Series 2 L67 Laking Power *Data Vid Added*

[l67poweredlss]

I have another bump in the road in getting the LSS back up to where it was before this incident.

viewtopic.php?f=8&t=15494

Recently I have noticed a huge drop in power. I know the plugs and wires are good as they are fairly new. There is no misfire as the motor runs smooth in all situations even under load. It just feels like the car is running out of fuel. I did have a fuel line leak that I had fixed. That did nothing. I have no codes, fuel filter is fresh, tranny shifts smooth and fluid is pink, high flow cat is only 3 years old, air box clean, MAF screen clean, engine idles/ runs smooth, yet my scan tool is telling me my O2s are 850-860ish and I have 2* of timing under WOT. It is the G8s tuner so I don't know how accurate it is with the LSS. Anyways, this is a video of how the LSS runs.

http://www.youtube.com/watch?v=JJqT2WdjO2U

[wjcollier07]

That car is PISSED.

I noticed the timing comment..but did you notice it detecting a LOAD of false KR?

Also...storing cars in damp conditions..I've seen even brand new cats clog up...you might want to do a backpressure test...just to eliminate that...smooth running and smooth, non jerky acceleration like that..screams lack of airflow.

Fuel pressure test wouldn't hurt either, just to corner a few things at once.

/$0.02

[olblueeyesbonne]

At first I'm thinking BCS or BBV, but with the timing being @ 2* I'm stumped.
Bad ECM, maybe a wire been chewed through.
What is the timing at just cruising?
Can you check your LTFT's?

[gonzo4191]

what about the balancer being off like it was on haro's ssei 40th?

[00Beast]

Juan, it was fine before he put it in storage.

[gonzo4191]

and there you go posting again ............

[00Beast]

and there you go posting again ............

Juan, Haro's balancer was caused by someone putting it on wrong. That is obviously not the case here. Check fuel pressure, and maybe test the coils.

[l67poweredlss]

Also...storing cars in damp conditions..I've seen even brand new cats clog up...you might want to do a backpressure test...just to eliminate that...smooth running and smooth, non jerky acceleration like that..screams lack of airflow.

This is what i'm thinking. How do I go about doing a backpressure test?

At first I'm thinking BCS or BBV, but with the timing being @ 2* I'm stumped.
Bad ECM, maybe a wire been chewed through.
What is the timing at just cruising?
Can you check your LTFT's?

I'll make a new video today showing the timing @cruise and WOT. I can run a display of 4 parameters at once on the G8s tuner. Which ones would you like to see?

[1fatcat]

Check back pressure at the o2 sensor by the firewall. Low air volume readings from the MAF sensor would indicate a possible restricted exhaust also.

[l67poweredlss]

Okay, took a video of some stats. The top two squares are O2 voltage, lower left is MAF flow rate, and lower right is timing. Beginning of video is cruising and the rest is WOT. I don't know where these numbers should be, so I hope you can help.

http://www.youtube.com/watch?v=NqkBs8ZyCGE

[gonzo4191]

where you comparing both o2's? or just have the front one going twice, because front and rear should not read the same last time i checked

and which lights are on, on the dash?

[1fatcat]

The MAF reading looks real low. However, I am unfamiliar with the "#/m" reading of that tool? I am used to "grams per second" readings. I would definately check the back pressure.

[repinS]

#/m is probably pounds per minute

[1fatcat]

That makes sense.

[geofffinlay]

The MAF /m is per mile. It's a conversion from Grams per Second which is easier to work in for your purposes. If you have the option of reading in gms/sec it's easier to diagnose. You should have around 4-6 g/s at idle. This will increase relative to rpm. If you create a simple graph for MAF & rpm, the values should increase in proportion to each other through the rpm range. You don't need to drive the car to take these readings.

A defective (dirty) MAF will often rise with rpm, then flat-line somewhere in the rpm range, limiting the amount of fuel delivered above that rpm value.

As well as running lean from a shortage of fuel, the amount of oxygen in the exhaust is greatly increased from even marginal misfiring. The O2 readings (front and back) should then be very low, possibly @ zero volts.

It appears that your timing is being retarded out of proportion. You may want to consider disabling the Knock Sensor and repeating the test drive carefully.
Of course you must be mindful of the engine actually knocking, causing the issue, which could destroy the engine. If the KR is reduced and the engine is knocking, that has to be addressed first.

The O2 readings appear to be full rich, which indicates very low oxygen in the exhaust, so it doesn't appear to be an actual misfire situation.

Geoff

[charliemax]

Okay, there are two other videos that I couldn't download on youtube and they are likely the most important. The first is the O2 B1 S1T %, which under WOT sits at 0.00 the whole time. The O2 B1 2ST % is at 99.21 under WOT the whole time.

Now my LTFT B1 % is at 5.5 under WOT the whole time, 6.2 cruising at 55mph 1600rpm. The STFT B1 % is at zero under WOT and -1.6 cruising at 55mph 1600rpm.

Where'd we go?

Those are decent fuel trims. If you were getting a load of fuel from an injector, regulator or pump problem, the LTFT would be pegged in double digit negative, and the STFT would be working like crazy in a positive direction trying to pull the LTFT back towards 0. The converse would be true, if you were lean.

The next would be air and that's the MAF and MAP. If you read their values off simultaneously, they should move in exact unison (at different value points). Pull the MAF and clean it, because it is quick to do.

If that doesn't garner any odd results, then we're back to the O2 sensor.

The only other thing I can think of is the EGR valve is not working correctly. And it is overloading the O2 sensor; or has wasted it, and the O2 can't do the chemical reaction to get a proper signal out.

That's my best shot, without being there to go over the info and car.

keep us posted.

Edit: Oops, geo(above) beat me on the MAF check. I guess the MAF/RPMs will work. I prefer the MAF/MAP readings because they are instantaneous. Good luck.

[1fatcat]

Have you tested the fuel pressure?

[l67poweredlss]

Well, I finally got a code today. P0141 O2 Sensor Heater Circuit Malfunction (Sensor 2). I have no clue what this heater circuit is.

[1fatcat]

It is a heating element inside the O2 sensor, that is why they call them HO2S. It means Heated Oxygen Sensor. The H means heated, the O2 means oxygen and the S means sensor.

I'm not sure, but I thought a 97 only had 2 sensors? One up stream of the cat and one down stream? If that is the case, then that code would apply to the post-cat sensor (the one after the cat).

HOWEVER, a failed heating element alone in the sensor should not cause your problem. The heater is only there to get the sensor up to opperating temperature faster so the PCM can go into closed loop sooner.

Do you still have a post cat O2 sensor in the system? A lot of aftermarket cats do not provide a bung for that sensor, because it is illegal to alter the emisions system for on-road use, so most performance parts are not equiped/rated for 50 state street legal...and may not have provisions for the post cat HO2S.

[geofffinlay]

Gentlemen,
Sounds like a couple of knowledgeable people responding here. The reason I like the MAF/RPM combo is because the relationship should be pretty much linear. If you include the MAP, then you really should have TPS at the same time to verify MAP.

The following is long and boring. No apology, just trying to help.

Here's my list of the information I believe we need to continue - I've listed it at the end of the post and your comments are absolutely welcomed.

FUEL:
How long has the fuel been in the car? If the fuel in the car is more than a couple of months old, it must be suspect. Is the fuel the appropriate grade for the conditions/season/temps? Where is the car being operated? Florida @ Sea Level, toasty? Colorado @ 5,000' a little chilly? As I'm writing this (in the Toronto Area) the outside temperature is a balmy -18C. (about -0.4F). The missing "winter required" components in the fuel would create any number of problems from no start to horrible performance, especially in an OBDII car. (where is this car?)

MORE FUEL: Someone already mentioned fuel pressure. I didn't see a response. Even if the pressure is @ spec, how much is it getting? The fuel pump can be turned on and the flow measured. Without a manual in front of me, I can safely say that there should be between a pint/quart per minute available. The combination of old fuel and time can certainly plug the fuel filter and seriously affect injector operation. It should be changed regardless at some time. This is that time to eliminate it as a suspect.

FUEL Pump: Does this vehicle have a PWM controlled fuel pump? Has that been checked?

SIMPLE DATA: Is the CTS data reasonably accurate. It's not the least unusual for a GM CTS to be out of range, even to the point of being wide open (Reads -40f) or shorted (read 260f?). Does the TPS read normally throughout the range? Don't need to drive anywhere to check these two.

NOTE FOR NEWBIES: A failure code will only occur when the particular sensor is OUTSIDE the expected range for a specific amount of time. If the TPS was say 0.5 volts @ idle, 2.5v @ half throttle and the same 2.5 @ WOT, a code will never be stored. The expected range (that the PCM is looking for) is between 0.5volts & 4.5volts. If it never wonders out of that range, the PCM won't set a TPS code. It will however respond with an appropriate amount of fuel/timing that it will calculate based on the incorrect input/s.

MORE SIMPLE DATA: back to MAF VALUES. Any serious technician works in G/S. If your code reader cannot read a MAF in that format, you'll spend a lot of time converting the per mile values or get a proper scan tool that can work in a usable format. Over the years I figured out a BASIC formula for MAF at IDLE.

Take the number of cylinders X 0.75 then add or subtract a little for larger/smaller CI. So for your V6, use 4.5G/S +/-. Since it's a little larger than average displacement, we'll add 0.5 for an expected idle range of 5.0g/s You should be close enough to track the MAF from there.

The other MAF issue (from a previous post) was the condition of the screen. This is an excellent indicator of local wildlife conditions. If there is no mouse fur and droppings in there, you're ahead of the game. The real issue is the sensor element. This is exposed to the environment and will need cleaning periodically. Some Bosch sensors have a self cleaning function, but even this may not be perfect. Look around the net and find proper cleaning procedures. Correct, MAF cleaner is available. One can will last the lifetime of your car for about $10.00. Cleaning your MAF once a year is good practise, but follow instructions, it's easy to destroy.

MAF SCAN DATA: The g/s readings are linear and proportional to both RPM & TPS. To be genuinely accurate, an oscilloscope is required, since the update rate of ANY scan tool is limited by the OBDII reporting capabilities, which is capped @ about 100ms. That means the fastest scanner can display a maximum of 10 screen updates per second. It's also essential to be able to plot the MAF through the entire RPM range for diagnostic accuracy.

When plotting MAF values, the simple rule is whenever the engine is accelerating, the MAF reading is increasing. If the RPM is increasing and the MAF reading stalls or flatlines at any point that needs investigating. If you're using a 2-channel scope, the MAF rise will always be ahead of the RPM rise.

Don't rule out false air issues, such as a loose or torn inlet air duct. (very common on BMW & Volvo). A smoke machine is ideal for that purpose.

INJECTOR ON TIME (BPW): Injector values are directly related to MAF inputs. The PCM is looking at O2 response to confirm INJ operation. A very high PW during acceleration would indicate that the PCM/O2 combo isn't happy with the amount of fuel that's actually being delivered.

FUEL TRIMS: GENERALLY LTFT +/-5% is a reasonable normal range. Higher, indicates the PCM is making abnormal adjustments when not enough fuel is available. Of course the reverse is true. We should have a handle on Short & Long Term.

OXYGEN SENSORS: We'll ignore heaters for now. We'll also assume that both front & rear can reach at least 600f to begin working.

A perfect REAR sensor (after the Cat) working with a "lit up" working Cat will read in the 200mv range and will stay pretty steady. If the Cat cools off, the sensor voltage will rise and likely pin high (rich) until the Cat lights again. A PERFECT Cat will stay lit. If the Cat can't light up, the O2 reading will be high (rich) all the time. (this is also one of the issues with aftermarket cats).

A quick Cat/Rear O2 test could be instructive. With the engine fully warm, remove one spark plug wire and ground the spark (take proper precautions, the spark can seriously hurt you) and hold the RPM around 1500. Have your scan tool ready to monitor O2s & RPM. The unburned fuel will VERY quickly cause a GOOD cat to light up and convert the unburned HC (hydrocarbons). The O2 reading will drop to zero (dead lean) instantly.

Return the engine to idle and replace the spark plug wire quickly. If the cat is WORKING (see explanation below), the O2 will sit around the 200mv range. GENERALLY, if the Cat doesn't light up in this test, it's defective. The whole test shouldn't take more than about 30 seconds.

If you have the luxury of an infrared thermometer, taking temp readings front and back of the cat is also helpful. When the cat is cold, front and rear readings will be about the same. As the Cat begins to work, the exit temperature will be higher than the inlet temp. A fully warmed up Cat that is plugged, will have the Inlet temp higher than the outlet. A cat that is not working (but not plugged) will have the temps about the same.

During the (remove plug wire) test, a working cat will have the outlet temp at least 10% (or more) higher than the inlet.

Cat WORKING: I'm using the word WORKING carefully. It does NOT mean that the Cat is good because it is WORKING. The Cat only works when there are sufficient unburned HCs to make it work. If the exhaust a/f ratio is close to perfect, the Cat isn't actually "WORKING" at that moment. During the test, we force it to work. I hope this is clear, if not let me know & I'll try to be more specific.


If you got this far, here's a little fun challenge for the better techs. It's a two part question I often use to quickly assess the skills of a tech I'm meeting for the first time.

SCENARIO: I have a perfectly running car in my bay. It's fully warmed up and I have my scan tool attached, monitoring the O2. The O2 is working well, toggling between 150 & 850mv. At this point, I remove a spark plug wire and observe the O2 response. Here's the 2 part question.

1 What happens to the O2 reading? Goes rich / lean / defaults to reference? / toggles normally? / other?
2 Why? - If you got #1 right, you should already know the answer WHY.

I'll follow up with the right answer and the why in a few days. Meanwhile if you want to add anything to my list below, feel free.

Did I miss anything here?

Geoff

FUEL PRESSURE/VOLUME/CONDITION TEST RESULTS.
CAT TEMPS - IF AVAILABLE

CTS - COLD START thru FULL WARM
TPS - KOEO @ REST, CONFIRM READINGS thru ENTIRE SWEEP (verrrrrrrrrrrrrrrrrrrry slow) confirm every 1/10th volt increase
O2 - B1 S1 COLD & FULL WARM - TOTAL RANGE HI-LO
B1 S2 COLD & FULL WARM - IDLE & 2,000RPM FOR 30 SECONDS
B1 S1 STFT & LTFT @ idle & 2,000rpm (may need to get them under load later)
MAF - KOEO @ IDLE / 250 RPM INCREMENTS TO 3,500 RPM or A SPECIFIC RPM RELATED ISSUE.
INJ PW - IDLE / 250 RPM INCREMENTS - COMPARE TO MAF