05' Elise surging at partial throttle - Page 2 - LotusTalk - The Lotus Cars Community
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post #21 of 50 (permalink) Old 06-04-2018, 01:11 PM Thread Starter
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Is there air in your cooling system? Sometimes that'll make the idle erratic when the pocket of air hits the water pump. I would try bleeding the cooling system before buying more parts you might not need.
Idle is not what I'd describe as erratic - see the data. You have to listen/look very closely to hear it - but it's most felt in the seat of your pants as a very not so subtle surging. I've been driving it for a year w/ no cooling system issue symptoms - including three track days. How subtle/consistent can this be? Also this issue is not tied to engine speed. It does however appear to be tied to the ECU's fuel trim when it's under partial load or idle. Thoughts?

The more I ponder how this problem came to be - it was gradual - but always kind of present during my brief ownership - and eventually culminated in the loud rhythmic popping on decelerations w/ hot exhaust. To me that gives a further nod to an issue somewhere on the fueling side of the fence since this could be a slow degradation of a pump or an injector.

Injectors are out of the car waiting for a friend to test / clean them - or worst case ship them out to a third party. Worst case I'll spend $100-150 to have cleaned injectors with verified flow rates. Regardless of the results though I'll have to make a trip to have the dealer reset my ECU so the old fuel maps can be ruled out as well. Part of me wonders if the aftermarket exhaust could be the cause of this - but the very consistent rhythmic popping situation would have been reported as a known issue w/ the exhaust if that were the case. I know what the fun burble and pops sound like - this is not it.

Any other sensor ideas for what could cause rhythmic surging/rhythmic deceleration pops?

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post #22 of 50 (permalink) Old 06-12-2018, 06:31 AM Thread Starter
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Injectors came back - none of them were too far out of spec. Re-installed with a radium fuel pressure gauge so I had some reading on the fuel pump.

I took the car out for a spin after letting it idle for a bit. Ran it through the entire rev range and up to operating temperature. Started and ran somewhat smoother but the almost identical problem returned, surging under partial throttle. To double check it was functional I did the coasting RPM test and indeed the inertial switch is working. Now the question is - is this an exhaust leak? bad ECU tables for fuel w/ no reset and a higher flowing exhaust? (PO installed). Watching the secondary o2 sensor readings I kind of get the impression my car is running super rich and perhaps at the edge of it's ability to compensate. Whether this be the exhaust alone or in concert with the ECU I cannot say. Anyone else have a larini exhaust?


Before I post the data I wanted to ask. Does anyone have a 2005 DBC Lotus Elise they can collect some warm up, partial throttle, and WOT data on? I'd be interested in the readings from the
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post #23 of 50 (permalink) Old 06-12-2018, 08:15 AM
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i can collect data if you give a very specific instruction set. my car is mostly a garage queen, so i'd not likely get to it until the weekend, though. also, my exhaust is the lotus/janspeed stage 2 one.

i can also help with random ecu stuff too, if you know what you're looking for.
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post #24 of 50 (permalink) Old 06-15-2018, 06:59 AM Thread Starter
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i can collect data if you give a very specific instruction set. my car is mostly a garage queen, so i'd not likely get to it until the weekend, though. also, my exhaust is the lotus/janspeed stage 2 one.

i can also help with random ecu stuff too, if you know what you're looking for.
Obeisance - I'd be interested in seeing how your car performs at 3000-3500rpm after being completely warmed up. That's the scenario which best showcases the 'hunting' or slight 'surging' I feel. I've attached a screen shot of what I see.

In other news I went ahead and checked out the exhaust system. Replaced the large header donut gasket and springs, replaced the small larini exhaust clamp with a larger band w/ sealant in the lap joint, and replaced the heat shielding on the cat w/ a wrap after inspecting welds (old heat shielding was not salvageable after removal). Re-started the car and brought it to operating temperature while hunting for any exhaust leaks. No dice, same behavior returned as seen in the screen shot.

So onto the next culprit: camshafts? Not sure this could cause surging but if the clearances were I suppose the combustion would be incomplete/poor and cause the ECU to hunt? I've attached some pictures of the two worst intake lobes AND one exhaust lobe... see what you guys think... From what I can tell this fits the bill of 'wiping' but it's not astronomically bad. I can feel ridges, but do stock cams have any ridge? This may explain the gradual worsening of these symptoms over my ownership. What was a very minor issue has slowly increased in severity and frequency of appearance. Notably though some of the low speed lobes even appear to have wear - though if oil temps are to blame it could be one of PO's driving habits (aka cold commutes in MI).
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post #25 of 50 (permalink) Old 06-16-2018, 01:17 PM
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I drove for a bit while logging. This was rather calm street and freeway driving, beginning with a cold start. Ambient temperatures today are ~28 C. I tried to hold the engine speed in the 3-4 k range and did not observe the oscillations in engine speed that you had.

I captured enough parameters that the logging resolution was rather poor (about 1 Hz per full cycle). Feel free to look through it and see if the data is useful. Later, I want to compare the rpm oscillations in your data that occurred when there was a step change in evap purge command with what my car does.

https://drive.google.com/file/d/1uR7...ew?usp=sharing

also, you cam lobes don't look much worse than the last time I saw mine a year ago (mine are also slightly worn- they should not have any ridge at the edge of the large cam profile).

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post #26 of 50 (permalink) Old 06-16-2018, 07:09 PM
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There is one behavior in your log that I am fixated upon: I can see a large oscillation in the fuel trim at the same time that there is a step change in commanded evap purge. I have a hypothesis: if evap purge delivers uneven flow or too much fuel vapor, it will be difficult for the car to control fueling leading to a surge in engine speed.

In the datalog I can see some things that are reasonable along this hypothesis: when the evap purge is active, the car will sometimes suddenly use the short term fuel trim to remove fuel and it will close off the evap purge. Both of these behaviors are consistent with your previous post stating an expectation of overly rich operation. I also think that this is consistent with too much/uncontrolled (uneven) fuel vapor delivery via the evap purge system.

When the fuel is removed (both at the injectors via STFT and at the evap tube via command on the valve), the engine speed begins to fall. The car then advances timing in order to catch the idle, leading to a somewhat lean condition with advanced timing-> this causes a surge in engine speed. Is this a reasonable explanation?

The fuel trim then oscillates as the system returns to stabilization, and the car begins opening the evap valve in a process that allows the event to occur again.

On my car, I can also see the short term fuel trim remove fuel at the injectors when the evap purge is initially opened. However, in my case the amount of fuel removed (extent of the trimming action) is not very severe and the car does not need to close the evap valve via command. I also see the STFT stabilize over most steady state conditions. Similarly, the engine speed does not experience a surge, but rather remains closely coupled to throttle position and timing advance (note: my throttle position range is 12-82%, since the OBD parameter returns a value that is not zero-corrected).

Finally, when I go to full open throttle, the car moves to open loop fueling (the STFT and evap purge command go to zero). Thus, it would be unlikely for a fuel delivery problem at the evap canister to manifest during full throttle or during warmup since the evap system and oxygen sensor-based fuel trimming action should be inactive. This is also consistent with your previous post indicating that this event is observed at part throttle and after warmup, and I believe that it is consistent with my hypothesis as well.

I guess that if I wanted to try to troubleshoot this system, I would see if there are partly clogged lines in the evap purge system, or if the carbon canister has a bypass leading to direct fuel vapor coming from the gas tank to the intake. well, I don't actually know how the flow lines are routed through that system.. so much of this is a guess.

Does any of this seem reasonable?
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post #27 of 50 (permalink) Old 06-19-2018, 08:18 AM Thread Starter
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Thank you for the data. What program did you use to graph? I need to do a clean catch of data today. I now realize the data I provided wasn't very clear or more importantly, complete. The software I'm using seems to juke the user into only recording 5 inputs for performance reasons. I'll see if I can collect a more complete picture tonight during a cold start, at least until the second 02 registers the cat coming up to temperature.

Had a friend and former Lotus owner inspect my camshafts - they are not to blame but do appear to be wearing. So we'll file that under future maintenance once I figure out the current problem.

Sprayed three cans of MAF cleaner and a cylinder of propane around my engine bay INCLUDING all of the evap/emissions parts. I have not found any location that will cause a consistent impact. To hedge my bets I've ordered a new MAF and TPS - I will install them prior to the cold start and see what happens - though the outputs from them acceptable...

Compression test: ~220psi across all cylinders
Spark Plugs: normal / clean - checked gap, all are consistent and in spec
Coil packs: no arching or burn spots

All else fails I'm also going to double check the o2 sensor and do a swap w/ my old ones and see if the data is similarly jumpy. Though they should be standard sensors I know some people on here have complained about the latency of some sensors over the denso ones for example.

This is starting to feel more like a fuel pump / FPR / filter issue possibly... that or an exhaust leak. After spraying the engine bay w/ flammable stuff and hearing no consistent tonality changes or stumbling - I really wonder...
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post #28 of 50 (permalink) Old 06-19-2018, 08:23 AM Thread Starter
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Another symptom that occurs is faltering but not stalling at a fast / hard stop. This did occur to me to be a possible brake booster leak... or a fueling problem w/ sloshing something around in the tank...

This data was from a drive home - https://drive.google.com/file/d/1WVD...ew?usp=sharing

Any reason why my 2nd post cat o2 sensor 's fuel trim is consistently high? Flat 99.2...
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post #29 of 50 (permalink) Old 06-19-2018, 08:54 AM
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Thank you for the data. What program did you use to graph?...
i plot my data in Microsoft Excel, and annotate in PowerPoint. I log with: https://github.com/Obeisance/Daft_LotusT4_OBD

The fuel trim reported along with the downstream oxygen sensor voltage is a fill-in placeholder; the number doesn't mean anything and is not used by the ECU for engine controls.

if you are feeling adventurous and are willing to humor me, could you please find a way to temporarily disconnect the evap purge flow from reaching the intake manifold? If there is an uneven flow (due, for instance, to a sticky purge control valve) the car could still be having problems even without a leak to outside air. if the symptoms cease after isolation of the evap system, then the problem can be isolated to be part of that system.

edit: note that disconnecting the evap system will generate a CEL.

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post #30 of 50 (permalink) Old 06-19-2018, 02:50 PM Thread Starter
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TPS was delayed, however I did install a new MAF and do a basic cold start to warm up. Here's the data w/ more inputs being captured:
https://drive.google.com/file/d/1AyE...ew?usp=sharing

I'll isolate the purge system and see if that changes anything.
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post #31 of 50 (permalink) Old 06-19-2018, 03:20 PM Thread Starter
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With the evap system disconnected - problem still persists:
https://drive.google.com/file/d/1fP6...ew?usp=sharing

It's also worth noting I went ahead and shorted the hoses for the PCV so the clamps and nipples are on fresh rubber. Not a guarantee - but wanted to cover anything I could think of which might have worn with age on the periphery... Everything was double checked for leaks afterwards w/ a healthy spray of MAF cleaner.

I notice two vacuum lines go to the front of the car. The large one I'd presume is for the brake booster. The other is a standard very small line... HVAC or a vacuum reservoir? I don't think this would be part of the problem as I'm able to disconnect the main vacuum line from the manifold and the problem still persists... so I'll let go of that fixation for now.

Everything I keep considering should have thrown a check engine light - or should also cause problems with starting... perhaps a struggling fuel pump?
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post #32 of 50 (permalink) Old 06-19-2018, 04:12 PM
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I get surging during cold driveaway in my Lotus (and other EFI vehicles I own). At a steady throttle opening doing 15-20 mph, I'll get an obvious surging condition that causes me to modulate the throttle before it gets so bad that someone notices. I imagine this as a PID loop where the values aren't quite set right.
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post #33 of 50 (permalink) Old 06-20-2018, 03:24 AM
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my hypothesis was wrong, since the problem persists when the evap system is isolated.

I'm not sure that i can help much beyond that; I'm running out of ideas.

I'm having a hard time in some of the logs at picking out the place where the surge in engine speed is happening. in the log from post #30 i can see something subtle in engine speed between 100-200 seconds (with a big stft swing), but I'm not sure that is what you are experiencing. in the log from post #28 and #31, i cannot clearly pick out the surge behavior.

i guess if you're convinced that there is a fuel delivery rate problem, you could try logging the ecu commanded injector pulse length (mode 0x22, pid 0x205). this parameter includes more than just the fuel trim influence on fueling.

further, in case the fuel system is compensating for some inefficiency, and that is causing the surge, then disabling closed loop fueling should remove the surge behavior (and possibly result in the failure that the car was trying to avoid, like stalling). i think that the car can be forced into open loop fueling by disconnecting the upstream O2 sensor.

@Roundabout , i also agree that this seems like some kind of a poorly responding PID, but i do not think that there is an explicitly written PID control on fueling- if i understand correctly the ecu is just trying to get the O2 sensor reading to reach two threshold values alternately by adding look up values without feedback beyond the threshold voltage.
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post #34 of 50 (permalink) Old 06-20-2018, 05:13 AM
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This still feels like an oxygen sensor to me. How does the car behave if you disconnect the upstream sensor?
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post #35 of 50 (permalink) Old 06-20-2018, 03:25 PM
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The O2 sensor connectors can get swapped on the Eliges and not throw a code and exhibit a surging idle along with emissions monitors for catalyst not being set. It's always worth while to check the wire colors to make sure they are not misconnected.

Beyond that, it's important to understand how the car is being driven when the problem occurs because that information can be useful in any calibration scenario to determine what strategy the processor is in at a given time. With the strategy information known, then the sensors in play are known. In different strategies, the proportional contribution each sensor makes to the commanded AFR can be different. If the calibration is trying to warm the engine, the O2 sensor is going to be allowed to go lean when you're in the cold drive-away type of strategy. I have never tuned an Elige, so this information is general in nature. It's also worth knowing that two different tuners can tune the exact same car to the same level of driveability and performance using different scalars, functions and tables in the calibration. That is where the art meets the science of tuning.
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post #36 of 50 (permalink) Old 06-23-2018, 04:37 PM Thread Starter
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I think I should be clear the surging issue is not really reflective in RPM's - it's in the seat of your pants or heard through engine tone changing. So perhaps this term is wrong. It's not so much apparent with engine speed as it's just ping ponging the fuel... so it's as if someone is softly feathering the accelerator pedal making you go mad. Likewise it does not seem to change oscillation based on engine speed.

You can see it in the data under idle but it's far worse 2000-5000 rpms. o2 sensor reading just oscillates as does the STFT.

Past few days I've tried to no avail:
reverted to OEM lead acid battery
isolate evap system
isolate brake booster system
isolated vacuum source from intake manifold
replace tps
replace iac
replace maf
replace pcv
replace throttle body gasket
replace clamps on the throttle body to airbox hose to quality band clamps
felt around for exhaust leaks more
sprayed more maf cleaner around the engine bay

I'll try unplugging the primary o2 sensor and see if it enters closed loop. Just so we're clear the entire project started with the o2 sensor being the culprit and thus they have been replaced AND verified to be correctly connected. So far everything points to the sensor reading correctly as it's mirroring the post cat o2 sensors prior to the catalyst reaching operational temprature. This tells me either I have TWO incorrect sensors, or even more unlikely - two broken sensors to start with then maybe two wrong or defective sensors? Again, two new sensors, behavior persisted. So really the question is - where's the leak?

" you could try logging the ecu commanded injector pulse length (mode 0x22, pid 0x205). this parameter includes more than just the fuel trim influence on fueling." - I don't have fastworks... unless I'm missing something I can't get that via my pretty basic obdII reader (BlueDriver).
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post #37 of 50 (permalink) Old 06-24-2018, 06:06 AM Thread Starter
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Disconnected the primary o2 sensor and the audible and digital artifacts disappeared. The STFT went steady and of course the primary o2 sensor was silent. So we can narrow it down to that loop and interactions with it...

My real question is - does this rule out the fuel pump / regulator / filter in the tank? That has been a source of possible issues in the back of my mind, but if the car can seemingly keep fuel steady flying blind on a safe fat fuel map - I'd say with the exception of edge cases the tank contents can be ruled out? Also I've had no issues at the track (Grattan) with fuel starvation or with daily driving conditions (aka fuel baffle / glue in the filter issue). Just this ever present partial throttle scenario slowly getting worse.
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post #38 of 50 (permalink) Old 06-24-2018, 06:19 AM
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Disconnected the primary o2 sensor and the audible and digital artifacts disappeared...does this rule out the fuel pump / regulator / filter in the tank?
I agree with your reasoning. More-so, this corroborates your evaluation of the injectors; if any part of the fuel delivery system was unsteady, then this would still manifest as misbehavior in open-loop fueling.


If I understand the short term fuel trim algorithm correctly, I do not believe that it has any 'learning compensation' capability. It is mostly the sum of values from lookup tables based on engine speed and engine load. It seeks to modulate the upstream oxygen sensor voltage between two threshold levels. Thus, I do not expect an ECU reflash to affect it's behavior unless the calibration is being updated.

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post #39 of 50 (permalink) Old 06-24-2018, 07:32 AM Thread Starter
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If I understand the short term fuel trim algorithm correctly, I do not believe that it has any 'learning compensation' capability. It is mostly the sum of values from lookup tables based on engine speed and engine load. It seeks to modulate the upstream oxygen sensor voltage between two threshold levels. Thus, I do not expect an ECU reflash to affect it's behavior unless the calibration is being updated.
Having a boutique car that has many variants within the product line, AND a relatively small dealer network - I submit this scenario for consideration (I have no CEL or pending codes): https://www.lotustalk.com/forums/f259...update-285081/

I will see if I can call the dealership near me and find out the last ECU update and if they said what firmware. Also ask them how much it will cost to update it...ufda. This however goes against the 'gradually getting worse' theory - unless my first Lotus experience was obscuring things as I got to know the hand built rattle trap.

Considered removing the rear clamshell to inspect further - however I have no good reason to make my life more complicated. Perhaps it'd give me better access to spray the intake manifold from below... but three cans of MAF cleaner I'm not sold. Additionally this access would allow a better inspection of the header - again, no real fingers pointing to exhaust leaks firmly, yet. I've had a few folks come look at my car and everyone confirms the current scenario, but have zero ideas how to proceed... HENCE, dealer + software = ???

I'd consider getting a BoE tune to just step on the stock tune - however I've read a lot of posts where versions of my current problem keep persisting despite the tune. Which would be a $1000 bitter taste in my mouth. HOWEVER BoE's fastworks software does interest me as it allows greater ECU access. Downside? If you want BoE's cable / software you need to buy a tune (~$1000). Any better options out there if I just want information and access beyond the basic OBDII?
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post #40 of 50 (permalink) Old 06-24-2018, 08:25 AM
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Any better options out there if I just want information and access beyond the basic OBDII?
i would love to help with this if you want to be a guinea pig and can stomach some risk.

I've spent a lot of time thinking about the ecu code. I'll pm you my contact info in case you want to discuss further.
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