'89 BX 16v Error Code 52 - Air leaks?

[krekov]

Hi,
This is my first post, excuse me if I omit some pertinent information.

Anyway, I've recently bought a sorry little 1989 16v for total restoration, sat for 10 years in a shed this one.
It's running alright currently, but there is one problem with it - a check engine light.

I've read off the error code and it's number 52, just that one.
According to the Haynes Manual for ECU diagnostics, this error stands for: "Mixture control, supply voltage, air or exhaust leak"
(I have no idea what "supply voltage" refers to, is it the voltage delivered to the main ECU?)

This is where things get complicated - there are absolutely no exhaust leaks, I'm as sure as I can be of that.
But, I'm positive there could be an air intake leak. The problem is, I've checked every air hose visually and with a can of brake cleaner (to see if it'd get sucked in, a change in engine operation would be noticeable I think) and I could not find any leaks at all.
Even with a completely disconnected breather pipe and petrol vapor valve (holes plugged tight of course), there was no change.

The main intake pipe going out of the AFM is solid, no leaks on that either.
The throttle bodies are completely closed with no throttle, they open and close smoothly.

The AFM is in great condition, it has never been messed with. The TPS sensor is brand new too.
I'm positive it's not an electronic fault.

I've followed some threads on here and I know many members are very knowledgeable about these cars, what could be wrong with it? Which hoses should I double-check, where do I look next? Maybe I forgot to look at something important?

[RobC]

Hi and welcome to the forum.
First off I would double check that the error code is the correct one: in 1991 the 16v changed ECU system from motronic ML4.1 to Motronic M1.3 (therefore it is likely you have ML4.1). An easy way to tell which one you have is the number of rows on the ECU: 2 rows for ML4.1 and 3 for M1.3.
Don’t believe anything you read in Haynes. I have before me the actual Citroen workshop manual pages for the 16v (with ml4.1) and there is not even a 52 error code listed!
53 is battery voltage, 54 is ECU, 55 is CO mixture.

[krekov]

Thank you for the reply!
This car despite being an 89 uses the Motronic 1.3 system, with a 3-row ECU. The ECU number is 0261200158.
I got the code by using the ignition method - turned the key a bit past the "ignition on" position and entered the diagnostics mode. I've read the error code many times to make sure I didn't count the flashes of the check light incorrectly. It's definitely number 52.
Do you maybe have a 100% correct error list for the Motronic 1.3 BXs?

[RobC]

This link (unverified) implies that 52 is lambda sensor- which is only fitted to m1.3 cars with a cat on the exhaust.

https://frenchcarforum.co.uk/forum/viewtopic.php?t=2084

[krekov]

Interesting, thank you!
This car has (had) a cat, someone cut it out ages ago. It's one of the earliest models with a cat and the 147hp engine, I think.

I knew something was wrong with the lambda, it was at ~1.2 on idle but dropped massively as RPMs went up, down to about 0.85 at 4000rpm (measured on a professional exhaust analyser). But, the wiring checked out good, and the sensor was new, so I thought it could've been be an intake leak.

To be on the safe side, I bought a 0261200158 ECU locally for just 20 quid a few days ago and decided to fit it following your advice today.
Lo and behold, that fixed it! It would appear the lambda circuit in the old ECU was somehow damaged.
The check engine light is no longer on with the new ECU, and measuring lambda on the exhaust gasses checks out perfectly, as well as CO and CO2.

An interesting fault, gave me a lotta headache. I checked the codes on this ECU just to be sure, and there are absolutely none.

The car still runs kinda rough on idle, though. It keeps solid 900-1000rpm, but the engine shakes plenty and the noise is "inconsistent" - kinda sounds like an idling Group B rally car or a motorcycle. It starts to run smoothly above 2000rpm.

The following ignition/air system parts have already been changed:
- ignition leads
- ignition coil
- idle air valve
- distributor cap
- spark plugs (though I wasn't the one who did it, the previous bloke did that and I don't know what plugs he used)

I did not change the distributor rotor arm yet.
Should I check out the spark plugs or the rotor arm first?

[RobC]

These engines will never idle completely smoothly, it’s just the BX 16v way!
Do everything you can to secure air leaks and ensure the spark is as strong as possible and the injectors are working as they should, and that’s it. You’ll be chasing shadows forever if you’re trying to get a super smooth idle on a 16v.

Glad you got the ECU problem sorted.

Now go and enjoy the car

[RobC]

PS the group B reference is apt by the way as the engine is distantly related to the pug 205 t16.

[krekov]

Yeah, I've read about that heritage somewhere.
I've already been enjoying it quite a bit, it's a lovely car.

I'm aware these engines idle a bit odd, but on mine it's like something is definitely wrong. To put it in the clearest way: putting a hand over the exhaust pipe I can feel the exhaust not being a constant stream of gasses - it goes like poof-poof-poof, but not in regular intervals, it just seems to do it at random.

[rutter123]

Do a compression check.

[krekov]

Alright, I could check that next week to be sure.
I'll make a short engine video and link it tomorrow too, in case my description was misleading.

[white exec]

Not necessarily the main cause, but I have distant memories of significant grounding problems with a 1990 GTi 8v, which caused running and starting issues, and were only resolved by cleaning up the many body and engine ground points. After that, the car ran really sweetly.

'89-ish was not a good date for PSA electrics, when cheap connectors were in use and many grounding points were push-on rather than bolt-down. This plagued early XM, and required warranty modification. Control voltages and supplies could be unstable.

Just a thought.

[krekov]

Oh for sure, I've already changed a few connectors on it, the electrics are not durable at all. If it turns out everything is ok, I'll look there.

Here is a video of the car idling after a little warming up:
https://youtu.be/JzC5lqU_Jqw

[RobC]

Mate that’s good for a 16v!
Much the same as mine- they’re always a little lumpy at idle and yours is by no means unusual. Perhaps if you had perfect compression, perfect wiring and perfect fueling with zero air leaks whatsoever it might sound a little better but I’ve had 3 16Vs and despite faffing around with them loads they’ve always been lumpy. It’s a highly tuned engine from a time when the management systems were still pretty basic so agricultural idle is par for the course.
Who cares about what happens at 1,000 rpm anyway, it’s 4,000 where the fun starts

[krekov]

Haha, absolutely, this engine starts to live only in that high range. But still, watching some nicely kept BXs on Youtube they seemed to idle a bit better, so I'll pursue improvement.

But, it's very reassuring to hear this is a good idle.

There are more pressing matters with it to focus on, too. (I'm sorry if I point out things that are just normal for these, but I never had a car this old before.)

The thing that annoys me is that it really doesn't like rolling below 2000rpm. Like, if I want to gently move in heavy traffic in 2nd at around 1300-1500rpm it keeps crabbing forward, it does it in 1st too.

And, most annoyingly, trying to quickly shift into 3rd often results in the gearbox grinding, same can happen with going into 4th from 3rd, but less often. It appears to happen completely randomly, regardless of the RPMs. I've made sure that I press the clutch all the way down. The clutch itself doesn't appear to be worn, the pedal isn't hard at all and grabs low as it should.

The thing that throws me off is the gears engage really nicely, even if they grind. The lever just clicks into position without any more force necessary.

I've come across a website claiming that grinding is just how these gearboxes were from the factory, but I find that hard to believe.
So, is this normal behavior, or is my gearbox just dying?

[RobC]

I usually have a little niggle going into third as well. Again, not every time.
But try adjusting the clutch cable so you’ve got some more pedal travel - even if you think you’ve got enough at the moment. I did this recently (having previously thought it was fine) and it’s made a bit of a difference - I can even get into reverse without crunching now