Fixed! Rough running GTi

[deltic]

I appreciate that this could be any number of issues ignition, fuel, etc. or a cracked distributor cap or worse... I'll outline the symptoms just in case anyone can offer any advice which would be gratefully received.

A couple of weeks ago the BX began to run a little roughly at idle but otherwise seemed to run smoothly. At the centenary rally weekend I had a nagging worry that perhaps it was just starting to worsen, thus I decided not to join the convoy to Motofest especially with a lot of queueing/idling likely. The return journey seemed to be OK but then the car began running roughly under acceleration on the M25 and then by home was just generally pretty rough. Sadly that put a dampener on a great weekend.

As a 1991 8v GTi I think it has the Motronic MP3.1 fuel injection system but not a more conventional distributor cap which threw me as I hoped to attempt to solve this myself by replacing the distributor cap and leads. Does anyone have a parts number for a set of ignition leads?

You can probably tell I'm not terribly mechanically minded and am probably not going to get very far with this on my own - so could anyone suggest anyone in the Medway/Gillingham (Kent) area familiar with BXs who might be able to diagnose the problem? Might be best to PM me.

Thanks!

[Tim Leech]

Hi Jonathan

Start with the basics, , a new set of plugs/leads/ dizzy cap and rotor arm is a good point, also check the coolant and oil for contamination which could be a blown head gasket (not unheard of but rare)

Anyone can fit those, its a case of replace old with new, if you change the cap do one lead at a time so not to get the firing order out of sequence.

They should be readily available as its the same engine a 205 GTI, try eurocarparts or even your local factor.

Any local garage should be able to diagnose this as its not Citroen specific,

[rutter123]

Air leaks can cause bad running issues on gti's, lumpy idling, stalling and generally misbehaving.
Check all the rubber hoses that are connected in any way between the ecu and the throttle body including the air hoses that go to the cold start valve, if any of these have the slightest leak or split it will cause a very lean mixture.
Other things to consider, injectors/wiring, ignition module, fuel pump/filter, fuel pressure regulator, or even perished/corroded fuel lines
I had running issues on my gti with Jetronic system Ultimately finding the fault was in the injector wiring loom, not saying that's where your fault is but the above are a good starting point.
It's a process of elimination I'm afraid.
Removal of the spark plugs will give an idea of how things are and will give a rough guide to weak or lean mixture and as to what's going on inside.

[deltic]

Thanks both for the advice. The photo shows where the distributor should be, am I correct in thinking that it is actually a distributorless ignition system?

To help me find my way around would anyone have a diagram of the various components (especially the wiring and hoses) of the ignition system?

[Jaba]

I can let you have a wiring diagram in a few days. In the meantime check your fuel quantity and quality by removing the fuel pipe from the engine, put it into a clear bottle then crank the engine and observe the petrol being pumped into the bottle. It should be clean and pump in reasonably quickly.
No there is no dizzy to worry about.
A compression test would be a good idea too.

[Tim Leech]

One less thing to worry about then, I would also pop the plugs out and see if any of them are particularly sooty, which could indicate a misfire.

[deltic]

Thanks for the further comments. Have only just had another chance to look at the car this evening and it looks like the coil (the thing in the photo above!) is only producing sparks to three cylinders so all being well an easy fix. Hopefully!

Assuming I get hold of a correct replacement coil is it just a straight swap?

[Jaba]

The coil provides a spark for cylinders 2 & 3 and 1 & 4 at the same time, that means two sparks per cycle where one is a wasted spark. So it would be a strange failure if only one of them is not sparking. Have you checked the HT leads and perhaps swapped some around to see if it is the coil or a lead or plug ?
Hope that makes sense. The usual failures are two cylinders losing spark due to HT coil or ignition amp failure

[deltic]

I see. What I did was remove each lead from the coil in turn and all but one continued to produce a spark. Only in the case of removing the lead from coil did the engine continue to run, for the other three the engine stalled.

[deltic]

Replaced the coil (as depicted above) which (thankfully!) fixed the problem. Top tip: access for removal is easier if you remove the battery...

I sourced a Hella coil on eBay, part number 5DA193175-421 for just over £32.00. This also seems to fit a large number of other Citroens.

[Jaba]

Good fix J. Can you fix the weather too?

[deltic]

I got wet doing the fix...