loss of power at 3-4K rpms; stalled out; no codes

[ericinboca]

2004 986S track car; 3.2L

20K+ miles

6 spd

stock motor, stock intake, maxspeed (NHP) primary cats, no software changes

There are several posts dealing with hesitation, but none quite match my symptoms.

There is a complete loss of power when I get below about 3.5 - 4K rpms. There is no CEL, and Durametric shows no codes. Problem is getting worse - meaning it is happening more and more frequently, almost all the time when hot - and by end of track day on Sunday, while trying to keep it moving after experiencing the power problem, the car shut off. (cranked right back up though).

I have to downshift to get the RPMs back up. I think I could replicate the stalling out by not downshifting. In other words, I think I could make it shut down, if, when experiencing the power loss, I just stayed in the throttle - it would drop off and stall out.

It seems I only have this issue when hot - at the end of track session - not while going to the grid when cold - just at the end of a session.

I recently put a new set of primary cats on, but the 02 sensor voltage readings on Durametric are normal, AND I had this problem for the first time before replaced the cats. BUT, the car was not hot when I tested the sensor voltage readings....

Guess I will take a look at MAF, check for vaccum leaks, take a look at the coil packs. Maybe change the plugs since they've never been changed. I also saw some postings about valve timing, but I am not sure how to check this. Or is this a fuel supply thing? Anyone have other ideas or experienced this before?

Edited April 20, 2009 by ericinboca

[ericinboca]

I have some data on the pre-cat 02 sensors.

I let the car warm at idle, then for each of these, you are looking at the pre-cat 02 sensors, starting at idle, and then run up over 5000 rpms, and then reved a few times, and then back to idle.

I do not know what the specs should be.

PDFs are voltage, sensor period and resistance. Voltage seems normal, but that is a guess. Resitance seems weird. Anyone see any problems here?

resistance.pdf

sensor_period.pdf

voltage.pdf

[ericinboca]

Bump and an update.

On the bump -

I'm still hoping someone can tell me by looking at the pre-cat O2 sensor data, if I have a bad sensor or two.

But in the meantime, I have pulled all the plugs - they looked fine - I replaced them since I had done all the work anyway. The coil packs also look fine; no corrosion, connectors were tight.

I also pulled the MAF. It was perfectly clean.

Idle is fine, so, while I haven't looked for vacuum leaks, it seems unlikely.

Anyone hazard an interpretation of the O2 sensor data or have a theory???

Edited April 21, 2009 by ericinboca

[Topless]

Bump and an update.

On the bump -

I'm still hoping someone can tell me by looking at the pre-cat O2 sensor data, if I have a bad sensor or two.

But in the meantime, I have pulled all the plugs - they looked fine - I replaced them since I had done all the work anyway. The coil packs also look fine; no corrosion, connectors were tight.

I also pulled the MAF. It was perfectly clean.

Idle is fine, so, while I haven't looked for vacuum leaks, it seems unlikely.

Anyone hazard an interpretation of the O2 sensor data or have a theory???

Just some thoughts:

The DME is pretty sensitive to mixture and timing. If it were a mixture or sensor problem you would surely get a CEL and error codes. Is it burning oil? Any oil in the coolant? Does it only happen in gear or in neutral also? It sounds more like something is binding when fully heated up. I used to do some motorcycle racing and my track bike would sometimes act like this when it was due for a rebuild. Rings, bearings, CV joints come to mind. Hopefully something simple. Good luck and let us know what you find.

[rprieto]

Bump and an update.

On the bump -

I'm still hoping someone can tell me by looking at the pre-cat O2 sensor data, if I have a bad sensor or two.

But in the meantime, I have pulled all the plugs - they looked fine - I replaced them since I had done all the work anyway. The coil packs also look fine; no corrosion, connectors were tight.

I also pulled the MAF. It was perfectly clean.

Idle is fine, so, while I haven't looked for vacuum leaks, it seems unlikely.

Anyone hazard an interpretation of the O2 sensor data or have a theory???

Have you any MAF data?

[ericinboca]

Bump and an update.

On the bump -

I'm still hoping someone can tell me by looking at the pre-cat O2 sensor data, if I have a bad sensor or two.

But in the meantime, I have pulled all the plugs - they looked fine - I replaced them since I had done all the work anyway. The coil packs also look fine; no corrosion, connectors were tight.

I also pulled the MAF. It was perfectly clean.

Idle is fine, so, while I haven't looked for vacuum leaks, it seems unlikely.

Anyone hazard an interpretation of the O2 sensor data or have a theory???

Just some thoughts:

The DME is pretty sensitive to mixture and timing. If it were a mixture or sensor problem you would surely get a CEL and error codes. Is it burning oil? Any oil in the coolant? Does it only happen in gear or in neutral also? It sounds more like something is binding when fully heated up. I used to do some motorcycle racing and my track bike would sometimes act like this when it was due for a rebuild. Rings, bearings, CV joints come to mind. Hopefully something simple. Good luck and let us know what you find.

No oil in coolant, or vice versa. No oil being burned. Don't know about the Q on neutral versus in gear. It has only happened in gear when I have slowed on track for something like an all black or the cool down lap.

If I am due for a rebuild, wouldn't the wear have shown up in my oil analysis? It is coming back spotless time after time. And I just had an analysis. He said it was perfect.

Rear CVs sound fine - I haven't taken them apart - just put my stethoscope on them.

[ericinboca]

Bump and an update.

On the bump -

I'm still hoping someone can tell me by looking at the pre-cat O2 sensor data, if I have a bad sensor or two.

But in the meantime, I have pulled all the plugs - they looked fine - I replaced them since I had done all the work anyway. The coil packs also look fine; no corrosion, connectors were tight.

I also pulled the MAF. It was perfectly clean.

Idle is fine, so, while I haven't looked for vacuum leaks, it seems unlikely.

Anyone hazard an interpretation of the O2 sensor data or have a theory???

Have you any MAF data?

Once I get it back together tomorrow or Thursday, I will gather some data on the MAF and post.

[Topless]

Don't know about the Q on neutral versus in gear.

Just a process of elimination. If it runs lousy or stalls when hot and in neutral this would eliminate other drivetrain issues and isolate the problem to the motor. If it only runs lousy and tends to stall at low rpms when hot and in gear I would look at the drivetrain. Does the car coast in neutral freely when hot? Sometimes a bearing will bind up when hot without making much noise.

[ericinboca]

Don't know about the Q on neutral versus in gear.

Just a process of elimination. If it runs lousy or stalls when hot and in neutral this would eliminate other drivetrain issues and isolate the problem to the motor. If it only runs lousy and tends to stall at low rpms when hot and in gear I would look at the drivetrain. Does the car coast in neutral freely when hot? Sometimes a bearing will bind up when hot without making much noise.

Yes, the car does coast freely in neutral. I've also checked the front and rear wheel bearings.

I have thought about the clutch, but can't figure out why a clutch would slip only in that power range and only at the end of a session - all other times, the car runs flawlessly, and I am flogging it - no hesitations, no loss of power, no feelings of clutch slip, no strange sounds - nothing - until I let off for a cool down lap.

I have trouble describing the issue. I'm going to look at my video from this weekend - maybe I will get lucky have have it on tape with sound and tach signal.

[ericinboca]

I have trouble describing the issue. I'm going to look at my video from this weekend - maybe I will get lucky have have it on tape with sound and tach signal.

This is of dubious value because it does not have data with it (I guess I forgot to turn on traqmate), but here is some video.

http://videos.streetfire.net/video/stalls_648185.htm

First, some context.

This particular clip is my last lap on my second day at Sebring last weekend. When I experienced my issue, I had run 50 minutes solid in this session - and the car, up to this point in this session, was flawless.

At the beginning of the "power loss" clip, you see me approaching turn 13. I rev match down to second, turn in, and then you see me wave the customary thanks and goodbye to the corner worker. Right after the wave, I upshift to third, and then see a GT3 coming through 13 still running hot laps, so I let off the throttle a lot to let him get easily by me.

Revs drop, I think down to around 3000. I start getting back in the throttle and nothing happens – no power. I wish I knew this for sure, but my recollection is, as I was mashing the gas to go, the revs were not really going up, or if they were, way too little for the throttle I was giving it.

I drop down to second, and off we go.

I keep the revs up all the way to the end of the backstretch in third. Then at about the 1:08 mark, I drop it into neutral to coast through turn 17 and on in to the pits. At about 1:19 or so, it just dies - shuts off.

As I pull into the pits, you can see me reach for the ignition, and it refires no problem.

This is the first time it has stalled out on me like this, but I had the power loss earlier in the day on a cool down lap on Sunday and a couple of times on cool down on Saturday. I also had the issue at Homestead in early March - same deal, on a cool down lap.

( Here's a video of it running hard with no problems - one gratuitous lap for anyone that cares here :D

http://videos.streetfire.net/video/986S-at...ring_647711.htm )

[Topless]

Eric,

Very strange indeed. We can eliminate drivetrain issues and focus on the motor. If the DME is working properly it would be throwing error codes for fuel mixture, timing or throttle body issues. Low fuel pressure would be more noticeable at high rpms than low. Internal mechanical binding when hot is still possible, faulty DME, what else are we missing?

[ericinboca]

Eric,

Very strange indeed. We can eliminate drivetrain issues and focus on the motor. If the DME is working properly it would be throwing error codes for fuel mixture, timing or throttle body issues. Low fuel pressure would be more noticeable at high rpms than low. Internal mechanical binding when hot is still possible, faulty DME, what else are we missing?

There are some posts talking about variocam and hesitation in this RPM range...but I am completely clueless when it comes to this.

I know we should get codes if there is an o2 sensor or MAF sensor problem, and we didn't...but it is acting like it has its mixture all messed up or fuel delivery is out of whack. Later today, after work quits interfering with life :D , I will gather whatever MAF data I can get through Durametric and post it.

But if the DME is the problem itself, it may not show anything. And what's more, if it is only doing it at the end of a long track session, I cannot replicate it in my home garage.

I'm getting desperate, plus I am kind of a nut about being sure everything is in top running order, so I am going to go ahead and install two new o2 sensors. I am also going to get a new MAF, but hold it out for now.

I go back to Sebring May 1 & 2. If I don't have the issue during the weekend, then maybe I can assume it was some sort of strange issues with the o2 sensors. If I get the problem with the new o2 sensors, then I will replace the MAF and see what happens. Not fond of trial and error diagnostics, but without codes, I'm unsure of what else to do.

[Topless]

I understand your frustration. I considered variocam timing also but if that were the issue you should get error codes as well. No clear indication of failure yet. The problem may need to get worse before the source becomes clear. Swapping sensors is a bit of a shot in the dark at this point but you might get lucky.

[RFM]

I have not the attention to give you more doubts, but under some conditions, low on fuel and the pump on full flow/ full throttle during a longer period of time, the pump will run too hot with temporary flow reduction as result. It's just a thought.

[ericinboca]

I have not the attention to give you more doubts, but under some conditions, low on fuel and the pump on full flow/ full throttle during a longer period of time, the pump will run too hot with temporary flow reduction as result. It's just a thought.

It is an intersting thought. I appreciate the ideas.

I wondered about the fuel pump too, and wonder if I am only experiencing this when low on fuel. I don't know for sure about the fuel level when this is occuring, and will pay attention. In the video where it stalls, that is after 50 minutes of hard running, after starting with a full tank - it would have been down to 1/4 when I quit and had the problem.

[ericinboca]

I understand your frustration. I considered variocam timing also but if that were the issue you should get error codes as well. No clear indication of failure yet. The problem may need to get worse before the source becomes clear. Swapping sensors is a bit of a shot in the dark at this point but you might get lucky.

Durametric I think gives some cam data - I will see what I can gather there too.

I think you are right - i will probably just have to keep going and hope a code comes up.

Part of the reason for changing the sensors is ease, but also some twisted notion of doing what I can. While it seems unlikely, I don't want this thing stalling out on me on exit when I need the torque to keep the backend planted. If I crunched the rear end, I would be kicking myself for not following my gut, eventhough there is no data to back it up.

[mikefocke]

Isn't there a flap that directs air from under the body to cool the fuel pump? Take a peak under there and see if all is well.

[Loren]

Isn't there a flap that directs air from under the body to cool the fuel pump? Take a peak under there and see if all is well.

The fuel pump is in the fuel tank and is submerged during normal operation.

Could be water or other contaminate in the fuel too.

[ericinboca]

I put in two new 02 sensors, as mentioned previously for purely emotional reasons.

I got codes. Pre-cat sensor drivers side, faulty circuit.

According to the DME manual, I:

* checked the heater wire resistance on the sensor and it is within spec

* checked voltage supply to the plug heater wires, and it is within spec

* checked reference voltage between pins 3 & 4 on jack; in spec

* checked the resistance from DME connector II pin 10 and sensor jack pin 3; in spec

* checked the resistance from DME connector II pin 16 and senor jack pin 4; in spec

The manual says to check reference voltage on DME control module using a 134-pin test adapter No 9637. Is there a way to check this without the pin adapter? Or can I get this adapter somewhere?

Using Durametric, I see the voltage staying steady rather than fluctuating. I don't think it is the sensor, because same happens no matter what sensor I put in.

[ericinboca]

I put in two new 02 sensors, as mentioned previously for purely emotional reasons.

I got codes. Pre-cat sensor drivers side, faulty circuit.

According to the DME manual, I:

* checked the heater wire resistance on the sensor and it is within spec

* checked voltage supply to the plug heater wires, and it is within spec

* checked reference voltage between pins 3 & 4 on jack; in spec

* checked the resistance from DME connector II pin 10 and sensor jack pin 3; in spec

* checked the resistance from DME connector II pin 16 and senor jack pin 4; in spec

The manual says to check reference voltage on DME control module using a 134-pin test adapter No 9637. Is there a way to check this without the pin adapter? Or can I get this adapter somewhere?

Using Durametric, I see the voltage staying steady rather than fluctuating. I don't think it is the sensor, because same happens no matter what sensor I put in.

I put it back together and drove it some. Once on the road, the voltage began fluctuating on the prblem side, however, not to the same low point that the other side dropped to.

I'm lost.

[ericinboca]

Update

If I let the car idle, I can see the voltage on the 02 sensor in bank 2 is not fluctuating. If I let it idle long enough, I get 02 sensor codes. If I let it go a really long time at idle, i can get a check engine light.

If I start it up, let it idle for a short time, and then rev the motor up and down, the voltage does fluctuate, not through its normal range, but close. It will dip to .2, while on bank 1, it will dip to .1.

Weird thing is I get this problem no matter what 02 sensor I use in bank 2. Further, I have done the diagnostics in the PST2 diagnostic manual except for checking the voltage out of the DME. The manual calls for a pin out box, which I don't have. But, I do get the proper 450mV at the plug, so that would mean I am getting the right voltage out of the DME.

I find it very hard to believe, but doesn't this point to a faulty DME?? Isn't it the DME that fluctuates the voltage? Could I run a separate wire from the proper pin on the DME straight to the plug, bypassing the existing wire from the DME to the plug to see if there is something grounding it out or weird like that?

Now, based on the discovery above, here is my working theory as to what is happening to me on the track during cool down.

On the track I am constantly up and down in revs. Accelerating hard, rev matching to down shift - rarely if ever, except on a cool down lap, maintianing a constant RPM. As long as the revs are rising, the 02 sensors fluctuates nearly correct, and does not trigger a code. If I stop revving, just maintaining, the voltage becomes stagnant and the DME messes up the fuel/air ratio, and it cannot accelerate and at worst, chokes out.

Anyone buy any of this????

[Topless]

Eric,

It looks like you are getting closer. Narrowed down to a failed DME, failed sensor harness on bank 2 or a mechanical problem in bank 2. When you get a CEL, what codes are you getting? If you get codes on bank 2 only that would eliminate the "DME rich mixture theory" as the mixture would affect both banks equally.

Depending on the codes you get I would look hard at the connectors and contact points between the bank 2 sensors and the DME. You may have a connector making poor contact but functioning until it gets hot. The connector expands a little and then sensor voltage fluctuates.

Edited April 30, 2009 by Topless

[ericinboca]

"When you get a CEL, what codes are you getting?"

Two faults show up.

P0050

H02S Heater Control Circuit

* resistance of 02 sensor heating too high

* open circuit

* 02 sensor faulty

* DME control module faulty

For this fault, I can get through all the diagnostic steps without finding anything wrong. Once step in this diagnosis does call for a pin adapter to check the resistance between the DME and the plug - i checked this without the pin adapter and think it was accurate. I just got into the little module connector at the DME and isolated the right pin, and checked resistance - it was within specs. (I think the pin adapters are just conveniant ways to isolate the pins????)

P0154

02 Sensor Circuit No Activity Detected

* loose contact in connector

* open circuit in 02 sensor wire

* open circuit in 02 sensor ground wire

* 02 sensor faulty (also heating)

* DME control module faulty

I also get through all the diagnostic steps without finding anything wrong. One step in this diagnostic also calls for the 134 pin adapter to check the reference voltage coming out of the DME. You do this diagnostic if you do not get the proper related voltage at the connector, which I did. So, I haven't actually checked the voltage at the pin on the DME, but it should be fine as the end of the wire shows the right voltage.

So, in other words, I cannot find a reason for the faults, unless I have four bad 02 sensors, since I get the same faults no matter which of the sensors I use - the originals or two brand new ones. Or, the DME is bad.

"If you get codes on bank 2 only that would eliminate the "DME rich mixture theory" as the mixture would affect both banks equally."

The faults say for bank 2, not for bank 1. I don't understand how the mixture is set and delivered to know why a sensor failure in only one bank eliminates my theory. I assume the mixture determined by the DME is the same for all cylinders. If it is messing up the mixture because it is getting the wrong signal from the bank two sensor, wouldn't that incorrect mixture effect both sides? and, if that were the case, would I get a mixture code? (grasping at straws)

"Depending on the codes you get I would look hard at the connectors and contact points between the bank 2 sensors and the DME. "

I haven't taken the air distributor off to confirm this, but it looks like the wiring from the DME to the sensor plug connectors is one piece - no connectors, except for the plug for the sensor.

Contact points - you mean anywhere the bundle, and the strands as they split off and get smaller, touch anything? That's gonna be fun ;) If it is a connection problem, the most likely culprit would be the plug. But I cannot find any wrong at the plug - I get the right resistance, find the wiring to be continuous, find the right voltages, etc.

In the spirit of let's see what else happens, I loaded it on the trailer today, and head for Sebring tomorrow afternoon. I'll be on track Saturday and Sunday and will advise.

I'll keep an eye on the codes, will run some sessions to almost out of gas to see if that effects anything (recall RFM said sometimes a hot fuel pump and low fuel can be problematic) and I will try to do a better job of gathering data so I can better explain what is happening. Hopefully pull a tach signal to overlay on the video so we can see how it behaves.

Thanks for the help.

Edited May 1, 2009 by ericinboca

[Topless]

Eric,

Good news! I think you have isolated the problem:

Intermittent contact between bank 2 O2 sensors and the DME. Your error codes point to this as well. This makes sense now. Your car runs fine until things heat up and get rattled around. When you back off the throttle something shifts, contacts are broken and the DME says WTF?? and your car stumbles. Reinspect the wiring and connectors between the two. Cheap and easy fix.

Possibilities:

1 Frayed wires to ground

2. Rats chewed wiring

3. faulty intermittent connector end

4. cold solder joint within the DME

Regarding mixture issues... Yes. Basic A/F mixture is set globally. Not independently for each bank or cylinder. The DME then fine trims each bank based on O2 sensor values. If the DME or MAF was sending your mixture out of spec you would get trim codes on both banks: 1123/1125 or 1128/1130. Since you have not seen these on both banks your basic mixture should be A-OK.

Good luck and good hunting.

Edited May 1, 2009 by Topless

[ericinboca]

More to chew on...

After the only session today I ran flag to flag, a 30 minute session, during the cool down lap, I shifted up to third after a corner, and was maintaining throttle at 4200 RPMs. The car started slowing and i could hear the engine dropping down in revs. I simply held my foot still - no increase in throttle, no letting off. You could see the needle on the tach slowly making its way lower and lower. I gave it some gas - nothing, so I clutched and revved match down to second, and it took off.

It did it again when I was on maintenace throttle on the backstretch before the pits. Seems to do regardless of the gear.

No check engine light. It did have the P0050 code. Once in my garage stall, I refired it before it had a chance to cool down, and interestingly, the voltage fluctuations in both banks were stagnant - whereas when it is cold, only bank 2 is stagnant. Also, on this particualr time, they were stagnant at .7 volts, rather than when cold, bank 2 hangs around at .4. When I revved it, they both started fluctuating.

Will see what else it does Sunday.