Series 2 L67 Laking Power *Data Vid Added*

[charliemax]

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

Finally. Can you pick up a freeze frame on your scantool?

The DTC is telling you either the harness/connector to the back O2 sensor, has a short or open. OR .. the heating unit is putting up too much resistance.

Didn't you just have the DP and cat replaced? If you did, they had to be working right on top of that O2 sensor and its harness.


edit1,2: I can type, I just can't spell...er... I mean....
edit3,4: Congratulations.... out of 17,201 problem threads for '92-'99s, you just threw a DTC which has appeared 5 times. And that's all the way back to 2002.
edit5: It has never come alone, and is usually accompanied by an EVAP Purge DTC, as a history record.
edit6: see edit 1.

[l67poweredlss]

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?)

It is my DD, so fresh fuel is put in weekly. It was stored over the summer and had stabilizer. Car starts, idles, and runs very smooth. I'm in Minnesota @ 1000ft and run top tier 91oct.

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.

I thought the fuel trims were an indicator of fuel pressure? If not, how can I test this? I replaced the fuel filter after storage as well as a rusted fuel line.

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

This I don't know. It should be that same as a 97-99 SSEi. The fuel pump is 5 years old, replaced under warranty when I bought the car. Even on the dying pump it ran perfect till it just died.

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.

I'll get TPS data tomorrow and make a video.

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.

Cleaned both the MAF and sprayed the MAF screen. The sensor I sprayed with MAF cleaner, the MAF screen with TB cleaner. The screen was not dirty but it was rusty and when I sprayed it orange came flowing out.

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.

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.

[geofffinlay]

I'll try to address your reply to this point.

1/ Your current outside temperature in Minne is -10c / or 14f. The air is hugely denser than it was in the summer. The amount/quality of fuel you're getting through your injectors is critical to proper operation. With this in mind, add Air Intake Temperature to the important scan data you need to verify as correct. Basically, it should be the same as ambient & coolant when you turn the ignition on - before starting it up, then APPROX underhood temp fully warmed up.

2/ To test fuel pressure, you need a proper fuel pressure gauge, with an Auxiliary Bleed Hose to check flow/delivery of the fuel. You can likely buy what you need from Harbour Freight or similar. You cannot bypass these tests, they are crucial towards a diagnosis.

Somewhere on the car there is a Fuel Pump Test/Prime port, where you can supply B+ to the pump to do the tests. You can also locate the pump relay and bypass it. A good scan tool has this capability too.

Someone on this site knows your car better than me and should be able to tell you where the test port is, as well as the fuel pressure specs.

You need to know the rest pressure, running pressure, dead-head pressure and flow values. Dead-Head refers to plugging the fuel return line to compare against running pressure (essential reserve under load). GENERALLY Dead-Head will be about double running pressure. That's going to get in the 80-100psi range so be aware going in.

It's quite possible to have all those values in spec, but a partially plugged system (filter? etc) can still prevent proper flow, so be sure to confirm it's OK.

2A - FUEL TRIMS. There are 3 kinds of data shown on a scan tool, they are: Inputs, Commands and PCM Calculations. CTS, TPS etc are Inputs. Inj PWM, EGR on/off/%, Ign Timing etc are Commands. Fuel Trims are Calculations that the PCM is making, based on all other results and conditions.

My original BASIC seminar on these rolls is a 2-day course. I'll try for the Reader's Digest version. CAPS are for emphasis, I'm not yelling

It's worth understanding that the PCM can issue a number of commands that you can read on a scan tool. That doesn't mean that the command IS PHYSICALLY HAPPENING.

If your car is running PERFECTLY, and air/fuel ratios are averaging around 14.7/1, there are no adjustments to make. The PCM will tell us what the calculations/adjustments are via its Fuel Trims, as a % of available fuel. As you drive the vehicle, fuel requirements change. The PCM needs to supply more fuel (longer injector ON time/richer - PWM) - for more load.

When fuel is being added (vehicle under load), the PCM reports an increase in fuel supply by showing it's increasing the injector ON time by xxx%. This could read as ST FT 5% or greater ( a positive figure as it's adding fuel)

The PCM's MAIN JOB is to protect the Cat by constantly checking the average a/f ratio via the oxygen sensor/s. This function is reflected in LTFT. GENERALLY, a good LTFT stays in about a 10% range +/-5%. This is just a rule of thumb, not a spec.

If the fuel pressure or delivery (volume) drops off due to a problem with the pump, filter, lines, regulator etc the engine will receive less fuel. As a result the O2/s will report a bias towards lean to the PCM. This bias affects the LTFT trim, because it is lowering the average a/f ratio. The PCM responds by adding more time to the fuel injector's ON time, and reports it by showing an appropriate increase in the LTFT.

You could say that a high LTFT is an indicator of a fuel pressure problem, but this ignores what a small vacuum leak would do to the LTFT. Of course it's going to do approximately the same.

3 PWM Fuel Pump: A number of 3800s used a Pulse Width Modulated control on their fuel pumps. The PCM controls the fuel pressure/delivery in the exact same way as it controls the Fuel Injectors. Again, I'd ask this group for a list of these applications.

4 You're going to get the TPS values tomorrow and make a video. Any particular reason for that? What about the rest of the info we need?

5 I have no idea what the orange material was and I don't care to guess. We need some proper readings from that MAF, that are presented with RPM through the whole RPM range. You don't need to be driving around to get that information.

6 There are a number of possible reasons why the fuel trims are not displaying expected values. They all come back to the PCM not being capable of displaying correct values. This is NOT to say that the PCM itself has a problem, it probably doesn't. What we do know is that it needs ALL of the Inputs working and reporting withing a predetermined, acceptable, expected range.

During WOT, your vehicle goes into Open Loop and a number of values are preset and not controlled by the PCM's algorithm tables. The only thing of interest to me in WOT is TPS B1 S1O2 and Inj PW.

You need to go through the same processes as a professional diagnostic technician to find the problem/s. Based on the total information you have posted to this point, not even god can tell you what the problem/s are.

Why don't you take a look at the information you're supposed to be getting and create a schedule for us when we can expect to get the results? DON'T FORGET TO CHECK INTAKE AIR TEMPERATURE!

Geoff

[1fatcat]

I like this guy!

[Archon]

Looking at the test description for the fuel pump indicates that the 97 LSS does use PWM for the fuel pump. The numbers correspond with the steps in the diagnostic table.

4. Ensures that the fuel pump speed control PWM circuit and the PCM are capable of controlling fuel pump speed.
8. Ensures that the fuel pump speed control PWM circuit is not shorted to ground.
31. Ensures that the fuel pump speed control PWM circuit is OK and that the PCM can control the fuel pump speed control circuit. Using the scan tool to command the FP Speed allows only a 2 second time in the commanded state.

[charliemax]

=============================================================================
DTC P0141

Heated oxygen sensors are used to minimize the amount of time required for closed loop fuel control operation and to allow accurate catalyst monitoring. The oxygen sensor heater greatly decreases the amount of time required for fuel control sensor HO2S1 to become active. The oxygen sensor heater is required by catalyst monitor sensor HO2S2 to maintain a sufficiently high temperature. This allows accurate exhaust oxygen content readings further from the engine.

Diagnostic Aids

1)Poor connections at the PCM or the HO2S.

2)Damaged harness.

=============================================================================

The reason I asked for the freeze frame was to see if you were Closed Loop or not. Plus pick up stats from the IAT, ECT, MAF, and HO2S2 sensors. I have been using my '98 FSM Diagnostic diagram. When you have no other DTCs,.... IF the Powertrain Diagnostic System Check was performed (we can't know that without a Tech II) then you check the connections and take connector readings for the Diagnostics as noted above. According to the FSM, there is nothing else pertinent to the solution, and you can see the relationship between OS2 and OS1 in the description.

Now, with that in mind, I went back through the other post to confirm that you had a DP and Cat put on your car. That means that the exhaust shop was welding within inches of the OS1 and OS2. Let's cast frivolous doubt to the wind, and say they were smart enough to remove OS1 and OS2 before they put a couple of thousand degrees on metal which could conduct the heat to these important sensors . That still leaves the possibility that the bunghole and the OS2 didn't work out well together, or they damaged or poorly connected the harness to OS2.

From my simpleminded perspective, the presenting symptoms are still the O2 sensors, with a secondary nod at the PCM (deferred for now). With the DTC telling you that you have a bad OS2 sensor, which can impede activation of OS1, and you are not going to get the car past an emissions test (at least in PA) with that OS2 sensor.

My first reaction would be to take it back to the shop, and have them figure out what they did. They are the best source because they know how they did the work and can retrace their steps. As an exhaust shop, they likely can fairly quickly check the sensors, as they work around them all of the time.

But, hey, that's me. I have this silly thing for smoking gun DTCs.

BTW, IMHO, O2 sensors which are 14 years old, are up way past their bedtime, for any hopes of optimum performance.

Let us know.

[1fatcat]

BTW, IMHO, O2 sensors which are 14 years old, are up way past their bedtime, for any hopes of optimum performance.

I will definately agree with that! I know they are spendy and CAN be very hard to replace, but O2 sensors do wear out, much like a spark plug.
And FYI, fuel pressure for your car should be 48-55 psi key on, engine off. And NO LESS than 45 at WOT.

[geofffinlay]

Hey, 1fatcat, Archon & charliemax,
Thanks for chiming in. I don't want to be the only source here. You guys drive these cars and fix them.

Aside from the L67 I'm working on for my Lotus, I last had a '92 SSEi, which I bought new and had for 4 years. It was easily the best all round (big) car I ever had. The highlight was having 4 teenagers from my kid's baseball team in the car & sneaking it up to a smidge over 200kph for a couple of seconds and seeing the silly grins. BTW it was a 6-lane hwy @ 6am on a Sunday going to a tournament; no traffic for miles.

I don't believe I can know each model as well as you, but I know a little about EFI and the bits and pieces that make it work. I'll never criticize anyone for inputting sensible information or asking for a clearer explanation. I will however try to provide factual information that leads towards a fix and maybe preventing the need for a fix down the road.

While waiting for more info, here's a couple of thoughts based on others' input:

A backpressure test is simple to do and can be done via a scan tool and the MAP reading, if the vehicle has one. Of course a simple vacuum gauge is easier to decipher.

The principle is to measure manifold vacuum @ idle (fully warmed up), then raise the rpm to about 2500 for about 2 minutes (steady) and compare the readings.
A free flowing system will result in the 2 readings being very close. If back pressure is developing, that will prevent the vacuum reading from coming up to a similar reading. The more backpressure, the bigger the difference.

Typically, vacuum @ idle (healthy engine) will be around 18" & steady. As the rpm is increased, vacuum will naturally drop away, and gradually come back to about the same reading (usually a little lower) as @ idle. Anything more than a couple of inches difference should be looked at closer.

If a standard MAP reading is about 1.5v @ idle, lower vacuum will show a higher reading. A full volt higher could represent a considerable loss of vacuum, indicating a possible problem. You can also prove the test by CAREFULLY-IT'S HOT THERE plugging the TPs with something appropriate momentarily.

Note that some Turbo/SC MAPs may not be linear. They may read from 0"/2.5v up & down indicating pressure & vacuum. I don't know what MAP equipped 3800 SCs use, if they use a MAP at all in any of the applications.

As for this vehicle's rear O2 code, I agree that it's something to keep in mind, but it's absolutely not creating the drivability issue. If you have access to a good scan tool (Tech 2 is obviously the ultimate for GM) that can display Mode #6 (OBDII) test information, you will see this particular condition (O2 Heater malfunction) frequently stored without issuing a trouble code.

I can't go too far into this as it's too long & detailed for this format. Here's a few simple facts: Less than 50% of professional technicians even know that Mode #6 exists or what it's for. Most only know that "drive cycles" exist and VERY FEW can actually quote what a drive cycle is and how many types of "drive cycles" there are and what they're for. OBDII systems have a number (usually 8 or 9) of Monitors that check & report the operational condition of every component that is involved in any way with emissions (even transmission shift solenoids are monitored) functions.

This is changing in jurisdictions that have moved to OBDII emissions testing, since a vehicle can fail an emissions test with the Check Engine Light OFF, but more than one Monitor in a NOT READY State. OBDII is not what most think. It is extremely complex, but works relatively well for its purpose. I would urge any of the more serious Members of the site to Google OBDII and get a better understanding of what's involved.

The rear O2 is exactly as you've described, but nobody has provided any actual expected values yet. Here's what the readings should be, ignoring Cold start ops for now. Before the Cat "lights off" the rear sensor will reflect what it sees at the cat's outlet. Some manufacturers "buffer" the rear O2's signal so it doesn't toggle like the front sensor/s.

From my personal observations on lots of GMs, the rear O2 moves slowly relative to the front. Having said that, I've also observed "blown through" Cats, where it was difficult to tell the front signal from the rear. In MOST cases, the rear O2 will provide a fairly steady voltage both before and after warm up.

If (as is usual) the heated sensor comes to temperature before the cat, the voltage reading will be high (rich), often at or above 1 volt (as read on the scan tool). You can observe the Cat lighting off by monitoring the rear O2 signal and raising the rpm (to get a little heat in there). As the Cat lights (and begins to "work") the O2 voltage will begin to drop.

If you were looking at a perfectly healthy Cat and a new O2, you'll see it settle around 200mv. Observed on an oscilloscope, it will be almost perfectly steady. Since it takes very little unburned HCs, a really good Cat, will stay lit and the rear O2 will stay low, around that same 200mv level.

The only reasons for it to move from there, are changes to the exit gasses. Both HCs and Oxygen are very low at this point in a healthy system. Oxygen will be less than 1% and HCs can be as little as 0.00%.

Extended idling may allow the cat to cool off and so HCs may rise, causing the rear O2 reading to rise. This is determined by the quality and content of the Cat. It's one of the main reasons that the EPA doesn't like aftermarket Cats. Even the big-name aftermarket Cats have this problem. To test the case, if you have an aftermarket Cat, just monitor the Cat/O2 relationship after a warm up test drive, then, drop it in Park and watch the rear O2 reading.

You may even find that your new, aftermarket Cat is working fine (low volts) when you park, then 30 seconds later the O2 rises to 900mv, then 30 seconds later, drops back to 200mv. The cat's ability to absorb oxygen is limited and so it stops working (voltage up). HCs rise when the Cat stops working and at a critical point the excess HCs cause the Cat to "lite up" again (voltage down). Again, viewing this on an oscilloscope is instructional. It appears as a giant, long term square wave. By the way, this condition is monitored and may be stored in the Mode #6 information of the OBDII system.

Did you ever wonder why GM OE Cats are so big? It's related to the type of fuel programming they use (across the model spectrum), to control NOx & high HCs. My personal opinion is that aftermarket Cats, don't always work on GM V6 engines as a Cat is intended to work.

By the way, at some point we may find the above info useful to diagnose this drivability issue. Anyone care to comment on how it could be used?

I hope this stuff is of interest and useful to all involved.

Geoff

[l67poweredlss]

Here is a video of my MAP in kPa, MAF, rpm, and TP. Tested fuel pressure today and it was between 48- 55 psi. Had a 3-10 psi drop when running

http://www.youtube.com/watch?v=lUJemuN3W3Q

[charliemax]

Here is a video of my MAP in kPa, MAF, rpm, and TP. Tested fuel pressure today and it was between 48- 55 psi. Had a 3-10 psi drop when running

http://www.youtube.com/watch?v=lUJemuN3W3Q

l67poweredlss and Geoff,...

My wife is going to smack me. I'm on staycation this week and supposed to be working on items on her Honey-Do list. But this is such a rare problem I can't resist.

Anyway...

I'm looking at the video and this is what I see. I'm freezing at these points in the vid,... 6 sec, 11, 12 ,13 secs.

I'm using the 6 sec as the base, as that is 50% throttle. Look at the Pascal units reading on the MAP, it's at 100kPa. Now look at the application of full throttle at 11 and 12 secs. It has barely generated 10% more absolute manifold pressure.

I realize that increments of pressure are a function, not linear. But this seemed like a distortion. This is why...

(Very late last night), When I put my car ('98 SSEi) at 50% throttle my dash Boost gauge (the second MAP sensor, there are 2 on a Series II L67) reads at 0. Which is the borderline between "normal" induction and application of available units of Boost. At that point, my crappy old scantool reads (about) 30 inches of mercury (inHG).

Then I nail it, which pushes my Boost gauge towards redline. The scantool MAP reading pushes through the 40s and hits over 50 before the cop's lights come on behind me. So best I know is that my full pressured MAP is in the mid 50s (inHG). How 'bout some conversions... (I'm just going to use the pressure at 0* C. The temp doesn't make a substantial difference, when we are looking for macro trends)

Half throttle
30 inHG = 101 kPa
(video @100 kPa)

WOT
53 inHG = 179 kPa
(video @110 kpa)

If you'd like, I have several thesis which take into account the new DP and Cat, the MAP sensors, the O2 sensors (with one failed), and the ZZP PCM. Yes, the ZZP PCM. At WOT, the PCM should be reading the voltage off of the MAP sensor, which looks to be too low for the TPS absolute position, and should be throwing a P0107. But it is not, and i may have the answer based on an obscure post by wilwren back in 2007. It isn't necessarily the cause, but may be hiding what would have been the primary symptom for the problem-solving process.

Let me know. I have to go look like I have been cleaning out the basement.

[1fatcat]

Did this happen ever since the car was taken out of storage?

[geofffinlay]

Hi Gents,
From what we have at this point, a couple of things can be established. Vacuum/MAP @ idle appear to be in the right place. I think it's safe to say that 19" of vacuum would be expected.

I'm less than comfy with the MAF format since I've never tried to use it for troubleshooting. Using the RPM reading as an anchor, the MAF appears to be rising pretty much in proportion. Maybe one of you guys can do a quick snapshot and confirm that those readings are OK.

charliemax, I think your numbers are significant and you're on the right track. MAP kpa basically stops at or above half throttle. Now 100kpa is the equivalent of 0" of vacuum also known as 29.9" of Mercury Absolute (Manifold Absolute Pressure). We'll have to guess (since vacuum @ idle is pretty good) that vacuum has dropped normally with load/open throttle as MAP kpa was rising.

I believe what we should be expecting, is kpa to keep rising as the supercharger begins to pressurize the intake, but we're not seeing that on this car. charliemax, as you point out on your car (below), MAP should be approaching a similar 180kpa / 53 inHG / 26psi (pick whichever you like). Actually that seems a little high to me for an untuned DD, maybe you can confirm that?

Half throttle
30 inHG = 101 kPa
(video @100 kPa)

WOT
53 inHG = 179 kPa
(video @110 kpa)

So at this point, the supercharger doesn't appear to be doing its thing, for whatever reason. We didn't get the exhaust backpressure result yet, but I'm thinking that the MAP wouldn't have settled where it did if there was excessive BP, but I could be wrong. Is it possible we have something as simple as the S/C pressure control misbehaving? It should be worth putting a little pressure into the MAP KOEO and see what it reads on the scan tool, just for giggles.

charliemax, tell your Wife that the idiot Englishman in Canada threw you a challenge you couldn't resist, since you're on the US team! (then duck)

[1fatcat]

So I re-read the first post and the link to the storage thread. Considering it came out of storage, and not a rodent proof storage facility, you should still test the back pressure. Im not sure if you did test it or just threw a cat on, but if the test reads high, then check the back pressure on the outlet end of the cat too. If it is still high on the outlet end, then your muffler is plugged and most likely with rodent nest/food stash. I have seen mufflers filled with nuts, dog food, corn and nest matterial. You would be suprised how much those critters can pack away in a few months.

[l67poweredlss]

I'll have to go to an exhaust shop for the BP test. What am I looking for in this test in terms of numeric values?

[1fatcat]

No more than 2 psi at 2500 rpm, and no more than 5 psi at WOT. If it is plugged though, the gauge will usually show 15 to 25+ psi when the throttle is snapped open.

[charliemax]

If you are going to spend the money at the exhaust shop, have them test the O2 sensors too.

But first, since I finally have the MAF/MAP readings let's take 5 minutes and check the Boost Control Actuator.. It's on the front right of your S/C as look into the bay.



Turn on your car and let it idle, then pull the top vacuum line off the BCA (Boost Control Actuator).

Does the Boost Control Actuator shaft travel in both directions fully when you do this?

If not, turn off the car, and put some light oil in all of the BCA ports and the vacuum lines that feed it. Also on the shaft that extends and retracts, and a little bit on the two pivot points on the front and back of the supercharger for the bypass butterfly valve.

Next without turning on the car, work the BCA shaft in and out (up and down). This will draw in the oil and distribute it, freshening up the seals and lubricating the internals.

Reconnect the vacuum lines.

Ok now turn on the car and try again.

[geofffinlay]

Gentlement,
Sounds like we're going in the right direction. I've nothing to add at this point

Well Done

Geoff

[1fatcat]

If not, turn off the car, and put some light oil in all of the BCA ports and the vacuum lines that feed it.

Oil is not good for vacuum diaphrams. It disolves the diaphram over time. Sewing machine oil would be ok, maybe that is what you ment by "light" oil?

[l67poweredlss]

I suppose wd 40 would be a bad idea?

[1fatcat]

Probably.