Di­ag­nos­tics

This ar­ti­cle is a true de­scrip­tion of an AECS tech­ni­cal help desk prob­lem and how it was solved. By H.P. Lei­jen (trainer/re­search)

Motor Equipment News - - ED SPEAK -

Ve­hi­cle

2011 Nis­san Navara, YD25DDTI 2.5-litre com­mon rail diesel.

Prob­lem pre­sented to the Helpdesk

This Nis­san Navara was towed into our work­shop; it is wind­ing over but does not start. We scanned it, it has no fault codes.

The cus­tomer (a col­league work­shop) said that it had start­ing is­sues when cold, but it would start and then cut out. Now it does not start at all.

“We have your ATS scope, I would like some help with the fol­low­ing record­ings please.

It looks like the rail pres­sure is too low. “

Pres­sure too low

I agree the rail pres­sure is far too low. In our ex­pe­ri­ence you will need at least 1.3V from that sen­sor be­fore the ECU will start in­jec­tion. There is no sense in driv­ing the in­jec­tors when there is no diesel pres­sure in the rail.

The suc­tion con­trol valve’s duty cy­cle in­di­cates that the ECU is try­ing to get the pres­sure up as it is firmly ac­ti­vated at the 56 per­cent or so it sits at dur­ing wind­ing over (non-closed loop).

The SCV con­trols the flow of diesel into the pump, so in­di­rectly con­trols the rail pres­sure.

Where could the fault be?

The pres­sure stay­ing too low could be the re­sult of sev­eral faults, and in re­al­ity ev­ery one needs to be elim­i­nated: • Diesel flow­ing into the pump could

be re­stricted. • Diesel could be leak­ing away from

the high pres­sure side of the pump. • The pump can be faulty.

On the in­put side of the pump you need to con­sider the fol­low­ing: a re­stric­tion in the tank (e.g. diesel bug), fuel line to the fil­ter, the fil­ter unit it­self, the line from the fil­ter to the pump.

On the out­put side you need to con­sider leak­age from the in­jec­tor re­turns to the tank, pres­sure relief valve to the tank, leak­ing in­jec­tor lines and con­nec­tions (e.g. reused lines), dam­aged in­jec­tors.

In the pump you need to con­sider fos­tuck plungers (e.g. cor­ro­sion), dam­aged non-re­turn valves, bro­ken pump shaft or drive gear.

Start point

The technician started at the be­gin­ning and looked at the pump sup­ply.

He sim­ply by­passed all the in­put prob­lems by let­ting the high pres­sure pump suck diesel from a can­is­ter with clean diesel. There is no prob­lem do­ing this as long as you work very cleanly. That made the en­gine start and fire up!

Found it!?

As soon as the orig­i­nal fuel line from the fuel fil­ter was con­nected to the fuel pump again, the en­gine would still start, but it took very long to fire up (more than two sec­onds) and was run­ning rough (surg­ing).

Strange

Mmm, that made the di­ag­nos­ti­cian think, no fil­ter good start, fil­ter fit­ted bad start.

He de­cided to re­move the fil­ter and fit a new fil­ter, just on the off chance that this virtual new af­ter­mar­ket fil­ter was blocked.

It was only now that he found out that this fil­ter was fit­ted directly lead­ing up to the start­ing prob­lems.

Solved!

The new fil­ter this di­ag­nos­ti­cian fit­ted was a gen­uine Nis­san fil­ter, which cured the prob­lem in­stantly. The di­ag­nos­ti­cian recorded the

“af­ter” pat­tern. The en­gine started well and ran nicely (no more surg­ing). A quick and clin­i­cal so­lu­tion for this towed ve­hi­cle.

Con­clu­sion

Fit­ting a brand new fil­ter out of the box does not mean that this item is cor­rect for the job, even though it is listed for that ve­hi­cle. The work­shop that passed the car on could have con­cluded that the fil­ter was the only item in the fuel sys­tem they had touched, so that the prob­lem very likely was in that item.

How­ever, would you have doubted the new fil­ter, or would you first have doubted some­thing else you might have pos­si­bly done wrong?

What are the chances that an af­ter­mar­ket fil­ter is ac­tu­ally faulty?

We at the AECS help desk have dealt in the last three months or so with about 10 faulty af­ter­mar­ket fuel fil­ters on com­mon rail diesel ve­hi­cles. I am not sure what is go­ing on out there, but we have found that they are not all branded the same – although they might all be com­ing from the same fac­tory, we do not know.

We are wait­ing at the help desk for fil­ter pa­per to fly out of the fil­ter into the very ex­pen­sive high pres­sure pump and in­jec­tors, or wa­ter traps not work­ing cor­rectly, with sim­i­lar very ex­pen­sive re­sults.

I am not sure if a fil­ter sup­plier takes care of the en­gine dam­age costs, be­cause how do you prove that the prob­lem is the fil­ter?

In this case it was easy, black and white, but that won’t al­ways be the case as not ev­ery shop that does main­te­nance has got this sort of equip­ment.

The fil­ter sup­plier re­funded the fil­ter and some of the labour in this very large com­pany, easy as no fur­ther dam­age was done to the ve­hi­cle.

An ATS scope and an ex­pe­ri­enced di­ag­nos­ti­cian made this job quick and cer­tain. No ar­gu­ments at the end of it.

ATS scope record­ing of start­ing and fir­ing up en­gine when the pump is draw­ing fuel through the fil­ter.

ATS scope pic­ture of Suc­tion Con­trol Valve (SCV) vs rail pres­sure.

ATS scope record­ing of start­ing and fir­ing up en­gine with the gen­uine fil­ter fit­ted.

Com­mon rail diesel fil­ter with very sim­i­lar fault

Ac­tual faulty com­mon rail diesel fil­ter

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.