I have had a problem with my engine, and I haven't been able to put my finger on and I'm stumped. I'm hoping the minds on here will be able to put out heads together.

I'm a 3 year mechanic and master in Dodge engines (have lots of experience on the 5.2/5.9) and I am having a weird Air/Fuel Mixture problem.

The problem happens when the engine is warmed up and not particular to when I'm driving. It has gotten worse lately and I've become stumped on what it may be.

What it has been doing is, I'll be at a stop light and it will have a rough idle then my RPMs will go from 400 to the normal 600 and fluctuate from there. It will do this but when I hit FOT it is fine and doesn't do anything. Once I let off the throttle it will go back down to the idle stumble.

When I am on the interstate sometimes I can hear backfire and I will lose power to the engine and then I hit the throttle and re-gain throttle control.

I am stumped because I have replaced both O2 sensors with factory sensors, replaced the CPS, the battery is less than a year old and checked out OK, and checked over the sensor wiring and it looks alright. Oh and I also have replaced the TPS and it's sending he correct signal. Ive also cleaned out my throttle body, and even replaced the IAC. I also just replaced the plugs and wires with MSD 8.5 and Champion Copper core .040.

According to the engine code index, it states that both upstream and downstream sensors are sending too high of a voltage signal. I am stumped as where to look next.

Anyone seen this happen or have a fix for this because I hate to keep driving in it with a possible bad problem. I had the CAT checked for too much back pressure and it read fine and not too much pressure.

I believe its a problem with my wiring or hopefully not my PCM because it's sending too much fuel and causing it to run rich. I believe this is what is causing the backfire and just after the CAT when it's heated up it glows red.

Someone please help as I think I've tried it all but I can't give up.

I have read possible P/S pressure switch but don't know exactly where to look and any direction to point me to would help.


Video of idle stumble:
http://www.youtube.com/watch?v=clKZMnZF0TQ

 

the ps switch likes to leak into the wires and cause shorts, this can cause all sorts of problems w/ the a/f mixture, if you see the switch, feel it to see if it is wet w/ fluid, if so replace the switch and clean out the wire harness

 

Whats your fuel pressure?

 

Getting around 50 psi.

 

That sounds about normal being 50-54 psi (at least that's where I like to see it).

What about indexing the distributor?


Also, Sharps brought up the Power Steering fluid leaks. When this happens it gets into the harness and messes it up.

 

I haven't done a distributor index yet so I'm going to start there and do a visual inspection of the wiring near the P/S switch.

 

The high exhaust temps and the popping would make me think lean not rich. Do you have anyway to datalog what is happening realtime data is far better to diagnose with than stored codes. There is a possibility fo an open circuit causing the O2 voltage readings themselves and the rest being a byproduct from the false info to the PCM. i would pull a couple of plugs and read them to check and see what the mixture really is. I have never really heard of one cutting and out and popping from a rich condition but lean definately will.

 

I have seen the backfiring popping noise many times because of a rich mixture. The reason for this is that there is unburied fuel in the mixture going to the exhaust and the "popping" noise is the unburied fuel combusting.

A popping noise due to a lean mixture is backfire typically found in the intake manifold. It is definitely backfire in the bottom headers and partially in the exhaust.

Also, yes I did hook it up to my real time analyzer and shows the air/fuel ratio is 11.3:1 when it was stumbling, stating its running rich at idle, as the proper fuel ratio at an idle is 14.6:1 IIRC.

Not to sound arrogant but I said I've been a mechanic for a little over 3 years now, I did do these tests prior to trying and diagnose it so I did know it was running way rich prior to posting.

 

While not a paid mechanic I have been working on cars for 17 years both my own and my friends as well as motorcycles. I would pull the plugs and read them. Are the O2's switching like they should or are they just staying on one voltage value. I know the computer systems are light years apart but my 85 TPI TA died an early death because despite what my datalogs said the car was lean although horribly but lean enough over time it split the piston in two and wedged the rod at the bottom of the cylinder taking out the crank. The plugs where all white tipped when I took them out. Had I pulled the plugs sooner I might have caught it in time.

One thing I have learned is somtimes old fashioned ways can help as much as any computer or scan tool. If you are getting a popping from rich it is from the cat lighting things off in the exhaust.

 

Yeah it's definitely being rich and I pulled the plugs to replace them and they looked about normal wear, not white from running lean. Also it is killing my gas mileage from running off like this, that's why I'm trying to find the cause of this problem and fox it ASAP.

BTW, totally agree with old school techniques. We use them on a daily basis and rely on them vs the computer and diagnostic tools.