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Recently my car developed some problems with high RPM sputtering. Power was dead by about 5000 rpm. OK so I had a similar problem a while back. Turned out to be bad Lodge plugs. Put in new NGK BP7ES and gapped it to 0.28mm and all was fine.

So I thought the plugs would be a good place to start this time. I also found that cyl.2 plug wire on the dissy was loose. OK found part of the problem. Next nefore I took off the plugs, I thought I'd play around with the ignition advance. At 24 BTDC the car would barely run by the time it reached 5000 rpm. Brought it up 27 BTDC and it improved. It would rev upto 6000rpm before the sputtering and loss of power ensued.

OK since my last problem the car has had a 1 point increase in compression. So I thought, maybe, just maybe the 0.28mm gap isn't suitable anymore due to increased cylinder pressure and the distance the spark has to arc.

So I took out the plugs and re-gapped it to 0.25mm. Max advance is at 27 BTDC. So far so good, power is present all around all the way to > 6000 rpm. Will report later if the sputtering still persists. Can't really explain why it didn't happen before though....

0.25mm?? OMG!

I run mine at 0.7mm, you need some improvements to the ignition system pronto.
An MSD ignition box would probably do it. I got two...

Fixed it on another car I had, opened up the gap to 1.0mm after mounting the box and it ran perfectly.
1.6 bar and shitloads of fuel (rich mixture to say the least), not a single misfire.

Why do you use 0,28mm gap?? I use 0,7mm but that is with wasted spark but that should not really matter...

Jarle

.7mm = 0.02755897"

Spacecraft have crashed into planets due to such misunderstandings!

1 day the US will let go of the British Imperial System. And become a true republic.

No it is mm. You are right stock spec should be about 0.028" or about 0.7mm but the car wouldn't run at high rpms at those gaps without coughing. I need to find out what is wrong. Could be the dissy cap or bad coil or something. I may try to regap it to 0.7mm and see how it works.

What are the chances of the coil going bad?

Mats,

Prior to the MSD was the car behaving like mine? On your 1.8T did you have this problem?

It wasn't the 75t...
The car was "hobo-modified", I had a cold start solenoid that was triggered by a rpm-relay. Imagine what that would do to the mixture, the fuel pressure was about 7 bar...

Anyway, as soon as the valve opened the car started to misfire badly and would not accelerate. Installed the MSD and the problem was TOTALLY gone, could even open the gap to 1mm without performance loss (spun the wheels in third gear when boost kicked in).
So if your mixture is fine, the ignition system is not experiencing a bad ground or any crappy connectors (measure everything) you might wanna give it a go.
I even have an MSD box on my racecar, and that has a std 2.0 carb engine.

What is the A/F ratio when the engine starts sputtering?

Jarle

Actually it was set at 0.6XX mm or 0.025"

Go for the most powerful spark you can get and a gap definitely more than 0,7mm (.028"). Here we all are spending all kinds of money on cams and headers and the ignition stays as is? Way back in '82-83 when I designed my CD ignition, I used to test it in a long full throttle uphill straight with the plug ground electrodes snapped off!! (In my 2liter gtv) It would only get to ~4500rpm before it misfired and I was looking for ways to improve that.
A high power (high energy) spark is absolutely necessary for a tuned engine and the std Bosch, reliable as it may be, is not it!
Spend some good money on the better MSD stuff (not the simple 6AL)AND a good coil and aim for something with over 200mJ of spark energy (200 in a single spark, not aggregate!!!!!) and you'll never deal with the issue again! I'm using Champion N2C plugs in my 3liter all year round even in the snow, without so much as a hickup (and I change plugs once a year) I start with 0,8mm gap (.032") and it goes to 1mm (.040") before I change or regap(more than likely!).This ground electrode wear is due to the power of the spark.The plugs are always clean and the right color(11:1CR). For those who don't know, N2C is an almost racing plug. They behave impeccably in the downtown bumper-to-bumper as well as the track. An added byproduct is the lower chamber temperature, at least theoretically anyway. They are equivalent to the NGK B9ES and none are projected nose type. Don't fall for weird plug ads claiming power and economy, they're not worth sheet! Classic type plugs+high power spark=No problems!
Jim K.

WHAT IS MSD??and where can i buy it?

Jim: Have you tried the NGK EGV-series? Those are pure race as I understand it...
Expensive as racing stuff anyway.

No Mats, I haven't. N2C and B9ES cost about 3Euros each and thats one one advantage of a good ignition-to work with the cheapest plugs around, heheh! Now, if you tell me that with EGV's I'm looking at 10 more hp, then we got a deal!
This friend of mine here, took his modified (by yours truly)182hp 2liter Renault Williams with a high power Jacobs ignition and coil to the dyno and took readings with different plugs and gaps. The high/low readings were 4hp apart at best. Taking into account dyno uncertainties (tolerance, repeatability etc.) it borders on the insignificant, I would say.
Jim K.

ok, the EGVs are over 10 Euros each depending on where you buy them from (this being the cheapest I've found so far).
I'm told these are pretty extreme when it comes to durability and performance. Thin wire electrode, Golden Palladium, with a racing style insulation.

"Competition Racing Sparkplug that we recommend for use in 8v and 16v turbo engine where the boost has been increased above standard." - Evocars in the UK (Not that they don't like to sell stuff...)

I'm going to try and run the regular plugs (B7ES or B8ES) but if they don't do the trick I'll try the expensive stuff...

MSD is a US made brand of ignitions and accessories. Some of their products are VERY good, like the MSD8 and MSD10 models. They command a serious price, but performance AND quality of this level don't come cheap. Spark energy is more than 300mJ with these models!!!
Jim K.

Jim,

What's your setup on the 3.0?