Flat spot and smoking, and NO it's not the MAF!

[pcman_jh]

...and before any says so - it's not the MAF as I changed it with a new one!!

1999 E300 Turbo diesel - 6 cylinder.

If doing hardish acceleration, not flooring it but a little more than moderate accelerating, and there's a load like going up an incline, at around 70mph it will start to noticeably flat spot and loose power and speed. If you try to keep the accelerator down to drive through it, it just smokes badly. The only option is to lay off the accelerator and its as if there's now enough fuel getting through and it goes smooth again. If you moderately try to get to this speed it's fine.

I've had the injectore refurbished (a hell of a lot quieter), MAF device has been replaced. EGR has been cleaned out. All air and exhaust pipes have been checked for leaks.

Don't think its a blocked exhaust as it runs fine unless you push the acceleration. I would have thought if the exhaust is blocked it would be choked at other speeds. It would sit at 70 all day!

This occurs both with straight diesel or straight SVO (straight vegetable oil from the likes of Costco/Makro).

The only clue I've had is I had flat spots at other speeds recently, and by changing the fuel filter, it was night and day. Could it be the Merc filters are very sensitive to SVO and any use of this coats the fuel filter, wiht the symptons showing after a few hundred miles until it gets that bad it needs it around 4000 miles (as was my last duration - but worth changin due to the savings with SVO).

My car's had the 2 tanks conversion - starts on diesel, then switch to SVO when hot. Switching back for the last 5 mins at night. It done this when I was running with SVO mixed in the tank, so it's not due to the conversion.

I feel its a fuelling issue since it's OK if accelerating lightly, but I can't see how fuel starvation would cause smoking if you try to accelerate throuhg it (which it doesn't do). Could it be the inline pump has built up an issue with some of its lift pump/extra fuelling circuitry?

It starts first turn of the key on diesel, so don't think it's compression either.

Any clues as I'm tearing my hair out.

 

[television]

Its too late tonight, put up your VIN first 6 numbers and I will have a look tues night.

Malcolm

 

[pcman_jh]

VIN number as requested

Malcolm, it's WDB210225
Cheers.

Its too late tonight, put up your VIN first 6 numbers and I will have a look tues night.

Malcolm

 

[television]

Searched everything, only one fault for your engine, but this is a 1995 mod where the engine oil is sucked into the combustion through the crankcase breather. Sorry don't have anything else.

Malcolm

 

[The Rock]

I've got exactly the same problem but without the smoke.
Last week the specialist plugged his computer in and the fault log stated that the Exhaust Gas Recirculation Control Valve was faulty. He cleared the fault in the log, started the car and the fault returned. £48 + vat later a new control valve was fitted and the car ran properly again but for less than a week. So obviously that was a red herring.
I'm reluctant to replace the Mass Air-Flow Sensor (at £275) because from what you've written that didn't cure your problem, however, unplugging it does make the car driveable, particularly at speed, because you don't get the flat spot at 70, but that's not really the final solution is it? And the low down acceleration is compromised.
I can't understand how a car can run fine for a few days and then go wrong again. It has to be a sensor somewhere surely? I could understand if the problem only appears as the car gets warm or something, but even from cold this morning I felt that it was being strangled.
This has all happened since I had a full service and new exhaust pipe. I'm wondering if a sensor has been knocked somewhere? :-(
I'll keep you informed.

 

[OmniCognateNeutronRangler]

Rock, it may be that your problem sounds the same but isn't. The original post shows classic symptoms of the MAF. Although his obvioulsy isn't it doesn't mean your's isn't. There are threads on this site that explain how to clean the MAF so you could try that first. If it runs fine with it disconnected then I think it's 95% likely that the MAF is the problem in your case.

I had exactly the same symptoms on my A6 and that was the MAF (interestingly only £105 including fitting on an Audi). Replacing it almost made it feel like a different car so it had probably been going for a while. Think with that was that I took it in for a service and told them it was flat spotting and they disconnected the MAF sensor to prove it was that. When the connectected it up again it seemed ok (but still not perfect) for some of my drive home but then got progressively worse. At one point I hit a hill and, much to the anoyance of the people behind me, the car would not go above 15 mph!! I pulled over and calle the garage and they told me to disconnect the MAF and it started working fine. So that went from being sort of ok to being undrivable in about 15 miles. When it was working it was fine some days and not others so the problem does sound very much the same as yours.

 

[230K]

Hi

I would check for bubbles in the clear fuel lines, for some reason these cars smoke when they get air, i remember one time about 50 miles after i had run out of fuel and re-filled that she let out a huge blast of smoke and never did it again, obviously air in lines at that time.

Check around the fuel shut off solenoid if there is any sign of damp at all then air is getting in and could be the o ring between the valve and the pump body.

The prefilter o ring can give bother to, as well as all the other plastic fuel line.

Poor fuel lines can give strange symptoms on these cars!!

230K

 

[Glenn Smith]

...and before any says so - it's not the MAF as I changed it with a new one!!

1999 E300 Turbo diesel - 6 cylinder.

If doing hardish acceleration, not flooring it but a little more than moderate accelerating, and there's a load like going up an incline, at around 70mph it will start to noticeably flat spot and loose power and speed. If you try to keep the accelerator down to drive through it, it just smokes badly. The only option is to lay off the accelerator and its as if there's now enough fuel getting through and it goes smooth again. If you moderately try to get to this speed it's fine.

I've had the injectore refurbished (a hell of a lot quieter), MAF device has been replaced. EGR has been cleaned out. All air and exhaust pipes have been checked for leaks.

Don't think its a blocked exhaust as it runs fine unless you push the acceleration. I would have thought if the exhaust is blocked it would be choked at other speeds. It would sit at 70 all day!

This occurs both with straight diesel or straight SVO (straight vegetable oil from the likes of Costco/Makro).

The only clue I've had is I had flat spots at other speeds recently, and by changing the fuel filter, it was night and day. Could it be the Merc filters are very sensitive to SVO and any use of this coats the fuel filter, wiht the symptons showing after a few hundred miles until it gets that bad it needs it around 4000 miles (as was my last duration - but worth changin due to the savings with SVO).

My car's had the 2 tanks conversion - starts on diesel, then switch to SVO when hot. Switching back for the last 5 mins at night. It done this when I was running with SVO mixed in the tank, so it's not due to the conversion.

I feel its a fuelling issue since it's OK if accelerating lightly, but I can't see how fuel starvation would cause smoking if you try to accelerate throuhg it (which it doesn't do). Could it be the inline pump has built up an issue with some of its lift pump/extra fuelling circuitry?

It starts first turn of the key on diesel, so don't think it's compression either.

Any clues as I'm tearing my hair out.

Turbo or intake problem? Is it black or white smoke?

 

[The Rock]

Well I eventually decided to take the MAF out and clean it. I firstly tried to see the MAF by looking down the air intake pipe and I noticed that the air filter in the pipe between the main air filter and the MAF was clogged in it's centre with oily soot and small bits. I took the whole assembly apart and I cleaned everything, including the MAF (carefully), and now it drives like a Formula One car. I just hope that I've finally found the problem. It sort of makes sense that that filter needs to allow air through unobstructed as it's designed to remove vortices from the air flow to allow smooth flowing over the MAF. Fingers crossed.

 

[dbanbery]

i know this post is well old... but

this is the same problem as i am getting - mine doesnt have a MAF, and i have replaced the turbo with a brand new merc item and its still there. fuelling? there has always been bubbles in the fuel lines so thats not different. the inlet manifold has a slight leak - the blue smoke has only come back today though after replacing the turbo.

 

[nickcc101]

i know this post is well old... but

this is the same problem as i am getting - mine doesnt have a MAF, and i have replaced the turbo with a brand new merc item and its still there. fuelling? there has always been bubbles in the fuel lines so thats not different. the inlet manifold has a slight leak - the blue smoke has only come back today though after replacing the turbo.

Blue smoke usually indicates burnt oil, black smoke indicates unburned fuel. When you fitted the new turbo did you charge it with oil before starting or allow the engine to tick over before revving up. If you did neither of these then you may have caused damage to the turbo seals/bearings. Keep your eye on the engine oil level incase the turbo seals have blown.

 

[dbanbery]

Blue smoke usually indicates burnt oil, black smoke indicates unburned fuel. When you fitted the new turbo did you charge it with oil before starting or allow the engine to tick over before revving up. If you did neither of these then you may have caused damage to the turbo seals/bearings. Keep your eye on the engine oil level incase the turbo seals have blown.

i injected oil into the turbo via the feed before i fitted it, i turned the engine a lot before firing it, then it ticked over for a few minutes before i pottered down the road. i pottered for a few miles and then heard it spin up - it didnt boost properly then, and so i slowly drove it off boost and got home - checked all my oil feed pipes etc and it seems fine. there was no smoke. i pottered it to work yesterday and tried out the turbo when it was warmed up. still boost problems. continued to not boost the turbo and it was just driveable. i noted an air leak from the acutator vacuum pipe. replaced that. still no joy. pottered it to work today and when i got to this big hill just before work it started running really poorly and smoking. i pulled over - engine was really lumpy, it righted itself after some ticking over and i set off slowly again and managed to get to work. could it be fuel feed? i think the fact that it is doing the same thing with two different turbos could eliminate the turbo being the problem [expensive exercise]

the smoke was when it was trying to accellerate.

 

[nickcc101]

Could be air starvation, try running it with the inlet pipe off the turbo (no prob as you don,t have a maf) if this cures the problem look for either intake hoses closing under load or a blocked air filter. Just clutching at straws now, hope this helps.

 

[dbanbery]

i'll try that.

i'm going to check all my boost hoses.

my air filter did look pretty dirty - i didnt do it when i got the car....

 

[dbanbery]

just run it up the road - no change. is there any mileage in disconnecting the wastegate solenoid to see if this changes symptoms?

also going to remove that small vacuum filter to see if that makes any difference

i have ruled out boost leak as there is no whooshing or hissing under boost - just the turbo noise.

 

[dbanbery]

Just disconnected the wastegate vacuum hose and run it up the road. no change [well there was no turbo boost]

i think its a fuelling problem. there is some air in the pipes but only on tickover - they disappear under revving and when its switched off.

 

[Alex Crow]

could just be a vacuum problem, have you verified there is good vacuum at the grey pipe at the vacuum modulator/transducer?

 

[dbanbery]

sorted it! it was the pre filter filter - full of black gunk! it took a load of other head scratching to get there tho!

 

[turbopete]

expensive too!

 

[dbanbery]

lol yeah but i think 300 quid for a brand new turbo isnt too bad, and since the old one wasnt the problem, i can hopefully sell it to recoup some costs. people spend more than that on a fluid service!

its one less thing to worry about too - i didnt want the turbo to blow big time and junk the engine.