Hi !

I have some little problems on my S4 engine.

Symptoms are:

- idle is too high, about 1000-1200 RPM
- idle is unstable, the RPM are stable but there is a lot of misfires (not sure of the word in english but they make bumps in the exhaust and the idle speed get down for a half second - can you understand ? ) when engine's hot.
- no power under 3000 RPM and then I have all the engine power (enough to make my exhaust line become orange. )

Engine is stock, exhaust too (but old and has leaks) and spark plugs are new (~400 km).

Do you have any ideas ?

Thank you for you help !

 

Check for a clogged catalytic converter.

Are you experiencing sporadic idle?

 

Check your leading ignition. Usually this is the cause, with out the lead plugs firing, your timing will be 15 deg late, giving you idle problems and you will have a ton of fuel burn in the exhaust over heating the cat.

Also, if you've got spark on the leading ign, then check fuel pressure in the rail, flow test your injectors and replace the fuel filter.

 

And check the timing as well as incorrect timing can cause this problem also.

 

Thanks for your answers

What do you mean with sporadic idle ? I know what sporadic means but I'm not sure to understand. I think it's not the same expression in french.
Idle is sometime at 900rpm, sometimes 1000 and sometimes 1200. And more rarely it oscillate between 1000 and 1200rpm.

And how can I know if my catalytic converter is clogged? By checking the temperature before and after the cat ?

I checked leading ignition with a spark gap (is it the good word in english ? image: ) and it's ok. I have ignition on all 4 spark plugs.

I tested injectors and they are good. I changed (months ago) the pintle caps on two injectors (I can't remember if it was the primary or secondary injectors). I noticed when I received the pintles caps from Mazdatrix that they weren't the same. Original ones were braun with a small gap, and Mazdatrix's are white, plastic with a bigger gap. Can it be a problem ? (when I changed them, I already had the same problems as I'm having now.)

How can fuel pressure be a problem if I have power at higher RPM ?

Question about overheating the cat, is it normal that if I run a moutain pass of 7km with full load the cat make a red glow that I can see at the exhaust outlet ?

Is it possible that timing change by itself ? Month ago I didn't have these problems. Idle was at 850RPM and there was not much misfires juste a little bit.

One more information, when I accelerate I can smell a fuel odor...

I hope my english is understandable, and if not, let me know !

Thanks for you help !

 

I tested the O2 sensor too. It regulates only from 2200rpm... Is it normal ? I don't think so... And the voltage value is between 0.7V and 0.9V... I know that wankel engines are running rich but so much rich is normal ?

 

good luck on the problem

 

Your English is fine. Very understandable.

Here are a few things you should do. (This is also a bit of scheduled maintenance. So, even if none of these are associated with your problem, they still probably need to be done. Your car is at least 24 years old.)

- (Do not drive your car.) Check your fuel pulsation dampener immediately. The screw in the end of the pulsation dampener may have backed itself out into the plastic cover/cap. It is a very common occurrance, and a big contributor to engine fires.

- Check for a clogged catalytic converter. You should drop the catalytic converter down from the bottom of the car to visually inspect it.

- Replace your fuel filter and fuel pump strainer a.k.a. - "fuel sock"

- Set your idle.

- Set your TPS. (Throttle Positioning Sensor)

- Set your timing.


It's safe for me to assume you have a European spec FC. Do you have a factory service manual? (That would help a lot.)

 

If its a turbo i would check the tube from the maf to the turbo for a crack. It could be breathing in unmetered air.

 

The screw have effectively backed itself out. But I don't see any fuel leakage. Can I screw it on or not ?

I noticed something else weird after I took down the intake manifold. I first turned on the key to look for fuel leakage (I didin't see any but smell a bit of fuel). While the key was turned on, I noticed that the front primary injector was making noize. Like if it was commanded by the "computer" it makes a "tik" about every... 10 seconds.
It can't be a short cut so what is it ? a CPU problem ?

 

So, I replaced the fuel pulsation damper with another one (used not new), set the idle and replaced the TPS (it was at 6.5kohms when full open).
Idle is now at 875-900 rpm (in Switzerland, it must be between 825 and 875) but to do that I had to completely close the screw on the BAC valve... is it normal ?

Now, how does the engine work:
idle is stable but there are still some misfires. And when I accelerate, I have power a little bit earlier.
I'll try to explain: before, when I pressed full throttle, the engine was hesitating until it reached about 3000 RPM and then turbo began charging.
Now the turbo charges a little bit as soon as I press full throttle, and when the engine reach 2700 rpm, turbo starts full charging. I made a little video. http://youtu.be/CoT9AS4uBSQ

I noticed that the turbo pressure indicator is variable for the same boost... Sometimes it goes almost to 400mmhg, sometimes 100mmhg but most times to about 200mmhg. There must be a problem somewhere...

thanks for your help

 

It looks like your twin scroll system isn't working, you should go into boost much earlier than that.

 

Twin scroll? On a FC?

 

Twin scroll not sequential. There is a flap in the exhaust manifold that is actuated by the ECU to open at 2700 rpm's. Below 2700 rpm's it covers one of the ports on the turbo causing it to build boost faster at low rpm's

 

Oh, I see what you're talking about. I was confusing that with the sequencial turbo of the FD.

 

Also if you have had the intake apart, check for vacuum leaks. Use a spray bottle with some water and squirt it around the gasket areas, also all the vacuum lines. One last thing is check all your electrical connections.

 

I thought the same thing yesterday while reading the manual. :-)
I will check this next weekend. The only problem to check for vacuum leaks is the place around the engine... Is there one particular line I should inspect first?

 

idle sensors?

 

I think i have a bad boost sensor. It is not reading vacuum other than 20mm/hg

 

It has been a long time but I'm back on my problem^^

My idle is now good (850rpm) but I still don't have any power under about 3000rpm. We thought it could be the twin-scroll, but I checked the system and it seems to work. I did the controls written in the manual "04b_fuel_and_emission_control_systems_turbo". The valve moves but when I test the solenoid, I have the opposite voltage of the manuel. Under 2700rpm I have 13V and above 2700rpm I have 0V... Is it a problem ? My valve still moves...

Any other ideas ??

thanks for helping

 

If the valve is moving your system is working... Could be clogged primary injectors, Your secondary injectors kick in at 3500 rpm and may be giving the engine the fuel it needs. I pulled mine after running fuel injector cleaner to find rust the cleaner pulled out of the tank had clogged all four. Running lean will cause your exhaust gas temps to get super hot and explin the glowing exhaust.

 

Thanks for the answer. Well, I finally found what was the problem I think. My fuel dampener was dead and I replaced it. I also changed the admission gasket that was in bad conditions. Now I have my power back at low RPM. Power's not much impressive but I think now it's normal (I don't remember how strong it was before the air leak.) I installed a boost gauge and boost pressure grows up linearly to 5psi. So I think everything's normal again