suspension and brakes. 70 is fine. I have power left to overtake something quickly though.

the 110 bhp engine should have no issues getting you up to 80 mph or more. I would do some checks on the air intake etc. and maybe some general maintanance of the engine?
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1973 BayWindow running 1.9 110 bhp TDI with flipped gearbox.

trev · Posted: Sun Jul 10, 2016 12:45 pm Post subject:

thanks for the input guys, good to hear I'm not the only one. I've had another chap tell me the same on another forum. Seems the fifth gear is VERY tall for a big vehicle like the bay window bus. I agree on the wind noise issue, the couple of times I had it over 70MPH, the kids in the back had their hands over their ears!!

@wilfred, re maintenance, the engine has had an oil service, new filters, new timing belt kit, new water pump. What else should I do? I'm thinking bigger turbo and/or injector nozzles for more torque to pull along in fifth.

Wilfred · Darth Admin Joined: 13 Nov 2013 Posts: 366

a 110 bhp diesel should be able to pull you along nicely. Already in stock condition.

Throwing a bigger turbo at it seems like you are fighting a symptom rather than a cause in my opinion. Do you have a turbo pressure gauge?

I would love to have a meet with TDI baywindows to compare speed, handling etc.
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1973 BayWindow running 1.9 110 bhp TDI with flipped gearbox.

trev · Posted: Tue Jul 12, 2016 4:26 pm Post subject:

I agree, 110BHP should pull along well. I will try to solve any underlying issues and get it back to normal before deciding if any upgrades are needed.

busbuddy · Force Sensitive Joined: 13 Dec 2006 Posts: 21

i would plug vagcom in and check you have 100% throttle movement, that the timing is spot on and that the indicated revs are correct, that rules the engine out

then i would play with rear tyres, some experimenting with sizes should make it much more driveable as is without costing a lot

mine is a 1Z with a rebuilt T25 3H box fitted with the bigger r&p only (29/7 4.14:1) and it shoves my bungalow along just fine with 255/55x18s on the back
the tall 5th gear is the reason i never went the flipped box route

trev · Posted: Sat Jul 16, 2016 12:35 pm Post subject:

thanks for the input busbuddy! I know I'm getting 100% throttle at least, I have that Torque app running on an old Android phone on the dash, it gives readouts from the sensors on the engine, the throttle put is reading 100% with my foot on the floor. It also gives a RPM reading from the Crank Position Sensor. As for timing, I have VAGCOM but I'd have to figure out how to get the timing reading and then look up what it's supposed to be to compare my reading against.

However....

one stupid thing: so many knock-on effects!!

as per above, the engine wasn't boosting properly, I could only use fifth if I wellied it up to 120KPH in 4th then shifted into fifth and it was a lottery whether it would maintain boost and road speed or the boost would fail altogether and the van would slow down gradually. Also the brakes worked better at high revs than low revs, i.e. the servo assist was variable. The ECU was showing a code associated with boost control after it lost boost in fifth gear. 00575 for those interested (boost regulation difference)

A bit of googling pointed towards the N75 valve and the penny dropped! Ropey vacuum assisted brakes, error with the valve that controls vacuum to the turbo resulting in boost issues. It must be a vacuum problem!! I parked the van in the yard with the engine running, crawled underneath and it didn't take long to find the hissing noise of a vacuum leak!!

The last bit of original 1974 vacuum pipe left in the van had sprung a leak. Off to the motor factors, some new high pressure hose, fitted it up and bingo! All sorted. No more error codes, brakes are better, the engine is boosting well and holding boost and best of all, 5th gear is now a joy to use!! RESULT!!

still a few small niggles to get through but the snag list is getting shorter!!

trev · Posted: Wed Jul 27, 2016 8:52 am Post subject:

After replacing all the servo vacuum pipes with new I was still getting a fault code associated with the boost control. Occasionally it would go into limp mode but only if I have it 100% throttle in a high gear at relatively low speed for that gear. I swapped in a spare n75 vacuum control solenoid I had and it's solved the problem. I can now drive in fifth from about 50mph and it'll pull nicely without any boosting problems. Got 46.5mpg on the last tank too. Best yet.

trev · Posted: Sun Aug 21, 2016 7:30 pm Post subject:

more than 2000 miles done on this conversion since the start of July. It's going really strong! I have some silicone hose elbows on order to cure some small boost leaks on my bodged together boost pipes and today I lost the little grub screw on the shift rod coupler but other than that, it's been hassle-free. MPG has dropped to 38MPG over the last two tanks but I've been doing a lot of motorway cruising at 120KPH/80MPH-ish. I'm going to try for a good MPG on the next tank by keeping the cruising speed down to 100KPH/60MPH. Just an experiment Happy

Bundy · Padawan Joined: 03 Sep 2010 Posts: 54 Location: Cheshire

Hi Trev,
I'm looking at doing a Tdi conversion on my Bay over winter as I managed to get the Scoob engine to catch fire in Switzerland earlier this month!
What gearbox code did you use in your conversion?
Cheers
Al

trev · Posted: Wed Aug 24, 2016 9:09 pm Post subject:

It's a B5 Passat/Audi A4 gearbox, late '90s/early '00s. It's been modified to run up side-down. There are two ways to do this: have 3" of the bellhousing cut off and welded back on 180 degrees around or machine X amount off the bellhousing and make an adapter plate X thick to regain the original engine to gearbox relationship but with the gearbox rotated 180 degrees.