Inj Pump belt question
 

Hi Guys, I think my pump timing has slipped back a little bit (retarded). I bought my '95 940 D24Tic at 111k miles and started using it on the road last January. The previous owner (who was the first owner) had a new timing and pump belt fitted at 89k miles. The car now has 129k miles on it so it has done 40k miles since the belts were fitted. Over the last few months the overall performance of the car has dropped slightly, nothing drastic but you do notice it. It still starts and drives fine but the acceleration is not quite as good as it was, the top speed has come down a few mph, the idle speed has dropped about 150 rpm and it's using a bit more fuel. I've checked all the usual suspects to make sure there are no fuel leaks or restrictions in the intake system and all is fine, the turbo boost is good and working as it should. My guess is the pump belt has "settled" or "stretched" a little bit resulting in the timing dropping back a bit. Is there a specified milage or time interval that the pump timing should be checked and adjusted if neccesary,,, and would you agree that after 40k miles the pump belt could have stretched and would need to be adjusted again? Any thoughts would be appreciated, thanks.

Hello Aidan,

It certainly is possible for your injection pump belt to have stretched -- or slipped a cog. Typically the most subtle of changes in timing result in noticeable operating characteristics. Naturally the definitive way to confirm your assertion is to check the pump timing.

I've experienced some of these symptoms before from a clogging fuel filter -- a different make and model, but it was a diesel; something to consider.

Isn't the IP belt fiberglass belted? Meaning no stretch? Is it loose? Are there missing teeth?

Belt shouldn't stretch at all. If timing were to change, your big symptom would be poor starting and poor running after a cold start. Since the belt's length doesn't change, the only way for the timing to be altered is if the rear camshaft pulley slips, the injection pump shifts on its mount, or the belt jumps a tooth. I doubt any of those happened: in the first case, once the pulley started to slip, it wouldn't slip a little then stop and hold position again; it would continue slipping and very quickly the timing would be too far off for the engine to run. In the second case, if the pump were loose enough to move, the engine would vibrate horribly and make noises, and in short order all the hard fuel lines (injector delivery pipes, to use the correct name) would fracture and disable the car. The lines are brittle and sensitive to pump vibration and movement, and they don't last long when those things are happening. If you've been able to keep driving it for months, then the pump is quite certainly not jumping around. And in the last case, of the rear belt skipping a tooth, the car would immediately either be exceedingly difficult to start and keep running, or not able to start at all. That large of a timing change would have a drastic effect that would render the car undriveable. And as a fourth item of note, a change in injection timing, unless very extreme, should have no noticeable effect on engine idle speed, since the injected quantity is not altered. For all of these reasons, I doubt your timing has drifted.

More likely, jbg's suggestion to check for fuel restriction is where you should be looking first. Checking for fuel leaks is not too meaningful on these cars, because the entire fuel system up to the injection pump inlet is under negative pressure -- any "leaks" would not manifest as leaks of fuel to the outside, but instead as leaks of air to the inside. So, it is true that a loose fuel filter or faulty fuel line connection could leak air in and cause a runnability issue. However, it's much more likely that your filter is simply plugged. For me, the first step in any diesel diagnosis of any kind that includes a low power symptom is to replace the fuel filter. Fresh, high-quality filter prefilled with clean fuel, odds are good will solve your problem right off the bat.

If not, the only other thing that occurs to me is that the jam nut on the injection pump fuel quantity/metering screw (sometimes called the "smoke screw") could have been loose and allowed the screw to back off slightly. There are not many ways for idle speed on a VE pump diesel engine to change. In fact, as far as I am aware, there are really only three: fuel restriction/air ingress (most likely), quantity screw position change, or low idle stop screw position change. Of those three, only the first two would also affect fuel consumption and power output; the third would affect idle speed only.

Put a new filter on and let us know what happens.

Thanks for the info and suggestions guys, much appreciated. I'll try to get a new fuel filter fitted this week end as I haven't changed it since getting the car. Re the belt stretch issue, I am actually a fully qualified mechanic, bt left the trade just as diesel engined cars were becoming popular so I have practically no experiance with them and this is my first diesel car. Way back when I was in the trade, timing belts were starting to replace timing chains and belt stretch was an issue in those days, some engines actually had spring loaded belt tensioners to address this issue, the 4 cylander Ford "Pinto" engine being one example, I did my aprenticeship with a Ford Dealer and when a car was due a major service, ie, every 12k miles, part of the service was to release the tensioner lock nut and rotate the engine twice to allow the spring to take up any stretch in the belt, so hence my query regarding the possability of it being an issue with these engines because my engine is behaving exactly as those early engines would when the belt had stretched. Re the fuel filter, in those days petrol engined cars with fuel injection had inline fine particle filters, much the same as diesels, but unlike diesels, it was quite common for a petrol engine to go 70, 80, even 90k miles without changing the filter and without suffering any of the symtoms described. So it seems that the roles have now reversed with diesels, belts not stretching yet fuel filters clogging very quickly. As they say, we learn something new everyday, and I'm quite happy to be corrected and learn new things. I'll pick up a filter during the week and change it at the week end and let you know how it works out. Thanks to all who contributed to this thread.

do you run on winter fuel since the drop of performance ?

black smoke behind you ?

No, I use the same fuel all year round, and no black smoke, even on full throttle, just a light haze.

like it was said a fuel filter is target here.

the fuel filter is supposed to be replaced all the 40 000 kms or 25 000 miles.

purge the water each month too.

that makes sence, I've done almost 20k miles since I got it, not sure how many miles the previous owner did since the last filter change so I'll start there and see how we get on, I'll also check the air filter and change it if neccesary.

the air filter every 12 000 miles max
oil change every 4000 miles maximum on a tic with semi synthetic or if you can synthetic oil with bigger oil change intervals.

the d24 do not like carbon build up in the rings grooves and it's what kill it the more often.
rings break because of build up and pissing injectors creating brutal incontroled pressure.

well adjusted injectors is the key of it's longevity.


give some news !