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.

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.

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?

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.

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.

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.

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.

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.

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.

Wouldnt I be able to tell if I had a dead cylinder? It doesnt feel like Im down one cylinder, just down overall.

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.

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.

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.

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.

Could hook up a temporary boost gauge to check out if the turbo is involved. Of course feeding it back into the cabin.

Your symptoms sound exactly like when my waste gate was frozen closed and the over boost protection cut in. I would lose power, and if I let off the accelerator pedal, it would return. Once I put a boost gauge on it, I could see that under a little more than half throttle, at about 2,500 rpm, boost would get to about 15 lbs and suddenly drop to about 6.

What does your gauge do right before and as you lose power?

Freeing up my waste gate was simple with some penetrant. I worked it lose until the whole valve slid out where the plate with four bolt/nuts is. You need to take the diaphragm off to do this, and can inspect it at the same time. With the carbon cleaned off the valve and hole it goes through, it slides open easily and I have no more loss of power from boost cut off.

————
1985 300TD

I took the ALDA off and tested it. It holds no vacuum nor pressure. Is it really suppose to? By the way, what's inside the ALDA make no sense to me. I was expecting a rubber diaphragm I guess. Those engineers.....

The purge return fluid was clean looking last time I did it.

Again, the turbo feels perfect. Tight and smooth.

This is a manual transmission so no issues there are possibly related.

It's not doing what you had happen tdhawk. I don't lose power. I never have it until later in my revving. It can't be turbo related in my opinion. The response when I do get the power bump is just too quick plus I'm monitoring the pressure (with my in-dash turbo gauge) and nothing out of the ordinary happens there. I think there's a 95% chance this is fuel-only related.

I don't have an overboost protection circuit on this engine (never had one).

I'm testing it tomr., running without the ALDA to see if there's any changes. And yes I plugged the manifold with the required M8 1.00 pitch bolt. (not many of those laying around)

The ALDA has 2 seals in it. There is one on the shaft where it connects to the IP and there is a perimeter seal where the 2 halves screw together. When working properly, the ALDA should hold pressure and/or vacuum, but over 30+ years the rubber dries out and fails.

The ALDA contains a set of copper bellows that compress as the manifold pressure rises and lift a plunger in the IP to enrich the fuel. If the pressure in the manifold is building, but the ALDA is leaking, you will get a skewed fuel enrichment curve. When it is working properly, you can't really even tell when the ALDA begins enrichment, it should be a very smooth transition when the turbo starts spooling up.

Sounds like your car is in far from factory condition. Turbocharged engine, but manual transmission. New fuel tank - why did that happen? ALDA doesn't hold vacuum or pressure and the screw was backed all the way out and removed - that tells me that your ALDA is probably destroyed.

I'd be looking for a good used injection pump with unmolested ALDA at this point.

I'd also be taking a real hard look at the turbo-charger and waste-gate operation.

Is this an OM617? OM617 valves should be adjusted annually and every 15k miles, whichever comes first.

How does it drive with the alda removed?

SOLVED!

First I wasted my time and money and got a 10x2.5mm O-ring for the ALDA and it did indeed hold a vacuum but I noticed the height of the plunger/shaft seemed off before and after, after looking at my other one while performing the repair. I pushed down on it with a screwdriver and noticed a lot of resistance, as if it had pressure in it, but there was none.

I got the other "good" ALDA I had from my screwed up inj. pump and noticed there was definitely a height difference in the plungers at rest. The one I was running seems to have had some issue with the screw, as you can see. This was causing a ton of irregular behavior apparently. The brass looking one is the bad one. It's mm's higher at rest.

I tested my good one but it wont hold a vacuum either. The screws on it are the tightest I've ever encountered. I tried my hardest, to the point of hurting my hand, as well as using an impact driver, and they won't move.

I left the ALDAs off and thought I should test drive it finally. On start-up I noticed immediately that the idle was slightly higher than it was, for whatever reason, so I had some confidence something was different. I took it very easy at first to heat the engine up a little and then got out to the main road and laid into it. WOW!!!!!!!!!!!!!!!!!!!!!!!! I have my engine back!!

I mean holy sh**! I swear I have 30hp+ more than I did, and at all revs.! My boost gauge slammed up to 11psi in no time. I may have one of the strongest 617's around... no kidding.

For TWO YEARS I have suffered with this issue in some way and it was truly a source of depression. If only I had taken this piece of crap ALDA off long ago I'd have had a much better life.

I did not notice any massive smoke cloud with the ALDA off. I was on a road where the sun would have back-lit it but still didn't notice anything obvious. I'll get someone to follow me soon and see what they say but for now I'm leaving it off and enjoying a very healthy engine.

This painful lesson shows how important it can be to simply take the ALDA off when looking into suspected problems with it. I was under the impression, like many others it seems, that backing the screw out all the way was the same thing as taking it off. That is definitely wrong. I also believe that these things are so old now that many may not be working correctly anymore. How many other motors are under powered due to these things?

Glad you figured that out, I'll be curious to see what impact this has on your fuel consumption and soot load in your engine oil.

For the record, backing out the screw too far will cause the ALDA to break internally.

From reading many guys posts who have removed it, it sounds like it causes few if any issues.

It behaved this way before I backed it out all the way. Either someone had already done that or it was really messed up overall. Either way, good riddance to it.

I've also heard that removing the Alda does not affect mpg hardly at all. It just allows more fuel if u need it, u don't have to stomp on the gas all the time tho.

It's great to have a solved thread on here. Does the forum let u edit your title to ad "SOLVED" to it. So other forum members and people doing google searches can see it?

Yeah I rarely step down on it like that anyway. From what I can tell with my vacuum/air pump is that the other ALDA wasn't working either, but in a different way, and I drove that thing 1000's of miles for years that way and it ran perfectly and very strong all those years.

So many people have removed them for so long without reports of issues that I can find. I'm not convinced its needed other than to comply with original specs. After all, it's a mild emissions control device and like most of those, when they wear out or break, cause even more emissions due to inefficiency and operator work-arounds.

I tried to edit it but no, it won't let me. You can see where I added SOLVED to the original post subject which I thought was the headline but apparently not.

It is also part of a safety system, so you don't melt your pistons if your turbo waste-gate fails in the closed position and turbo pressure drives the combustion temperatures too high.

I prefer fact-based decisions. I'd like to see some data on engine oil soot load and MPG, baseline with before removal data, before I'd do it to my car.