mixture adjustment for a 3.2 ss

code7rpd · 06-20-2006, 06:28 PM

I have a 3.2 ss with sport cams and I set the CO to .8 with the 0xy sensor unplugged during the adjustment. It hesitates at about 5500 rpm and this symptom goes away if I richen the mixture. So my question is, what should I set the mixture to?

Thanks.

pjv911 · pjv911's Garage

Close your spark plug gaps to .025" and retry it. If they are worn get new ones. Im assuming its cutting out/missfiring rather than hesitating. Its a common problem once you mod the 3.2. The ignition output is not up to the task of higher combustion pressures.
The lean mixture is harder to ignite and compounds the issue.

Kurt Williams

code7rpd · 06-20-2006, 07:24 PM

Thanks Kurt! I'll change them this weekend.

pjv911 · pjv911's Garage

Report back with your results. It helps feed the information available here on the forum. If your problem gets resolved it will be the 3rd time I have seen this on the 3.2 engine.
For what its worth the leaner mixture causes higher cumbustion temps which makes more resistance at the plugs firing tip.
Timing affects this too. If you have a modded chip your timing is likely a few degrees further advanced at 5500 rpm. This too raises combustion pressures causing the term" spark blowout" .
It doest happen to all of them but it is a common syndrome with that ignition system.

Kurt Williams

JBO · 06-21-2006, 05:51 AM

Kurt - I think he has CIS, as he says he has a 3.2SS, which I presume started life as a 3.0 SC engine. Your analysis probably works either way.

stlrj · 06:11 AM

Then again you might be able to fix this with an ignition tune up.

Joe

Gunter · Gunter's Garage

code7rpd:
I am building a 3.2SS from an '82 engine with an early large CIS intake, 964 cams, 98mm Mahle cylinders with JE pistons 9.8 CR, SSI's, Ox sensor disconnected.
Would like to hear more details about your set-up.
What year is your engine?
What cam-timing did you use?
What plugs? W5's?
Ignition set at 5 deg BTDC?
JW likes to set the CO rich

code7rpd · 06-21-2006, 06:13 PM

My motor started as a 1981 SC with xtock CIS. It has 98 Mahle cylinders and JE pistons that have a CR of 9.8. I am currently running ssi's with a sport muffler. I am running sport cams that I got from Ted RObinson at German Precision - he recommended that I run the cam timing at 1.7 which is what I did. Ignition timing is set to 6 BTDC. Since this is a CIS motor, will the resetting of the plug gaps still work? What CO does JW recommend?

pjv911 · pjv911's Garage

Yes it may still help you but your SC ignition is quite strong and would likely overcome spark blowout in your case. It cant hurt and may improve the way it runs anyway.

Kurt

timlooney · 06-21-2006, 07:11 PM

Gunter, I have the same setup that you are building. 3.2SS 964 cams, SSI's, etc. I am still running the stock CIS and it runs decent, its quick and sounds great with a stock '74 muffler. I have an MSD ignition but I have not needed to put it in yet. I think the CIS is robbing some power so I will eventually convert it to EFI using the tbitz kit or something similar.

Gunter · Gunter's Garage

code7rpd:
I don't know what profile sport cams have.
The CIS doesn't tolerate most cams; Camgrinder John would be able to tell you if sport cams are compatible with CIS.
Also, did you get the early '78-'79 CIS intake with the larger runners to replace the smaller '81 intake?
What plugs do you have?
JW told me to use the stock W5DC plugs which have o.7 mm gap.
I recall JW recommending 3.5 % (Send him an E-mail to confirm)
Are you running stock '81 CIS with OX connected?
Tim:
I like CIS and will keep it. If you have the early intake sitting on top of a later case, the heads need to be ported to match the 39mm I.D. intake runners. The ideal would be a '78-'79 engine which already has the larger intake and heads for a 3.2SS conversion.
Do you still have the smaller CIS intake on your '82?
To match the larger 98mm P/C's, you need the whole early CIS, not just the runners. The FD is different for the '78-'79 CIS.
I intend to keep the reliable Bosch CDI but heard good things about MSD.
What cam-timing do you have on your 964 cams?
JW recommended 1.4 mm.

code7rpd · 06-22-2006, 07:55 PM

I have the stock CIS for the 81 and I was using NGK Iridium plugs at the stock gap - I will change those tommorrow with the W5DC's and re gap them. I set the CO to 3.5 with the o2 disconnected today - it sounds better, idles better, and runs stronger. I will report back on the plug change to see if it solves my problem.

jpahemi · 06-22-2006, 08:10 PM

Kurt helped me figure out my misfire @ the 5-6K rpm range; I had the plugs gapped to wide and spark blow was occuring. thanks to Kurt and reduced gap the problem was solved.
This was a 3.2 with a modded chip.
j.p.

jpahemi · 06-22-2006, 08:15 PM

Kurt you have a PM.
j.p.

stlrj · 06-23-2006, 06:30 AM

If your ignition system will only function with a smaller plug gap then you must have a problem there.

I have my plugs gapped at 0.060" on my 86 3.2 without any problems.

Cheers,

Joe

Gunter · Gunter's Garage

Joe:
He doesn't have a 3.2; It's an '81 - 3.0 liter made into a short-stroke (SS) 3.2. Read his post.
code7rpd: Use the copper plugs recommended for your year with the 0.7 mm gap.
In my stock '80 - 3.0 liter, I also use W5DC (Copper, not Platinum) with the standard 0.7 mm gap.
Runs great.
In the '82 - 3.0 liter that I am rebuilding into a SS 3.2, I'll use the same plug/gap as for my '80 SC. (Recommended by JW)