Syscrush

I've got a ported NA S4 motor that has always seemed to run too rich since the porting/rebuild. It's a bit prone to flooding on warm starts, but not exceptionally bad compared to other rotaries I know of.

For a while, I was concerned that the warm-start flooding was a symptom of internal damage, but the compression checked out fine.

I usually change the plugs twice a year - last time I changed them, though, they were way overdue, and the car had actually flooded so badly that I couldn't get it running again until I changed the plugs. They were pretty badly fouled, with lots of deposits. I didn't think anything of it because I had been running on them too long.

But yesterday it flooded pretty badly and wouldn't deflood with the usual pulling of the fuel pump fuse, so I pulled the plugs to clean them. I was amazed at how much crud there was on them given that they'd only been in there for about 3000 kms.

This week, I've also been measuring my mileage. The motor is in an '84 GSL, and I've been steady-state highway driving almost exclusively, at 100-120 kph. My mileage has been 18-19 miles per (US) gallon. I've always known it was bad, but hadn't really measured it consistently... 18-19 mpg for steady-state running at such moderate speeds seems excessive.

So, my questions are:

1) Is this normal behavior, or do I have some problems to solve?

2) I'm suspiscious of both the EGI system delivering too much fuel, and the ignition system providing insufficient spark. Which is more likely, given the symptoms? Fuel, spark, or both?

3) Any thoughts on where to start trouble-shooting? I'm thinking O2 sensor, but other than that, I'm not sure about specific stuff to look at, or how.


I was thinking that maybe I'm running too cold a thermostat, and that the car continues to run rich in a vain attempt to get it up to temperature... But a search here showed that most S4 motors are running in the bottom 1/4 of the temp range on the gauge, which is where I'm at currently.


Thanks for any insight or info,

Rotorific

iTrader: (1)

you could check for spark from both coils....i would check out the injectors for cracks in the covers or o rings.

Bambam7

I'm asuming it's fuel injected and controlled by an S4 ECU?
You're o2 sensor is probably gone. Highway mileage is usually really good because of the closed loop feedback setup, but when it doesn't work, it sucks.
Get a new one from NAPA or Canadian tire, they are about 30 bucks.

Your engine could be flooding because you have semi-stuck seals from all the carbon buildup. Not good either, it can lead to carbon lock.

Replace the o2 sensor, check the vacuum hose to pressure sensor (if it's off, broken, or plugged you won't go into closed loop) and take the plugs out and fill the engine up with ATF through the plug holes (make sure to get each of the 3 chambers) , let it sit overnight, put yer old plugs back in because it will foul. Start it up, run untill the smoke clears, and replace the plugs.

Definatly do what you can with the injectors. Even running a few bottles of good fuel injector cleaner can help.

Syscrush

Thanks very much gentlemen. I'll follow up with details of my findings and results in the hopes that they're of interest to some other poor shmoe on here.

Thanks,