Diagnostic light on when cold,goes off when normal temp.Why?

unicorn · Post by **unicorn** » 15 Jul 2009, 20:12

Hi all. Need some advice from the pros. Just purchased an 1998 Xantia 1.9 TD (DHX/XUD9)with 88K on the clock.
It was a mess being in limp mode. With air in the diesel, glowplugs not working and was just running bad. Replaced air/fuel/oil filters, glowplugs, changed engine and gearbox oil.Starts first time and runs smooth.Revs quick however not underload. (Limp mode) Found that the instument panel was opened and ABS/Engine Diagnostic/Airbag lights missing. Replaced lights and found that the Engine Diognostic ligtht stays on untill engine is at opporating temp. Goes off and goes on again as soon as I try to excellerate (in limp mode. No power, work the gears to get her going to 70). I tried to read the CPU by inserting a paper clip in pin5 and 6 in the 16-pin ALDL connector. Did not even work. What does it sound like and can I find the fault myself. How?? Thanks in advance.

Post by **CitroJim** » 16 Jul 2009, 00:29

Hi Unicorn and welcome to the forum

The only way to read the ECU is by use of the dedicated Citroen Lexia diagostic tool. The old paperclip trick won't work and may end up damaging the ECU.

The usual, and about the only real cause of the engine management light coming on is failure of the needle lift sensor attached to No.3 injector. This is quite a common problem. Look at the injectors until you find one with a thin black wire running from it. Follw this wire to the plug, disconnect it and use an ohmmeter to check ithe sensor resistance. If good it'll read about 109 ohms.

Another test is to disconnect it with the engine running. The engine note should change quite dramatically. Also ensure that with the needle lift sensor disconnected, the tacho still reads. This proves the TDC sensor is good.

Another reason for the light coming on can be to do with low fuel pressure due to a blockage somewhere causing a timing actuator fault; basically there is insufficient pressure to fully drive the actuator which uses the diesel fuel as a hydraulic fluid for this purpose. A favourite cause is a blocked tank strainer or a blocked fuel return line. Both can occur if the car has been run on alternative fuels such as veg oil.

If all else fails and given you're fairly local, run over to me and I'll pop it on a Lexia for you.

unicorn · Post by **unicorn** » 16 Jul 2009, 09:47

Thanks Jim for the advice.
Going to put my overalls on and have a look.

Xaccers · Post by **Xaccers** » 16 Jul 2009, 11:16

Did you replace the leakoff pipes between the injectors?
They can crack with age and let in air, so if they're not flexible, it's probably time to replace them anyway

unicorn · Post by **unicorn** » 16 Jul 2009, 17:00

Ok. So this what I have done now. Did the ohm check on the 2nd injector and it gave me 105 ohms. (Is that OK?) Had the pipes replaced when I had the injectors first cleaned. Started the car, unpluged it with no change in the way the car ideals however, the rev counter was still working.(Good).Disconnected the return pipe from the pump as well as pipe before hand pump.Opened top of fuel tank and cleaned filter in tank. (Was not that dirty)Blew air through the pipes and all is clear.Then sucked on the return pipe and diesel returned with ease.( Is that normal.Is there a none return valve?) Cleaned out the hand pump and found a brown substance that looks like tea leaves that has come from a tea bag. Cleaned replaced all and primed the system.Cracked the injectors to clear air. Built up pressure by using the hand pump and took her for a test drive. Diagnostic light still came on. Put my foot down and she took of like a rocket. 100 meters later back to her old self. Now power,fuel starvation, worse than before.Opened the hood,pumped the hand pump and then took off like a rocket then back again to her old self. My question is how does the pump creat that pressure because if I look at the clear line from the filter to the pump, it looks like air is comming from the pump. I have no leaks from the pump.Where the return pipe connects to the pump would it be possible for the air that I blew down to clear to have not been forced out my the pump and now it working against the pump.There must be a none return valve somewhere in the pump? Really hope we can solve this one.Any advice is apprecited!!

unicorn · Post by **unicorn** » 16 Jul 2009, 17:04

Just to let you know I have half a tank of diesel. Would it be wise to fill her up and use the pressure in the tank to purge the air out?

Post by **admiral51** » 16 Jul 2009, 19:46

This may just be a long shot but from what ive read of your problems you say that you have cleaned out the primer bulb.I believe this could be your problem as you say the bubbles are present between the filter and the pump.
You can get the primer bulb from B & Q or a good motor factors but as youve had the pipe work apart try running a clear pipe to bypass the primer bulb.Obviously this will mean it will take a bit of cranking to start it up but you should be able to see if air still gets into the system but your problems sounds like fuel starvation not air alone.
I suppose its like haveing bits of crud in the washer jets you can blow air through but liquid moves the crud and blocks the holes

When you are asking the pump to suck fuel at the rate you need under load the vacumn created will force any crud to block the tiny joiners and primer bulb whilst on tickover etc the vacumn will be lower.

As an aside i would again check the filter as you have disturbed the system and any crud could well have been dislodged and also check the blank plug on the injector leakoff pipes as this has a nasty habit of causing trouble first

Colin