Stutter when on full throttle.

[Marcus_uk]

Hello all,

My car has a very anoying stutter when on full throttle, maybe its a missfire (but never having had a missfire I dont exactly know how to recognise one!). Ive done an elan scan and am hoping that you maybe able to give me a diagnosis as to what is wrong, the area of interest are the full throttle runs around 520-620s in. The were several times when there was a cut in power during each full throttle phase on all of these full throttle periods.

Here is some back ground on the car:


1994 S2 71K miles
New plugs 8 months (10K miles) ago
New HES (new style) fitted 7 months ago
New cam belt and HG 7 months ago.
Wastegate wiggle 6 months ago to cure overboost.
New CAS 2 months ago
New HT leads last week
New MSD coils fitted yesterday
Timing was checked 3 months ago (isnt rock solid, it flutters a very small amount, but this could be down to my budget gun as there was little difference between the old and brand new CAS unit)

Any input would be welcome, as everything ive uncovered from previous posts has been already been addressed and now its starting to annoy me

Thanks in advance

Marcus

[Monty]

Is the earth wire on the Coil pack base plate ok?

[Marcus_uk]

Im pretty sure its ok.
Ive had two different base plates on there, Orginal plate and coils died so i though the stutter might be due to coils being on there last legs, I then replaced them with a spare plate/coil set up from dave eds to get me home, but still had the stutter. I then put msd coils back on the original plate and installed them. I lost a nylon washer in the process but am using a smaller diameter but same thickness nylon one as a temporary measure.

I will double check with the manual that i re-installed the base plate ground correctly. It there anyway I can check the base plate ground with a multimeter?

[saska]

My car has a very anoying stutter when on full throttle, maybe its a missfire (but never having had a missfire I dont exactly know how to recognise one!). Ive done an elan scan and am hoping that you maybe able to give me a diagnosis as to what is wrong, the area of interest are the full throttle runs around 520-620s in. The were several times when there was a cut in power during each full throttle phase on all of these full throttle periods.
Timing was checked 3 months ago (isnt rock solid, it flutters a very small amount, but this could be down to my budget gun as there was little difference between the old and brand new CAS unit)

Marcus you've got 39 knock events during that run and on 2 occasions knock retard was applied; the first retard begins at Time: 538.7sec (a max of 3.9 degrees of Retard was applied) on the second at Time: 767.7sec 1.9degrees of retard was applied. On both occasions the Air/Fuel Ratio was low 10.4 -11.7 If in Elanscan you choose the curve parameters of Knock Counter and Knock Retard you can see the events clearly. It is also worth noting that at the end of the run when it was fully warm and idling at 975RPM there were a bunch more knock events and the Spark Advance (timing) was varying between 9.8 and 23.2 degrees -- see Time 1311.4sec and Next it forward.

Others may be able to offer better opinions but it looks to me as if it is a timing control issue possibly CAS/HES.

Any input would be welcome, as everything ive uncovered from previous posts has been already been addressed and now its starting to annoy me :evil:

Other than the above it appears a pretty good run; boost gets to 1.0 bar and the turbo spools quickly -- Power is calculated but gives a max of 141.4 Hp? I reckon that's probably quite a quick car even with it's stutter ;)
HTH

[Marcus_uk]

Marcus you've got 39 knock events during that run and on 2 occasions knock retard was applied; the first retard begins at Time: 538.7sec (a max of 3.9 degrees of Retard was applied) on the second at Time: 767.7sec 1.9degrees of retard was applied.

Forgive my ignorance but would a knock event produce a noticable decress in power? The knock pattern roughly matches the "stutter" that i feel.

On both occasions the Air/Fuel Ratio was low 10.4 -11.7 .

Does this point to anything that is not quite right with the car? Thinking back to the run, these periods might tie in with a small amount of wheel spin, could these events be tied to this? would this shed light on anything?

Others may be able to offer better opinions but it looks to me as if it is a timing control issue possibly CAS/HES.

The CAS is brand spanking new, as was the HES when it was fitted 7 months ago. Is there anyway to test that the wiring loom connection was installed correctly?

Other than the above it appears a pretty good run; boost gets to 1.0 bar and the turbo spools quickly -- Power is calculated but gives a max of 141.4 Hp? I reckon that's probably quite a quick car even with it's stutter

As to the hp figure is this an at the crank or at the wheels figure? I was a bit disapointed to be honest but then again i wasnt looking to do several high rpm runs, although im guessing the 3rd gear wheel spin may have upped my calculated hp a little.

Thanks for taking the time to look at my log. Would it worthwhile doing another run doing anything in particular to try and work out what to do next??

Edit: Does the detection of each knock event effect the engine in anyway, or is it a summation of these events over a particular window. I dont hear any metallic knocking noise so could the knock sensor be faulty?

[theelanman]

Markus
I had this a while back after Id put a new HES in......turned out one of the wires Id pushed into the plastic connector Id not pushed in quite far enough....
pulled the wires.....pushed em back all the way this time.......problem solved
well that was my 'stutter'
cheers
G

[saska]

Forgive my ignorance but would a knock event produce a noticable decress in power? The knock pattern roughly matches the "stutter" that i feel.

The knock events are just measurements reported to the ECU from the knock sensor in the block of the engine. The knock retard backs off the timing in response to the knock events and nearly 4 degrees of retard would cause the stutter.

On both occasions the Air/Fuel Ratio was low 10.4 -11.7 .

Does this point to anything that is not quite right with the car?

Dunno -- I've mostly provided my analysis of your log in the hope that someone cleverer than me will come along and say; 'Aha, your problem is here'. The O2 sensor in an S2 should keep it nailed at 14.7 which it was during most of the run but should enrich the engine (lower Air/Fuel ratio) when needed to stop from burning a hole in a piston.

The CAS is brand spanking new, as was the HES when it was fitted 7 months ago. :? Is there anyway to test that the wiring loom connection was installed correctly?

Again -- dunno. The bit at the end where the car was idling and the timing was all over the place is what lead me to think CAS/HES

As to the hp figure is this an at the crank or at the wheels figure? I was a bit disapointed to be honest but then again i wasnt looking to do several high rpm runs, although im guessing the 3rd gear wheel spin may have upped my calculated hp a little.

Dunno the HP figure, it is calculated by the Elanscan program and I don't know what algorithm is used.

Would it worthwhile doing another run doing anything in particular to try and work out what to do next??

Mark the timing as it is now then wind the timing +5 degrees and log a run. Then wind the timing -5 degrees from where it is now and log a run. Post them up

Edit: Does the detection of each knock event effect the engine in anyway, or is it a summation of these events over a particular window. I dont hear any metallic knocking noise so could the knock sensor be faulty?

The detection of knock events doesn't affect the engine unless timing retard is applied to protect the engine. Knock events don't get logged as faults by the ECU. Unlikely that the knock sensor is faulty -- it just picks up 'pinking' caused by pre-detonation and if it is severe enough retards the timing to prevent engine damage.

[Marcus_uk]

Markus
I had this a while back after Id put a new HES in......turned out one of the wires Id pushed into the plastic connector Id not pushed in quite far enough....
pulled the wires.....pushed em back all the way this time.......problem solved
well that was my 'stutter'
cheers
G

Thanks for this, do you mean just unplug the connector block and then plug it back in again? Or pull each of the wires from the block thats wire into the loom? I will have a good look at the HES tomorrow.

[theelanman]

mine was loose on the HES side of the connector block......
I'll try to look at the connector again in the next couple of day....
I just remember putting a new HES in and every now and again itd stutter for no apparent reason...
also wouldnt give me a fault code......just had a wiggle of the wires and could see that one of them was loose....hence taking it appart and putting it back together....

good luck...



cheers
G

[Marcus_uk]

I havent had time to do different runs with different timing but i have checked out the HES connector wiring on both side and it seems fine.

I have also done another quick run and can confirm that knock events match the stutter/durations of loss of power that im experiencing.

I also did an idle and constant revs log (which ive attached to this post) which highlights the following:

1) at idle the spark advance seems to change by +/- 5 degrees (ie 10 degrees max variability)

2) however when held at constant revs (but no load) the spark advance seems to match the revs with virtually no variability.

Could someone confirm if variably spark advance at idle is normal on a s2?

Cheers,

Marcus

PS Happy new year

[Marcus_uk]

Mark the timing as it is now then wind the timing +5 degrees and log a run. Then wind the timing -5 degrees from where it is now and log a run. Post them up

Ive still not solved this one But I have had time to do as you suggested and have done two runs which ive attached:

adjusted run 1 (21 degrees).ecu : The stutter symptons were reduced (but still present to a lesser extent) However I did for the first time ever get a light metallic rattle noise when under full throttle (is the pinking?) and lots of knock events

adjusted run 2 (11 degrees).ecu: The stuttering increased but no metallic noise. The knock events were vastly less than run 1

Would I be right in assuming that the knock events that are detected at 16 and 11 degrees arnt due to pre-ignition but is the knock sensor detecting my stutter problem?

Any input and suggestions would be welcome.

Am I best of reposting this under the problems section???

adjusted timing.zip

[rip]

I did for the first time ever get a light metallic rattle noise when under full throttle (is the pinking?) and lots of knock events

Yes, the knock sensor is effectively a microphone & the ECU can hear knock happening.
It can sometimes be heard from the driving seat as the noise described above, but remember that the sensor is placed in the engine in a location where it can detect the noise more easily. This is a lot better than from the driving seat!
Have you tried fuel with a different octane rating? The higher the RON value, the more resistant the fuel will be to knock. If knock is causing your hesitation, changing fuel should make a difference. If it does not, then chances are, your hesitation is caused by something else.

With reference to your 2 scans: when did the hesitation occur? Ove this is known, events around the same time can be examined.

[lotuska]

I had an issue under full throttle conditions, the problem was caused by having an incorrect gap on the CAS, the fix was easy.

See the following link to see the details of the problem.

Thanks
Mark

[Marcus_uk]

I had an issue under full throttle conditions, the problem was caused by having an incorrect gap on the CAS, the fix was easy.

See the following link to see the details of the problem.

Thanks
Mark

Mark you maybe onto something here!! It looks like mine is just touching the wheel in places as there are marks on the wheel, im going to go and adjust it and report back. Fingers crossed!

[Marcus_uk]

No joy im afraid, regapped the CAS to 0.5mm (it was much much less than this)

Rip: I will try some higher octane fuel at some point this week and maybe closing the gap on the plugs.

The stutter does coinside with the knock counter increasing on runs, probably best to either look at the original run around 520-620s or adjusted run 2 (11 degrees) around 153-200s and 380 to 420s.

I wouldnt look at the adjusted run 1 as I got a lot of very audiable pinging in this run (and when this occured it not give the same stutter/loss in power feel that im trying to cure)

Many thanks for your help somtimes i feel like

[Marcus_uk]

Fixed with a new set of plugs... :