05' Elise surging at partial throttle - LotusTalk - The Lotus Cars Community
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post #1 of 50 (permalink) Old 05-31-2018, 12:04 PM Thread Starter
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05' Elise surging at partial throttle

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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Last edited by yorkadam; 06-29-2018 at 03:33 PM. Reason: updated what i've done
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post #2 of 50 (permalink) Old 05-31-2018, 01:09 PM
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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.
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post #3 of 50 (permalink) Old 05-31-2018, 01:29 PM Thread Starter
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Originally Posted by +TSRAGR View Post
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.
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.
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post #4 of 50 (permalink) Old 05-31-2018, 02:18 PM
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Do you have an easy way of datalogging? If not, and if it doesnt rain, and if you feel like driving a few hours, there is a cars and coffee at FCA this weekend. I am offering to meet and try out my datalogging tool and try to help troubleshoot.

https://www.prnewswire.com/news-rele...300654770.html
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post #5 of 50 (permalink) Old 06-01-2018, 05:47 AM Thread Starter
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Originally Posted by Obeisance View Post
Do you have an easy way of datalogging? If not, and if it doesnt rain, and if you feel like driving a few hours, there is a cars and coffee at FCA this weekend. I am offering to meet and try out my datalogging tool and try to help troubleshoot.

https://www.prnewswire.com/news-rele...300654770.html
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?
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post #6 of 50 (permalink) Old 06-01-2018, 06:13 AM
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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.
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post #7 of 50 (permalink) Old 06-01-2018, 07:10 AM Thread Starter
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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.
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.
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post #8 of 50 (permalink) Old 06-02-2018, 09:02 AM Thread Starter
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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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Last edited by yorkadam; 06-02-2018 at 09:18 AM. Reason: forgot to mention timing
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post #9 of 50 (permalink) Old 06-02-2018, 09:57 AM
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So this is a new O2 sensor? What does the TPS read at idle? Does this only happen when the car is warm?
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post #10 of 50 (permalink) Old 06-02-2018, 11:54 AM Thread Starter
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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=1rP...HUecWu6kbca7Yh (csv files not allowed heh)
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post #11 of 50 (permalink) Old 06-02-2018, 12:16 PM
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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.
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post #12 of 50 (permalink) Old 06-02-2018, 12:32 PM Thread Starter
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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?
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post #13 of 50 (permalink) Old 06-02-2018, 12:50 PM
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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?

Last edited by Obeisance; 06-02-2018 at 01:09 PM.
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post #14 of 50 (permalink) Old 06-02-2018, 02:33 PM
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Would a bad injector in one cylinder cause such a rhythmic oscillation?
You can quickly find out by unplugging an injector and its coil pack one at a time to test if the RPM hunting goes away. Obviously unplug them with the engine off.
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post #15 of 50 (permalink) Old 06-02-2018, 02:50 PM
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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?
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?
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post #16 of 50 (permalink) Old 06-02-2018, 03:21 PM Thread Starter
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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.
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post #17 of 50 (permalink) Old 06-02-2018, 03:32 PM
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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?
Yes, I mean to say that I think this is normal behavior.

Here are a few similar observations from my car (ignore my complaints of CELs in my thread- keeping the battery voltage up and allowing the car some time to save the learned values before battery disconnect has alleviated that issue):

https://www.lotustalk.com/forums/f334...1/#post5113690

https://www.lotustalk.com/forums/f334...0/#post5110361
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post #18 of 50 (permalink) Old 06-02-2018, 04:52 PM Thread Starter
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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.
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post #19 of 50 (permalink) Old 06-04-2018, 06:59 AM Thread Starter
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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/p...-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.
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post #20 of 50 (permalink) Old 06-04-2018, 11:52 AM
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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.
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