Diesel Engine Problem

2 things I can suggest: O2 sensor and coolant temp sensor. These things tend to go bad on Nissans without throwing a code. On a diesel I'm not sure the O2 sensor will apply. Change the coolant sensor first,much cheaper.

The symptoms of a fault coolant sensor are: car does not feel as powerful when warm gas mileage goes down the temp gage remains slightly lower than normal

This symptoms happen when the sensor is faulty because the car "thinks" it cold when it's not, so the computer keeps running a richer mixture (white smoke from excessive feul?)

For the O2 sensor, it's much much harder to diagnose. The car just doesn't feel as snappy as your used to. I recently changed my O2 on my Sentra after 100,000 miles and the car just came to life. The old O2 was not throwing a code at all.

Hope this helps

CD

Thanks CD

Checked both the coolant temp sensor and the MAF sensor according to the service manual.

The temp sensor reads ok on both ohmic values and output voltage to ECM. I have always doubted in the back of my mind whetther this sensor is correct, from an electronics engineering angle it looks good but I think from a mechanics angle he would probably change this anyway.

And the MAF gave the correct signal voltage readings for the relevant engine speeds.

StuH

Usually MAFs are either good or bad, no inbetween. For the coolant sensor, do you experience any of the symptoms? Gas mileage lower than normal, car runs cool, less power than you remember, especially at the top end?

For example, my wife's 98 Altima had a bad coolant sensor. I suspected it due to all those symptoms, especially when I tested it and it could barely reach 100 mph (160 kmh.) I knew that the 2.4 l, 150hp motor should do better. I replaced the sensor, and after 2 tankfuls saw the difference. Power came back, gas mileage went up and the temp gage settled closer to the middle than previously.

Remember, if you do change the coolant sensor, it usually takes 2 or 3 tankfuls for the computer to adjust its fuel maps to the change.

CD

CD thanks again.

Another symptom that has become more apparent over the last few days is noise from the timing chains, there is a primary and second chain.

The car ran terrible yesterday, the worst I've experienced it.

Yesterday was a warmer day in the mid teens Celsius, I'd just fill the tank which had previously had a redex diesel treatment in it. And the timing chains not only rattled on cold start up but carried on rattling when the engine became warm (normal running temp)

Now was this down to a problem with the fuel treatment (readjustment of ecm to cleaner fuel) will it take time to adjust again, or perhaps the timing chain is stretched/damaged and its guides or tensioners at fault. There is no engine management fault indication appearing. I read somewhere on the Nissan website that timing chains are designed to last the service of an engine and that if a chain became stretched this would be sensed at the ecm (camshaft/proper shaft timing out) and a fault indication would appear.

As the days/weeks go on the fault may develop further hopefully without engine damage (risk of timing chain breakage).

I am currently seeking out some garages to help but will have to find some funding, it may become a long wait.

StuH

Are you certain that the rattle is from a timing chain, and not the result of faulty Diesel fuel injectors? An improvised stethoscope (like a long screwdriver held from ear to various points on the engine, like timing cover) should help identify the source.

The simpler explanation (where there's only one fault causing multiple symptoms) is much more likely to be the correct one.

John

The type of fuel has no effect on timing chain noise.

If your timing chain is rattling, your tensioners are loose and need replacing. If your engine is an interference motor, most Nissan engines are, then get this taken care asap. If the chain breaks, the valves will hit the pistons and your motor is toast.

CD

The car has been stood for about 24 Hours.

The engine started first time as usual.

A little engine noise at first which is expected then idled very smoothly.

Warmed up the engine in situ. Tried to take revs above 1500, same old story misfire with white smoke.

Once coolant temperature had risen took the vehicle for a spin.

Unlike yesterday, the car ran perfectly smooth right through the rpm range.

The car was basically the best its been for a while. You would not think there was a problem.

If there was no rattle today does this more or less show the the timing chain and its tensioners / guides are probably ok. How can there be a mechanical fault (broken guides, stretched chain etc) one day but not the next?

With what John is saying is the fuel injection system playing up? The sure fault every time is that the car will not run well until its warms up. But after that it usually runs well although it intermitently runs badly when warm with spluttering and some puffs of white smoke (loss of power).

When the fault appears especially when revving the engine whilst vehicle stationary I'd say it feels like a 4 pot petrol engine only firing on 3.

StuH

That's not yet proven absolutely. When it is rattling, can you eliminate the timing chain area as the source of the noise by "stethoscope"?

My Nissan with a GA16DE petrol engine occasionally has very noticeable timing chain noise for a few seconds after starting.

If you've got an injector fault, they could be causing all the problems you're seeing. And injector cleaner may or may not fix that over time.

The only likely reason a running Diesel engine will intermittently not fire on one cylinder is lack of atomized fuel there at the right time. Unfortunately, dirty injectors are not the only possible cause of this. But they're number one suspect.

John

I see that different fronts have been attacked trying to solve the problem.

In diesel engines in the past, I have seen that pinging is hardly discernible from other mechanical noises.

I suggest sticking to the oil and fuel recommended by de owners manual or to the ones that worked well prior to the appearance of the problem.

I would also make sure that the engine is reaching propper operating temperature as measured with a thermometer. The fact that the car ran perfectly after warming it up car standing still could indicate a faulty thermostat.

I am not an expert on diesel engine control systems, and I do not know if they are equipped with the usual sensors or not, but I would look for any problems with units that could lead to a rich mixture, e.g. TPS, MAF(already tested), Manifold pressure sensor, coolant temp sensor, etc.

Good luck.

Codifus wrote:

By way of background, mixture ratio itself is unimportant to ignition in a Diesel engine.

A Diesel engine is never "throttled". It takes a full charge of air every intake cycle. Only after compression is the fuel injected, and the amount of fuel is controlled by the accelerator setting. And that amount is delivered as a certain time _duration_ of fuel injection. Ignition is immediate and spontaneous (due solely to the heat of the highly compressed air). So (depending on the accelerator pedal setting) the effective mixture varies from ultra lean up to optimal for complete combustion of as much fuel as practible.

Introductory reading at

John

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I never knew that diesels didn't have throttles. I knew they didn't have spark plugs. So when a diesel is idling, its producing a lean mixture? That would explain, at least partly, about why diesels have a hard time with emissions.

CD

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I have an old VW diesel. It used to start on less than 4 cylinders when near 0 C. Lots of white smoke. This only lasted a few minutes until temp gauge moved from Cold. All original 1981 VW - old..... Checked glow plugs - all good - changed anyway. No improvement. Changed fuel filter although it was not time. Improved for one month. Got to thinking I had a suction problem rather than a pressure problem, I added an electric boost pump to suction side of injector pump. It worked. Later found clogged strainer in tank which may have been the real problem, but I am keeping the boost pump as I don't like to be wrong...LOL.. Bottom line...check suction side of fuel system also...

Mike