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Diagnosing loss of power under acceleration


New Member
May 21, 2023
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Hello all, hope you are doing well. I have recently purchased off a family member a 03 KDJ120, D4D engine. It has worked perfect for a few months, but recently I've been having some trouble with it.

It seems to be an intermittent issue. Sometimes, when accelerating, specially if going up a hill, it will lose power. No matter how hard you press the accelerator pedal, it will not respond. It does not lose all power, however it's like stuck at a power level (which, if on a hill, will make it slowly decelerate), losing power gradually. This will typically last for a few seconds, and then all of a sudden it will regain power as normal. Sometimes, while it's at that state of 'power loss', it will surge for half a second. It's like it's trying to get back power. It will do this sometimes a couple times, until finally it kicks off and regains power. Has happened in different gears. Only recently engine light turned on.

Recently got a VCI and installed Techstream, was able to get into the car and also read codes. It had 31 (air flow meter circuit), 24 (intake air temperature circuit) and 78 (fuel pump system malfunction - short). I am unfortunately not sure if these codes are all new. Today I erased all codes and will be on the lookout for new codes. I also recently cleaned the MAF, after this happened.

I have attached the codes, and a few freeze frames that the system had saved. I am new to this car so I don't have much technical knowledge, perhaps I should take it to the shop, but wanted to ask here previously in case someone could point in the right direction.

Thank you!


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Well done getting us some data to look at. Can you get us some live data when the engine has warmed up properly (coolant around 83-85c) and is idling? That's normally the numbers we want to check initially.

How many miles are on it? EGR clean always worth considering on these if it's never been done.

Please get us that other data and let us know if the codes come back!
Thank you all for the quick replies and suggestions. I have attached live data with engine warm as requested. I will also check with the previous owner (my father) whether the EGR has been cleaned or not. It is at 185k KM, 115k miles.

I found a thread on how to do the EGR clean and it looks easy enough, I might try that first. If not, perhaps go with the SCV.

Does this work, or do you need a live record? Side note, I read a service bulleting today saying that deviation over +-3.0 on the injection volume might be a symptom of these going out. Thoughts?


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Thanks for the data. Injectors are a bit of a minefield on the 120, you probably know there were problems with the injector seats on early ones - theres a thread on here, you can check your VIN to see if you may be affected. By this point, most 120's need to have their injectors changed if they havent already!

I think early models (up to aug 2004) give more limited data on techstream, so theres not that much to go on.

MAF, MAP & Common Rail pressure look about right to me.

Injection Volume and Pilot injection look OK.

As you've noticed the feedback value for cylinder 3 is 3.4, which is outside the widely accepted -3 - +3 range. However, the original range was -5 to +5, so it might point to injectors that need replacing, but I dont think its catastrophic. It's also worth checking the values a few times before making a decision.

Might be worth running diesel purge through the injectors, or something else to clean them and retesting.

1) Did the codes come back? If they did, let us know and we maybe able to help where to look next.

2) SCV are always worth replacing on a 120 if theyre the original short type, or possibly red / green ones

3) The most important thing on the 120 is check the oil pickup when you do the next oil change - make sure its not blocked. Threads on here cover this.
Little late here, just wanted to say that code 78(8) came back! Now just need to look into this. Seems like it could be the SCV.

Thank you for the detailed reply. I’ll look into it tomorrow when I am more awake!


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Can you confirm you've got the red/green SCV's?

I cant find any specific info on 78(8) - but heres the info for 78(2)/(3).

78(2) also identifies at 'Fuel Pump System Malfunction (SHORT)' so the diagnosis steps here may be similar.

On your techstream pic, is that all the data thats available? Do you have a 'Calculated Load%' value or any relating to Fuel Pressure and Target Fuel Pressure? I know they're on post 2004 models, but not sure about yours....

A lot of us on here have used RoughTrax for the replacement SCV's if you're looking for a supplier


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Took a quick look and yes, it's the old red/green version. I hope I don't have much trouble taking them out, I am going to try from the wheel. I'll post the freeze frame later in case there is more data.

They are out of stock on RT and seem to be available on Autodoc, so I am going to get them from there for 195€.

I also found this on a different forum:

Code 78(8) is a known issue on that generation of D4D engine subject to a TSB;


: 1CD/1KD Lack of power and DTC 78(8), 78(2) or P0627


Model codes: CDT220; CLM20; CDE110; CDE120; KDJ120; KDJ125; CLR30; CLA20; CLA21

INTRODUCTION This Technical Service Bulletin is to inform you of the production change and repair method for the subject concern. Applicable to vehicles produced with common rail pump with two SCV (HP2 supply pump)

DESCRIPTION OF PHENOMENON Customer may complain about lack of power or MIL “ON”. Following DTC might be triggered for DTC 78(8), 78(2) or P0627.

PRODUCTION CHANGE Diamond like coating (DLC) has been added to prevent SCV valves are sticking.

PRODUCTION CHANGE INFORMATION Not applicable, all models with HP2 supply pump are out of production.

I was not able to find the TSB referred by that reference number, but hey - it does make sense!


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When I changed my SCV I went in from the top, but mine is a single valve rather than the two coloured ones. Good luck let us know how you get on!
Top with mine too, a bit of a stretch over the wing, but easier on a step.
Like Karl, my scv is the single too, updated from short to long, so can't give any advice on getting at the 2 you have. Sorry.
Good luck with it.
I think I have seen that the large one is sideways, isn't it? The ones I have are pointing at the back of the car, so it does seem harder to reach from the top. From the side with an extender I think it will be easier, but I need to see. I just hope the screws give no problem.
The single scv points to the back of the car as well.
You should have no problem undoing the screws,, new ones come with the singke type.
They require an Allen key/wrench/socket on the single ones, not sure about your 2 though.
Swearing obligatory !

The handy thing about dropping screws and can't find, (if it is handy - not) that if yours are supplied with new screws, you get 2 free goes on each.
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Also important, be scrupulously clean in replacing, clean thoroughly around bigger area first before any work. You dont want any s**t getting in the fuel pump.
I would like to share this for future possible self diagnosers - it was indeed the SCV. I was unable to replace it, but bought the part, brought it to my trusted shop where they changed it and charged for 1hr - and it's running like new!

Thank you all again... hope to not have to see you again!! :)