87 300TDT performance - PeachParts Mercedes-Benz Forum

aersloat · #1 07-31-2009, 01:34 AM

I have been having some uphill performance issues with the 300TDT. The problem is not constant but it is fairly regular. I only started noticing this a little over a month ago. On uphill starts, city streets, or on the highway or freeway the car will struggle to accelerate or even maintain a speed most of time.

Over the 4th we drove to the coast from Portland and going through the coast range I had no problems on the flats or downhills but on the uphill grades I was the guy who had to get over in the passing lanes. Halfway through the trip I mashed on the throttle to pass two cars on a flat and the rest of the trip the car was fine -- regular old power -- but it didn't last long.

I took the car into my indy for some AC work and had them look at things. I had started diagnosing things and took off the ALDA. All they did was put a new (well, to me) ALDA back on. That of course did not do it. I have also cleaned the pressure line and tap from the manifold through the switchover to the ALDA. Replaced fuel filters. Checked air filter. Checked tranny fluid level.

So, my father in law drove up to visit us in his 87 300TDT. We put a boost gauge on his and what we found was that his boost ramps up pretty quickly from zero to just over 10 psi. It pretty much stays there when accelerating. When he pulls off the throttle it ramps down pretty quickly back to zero. This is just in the hilly streets around our house -- no freeway cruising.

On mine the boost ramps slowly up to about 5 psi where it will often hang out. If I stay on the pedal hard it will continue to ramp up to 10. When I pull off the throttle it often does not ramp right back down. It usually goes back down to about 5 and will often stay there until I stop or really slow down. I have noticed that the boost will creep down to between 2 & 3 on some of the gradual highway grades where I have trouble maintaining a speed -- even when I basically have it floored.

I have no problems starting & it idles well. New ALDA has been backed out a bit and it shows near zero leakdown with a mityvac. I haven't done any zero to 60s but on flat ground pickup seems fine and I don't have any trouble getting right up to 80. It doesn't appear that I have any fuel leaks and no indication of air getting into the fuel system.

My best guess would be a wastegate issue given what we have already addressed. Does that sound right? Is it possible to address a sticky wastegate without removing the turbo? I guess it could still be fuel but it seems that the basic problem is with what kind of boost I am getting. Any other ideas? Thanks in advance.

JimmyL · #2 07-31-2009, 01:37 AM

Quote:

Originally Posted by aersloat

I have been having some uphill performance issues with the 300TDT.

aersloat · #3 07-31-2009, 02:03 AM

How is that rouge exactly? My manual says 300TDT, as does anything Mercedes seems to publish on the 87 W124 diesel wagon.

Wodnek · #4 07-31-2009, 09:04 AM

Quote:

Originally Posted by aersloat

How is that rouge exactly? My manual says 300TDT, as does anything Mercedes seems to publish on the 87 W124 diesel wagon.

They are factory badged as 300D for the sedan
and 300TD for the wagon.

Everything sounds like a fuel delivery issue. Have you tried changing the filter screen that threads into the fuel tank?

A waste gate not dumping boost fast enough wouldnt rob you of power.

tbomachines · #5 07-31-2009, 09:23 AM

It could be the overboost protection valve. Clean the banjo bolt coming from the intake manifold (I assume you did because of the boost gauge), make sure none of the vacuum lines are blocked from the OBPV. Do the wastegate springs wear out after a while? I would suspect the wastegate for your problem as well, I think you're on the right track.

babymog · #6 07-31-2009, 10:09 AM

Change fuel filters, sounds like a fuel filter problem.

Does it shift early? If so it will never develop proper boost.

Switchover valve. Bypass temporarily, be sure the connection to the intake plenum is open (blow through it), then temporarily run a line directly to the ALDA.

Three most common.

rrgrassi · #7 07-31-2009, 10:54 AM

Quote:

Originally Posted by JimmyL

It's the weight of the roque "T"

Most everyone knows where the overboost protection is on the w123 or w126.

Where is it located on the w124?

aersloat · #8 07-31-2009, 11:58 AM

It is on the firewall. I had some extraneous plumbing that someone here (I think gsxr) said was a retrofit to correct cruise surging (if anyone is interested I posted the diagram in a post a few years ago). Basically it was two valves in series with some filters.

Anyway, as part of the troubleshooting I bypassed that stuff to take back to stock and as noted I removed and cleaned the tap to the intake (not a banjo bolt on the 603), the pressure line to the overboost, the overboost itself (removed and cleaned out with brake cleaner), and the line to the ALDA.

I guess it could be shifting early, although it doesn't seem to shift any differently than say a few months ago when power was fine. When I got the car four years ago shifting was terrible. Cleaning up the EGR stuff and replacing some vacuum lines & fittings really made a difference and it shifts pretty nicely now. Would that be a matter of adjusting the bowden cable?

I have not replaced the tank screen. I did replace the primary and secondary fuel filters. I run commercial B99 in the summer and B50 ish in the winter and have been for a while. About a year ago a careless attendant gave me 5 gallons of premium unleaded, which among other things is a decent solvent and cleaned up whatever the biodiesel hadn't. The problem seems unrelated to whether I have a full tank or not so I doubt there is a problem there, but it is something else to check.

babymog · #9 07-31-2009, 07:18 PM

Quote:

Originally Posted by rrgrassi

It's the weight of the roque "T"

Most everyone knows where the overboost protection is on the w123 or w126.

Where is it located on the w124?

On the left inner-fender/strut tower.

Jeremy5848 · #10 07-31-2009, 09:57 PM

Quote:

Originally Posted by rrgrassi

. . . Most everyone knows where the overboost protection is on the w123 or w126. Where is it located on the w124?

The over-pressure switch is on the intake manifold, above the IP. The solenoid valve that cuts off boost to the ALDA is attached to the forward firewall, next to the windshield washer reservoir.

aersloat · #11 08-07-2009, 01:14 PM

So, I have done some additional troubleshooting and am making some progress after some advice from gsxr.

My wastegate is at the least sticky. I took it into my indy to chat and he tried to move the wastegate with pliers and was not able to get it to budge. He recommended blasting the connection on the turbo side with WD40 overnight, which I did. Later I disconnected the wastegate hose and put some pressure on it. 16 psi would not actuate the wastegate (and was all my mityvac would do) but with the pressure sitting behind it I was able to move the wastegate with pliers. Removing pressure would cause it to return, but re-application of pressure would not cause it to move -- only mechanical force plus pressure. My air compressor is on loan right now or I would put a little more pressure behind it.

I took it for a spin around the block w/o the wastegate hose and the boost pressure topped out higher but there was no significant difference. I was not able to push it though.

-- Looks like it is at least partially a wastegate issue and if the wastegate is not seating closed completely I could be dumping boost prematurely causing boost to build slowly... does that sound right? Dieseldiehard has mentioned a few times that the wastegate seat can get junked up and can be cleaned. Does anyone know if that area can be exposed and cleaned up without removing the turbo? I had a #22 head put on 18 months ago so my manifold bolts should not be too frozen, but the turbo housing itself might be. I asked my indy about removing the turbo but they usually ship out turbos to a shop in Eugene for work did not seem too eager. I guess his boat payments are not falling behind.

Thanks for any advice.

gsxr · #12 08-08-2009, 10:20 AM

I'm leaning towards a sticky wastegate as well. If it were fuel related, the behavior wouldn't be intermittent. The testing with the ALDA removed rules out anything with the overboost circuit or ALDA signal. When the indy couldn't move the wastegate rod with pliers, it may have already been stuck open (and therefore would not extend further). I'd mark the wastegate rod with a dab of paint, or magic marker, etc so you can tell what position it's in. If you have compressed air available, it would be nice to cycle the wastegate open & closed a few dozen times.

aersloat · #13 08-08-2009, 04:34 PM

I was able to take the car out on a nice 2 hour drive around the greater Portland metro area this morning-- the 1 year old napped pretty much the whole drive and the 4 year old talked non-stop -- but the car performed very well. The boost behaved much differently than it did before I worked on the wastegate -- rapid and even spool up to around 10 psi, no malingering around 5 psi on the way up. I dropped it into third on 26 and hit the throttle up to around 4000 rpm and boost was right around 12 psi - which is about right I believe. No problem with uphill power at all. I still have not done a 0 to 60. Not a lot of good, flat places around here to do that.

Seems like the wastegate was the problem. I think there is still some improvement to be made and I will hit the linkage with lubricant and cycle some compressed air behind the pod once I get my air compressor back. Thanks Dave for the advice.

aersloat · #14 08-20-2010, 03:21 AM

An update...

While working on the wastegate did improve things I was still having some issues. I also had a new timing chain put on since mine was a little on the stretched side. That improved things as well.

One symptom that I had been having was that occasionally my engine would die when I let up after being under load -- never at highway speeds though -- like at the top of my steep driveway. On Tuesday the car died in stop and go traffic while the AC was on. It started right back up but it was the same symptom of coming off of a load. I figured that it had to be fuel starvation of some kind.

So, I popped off the shut off actuator/valve and, sure enough, it was not working properly. I had pilfered this one two years ago from a spare injection pump. I still had the old one. The throw on the actuator arm was only half of what it should have been -- it only went down and not up. So my replacement actuator was starving the injection pump. It did shut off the car just fine -- something that the old one had stopped doing. My stop lever never came up to the full open position. The stop lever would also move with RPMs - a little up and down at idle too. It is also possible (or maybe likely) that I did not manage to get the replacement actuator seated correctly with the stop lever which may have compounded things.

Got a new shut off valve and made absolutely sure to get it seated correctly. Car turns off, but more importantly, it drives like it should. Good turbo ramp up and zips right up the hills that it was dogging up a few days ago.