Oz Chuck

Hi to all. My name is Chuck and I am in Brisbane in Australia.
I have a 1981 cis 5sp with a holset hx35 turbocharger that I have just got running. It has been on the dyno and the mixtures are happy enough but as soon as the boost climbs above 4 psi the motor feels like it cuts out. We had a timing light on it on the dyno and it still was firing the timing light after it cut out. If I hold it at 3 psi it will run fine through to the limiter at 6200.
I am running standard ignition system with bosch copper plugs (with the recessed style electrode) gapped down to 0.020 now. It was the same with standard plugs.
My question is do you guys running boost have to change coils or leads etc to cope. I have tried the timing at all different settings and it does not change.
Thanks
Chuck
81 5sp turbo Guards Red
79 5sp Black

Fabio421

4psi is not much at all but are you retarding the spark timing with the onset of boost? You should be.

You say the mixtures are "happy enough" but do you have hard #'s to back this up? You shouldn't have a problem with the ignition at 4psi. The stock ignition system (in good working order) is good to well above 12 psi.

To answer your question, I am running 7psi w/ a plug one step cooler than stock at .035 gap. My ignition is stock otherwise.

Oz Chuck

Graphs from the dyno run. You can see where it dies at 2800. The top lines of each graph. Torque climbs until 2400 where it gets to 7 psi then pulls smoothly til 2800.
The second graph has the mixture unchanged at those revs until after it dies. The two fat lines are the run where it dies out. It is on 7 psi on the wastegate at about 2400 and pulls sweet til 2800 then dies.

"To answer your question, I am running 7psi w/ a plug one step cooler than stock at .035 gap. My ignition is stock otherwise."

I used standard ignition bits except I have a custom vacuum advance that gives stock advance curve but also can move the other way to give 4 deg retard at 10 psi.
We tried the timing all through the adjustment range (single dizzy motor) but still get the cut out. No detonation though.
Chuck

Fabio421

Chuck,

So the green line is the air/fuel ratio? I don't understand what those numbers on the graph represent. What do 0.825 - 0.925 equate to?

Also, 4 degrees isn't very much retard in my opinion.

dprantl

+1. 4 degrees at 10psi, wow that would definitely not work on my car. But he said there was no detonation.

Dan
'91 928GT S/C 475hp/460lb.ft

hacker-pschorr

I didn't start to have issues with my ignition system on the 81 until 15psi.

The ignition system on my 81 is the same as your euro.

You need to make sure the cap, rotor, wires, ends etc... everything is perfect. Including the connection to the ignition module. Early on I was having all kinds of random ignition misses under boost. I found the plug on the ignition module had a couple of corroded ends. Luckily there was enough slack to cut off the green wires and crimp on a new end. Like any other electrical issue, check your grounds, check your grounds then check them again. Make sure you have full voltage everywhere.
Hell, make sure the coil isn't connected backwards. I would imagine that would cause more issues, I've heard some strange stories from cars with mis-wired coils.

Green wire perfect and routed away from plug wires.

Coil wire not running parallel with any plug wires.

Do a search for theories on plug wire routing. I've spent a great amount of time making sure my plug wires are routed a very particular way.

There are a lot more "tricks" out there dating back to the early days of hot rodding. I've spent countless hours on the dyno testing a lot of these theories, and have almost completely eliminated my ignition miss.

Assuming he's running stock plug gap now, making it wider isn't going to help. You want to close up the gap to make it easier for the ignition, not wider.

Stock is 0.028-0.032 in

I know for a fact if I gap my plugs to .032 my ignition miss will "kick in" much sooner. I'm running tighter than stock with a very cold non projected electrode spark plug normally used for high RPM racing snomobiles.
I'm a bit surprised you would recommend a Bosch plug since all of the turbo guys up here making really insane HP turned me onto the plugs I'm using.

Running too tight of a gap can result in cold starting and idle issues. I've played with very tight gaps and found a rage where the car is quite happy.
Thankfully plugs are very easy to change on the 16V cars, some trial and error is in your future. I have a few routes mapped out in my town that gives me a few miles of clear driving with parking lots staggered out. Gives me a safe place to stop, change plugs, gaps, or anything else I'm testing.

I'm running stock base timing which is pulled back under boost. At 4psi this should not be necessary. I originally ran my car up to 8-9psi without pulling out any timing. Then again, I'm not familiar with the timing curve on the euro distributors. Might be the same, I have no idea.

Retarding under boost is possible for any 16V car with the distributor with dual vacuum ports. As stories go, Reeves Callaway used this method with his turbo cars, who later shared this knowledge with Turbo John who then shared it with a few of us some time ago.

Basically if you disconnect the lower vacuum line, boost entering the upper port will push back on the advance arm retarding the timing under boost. This is assuming all of your vacuum lines are in good working order and hooked up correctly. John also suggested trimming the arm down by an amount I cannot remember (1mm - 1.5mm?). I have not tested this yet.

I went one step further and added a one way valve to keep the "stock" connection when not under boost.

Oz Chuck

Numbers down the right side of the second graph are Lambda ratios.
Lambda 1 is 14.7:1, 0.85 is 12.5:1 I think. So it is a 0.86 or 12.6 : 1 AFR.
The turbo draws through the air flow flap on the cis head and still has the vacuum line on the WUR so I was hoping that the metering would work out fairly well and it did.
The green wire from the dizzy to the coil is new and I have the ht leads away from the coil lead.
The motor is M28-09 but with early pistons, heads and cams (78). CR is 7.8:1 (measured with volumes) and the head chamber has had the valves "deshrouded" so to speak and the surface pollished. We have 40+ degC temps here a lot and I really didn't want to worry about det problems.
Gap has been tried at 0.03, 0.025 and now 0.02 and no difference. I have changed out most of the ignition bits for other ones also with no change.
I am sure it is blowing the spark out as the pulse was still there in the ht lead but I am puzzled as to why the whole motor dies out. I would have thought that 1 or more would go first.
Hacker, when yours begins to miss is it all or nothing or do you get some cylinders miss and others still going.

Fabio421

I'm glad you chimed in. I was thinking that you would be the pesron who had pushed the stock 16v ignition the furthest and found it's limits.

The arm needs to be ground down or it will stop at or near the at rest position. Are you running it without grinding it? How much does it allow the ign. to retard without grinding? Have you tested it? Mine is ground and pulls 10 degrees at 10 psi. I tested it with a small pump. The gauge doesn't allow me to check at a lower psi.

Fabio421

Have you changed the coil yet? Is it possible that the head work you had done is adding to this problem?

WallyP

"The green wire from the dizzy to the coil is new and I have the ht leads away from the coil lead."

Porsche put out some faulty green wires a couple of years ago. A search on here should get you some info - search for "jim" and "green wire".

Fabio421

https://rennlist.com/forums/928-foru...ght=green+wire

Roy928tt

Hmm, must be something fundamental, I'm running 7 psi, stock original ignition components, I went a couple of ranges colder with the plugs, recurved the distributor and boost retard and have had no problems firing my LPG mixtures. LPG is renowned as being harder to fire.

Good luck

Cheers Roy

hacker-pschorr

I can dial my ignition miss up / down the RPM range by re-gapping the plugs. It's very consistent and repeatable.
Like I said before, I never noticed anything amiss until I reached around 15psi. Something is definitely "broken" in your ignition system to misfire with only 4-5psi.

Are you using copper plugs? If not that could be your problem.
A good way to cause the 1.8 Turbo VW / Audi motor to misfire is the wrong plugs. Heck, even the 2.0 non-turbo motor is very finicky with plugs.
If you haven't already, I would check closely the plug to the ignition module. Make sure those connections are spotless.

Maybe the two resistors that feed the coil? There has been talk in the past about bypassing those to increase spark. I didn't notice anything when I tried it, but not sure what effect they would have if failing. Those are located behind the drivers side headlight, bolted to the fender. It's quite easy to loose up the screw that holds down the wire and install a bypass. Go for a quick drive and see if there's any difference.

My miss was always 5,000rpm + and the physical sensation was the car shuttering (not sure how else to put it) it was not violent, but you could feel it. The car would keep accelerating as the ignition system caught up and would seemingly fire at random. You can feel the car "fighting" to accelerate in-between cylinders misfiring.
Exhaust sound was quite noticeable too since I have open pipes.

Yea, I'm WAY behind on this project. It was pretty much sidelined in 09 due to a Ferrari I became the caretaker of and a boat. Funny how that happens....

I have not modified the arm, it is retarding under boost but I cannot remember how much. Since we've never seen or heard signs of detonation with my car, decided just to leave it.
My goal has been to data log the timing on / off boost. That was supposed to be completed a long time ago.... It looks like I have all of my ducks in a row to have this data measured on the dyno this winter.

Lizard928

No C in Erik's name,
And it would be nice if you would send something for that crank wheel one of these days....

Oz Chuck

I have just rang re a coil.
Bosch 0 221 122 001 is available but Aus $400 ish. What else can I look at, ie is there something available that will work better.
Plugs on module and dizzy look perfect, I put some inox on the contacts and put back and still the same.