2 cylinders aren't firing

[Pontual]

Hello, I'm having an annoying issue with my old. Car Citroen C5 2.0 16v 2001, gas, equivqlent to 95k miles. Was running poorly yesterday. I replaced the sparkplugs with iridiums, but no joy. Took a new coil loaned, no joy. Took the iridium out to inspect and the 2 middle one are new as installed (or not sparking or not getting fuel feed), but #1 & #4 are burning. Injectors are new also. Maybe Ecm or wiring, right? Computer said injectors command not present at #2 & #4, but #4 is burning. They click normally with external energy. I'm out of ideas, anybody?
Thanks in advance.
Ozz

 

[KingCake]

If the injectors are not being commanded to fire then you have a problem with either the cam or crank sensor, depending on the car. But usually fuel injector firing is controlled by the cam sensor.

Try to scope the signal and look for hash or dropouts. Google for what a hall effect or variable reluctance sensor should look on a scope. (Depending on type your car has)

If the cam sensor signal looks good then you might have a bad driver transistor in the engine computer.

 

[Trav]

When you had the injectors out I would have put the 2 that were firing in the place of the ones that were not, that would have eliminated or condemned them right there.
Get a noid light and connect it to the not working injector plug and crank the engine it should flash.

Citroen has some bad habits in their FI systems because some Citroens trigger positive 12v in the ecm not the common negative so common diagnosing techniques may or may not work on these.
Check for 12v at each injector plug and use a noid as the first step. With the key on not running check the known good injector plug for 12v if it does you are dealing with the common negative trigger system if not you have 12v positive trigger.

In this care you need to check the continuity of the negative and should have 12v flashing at the other wire while cranking.

 

[Pontual]

WOW, great tips, Kingcake and Trav, thank you! Gonna chech the injectors. Now I have ammo to deal with that sucker. The cam sensor I've already changed, when the car began to stall ramdomnly a few thousand mikes ago, but no joy, maybe the crank sensor? The dtc isn't as good as my old eec-iv 95 Taurus... It is a CAN system for a Lexia reader ...

 

[Pontual]

The ecu had 2 little diodes loose out... could that be the culprit?

 

[mk378]

If some but not all of the injectors are being driven, it must be either a bad ECU or a break in the wiring.

 

[Trav]

Originally Posted By: Pontual
The ecu had 2 little diodes loose out... could that be the culprit?


Sure it could, any loose component in the ECM can wreak havoc with the system.

 

[Pontual]

New ECM coming in. Very expensive part!

 

[Pontual]

Originally Posted By: mk378
If some but not all of the injectors are being driven, it must be either a bad ECU or a break in the wiring.

I tested the wiring, all negatives (one of the wires of each connector koeo) had continuity, the others has roughky a voltage of 1,8V at one wire at each connector. Then I ruled out the wiring and went to open the ecm (very hard grey silicone high temp sealing all around) and found those 2 diodes sitting in the bottom of the case.
Thank you guys for the hands!

 

[Trav]

That is an expensive part new, no used ones you could be flashed with your info?

 

[Jetronic]

Originally Posted By: Pontual
Hello, I'm having an annoying issue with my old. Car Citroen C5 2.0 16v 2001, gas, equivqlent to 95k miles. Was running poorly yesterday. I replaced the sparkplugs with iridiums, but no joy. Took a new coil loaned, no joy. Took the iridium out to inspect and the 2 middle one are new as installed (or not sparking or not getting fuel feed), but #1 & #4 are burning. Injectors are new also. Maybe Ecm or wiring, right? Computer said injectors command not present at #2 & #4, but #4 is burning. They click normally with external energy. I'm out of ideas, anybody?
Thanks in advance.
Ozz


#2 and #4 in the firing order would be cilinder 3 and cilinder 2 respectively. Check if the coil gets feed and ground (through the ecm). similarly check the injectors if the coils get what they need.

 

[Jetronic]

see you've found the issue already (most likely anyway).