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Old 09-29-2009, 10:03 AM   #1
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Default 2000 Camaro Z28 - stock LS1 trouble

My car has been having a hesitation problem for a while now, and in the past month has been acting worse. I apologize for the length of this post but it's my cry for help on something I've been fighting with for a long time.

On days that it's running well, the following happens:

1) Put the throttle down to about 30%
2) Car accelerates swiftly, as expected; not fast but faster than most people leave a stoplight
3) The car hits 2500rpm and simply stops accelerating. It's sudden enough that it can throw you into your seatbelt
4) The car may continue to accelerate slightly; once it gets above 2700rpm or so (several seconds), it will pick up acceleration a little but will probably jerk a bit

The car also has a general loss of power, when I first purchased it two years ago I couldn't floor it in first gear without spinning the tires. Now, even after just having replaced the spark plugs, I can't get it to spin out (unless I'm turning a corner and rely on the limited slip differential to break the tires loose).

The car has thrown codes for a few things: Secondary Air Injection Failure (one of the check valves was shot and so was the pump, both have been replaced), Left/Right Catalytic Converters Below Efficiency (they had a recall so a dealership replaced them for free), and left/right O2 sensors Insufficient Switching (it throws for sensor 1 on both banks at the same time). When it throws the O2 codes it seems to stop using the O2 sensors and the car hardly works, more on that in a moment, and will eventually throw the code for random/multiple misfires.

When the O2 sensor codes are thrown, the car is barely drivable. For the first few minutes after the car starts the only way to get it moving is to put it into too high a gear and lug it, let it idle its way up. Any attempt at touching the throttle results in the car jerking horribly and not accelerating at all. After a couple of minutes the O2 sensors warm up and it goes into closed loop, at street speeds (30mph) it will mostly be okay if you're only feathering the throttle or flooring it, the middle range does almost nothing. At highway speeds the fuel system says "Open Loop, Detected Fault" in EFI Live. If you floor it, you can get light acceleration out of it (drive a Geo Metro and floor it, you'll get the same result as flooring the car in this state, I kid you not... and this is only if you remain in top gear, trying a lower gear results in deceleration even at WOT). At highway speeds, the only way to stay above 60mph is to keep it almost constantly floored, anything else will only result in the car slowing down. In short, barely drivable. However, at idle the car runs perfectly and it has no trouble starting.

Those are the symptoms, here's where I've started on trying to fix it:

I've replaced the O2 sensors due to the codes, as well as other items for a tune-up (fuel filter, spark plugs, and spark plug wires). I have a K&N oil based filter, but even after a cleaning earlier this summer didn't take care of the 2500rpm problem (though I haven't cleaned it since it started throwing codes and barely driving... perhaps I should do that).

I had planned on putting some upgrades into the engine this winter and purchasing EFI Live to retune after; at this point, it seemed a good idea to go ahead with EFI Live to troubleshoot first, and then do the engine later. I now have it and after pulling data for a few days I suddenly realize how little I know.

A couple of things I have noticed: when the car is barely drivable, the O2 sensors are a lot of time flatlined (low voltage, car is running lean). I also mentioned that once it starts hitting highway speeds it goes back to Open Loop fuel control (note that yes, I do know that I mentioned driving it in WOT which would also put it into open loop, but in that case the status becomes "Open Loop, Driving Conditions" which I do see briefly rather than the "Open Loop, Detected Fault" that I'm seeing).

When I clear the codes and the car is running mostly normal except for the 2500rpm hesitation (etc etc), I see a few misfires. Mostly they are at idle and not when I see the hesitation, I haven't yet been able to link the hesitation to anything either. And the hesitation and O2 sensor code may be two separate problems, I know, though I would assume they are linked somehow.

The only mods to the engine are an SLP airbox lid and a catback exhaust. There is a rattle in the exhaust, I think the Flowmaster muffler must have had something come loose; since the cats were recently replaced as I mentioned above, I don't think it would be them. All that stuff was done before I got the car, so if other things are common (e.g. replacing MAF with the airbox lid?) I don't know about them. Also, the guy who had it before me had a guy change the tune so that 1) skipshift wouldn't work, 2) the fans would kick on earlier, and 3) the speed limiter was disabled. He claimed that was all that was done, and the car did run well when I first got it.

In closing: I'm stuck. I've got EFI Live and I'm willing to pull data on whatever the heck anyone suggests. For the love of Pete, I just need a place to start.
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Old 09-30-2009, 02:57 AM   #2
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start with the basics. What does the timing do when the engine loses power? Fuel pressure? However, from what I've gathered it sounds like that problem is sensor related.

I'm not sure this is the appropriate location for this post though.
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Old 09-30-2009, 03:57 AM   #3
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have you changed anything in the tune? if so, post it up
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Old 09-30-2009, 06:00 AM   #4
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Default Maf ?

Does it throw any MAF codes, IE P0171, 102 ? If it throws this "Open Loop, Detected Fault" Maybe the MAF has failed and it's using back up open loop mode ?

Verify all your sensors are working.
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Old 09-30-2009, 09:10 AM   #5
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Timing: As near as I can tell it's fine. Watching the base spark and run spark, they are rarely more than a degree or two off from each other. And when I floor it I do see about 40 degrees of advance. Not sure if I should be watching for something else in here (as in figuring out if the tables are being utilized correctly or if they were corrupted somehow)?

Fuel: I put a fuel pressure gauge on and drove around, no matter what I did I couldn't get it to drop. It remained steady at around 50psi during normal driving conditions, WOT, and when the hesitation occurred.

Tune: Other than what was mentioned above (Speed limiter eliminated, fan setpoints changed, and skipshift disabled) I haven't changed anything. Those were done when I got the car and it didn't have this issue at that time.

SES light: The only codes it's thrown have been for the O2 sensor, unfortunately. Since they're considered part of the fueling system, I think that's where the "detected fault" comes in. The way that it acts, it seems like the O2 sensors are helping the ECM correct some other problem, but since the ECM is seeing strange data from them it blames the O2 sensors and throws codes for them (insufficient switching). When the engine is running mostly normal, the O2 sensors seem to switch correctly for the most part but sometimes stay rich or lean for no apparent reason (like the ECM is supplying the incorrect amount of fuel for the amount of air available). That's my best guess anyway.

MAF: I've watched the MAF data and I don't see anything strange. When I floor it at highway speeds and the car is having severe issues (will barely move), the MAF shows that there is a lot of air coming in; the ECM just doesn't seem to want to do anything with it (i.e. the O2 sensors stay flatlined, meaning the engine is running lean).


Thanks for the replies guys. Keep in mind that though I'm looking over this data I'm no expert and have no idea what I should be seeing, so if anyone would be generous enough to glance at some logs I'd be more than happy to pass them along. Also, sorry if this is the wrong place to post; I'm new here and may have misunderstood the meaning behind "diagnostics", perhaps this area is more for tunes. If the thread needs to be moved let me know who to contact to do that.
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Old 09-30-2009, 07:49 PM   #6
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change your stoich to 14.2 and see how it effect the car and what brand of software are you using?
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Old 09-30-2009, 08:17 PM   #7
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I'm using EFI Live. Monitoring the AFR, it's typically 14.7 I think, but when I floor it at highway speeds it drops to 11 or so (14.7 is best for emissions but the 11 lets it have more power is my understanding). Even then it doesn't seem to do well, though it picks up just a little.

How would I go about modifying that setting if I wanted to? I'm completely new to EFI Live, but I grew up on a farm and know a bit about engines and I'm handy with computers. Simple instructions should get me through.
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Old 10-01-2009, 09:19 AM   #8
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my camaro had the same problem, First off I had to use hp tuner to shut off the rear O2 sensors, and then I had to switch back to the stock MAF from chevy, cause the SLP one that I bought made it hard to tune. your throwing the codes cause your running to lean. You should be at 55 to 60 psi fuel pressure, not at 50psi... does the car fire right up or does it crank a bit before it starts. also try unplugging the O2 sensors and then drive it around and see if you have the same issue
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Old 10-01-2009, 10:33 AM   #9
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Unfortunately the stock MAF didn't come with the car, I'd have to buy a replacement if changing it is necessary. One thing, keep in mind that this MAF has been on the car for over 2 years and it's just now failing the O2 sensors from running lean; though it's easily possible that the MAF is bad. Does anyone have suggestions on testing it?

As far as fuel pressure, I had thought it was around 50psi but I could be wrong. I'd have to throw the pressure gauge on it again, likely this weekend (it belongs to a friend about an hour drive away). If it's too low, would that be the pressure regulator? Low fuel pressure could easily cause it not to put enough fuel in, though I would have thought the LTFT should take care of that. Still learning how everything works though, so input is appreciated.

The car almost always fires right up; occasionally it has to crank over a time or two. Comparing it to other vehicles I would definitely call it normal.

Unplugging O2 sensors: I thought about doing that but wasn't sure what the best plan was. As I mentioned it seems to run better for a while if I clear the codes. Should I clear the codes and then unplug the sensors, or unplug them now while it's running like crap? Should I unplug all the sensors, or just the front two or just the rear two? If I haven't heard back in about 6 hours (when I get off work) I may just start unplugging them and see what happens.

Thanks everyone for the suggestions. I feel like I'm at least getting some ideas.
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Old 10-01-2009, 04:59 PM   #10
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Default Egr?

Though the car hasn't thrown any EGR codes, one of the metrics I was collecting was the "Exhaust Gas Recirculation Pintle Position Error". Over the course of a 20min drive, the average was -97.4%. It was -100% almost all the time, on rare occasions (and for no apparent reason) it would jump for a brief moment up to the +90 range and drop back down to -100 again. For all I know this is normal, any thoughts?
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Old 10-01-2009, 07:45 PM   #11
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First off, your timing should not be 40 degree at WOT, if its a stock tune it should be somewhere between 22-25 degree. What does KR look like when you punch it? That right there sounds fishy.

Have you tried driving it with the maf disconnected?
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Old 10-01-2009, 07:47 PM   #12
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Quote:
Originally Posted by daemon View Post
I'm using EFI Live. Monitoring the AFR, it's typically 14.7 I think, but when I floor it at highway speeds it drops to 11 or so (14.7 is best for emissions but the 11 lets it have more power is my understanding). Even then it doesn't seem to do well, though it picks up just a little.

How would I go about modifying that setting if I wanted to? I'm completely new to EFI Live, but I grew up on a farm and know a bit about engines and I'm handy with computers. Simple instructions should get me through.
Is that commanded a/f ratio or has that been verified with a wideband?
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Old 10-02-2009, 09:48 AM   #13
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My apologies, I remembered the spark hitting 40 degrees at one point and thought it was while floored, but it wasn't. It does hit that occasionally but I'm not seeing consistency with it using my untrained eyes.

Driving the car when it barely wants to maintain road speed, at WOT (over the space of several seconds in 6th gear, the only way to maintain 65mph) the base spark is around 36, while the run spark is around 29. KR is completely quiet. FYI, I'm running 93 octane in it.

Although I graphed all the spark parameters I could find on that run, I don't see the cause of the discrepancy - I grabbed PIDs with the following identifiers: Base Spark, Burst Knock Retard, EGR Spark, Equivalence Ratio Spark, Induction Air Temp Spark, Retard Due to Knock, Run Spark, Spark Smoothing, and Total Torque Control Spark Retard. There's a good chance I missed one, I grabbed the ones that made sense to me but left off a few (such as the one for A/C, Cat Light-off, Cranking, etc.).

So, does this mean that it may be doing incorrect things with the spark?


I did try driving it with the MAF disconnected, but only for a very short period of time. Also, I can't remember if it had codes thrown before I unplugged it or not. Do you recommend clearing the codes so that the ECM forgets the "O2 sensor" problem (so to speak), then running with the MAF disconnected for a few days and see what happens?


That was commanded AFR only. I don't have a wideband, unfortunately, nor do I know of one I can borrow; it's also an expense I can't spare right now.
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Old 10-02-2009, 06:04 PM   #14
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well the reason I say try driving it with the maf disconnect is because that would rule out the maf. The reason i ask about actual or commanded a/f ratio is because the computer can tell you what it thinks is the correct a/f ratio but that isn't necessarily true. But anyway, IF IT WERE MY CAR, I would stare it it for like an hour looking at all the sensors and connections looking for something obvious then, I would try running without the maf and see what that does, then I would set it up for open lope mode and try that......as that would rule out the O2 sensors. Like I said IF IT WERE MY CAR.
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Old 10-02-2009, 07:05 PM   #15
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Sounds like you need to recheck the fuel pressure. If its not a constant 55-60 psi you will have all those symptoms. If its not 55-60 then fuel pump is bad.
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Old 10-02-2009, 07:30 PM   #16
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Remember pressure is not all you need to check as far as fuel. Volume it just as important. You can have 55psi in a straw sized hole and 55psi in a garden hose sized hole but obviously the garden hoes will technically flow more. My fuel guage has a button with a hose to test volume with the engine running. The pump should be able to support at LEAST a 1/2 pint in 15sec with out the car stalling.
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Old 10-05-2009, 10:07 AM   #17
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Default MAF sensor results

Well, disconnecting the MAF seems to have corrected the problem. I had disconnected it for short periods before, not long enough to throw codes as I didn't know what effect it might have on the vehicle and I was nervous. Now, after leaving it disconnected for my drive home on Fri it threw codes, and the next time I drove it (with the MAF still disconnected) it was running WAY better. I didn't have a single problem with it all weekend, it's running better than it has in months.

Looks like you nailed it, JDMC5. One more question, though: one of my friends suggested that disconnecting the sensor may have caused the computer to run the engine in a "dumb rich mode". Considering that it's still in closed loop with the O2 sensors I assume that's not the reason it's running better, but I just want to make sure. My question is, since disconnecting the MAF caused the issue to go away does that guarantee that the MAF is bad, or is it possible that it's just covering up another issue? I can see low fuel pressure or a leak on the intake after the MAF being covered up by disconnecting it, any chance of that?
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Old 10-05-2009, 11:59 AM   #18
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Your problem may have been K&N related. Did you start having problems after cleaning it? If so you probably put too much oil on it and it got on the MAF possibly causing it to fail. Do a search on failed MAF's and K&N. You will find postings all over the place.
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Old 10-06-2009, 01:17 AM   #19
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Quote:
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Your problem may have been K&N related. Did you start having problems after cleaning it? If so you probably put too much oil on it and it got on the MAF possibly causing it to fail. Do a search on failed MAF's and K&N. You will find postings all over the place.

Nice to hear.....I take paypal haha j/k.


Its possible what Ghost said is true, buy some MAF cleaner and spray it down. If that doesn't work buy a new maf, you can get them pretty cheap used.

Running with the MAF disconnected does still use O2 feedback, yes and I seriously doubt it being disconnect is masking another issue. It is perfectly fine to run your car that way and in some instances it will run better. For example on my C5.....when I disconnected my MAF, just for the heck of it, cruise ratios were right on (O2 feedback) and my WOT ratios were right about 13.0:1. (Keep in mind, I deleted all SES codes and monitored my wideband to make sure my WOT a/f ratio was ideal) Come to think of it you already had the answer, if you are scanning with the MAF disconnected and you see ltft's and stft's compensating, then..........hello.

Anyways, if you don't plan on replacing/ cleaning your maf anytime soon then this is what I would recommend. I'm sure you've noticed the service engine soon light is on.....save a copy of your current bin and store it away. Then, scan for the codes, they should all be maf related....delete them in the editor and reflash your computer, your SES light should be gone now. Now, while scanning make sure your WOT timing is the same as it was with the maf connected, make sure your trans shifts the same as before and not super hard (even at part throttle) and check out your fuel trims to see how close to 0 they are. BTW, you should reset them since they will be different without the maf. You could go as far as running a MAFless intake setup which could potentially free up more horsepower but thats completely up to you.
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Old 10-06-2009, 01:23 AM   #20
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Quote:
Originally Posted by 69 Ghost View Post
Your problem may have been K&N related. Did you start having problems after cleaning it? If so you probably put too much oil on it and it got on the MAF possibly causing it to fail. Do a search on failed MAF's and K&N. You will find postings all over the place.

Nice to hear.....I take paypal haha j/k.


Its possible what Ghost said is true, buy some MAF cleaner and spray it down. If that doesn't work buy a new maf, you can get them pretty cheap used.

Running with the MAF disconnected does still use O2 feedback, yes and I seriously doubt it being disconnect is masking another issue. It is perfectly fine to run your car that way and in some instances it will run better. For example on my C5.....when I disconnected my MAF, just for the heck of it, cruise ratios were right on (O2 feedback) and my WOT ratios were right about 13.0:1. (Keep in mind, I deleted all SES codes and monitored my wideband to make sure my WOT a/f ratio was ideal) Come to think of it you already had the answer, if you are scanning with the MAF disconnected and you see ltft's and stft's compensating, then..........hello.

Anyways, if you don't plan on replacing/ cleaning your maf anytime soon then this is what I would recommend. I'm sure you've noticed the service engine soon light is on.....save a copy of your current bin and store it away. Then, scan for the codes, they should all be maf related....delete them in the editor and reflash your computer, your SES light should be gone now. Now, while scanning make sure your WOT timing is the same as it was with the maf connected, make sure your trans shifts the same as before and not super hard (even at part throttle) and check out your fuel trims to see how close to 0 they are. BTW, you should reset them since they will be different without the maf. You could go as far as running a MAFless intake setup which could potentially free up more horsepower but thats completely up to you.
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Old 10-06-2009, 01:23 AM
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