Weird surge and flickering glow plug light issue! - PeachParts Mercedes-Benz Forum

psaboic · #1 03-23-2013, 11:31 PM

Ok, this one has me stumped. I noticed today the return of my power loss/surge. It is very intermittant, but when it occurs, here is what happens. If you are cruising at highway speed, it will feel like a light miss/skip/stumble.... almost like a filter is starting to clog a bit. If it happens while you are accelerating from a stop, at about 35 MPH it feels like you are trying to accelerate while applying the brake, and no amount of additional throttle will cause the power to increase for a couple of seconds, then it feels like you released the brake and the car will take off.

Now for the kicker, I also noticed starting today that whenever you apply anything more than half throttle and are accelerating hard, the glow plug light will start to flicker and will keep flickering until you go below half throttle. I was able to duplicate this easily several times by simply applying half or more throttle.

What on earth could cause the glow plug light to flicker like that (It did it while the car was doing the surge thing, and then it did it while the car was accelerating normally, but NEVER below half throttle!

Oh yes, I replaced the glow plug relay last year with one that has the three minute afterglow feature.

Got to drive the car tomorrow, so I would like to have a rough idea what might be going on.

Glenn

Stretch · #2 03-24-2013, 03:53 AM

Although you didn't specifically say I guess this is for your 83 300D

I think you have two separate problems. The glow plug light flickering could be a dodgy earth.

The intermittent stumbling under acceleration / high speeds => so is it fair to say it occurs in the higher rev range? <= could be something like a weak lift pump.

psaboic · #3 03-24-2013, 09:22 AM

Possible a bad earth (ground) but I wonder why it only does it above 1/2 throttle or more? Also you are correct it is for the 83 300D (Sorry). Lastly forgive a silly question, but what is the difference between the lift pump and the IP. I thought that they were one and the same.

Thanks,

glenn

psaboic · #4 03-24-2013, 09:31 AM

Actually, never mind.... I know what you are talking about regarding the lift pump. It does not appear to be leaking and is the newer type model with the black primer pump on it. Is there another way to check it?

Funny thing is, outside of the random/intermittant surging issue the car has been running better than ever!

Diesel911 · #5 03-24-2013, 11:32 AM

Concerning the Ground issue. During different or changes of loads your Engine wants to Twist one direction and with reduced load go back to where it was. There is a Ground Cable/Strap from the Chassis to the Bell housing on the Drivers Side about below your Feet under the Car.
When the Engine is moving the Ground Cable attached to it is also moving.

Also during acceleration the whole Car vibrates more. If there is a loose connection somewhere it can also vibrate.

A small Air Leak could gradually build up an Air Bubble inside of the IP Housing and then when the Bubble is large enough it would pass through the Housing and out the Fuel Pressure Relief/Overflow Valve. in the process of moving some of the Air could get into one or more of the Elements and cause a Miss.

An intermittently seating Valve in the Fuel Supply/Lift Pump or the same in the Fuel Pressure Relief/Overflow Valve could do the same.

One way to deal with a possible Air leak is simply to replace the 2 Sections of 5/18" Fuel inlet Hose with Regular Fuel Hose you can get at any Auto Parts Store (it is rated for Diesel Fuel).
You could also replace the Plastic Primary Filter as they have been know to develop tiny cracks that allow Air in.

I am anticipating a why something can have an Air Leak but no exterior leak question. The answer is that there is about 14.5 psi of Atmospheric Pressure on the outside of the Hose. If the leak is tiny the Atmospheric Pressure can keep Fuel from leaking out of a Hose.
Look at the Hoses in the rear under the Fuel Tank and inspect for cracks.

barry12345 · #6 03-24-2013, 12:08 PM

Air bubbLe could only be processed through the return of the injection pump if there were enough fuel pressure available to open the valve. If not retained air in the injection pump would have to pass through the injectors.

I might start the attempt to locate the problem by seeing if there is overflow present from the relief valve at idle. If so is it also spewing any air at the same time?

Stretch · #7 03-24-2013, 12:51 PM

Quote:

Originally Posted by psaboic

Actually, never mind.... I know what you are talking about regarding the lift pump. It does not appear to be leaking and is the newer type model with the black primer pump on it. Is there another way to check it?

Funny thing is, outside of the random/intermittant surging issue the car has been running better than ever!

Just in case there's a bit of terminology confusion the lift pump is the pump that draws the fuel from the tank and gives it to the IP. It isn't the little hand pump used for bleeding the system.

barry12345 · #8 03-24-2013, 03:13 PM

Also make sure you crankcase ventalation system is clear. If you build base pressure it will tend to attempt to shut down the engine.

Stretch · #9 03-25-2013, 04:41 AM

Quote:

Originally Posted by barry12345

Also make sure you crankcase ventalation system is clear. If you build base pressure it will tend to attempt to shut down the engine.

If you're suggesting that the shut down valve on the IP operates at high crank case pressures then I think that's a myth Barry - I'm still trying to figure out a way to bust it though!

http://www.peachparts.com/shopforum/diesel-discussion/332890-searching-data-official-limits-maximum-crank-case-pressure-om617.html

It seems to me that high crank case pressure is as equally likely to blow out a seal as it is to stall the engine at idle. I've yet to find any suggestion / evidence that high crank case pressure at engine speeds higher than idle speeds causes this kind of trouble.

Please note I'm not saying to not check to make sure that the crankcase ventilation system is working correctly - that's very good advice; I just don't think it'll cause engine stuttering under acceleration. In that situation I reckon high crankcase pressure will more likely blow a seal...

...but again I have no way of proving this theory of mine just yet (but I'm working on it in a part time when I get the time kind of a way!).

vstech · #10 03-25-2013, 07:43 AM

so... the GP light is flickering/dim and bright?
any chance you had the instrument cluster out recently? I ask, because it's easy to mix the alternator light with the GP light bulb, and the flickering etc could be caused by an alternator failure. it could also explain the difficulty accelerating if the alt is partially siezed, or the bearings are grabbing.
however, the accelerating from a stop symptom sounds like the beginnings of the infamous B2 piston failure in the transmission.

charmalu · #11 03-25-2013, 11:10 AM

Hey Stretch, remove the Blow By Tube and place your hand (or something it may be too hot) over the VC opening with the engine running. the eng will shut down from the internal pressures. The pressure will push against the Vac Shut off Valve from the iside to move the lever and shut the eng down. the time it takes will depend on the health of the engine.

Charlie

Stretch · #12 03-25-2013, 11:24 AM

Quote:

Originally Posted by charmalu

Hey Stretch, remove the Blow By Tube and place your hand (or something it may be too hot) over the VC opening with the engine running. the eng will shut down from the internal pressures. The pressure will push against the Vac Shut off Valve from the iside to move the lever and shut the eng down. the time it takes will depend on the health of the engine.

Charlie

That's what I think is the myth Charlie. I don't think it is to do with the vacuum shut off valve on the IP at all.

I'm sorry to be a pain in the arse - it is one of my little hobbies to not necessarily go along with common belief. I've suggested an alternative explanation in that thread that I gave a link for. I could be wrong (and if I see enough evidence I'll own up and say so) but it is a particularly dangerous thing to test; I'm trying to think of a safer way of doing it =>

@everyone - please be careful when trying this little experiment. You could be lucky - but if you are not you can blow out a seal which in turn could result in serious oil loss which could then really ruin your day.

Stretch · #13 03-25-2013, 11:25 AM

Anyway - back to the thread (sorry for the little interlude)

Diesel911 · #14 03-25-2013, 04:10 PM

Quote:

Originally Posted by Stretch

If you're suggesting that the shut down valve on the IP operates at high crank case pressures then I think that's a myth Barry - I'm still trying to figure out a way to bust it though!

http://www.peachparts.com/shopforum/diesel-discussion/332890-searching-data-official-limits-maximum-crank-case-pressure-om617.html

It seems to me that high crank case pressure is as equally likely to blow out a seal as it is to stall the engine at idle. I've yet to find any suggestion / evidence that high crank case pressure at engine speeds higher than idle speeds causes this kind of trouble.

Please note I'm not saying to not check to make sure that the crankcase ventilation system is working correctly - that's very good advice; I just don't think it'll cause engine stuttering under acceleration. In that situation I reckon high crankcase pressure will more likely blow a seal...

...but again I have no way of proving this theory of mine just yet (but I'm working on it in a part time when I get the time kind of a way!).

So far the actual evidence is that it has blow out only one Seal.
Clearly different Engines have different Crakcase Pressures so I am thinking some Engines might blow the Seal when tested and some not.

Stretch · #15 03-26-2013, 04:20 AM

Quote:

Originally Posted by Diesel911

So far the actual evidence is that it has blow out only one Seal.
Clearly different Engines have different Crakcase Pressures so I am thinking some Engines might blow the Seal when tested and some not.

I totally agree but as it has been reported to have happened I think it is worthwhile saying that you might be OK or you might be unlucky - I'd rather not hear about anyone else being unlucky.