Misfire at/above 6500

[rmicroys]

Hi,

Here's the deal. I need some insight in to where I should look for help...

VW Jetta:
ABA 2.0l 8V cross-flow engine
Mikuni 44PHH carbs
locked out distributor
OE ignitor
Kent racing cam
Race valve springs
Titanium retainers
NGK wires
Accel coil
champion racing spark plugs

At 6500 RPM in 4th and in 5th (not quite sure about third - I'm hardly in it much at Mosport) I get regular sounding misfire and the car will not pull much past 6500 rpm

I'm figuring that this is either an ignition issue or valve train. I'm thinking that it is not fuel as it happens at the same rpm in both 4th and 5th, and in straights and corners, always at the same rpms.

My first suspect is the Accel coil. I will be replacing that shortly with an MSD blaster coil and MSD 6AL ignition box. I hope that this solves the problem.

The questions are:

- is there any rpm limitation on any OE ignitors? Do any have rpm limits built in to them? What sort of rpm is the OE ignitor capable of working at?
- Just how crappy are Accel coils?
- Is this valve float? In 4th gear the car pulls pretty strong and then quickly fades as I close on 6500 and develops a very fast and even misfire. The closest to which I can describe it is that the car starts to sound a bit like a air cooled VW bug...

 

[Bill Miller]

I had this problem w/ my car, but it turned out to be the KJet box. Not sure in your case.

------------------
MARRS #25 ITB Rabbit GTI
SCCA 279608

 

[JohnRW]

Make sure you've got everything locked down correctly in the Mikunis. If my memory serves me well, they're just like DCOE's, and if the emulsion tubes aren't right, you can develop all sorts of odd misfires.

As it happens at the same RPM, it means that it COULD be the fuel system, as the engine is drawing the same air & fuel at a given RPM (assuming throttle WFO), regardless of the gear.

Ditch the Accel coil and try a Bosch Blue Coil (available at your friendly local VW/Audi/Volvo/Saab/BMW parts place) before you try an MSD system. The stock Bosch VW system will pull to at least 7800rpm (it does in my ice racer), and probably goes to 8K without a problem. IMO, the MSD creates more problems than it solves.

Questions for troubleshooting:

Did this problem just show up on a known-good engine/head/ignition/fuel configuration, or is this an all-new engine package ?

What fuel pressure are you running ? Too much and you'll blow the needles off the seats....too little and you'll starve under load. Are your float levels set correctly ?
Does it only do it under load, or will it do it static (i.e. in your garage) ?

Is it a solid lifter or hydro head ? The solid heads will pull to at least 7500 without float with a standard valvetrain. Depending on how radical your cam ramps are, you might have valvetrain issues. Have you degree'ed the cam in the head ? Cam pulley
marks can be off a tooth or two, which will create new problems.

Have you waited till dark, raised the hood and fired the motor ? Look for flashes etc. that indicates captive spark trying to escape the ignition prison.

I hate MSD's. I have them in two cars, and I still hate them. Avoid them unless you're forced to go to them. The stock Bosch system is a beautiful creation.

You could have an ignition problem, or a fuel problem, or a valve-train problem. You need to go searching.....

 

[rmicroys]

Originally posted by JohnRW:
Make sure you've got everything locked down correctly in the Mikunis. If my memory serves me well, they're just like DCOE's, and if the emulsion tubes aren't right, you can develop all sorts of odd misfires.

Yup, I keep everything good and snug in the carbs. Yes the Mikunis are basically a Japanese copy of the Weber. dual independant individual cylinder carbs sharing a single float bowl.

As it happens at the same RPM, it means that it COULD be the fuel system, as the engine is drawing the same air & fuel at a given RPM (assuming throttle WFO), regardless of the gear.

Yup.. same RPM. 6500 and WFO.

Ditch the Accel coil and try a Bosch Blue Coil (available at your friendly local VW/Audi/Volvo/Saab/BMW parts place) before you try an MSD system. The stock Bosch VW system will pull to at least 7800rpm (it does in my ice racer), and probably goes to 8K without a problem. IMO, the MSD creates more problems than it solves.

Accel is on the way out. I will use the MSD coil first.

I haven't tried it under no load - so I don't know.

Questions for troubleshooting:

Did this problem just show up on a known-good engine/head/ignition/fuel configuration, or is this an all-new engine package ?

I'm new to the car this year. I'm not sure the previous owner ever reved it this high - as I have changed the intake manifold with a much better one, and the car is MUCH faster since last year.

What fuel pressure are you running ? Too much and you'll blow the needles off the seats....too little and you'll starve under load. Are your float levels set correctly ?

I'm running about 4.5 psi, the float levels are correct. I was running too much fuel in one of the carbs, as I noticed the car would always leak fuel out the venturies when the pump was on - fixed that, still the same problem.

I do have an EGT system - I have always completely forgotten to look at the EGT when this is happening (too busy shifting usually) so that will be my next observation on the track when this happens to see if I get a EGT spike or dip in temps.

Does it only do it under load, or will it do it static (i.e. in your garage) ?

I haven't tried to rev it that high under no load... hmmm... worth a try at least.

[/quote]
Is it a solid lifter or hydro head ? The solid heads will pull to at least 7500 without float with a standard valvetrain. Depending on how radical your cam ramps are, you might have valvetrain issues. Have you degree'ed the cam in the head ? Cam pulley
marks can be off a tooth or two, which will create new problems.
[/quote]

ABA 2.0l 8.0v cross flow hydraulic head, again, It does have racing valve springs along with titanium keepers. Not sure about the cam markings. I've never had the engine apart, or the timing belt off...

Have you waited till dark, raised the hood and fired the motor ? Look for flashes etc. that indicates captive spark trying to escape the ignition prison.

Next nighttime experiment to annoy the neighbors!

I hate MSD's. I have them in two cars, and I still hate them. Avoid them unless you're forced to go to them. The stock Bosch system is a beautiful creation.

Dunno... it's worth a try.

You could have an ignition problem, or a fuel problem, or a valve-train problem. You need to go searching.....

That's what I figured, it's a matter of diagnosing it...



[This message has been edited by rmicroys (edited August 22, 2002).]

 

[mogren]

Spend some time degreeing the cam and the crank to a true TDC. TRy a stock cam, look at the plugs to see that they match and are brown or dark gray. Time the engine at 4000 or more and be sure that it doesnt get much more than 35* total at 6000. If the timing light scatters the spark light, try a diff distribiter.... Valve springs. Coil bind. uneven seat ##. Stock cam and springs will go pretty high, much more than 6500.

 

[rmicroys]

Originally posted by mogren:
Spend some time degreeing the cam and the crank to a true TDC. TRy a stock cam, look at the plugs to see that they match and are brown or dark gray. Time the engine at 4000 or more and be sure that it doesnt get much more than 35* total at 6000. If the timing light scatters the spark light, try a diff distribiter.... Valve springs. Coil bind. uneven seat ##. Stock cam and springs will go pretty high, much more than 6500.

All valid stuff! Thanks!

I did play with the engine a little on the weekend in the driveway. It certainly revs above 7 in neutral under no load, quite nicely, so it's not a ignitor or distributor issue by the looks of it.

I am going to start to consider fuel - I'm building a swirlpot, and going to run two pumps, one,the in tank transfer pump, and the second will be holley blue 70 gph pump. So I don't think I'm going to have any more fuel issues after this weekend once this setup is in. If the solution is fuel, I'm going to be fairly happy as the fix is really simple and cheap as I have most of the parts kicking around (spare pump, etc) and the swirl pot is really cheap to make. I'm thinking that the OE in tank pump might not have enough 'umph'...

 

[Vantage #51]

We have run into hydraulic lifter pump up on our hydro head IT-B cars at these rpm,it goes away 5 to 10 seconds after you shift,
the only way we could fix it was to shift
before it happens [6300-6500]

 

[rmicroys]

Originally posted by Vantage #51:
We have run into hydraulic lifter pump up on our hydro head IT-B cars at these rpm,it goes away 5 to 10 seconds after you shift,
the only way we could fix it was to shift
before it happens [6300-6500]

I don't think that's it. If you say the problem goes away 5/10 seconds after the shift, then that's not it. My problem goes away immediately following the shift.

 

[rmicroys]

Okay... any distributor experts out there? I think I found the problem. I bought the car pretty much as it is, and haven't changed anything in the ignition. BUT, one thing I noticed is that the cap and rotor are not getting scorched in a manner one would expect of a normal dist/rotor. Only the leading edge of the rotor and pins are marked from sparks. I'm not sure what was done to the distributor that is in the car. It has the OE ABA 2.0l 8V housing, but not sure if the internals are stock for the motor/computerized ignition, or if the previous racer has changed the timing wheel inside the distributor.

So, what's happening, I think, is that the distributor sends the signal to the 'computer' which isn't there which normally 'retards' the actual spark from firing with respect to the signal provided by the distributor. See, this of course stems from the fact that it is impossible to advance and event that already happened. So internally the distributor must signal much earlier than it gets fired through. So, the spark is actually having to jump two gaps, one in the distributor, and one in the cylinder. I just put an MSD in so that may mask some of the symptoms, and get me a little better drivability, but the root of the problem is still there...

Here's a question for all you distributor experts. If I were to change the timing wheel in the dist with one from a CIS (non electronic controlled ignition), would it spark at a more appropriate time?

 

[JohnRW]

AHA !!! You need to determine your base timing, and how much advance that distributor is giving you at ~4000rpm (when it should have gotten to full advance).

I don't really understand your theory in the second paragraph, but don't go swapping distributor parts until you get some data with a good 'twist' timing light...one of the ones with a knob on the back that re-zero's the mark so you can measure actual, dynamic, running-on-the-car, noisy, neighbor-annoying advance. That is...don't go swapping parts unless you own stock in a company that makes VW headgaskets.

Take that freaking MSD out of there until you find the problem, or you might just be buying a new motor.

Find the engine builder, or somebody familiar with that motor and THOSE MODS, and find out how much TOTAL advance you should be running.
Is it a vacuum distributor, or a advance weights, or what ?

You need to know your static timing and the required fully-sucked open advanced timing, before you start screwing with stuff.

Baseline data, Bud...baseline data.

 

[rmicroys]

Originally posted by JohnRW:
AHA !!! You need to determine your base timing, and how much advance that distributor is giving you at ~4000rpm (when it should have gotten to full advance).

Okay... this has been done. NONE. ZERO. NO ADVANCE. It is a distributor from a electronic computer controlled ignition - hence no vacuum pot, no weights, no nothing. It's LOCKED. So, what ever the base timing is set to, that's it under all RPM conditions. That we know.

I don't really understand your theory in the second paragraph, but don't go swapping distributor parts until you get some data with a good 'twist' timing light...one of the ones with a knob on the back that re-zero's the mark so you can measure actual, dynamic, running-on-the-car, noisy, neighbor-annoying advance. That is...don't go swapping parts unless you own stock in a company that makes VW headgaskets.

Understood... but I'm only using what came with the car right now.

Take that freaking MSD out of there until you find the problem, or you might just be buying a new motor.

It will do just fine with the MSD

Find the engine builder, or somebody familiar with that motor and THOSE MODS, and find out how much TOTAL advance you should be running.
Is it a vacuum distributor, or a advance weights, or what ?

Doesn't anybody understand what a locked out distributor is? I thought I made that pretty clear at the beginning. This car runs a locked distributor, likely (this is what I'm trying to confirm) the OE original distributor made for the ABA 2.0l 8V crossflow using electronic computer controlled ignition. It has NO, mechanical vacuum advance, no springs, no weights, no nothing. Locked SOLID.

So... getting back to the theory of time and relativity. A distributor for a computer controlled ignition needs its reference signals well in advance of ANY spark it is ever going to fire. As one cannot 'advance' an event that has already happened, the computer needs to now in additional advance of any spark event. Hence, since the singaling and spark delivery are controlled by the distributor, the signal gets sent first say, 30 degrees prior to the rotor getting centered up with the pin in the cap. The computer knows this physical property of the dist., and of course, says, well, assuming the base timing is set to say, 15 degrees BTDC, and I'm at WOT, full tilt at 6000 rpm, then I need 30 deg of total advance, then I should wait about (say 30 - 15) at least 15 more degrees of rotation before firing off the spark so that it lined up. The computer will only ever truely 'retard' the spark from the base setting of the distributor. The problem that I'm having is that the rotor and cap are offset due to this, as the setup makes the coil fire as soon as the signal is sent, rather than have the computer control the collapse of the coil.

You need to know your static timing and the required fully-sucked open advanced timing, before you start screwing with stuff.

Baseline data, Bud...baseline data.

Done, been there done that. Static timing has been set at 20, or 30 deg. It's a very hard motor to start... 30 deg at 0rpm, 30 deg at 2000 rpm, 30 deg at 6500 rpm.

BUT in a nutshell, the spark ALWAYS jumps the cap/rotor at EXACTLY the same spot. The rotor that is in the car has been run for at least 6 events, and it looks BRAND NEW - other than some discoloration right at the leading tip. The pins in the cap are marked heavily, only at the leading edge of the pins.

What I need to know is if I can take a timing wheel from the mechanical distributors and swap it in to the electronic one, and have the spark actually fire in a physically appropriate location with respect to the cap/rotor - because it isn't doing it now.

Short of getting a distributor from a CIS non computer controlled ignition, swaping the distributor gear, and making a bushing to have the block accommodate the smaller housing, I can't do much - but I would have to be very careful not to cover the oiling hole with the conversion bushing, otherwise the distributor will burn out. I've seen that happen before.

[This message has been edited by rmicroys (edited August 29, 2002).]

 

[rmicroys]

Ah... another thing I just thought of. I've never had a bosch distributor apart, but I understand the timing wheel is keyed with a pin. Couldn't I just repin the wheel to sit in a more appropriate spot so that when the hall sender fires the signal off, that the cap and rotor and in the appropriate position to fire the spark in the centre of the rotor? I'll have to take all this stuff apart and take a look see at all the other bosch distributors I have kicking around from my other VWs.

 

[JohnRW]

Yes, I understand what a locked distributor is, but maybe I should restate the question: Have you had a timing light on the motor to see what the actual timing really is ?

You said: "...Static timing has been set at 20, or 30 deg. It's a very hard motor to start...". Well, is it 20 deg. or 30 deg. ? Are you sure that your TDC mark is correct ? I've seen VW flywheels put on all sorts of crazy ways, and the motor will start and run, but the timing marks are whacked and the motor acts bizarre.

I haven't seen a ABA 2litre crossflow motor, but if it's anything like all the other VW motors I've seen, while the distributor can be locked down, you still have the option of getting the timing all screwed up. Does the distributor hang off the end of a cam (a la Cosworth), or is it off the jackshaft ? Is the locking collar tight ?

Please tell me that you own a timing light. Please please please please....

Until you know for sure where it's firing relative to pistons and cams, you're just re-arranging the deck chairs on the Titanic.

 

[mogren]

What you guys mean is distributer phasing. The spark needs to show up at the rotor at the right time. So that the rotor is pointing at a plug post ,not between them. this happens a lot when you go from one type if ignition system to another and only change part of it.
Drill a hole at the # 1 post in the cap, set the timing at 32* . start the motor and check to see that the rotor shows up in the hole. You can do it other ways, crank it by hand etc. but the light dont lie. T he rotor needs to be visable all the way up. If the computer moves it too much the spark will be out of phase. Some systems require some amount of OUT of phase . Mess with the trigger system until it is in phase at 4000 and above. Sprk requirement is greatest there (MAX combustion pressure) and the race cars dont care about RPMs less than that.Hope that this helps.
PS the stock system will fix all of this BS. The knock sensor will help tooif you can get it to work. A small spacer sometimes helps.
MM

 

[rmicroys]

Please tell me that you own a timing light. Please please please please....

Yes, it's even a dial back too

Until you know for sure where it's firing relative to pistons and cams, you're just re-arranging the deck chairs on the Titanic.

True... that's the winter's project. Probably will refresh the motor and finally figure out all this crap once and for all.

 

[rmicroys]

Originally posted by mogren:
What you guys mean is distributer phasing. The spark needs to show up at the rotor at the right time. So that the rotor is pointing at a plug post ,not between them. this happens a lot when you go from one type if ignition system to another and only change part of it.

Ahh! Somebody who understands!

Drill a hole at the # 1 post in the cap, set the timing at 32* . start the motor and check to see that the rotor shows up in the hole. You can do it other ways, crank it by hand etc. but the light dont lie. T he rotor needs to be visable all the way up.

Jeeze, why didn't I think of that... brilliant. That will certainly answer my question and allow me to see if I've been smoking too much cheap stuff - or at least stop breathing too much exhaust fumes.

If the computer moves it too much the spark will be out of phase.

Ah... not a problem, you see, no computer in car. Just the ignitor.

Some systems require some amount of OUT of phase . Mess with the trigger system until it is in phase at 4000 and above. Sprk requirement is greatest there (MAX combustion pressure) and the race cars dont care about RPMs less than that.Hope that this helps.

Certainly does...

PS the stock system will fix all of this BS. The knock sensor will help tooif you can get it to work. A small spacer sometimes helps.

I wish I could... The carbs certainly influence what I can do - I got the car 'as-is' without the OE fuel/ignition system, so I'm a little stuck with at least working with what I have to some extent and to get it working properly. I'm really thinking about putting back on a CIS-E computer controlled ignition. I have most of the bits from an '85 GTI sitting in the basement - I just haven't had enough time to get it together.

 

[rmicroys]

Found the problem! It was a rich misfire. The carb jetting although good (and maybe a touch rich) for mid rpms, was far too rich for when the cam came on above 6200. It ended up just dumping fuel down the carb throats. We went down a few jet sizes, and voila. No more misfire. Car ran great with the MSD, and manged to get the car to pull up to 8000 rpms.