Strange hiccup on heavy acceleration

[tigerdog]

And you are running the correct plug-gap of 0.8mm … right?

This is worth checking even when everything else is sorted. If running NGK plugs, last I looked they didn't make one pre-gapped to 0.8mm, so it needs to be manually set. At greater than stock boost, Smaug had a similar misfire until I double-checked the gap on the plugs (NGK iridium.)

[LeedsMike]

And you are running the correct plug-gap of 0.8mm … right?

This is worth checking even when everything else is sorted. If running NGK plugs, last I looked they didn't make one pre-gapped to 0.8mm, so it needs to be manually set. At greater than stock boost, Smaug had a similar misfire until I double-checked the gap on the plugs (NGK iridium.)

@tigerdog - after a 30 minute search for some feeler gauges and an SP socket, I eventually got the plugs out and tested. Guess what, they were all between 0.85 and 0.9 - so I made the adjustments and went for a test run and the problem appears to have gone away.......the annoying thing is that the car has been 3 times to a Lotus specialist since I've had it and I naively assumed they would check things like that.... anyway, a lesson learnt...

Hi, sorry busy for the rest of the week.

The injector pulse width is briefly constant (that means that there is no increase in fuel) as it switches to open loop. zoom in to one of the peaks and plot Pulse width and closed loop.

Also plot secondary throttle and rpm or throttle position - you lift off just as it opened hence the suggestion to change gear later - did you notice the difference?

Thanks @Simon_P I had a good look through that data and will record some more runs tonight when there is less traffic. Notwithstanding the above good news, I need to repeat the same runs I was doing before and compare the data. I will share in this channel as it gives a good before/after I guess....

Thanks so much to everyone who has helped on this one....I learnt quite a bit along the way which is always a bonus!

[HJ2]

Not sure if the gap difference is large enough to explain all of this…

[Tuga2112]

I agree with HJ
i would expect something like that to be more noticeable with hard starts than high revs (lower voltage while cranking would have more dificulty to spark than the while the alternator is pumping out health amounts of pixies

[LeedsMike]

So a little more on this topic......

The stutter has re-occurred since the re-gapping, but is much less noticeable than before.....

MOT test just failed on emissions with the suspect being a faulty O2 sensor.

There is a post above noting the stutter occurs when the ECU switches to closed loop - is the faulty sensor and this fact potentially related?

Anyway, it will be re-tested tomorrow with a new O2 sensor and I should know more....

[dapinky]

Mike,

What you ask, concurs with what you say, and leads to the presumption which is valid.

Which is a posh way of saying that the O2 sensor is suspect and should sort it out!!!!

If the O2 sensor is giving 'bad' readings to the ECU it will affect the fuel delivery volume/speed from the injectors (either too rich or too lean) and can give the stutter you describe.

This agrees with the timing of it switching to closed loop - as you know, the 1499 MEMCAL ECU starts running with open loop readings until it gets up to operating temperature, and then switches to closed loop and starts to make calculations from the input from the O2 sensor - so if the sensor is wrong, then it will have to try and compensate for it, which it may or may not be able to do fully - but certainly not instantly.

[lotusflasherman]

I've only scanned this thread and haven't seen anybody asking the most obvious ... Can you confirm you are using PREMIUM FUEL? if not the extra boost from the Everest chip will have your Knock Sensor working overtime! There is no point in having an Everest Chip and putting sh1t in the tank.

[LeedsMike]

A little update on this saga:

MOT failure on emission WAS down to faulty O2 sensor and it passed without issue once replaced. The test drive afterwards showed a significant improvement on the "stutter" but not fully removed.

I next looked at the coil packs and leads which were all original - so all replaced along with some new correctly gapped plugs. This gave an improvement again.

I thought there was progress...... then after a slightly longer test run and cool down, I did a motorway run and on the slip road had zero boost, same at speed. The car felt down on performance so I know it was not the gauge earth. When I came off the motorway and set off again at the junction, boost came back. So I thought the wastegate was either stuck open or there was a fault on the boost control solenoid or there was a boost leak due to poorly fitted pipe or pipe blow off.

Ran a smoke test to look for leaks in all the plumbing, used a pump to wiggle the wg arm so i could make sure it had a full range of movement and as I had a new boost control solenoid, replaced that (although i think i should still get boost even if it was faulty?).

Test run last night was great and I repeated exactly the same run profile that produced the previous fault. One thing that is still present is that the boost going up through the power bands comes in steady waves rather than a smooth growth. But much much better than before.

One thing I did notice when the previous zero boost issue was produced was that when i started the car (whilst warm), it was a hesitant start and a dog rough idle for about 5 seconds. This had happened before, but i thought my coil pack renewal had fixed that.

There are not many more things to replace now - MAP, MAT sensors? Could this be a fuel injector issue?

I might be mixing 2 different problems here, but it's all fuelling and ignition at the end of the day so would certainly welcome some input.......

Thanks!

[Tuga2112]

an elanscan log of your test run may be usefull to check the map values overtime and other related issues.

being a close loop system it may be relevant to try and pinpoint if the issue only happens when the ecu changes to close loop or while its runnign open loop to warm up the sensor.

[Simon_P]

All very interesting background but not much use without a scan.... Looks like the weather may improve!

[LeedsMike]

Here is a scan:

hot-run4-short2-300324.zip

It looks like at 100% WOT the voltage on the TPS varies between 4.02v and 4.16v and roughly follows the unsmooth progression of engine speed - is this normal?

Whilst there is not a distinct hiccup this time, the test on the Elanscan is consistent with the acceleration feeling like it is coming in waves.....

Anything odd anyone can spot here?

Thanks!

[Tuga2112]

Here is a scan:

hot-run4-short2-300324.zip

It looks like at 100% WOT the voltage on the TPS varies between 4.02v and 4.16v and roughly follows the unsmooth progression of engine speed - is this normal?

Whilst there is not a distinct hiccup this time, the test on the Elanscan is consistent with the acceleration feeling like it is coming in waves.....

Anything odd anyone can spot here?

Thanks!

without looking at the scan, and just from your description,
i would suggest checking with the manual the voltage at closed and full throtle. its possible your TPS may need adjusting. and its a doodle of a task to do when you have elanscan telling you the reading.

i dont know what are the expected voltage at full throtle, but from a general understanding of common electronics. things in a car usually run at either a range of 0-5v or 0-12v i would expect a sensor reading full throtle to be reading something higher than 4.85v.

i can plug mine in later and have a look, I did have to

[Barrykearley]

We have this on ours and frankly it’s doing my head in.
TPS have been stripped cleaned and resoldered. Setup on elanscan just fine.

Unplug the O2 sensor and it pulls like a train with no issues at all until the engine light comes on.

Can’t seem to source a uk based sensor and the one from Amazon from the USA has been lost in transit.

[Tuga2112]

We have this on ours and frankly it’s doing my head in.
TPS have been stripped cleaned and resoldered. Setup on elanscan just fine.

Unplug the O2 sensor and it pulls like a train with no issues at all until the engine light comes on.

Can’t seem to source a uk based sensor and the one from Amazon from the USA has been lost in transit.

my o2 sensors have been putched from rockauto. no problems with them

[chrism]

+1 for RockAuto...
I can confirm that their Walker 350-33027 and Bosch 15701 both fit fit okay
I found with the Bosch 13277 (that's recommended on wikiLEC) that the sensor lead was far too short to reach my '90 SE m/plug .

[chrisP]

Have you checked the coils are good, they will show if they are on the way out - under heavy boost when the spark has a harder job to make the jump?

[Barrykearley]

Replaced O2 sensor today. Runs slightly better and less popping on reving. However stutter still present but slightly improved.

I’ll elan scan on a run tomorrow to check boost pressure etc - but I’m fast becoming annoyed with this. Having come from Esprit’s where we have freescan and esprit mom - elan scan seems rather lacking

[chrism]

Good to know there's an improvement with the new sensor. Do an EScan, wrap it up in a zip file, post it and let's see what's happening.

I've heard it said that basic timing is always the first suspect. EScan might show a few clues; the ecu tries its hardest to compensate but...

[HJ2]

Hmm.. and the turbo is good yes?
If you pop the intake hose off and have a look at the compressor it is undamaged, nearly oil free and moves spins freely!?
And if you push / pull firmly (axially) the turbo shaft, there is no more free play then, say 0.6mm?