How to Tell If Mixture is Rich?
 

I just had a new muffler and cat fitted. The service manager said that my car was running rich, and needed to be looked at, since a rich fuel mixture could end up burning up my new exhaust. He couldn't diagnose the cause at his shop, and I haven't found a rotary specialist in my area. How do I confirm that the mixture is too rich? Is this a concern? What can I do about it? I have a high mileage vehicle and don't drive it daily.

Rotaries always run "rich" with the stock ECU. Your profile says '84 GSL-SE, so that's what I'm going off of. You're not going to burn up your exhaust. That doesn't say much about the service manager's car knowledge. The only thing to consider is making sure the air pump is working properly, so the cat gets the oxygen it needs. A non-functional air pump and emissions system will reduce the life of the cat.

These cars generally run on the richer side of things, but not super rich. Why does he say it is running rich? Does he have air fuel readings? Or is he just smelling it with his nose?

However he was right if it is too rich the excess fuel will cause your new cat to get extremely hot and melt in the long run.

my 90 gxl is very rich too. i have a a/f digtal guage that just has the semi ring of led light and it says fuly rich at idle, my ek. manifold glows red after warming for 15 mins.

Is it possible to install a a/f wideband gauge on a stoc ECU? <---- 91' TII, racing beat Rev II exhaust system front to back.

While a narrowband isn't the type of gauge you'd use for this, it sounds like there is an issue. Reading full rich at idle (does it read properly everywhere else?) indicates there is a problem with the secondary air system.

Or some idiot has cranked the idle mixture adjust screw.

The ECU has nothing to do with it. Weld a bung onto the downpipe and install the wideband as per the instructions that come with it.

yeah it should read lean at idle.

maybe i have heard different termonology but i have never heard or found anything tht could be a mixture screw? where should it be on a s5 N/A?

There is no variable resistor ("mixture screw") on S5s. Only S4s (and S3 GSL-SEs in this case) were special enough to be blessed with an adjustable idle mixture.

lol.. or maybe we just needed the extra help so Mazda said "let's give these guys a dummy-proof method."

... wait a sec ... "special" enough .. I get it now :lol:

Change your profile to indicate your accurate location so we can refer you to someone who can answer your question.

changed location:bigthumb:

I called the service manager back about the rich mixture he noticed when doing the exhaust work. He didn't take readings, but he said there was evidence that the car was running very rich, ie.: very strong exhaust fumes and black soot. He also said he didn't have the proper tools to assist further, including a pre-1996 scan tool and a five gas exhaust analyzer.

My profile has been updated. I'm in New Bern, North Carolina, which is in the eastern part of the state, and also near the coast. Virginia and South Carolina are less than three hours north and south.

Yes, I've had idle problems in the distant past (low speed and stall, and surging), so it is possible that the technician adjusted the mixture to correct the idle.

The Haynes manual doesn't advise that the home mechanic adjust the idle mixture, although it does give the procedure for adjusting the idle speed. Perhaps I should get the wideband analyzer and tackle it anyway. I didn't get much mileage out of my last exhaust.

hi there i have no help as far as why but i read somone had information on how to lean out a s4 engine?! that would be great help as my car runs very richly almost max on guage. does not lean out when driving only gets richer

Are you using a wideband AFR set-up or are you using a narrowband guage with your stock sensor?
Do a decent search for AFR wideband information and you'll find that narrowband sensors aren't accurate enough to display the AFR properly.
Your description sounds as though that's the problem, as described by ALOT of other members.

i am using a afr guage with my stock o2 sensor. would i ahve to replace this o2 sensor with a brand new stock sensor or a aftermarket sensor. what would you recommend. andhow does a wideband hook up . is it hard or expensive and what does it take to do it?

Unfortunately, the stock O2 sensor is of limited use in these cases. It has a very narrow range of accuracy, only around 14.7:1.

Start by testing all your sensors. The ECT could be reading wrong, causing the ECU to stay in warmup enrichment.

lol canonize, what aaron cake means to say is that you will need an aftermarket wideband o2 sensor, and a wideband guage (if the one you have is not already) because the stock sensor is only meant to read whether or not your car is rich or lean, not to tell you what the AFR mixture actually is. You can get a kit with both the guage and sensor but they are quite expensive. so, BEFORE doing this, check your engine coolant temp. sensor (consult factory service manual) for proper operation, according to aaron.

BUT, so that I dont hijack this thread any more, here is a link to a good wideband writeup that someone sent me before. http://www.diyautotune.com/downloads...20Shootout.pdf
and here's the link I use for the FSM http://www.rx7city.com/techconnect.htm

After reading into those, post a new thread into the new member tech section if you still have questions, to avoid taking over someone elses thread.

where and what is a ECT?

engine coolant temperature (ECT) sensor.. loacated near the bottom of the rad I'm pretty sure

The water temp sensor (called ECT above) is located on the back of the water pump housing. The temperature switch at the bottom of the radiator is emissions/cold start related. The ECU doesn't use this one for fuel calculations.

woops:) thanks RR

These guys are in NC but far from you:
http://www.rotorsportsracing.com/

You can also get familiar with the regional sections near you to find rx7 specific shops:
https://www.rx7club.com/ne-rx-7-forum-30/
https://www.rx7club.com/se-rx-7-forum-35/

If you are taking the car to a dealer, they probably haven't seen an rx7 in decades and have probably lost any knowledge they had.

Troubleshooting idle issues can be a bit tricky and time consuming. While adjusting the mixture screw can get it idling more normally there will be other unwanted effects from doing so w/o addressing the underlying problem. I'm sure you know this last bit already.