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Discussion Starter #1 (Edited)
Hey guys,

I have a 2008 Suzuki XL7 with an auto trans, that I've recently have thrust upon me. The previous owner was sort of ignorant and did not take very good mechanical care of this car, so now I'm trying to bring it back to life. Vehicle has 120k miles on it.

Sometimes starts fine, idles decently, and throttle response seems pretty good, but after about a minute or so of running it starts to idle pretty rough and will throw error code for random misfire, and misfire on 2, 4, and 6. Sometimes it will just start rough. I suspect that if I give it throttle it will also throw codes for misfire on 1, 3, and 5, but I'm a little hesitant to test this theory.

I've checked a few things:
- I checked the fuel pressure and it seems decent at 45 PSI. I couldn't find what the spec pressure is, but I feel 45 PSI should be within operating margin.

- I also checked the compression. Readings were between 135-140 for various cylinder, which according to the internet is "low", but I think for a car to tool around town with it should be fine? Not really sure.

- Spark plugs are brand new, and I looked at the coil packs they seem fine. Besides it doesn't make sense for it to be coil packs since is an entire bank (possible all cylinders). I have a hard time believing that every coil pack, or all the ones on one bank decided to let out the smoke all at the same time.

- Cam sensors, I checked them all, they seem fine.

So I'm down to vacuum issue, or electrical issues. Have you guys seen anything like this before or is there anything else that I'm missing? I need to get a vacuum gauge to check the intake vacuum which I will probably do in a few days. I'm sort of at a loss, and if it ends up not being vacuum I don't really know where to go from there.

Thanks,
Alan
 

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Which engine?

Might you have a fuel quality issue?

Have you tried a fuel additive course of action? (water dispersant / injector cleaner)

Clear the codes and provide us with the precise new code number (numbers?) as they appear. ;)

Cam sensors. You checked them 'all'? There is typically only one, so what and how did you check them? :huh:

Compression seems down a bit UNLESS the battery not fully up to charge, throttle not open, all plus removed and engine warm for test purposes.

Welcome aboard too! :)
 

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To rule out timing chain issues I would do a CAM/Crank correlation test.

For fuel and spark I would connect a scope with a low current clamp, check the wave form

Using a Live Data Scanner, record the fuel trims and O2 switching... this will advise of the general health and direct you to the misfire issue.

Diagnosing without tools is tantamount to guessing...
 

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Discussion Starter #5
Which engine?

Might you have a fuel quality issue?

Have you tried a fuel additive course of action? (water dispersant / injector cleaner)

Clear the codes and provide us with the precise code number (numbers?) as they appear. ;)

Cam sensors. You checked them 'all'? There is typically only one, so what and how did you check them? :huh:

Compression seems down a bit UNLESS the battery not fully up to charge, throttle not open, all plus removed and engine warm for test purposes.

Welcome aboard too! :)
As far as I'm aware the gen. 2 XL7s were only available with a single engine configuration, LY7/N36A, the 3.6L V6.

I have no tried a fuel additive, I guess that could be an issue, but in my opinion chances for that being the issue I feel are low. Worth investigating though since its low hanging fruit.

I'll clear the codes out and grab them as they come in, but it probably going to be P0300 (random misfire), P0302 (misfire on 2), P0304 (4), P0306 (6).

It's a V6, are there not 4 cam sensors? Intake and exhaust for each bank? There is one crank sensor if that is what you are referring to?


The compression test was dry and on a cold engine. I could definitely tell the battery starting to die for the last few cylinders, so it could defiantly be artificially lower than what it actually is. The test was preformed in clear-flood modes so the injectors were deactivated.

To rule out timing chain issues I would do a CAM/Crank correlation test.

For fuel and spark I would connect a scope with a low current clamp, check the wave form

Using a Live Data Scanner, record the fuel trims and O2 switching... this will advise of the general health and direct you to the misfire issue.

Diagnosing without tools is tantamount to guessing...
Yeah I was looking into trying to figure out how to do the cam/crank correlation test. Honestly if the timing is out, I'm probably just going to be done with this project.

You're definitely right about the using the correct tools parts, but sometimes you're in a situation where you just go to run what you brung.

Thanks for the welcomes and the advice. I'll keep ya'll posted.
 

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Discussion Starter #6
I made a post earlier, but it seems it's stuck in the moderator approval stage since I included a diagram.

For the cam/crank correlation test, would you get the sensor signals from the ECU? Would there happen to be a ECU wiring diagram floating around somewhere? I look around the forum and the internet and haven't been able to find anything conclusive.

Thanks,
Alan
 

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You could get it at the ECU, if it is an easy access, or back prob the signal wires at the sensors..

The CAM will be a digital square wave 0-5vdc, the Crank will be an ac sine wave with changing amplitude at >RPM. Once you have the wave form, you can download a known good for comparison.. This is all done via a scope..
 

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Discussion Starter #9
Checking the code numbers yours is not throwing the codes for worn cam chains. It was just the first thing that came to mind as one bank is misfiring. Yes it does have four cam sensors.

https://static.nhtsa.gov/odi/tsbs/2013/SB-10052514-8788.pdf
Yeah it's not throwing out of time codes, but if it's just slightly out of time I guess it could cause it to misfire. Probably still worth investigating.

You could get it at the ECU, if it is an easy access, or back prob the signal wires at the sensors..

The CAM will be a digital square wave 0-5vdc, the Crank will be an ac sine wave with changing amplitude at >RPM. Once you have the wave form, you can download a known good for comparison.. This is all done via a scope..
Finally have a good use for my oscilloscope. I think it makes the most sense to get it at the ECU, but it would be nice to have a pinout. I'll dig around some more. If I find a diagram I'll post it up.

Thanks,
Alan
 

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i'm tossing in 2c here, I know its had a set of plugs but looking at the lances doesn't confirm electrical condition, when were they last replaced or thoroughly cleaned?

Check the basics as well, smoke test the inlet tract, many times these misfires are plugs, lances or vacuum leaks. The fact its one bank makes me think its possibly a vac leak, but a bad chain or cam sensor will do it, but I would think other symptoms would be present if they were faulty.

if you have done this then ignore me, but swap coils between banks and see if the misfire transfers, simple check and people forget to do these simple things. Simple stuff, check ground straps off the engine as well.

Low or dying battery can cause random misfires, especially if idling as the alternator barely outputs enough to keep the car running at idle, 1500 rpms and its charging fine, at 900, its on its limit, if its old and brushes are getting worn, the regulator might not be working as well as it should.

What happens if you fully charge the battery? how does it idle then?
 

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Discussion Starter #12
Thanks Darrell, this will definitely help.

2013GV, Thanks man I appreciate the input. Yeah personally I think the timing is fine since it's not throwing a code for cam/crank out of time, but maybe something funky is going on where its slightly out of time but not throwing code (seems unlikely to me).

I defiantly did that test of moving coils around and the misfires always stay in bank 2, which is what initially led me to thinking vacuum leak, or something electrical.

Something else that someone was telling me is that it could be a plugged cat. on bank 2, which I think would make sense. I defiantly overlooked that along with the battery being low. I never though to stick the charger on it. Let me check out some of these things I'll report back.

Thanks guys,
Alan
 

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Discussion Starter #13
Update on that happenings around the Suzuki. Pulled the cat from bank 2 and it was completely blown to bits.

IMG_2625.JPG

Not sure if this was the only problem, but this is certainly a pretty big one.

Thanks,
Alan
 

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Update on that happenings around the Suzuki. Pulled the cat from bank 2 and it was completely blown to bits.

View attachment 94630

Not sure if this was the only problem, but this is certainly a pretty big one.

Thanks,
Alan
The CAT MIA, will not cause a miss fire (it will skew the BxS2 reporting data), use your scanner and watch the fuel trims,
  • if the trims lessen when you raise the idle, you probably have an intake leak (pirate air),
  • if the trims go positive you most likely have a fuel or MAF issue.
The absence of any timing codes does not rule out intermittent CAM/Crank signals..

Again, the use of scope and low amp clamp can/will, provide a wave form for the coils (primary/secondary) and injectors (health check and mechanical pintle movement)... the only item it wont check is the flow rate, but unless there are any other indicators, that would be last on list..
 

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Discussion Starter #15
The CAT MIA, will not cause a miss fire (it will skew the BxS2 reporting data), use your scanner and watch the fuel trims,
  • if the trims lessen when you raise the idle, you probably have an intake leak (pirate air),
  • if the trims go positive you most likely have a fuel or MAF issue.
The absence of any timing codes does not rule out intermittent CAM/Crank signals..

Again, the use of scope and low amp clamp can/will, provide a wave form for the coils (primary/secondary) and injectors (health check and mechanical pintle movement)... the only item it wont check is the flow rate, but unless there are any other indicators, that would be last on list..
If the CAT is clogged and restricting flow it would cause misses wouldn't it? I'm not saying its the only issue, but it seems fairly relateable since it's bank specific.

Timing chain problems should manifest on both banks wouldn't it? I'll still check these items, but I'm just saying.
 

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If the CAT is clogged and restricting flow it would cause misses wouldn't it? I'm not saying its the only issue, but it seems fairly relateable since it's bank specific.

Timing chain problems should manifest on both banks wouldn't it? I'll still check these items, but I'm just saying.
You reported the CAT was destroyed, not clogged... Did you install a pressure gauge to the O2 bung to verify back pressure?? Anything >2psi @ 2000rpm indicates restriction.. also if restricted, RPM would be inhibited.. (never reported as symptom)
Keep in mind we are not beside you, so solely rely on your accurate reporting...
 

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Timing chain problems should manifest on both banks wouldn't it? I'll still check these items, but I'm just saying.
not necessarily, not uncommon for one chain to stretch and the other one doesn't.
 

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Please dont take this the wrong way..

Today's vehicles are mostly monitored by electronics which react to variables of a set matrix (programmed logic table).. they must be diagnosed properly rather than the old method of guessing and tossing a few basic parts, then adding additional parts if the first did not rectify the issue.

You apparently have a scanner and scope, these are your first go to diagnostic tools.. (they are like a Cardiologists ECG and BP...) they would never dream of opening the chest before a full diagnosis.

Once you meddle with components and connections, you potentially add variables to the original issue.. making it much more difficult to locate the original problem..
Moreover "codes" are an aid, not a destination, more often than not they are a result of a completely different fault (coded or not).

Enough of my rambling... lets try and fix your ride..
 

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Discussion Starter #19
You reported the CAT was destroyed, not clogged... Did you install a pressure gauge to the O2 bung to verify back pressure?? Anything >2psi @ 2000rpm indicates restriction.. also if restricted, RPM would be inhibited.. (never reported as symptom)
Keep in mind we are not beside you, so solely rely on your accurate reporting...
Fair enough, but the cat. is clogged. All the ceramic has completely broken down and is plugging up the mid pipe. There are stutter in the RPM, but I just assumed that was caused by the misfiring on the bank.

not necessarily, not uncommon for one chain to stretch and the other one doesn't.
Yeah, you're right. For some reason I though there was a single chain, like timing belts, but I guess there are multiple.

Please dont take this the wrong way..

<I'm just going to snip this to make room>
No offence taken dude, I'm just glad that there are knowledgeable people on the web willing to help out. To be honest this is a learning experience for me too. I'm used to working on Hondas and easy inline 4s but these V6s are a new beast for me. I'll get those waveforms, also need to find a replacement cat. for bank two.

Thanks,
Alan
 

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Dont get caught up with the engine architecture, they All work the same way..

  • Suck
  • squeeze
  • bang
  • blow
 
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