I am currently running rich, and I tackled my CELs first. It was running rich and was getting p420. Using an infrared thermometer, and it was 100 degrees hotter going in to the Catalytic converter, than going out. This proved the catalytic converter was not working as it should. I replaced cat this week. Upon removal, the cat was internally destroyed, even the O2 sensor was broken. I actually replaced both 02 sensors at this time. There was a noticeable performance improvement, which I originally thought was a slipping transmission on my 219,000 mile 1997 Honda Accord LX(automatic, stock). Now seems to shift better. I checked for exhaust leaks after replacing the Cat, it looks great.

Seems better, but theres still a problem. It's still running rich. Not as rich as it was before the new Cat was installed, but it's still rich. The CEL is gone now, and exhaust rattles now, but not the reason why it's running rich...

After warming up, the car likes to sit at about 800-850 RPMS. Normally, I believe the car should be at 650-700RPMS. I'd love to know where to look next, or what could be causing a rich condition.


I would love to know what needs to be looked at there. There isn't a whole lot on Hondas running rich. I will say, the car seems to idle fine. No surging or rough idle.

I've checked all the basics. Air filter and spark plugs are new. Wires aren't too old, (i think, may have been replaced at 100K) but are factory wires, do not appear to have any issues. I swapped a new set of wires on, just to confirm and the issue hasn't changed. The fuel filter is old, I will be replacing that soon. New cap and rotor will be ordered soon too. Coolant has been bleed and filled to spec, to ensure there is no air in the coolant.

What do you guys think? What am I missing? Where should I look next? I'm not interested in throwing parts at it without a good logical reason.

 

Have you reset the PCM since replacing the O2s and catalyst?
This will reset the Long term fuel trims in the PCM and it will better adjust to the new sensors.
Are the sensors quality units such as Denso? Or did you use Beer can Bosch units? If using the Bosch style sensors they tend to be lazy and slow to react. If you have the upper style of O2S(BOSCH), replace them with the lower style O2S(Denso).

 

Mad Mike,

I unplugged the battery while swapping the Cat. Shouldn't that have reset the PCM?
I ordered Denso oxygen sensors, NGK spark plugs, and Gates belts. I literally try to keep the car as stock as possible. Both 02 sensors are Denso.

 

Have you checked to make sure your car is going into closed loop mode? A good obd2 will show what mode your in? Also, i would test your engine coolant temp sensor(The one that the pcm uses, not the one the fans or gause uses).

 

Seems like you're fairly knowledgeable to begin with, have to say thats refreshing on here. So the cat and 02 being destroyed would most likely be caused by excess fuel and heat. So those were the aftermath of the problem. How is your fuel pressure?

 

As long as you don't know what actual fuel trims are, you don't know are you really running rich or not. There is no CEL, O2 sensors are new, so I quess fuel trims are at acceptable level. You don't have driveability issues also. What about fuel consumption?

 

Check this. If the fuel pressure is excessive then the car will run rich. Being a SD system if the MAP or IAC are out of spec this will affect the A/F ratio. Verify there is no false air leaks before the O2.

 

Modern vehicle with plenty of data available, connect a scan tool and view the PIDs....(and that "Cat test" 100 degree difference, isn't reliable and is completely useless if not done under a load.....)

 

^This and add checking the fuel pressure regulator diaphragm to the list.

 

hey mike does the stock FPR fail in any particular way? Such as stuck open or closed etc?

 

Also if the thermos sensor for the computer is reading wrong it may cause the engine to run richer than normal as well.
It's a spring loaded, vacuum controlled(via a diaphragm) valve. It has multiple ways of failing. From the valve itself being stuck open or closed, diaphragm spring failing or weakening, diaphragm rupturing, foreign material clogging the valve, to outside physical damage to the FPR.

 

well ****. haha. Second question if you dont mind so I can eliminate some ideas with this im thinking through, if you check fuel pressure via the service port next to where the fuel comes in im assuming the fuel goes into the rail through a center section and then through the fpr and back into the lower portion where the fuel injectors are? Never taken one apart so Im curious how the design works thanks buddy

 

On USDM 94-97 F22 PGM-FI Accords there are three fuel lines. Open the hood and look behind the engine, under the master cylinder for the fuel filter.
There will be three lines, Fuel filtered line is the feed line(right most) from the pump/tank. Middle line is the return line of fuel to the tank, and the far left line is the vent line which reaches across the firewall bulkhead and over to the charcoal canister.

Pressurized fuel is pumped from the right most line. Goes through the filter, then the banjo bolt hose attached to the fuel rail.
Fuel rail has the service port first, then the four ports that the injectors sit in, and bolted to the end is the FPR itself. Excessive fuel is then relieved through the FPR(depending on demand) and that fuel returns to the fuel tank via the return line bolted to the fuel rail which has another hose that attaches to the middle return line car on the car.

Fuel Line > Filter > Banjo hose > Fuel Rail> Injectors 1-4(installed in rail) > FPR(bolted to rail) > short rubber line > hard line bolted to fuel rail> another rubber hose line > middle hard line on firewall.

If the return line is blocked/crimped it will cause higher than desired pressure in the fuel rail as well.

 

gotcha that makes sense now. Also if you're using a higher flow pump it can over ride the fpr unless modified right? Interesting system!

 

A higher flowing(volume) pump may or may not cause issues, as long as it is capable of maintaining the desired pressure. FPR will not know or care about volume, it is a pressure controlled/controlling device.