No power over 40 check everything - PeachParts Mercedes-Benz Forum

jake12tech · #1 10-09-2017, 07:49 PM

I am at a loss with this 87 300d. It makes 0-60 in about 14-15 seconds which I am fine with. It is an old car that's 30 years old amd don't expect it to run like a new motor. I think it's because the transmission shifts a little late wjen you get on it, but otherwise it shifts smooth and on time. Again it's old.

I checked compression and have 350-360psi across the cylinders, adequate fuel, clean fuel filters. I checked the crossover across the valve cover and it Doesn't look too sooty inside the manifold. I checked the alda line and it's clear. The turbo spools up at like 1600 and it pulls good. But if I'm on the highway and nail it WOT it Doesn't really pull and creeps. I'm not sure if that's how this single cam 12v is supposed to perform. I'm used to dohc 24v om606 engines that pull like a freight train.

This car pulls torquey off the line but little up top.

Any thing else I should check? Will removing the alda possibly resolve the lack of top end power?

I figured if all the engine bay filters dont look dirty, the tank filter is probably fine. I also have little chain stretch and good IP timing.

At a loss. Ideas.

Diseasel300 · #2 10-09-2017, 07:57 PM

How much boost are you making? You certain the waste-gate isn't opening early? The 603 has a weird power band, the sweet spot seems to be between 2000-4000 RPM. If you're too far down in the rev range, hit the downshift button and it should light a fire under it. If you're close to or above 4000 RPM, back off the pedal and let it upshift.

My experience with the 603 is that it is NOT a rocket-ship, however it is very capable. Spunky around town, competent on the highway. Passing someone at 60+ may take a while for a run-up... Make sure your kick down switch is working. The 603 likes RPM, especially when trying to accelerate. Too much RPM and it'll accelerate slower than if you let it upshift and stay in the peak torque band.

sixto · #3 10-09-2017, 10:57 PM

Is the throttle pedal moving the IP to WOT? Has anyone messed with the full load stop? If that checks good, temporarily remove the ALDA and check for performance improvement including boost at 2500 rpm with the pedal to the floor. I'd expect at least 15 psi. Conversely, is there much performance loss if you plug the ALDA signal line?

Sixto
98 E320s sedan and wagon

Turbo300Mercede · #4 10-09-2017, 11:09 PM

I also have a 87 300D. Not quite as good of compression as yours.
I've done lots of things to mine to get it to run better. It is night and day different from when I started. But it was really slow when I acquired it 6 years ago. It now runs like a stock V-6 gas motor, but it has more torque than upper end horsepower. It runs out of steam around 3600 rpm.
Installed Monark injector nozzles and set the pop off pressures.
Advanced the timing a few degrees over factory.
Adjusted the ALDA / disabled it-this was one of the most noticeable increases.
Disabled the EGR and cleaned the crossover pipe and entire interior of the intake manifold.
Upped the boost to 14 psi from 11. (not that noticeable of a difference, maybe just a little)
Addressed a clogged catalyst. (this was noticeable compared to when it was clogged)
Fixed the flapper under the air filter to always stay open. (no noticeable difference).
Run one quart of marvel mystery oil per oil change. This provided a noticeable decrease in blowby. I catch the blowby oil vapors that separate back into oil in a catch can and return the oil to the crankcase manually. So I know from one week to the next how much blowby it has.
I monitor inlet fuel pressure to the injection pump using an aftermarket Dodge Cummins fuel banjo bolt that has a pipe thread in the hex. Same thread pitch and diameter as the Mercedes. It is: BANJO BOLT - TAPPED - 12MM FITTING ('89-'93 and '98.5-'07, 5.9L) @ $7.00 quite a bargain. Place is in Cumming, Georgia. Kind of ironic, town name so similar to the products they carry...

sixto · #5 10-09-2017, 11:40 PM

Quote:

Originally Posted by Turbo300Mercede

Addressed a clogged catalyst.

Yes, the cat! Jake, are you able to run a straight pipe for testing?

Quote:

Originally Posted by Turbo300Mercede

It now runs like a stock V-6 gas motor, but it has more torque than upper end horsepower. It runs out of steam around 3600 rpm.

Umm... my '87 300D was pretty quick without touching the full load stop. There's no way it could keep up with either '98 E320 which I think run 0-60 in the low 7s

You're probably running out of breath because of (IP?) timing. Tweaking the full load stop should help some but take small steps if you don't have overboost protection.

Sixto
98 E320s sedan and wagon

Maxbumpo · #6 10-10-2017, 07:40 AM

My OM603 pulls like a freight train "at speed" and passing on the highway easy, and I know that I've still got several things to tweak to get it really good. I'm getting about 13 psi of boost.

(1) Install a blocking plate to disable the EGR. When this fails open, it robs power and causes what you describe with lots of smoke at speed.

(2) I also like the plugged exhaust (cat) idea, if the engine cannot breath because of an obstruction in the exhaust, you'll have a similar loss of power.

(3) On the breathing note, check air filter and the MAF flap in the assembly just below the air filter to make sure that flap is not jammed closed.

jake12tech · #7 10-11-2017, 06:08 PM

I failed to check everything except the Bowden cable. The Bowden cable 1/4 turn adjustment lit a fire under this car ***. It has way more power than it ever has before.

Maxbumpo · #8 10-12-2017, 09:20 AM

Excellent, I love those simply fixes!