Running really rich

[Dan Babb]

Not sure what's going on, but my car started running rich today. Here's the story:

Motor is 5.0 with a decent (but not radical) cam and mass-flo efi

Filled it up this morning on the way to the Charlotte Autofair. On the way home, I was surprised that I was down to 1/8 of a tank (I only got about 100 miles on the tank of gas).

I filled it up on the way home and used up about 1/2 tank to get home (around 50 miles). The car smelled rich too. When I filled it up, I looked around the intake for signs of gas leak and found nothing.

The oil has a gas smell to it. I sniffed in the oil filler tube and wiped the dipstick on a paper towel and both have a gas smell.

Also noticed today that while riding on the highway, the water temps stayed at 180, but the oil temps never got about 160 (usually, the oil temps get up to water temps after a short while). Would gas dumping into the oil have the effect of keeping it cool?

Oil pressure stayed in the normal range. I would think that gas fouled oil would cause my engine temps to rise and oil pressure to drop...am I wrong?

Also noticed that car isn't very smooth at low RPMs...sounds like it's missing.

This is all new stuff and no changes were made lately.

Car ran fine last time I took it out...so not sure what's going on.


What do I need to start checking to figure this out?

I know I have to get the oil changed...but how do I start diagnosing the problem without messing up another batch of oil?

[Lex]

Don't worry about messing up a batch of oil. It's still cheaper than an engine. Ask me how I know. I can't diagnose your rich problem because I've never fooled around with mass-flo but I can tell you that it doesn't take much gas at all in the oil to wash down the bearings.

[ROADRACER83]

Dan:

One of your O2 sensors plugged up or defective? I'm not sure what the default fail mode is for a MassFlo but if it can't read the O2 the computer may go rich rather than lean. Better to be rich and foul the plugs than go lean and melt a piston.

Ron

[Bob Taylor]

Dan , if the car is not coming up to temp it will use more fuel maybe not to your extent. 1st since you offered that up verify you have a 195 thermostat , then verify the coolant temp sensor is hooked up and working. Rough running = low vacuum so computer adds more fuel. Also vacuum leaks will cause this . and ....is the distributor hold down tight?? Hope this helps.. Bob

[Dan Babb]

The thermostat in the engine is 180 and the coolant stays right there.

It's the oil temp that seems to be staying cooler all of a sudden. I'm thinking that fuel is washing into the oil pan and addition of cool fuel is keeping the oil temp down. I'll check the oil again today to see if the oil level is much higher than it was before I left for yesterday's trip.

The distributor is tight. I actually checked the car out on Saturday night before I left and checked it to make sure...it didn't twist.


Plan for now is:

Check & change oil
Confirm fuel pressure...when I cycle the key - but don't start the engine - it reads right around 40psi.
Pull & check plugs...see if any are fouled.
Check timing and vacuum readings
Use my stethoscope to see if all injectors are firing - make sure one isn't stuck open.
Check O2 sensors to see if they are fouled.


Hope I find something...if I don't, I really don't know what to do next.

[MJN]

Dan the sensor that the water temp gauge uses is not the same one that the computer is monitoring. If the sensor is bad and the computer thinks that the engine is still cold then it will run very rich. Get the engine up to temperature and check the sensor resistance. You can find the correct readings here. Fuel Injection Technical Library » Engine Coolant Temperature Sensor (ECT) Also check the sensor plug contacts for corrosion.

[canuck1]

If you get no joy with any of the simple checks listed above, it may be time to check the mass air sensor.

Are you using the older style 'little black box' (F to V converter) between the actual MAF sensor and harness?

It's probably not common but my old black box was wonky at temperature and would provide loopy air flow info to the computer causing it to run (at times) undrivably rich. I discovered it by having tech monitor MAF signal with scope when engine was hot. Hope it's simpler than that!?

If you have the newer style, integrated F to V converter, look elsewhere as it doesn't have the same heat soak issues.

Sean



Sent from my Autoguide iPhone app

[fastco]

I would check to see if the vacuum hose is still attached to the fuel pressure regulator. Also make sure it isn't split or kinked.

[Dan Babb]

I will test the ecm temp sensor...good info on that site.
I have the newer style meter.
Vac hose to fpr is connected..will make sure its not leaking.

Keep the tips coming.

[Wayne Presley]

Ditch the MassFlow Look at the MAF thin wires very closely and see if any are broken.

[Dan Babb]

Update:

MAF meter wires are good...nothing broken.
Pulled a couple plugs on the passenger side and they were pretty sooty.
Pulled both O2 sensors and they have a fuzzy black coating on it.

Questions:

Can the 02 sensors be cleaned or do I need new ones?
What should the fuel pressure reading be with a Mass-Flo efi setup?

[Larrys109]

Did you pull the codes from the computer? I had alot of trouble with mine, the only way for me to get it to run right was to install a Anderson PMS and a wide band o2 sensor. It was kinda expensive but I spent alot of time chasing my a$$

[Bill Hughes]

Could it be that you filled your tank with something that the computer did not recognize as gasoline?

Could you have gotten an incredably bad tank of gas?

I was always under the impression that the system leaned until it sees o2! Is there a fuel charastic that will demand rich?

The Mass flo systtem is basicially a FORD A9L with a chevrolet air meter.

Check all the plugs, on both sides.

[trevor]

I thought the ford computer required a 195 T stat. The computer will run rich if the motor isnt up to temp. With a 180 T stat it will never be up to temp. 180 T stats are for carbed motors

[Dan Babb]

I will research the thermostat...thanks for the heads up.

With luck, I might have found the root cause. I checked the fuel pressure today and with the vac line pulled, it was reading close to 48lbs. I remember setting it when I got the system installed and it was at 40.

My theory...If the fuel pressure was about 20% too high, I'm thinking that could cause it to run a bit rich. Over time, that could have fouled up the O2 sensors and then caused it to really run rich enough to mess things up worse.

Does that sound possible?

[Wayne Presley]

fuel pressure with vacuum line disconnected should be 39 psi

[Bill Hughes]

I had a problem where my car stalled while hot and after restart, ran super lean.

The next morning I had great difficulty starting and the car ran badly

I disconnected pin one of the ecu for one minute, and reconnected.

All was solved.

If no seperate line, disconnect the battery!

[hind sight]

Think Trevor has it.
Stat needs to be 195* so engine temp comes up high enough to let computer come out of closed loop.
Otherwise computer thinks engine is still cold so makes it run rich similar to a choke on a carb'ed engine would.

[Wayne Presley]

I do not think the thermostat is the problem.