2.3 runs rich when cold

[fivestring]

96 5sp, recently replaced IAC, maf,full tune up,all filters,rebuilt Injectors, IAT sensor, downstream o2. No codes.

Runs rich for first 10 minutes or so. Sometimes stalls out when going to idle. Def rich con dition. After warm, runs great.

Why?

 

[rrbrian222]

Is this the same truck where you fixed the low power under 3000 rpm/poor fuel economy? If so, didn't you delete the cat and upstream O2 sensor?

 

[fivestring]

Yes, same truck. I did remove the cat but I am still running both 02 sensors.

This problem seems to have developed over the past few weeks.

 

[rrbrian222]

Does your Torque app monitor "pending" codes? The OBDwiz program on my laptop scanner does so I'm guessing yours might too.

(demo screenshot from their website)

 

[fivestring]

I think it does. I don't have any codes showing at all.

On cold start, truck will idle normally until I rev up to 3000rpm or so, either by driving or just in neutral revving the engine.

Then as it returns to idle it loads up with extra fuel to the point of almost stalling, sometimes it will shut off. I don't know if it's all cylinders or just one flooding, but I can smell the richness from the exhaust. It will run/drive ok at higher rpms (2000+) but will run wet at lower rpms for the first 10 minutes or so. Then it will be fine until it cools completely.
I put a new IAC on it-no change. Replaced MAF-same scenario.
The only thing I can guess would be a leaking injector that works fine once warm. I removed and cleaned injectors with new seals and filters a couple weeks before the problem arose.

What else could cause a very rich condition on cold start, not throw any codes and disappear after warmup?

 

[rrbrian222]

Maybe your engine coolant temperature (ECT) sensor is starting to go. If you replaced it last time(when you were diagnosing low power/poor mpg), you might want to try putting the old one back in. If the PCM is getting incorrect engine temp data I'd imagine that would effect fuel mixture. I know you can back probe them for voltage too.

 

[fivestring]

I just replaced the ECT sensor while you were posting!

Reset computer, and started it up. Now I know it will take a few miles for the ecm to relearn setting but initial results are exactly the same as before, flooding on quick deceleration. A slow decel seems to help it burn the extra fuel before getting to idle. Also, opening a vac line while it is sputtering at idle will slightly speed up rpm and smooth out so it definitely is too much fuel in there.

Arrgh!!

 

[fivestring]

After a few days, the results are:

The new ect sensor is reporting a different temp according to the OBD realtime scan. The new temp is about 20° cooler than before.

But the rich condition continues. While cold, it will idle great. From idle to 2500 rpms it does fine, decels to idle (700-800) and sounds good. If I rev to 3000 rpms and let it go back to idle, it will pop or sputter on the decel (indicating a rich condition) and when it gets to idle it is rough and will sometimes die. If I then hold the rpms around 2000 for about 10 seconds, it will clear out the extra fuel and once again go to a smooth idle. It is only running it at or above the 3000 rpm zone that causes this rich condition when returning to low rpms, like when shifting between gears. If I drive away and shift below 2500 rpms, it is fine. After about 10 minutes, all symptoms disappear.

What is causing this? It might not seem like a big deal but something isn't right here. And fuel economy never goes above 21.5 mpg so that makes me wonder if this problem is associated with less-than-optimum fuel mileage.

 

[rrbrian222]

You're like me in that if something is wrong, you want to fix it, even if you can drive the truck without issue "most" the time. It would be driving me crazy too.

My OBD scanner reports my truck runs around 185 degrees under normal operating conditions (although that was a month or so ago when the outside air temp was 20 degrees warmer here in WI...

Can you try and make the truck throw a code by running it in the "crap zone" for as long as possible before symptoms disappear, while monitoring OBD for pending codes? You really need some solid lead from the PCM as to what is going on...maybe even look at the freeze-frame PID values when it floods out with gas.

I found a .pdf on Ford Heated Oxygen Sensors and drivablilty issues that you should read through. Something is weird on your truck but it's not bad enough to set a CEL. On thing it says (towards the end of the document) is that if you have a exhaust leak where atmospheric air could get in the exhaust before the O2 sensors it would trick the sensor in a false lean condition. Same goes if you have a misfire, the unburned gas and oxygen in the exhaust will generate a false lean condition resulting in rich fuel trim. But then again, you don't have a cat so that's another variable.

Not that these are necessarily your issues, but it gets your brain thinking outside the box for possible things to look at.

Here's the link:

http://fordfuelinjection.com/files/HEGO_OBDII.pdf

 

[06RangerXLT]

put your can back in, and run it. you should have a downstream after the cat. that will throw everything off. the sensors are fine, and they are doing the job.

 

[rrbrian222]

He has both O2 sensors(upstream and downstream), but no cat. His truck ran fine for awhile (several months, I assume) without a cat, but I don't disagree with installing a new cat again just to remove that variable.

I was looking on amazon, the Walker Direct-Fit cat is like $185 shipped.

http://www.amazon.com/Walker-Exhaust-15828-Domestic-Converter/dp/B000C935II

 

[fivestring]

The problem exists in both open and closed loop. So the o2 sensors aren't always in the mix. Am I correct on this?

It will load up every time I rev to 3000 or more then decelerate to idle until the engine warms up to the point of the temp gauge being half way to normal. And the condition is very constant,, i.e. it will do the exact same thing every time.

 

[fivestring]

I appreciate the thoughts guys. I need some brain storming here. Excuse me while I think out loud...

I'm going to try shutting the engine down after it loads with gas and pulling plugs to see how many and which ones are wet. If not all are drenched with gas I guess I'm going to remove the fuel rail and pressurize the system to check for leaking injectors. Maybe when i rev up on cold injectors, the rise in fuel pressure from dropping the vacuum off the fuel regulator is causing an injector to leak. (note to self - first test the fuel pressures while the engine is running and see if it acts up at a certain rise in pressure).

The extra fuel dump seems to be very short duration just after the pedal is released from 3000+ rpms as the engine will recover in 2-3 seconds if held to 2000-2500 rpms. Even at idle it will clear up after 10-15 seconds.

It is a really odd problem as I have driven around the parking lot at work (cold engine) at 2500-2700 rpms in first gear, then push the clutch in and let it go back to idle and it is a perfect, clean idle. Then I take off again and take it to 3000+ rpms and return to idle and it is sputtering and shaking. Weird.

 

[rrbrian222]

Any progress fivestring?

 

[fivestring]

Not lately. I haven't had time to work on it. It runs great as long as you stay under 3000 rpms till warmed up. Also the odometer/trip stopped working so I can't check gas mileage again until I rip the dash apart.

I'll post updates when I get anything done on it.