Hey guys,
I’m running into a problem with my latest turbo build on a gen 3 5.3. The car starts up (nearly) perfectly except for a slight misfire that I can’t diagnose as I don’t have HPtuners etc, but it under normal cruising/driving conditions it’s great, and I can very slowly rev it up to 3-4K without issue.
The problem happens if I step on it quickly or even just slightly accelerate too hard (see video attached) and a hard backfiring/hesitation occurs and the car won’t rev any higher.

I recently had the coils/wires relocated and replaced by a reputable shop so those should be fine, I also replaced the plugs (ngk tr6), recently installed a new fuel pump (aem 400, works great) and made sure my fuel filter looks good. Even replaced the fuel pressure regulator (stock truck rail with return and boost reference) and have also installed a fuel pressure sensor on the rail to ensure I’m getting good fuel pressure, which you can see in the video (red gauge). I’ve also cleaned the injectors, and am nearly positive this tune is very close to being correct for the car. Also for reference this has a stock truck cam.

my next thought would be to check all sensors, but at this point I’m pretty stumped and wouldn’t really know what to look for. If anybody can help me out I’d greatly appreciate it!

 

I'd start with what was just touched -> plugs/wires/coils. Pull plugs and maybe one doesn't look like all the rest.

 

I should have mentioned this is the second set of plugs I’ve replaced and all look similar and okay, but even so I wouldn’t think a single plug would cause that backfiring/inability to rev up.

 

Air metering or vac leak. This sounds exactly like how a MAF car behaves when you dont have the maf plugged in.

 

You need some live data to formulate a guess. O2 readings at a minimum. I'd confirm spark from each of the relocated coils as well with a spark tester.

Assume nothing if you expect it to live. A quality tuner in the passenger seat or on a dyno will figure it out pretty quick.

 

No MAF in this car, and I can see car builds boost to about 6-8 pounds when it’s backfiring like it does in the video (see the fuel pressure rise as the boost kicks in).

 

Agreed, I wish it was this easy. Where I live there aren’t many tuners and the guy I’ve been using is about an hour away, and very busy for not much else besides dyno tunes on cars that are ready to go. I’ll check spark on all coils and inspect all the connections.

Calling my tuner again today to see if I can get his opinion. Thanks for everyone’s help so far!

 

Do you have a WB02? It sounds like it's going lean. Double check your MAP sensor to make sure it is at least a 2BAR.

 

I do, but it has been acting up and coincidentally yesterday was the first day I got a reading from the sensor, but it was intermittent. It was also lean. I’m going to replace sensor as it’s a few years old and see what I get for AFRS. Assuming it is in fact lean, would that suggest the tune? Or injectors? I’m pretty new at diagnosing fuel injected setups.

 

MAP is 100% a 2 bar. OEM ac Delco part

 

Bumping this to the top!

 

Whats the wideband say?
Where is Map data?
Where is your log file?
Where is the tune file?

This issue cannot be solved easily without these

 

So the coils were relocated and the pump replaced. What did it run like before? Curious to see results of spark testing each cylinder as others have suggested. What's the plug gap?

The o2 sensor acting up sounds suspicious like you could have a grounding issue? I'm also confused that you say the tune is perfect for car then question the tune since it shows lean.

 

How did you clean your injectors? Thats a tricky thing to do properly. Are these stock injectors from the NA setup? My bet is that your increased airflow at WOT is outpacing the fuel system's ability to ramp up fuel injection. this would be easily diagnosed with comparing afrs ar 4k rpm cruising vs 4k rpm wot. Don't be peddle happy right now though, you're liable to Crack a head or a con rod if you don't get this figured out. if your pump is good (which your guage looks like you're holding about 3 bar fuel pressure) then ill bet your injectors are not up to snuff - either dirty or undersized.