Low Power 603

[ewstan]

I have gone through a long process of trying to determine the cause of the low power problem with my '87 300D. The problem occured gradually over 2 month period. The car is very slow off the line and struggles to reach 3500 RPM where it just runs out of steam.

I had the throttle linkage replaced last summer and had the shop check for full travel when I started having the problem. Getting full travel they say.

The car idles well and doesn't smoke. All filters are new. Fuel in prefilter is clean. All pressure lines are new and clean. EGR and ARV are disabled.

When I checked boost pressure between manifold port and ALDA I was only getting 3-4 PSI.

The ALDA was not holding pressure, so replaced shaft seal and it now holds 15 psi with very slow leak down. No improvement in performance.

Discovered a few loose intake manifol bolts. Replaced intake manifold gasket and torqued bolts. Replaced air pipe gasket and O rings.

Exhaust sounds normal, not restricted.

In looking at the turbo, the shaft seemed somewhat hard to turn. Sent turbo out for rebuilding. Tech said that waste gate flap had come loose from rod in turbo so it was open all the time. After rebuild, turbo tested to 14.5 PSI before waste gate started to open.

Got everything back togeather this morning and went for a test drive. Very little improvement if any in performance. This is becoming a bit depressing. Makes we want to buy my '83 300D back from my daughter.

Am I looking at a fuel delivery problem or possibly a computer/electrical problem?

Any and all suggestions will greatly appreciated.

Thanks
ewstan

[CSchmidt]

ewstan,

I have a 603 as well. It lost power ... I did lots of looking around, but am still learning. Turns out a vacuum line/connection was bad so no signal was getting through all the plumbing to give the aldi the go signal. An independent found it for me. After it was fixed and driving it again I asked if he put another engine in the trunk! The turbo boost should start around 2500 rpm and be pretty strong by 3000.

As I understand it, the vacuum signal for the aldi takes a complicated route, including a delay/restriction mechanism (drivers side firewall near the hood hinge) to smooth out the throttle while the cruise on.

Good luck!
Chuck

[ewstan]

Chuck,

Thanks for the suggestion, but I have run a pressure line directly from the manifold pressure port to the ALDA to bypass the other items. Still no improvement.

ewtsan

[pentoman]

Seeing as you have spent a lot of time looking at the other areas, I would definitely be looking into fuel delivery now. Have you tested fuel pressure and/or changed the fuel filter?

[ewstan]

Russ,

The fuel filters are new. I haven't tested fuel pressure.

Thanks,

Wray

What about the screen in the fuel tank? Sounds like a fuel delivery problem in that not enough fuel is getting to the pump. Also look for a collapsed or pinched fuel line. My old 200d had this problem when I bought it. Would run great till you needed full fuel delivery. Then it would just drop off and slow down till you stopped and let it build up enough fuel in the filters again.

[Tom Sweeney]

Have you tried running it with the fuel cap loose to allow air to enter in the event that the tank vent is plugged? I found my tank vent was plugged while I was replacing the tank screen. I wish I had checked that first.

Tom

[Gilly]

I'd start with the basics before going over all the "gizmos" on the engine. Check compression, check fuel pump timing, check for chain stretch (especially on a 60 series, seems common).

Good thought on the fuel strainer. Usually the strainer problem will cause lack of power/engine shut down after driving it at highway speeds awhile though.

Was both the main AND prefilter replaced?

I wonder if pump timing could have inadvertantly been thrown off of adjsutment, that possibly is why it happened over a few months time. Anyone possibly loosen the bolts that attach the injection pump to the timing case?

Gilly

Why is the screen in the fuel tank in the first place? Seems with a pre-filter and then a main filter that it would be enough and much less work to fix if you got a bad batch of fuel out on the road.

[Gilly]

I believe to keep the finer filters from being plugged by real coarse contaminants. Kind of like the strainer in the tank strains out "the rocks and sticks", and the prefilter keeps out the "sand and grit" and the main filter keeps out the even finer "dust and powder" so the fuel injection pump and injectors are undamaged.

Gilly