Hijet Failed MOT (Emissions)


Any suggestions will be appreciated. I have a Daihatsu Hijet 998 which has failed the MOT on emissions, totally. Every measurement was off the scale. It has 57000 miles on the clock and has had a new head gasket fitted recently. The engine managment light has not shown on the dash. The garage that does my repairs has now run out of ideas as to what could be wrong!
It has had a new oxygen sensor fitted as he thought that might be at fault, but no. Now I have a new oxygen sensor. Rather than pile on the expense I now have the motor at home and am attempting to diagnose the fault myself. As of now I am in the process of ruling out any sensor related faults using an oscilloscope and waveforms for various components that I found on the net. I know I could throw money at it by changing the engine management unit but loathe to do so until I can say that is the problem.
If anyone can help me I will really appreciate it, thank you in advance.

Doesn't the ECU have an outpu

Doesn't the ECU have an output to connect a fault code reader Unknw
You then convert the codes to what ever component is faulty - this is how the garage should have been dealing with such problems rather than trial and error method.

I assume you've done basics like compression test, plug change, clean air filter, checked ignition and cam timing etc to ensure no mechanical problems Unknw

I'm a luddite and prefer carb to injection but to be fair modern systems are very reliable. Rather than ECU faults it's things like temperature senders which cause problems. IE the ECU thinks engine is still cold due to duff sender so sends rich mixture to engine. This is direction I'd check on your problem. Just because temp gauge works don't assume there isn't another sender hidden just to send information to ECU.
In fact I've run injection cars on original components at over 200,000 miles without any problems at MOT time so suppose it's time I accepted they are OK !

First step is get the fault codes interpreted.
There are numerous web sites that detail these.
I've a Haynes book that tells you where to attach a LED, count flashes and then decode - but unfortunatley it's on loan. I'll try and get it back asap if you don't manage to sort before. I can scan and email details direct idc if necessary.

Paul Humphries.


Thank you for the input Paul, you are quite right in what you say. However this model dosen't want to give up where the output port is, ie I can't find it. Haynes don't do a manual for the hijet and neither does anybody else.
The fault turned out to be a couple of vaccumn pipes that had been swapped around when the very same garage changed the head gasket for me.
This is the first injector beast that I have run, but better get used to it as they are all going this way now.
Thanks again.

Lets hope the garage accepts

Lets hope the garage accepts it's their fault and foots all the costs involved.

Paul Humphries.

over fueling

I had the same problem after a cylinder head gasket change on my hijet 993 cc van. Turned out garage (Diahtsu dealer who then passed it on to another garage in Stirling without my permission) had omitted to reconnect a hose and the lamda sensor got damaged causing the engine to overfuel. After paying £300 to have the gasket changed had to pay another £77 at another garage for them to replace the lambda sensor which fixed the problem. Took original garage (Diahtsu dealer) to trading standards but got nowhere. I have noticed that they have recently 'disappeared' overnight from their premises after moving to a new location so they may have gone out of business, which I'm not entirely unahappy about :-).

The second garage I took it to was Automotive services in Dunfermline they know what they are doing. Diagnosed the fault in about 2 seconds and had it fixed and tested within an hour. you may have to wait to book it in though if you can take it there as they are extremely busy which is to be expected as they seem to be one of the few garages who know what they are doing....


Hi Can you help me or any body else RE YOUR HIGH JET EMMISIONS WHICH PIPES WHERE ON WRONG? AS MY HIJET IS DOING THE SAME AS YOURS AFTER A HEAD GASKET Change i Have two Hijets the same and one has failed the mot the other passed so i have changed the parts off the one that passed over CAT + exhaust Lamba senser engine air temp switch It has new air filter plugs etc Engine temp switch not dash one ECU still having lots of un burnt fuel Tryed booking it into Daihatsu garage for fault finding but cannot do it for 2 weeks and nobody has a code reader bosch etc to do it Does the battery have to be disconnected to re set the ECU after changing parts as i have tryed that Many thanks Annette


Hi annettelee, it's going to be difficult explaining which pipes I had wrong because I cannot find out what the component is called that was connected up wrongly, but here goes. The component is positioned under the driver seat at the front of the opening, it has three pipes and a two wire connector going to it. One of the pipes runs from the air filter. All the pipes are small diameter. The way I found the problem was to swap one by one all the vaccumm pipes and swap back again if there was no effect, also I noticed if I put my finger over the end of the pipe running from the air filter, with the engine running, there was a small suction felt enough to pull my finger to the pipe and the engine tone would change.
As well as what I have attempted to describe above I had connected a volt meter between the oxygen/lambda sensor and ground so I could read the output of the sensor. It should read approximately 0.45-0.5 volts, whilst the voltage fluctuates because of a switching operation you can still get a good idea of the output.
It is always a good move to disconnect the battery when changing sensors as the output will vary, even slightly, and the emu will need to be reset.
I hope all this makes sense to you and is helpful. I will dig further and try to find out what the component is called and report back. I have posted an image in the image galleries/cars and commercial section. It is named Hijet Pipes and the component is highlighted with arrows.

There is one online vendor th

There is one online vendor that apparantly stocks a manual for the Hijet...its an American website...scroll down this page untill you come to 'workshop manuals'
Its listed as 'Hijet chassis'

Email them and ask what the manual includes...I reckon it must be a full manual at $129 its not exactly cheap