Lean Knock - Best practices for testing ROOT cause?

[harpkatt]

Long Story I supposed.

03 Denali 6.0 Drive by wire non flex fuel . In a c1500. As stock as can be though,no aftermarket upgrades. Was tuned to remove VATS and allow a 5 spd conversion. There are no rear o2 sensors and no means to connect in the aftermarket harness. Fronts were left. Evap/emission were are not installed.

I've had issue with this engine since I've had it in the truck. The RPM would hang after hitting the throttle,otherwise ran great, took a second to drop back down though. My first thought was bad tune. Truck wasn't plated or legal so I thought I would address it once it was driveable. So of course I made it legal and the next day I started it and heard a knock/ping. Plugged in the scanner and sure enough Lean bank 2 p0147(only code I remember). Ok makes sense revs hang, probably a vacuum leak. A day later it barely wanted to stay running at all. Got out the throttle body cleaner sprayed the intake and saw now changes. Then Borrowed a diagnostic smoker, no visible leaks in the intake or brake booster. Pull the intake anyway regasket and we're back up and running. When I pulled the intake-I didn't think and I disconnected the battery and lost all the codes that were stored.

Truck is running again though,but still knocking, it is not a consistent knock. I'm trying to be methodical with my testing and not fire up the parts cannon but I'm really not too familiar with reading live data on the scanner,especially since I don't know what the readings should be.

I just tested fuel pressure, I'm seeing as low as 48 PSI at idle, and when given throttle. when I prime the pump a few times I will see 55 or 57psi without the truck running.

I don't have any misfire codes since I wiped them all out.

My thoughts are fuel pump may be too low-but I've also seen 48PSI is ok. if it were an issue I would expect lean on both banks.
I've cleaned the mass air flow sensor.
Could be a bad injector as well,but a cylinder misfire code hasn't popped up still.
pre cat o2 sensors are both newly installed bosch If I recall.
This is unfortunately a build in progress, the exhaust was welded in by me but there are leaks. I planned to drop it soon and do everything right but didn't have complete access to the top of the pipes but now I'm thinking that might be a contributing factor as well.

What should I test next? What data should I look for on the code reader? Any thoughts on what could cause my lean condition?

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

I cannot personally assist you with your issue, but other members of this Forum much more knowledgeable than me in this area will chime in.

 

[Marky Dissod]

No mention of plugs, wires, coils, or checking of fuel trims or anything like that.
If you find which cylinder has the problem, try moving the coils / plugs around.
If the problem follows your movement, you found the culprit.

It's electronic signal throttle, ok; is it 'returnless' or 'return' fueling? They have different pressure specs.
Pressure up to 'spec +8psi' is fine, anything under 'spec -4psi' is ok, but you need to check during different conditions -
1st key on before cranking - how long does it hold pressure? Under 15min is a problem.
During cranking, during warmup/idledown, warmed up idle, driving miss daisy ...
then push it gradually; how does fuel pressure behave?

 

[harpkatt]

Plugs and wires are all new, I put them in when I did the swap. I don't have any CEL's , so I'm not sure which cylinder is has the issue.
The fuel system is a return type. Keyy on, Priming the pump I saw 55psi. Idle's at 48 after 10 mins of running. 1000rpm hold same 48 psi. 1500rpm and 2000rpm all saw the same fuel pressure. I didn't check idle down, but I have been having an issue of the revs hanging. I haven't been able to drive the truck because it has been knocking and since it's new to me I don't have anything else to report.

I ran the truck today , tank has about 5 gallons in it. I dumped a whole bottle of injector clean in. Just to see. Well interestingly enough the knock stopped after a few mins. But the bank 2 fuel trim is still reading high @ 20%.RPM still hang. I pulled the vac line off the pressure regulator and that brought the pressure to 58. The fuel trim actually did change to 18% when that happend.

Why don't I see a misfire code or something though? Theres no check engine lights. I checked the exhaust it doesn't appear I have an exhaust leak before the o2 sensors. (definitely do post cat)

I'm going to pull the injectors next and test and clean them. But I still feel like l'm flying blind, I wish I was better at diagnosing fuel injection stuff.

 

[Marky Dissod]

Check for intake and/or exhaust manifold leaks. When it's more than one cylinder consistently on one side, those are the most likely culprits.
Actually had my intake manifold leak repaired, only to find out that they missed the exhaust manifold leak.
Neither showed ANY misfire codes, maybe because it's not easy to have a rich misfire?

 

[S33k3r]

While trying to figure this out, you might try running some octane booster and see if that helps. It's a bandaid for sure, but it'll likely allow you drive it a little more.

 

[Doubeleive]

Plugs and wires are all new, I put them in when I did the swap. I don't have any CEL's , so I'm not sure which cylinder is has the issue.
The fuel system is a return type. Keyy on, Priming the pump I saw 55psi. Idle's at 48 after 10 mins of running. 1000rpm hold same 48 psi. 1500rpm and 2000rpm all saw the same fuel pressure. I didn't check idle down, but I have been having an issue of the revs hanging. I haven't been able to drive the truck because it has been knocking and since it's new to me I don't have anything else to report.

I ran the truck today , tank has about 5 gallons in it. I dumped a whole bottle of injector clean in. Just to see. Well interestingly enough the knock stopped after a few mins. But the bank 2 fuel trim is still reading high @ 20%.RPM still hang. I pulled the vac line off the pressure regulator and that brought the pressure to 58. The fuel trim actually did change to 18% when that happend.

Why don't I see a misfire code or something though? Theres no check engine lights. I checked the exhaust it doesn't appear I have an exhaust leak before the o2 sensors. (definitely do post cat)

I'm going to pull the injectors next and test and clean them. But I still feel like l'm flying blind, I wish I was better at diagnosing fuel injection stuff.

which plugs did you use?

 

[harpkatt]

I'm currently running 93 octane. Didn't help. No clue at all what plugs I have.

Update though. Tested each injector by removing the rail and filling with carb cleaner. cut and injector clip of an old harness and powered it with my jump box.7/8 sprayed one did nothing. all Ohm tested the same but no fuel from the 1. I replaced it and the truck is running much smoother. Fuel trim is/was better?
truck still showed 20% trim when I ran it after swapping the injector, I let it run to get into closed loop and the trim dropped to 3% great...but then went back up to 10.8. Which is still I believe just outside of spec. Progress though. Still No lean codes or misfire codes. The exhaust is a little quieter than it was which is nice.

I have a better scanner I will bring back home this weekend so I can see misfire data and hopefully get it under 5%.
I heard a single knock/ping while it was running this go around so there is still something ascue.

 

[S33k3r]

I'm currently running 93 octane. Didn't help. No clue at all what plugs I have.

Update though. Tested each injector by removing the rail and filling with carb cleaner. cut and injector clip of an old harness and powered it with my jump box.7/8 sprayed one did nothing. all Ohm tested the same but no fuel from the 1. I replaced it and the truck is running much smoother. Fuel trim is/was better?
truck still showed 20% trim when I ran it after swapping the injector, I let it run to get into closed loop and the trim dropped to 3% great...but then went back up to 10.8. Which is still I believe just outside of spec. Progress though. Still No lean codes or misfire codes. The exhaust is a little quieter than it was which is nice.

I have a better scanner I will bring back home this weekend so I can see misfire data and hopefully get it under 5%.
I heard a single knock/ping while it was running this go around so there is still something ascue.

Octane booster can be purchased from an auto parts store. We used it to get an old, Ford minivan to pass inspection is how I know.

 

[rdezs]

I experienced a lean knock at higher RPMs last year..... I had one injector o-ring that was split. That reduced the frequency, but about once a month the knock sensor would go off again. Turned out the upgraded valve covers to do away with the PCV valve were flowing too much air. Put a 3.2 mm restrictor PCV hose and it cured it.