Hi,
Thanks for all of the great ideas re: 300D fuel starvation. Does anyone have any experience with what would happen if the fuel overflow valve or circuit were clogged?
The car starts well hot and cold (25 degrees this morning without being plugged in) and idles very well. The power is good up to 2500 rpm and then goes soft.

The entire fuel system is dry and without any apparent leaks. When I replaced the spin-on fuel filter, I installed a NAPA Gold and filled it with Redline before installing it. I didn't disturb the hand pump... I just started the car and it roared to life. Everything is dry so I don't believe I have any leaks.

BTW, the smoke is whitish gray and is more visible the farther I drive the car i.e. it is ok on my street, but 1 mile away it gets worse. (This on an already warm engine.)

Does this sound like a clogged fuel overflow valve? Thanks in advance.

John
Wheelman

82 300D
90 Volvo 760T
88 Volvo 745 256000 miles!

I suggest two easy ways you can try:

(1) The in tank fuel filter may be clogged. Disconnect the plastic fuel filter and blow air into the tank to clean it.

(2) Negative pressure is created in the fuel tank. Remove the fuel cap to see if the problem goes away.

Good Luck.

David

Hi David,
I already tried removing the fuel filler cap... no dice. I don't think its the fuel strainer because when I perform the boost test (the car in drive, foot firmly on brake, floor the accelerator, I get the same symptoms as I do on the road and the inline fuel filter still appears to be full.
Thanks for your help. Keep sending the ideas... I don't want to drive the Volvo to Thanksgiving dinner!
John

John,

I do not understand the concept of the boot test. How can the boot test tell the conditon of the fuel strainer?

David

Hi David,
>>How can the boot test tell the conditon of the fuel strainer?

Because the engine was still suffering from fuel starvation, as evidenced by the lack of power, but the inline filter was still full of fuel. If the clear filter were empty, or nearly empty while under load, I would surmise that the fuel blockage was aft of the first filter. Since it remains full, even under maximum load, I believe the obstruction to be forward of it. I'm still going to try your suggestion, though. I've done everything else possible in the last three days!
Many thanks.
J.

John,

I think the fuel filter will still appear to be full if the in-tank filter is clogged. The only time it shows empty is air leaking into the fuel line or no fuel in the tank. If the in-tank filter is partially clogged, it allows only small amount of fuel to feed the engine for light load. It will feed the same small amount of fuel for the heavy load but that is not enough. I am not saying that is your problem but at least, it is a quick way to check to eliminate one possibly cause.

The only way I know to check a clogged in-tank filter is to connect a vaccum gauge to monitor the fuel line pressure before the fuel pump while the engine is running.

Let us know what you find.

Thank you.

David

[This message has been edited by be459 (edited 11-21-2000).]

Hi David,
I swapped the intake and return lines on the inner fender to determone if the strainer was clogged... i.e. I was drawing fuel from the fuel return line. I also removed the filler cap and had the same problem going down the road.

Further, I removed cleaned overflow valve and set the spring to the proper tension as per the factory service manual. I'm running out of ideas!

Thanks for your insights!
J.

John,

If this problem happened after you put in a new fuel filter, is there a chance that you use a wrong filter?

David

I thought of that too. To make sure I had the correct filter, I picked up another new one at the Mercedes dealer today. Same problem! Basically the car runs out of fuel at 2500+. I'm almost ready to drop it off at the independent mercedes service shop. This will be very damaging to my ego. Usually if I'm going to drop a vehicle at the shop, I prefer to have made the diagnosis going in. If this were a Volvo... Many thanks for all your help.
John

My 86 300E does pretty much the same thing that your describing. I dont know what kind of components your car has but I am pretty sure its my KE-Jetronic or K-Jetronic (whatever my car has) malfunctioning, I have replaced the OVP which is needed to operate the fuel control, but it didnt do any good, the car ran good for about 2 miles after I replaced the relay but then started the same thing over again.

------------------
Adam,
1986 300E
1997 Acura Integra GS-R

John's car is a diesel which is very different from the gas model.

For the 1982 model, the turbo starts working around 1300 to 1500 rpm. I assume that you have tested the ALDA boot circuit to be sure that the switch does not cut out the fuel too early. The turbo has a wastegate valve to prevent overboot also. If it starts open too early bleeding the manifold pressure, the turbo will slow down.

Why this happen after you change the fuel filter? Did you work on any other areas at the same time that could restrict the flow of air or fuel? There is a fuel pump attached to the fuel injection pump. I do not know how to test this fuel pump if it is dying.

David

For the 1982 model, the turbo starts working around 1300 to 1500 rpm. I assume that you have tested the ALDA boot circuit to be sure that the switch does not cut out the fuel too early. The turbo has a wastegate valve to prevent overboot also. If it starts open too early bleeding the manifold pressure, the turbo will slow down.

Why this happen after you change the fuel filter? Did you work on any other areas at the same time that could restrict the flow of air or fuel? There is a fuel pump attached to the fuel injection pump. I do not know how to test this fuel pump if it is dying.

Howdy,
I cleaned out the boost sensor line and for the purposes of this problem, have bypassed the cut-off valve thus running sensor line stright to the ALDA from the intake manifold. I tested it under load and was in fact getting positive (boost) pressure from the manifold. I don't know how to further test the ALDA without getting into some fairly complicated plumbing. I'm hoping the shop guru can discern thr problem with the same ease possessed of a Palm Beach ballot official counting a ballot.

I didn't get into any other areas whilst doing the filter change. I am a firm believer in limiting the number of variables in an equation. Following the filter change, I went on the cursory test drive and noticed the symptoms. I've been doing my own maintenance for years and while this is my first MB, I I do feel comfortable under the hood. On the plus side, since this problem occurred five days ago, I have become much better acquainted with the inner workings of the 300D. Having driven SAABs and Volvos for years, the MB is a real treat to service. The build quality and materials are remarkable. I'm really enjoying it.
Thanks agin!
J.

John,

Did you actually use a pressure gauge to measure the boot pressure? According to Steve's post dated 3/15/2000, "waste gate on 300sd", the pressure should be 9 to 10 psi. Since you have the turbo boot up to 2500 rpm, you should get positive (boost) pressure from the manifold. But is it within spec?

David

1984 300d turbo 147k
replaced engine and trans, always replace fuel pump or lift pump $126-$200 the primer pump is new on the unit, one 19 mm deep socket to remove the right side fuel in, remove the left side line out and 3 10mm nuts use 10 mm deep socket left side, use a pan under engine oil will leak out, new unit have 4copper seals, gasket, prime pump new elect pumps almost same price max pressure 10 psi mercedessoure.com $160.00, good power, no smoke, fuel miles up