Reason for Misfire/Extremely Lean on Single Bank?

Alan Engineer Oregon Posted   Latest   Edited  
Discussion
Driveability
Propulsion
2008 Suzuki XL-7 3.6L (N36A) 5-spd (AF33)
Misfire

Hey all, been having some strange problems with a Suzuki I've been working on.

The primary issue is that it is having random misfires on all bank 2 cylinders. I checked the few obvious things, replaced spark plugs, shifted the coils from bank 1 onto bank 2, shifted the bank 1 o2 sensor onto bank 2, all these items came back showing good on bank 1. I also checked compression and fuel pressure on the second rail, and they were all within reasonable values. The cat. was destroyed and plugged from all the raw fuel that was being dumped into it, that has since been repaired as well.

One strange thing I am seeing is the upstream o2 sensor on bank 2 is constantly reading less than 0.1v, yet the down stream sensor is reading 0.45v. I checked the wires/continuity for the upstream o2 sensor and all seem to good, so I assume that the engine really is running that lean, the strange part is though you would think that the ECU would just adjust the fuel trims and bring it back to the correct ratio. Secondly the data is not being corroborated by the down stream o2 sensor. You would think that if the upstream sensor was reading extremely lean, the down stream sensor would show something abnormal, but instead its showing a normal reading. I wonder if the exhaust manifold was is cracked, or the gasket has developed a leak but it seems strange that leak would skew the readings that aggressively since the exhaust should create positive pressure.

I'm also wondering, has anyone seen a vacuum leak that only caused degradation in a single bank?

Thanks,

Alan …

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Jj Technician
Massachusetts
Jj Default
 

Can you force the O2s rich with some propane or something? This way you know they aren't lying to you and you can count them out.

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Alan Engineer
Oregon
Alan Default
 

I did the propane enrichment test, but couldn't find any leaks. If there is a leak it could be in the EGR, PCV or break booster. Break booster seems fine though. I disconnected the boosted and plugged the vacuum line and the problem persisted.

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Jj Technician
Massachusetts
Jj Default
 

Did the sensors go rich? Forcing the engine rich with propane or another fuel source is more to see if the O2s react accordingly than it is to find a leak. If you pump extra fuel into the intake, the O2s should all head for 1.0v in a hurry and at the same time. What are fuel trims showing? With B2S1 stuck so lean I would think trims would be pegged rich trying to correct, if B2S1 is giving a…

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Rudy Technician
California
Rudy Default
   

When are the misfires occurring? At what point in the drive cylce? The freeze frame data should provide a clue to that. Are you certain it is all cylinders in bank 2? What scan tool are you using? Have you tried current ramping the coils? Swapping the coils is a good start,but current ramping them will show coil health AND circuit integrity. Finally, what exactly are the trim readings at…

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Alan Engineer
Oregon
Alan Default
 

I have that freeze frame data, but I don't remember it off the top of my head. I'll post it up when I get home. The codes are for random misfire and and misfire on cylinder 2, 4, and 6. Scan tool I have is an Innova 3040e. Not really the greatest OBD scanner I know. I have not done current ramping. I'm waiting for a current clamp in the mail. Once it arrives I will make this test. I don't…

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Anthony Technician
Indiana
Anthony Default
 

A vacuum leak can absolutely cause this problem. Did you check the intake gaskets? You could spritz a little brake cleaner down around the gaskets and look for a change in RPM as you go. Beware of dry rotted plug wires though. As for the downstream o2, I wouldn't expect to see much variation in the downstream o2 since it's after the cat. Does your scan tool allow you to add or subtract fuel for…

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Alan Engineer
Oregon
Alan Default
 

I didn't directly check the gasket, but didn't find any apparent RPM change spraying propane around the area. Unfortunately my scan tool does not allow manual adjustment of the fuel trims.

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Eddie Diagnostician
Alabama
Eddie Default
 

Have you scoped the cam sensors sounds like one bank is outta time a couple teeth.

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Alan Engineer
Oregon
Alan Default
   

Yeah I scoped the cam and crank signals at the ECU. They seemed in time at least according to the references I could find on the internet. I've attached a timing diagram. Yellow - crank Green - Ignition on cylinder 2 from ECU blue - bank 2 intake purple - bank 2 exhaust

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David Owner/Technician
Alberta
David Default
 

I would add to put the scope onto the CKP and CMP sensors to verify correct phasing. 3.6 engines certainly have their share of chain problems.

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Alan Engineer
Oregon
Alan Default
 

Hello David. I checked the timing and everything seems to be in phase. I have a diagram posted above.

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Scott Mechanic
Arkansas
Scott Default
 

I don't think you're going to have much luck with online help until you post very detailed data. It's hard enough to diagnose a car that's in front of you. Diagnosing one on-line is exponentially harder. Gauge and meter reading are great but, the tool you start with is a scan tool. Hopefully an OE level scan tool. Meters and gauges can help after that to verify the information you receive from…

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Albin Diagnostician
Washington
Albin Default
 

If you are having problems as you describe, grab your scan tool and take a FRTD, then post up the captured information. That short test drive will answer most of your questions, and give you a great direction for your next move. Without proper data, we are only guessing.

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Tim Technician
Hawaii
Tim Default
 

Check exhaust back pressure on that bank, compared to the good side. Possible plugged catalytic convertor on the bad side.

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Stephen Owner/Technician
California
Stephen Default
 

Whenever you have a condition that affects one bank, check for a vacuum leak (intake gasket or perhaps brake booster) and a clogged cat. Usually that bank will go lean if the cat is packing up. Exhaust back pressure check I like to see 1.5 pounds max at … rpm

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