Fixed exhaust leak -- What will change? - PeachParts Mercedes-Benz Forum

Jeremy5848 · #1 07-10-2007, 08:56 PM

1985 300D-T (CA version w/trap cat) W123 w/223000 miles

I found and fixed a crack in the flex pipe that leads from the trap catalyst to the EGR valve. The flex pipe was effectively broken in two, with the ends perhaps a millimeter apart. A fair amount of exhaust vented from this crack but, being located down under the trap cat, couldn't be seen. This effectively robbed the turbo and meant that boost was delayed a good 1000rpm.

Having now found and fixed this problem (discussed in another thread here somewhere), I find that the turbo spools up faster and, although the wastegate still limits the top to about 10psi, the pressure is higher for given conditions than it was before.

For example, at 55mph in high gear on the flat road, the boost gauge previously barely read 2psi whereas now it's solidly at 5psi. Give the engine some throttle at this speed and the boost used to absolutely creep up in pressure, as did the car in speed. Since the fix the car responds much more rapidly and is especially noticeable on hills.

I understand little of turbocharged, fuel-injected engines. Apparently the IP provides a calibrated amount of fuel and it's then a question of how much air can be stuffed into the combustion chamber. Air at STP (in, for example, a NA engine) doesn't contain enough oxygen to completely burn all of the fuel. A tubocharger stuffs more air, hence more oxygen, into the engine, allowing more of the fuel to combust. Clearly, this increases horsepower and torque -- one need only look at the published specs.

What other things might I expect to see? (The car has been driven around town since the repair but will be on the road later this week for a ~2000 mile trip.) Better fuel efficiency? That would be nice, if I can keep my foot out of the firewall.

Any other performance issues to watch for? The car still has the trap cat, unfortunately, my "test pipe" isn't done yet.

Jeremy