Rich condition case study

There are tons of excellant videos on troubleshooting lean conditions.Im having a hard time finding case studys on rich conditions.I have a freind that has a random missfire and his fuel trims are running on the edge of being out of spec.1 garage already charged him and didnt solve anything.He has put a list of parts on his truck on his own and is in a hard spot.Id like to help

IMO, rich condition case studies (and videos) are less common because rich conditions themselves just aren't very common. :silly: It's inherent to the design of fuel injection and direct fuel injection. It's tough to get too much fuel (or too little air) into the engine, but there's tons of ways to run short of fuel (or too much air).

Year/make/model specifics will be needed to get you and your friend help on his car. As always with fuel trim concerns, it's important to ask if the engine is actually getting too much fuel, or does the engine controller just think it's getting too much fuel.

Thank you very much,the truck is a 06 2500 chevy silverado with a 6.0ltr.,I have had limited time with this truck due to our work schedules and distance we live apart.He has a random missfire code,he sez he can feel the miss when it occurs,1 thing to note he hauls a Lincoln 200 welder ,oxy acetlyn bottles and various tools around all the time.Its a welding rig with a regular bed.He has sunk some money into this truck in parts ,He since has replaced plugs ,wires,both cats,crank sensor, and maf sensor,He was going on assumptions from other people and what he read.1 more note he has installed a cold air,intake and aftermarket throttle body also,I cant remember the brands,He took this truck to a garage,he took it there because he wanted the computer flashed,somewhere he read that and wanted to try it,there I guess they did a compression test,checked his coils and wires,they told him that it was probably from carbon build up,he said cylinders ,I'm thinking maybe they said valves ,hes not a mechanic by no means so hes unsure, what they did do is not fix the problem and billed him .He had a few mins one day and stoped by,i myself confirmed the code,truck sounded good at idle,I checked his trims both banks were the same ,they both were -8 on the long term and 0 on the shortpretty steady,which isnt the worst but my thought being intermittent and random maybe they went really bad,I idled it up,and did a few snap throttle test,it didnt get any better or worse really at that time,I couldnt hear any missfires also,I wish I would have grabbed the freeze frame data,I'm still learning my scanner,I looked at missfires on the cylinders ,nothing significant there,he was talking about changing his fuel pump next so I said let's test the pressure,it was around 60lbs,I snapped the throttle and it went up a few lbs and maintained,the next thing I did was a cylinder leak down test,all 8 cylinders were identical,He had to leave then,i know i was all over the place too, i was pressed for time,I'm hoping our schedules will line up to where I get more time with the truck,so that's where I'm at

To be clear, there's no actual fuel trim codes? Just a P0300?

If that's the case, I wouldn't worry about the -8% trims at all. Given the aftermarket parts he has installed, -8% is really pretty good. :lol: I usually don't sweat any values less than 10% +/-. Some professionals open that rule up even more to 13% +/-.

There were no history misfire counts on any cylinder with the P0300 stored? :huh: That's surprising.

There were some history missfires yes but nothing really high on a certain cylinder, I have to add he has a code reader and has been clearing the codes too,from what I understood the trims were in spec but I was wondering what happened if they were under a heavy load ,maybe they went further rich,again I wasnt sure and time was limited,I'll also add I kinda froze up,I understand fuel trims and theory and operation on paper but when it was in front of me I kinda hit a mental block if th hat makes sense

As stated, the fuel trim numbers are nothing to get crazy about....

What are the conditions when your friend is able to "feel" the misfire? Can you read mode 6 data and is it possible to look at secondary ignition?

He claims he could only feel the miss when cruising on the interstate,he sez now he can feel it sometimes at idle,I didnt hear anything when I got to look at it but the code was there.I have a modis ultra scan tool

Cruising makes me think of a possible soaked canister where vapors are being sucks in during purge. Could be a stretch, but it's possible. Sometimes there is a canister weight spec, and if it's too heavy, it could be full of gas.

He notices it during idle too though. The purge wouldbhave to be stuck open AND the canister full of gas then, so maybe it's too far fetched, ha.

Nissan Technician

I guess it's possible it could be sticking intermittently,I told him not to clear his codes anymore,he sez the light drives him nuts ,I told him it's just gonna come back,and I didnt hear it miss even slightly at idle ,but it may every now and then just not when I was there,the truck sounded pretty good in my opinion,fored right up every time