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  #1  
Old 11-28-2017, 12:19 AM
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Help with weird power issue 617A (SOLVED!)

I have a very weird power thing going on:

If I hold the throttle down half or 3/4 way or so and I'm not climbing a hill (engine not under stress) and I keep it at a constant rev in the same gear for several seconds (5-10 seconds) I will suddenly get a 20% boost in power. It feels just like I've stepped down on the throttle the rest of the way, or that the fuel was being restricted but then suddenly released. If I give it full throttle, it won't make the power jump and will continue to climb in revs but be very be under-powered or plateau quickly and keep me barely at highway speed.

Even more weird: If I let off the throttle at any time after the power boost has occurred, it goes back to the way it was and I have to do this technique again to gain back my 20% lost power.

To be clear though, this boost is actually power that's being lost otherwise as it feels back to normal during this boost.

I have a turbo pressure gauge and can watch my needle at, say, 5lbs, suddenly push up to 9 or 10 as I gain power. This leads me to believe it is not a turbo issue and definitely fuel related.

I've done the usual stuff already. New fuel filters (twice!), new fuel lines after the lift pump. ALDA is backed all the way out. Turbo feels perfect, hoses are tight and good. No air filter issue that I can see. Valves are perfectly adjusted. Im noticing any smoke issues. No different sounds.

The problem is consistent and repeatable. If I am in my final gear it wont do it usually as it's struggling to reach 60mph and the engine is under stress. If I'm on level ground or going downhill slightly, I can get it to do it in the final gear which suddenly makes keeping up with highway traffic much easier.


Last edited by 300 Super D; 12-07-2017 at 09:05 PM. Reason: edit
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  #2  
Old 11-28-2017, 08:03 AM
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Join Date: Oct 2007
Location: Charleston SC
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What is the engine RPM when this happens?

Have you checked that the throttle linkage is all sound and correct?

What car is this engine mounted in?

My initial thought is throttle linkage.

After that, ALDA but I see you've adjusted that. Maybe the next thing would be replacing the O-rings in the ALDA?

My next thought is that your turbo boost is low. Boost should peak at around 13 psi at 2400 RPM under full throttle while driving (your engine will probably not produce full boost if you rev the engine in neutral). You may need to adjust the waste gate so that you get full boost.
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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC
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  #3  
Old 11-28-2017, 09:07 AM
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Start with the basics. Clean out the lines and fittings going to the ALDA. They have a tendency to clog with soot. There's also a switchover valve on the firewall in the ALDA line that can clog or fail. Check that it is clear.

One of the often suggested tests for air is to install a clear piece of vinyl tubing in the return line to the fuel tank. If the fuel system is working properly and you have no leaks, it will be a solid column of fuel. If you get foam or bubbles, you have air ingress somewhere.

Check for excessive axial or radial play in the turbo. If the turbo is worn out, all bets are off as to how well it works.

I see you're in California. You neglected to mention which year model you're dealing with. Does this car have the trap oxidizer?
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  #4  
Old 11-28-2017, 02:02 PM
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I don't have a tach so I dont know. The RPM varies somewhat anyway, as to when this happens.

Yes the linkage is in perfect shape and nothing looks out of place or different. There is also no change in the feel of the physical throttle position when the power surge happens.

I don't see how the ALDA could be at fault since I have adjusted it all the way out, and in, and everything in between and this issue still occurs to some degree either way, although when in all the way it basically had no power at all. Right now the screw is removed completely and the issue still happens. Should I just take it off to test it more, or is there any difference compared to removing the screw completely?

Yes the boost is low, peaking at about 5, but only until the issue occurs then it jumps to 10 or so pretty fast as fuel starts to flow but I don't think this can have anything to do with the turbo itself as it feels like its just having to wait until there's fuel flowing/more exhaust, before it can boost up. I have read a lot of posts from guys who don't get more than 10 or 11. Regardless, I don't see that as being an issue right now as this lack of power issue has more to do with basic power needs further down the line.

Thanks diesel300 but I've dealt with just about everything having to do with the injection pump (externally) over time and am used to checking the typical problem areas. As stated, I already put new lines in and checked the turbo, checked the ALDA line and bolt, etc.. and there is no trap. There is no air in the lines that I could see although I can't see it under the conditions when it happens anyway. It doesn't make much sense that it has anything to do with air leaking in anyway due to how repeatable this problem is.

The power gain is also almost instant so this is something happening almost like a switch is being thrown.

Is there some theoretical way the injection pump could cause this internally? I feel like I've eliminated everything else that a do-it-yourself guy can do. Taking it to a Bosch center is a last resort but I can't afford that anyway.
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  #5  
Old 11-29-2017, 07:37 PM
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If you suspect the pump and it may be a possibility in my mind. It is possible something may be sticking a little. Like the rack.

You might entertain the possibility of good injection pump solvent soaking in place. There are two sections internally. So you have to soak the section where you suspect the problem might be. Or both.

Some pumps that are just seriously gunked up internally have been found. Especially those that used alternative fuels like waste vegetable oils at one time. Also keep in mind that a twenty percent difference in power is also just about consistent with a cylinder on and off line sporatically.

One quick test is to close off the return line from the injection pump and test drive. A gummed up injection pump relief valve might open and be slow to close. Reducing the fuel supply pressure in the injection pump until it does.

These two things mentioned are not high probabilities. Just remote possibilities. As your symptom in general is. I do not think over the years we have even had another posted complaint identical to this one.
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  #6  
Old 11-29-2017, 07:51 PM
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Ive done two Purge treatments with no effect at all. What do you mean by soaking two different parts of the pump? How so?

How would you close off the return line? I took out the relief spring and it was clean and measured to spec. (27mm) just so ya'll know.
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  #7  
Old 11-30-2017, 11:40 AM
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The fuel line at the tank is sometimes not replaced often enough ,these get hardened and sometimes leak with their age ,sepping air or leaking.The tank screen if not mentioned above could be another.Any lines blown out for safe measure while its opened up would be another quick and easy step to eliminate the questions.Kinked line if someone else has worked on the car in the past, people send jacks underneath these cars without looking for lines first , tire shops are the 1st ones to watch .It can be easy when looking at fueling issues if you start first with the tank ,start here and then work forward would be my advice ,this if all your filters have been changed and the primer pump is not leaking and a newer one has been installed .Diesels tend to not have nearly the problems as gas MBs come up with as they age ,you should find a remedy soon .Not a veggie car will be the last reveal,if the tank line is replaced youll have some evidence of veggie .Veggie cars will have a scent from the tank ,aroma is deep fried for sure.
Ill throw some hail marys to lookout for -banjo bolt cleaned ,always the first item ,brakes , trannie fluid ,filter , torq converter ,excessive carbon build up in intake and or exhaust pipe .ALL forward moving reducers if not functioning or filled properly.

Last edited by chasinthesun; 11-30-2017 at 12:08 PM.
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  #8  
Old 11-30-2017, 03:16 PM
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Thanks. I have eliminated most of those. It actually has a new fuel tank in it too, from a few years ago. No veg fuel. The line has been checked the whole way. Little carbon overall (had the manifold off not too long ago). Compression is good, etc..

Regardless, none of these could make the exact issue I'm having, in theory anyway. This is "fuel fully flowing, or fuel flowing 80%". There is no middle or gradual increase and again, it's repeatable and consistent. It's really like a valve or switch is opening.
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  #9  
Old 11-30-2017, 05:49 PM
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I would have your injectors pop tested ,may have a failed spring in one .Take the fuel lines off and blow out also.If its been replaced with any used parts the engine area is subject to get alot of these thrown at it over the yrs of ownership.Lines are common due to getting bent out of shape and at a junkyard may get debree in the fine lines. Shot in the dark.
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  #10  
Old 12-01-2017, 06:52 AM
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Wouldnt I be able to tell if I had a dead cylinder? It doesnt feel like Im down one cylinder, just down overall.
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  #11  
Old 12-01-2017, 09:42 AM
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The fact that you have a "global" fuel delivery problem points to fuel enrichment or turbocharger issues.

When you romp on it with the ALDA turned out, do you leave a massive black cloud? If so, the turbo is probably on its way out or in need of rebuild.

If it doesn't churn out a Chernobyl cloud, the fuel isn't being enriched. You could have air ingress, ALDA line issues (if the ALDA is hooked up, it's still doing something), weak lift pump, improper timing, a weak/broken timing device, or even a linkage issue.

If you have a hand vacuum pump, try pulling vacuum on your ALDA. If it doesn't hold or if you can't build vacuum, reseal it with new O-rings. If it does, take it off the engine and make sure the plunger it works on is free to move. There have been a couple of folks post on here that theirs were seized up. Check your linkages for the correct lengths and make sure that pressing the pedal to the floor causes the IP linkage to move to its stop.

Lastly - put that clear line in place of the return line and look for air.
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  #12  
Old 12-01-2017, 04:31 PM
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I was just thinking check that acceleration linkage for a wonky part. Could be you press the pedal and it takes some excess time to eventually totally comply. Just a wild thought. Hopefully something simple in the long haul to find. Could be a pain getting there.
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  #13  
Old 12-01-2017, 07:13 PM
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Quote:
Originally Posted by 300 Super D View Post
Ive done two Purge treatments with no effect at all. What do you mean by soaking two different parts of the pump? How so?

How would you close off the return line? I took out the relief spring and it was clean and measured to spec. (27mm) just so ya'll know.
You would have seen if the relief valve was gummed up. When you did the purging of the injection pump was the returning purge really dirty or fairly clean?

Check you transmission fluid level by the book. I have noticed that long ago one of my 300d cars became strange when it was only about a pint low. Do not remember now what the strangeness was. Excess engine blowby can impact the shut off as well in a few cases. Clean the engine vent hose line or check it for being fairly clear inside.

A fairly simple unusual symptom overall with a really substantial possible list of causes. Hope some member has had this same issue before and catches your thread.

This is one I want to see how it is resolved. A car following your when this occurs may reveal some change in the exhaust output. Doubt it but almost any additional clue might help indicate something. More probable than not.

For example dragging turbo bearings could produce some smoke until the turbo came up to proper speed. Then exhaust would then clear up. Smoke if any present or not and no change. It would not likely be coked up and dragging turbo bearings.

A driver comes in off a highway. Shuts the engine down to refuel. A good turbo that is almost if not red hot remains spinning at about 150k for a time. The oil cooling the bearing as well as lubricating it starts to cook. Because the oil has stopped flowing. Done enough times it is cumulative.

The proper operation of these cars and most diesels under that scenario especially. Is to let the engine idle for a minute or so before shutting it down. On the alloy headed engines especialy it also allows hot spots to equalize in them. This is probably not the primary reason for the eventual cracking of their heads but certainly does not help.

I have often wondered why. Beside other than the lack of frequent enough oil changes many of these engines do not survive longer.
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Old 12-02-2017, 09:54 AM
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I'd take a good look at the wastegate. If it isn't operating smoothly it may be bypassing exhaust gas when you need it to "feed" the turbo. This is an over-simplified explanation but a definite maybe. Perhaps when you have it at partial boost the waste gate finally opens to the turbo and the turbo can then get busy like it should. Worth checking.

Dan
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  #15  
Old 12-02-2017, 11:06 AM
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Quote:
Originally Posted by Dan Stokes View Post
I'd take a good look at the wastegate. If it isn't operating smoothly it may be bypassing exhaust gas when you need it to "feed" the turbo. This is an over-simplified explanation but a definite maybe. Perhaps when you have it at partial boost the waste gate finally opens to the turbo and the turbo can then get busy like it should. Worth checking.

Dan
The wastegate should be CLOSED until the actuation pressure is reached at which point it opens, bypassing exhaust gas around the turbine.

The valve could be stuck from carbon and held slightly open, which would require a much higher flow of exhaust gas for a given compressor pressure.

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