Exhaust smells bad and fluctuating idle

BX Tech talk
Jugostran
New Member
Posts: 9
Joined: Fri Sep 10, 2021 6:22 pm
Location: Subotica
My Cars: 1989 Cimos-Citroën BX 16 TRS

Exhaust smells bad and fluctuating idle

Post by Jugostran »

So hey, I am trying to diagnose this issue with my 1989 BX 16 TRS. Basically, the exhaust smells like an old Lada. Now, I don't know whether this is an exhaust issue or a Solex carburetor issue. I would really want to fix it since I am quite embarrassed to drive the car like this.

The other issue is that when the car is at idle, it often makes a hissing noise which drops the RPM from 1000 to 800. This makes the whole car shake (I can tell the engine is struggling). And then the hissing noise disappears with a click and the RPM returns to 1000.

Both of these issues have been plaguing my car for months now (ever since I bought it). I would greatly appreciate it if someone gave as much as a hint as to fixing these two (very) annoying problems.

Thanks in advance for all your comments!

RobC
BXpert
Posts: 555
Joined: Tue Aug 15, 2006 11:15 am
Location: East London
My Cars: 1991 Citroen BX 16v
x 26

Re: Exhaust smells bad and fluctuating idle

Post by RobC »

The hissing and the Rev drop is the hydraulic pressure regulator cutting in and out. This is normal. But if the Rev drop is excessive it could indicate the system is putting a bit more strain on the engine than is strictly necessary. All things being equal and in good condition the hiss-click cycle shouldn’t really be any less than every 30 seconds. A minute even better.
If the interval is less than 30 seconds and/or if the hiss is quite prolonged before the click, a number of things need to be investigated:

- HP pump could be tired
- pressure regulator could have some internal leakage in the wrong places
- accumulator sphere flat
- HP pump belt loose
- brake valve excessively worn
- probably others…

Can’t help with the carb sorry but I’m sure others can!
1991 Citroen BX 16v

Jugostran
New Member
Posts: 9
Joined: Fri Sep 10, 2021 6:22 pm
Location: Subotica
My Cars: 1989 Cimos-Citroën BX 16 TRS

Re: Exhaust smells bad and fluctuating idle

Post by Jugostran »

RobC wrote:
Tue Oct 12, 2021 9:45 am
The hissing and the Rev drop is the hydraulic pressure regulator cutting in and out. This is normal. But if the Rev drop is excessive it could indicate the system is putting a bit more strain on the engine than is strictly necessary. All things being equal and in good condition the hiss-click cycle shouldn’t really be any less than every 30 seconds. A minute even better.
If the interval is less than 30 seconds and/or if the hiss is quite prolonged before the click, a number of things need to be investigated:

- HP pump could be tired
- pressure regulator could have some internal leakage in the wrong places
- accumulator sphere flat
- HP pump belt loose
- brake valve excessively worn
- probably others…

Can’t help with the carb sorry but I’m sure others can!
This is some great info! Thank you so much!
The interval of the clicks is often less than 30 seconds, and sometimes it is quite prolonged.
Now, I would like to check over all those parts. I am quite new to DIY so bear with me :P
Where exactly is the HP pump? Also, where is the pressure regulator? There is a very mild leak in the distribution block right next to the accumulator sphere. However, the accumulator sphere itself was changed recently. Also, the whole brake system (including the valve) was refurbished recently as well, so I think the issue lies either in the HP pump or pressure regulator.

RobC
BXpert
Posts: 555
Joined: Tue Aug 15, 2006 11:15 am
Location: East London
My Cars: 1991 Citroen BX 16v
x 26

Re: Exhaust smells bad and fluctuating idle

Post by RobC »

I’m afraid I don’t know the 1.6 engine at all, so I can’t tell you exactly where the pump is. It’s driven either by a pulley on the camshaft or crankshaft.
I would get a Haynes manual if you haven’t already, while not always 100% accurate it’s a very useful guide.
What’s the mileage of the car? In my experience after 100,000 miles or so, the HP pump will certainly be in less than ideal condition, especially if the fluid hasn’t been changed regularly.
The pump does put quite a strain on the engine when it cuts in- you note that the engine isnt running very well so it may well be down on torque at idle, hence the noticeable drop in revs.
There’s a technical topic on “fast tick times” on here which would be worth a search as well. Good luck
1991 Citroen BX 16v

Jugostran
New Member
Posts: 9
Joined: Fri Sep 10, 2021 6:22 pm
Location: Subotica
My Cars: 1989 Cimos-Citroën BX 16 TRS

Re: Exhaust smells bad and fluctuating idle

Post by Jugostran »

RobC wrote:
Tue Oct 12, 2021 10:39 am
I’m afraid I don’t know the 1.6 engine at all, so I can’t tell you exactly where the pump is. It’s driven either by a pulley on the camshaft or crankshaft.
I would get a Haynes manual if you haven’t already, while not always 100% accurate it’s a very useful guide.
What’s the mileage of the car? In my experience after 100,000 miles or so, the HP pump will certainly be in less than ideal condition, especially if the fluid hasn’t been changed regularly.
The pump does put quite a strain on the engine when it cuts in- you note that the engine isnt running very well so it may well be down on torque at idle, hence the noticeable drop in revs.
There’s a technical topic on “fast tick times” on here which would be worth a search as well. Good luck
Hey thanks. My car is at 133k kilometers (approx 80k miles). Also I reckon the engine runs well. It pulls nicely and doesn't feel down on power.