Multiple misfires after rebuild ** FIXED **

I wanted to change out the idle air control valve but realized for the money I could just get a new throttle body. I also wanted to eliminate another possible issue.

 

this thought crossed my mind, unfortunately I threw away my stock ones so I would have to go buy 4 to test with.

 

Here’s the latest data from a longer drive.

https://youtu.be/CMHeXwSGcTU

 

And you already swapped the O2 sensors from bank 1 to bank 2, front and rear, right? Just to make sure it's not following? I think I mentioned that earlier, but damn this thread is getting long

That would be the thing to rule out if the sensors are throwing bad data.

If it doesn't follow, then I'd start investigating why every O2 you put on bank 1 of the engine thinks the exhaust ratio is wrong. I'd guess exhaust leak also, like I think dbittle mentioned.

Why? If some exhaust is leaking out, it means your O2 would only get a partial reading due to some exhaust leaking out, potentially making it think the bank was lean. The ECU would then force more fuel into the cylinder, to try and compensate.

 

I noticed something different on this last run. On bank 1, the fuel trim is negative 14, and on bank 2 it is positive 9. So the computer is pulling fuel out of bank 1 now. It's adding extra fuel on bank 2. I'm not sure what to make of that.

 

Sir here’s my take on things. You changed and touched a lot of stuff. We’re it me I’d be back to stock, verify it works as it should, then change one thing at a time. You have no idea if it’s 02 or fuel injector related. You changed both. Put stock fuel injectors in it and see if that clears it up. I know that sucks but you haven’t solved your original problem and don’t seem much closer. Not trying to be a dick or anything, just trying to help you get a resolution.

 

I agree. I have ordered a set of stock injectors on eBay. When they get here I’ll throw them in.

 

Ooof. Hopefully from a dealer that sells on there (there are surprisingly many who do). fleaBay can sometimes be a boon for fake parts otherwise.

 

I thought a lot about it over the weekend. It seems to me that obviously I’m getting too much fuel in bank one. I don’t think it’s a coincidence that the most offending cylinder is number seven which is right where the fuel comes in. I’m thinking more and more that it’s possible that the injectors I’m using are just giving too much fuel. Hopefully the ones I bought will fix it.

The problem is it’s gonna be a while before I get them. I can get one injector locally to test with. Do you think swapping one injector would make a difference? I’m thinking I will put it in cylinder 7 since that is the worst for misfires.

 

That would also explain why I’m not getting any misfires when I’m driving. Because there’s more air mixing with the fuel that’s already too much in the cylinder.

 

You need to pinpoint what’s going on. Changing one out of eight injectors isn’t going to put you to a known good state. Wait till your injectors get there.

 

I disagree. Swapping out one OEM injector on cylinder 7 to replace the DD 12-hole injector, which is clearly dumping too much fuel based on plug condition and misfire, would be a very valid test.

If the OEM injector replacement isn't dumping as much fuel and misfiring, then OP knows it's the injectors, and rolling back to OEM should resolve the issue.
If the OEM injector replacement is still dumping fuel, then it's pretty clear the ECU believes bank 1 is getting more air than actual, thus pushing extra fuel.

If it's the latter of the two, I'm going to guess there's a leak somewhere, which is tricking the b1s1 O2 sensor into thinking it's leaner than reality. Maybe an exhaust leak, cracked manifold, ???

 

OK. Except he’s already swapped injectors around with no resolution so it’s not a single faulty injector. And you yourself are saying that he’s got an O2 sensor issue potentially. So which is it?

You would be doing the same thing by swapping one of these 12 holes injectors from seven to another bank and see if it follows the injector if that’s your theory. And then you’re using an injector that’s a known good injector on seven. Introducing more random things in the equation doesn’t solve anything. It’s just adds another variable.

 

I don't believe it is a faulty injector. I think they are working as they should. I think that do to the fact they bank 1 is right where the fuel comes in that the pressure in the fuel rail is higher there and so 7, 5, and 3 are pushing more fuel through them due to the pressure in the rail.

I could be way off, but that is what I am thinking now.

Also, it is only misfiring at idle, when the rpm is low and there is not as much air flow. Once I rev it, or start driving, the misfires go away, again, I assume due to the increased air flow to match the increased fuel flow.

Again, I could be way off, but it's all I have left to cling to.

 

That's the big question - which is it?

Exclusionary stuff has taken it to this point, 15 pages later and OP has swapped a gaggle of stuff to boot. Injectors were swapped from side to side, but to ignore the fact all of the injectors are 12-hole and added at the same time the issue started, 12-hole potentially capable of more flow, I think could be a huge mistake/oversight.

For some reason, b1 is getting more fuel dumped in the cylinders. The plugs prove it. But why?

Anyway, just swapping out a single stock injector now, before the full set arrives, could be the difference between OP being able to refuse delivery and/or flat-out return the item to recoup some expense. Obviously, if one OEM injector doesn't see resolution on that cylinder, replacing all 8 won't either. But I do hear you, totally.

I don't think you're way off. It's ultimately what's happening. But back to the question: Why? Is it a lack of pressure regulation at b1 rail? Is it that the ECU is sensing a condition that's wanting it to fire?

The ECU should natively be able to correct for air/fuel ratio though. If everything it's sensing is accurate. If it was a problem at or before the TB, I'd expect it would impact both banks of the engine.

It's so weird to me that it's only on the one bank, almost like there's something specific to that bank causing the issue. Gasket or manifold leak, some other ring or seal, a sensor at or after the TB, that type of thing.

 

I wouldn’t chase that Theory very far. Fuel injection is metered fuel controlled by a computer and measured against feedback. If it’s getting too much gas, it’s because the injector is faulty (think you’ve ruled that out with a position swap already) or the computer is getting bad info from one of the sensors, or it’s getting good info based on a problem in the system, like air leaking in and not being accounted for. You’ve got several wildcards in there now. Aftermarket injectors, aftermarket headers, and O2 sensor extensions. These would be my culprits until proven otherwise.

 

If you're playing Uno then this is a good thing.

 

Haha

 

While waiting on the injectors, could the OP put up pictures of the other 4 spark plugs? I’m just curious what they look like.

 

I pulled 2 out over the weekend, they looked perfect. But I might be able to pull them again, that side is easy to get to.

 

That's what I'm doubling back and checking, to see if the other side is really totally ok, or if it just has a lesser set of symptoms.

 

I just pulled the plugs. Here are the passenger side:



but here are the drivers side:



They seem fine now. But I am still getting misfires at idle but only when not under load. Once I put it in drive the misfires go down to just a few. While I am driving there are no misfires. I am really perplexed now. I did swap in one stock injector into number 7 but it didn’t make a difference.

I don’t think the injectors are the issue now. The ECU has the LTFT for bank 1 at -13% and the LTFT for bank 2 at 3.87%.

I’m thinking it might be time to reset the ECU again and see if it can figure it out.

 

I swapped the plugs and coil packs to the other banks. How long do I have to leave the ECU disconnected before it resets?

 

Use a code reader. Instant reset.

These don't forget the same way older obd1 ECU's do iirc.

 

I have a code reader, how do I reset the fuel trims? Is it possible?

 

Just do a 'clear all codes', usually the ecu has to go through and relearn from there.

 

So I did a quick test, at idle, when I unplug the injector for 7, there is no rpm change. Same with 5, no noticeable difference in the idle. I didn’t really notice an idle difference with any on the drivers side bank. I did notice a difference when I unplugged the passenger side injectors.

i also checked all the header bolts I could reach. They are all super tight so I don’t believe I have an exhaust leak. I guess I am going to have to give it to someone to diagnose.

 

I have a buddy at work also pulling his hair out over this issue, so if you can let us know what the shop finds out, he and probably others will be humbly grateful.

 

If he finds the issue first, please let me know.

 

I will, but the last time I talked to him, he sounded like he has about given up on it. He hasn't worked the problem nearly as hard as you have either.