I own a 1984 300D Turbo Diesel with 304,000 miles. It is a California spec car.

It is sidelined now and I need your help to figure out what is wrong with it. When cold it will start on what seems like three cylinders with little power. When I start to drive it, it still misses until it "clears its throat", which happens quickly, and then it runs ok. But even then it doesn't have a lot of power, and the turbo doesn't seem to make much power. (When it was running well, it was quite quick and fun to drive. This problem seemed to develop suddenly) When it is warm, andI shut it off, it is VERY difficult to restart, and I have run the battery into the ground once just cranking it.When it does start warm,it is barely running and generates no power. If I keep trying to rev it it eventuallysmooths out and I can drive it.

I have changed the two fuel filters twice now. The first time I changed the main filter, the fuel seemed to be cloudy with little tiny bits of something or other. The small filter had some black stuff in it, but not a lot so I didn't suspect it of being a problem area. After I changed the filters the situation did not improve.I drew a sample of fuel from the gas tank using a hand pump, and it looked ok. I opened up the larger fuel filter and the fuel seemed ok. The inline filter was clear. But I changed them both again just to make sure. I have not checked the filter in the fuel tank. I manually bled the system at the main filter both times. The valves were adjusted 3,000 miles ago.I have run Sea Foam (I think) in the gas to keep the injectors clean. It did improve power noticeably.

How can I get this beauty back on the road. What should I do next?

It is now 9/6/07. I wrote the above message on 9/1. I have received no replies at all. Everyone on this page of the forum has received a reply except me. Am I doing something wrong? Everyone says that this is a good forum, but I feel like I am wasting my time.

 

When you replaced the filters and purged the system with the hand pump did you see a tiny stream of bubbles appearing in the primary (clear filter) during the hand pump operation? If so the hand pump o-seal or fuel pump is leaking. Another indication of a leaking hand pump or fuel pump gasketare fuel drops on the ground beneath the fuel pump. It's much easier for the pump to suck air than draw fuel from the tank. This effect occurs both at start up and at top end. Did you notice if top end performance appeared starved?
The black specs were likely algae that had lived in the diesel tank when fuel contained sulfur. Without sulfur the algae dies and clogs filters.I have found that use of ULSD tends to cause the hand pump seals to fail morefrequently.

You also mentioned turbo. Have you pulled the inlet to the turbo to ensure the impeller spins freely whenthe engine is cold and hot? Pleasecheck this with the engine off. I don't want someone typing with 3 fingers.

 

Grateful,
Thanks for your reply. No bubbles thru clear filter. I've ordered a replacement manual pump. I'll let you know if that is it. And I will check the turbo. Then it is on to new brakepads as the abs light is coming on. Thanks again.

John

 

I replaced the manual priming pump with no improvements. I bled the fuel lines at the injectors with only some improvement for a short time. The current symptoms are:

Hard to start
Misses badly once started then smooths out a bit by pumping the throttle
Nailing for quite a while now.
No power.
Sometime misses when I am driving as well as at startup.

My next step is probably rebuilt injectors. Any thoughts?

 

Hard starting while cold is usually tied to the glow plugs or a cracked cylinder head. If the plugs check out OK is the coolant clear or is it brown with an oil sheen? I'm trying to work from your comment that running ahigh cetane cleaner improved performance.Is the vacuum system Ok? The next thing I would check is for a stuck open or weak/leaking EGR valve,the relief valve on the turbo for leakage, plugging of the tubing on the rear of the manifoldthats runs back to the ALDA sensor on the fuel injector pump.

 

Grateful,

Thanks for the tips! I have replaced the injectors with rebuilt Bosch units, but it didn't seem to make much of a difference [:'(]. I checked the glow plugs and got a voltage measurement of around 9.8 volts to all of them. Couldn't figure out how to get the resistance, but I will try again. I am trying to locate a compression gauge to find out if there is a leak somewhere [:@]. The car isn't really hard to start when it is cold, it just runs on 3 cylinders or so and makes a mechanical noise. It revs slowly, but will smooth out at 2500 rpm. No smoke. The coolant is relatively clean, with no oil slick. "I'm trying to work from your comment that running ahigh cetane cleaner improved performance." The cetane cleaner worked quite well, but that was before all these troubles started. The vacuum system is OK, which took almost a month or so of trial and error. I haven't looked into the EGR valve. Is there a write-up on how to do that somewhere? I will check the relief valve on the turbo for leakage. I cleaned thetubing on the rear of the manifolda while ago. There wasn't much junk in it. Should I adjust the ALDA and if so how should I go about that? All for now. John

 

I checked the turbo inlet impeller when cold and it spins freely. Not sure I want to check it when hot.

I pulled the cam cover because the engine is making a mechanical noise, which at first I thought was nailing. I guess that was my mistake. The area under the cover looks fine. I check the valve clearances and there were only three that were off, and then only a little bit.

I want to do a compression test, if I can find a diesel gauge. Any thought. This whole thing is not going well at all [X(].

 

The absolute fool proof way to check glow plug and timer performance is to remove the injectors and turn the ignition on. You'll see if all plugs glow come to a bright yellow within spec timeout. Since you have new injectors, instead remove the cover from the timerrelay box(on your lower left after raising the hood). After lifting the cover you will see a fuse between two philips head screws and a wiring harness ending with a plug connector. The fuse should be intact. I always take a tiny drop of crank case oil put it on my finger and then wipe it across the fuse to expose any hair line fractures. I had this happen once, a hair line fracture, that a visual did not reveal but as soon as the black film was wiped across the fuse a line appeared and the culprit was found. Next, remove the glow plug connector from the timerbox.The connectoris the end of the wiring harness that runs to the glowplugs. With the ignition off use an ohmeter with positive in one of the five holes in the connector and the negative on a good ground on the block. Resistance should be about 1-2 ohms. If any of the holes reads an open you know the glow plug is shot or the wire to the plug open. 99% of the time its the plug thats open.
For the EGR, disconnect the vacuum tube from the top and plug the hose. Drive the car watching for changes from previous observations of exhaust smoke during heavy acceleration. If the change is significant the EGR diaphragmis likely leaking. A broken diaphragm is common. EGR's are expensive. Search on this site for EGR's and read the recommendations.

 

An update. After much work and no results I took it to my local mechanic, who diagnosed and solved the dreaded algae around the fuel tank strainer. Car runs good now. [&:] If I can just keep it that way. Thanks to everyone for your help.

John

 

Hi John,

Thanks for posting this thread. I have a 1981 300SD that I just swapped a 83' 300SD engine into and replaced all gaskets (except the head gasket) on the engine and transmission. The original engine died on a road trip last summer and I've been working on getting it running again since then.

To my dismay, I am now having power problems at startup that seem to go away once the engine is warm. Like you, I have changed the filters, checked the fuel priming pump for leaks, checked the turbo, and the cold engine starts just fine. I haven't been able to try out blowing air back to the tank because I do not have an air compressor handy... though I suppose I could figure out a way to connect a bike pump to the air line.. hmmmmm

Before I found this forum I also suspected the fuel tank filter, especially since I ran a few tanks of 100% biodiesel (B100) in this old car before the original engine overheated.

Sorry for the long intro, but I wanted to share this tool. I will try out to replace the fuel tank screen. The video at the link should also be helpful to anyone else facing the same situation. After I've replaced the fuel screen using Kent's adapted socket I'll post how it went and if I found that the screen was blocked.

More soon,
Jonathan