Hijet failed MOT on emissions.

Hello folks,

I am the proud owner of a 1995 EFI 993 3 cylinder pick-up.
I have taken it for MOT and it has passed everything except the emissions test.
Here is a list of what I have done so far.
1) Replaced plugs.
2) replaced HT leads.
3) replaced Lambda sensor.
4) Removed throttle body, cleaned and refitted.
5) removed throttle position sensor, stripped and cleaned contacts and refitted.
6) Replaced waterpump and cam belt.
7) Reset ignition timing.
Replaced air filter.
9) Checked all vacuum pipes.

The little beast runs as rich as hell, so rich in fact that it puts out black smoke from the exhaust, the CO is high, the HC is high and the lambda is high.

I have even gone as far as wiring in line a wire-wound potentiometer so I can reduce the speed of the fuel pump, thus reducing the fuel pressure. This helps to bring down the CO and the HC, but the Lambda still will not come into the limits.

Today I changed the engine oil and filter and put a can of fuel additive in as well as a can of "Cataclean". When I took it back again this afternoon, it seemed to run much better and was MUCH more responsive to the throttle, but now the CO and the HC are WAY high, but the Lambda reading did come in within limits some of the time !!!!
I had hardly any fuel in the tank when I added the additives, but I put in 10 ltrs of petrol as well, I am wondering if I should have filled the tank ????

If anyone has ANY ideas what else I can try, PLEASE, PLEASE help !!!!
I have put a lot of cash into this truck now, including a set of tyres too and don't really want to have to give up on it, but it's getting to the point where I just cannot justify throwing much more cash at it !!!

If nobody can help then I'm afraid it will have to go on ebay and I'll just have to take a beating.

Thank's for reading my tale of woe, I just hope that someone can help.

Best regards to all, John. (feeling VERY depressed) !!!!!!

Hi our MPV was very high on everything and it was the map sensor which is the manifold absolute pressure sensor I don't know if the pick up is layed out different but in the van it is under the center plastics and the wiring also has the handbrake switch with it it is a little black box about a inch square with a block connecter one side and under neath is a vacuum pipe ours had snapped at the point the pipe connected and had been stuck back together previously and had come off again once changed the emmissions dropped and the mot tester squeeased it through as I was running out of time to run it to clear the exhaust he did say that if it had been like it ages then the cat may have failed and as it's due this mounth we will find out. Hope this helps.

Hi Rich,
Many thanks for the swift reply !!!!

I haven't checked that, I think I know the part you mean, I think I can just see it with the engine cover off, if it's the bit I am thinking of, it's located on top of the engine in a steel bracket, almost out of sight !!!! As you described, near to the handbrake lever.

I'll have a good look at that tomorrow and report back.

Many, many thanks, you have given me a little hope !!!!!

Best regards, John.

Mine is in the cab and the pipe runs through a rubber bung but the van I got some spares from at a breakers it had been relocated to inside the engine bay probably because one had been broken while being taken apart. it was only then that I realise mine was broken as I thought it was the atmoshperic sensor it was such a clean break.

I too would suggest the map and the tps sensor.

These are both easily testable.

Suck on the pipe with your multimeter attached to the signal wire, watch the voltage go from (off the top of my head) about 2.5v at atmosphere down to about 1 volt when your sucking so hard you might bust a blood vessel. Test the tps in a similar manor but just spin turn the throttle by hand. You should see a nice smooth voltage change, if it jumps about its knackard.

Its very common on cars that fail the emission that a garage will recommend a new Cat and a lambda sensor. This sometimes scrapes them through the test, but the second year it will fail again... and they try and fit a new cat and lambda sensor again. Garages don't do electronics.

Hi guys,

Well, how can I ever thank you enough ???????????????????????????????????
I had a look and found the map sensor where you said it would be, and sure enough, the vacuum pipe was not connected.
I started the beast up without the pipe on, then connected it, WOW!!!!!!!! what a difference !!!!!!!!!!!
The engine instantly changed note, smoothed out and ran like a dream !!!!
Got it booked for a re-test again at 8.30 Monday morning, I think it will sail through this time, I'll keep you informed.

Again, thank you, thank you, thank you !!!!!! I was getting to the point of repairing it with a gallon of unleaded and a match !!!!!!!

Best regards to you all, John.

Bet you've just found another 30bhp and doubled your mpg too

If you can go for a good run as on ours after 30 mles it was still showing high on something as the crap was still in the exhaust.

Well, I have to thank you guys again, when I took it in the emmissions were still on the high side, but after a good long run and a re-check everything came down to how it should be, just watching those three red sections on the gas analyser turn green, one after the other, was like magic !!!!!!

Thanks so much, without your help I would NEVER have found the problem !!!!!!!

One more Hijet back on the road again

Best regards to you all and I'll still keep popping in here from time to time to see if there might ever be a chance of me being able to return the favor by helping someone else !!!

Undepressed John !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Try disconnecting the pcv valve hose that connects to the oil filler cap.