5.0L Running Rich

[Scott B.]

As the title says, my 5.0L is running rich. You can smell it in the exhaust, and the mileage is not great. It starts and runs fine. Currently has 18K miles on it.

In my '93 Ranger, I have a '91 Mustang A9P ECU and no EGR. The EGR is bypassed with resistors to stop the computer from throwing codes. I am running a Comp Cam with specs similar to the Ford e303, headers, O2 sensors, MagnaFlow hi flow cats and dual exhaust. The timing is set at 10 degrees.

Any thoughts as to why it is rich and how to adjust it?

Thanks.

 

[RonD]

Mechanical issue could be a leaking Fuel Pressure regulator(FPR) on the fuel rail.
It has a vacuum line attached, if FPR diaphragm starts to leak raw fuel is sucked into the intake.
Remove vacuum line and check it for fuel or fuel smell.

Also an injector could be leaking, testing fuel pressure hold time after engine is shut down would help ID this or the FPR.

A simple test for mechanical issue is to warm up engine, then shut off, press gas pedal to the floor and hold it there, turn on key, then crank engine.
It should not start or even fire, if it fires you are getting fuel into the intake from a leak.

EFI computers have a "clear flooded engine" mode
Key on, TPS above 4.5volts(gas pedal to the floor) = Shut off injectors
So when cranking no fuel should be going to the engine
As soon as you release the gas pedal injectors should start up again


Electronically there are 3 main sensors that the computer relies on to set air/fuel, the '91 should be MAF
MAF sensor, tell computer the amount of air coming into the intake
ECT sensor, tells computer if engine is cold or warm, if cold, computer runs engine in Choke mode, so rich mix with advanced timing.
IAT sensor, tells the computer the air temperature, colder air requires richer fuel mix
These 3 sensors can be checked with volt/ohm meter, never replace sensors, they rarely fail, test them.

The O2 sensors are used once engine has warmed up, computer uses these to fine tune the air/fuel as Feedback sensors.
You don't mention the CEL being on so O2 sensor may not be reporting a Rich mix so is faulty, or there is an air leak in the exhaust manifold.
O2 sensor measures oxygen in the exhaust gas, if outside air is getting in then O2 sensor reports high oxygen so computer runs that bank richer, in this case O2 sensor is working fine.
I had an O2 sensor unscrew itself, it was about 1/2 way out when I discovered it, I was running rich as well, because air was being sucked in around the loose O2 sensor.

 

[Scott B.]

Thank you for the suggestions. I will check them this weekend.

All the sensors were new when I put the engine in 18K miles ago. I also used Motorcraft parts. Not saying none could be bad - I have had to replace several "new" parts because they didn't work out of the box.

You are correct - the CEL is not on.

 

[RonD]

That almost makes me think it is a computer issue.
CEL does come on with the key right?
Computer should turn on CEL if it can not lean out mixture enough, so a mechanical issue(leak) should cause the CEL to come on.

Bad O2 sensor could let one bank run rich, but usually a failing O2 sensor will set CEL because it isn't switching fast enough.
Air leak in exhaust, pre-O2, wouldn't set CEL on rich mix on that bank.
Corrosion on an O2 wire connection, has higher resistance so O2 shows a lower voltage overall, which = lean exhaust to computer, so it adds more fuel, no CEL is set because computer is relying on O2 voltage.

I would pull the connector on the Computer just to see if any corrosion is seen


If exhaust is rich then cats should be getting very hot, are they?

 

[Scott B.]

CEL does come on with key - but I will check again just to be sure.

I never checked to see how hot the cats get.

I will also check the O2 wiring and connectors for corrosion or melting or ??? They are tie-wrapped out of the way, but I will check again.

 

[RonD]

If the wires for O2 were bad CEL would come on once engine warmed up, but a little corrosion wouldn't turn on CEL, because connection is still good, just incorrect voltage at computer, long shot but not a no shot, lol.

Computer can also store codes that don't always turn on CEL, short duration out of parameter that was corrected, might be worth a read just to see if memory is clear, also to see if computer is "sane", lol.

 

[bobbywalter]

is there power to the 02 heaters?


where are the o2 sensors?


they need to be the right temp range and with cats i would think your fine, open exaust often lets them run too cool.

 

[Scott B.]

is there power to the 02 heaters?


where are the o2 sensors?


they need to be the right temp range and with cats i would think your fine, open exaust often lets them run too cool.

I assume there is power to the heaters. I will check this also.

The sensors are right after the reducers off the headers.

I am running dual 2 1/2" pipes all the way to the back of truck. The O2 sensors are ones specified for a '93 Mustang 5.0.

 

[bearsrngr]

I would also suggest you add a few degrees of timing to that settup. You will most likely see some gains in performance and milage. Try 14 degrees initial and if it pings back it off a degree or so untill it stops.

 

[Scott B.]

I ran some tests on the engine over the weekend. Here's what I found:

Computer can also store codes that don't always turn on CEL, short duration out of parameter that was corrected, might be worth a read just to see if memory is clear, also to see if computer is "sane", lol.

There is a stored code - 33. Since I have bypassed the EGR, this is expected. My understanding is this does not affect how the engine runs.

Mechanical issue could be a leaking Fuel Pressure regulator(FPR) on the fuel rail.
It has a vacuum line attached, if FPR diaphragm starts to leak raw fuel is sucked into the intake.
Remove vacuum line and check it for fuel or fuel smell.

No fuel smell in the vacuum line.

Also an injector could be leaking, testing fuel pressure hold time after engine is shut down would help ID this or the FPR.

At shut down, the fuel pressure was 38 lbs. 15 minutes later, it was down to 30 lbs. This sounds normal to me. Is it?

A simple test for mechanical issue is to warm up engine, then shut off, press gas pedal to the floor and hold it there, turn on key, then crank engine.
It should not start or even fire, if it fires you are getting fuel into the intake from a leak.

EFI computers have a "clear flooded engine" mode
Key on, TPS above 4.5volts(gas pedal to the floor) = Shut off injectors
So when cranking no fuel should be going to the engine
As soon as you release the gas pedal injectors should start up again

Behaved as described.

Electronically there are 3 main sensors that the computer relies on to set air/fuel, the '91 should be MAF
MAF sensor, tell computer the amount of air coming into the intake
ECT sensor, tells computer if engine is cold or warm, if cold, computer runs engine in Choke mode, so rich mix with advanced timing.
IAT sensor, tells the computer the air temperature, colder air requires richer fuel mix
These 3 sensors can be checked with volt/ohm meter, never replace sensors, they rarely fail, test them.

The O2 sensors are used once engine has warmed up, computer uses these to fine tune the air/fuel as Feedback sensors.
You don't mention the CEL being on so O2 sensor may not be reporting a Rich mix so is faulty, or there is an air leak in the exhaust manifold.
O2 sensor measures oxygen in the exhaust gas, if outside air is getting in then O2 sensor reports high oxygen so computer runs that bank richer, in this case O2 sensor is working fine.
I had an O2 sensor unscrew itself, it was about 1/2 way out when I discovered it, I was running rich as well, because air was being sucked in around the loose O2 sensor.

No loose O2 sensors. Also, the wiring is not burnt or damaged.

I also ran the KOER test. This gave me 3 codes - 94, 44, 33. 33 and 44 I expect (I also do not have the thermactor system installed.) 94 I did not expect - should I see this with an automatic trans?

 

[bobbywalter]

i suggest a moates 1/4 horse and some time on the related forums, or take it to a tuner. actually do both.



theres so much to get these dialed in i could never cover it with my chicken pecking....