Left bank rich

Need help...have looked for direction till my brain is fogged. Working on 2008 Dakota 4.7 flex fuel dual plug per cylinder. Work performed: head gasket and timing chains and sprockets. Repaired vacuum leaks and verified. Installed new upstream O2 bank 2. Issue is wont idle or stay running below 1500 to 2000 rpm. Bank 1 fuel trim is good at +2 to -5% Bank 2 is at -32%.
Injector balance drop test from 52psi to 31psi all injectors. All plugs on bank 2 covered in carbon as well as upstream O2 confirming rich condition. No codes but blinking money light.
Coil current ramp are identical for both banks.
Had 2 severe backfiring through intake causing damage to plenum. Is it possible that this could have caused bank 2 side of manifold to have internal restrictions causing rich condition? Hopelessly lost any and all help appreciated.

No offense meant here, but are you confident about the timing chain installation? If this is similar to the 4.7L single plug design, it can be challenging to get the timing right on the idler sprocket. A timing issue would definitely explain the black plugs, fuel trims and backfiring.

A quick and easy way to test for this would be a clear flood crank for a relative compression test. If there truly is a timing problem, the cranking sound will be irregular. Every other cylinder will sound weak. If you have a scope available, we can talk you through setting it up for this test.

Another way would be to test compression in one cylinder on each bank. If there's a clear difference between the two, you know you're onto something.

I'm 99 percent on timing. That cam is under tension when chain is installed so we checked it several times. Also that cam is the one that has the reluctor on it so my thoughts are if this one is off by a tooth wouldn't it be the other bank acting up. Either way my tool availability is an older modis with 9.4 version which gives me access to oscilloscope and I did a relative compression with low amp clamp on pos. Battery cable but did not resemble anything similar to what I have found on videos and forums. Thank you for suggestion. I will do compression check on both banks and look for significant differences. Also thinking maybe do a cam crank relationship check if I can figure out the hook up. Thinking back probe cam and crank sensors and one to injector for cylinder reference. Will update after compression test.

kwhooper wrote: Either way my tool availability is an older modis with 9.4 version which gives me access to oscilloscope and I did a relative compression with low amp clamp on pos. Battery cable but did not resemble anything similar to what I have found on videos and forums. Thank you for suggestion.

Gotcha, sounds like your timing is good.

Also thinking maybe do a cam crank relationship check if I can figure out the hook up. Thinking back probe cam and crank sensors and one to injector for cylinder reference. Will update after compression test.

Let us know if you need more info or details on the connections. Happy to assist!

Does it run well in open loop? As in, right after you start it up? Or does it never run well?

kwhooper wrote: . Also thinking maybe do a cam crank relationship check if I can figure out the hook up. Thinking back probe cam and crank sensors and one to injector for cylinder reference. Will update after compression test.

If you're going to use something as a sync for cylinder reference I would normally use ignition rather than an injector. The reason I say this is because the ignition event will be somewhere 'near' TDC for whatever cylinder you choose, the injection event can be pretty far off, depending on different variables. Just my .02.

Also, any chance you could post your relative compression results?

Sorry so long to reply got pulled away on honey do list. Cant find capture of relative compression however upon looking at pics of primary on coils i think my problem is in voltage. Bank 1 is registering battery volts while bank 2 is only at 6 volts, thinking this is causing weak spark to bank 2.

If you don't mind, can I ask a question real quick? I use a Pico and have no experience with Snap On scopes, but what I don't get in the pictures you posted is where it is measuring the 6v from? Is there a cursor I don't see or something?

When I look at the scale on the left, it sure looks to me like that voltage before the coil is pulled down is higher than six volts. I'm probably wrong, just trying to understand what I'm looking at here.

I dunno that I'd read too much into that 6.8V reading. Because the waveform says there's strong spark taking place.

It even looks like the burn line is tilted down at the end, which agrees with a rich condition. It's tough to tell with the different time settings, but it looks like the burn times are pretty similar.

So I found an injector that was loosely connected on bank 2 and that eliminated the low voltage and a misfire. It started and ran at high iddle (1100) but when it warmed up it sputtered and died. Guessing went in to closed loop. Hoping to get scanner on it to monitor stf and O2s to see what's going on.

this tool as well the use of a scope is new to me and i really cant explain where that reading is being captured from. my hookup was to control side of coil on bank 2 and i found it odd that the reading was so low in comparison to bank 1 which has good fuel trim #. On the left top corner of the scan tool in the view icon you can select digital and that display appears on screen.

kwhooper wrote: So I found an injector that was loosely connected on bank 2 and that eliminated the low voltage and a misfire. It started and ran at high iddle (1100) but when it warmed up it sputtered and died. Guessing went in to closed loop. Hoping to get scanner on it to monitor stf and O2s to see what's going on.

Might be that it went into closed loop with those extremely negative fuel trims, and inadvertently took all the fuel away from that bank. Maybe see if you can reset the fuel adaptives with the scanner? Or disconnect the battery for a minute or two.

Still can't figure why a loose injector connector would cause negative trims. :silly:

I still would like to see a relative compression test if you could get one. I think it's about time to start from zero here, but one other thing.

On the bank that is running rich, I understand that you put a new upstream O2 in it. What does the downstream read? I have seen downstream O2's drive fuel trim way more than you'd think. They're not just there for catalyst monitoring.

I will capture short and long trims along with upstream and downstream O2 and relative compression asap and post. Thanks for your input I appreciate it.

One more question.

I was looking over your original post, and you said it had 2 sever backfires. Was this before the work was done or after?