No power

[cbum33]

Sorry not much luck searching. I have an 82 300d. I had been have rough idle hard to start and car wouldn't idle till car was warmed up then idled fine also low power whentami g off. I Car has 215,000 miles on it and as far as I know never had nozzles changed. I first cleaned fuel tank, purged the fuel system with moly purge, changed filters, Checked the valves. While I had everything apart did compression check which was a cold engine and all cylinders checked around 300. I had the nozzles rebuilt by a local shop and they told me 3 of my nozzles were bad when they got them. Since then I put it all back together and now the car will start good and idle. But when push the peddle down doesn't really rev up at all. Once start driving the car seems to have normal power and drives fine but it takes till car gets up to 10-15 mph oR so before really seems to start running right. After installing rebuilt nozzles I had to adjust my idle because it was low. Now 2 weeks later it seem slow again and the power issues is still there.

Think might try to get a another set of heat shields and check compressions when hot. But wondering if it's bad rebuilt nozzles or possibly bad injector pump. I have the stuff to rebuild turbo. Maybe possibly waste gate issue just not sure where to go. Can def feel it kick in when it's starts to recover. Even once it's warmed up hard to rev engine with peddle

Any advice would be greatly appreciated.

[t walgamuth]

Is your car taking off in second?

[cbum33]

Interesting question haven't really given that a thought. Will try to check that tomorrow. Thanks

[bigpanda16]

Back the Ada or Alda out a half or one turn and see if that does anything. If not you can easily put it back

[Mxfrank]

Before you mess with the Alda itself, check the boost sense line.

Mercedes ALDA boost system service

[tyl604]

How about a bad or mis-connected switchover valve?

[barry12345]

Since it cost nothing. Temporarily close the return line from the injection pump off. This having to adjust idle and it changing could be very low fuel pressure. Doing so for a test will hurt nothing.

Even at idle fuel should be coming out the return line as well. With no air in it. Two simple tests. If it does not pass them this area will need attention. Or should receive it as it could be the issue or part of it. Before moving on.

My thoughts are that I would want to make sure I did not have any of the common fuel supply problems existing on these cars before looking further.

Also a check of the boost circuit for obstructions is also another item that is just good housekeeping. You did your injectors already perhaps a little early but a good thing as well. .

These things even if not the problem now or contributing to it. Show up as needed maintenance too many times to ignore. At idle or low speeds. if any air is in the fuel it could have a more pronounced effect than at higher engine revolutions.

Over the years I have had cars. That I was uncertain what the problem really was. I then just started to give them basically a tune up. More than a few times this found the issue. Or indicated what it was.

I believe your compression test was good enough to ignore doing another. To me your idle issues seem to be fuel system related. Perhaps the number one problem we usually experience with these cars. Is in the fuel supply system. So it just has to be checked.

[cbum33]

Sorry for taking so long to get back with details. So I went ahead and changed the fuel filters again to make sure it wasn’t that issue. The tank screen was clean also. I checked the wastegate and it seems to be actuating with Air pressure I can hear it pop back and forth. The air line appears to have no blockage and no leakage.

Back to the fuel I am noticing that the clear line coming from the injection pump to top of filter which I think is returning fuel seems to always have a lot of air in it. Especially at idle and lower RPM. But when the car gets warmed up and the RPM gets higher the air seems to go away and the car seems to be running much smoother. Not exactly sure how to tell if it’s to much Air but curious as to where to go with that assumption.

When you said to close the return should I just clamp it off and see if runs better without being able to return fuel? Thanks for any help

[cbum33]

Another quick update. Should of tried before I posted. But I clamped the return hose going back to tank and that took care of the air in the fuel line and the car seemed to be way more responsive to throttle it reved up a lot faster than before. As soon as I took clamp off return hose Air appeared back in clear fuel line.

Thanks for the help

[barry12345]

First of all find the source of the air getting into the system. There should be none other than a constant fixed amount in the pre filter. You may or may not have another issue as well. No way to tell until the air situation is eliminated.

[cbum33]

So I have now changed the primer pump, the fuel lines to the injectors, installed a new tank screen and hose, installed 2 new lines from the tank to the hard lines, installed new line coming out of the primer pump housing the the pre filter and new line from the pre filter to the supply hard line. Still have a large amount of air in the fuel system. If I clamp off the return line it seems to go away. (have changed all fuel filters and the injectors have been rebuilt)

Also have noticed now that it has gotten cold the last few days the car seems to have its power back once its warmed up. But didn't get the chance to check the fuel lines for air during this time frame.

The power being back is that when I step on the pedal the car seems to accelerate and take off like normal where as before it took till you got up to around 10-15 MPH before could feel the car take off and have power. It might literally 2-3 blocks before car would get to 15 mph. Had to stop driving it because it was a little dangerous when having to pull out. Any ideas or suggestions would be greatly appreciated.

[barry12345]

I would want to know what the fuel pressure is. In the base of the injection pump. Obviously the source of the air has to be found as well. When you clamp off the return line at the injection pump. You are in effect raising the fuel pressure.

This could indicate the relief valve that controls the fuel pressure is weak. Plus the lift pump is still serviceable usually.

Assuming you do not own a liquid dampened pressure gauge to check the fuel pressure available in the injection pump. You probably have the relief valve that you can take apart and stretch the spring back to 27mm if it is shorter. This increases the fuel pressure back to normal before the relief valve opens.

As for not seeing any air when the return line is clamped off. I think in that situation it might be normal as you have stopped the line from flowing. Yet there may be another explanation. I will get to it.

If you do not see bubbles flowing through the small filter. Chances are good it is leaking air in somehow after that point. The rubber hose connections from it to the pump are a common point. There also have been cases where that small filter itself is the source of air leakage. You have covered that plus the lift pump.

It is not abnormal to have to use a substantial effort to locate the source an air leak into the system. I read you posts over again just a moment ago. I am starting to suspect that you may have two problems in the fuel system. Or one is creating the second somehow.

I might forget the air ingress for the moment and work on the fuel pressure. There are indications it is too low. So take the relief valve apart and clean it and stretch the spring back to 27mm if needed. Or perhaps the spring in there is broke. .

There once was a situation where one of these engines would still run with that relief valve totally defective. On most of these cars usually they will not run at all. Then there are those engines that will run to some extent with very low fuel pressure but poorly compared to what they do with good fuel pressure. Actually what we call the relief valve is really the fuel supplies only pressure regulator.

It troubled me to some extent for a long time. How does air get into the system after the point the fuel is pressurized? Yet there are no obvious fuel leaks. Someone mentioned venturi effect. I automatically knew the fuel flow was too slow for that. Then it occurred to me the vicious spikes that are created by the injection pump. As the peak pressures of those pulses drops off so fast and it is in a hydraulic based system. It will try to stop the rapid decline by sucking air in wherever it can.

As the pressure wave goes negative. A non dampened pressure meter on the system shows this as the needle slams hard from one extreme of the pressure gauge to the other in practice. Making the constant fuel pressure unreadable. Where a liquid dampened 0-30 pound gauge like harbor freight sells. Does not respond quickly enough. So it is not able to track the pulses.

It just reads the stable fuel pressure instead. I often wondered how many people wondered as I did just how atmospheric pressure could overcome higher pressure. Well it cannot in reality. Yet it can service a rapid frequent occurring negative pressure demand. The exact same way that it makes a pressure gauge slam from one stop to the other. Just a thought.

I may as well take it to the end. With low potential fuel pressure exisiting. There might be more ability to suck air in. When he clamped the return line off he saw less to no air. This is why I suggested to pay attention to the possible and suspected low base fuel pressure first. Correcting that may reduce the apparent air intake. It also may not. Still it is what I would pay attention to first.

There are other clues here like why no power until 10 to 15 mph. The lift pump recharges itself once every second rotation of the crank. The pressure at slow speed it creates may be dissipated all too fast. As the lift pumps speed eventually increases so does the volume of fuel processed. There are some natural restrictions in the system. This may allow a marginal increase of fuel pressure in the injection pump to occur. With the higher volume of fuel. The lift pump then delivers.

Then again the air ingress alone might account for this problem. All I know is I would check out the fuel pressure first to verify it is okay. Otherwise the air leakage could be found and the hunt for another leakage point started because the engines power remained about the same.

When I post thoughts like this. At those times I have to wonder if I should be on meds. As I am seldom positive I have it right. It takes time and evidence to verify them usually. At the same time it is basic physics of just how air can get in the pressurized portion of the fuel system.

There are violent almost instantainious forces at play here remember. That are frequent enough but of very short duration . These pulses are created by the fuel elements in the injection pump as they function. Some inline injection pumps even had steel plates inside for the pulses to beat on.

[cbum33]

So I pulled the relief valve today and the spring was 20mm. Stretched it out to 27 and put it back in and that made a huge difference in the way the car was idling and the vibration at idle. Almost all the air at idle has stopped there is just a little but a huge difference. When I increase the RPM however the air returns.

I drove the car a little and definitely could tell the power was better but not gonna say for sure that cures that problem. It was still pretty cool outside and that has seemed to help it a lot also for whatever reason.

I don’t have a pressure gauge but have no issue getting one. Where would you connect in to check it. I have read a few posts and people are talking about Drilling and tapping the banjo bolt. Wanna make sure I am checking in the right place.

Thanks very much for all your input. It’s greatly appreciated.

[barry12345]

You have mitigated a contributing problem. It may have been the more important one. Actually probably was.

You still have the other problem. They were acting in unison. The changes with ambient temperatures you reported. Was an astute observation. I would tend to label it as an effect of the fuel temperature and ignore it. Rather than an expansion or contraction of a hose or sealing washer. In the past people possibly never considered this if the air was being pulled in.

The vacuum pulled by the negative portions of the spike pulses just might vary. With the fuels changing viscosity with temperature to some extent. By elevating the fuel pressure you have also established a higher baseline for those pulses. You may not be seeing as much air as the pulses may be producing a lesser vacuum component.

There are many ways to locate the still existing air leak.. First I would concentrate on the stem area seals of the secondary fuel filter. Replace them if cheap. Plus check for cracks in the housing. The cracks are not all that common but not unknown as well. Then you can go higher tech or lower.

Lower is basically remove the banjo bolts and replace the sealing washers. Or heat them red hot if they still appear in decent condition and let them air cool. This annealing removes any work hardening by softening them if they are copper. Do not over torque the hollow banjo bolts.

Higher tech is using a can of cold spray. Spraying a banjo bolt will shrink the fitting a little. Compressing the sealing washers a little more. Frost will build up as well. This frost will also act to reduce the amount of air the fitting can take in.

You just watch for air reduction or signifigant change in the relief valves output. It may take a little time and keeping that fitting really cold to see a difference in air output.

You can easily verify the test if you find something. The relief valve banjo bolt can also be a point of air ingress so test it as well. Remember as you freeze the fitting the attached hose may be the culprit. except for the relief valves hose end. You will be shrinking the hose end as well with the cold spray. When addressing banjo bolts this way.

If the leak is more obscure and it probably is not. There are other simple tests to locate it. Or to determine you have not missed it in the previously tested area. For example running a hose around the whole secondary fuel fixture and filter. Obviously if the problem is gone it is there somewhere. Problem remains it is not of course. A short duration run without the secondary filter system in the loop is not a big issue.

If you see air you do not want to. If some assumptions that your ingress of air is temperature sensitive. Perhaps a lot of the others over the years where as well.

This was just not noticed perhaps. Careful use of say a heat gun may locate them fast as well if that is the case. Air leakages into the fuel system are very common failures. The majority get resolved with no great production. .

[cbum33]

I know this thread was started a few years back but the problem still persists. I have changed all fuel lines I have had the injectors checked again and even changed the clear fuel lines. What I now notice is that all the air in the line is in the return line only. So I am now down to trying to find a good used injection pump. Any one have any thoughts on any of the fitting or even the ALDA possibly leaking air into the pump before I go down the road of finding a used pump and changing it out. Any info would be greatly appreciated.

! more thing to add the car blows a lot of white smoke on start up and when idling to the car gets warmed up.