Hey guys I'll try to make this as easy to read as possible. I have a gen 3 6.0 with a cam in it, I tuned it myself and it's been running great for a few months, yesterday I started it up, went to get gas and when I started it up again, it felt like there was a strong misfire, shakes the whole 6,000 lb truck at idle. I drove into town and back hoping to get some codes, and I got two, random misfire and the maf performance/range code. I cleared them and went back to my speed density tune, and my fuel trims were all crazy, and I had them dialed in to where I was comfortable last time I had this tune in, it also idles at 40-45 Kpa, and I always thought it was around 30-35, and it's hitting 105 kpa at around 35-45% throttle. I have five potential culprits, I'm hoping you guys can help me decide where to start. I'm thinking map sensor, an injector, a coil, my fuel pump, or possibly my maf, but now that I'm in speed density, I can probably rule that out. I don't have my wideband right now, since I burned the sensor out, so I can't actually see what my AFRs are at the moment

 

How about a vacuum leak??

Rick

 

Well I guess that's a logical first place to start, I always seem to jump over the little things. Now that you mention it though, it could definitely be a vacuum leak, the symptoms seem to line up pretty well. I guess I was just hoping it was something else since it's an express van and I really don't relish the thought of pulling the doghouse to search for a vacuum leak 😂 there's not a whole lot of room to navigate down there

 

Seems like it should be a decent leak though, so hopefully easy to find. My fuel trims were 7-15 points too lean almost across the board

 

Bad fuel pump?

 

I'm thinking it could be, I was hoping that fuel pressure was available to the scanner so I could log it, but I couldn't find it. And the auto parts stores are already closed so I can't get an actual fuel pressure gauge until tomorrow

 

60 psi fuel pressure at idle, 55 key on not running. Seems pretty normal to me 🤷 I guess next step is check for vacuum leaks

 

58-60 is actually normal.

 

Running or with the key on? Could a bent valve cause these symptoms? I haven't been able to find a vacuum leak yet. But I am starting to get my fuel trims back into a good range and they're staying stable. I need to get a wideband sensor still, but the engine picked up some kind of new noise in the past few months. I thought it was a bent pushrod at first, but I'm only really able to check one bank in the vehicle without practically pulling the engine

 

That was kind of a dumb question, wasn't it? I'm not boosted, and my ptv clearance was fine. I don't think my timing jumped a tooth, so there's no way I could've bent a valve

 

Is evap system still hooked up?
just had an 02 k2500 6.0l in the shop with random missing and bizarre fuel trims, turns out when he filled the fuel tank he overfilled it right to the cap and purge valve was sucking in raw fuel through the canister

 

So is the problem random(intermittent) or constant? If problem occurred after fueling and evap is hooked up, I agree with Creekin. It could have issues with evap system and sucking raw fuel through purge valve. Disconnect to check. The MAF error is interesting. Depending on PCM, disconnecting MAF will allow things to run from default table. Changing tunes throws a major variable in there, unless your confident that nothing was changed since the last time the tune was run.

 

Evap system is still hooked up, I'll disconnect to test it next chance I get. It's not an intermittent problem, its pretty constant at low speeds, seems to drive okay once I get going, but it surges a little bit every now and then. I haven't changed anything since the tune was last run, I only put it in to double check my maf since my pcm won't even run with the maf disconnected on a non Speed Density tune. I took it out of the driveway for the first time in a few days to get a log (it was short, but I have some new info). It takes off like garbage, but once I hit about 10 MPH, the rpms shoot up and it takes off like a rocket. The log showed me that its at -10 or so degrees of timing when I take off, which explains the poor performance, now I just need to figure out whats pulling 30 degrees of timing I'll upload my tune and log incase anyone wants to take a look at it and give me some pointers. IATs were pretty high, but i don't think they were high enough to pull 30 degrees, I'll have to check the chart.

 

Would it be bad practice or potentially harmful to the engine to just raise the high MAP low RPM portion of the spark table up to 18-20? I'm pretty sure I'm losing most of my timing with the odd MAP reading. I checked the table, and that area commands -2 to -4 degrees as it is, that with the IAT tables seems to account for all of the lost timing