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05' Elise surging at partial throttle

10K views 50 replies 8 participants last post by  mm3boost 
#1 · (Edited)
I have a 2005 Elise w/ ~50k miles. Purchased it about a year ago from the previous owner, of which I am number 5. Since taking ownership I've noticed that at partial throttle the car will surge. The behavior seems to start as the car warms up and it only gets worse as the car reaches operating temperature. This doesn't appear to be limited to throttle input either, just more apparent under those conditions since the car can be felt surging. At the track it will rhythmically crackle and pop w/ a hot exhaust as you decelerate and or idle. Even when the car is on jack stands I can hold the throttle down and hear the engine and watch the tachometer needle ever so slightly wiggle. This leads me to believe it's something related to the air and fuel ratio modulating, but it hasn't thrown any codes yet... and I'm all out of ideas especially w/ it throwing no codes or CEL... and trust me I've read most if not every post on here...

Modifications:
Larini Sport Exhaust (PO installed)
Sector111 Motor mount and transmission stud upgrade
Sector111 gPan3+
BAB26-12 Lightweight battery

Things I've addressed / refreshed in the last 2-3k miles attempting to get rid of my issue:
Adjusted throttle cable & stop
New spark plugs
New air filter element
New coils + dielectric grease
New Pre Cat o2 sensor (generic Bosch 15733 wired in w/ OEM plug)
New Post Cat o2 sensor (generic Bosch 15733 wired in w/ OEM plug)
Verified o2 sensors are attached to their correct wire harness location AND wire colors match (see attached image)
Cleaned ground(s) on driver side bulkhead
Cleaned ground on head for ignition system
Hunted around for obvious exhaust leaks but found none except at the Larini narrow exhaust clamp - replaced with a wider one

Things I've tried AFTER initial posting - to no avail:
New MAF & cleaned connector pins
New TPS & cleaned connector pins
New IAC & cleaned connector pins
New TB gasket
New PCV valve
brake booster vacuum nipple at intake manifold was checked and reinstalled w/ teflon paste
New intake hose t-clamps
Clean/inspected throttle body thoroughly during IAC replacement
Clean ECU pins on both connectors
Inspected/Replaced all engine compartment fuses except for the 3.5A (didn't have any on hand)
Checked and double checked for vacuum leaks - no variance in idle w/ judicious application of propane & maf cleaner.
Cleaned / Flow tested injectors - all were good - no change
Disconnect / Isolate brake booster - no change
Disconnect / Isolate evaporative emissions system - no change
Reverted back to good OEM lead acid battery - no change
Smoke tested intake post MAF w/ the stock intake tube - no leaks seen
Smoke tested exhaust up the tail pipe - only leak was very minor at the exhaust clamp POST secondary o2 sensor - no effect
Unplugged primary pre-cat o2 sensor - STFT went to 0% and car ran normally
Swapped o2 sensor connectors - car warmed up but once cat was at temp car was hunting towards a stall. Reverted - original symptoms returned.
Called Lotus dealer and all they found on my car's software was the VIN update - uncertain if this could be to blame (bad software load?)

Ideas? I've heard fuel can be a cause but I'm not sure if that would manifest itself in surging... Anything I can / should test there?
 

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#2 ·
Just how much of a surge are you noticing? A little variation of 100 RPMs or less is acceptable, and that sounds like the slight wiggle of the tach needle you're describing.

Inspect the throttle body for sure. The throttle blade is probably gummy from oil in the PCV line, especially if it hasn't been cleaned in those 50k miles.

A vacuum leak at the throttle body may also be the culprit and they're not always obvious to spot.

Also, if you mismatched your O2 harnesses that will cause repetitive surging.
 
#3 ·
The wiggle of the needle is just a visual version of what you can easily feel in the seat of your pants. I'm sure it could make some people feel ill. It's a on/off of the throttle.

Any suggestions for vacuum leak identification? I can spray my favorite flammable rubber safe libation around... I did that previously when I installed the new air filter but I'll try again after I clean the throttle body.

Already said above I verified the o2 harness is correctly wired for pre and post cat. Doing that I also double double checked the pre and post cat are wired into their respective, and correct plugs.
 
#5 ·
Thank you for the offer! Unfortunately I can't make it this weekend. If I spend more time chasing my tail I will figure out a way to get in touch / make the trip.

Tonight I'll start trying to pull the nightmare hose off and clean the throttle body / look for vacuum leaks... Not optimistic it'll be any easier than my last attempt. On the off chance I tear it (ya it's THAT stuck) - is this a common Toyota part that's shared, or custom Lotus?
 
#6 ·
You cleaned the MAF but you may need to replace it. The O2 sensor may be bad. Could be a vacuum leak, could be a bad TPS. Lots of other potential culprits with an engine surge. The best way to trace it down without just replacing parts that may or may not need it is to see if the sensor readings are reasonable though an OBD2 data logger.
 
#7 ·
Very true. Alright I'm going to just suck it up and buy a better OBD2 scanner that can log / display live data. It's easy to get target fixation and forget to take a step back. Plus if it arrives before I get that damn hose off I'll at least have an idea what I'm working with and data to share here. Logger should arrive tomorrow.
 
#8 · (Edited)
Friday - I went ahead and cleaned the throttle body and MAF (second time + cleaned contacts). Inspected the ribbed intake hose and didn't see any cracks. Re-assembled and started the car. Hooked up everything and took it for a test drive - same symptoms of what feels like constant hunting / surging in a rhythmic fashion. Doesn't appear to be based on engine RPM so it doesn't seem related to miss firing... which brings me back to AFR and fuel trim (later confirmed a little further w/ data logging).

Today - Data logger arrived so I hooked it up. Appears all inputs are nominal with no fluctuation or spikes (MAF, throttle position, timing advance, voltage to the ECU... etc) EXCEPT the 'short term fuel trim' and the pre-cat o2 sensor. I went ahead and took a screen shot of the trend I saw through the rev range both partially cold and fully warmed up (See attached screen shot). This coincides with the rhythmic surging I can feel and hear. No other inputs appear to be oscillating...

So I'm thinking it's two likely scenarios: unmetered air and or a bad voltage / sensor. So I gave the 'propane vacuum leak detector' trick a go. After a few passes of the entire engine there was no fluctuation in idle. Which makes the unmetered air / vacuum leak less of a reality, but not fully ruled out yet... esp if it's small or in a very strange spot. Never the less I covered all of the big hitters and even the minor ones.

The next step I was going to try is unplugging the battery and cleaning the ECU contacts. That should at least help rule out the common dirty ECU connector problem AND a possible issue w/ my fuel maps in the ECU.

Anyone have issues w/ the generic o2 sensors? This issue was present w/ both my previous OEM sensors AND after I installed the Bosch 15733's. One thing that did occur to me is that visually they were NOT the same - however they both claim to be narrow band sensors. Both sensors COULD be horked, but I think that is unlikely. More likely would be the electrical side of the fence.
 

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#10 ·
As stated in the original post - NEW bosch 15733 sensor, that has not changed. Neither have the symptoms.

TPS % and absolute reads steady at idle. The bad behavior appears to happen at idle shortly after start up - or when the ECU starts to use the o2 sensors.

I disconnected the battery, removed the ECU, cleaned contacts. Doubt the ECU was disconnected long enough to reset the fuel maps given how easily it started - plus there seems to be some debate if you can reset the ECU fully w/o the Lotus tool... I started the car then logged data for the entire warm up period. At about 6-8min I started to check for vacuum leaks again. At about 8-9min you'll see large movement in the fuel trim. That was just me double checking the engine would react to the propane directly into the intake. Duh, it did. After returning to normal idle I stopped hunting for vacuum leaks and applied the throttle a several times. The behavior seemed to be consistent (o2 and trim reading) and again none of the other input seemed to be off or bad.

data: https://drive.google.com/open?id=1rPGjVHHJ_Wa1Dnfw-6HUecWu6kbca7Yh (csv files not allowed heh)
 
#11 ·
I missed the new O2 sensor initially. O2 sensors have a need for air to be available on the back side which comes in with the wires. This is why they state that you should always crimp the flying lead to the connector from the factory instead of solder. Hopefully you crimped it? I do think your problem is either a stuck/dirty injector, a weak fuel pump or a malfunctioning O2 sensor.
 
#12 ·
Yes I've heard the argument about crimping vs soldiering. I soldiered the post cat sensor but because I ran out of shrink wrap I went ahead and used the bosch generic splice provided w/ the kit to attach the OEM plug.

Would a bad injector in one cylinder cause such a rhythmic oscillation? I guess I'm ASSuming anything related to one cylinder would change w/ engine speed directly... but if the o2 sensor is a trailing correction I guess the frequency of the oscillations are more driven by however frequent the ECU corrects the short term fuel trim - ja?
 
#13 · (Edited)
The short term fuel trim algorithm oscillates linearly between values that make the oxygen sensor switch between two threshold values when it is functioning properly. Thus, a swinging O2 voltage and zig-zag STFT is not indicative of a problem, as far as I know.

As I understand, engine idle speed is primarily modulated by timing adjustments.

I've never observed my car run the carbon canister purge, either (I haven't taken many logs). Does anyone know how often this happens?
 
#15 ·
That's interesting. The scale on the O2 sensor shows it swinging from one end of it's total range to the other. Admittedly, this isn't a huge ARF swing if the actual value is within the sensor's range, but there's no way to tell with a narrow band like this. You're saying this is normal function at idle?
 
#16 ·
That's interesting. The scale on the O2 sensor shows it swinging from one end of it's total range to the other. Admittedly, this isn't a huge ARF swing if the actual value is within the sensor's range, but there's no way to tell with a narrow band like this. You're saying this is normal function at idle?

Asking me? Or asking about the interplay with the sensor and the STFT?

In my case it's the new normal but I only feel it under partial load at cruising speed. WOT it's not noticeable but I don't know what the sensors are seeing because I didn't take it out on the road again yet. However... I wouldn't describe my gas mileage as on par with most elise owners... So I'll be testing the injectors one at a time when I head back home tonight. See if that changes the behavior of the o2 sensor.
 
#18 ·
I checked out the post-cat secondary o2 sensor and it appears to be working as expected. It has a nice constant output w/ very little fluctuation. Kind of what I'd expect to see on the pre-cat sensor to some degree.

As for removing one coil/injector at a time - it did not change the pre-cat o2 sensors behavior in a very obvious way. However with certain injectors out of the loop the engine would run objectively and slightly 'worse' - at least with two of the four that was the case. Though nothing jumped out and grabbed you by the short curly's... it's running on three cylinders after all.

For kicks I gave the injectors a little wiggle and finally a few taps here or there to see if anything could be dislodged or cause an intermittent fault. No dice. Also I was hoping for an obvious vacuum leak post wiggle, but I didn't find any of those either.

If my injectors are out of spec in any direction across more than one this might be a bit of a guessing game... I'd need a good known set to test against.
 
#19 ·
Anyone know the flow rate of the 05' Elise OEM injectors? I was going to have my OEM ones I just took off cleaned and bench/flow tested... but I was also looking at other options should any of them be DOA for be poorly mismatched.

Poking around I've found OEM injectors for approx. $150ea, and the next best thing I found were these:
https://www.monkeywrenchracing.com/...fuel-injector-set-4-lotustoyota-1zz2zz-370cc/

If what I've read is true the OEM injectors are 320-330cc... wouldn't a 370cc require a tune or adjustment to my (stock) tune? - found a dead thread but no answers on here.
 
#21 · (Edited)
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?
 
#22 ·
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
 
#24 ·
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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#25 · (Edited)
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/1uR78HtngtIic8Av9baK0apsdBcUES8qr/view?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).
 
#26 ·
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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#27 ·
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...
 
#29 · (Edited)
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.
 
#28 ·
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/1WVDEXCC16dEm6utXp5s2bxte51iIg35m/view?usp=sharing

Any reason why my 2nd post cat o2 sensor 's fuel trim is consistently high? Flat 99.2...
 
#31 ·
With the evap system disconnected - problem still persists:
https://drive.google.com/file/d/1fP6YEgED9QWpO8iyUw_wTdXEWmbwUVJl/view?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?
 
#32 ·
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.
 
#33 ·
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.
 
#35 ·
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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