My SC detonates, even with low advance.
 

I've been having an ongoing problem with timing advance on my 83 SC.

I know that "proper" advance is 5 BDTC at idle, and "not more than" 25 BTDC at 4K rpm, vacuum lines unhooked and plugged.

Ok.

My SC has started 'pinging' under load at lower rpms (2000-4000). FWIW I'm using the best gas I can get here (91.)

I checked my timing, which was right around 20 BTDC at 4000 rpm. To make the engine not 'ping', I have to reduce the (high RPM) advance to about 12-15 BTDC or even LESS . :confused: This makes my idle timing right around 0 (TDC) with the retard vacuum unplugged.

I'm just worried that I'm losing some performance by having the high RPM timing so tame., or compensating for something else that is not right.

What can I look for? So far I have checked:

Idle mixture: is fine, about .8 to 1.0

Vacuum leaks: I can't seem to find any vacuum leaks. In addition, when I remove my oil cap, the idle changes (as I've heard it should.)

Distributor? I thought my distributor may be dirty or advancing improperly, so I borrowed a known good, recently rebuilt late SC distributor from my wrench and installed it, with same results. It seems my distributor is functioning ok.

Lambda: I had my Lambda checked, and it is reported to be functioning as it should.



My most recent guess is that I'm not getting proper fuel flow, maybe I have dirty injectors or something? (causing a lean condition and the pinging?)

I'm right about at the end of the things I know how to check, so any input would be appreciated.

Thanks!

When was the last fuel filter change?
[edit: have you checked your fuel pressures?]
How much gas do you have in the tank?

I had my 911 run lean when tank was below 1/2 full, ended up being a bad fuel pump, above 1/2 symptoms were nill

YMMV

Thanks, Freak.

Hot and cold pressures are in spec. Fuel filter is 2.5 years old, Tank is full.

I'd swap the fuel filter out. 2.5 years and it could be clogged, especially if you got a few bad batches of fuel or ran some old fuel through it. This (potentially) wouldn't reduce the flow enough to affect idle pressure, but cause it to fall at high power.

I'm also assuming you are running premium.

Question, is the pinging only when fully warmed? If so, you may have some carbon buildup causing hot spots that are causing problems.

If it were me, I would run a some [engine cleaner of choice] through there for a tank or two, see if that helps. Just remember to change your oil after you've run the tank out as the fuel cleaner will get into your oil and accelerate its breakdown.

Personally I've used Techron with decent results. I've heard others swear by Seafoam, but I haven't tried it myself. Perhaps said others will chime in.

What heat range spark plugs are you using?

We recommend a Bosch W4CS if you are having detonation issues.

Fuel pressures.......
 

Gogar,

Do you know the values of your fuel pressures (control & system)? Both cold and warm conditions too. Have you done a vacuum test for the system? Keep us posted.

Tony

I can't remember the values, it's been a few months. Perhaps it's time to check again and if so I'll post my numbers. Thanks!

Jeremy
Do you have an AFR meter? You need to check them I have an lm2 you can borrow also have a set of fuel pressure gauges too
A programmable MSD would ultimately help
Call me if you need to borrow anything

Gogar,

This is not unusual, I've seen it in several high mileage SC's over the years. It is caused by a combination of factors, but not vacuum leaks, O2 sensors, fuel filters, or preignition. Ultimately, detonation is caused by heat, and higher octane fuel just has a higher heat tolerance. The later SC is designed to run on 87 CLC fuel, but as the engine wears, vacuum drops, sensor plate deflection drops, ring seal degrades, temps go up, the distributor springs wear advancing too quickly, and the octane requirement goes up. Besides the octane label on the fuel pump, several other factors effect the detonation resistance of the actual charge in the cylinder. Intake air temperature is around one RON per 10 C and oil dilution has a big effect. Here is what has worked for me. First do a compression test to determine if your ring seal is bad. Use Normal Bosch 5 plugs. Disconnect and plug the breather hose at the top of the oil tank and fit a fresh air vent. I use a foam sock air filter and a pipe with two 90's to allow drain back of blowby oil. Disconnect and plug the vacuum retard hose to the back of the distributor. Rest the idle speed to 950 and the timing to 5 BTDC. Warm up the car by driving, connect an analog dwell meter to the test port, set the mixture to 30-40 dwell. You also want to make sure that the oil cooling system is working properly, the cooling fins are clean and the fan belt is not slipping. If you have the factory exhaust, make sure the heater plumbing is intact and air is going through the exchangers. If you want to isolate the problem at the source, you need to monitor cylinder head temperature, and having the stock heater with the fan on lowers it. You should be able to reduce or eliminate it with the optimum tune up, if not, you may have another issue. What is your altitude up there ?

The lambda relay under the seat, its aluminum usually and has a VW mark on it. When this is defective it acts like a faulty warm up regulator which is a pressure control.
Bruce

detonation can also be caused by build up of carbon on the pistons. it gets hot a creates an ignition for the fuel. it is also a source for preignition which is worse.

in my case, my cams where advanced 15 degrees. anytime i floored it, i got detonation and i could not go above about 4k. the more i retarded my timing, the better it got. but, i bought my car like this, so unless someone has messed with your cam timing, this is not your problem.

Thanks for the replies.

Psalt, thanks; I I suppose I need to add that this engine has a fresh top/bottom about 14K miles ago. also in your post you mention to use Bosch 5 plugs, but I think SCs are supposed to take 7s? Right now i have NGK BP7ES plugs in there.

Flat6pac, I DID have a faulty lambda relay last spring, which made startup and cold running really poor. Replaced that and everything got better.

Psalt, thanks; I I suppose I need to add that this engine has a fresh top/bottom about 14K miles ago. also in your post you mention to use Bosch 5 plugs, but I think SCs are supposed to take 7s? Right now i have NGK BP7ES plugs in there.

Gogar,

No, 83 US SC spec is WR5DC, the higher compression ROW is WR3CC. NGK has a different heat range number and higher is colder. I like NGK's in many other engines, but have had pinging problems with 911's, especially with the EV plugs. If you want to understand the problem, I recommend a compression test, swapping in the correct plugs and doing everything you can to lower cylinder head temp. If you are at a high altitude, the octane requirement should be lower. Was the engine rebuilt with stock parts, what is the compression ratio and what is the oil and air temp when you have this problem ?

Its getting cold in the mountain, Jeremy. I'd check your CO level with a meter or richen it up a bit using the field method to see if the pinging goes away. A fuel filter is cheap, I'd replace that too just because. If it's really clogged, you may be fine at low RPM, but the car may lurch at higher RPM (even at low throttle opening).

I'd pull the plugs and see if there is maybe just one or two cylinder is leaning out. You can also pull the injectors and get a six pack Corona bottles (I'm sure you won't have a hard time emptying them out). Put an injector in each bottle, then spray fuel into them to see if they are all injecting the same level of fuel.

Thank you

I'm at 5300 feet. The engine was rebuilt with stock parts, and 9.3/1 pistons.

Oil and air temp don't seem to matter as to 'when' i can make it happen, but in the spirit of that idea I feel that this car runs too hot (long drives = 230F on many days), even though I have installed a 28-row cooler in the front to try and help that out.

How's the cold idle and start up?

Start up is easy, with a little bit of idle bounce for about 2 minutes, then no prob. The car does not idle high then settle.

Without much effort, I would let it reach operating temperature, then open the airbox, remove filter and just lightly push the airplate up to see if your idle increases from 950 or so. If it can stand a little bit more fuel without going high, I would add more idle fuel and see if things change.

Unfortunately, an air cooled engine's octane requirement is extremely sensitive to heat. In my opinion, you just answered your own question. Are you still running the vacuum retard ?

No, right now my idle timing is 2-3 BTDC, retard line removed and plugged, idle adjusted back to 950. Which makes my 4k timing 12-13, ish.

Maybe you're right, Paul. I'm just kind of stuck because I can't figure out if I have a lean problem or a heat problem, or a lean problem that's creating a heat problem, and my limited knowledge just tells me to buy the highest octane I can. I'm trying though.

As a test, get some unleaded 101 octane:
Pynergy Petroleum Company (used to be Duggan)
4495 S. Santa Fe Dr.
Englewood, CO 80110.
Phone: 303-781-0546


This is just north of Union on the frontage road west of Santa Fe.
It is $7.98/gal but worth it for the test.

Be sure to drain your tank so you get 100% fresh high octane.
Raising the octane, with no other changes, will let you know it is actually detonation and not some other combustion/mixture issue.
A valuable test.

Best,
Grady

Gogar,

The stock 83 SC distributor has 10 degrees of mechanical advance in the distributor and should advance the crank reading 20 degrees, from 5 BTDC to 25 BTDC. If you are only getting 10 crank degrees, something is wrong.

Maybe this will help....The ideal spark timing for output in a 70 degree VIA hemi with domed pistons is around 35-40 degrees BTDC. The 83 SC is limited to 25 BTDC, because it was spec'd for 87 CLC fuel and the mfg has to build in a safety margin from detonation to cover all temperatures. Most of these cars are OK unless they burn oil or run hot. Retarded ignition timing raises the engine temperature in itself, and is less than ideal. Plugging the vacuum retard drops the operating temp at idle, but your further retarding the timing may be making the problem worse. Does the vacuum advance work ?

Your question adds up to me like this, you are at +5000 ft, that should drop your octane requirement around 2, and you are using 91 CLC octane fuel, 4 points above spec.... on paper you should have no pinging problem. Are you sure you are hearing pinging and not the CIS injector rattle ? They both respond the same way to the throttle. Pinging is very sensitive to temperature and you should notice a difference between cold and hot engine and air temp. One way to diagnose this is to fill up with some Sunoco or Cam2 race fuel and see if the problem immediately goes way. Knowing your compression pressure would be key to figuring this question out. If your compression pressure is on the high side, my advice would be to pursue all of the cooling issues, and get the hot, oil laden breather fumes out of the intake.

Thanks you guys. These should give me plenty of things to try for a while!

did it run right after the rebuild? (cam timing). was anything done to it before it started running bad?
was it a sudden problem?

the WR3 or 4 is probably too cold for a NA car with that compression, that is what turbo's are running. a too cold a plug will be black, or too rich on the mixture and it will be black. you need the hotter plug for cold starts and idleing, where the mixture is richest. it prevents fouling under these conditions. normal driving you can use a W3 or 4 because of the leaner mixture.
i put a W4 in my car for a long trip. when i stopped, the plug was like new. after driving around town, it was mostly black.

something that i noticed when experimenting with heat ranges. when i went to a cold plug, WR4, about the same as an NGK 7, my oil temp went up. here is why i think this happened. the plug had to dissipate that extra heat, so the heat went into the head, making the temp go up. i would not put a hot plug in there just to make my temps go down though. when the plugs are right, the mixture and timing are right, it should run as designed.
i am usiing BPR6's but i think i am going to the 5's.

carbon can raise the compression and cause hot spots in the combustion chamber, but if your engine is low miles, this is not likely.

Hey Gogar, If you don't mind keep us posted on how this develops.

There are a lot of us with SCs who may encounter this symptom and your findings would be very helpful...

I had similar issues when I switched to a MSD ignition, it would ping like mad above 2500rpm, I could never get the mixtures correct so I switched back to the CDI and have had zero issues since, but Psalt's insightful analysis of the aging systems makes me think sooner or later our high mileage 3.0l will need a bit of fine tuning...

Thanks guys!

yes, i think the high mileage, actually the blow by past the rings is causeing some stumbling off idle for me.
but, i have always thought that if the compression was low, and the piston does not pull in as much air, the sensor plate does not move up as much, but the mixture is still correct for the amount of air coming in. hence the purpose of the air flow meter.

update:
 

So, since I last visited this thread I:

Cleaned out my distributor a-la the "Gunter" thread. Fun. Easy.

Upon reinstalling, I set the timing at 5 BTDC, and can achieve between 20-23 after 4Krpm, vacuum advance NOT attached, and between 25-27 WITH vacuum advance attached. I feel good about that.

It did not change my 'detonation" issue, but I didn't really expect it to. I just like knowing my distributor is in order etc.

In addition:

I pulled all 6 injectors and took to my mechanic, who has one of those CIS injector hand-pump thingys.

All were dirty, #5 was SO DIRTY that it just bubbled and shot a stream out SIDEWAYS, , which likely made a puddle in the runner and led to really poor combustion.

As we were cleaning all the injectors, I had an impulsive moment and decided to replace all 6 injectors. Once every 90,000 miles? I think that's fair.


So, with 6 new injectors and seals, etc., we reset the CO, which was VERY LEAN due to all the unburned fuel that dirty one created.

This fix seems to have reduced my engine temps, which is a bonus, and also has slightly helped, but not eliminated, my DETONATION issue. I still can make it happen if I'm cruising at 2Krpm in first or second, and floor the throttle.


As a side note, during this parts-hurling process I also installed some Magnacore wires, and found that a few of the old stock wires had a much higher resistance than they should.

This also did not eliminate my pinging, but gave me a nice placebo effect for a few days. I know deep inside that it is a good move anyway.

So, in order, this is my progress:

1. fuel filter (old one 4 years old.)
2. Distributor clean and lube, seems to be good.
3. 6 new injectors
4. New plug wires.

Slight, but not complete improvement with the above things.




So, I'm still looking for suggestions. I am going to run a tankful with some Techron, and see what happens. If that does not help i'm thinking (correct me please if I'm wrong) that I will pull the fuel distributor and the hard injection lines and clean by hand, just to make sure. With that I would pretty much call my 'fuel delivery' system clean as a whistle, and my ignition stuff in pretty fair shape, and I will have to look for something else in the system.

Any suggestions? thank you SmileWavy

measure the fuel delivery of all 6 injectors. do this by placing each in a seperate jar, turn the key on, then liift the sensor plate all the way up. the more fuel you can put in the jars, the more accurate the test.
i found a bad (plastic) injector line. i was only getting half the fuel from one injector. mine was obvious, but i also poured each jar seperately into a common container and weighed each one on a postal sacle. i dont think i would worry about small differnances. when i cut the line open, it looked like a manufacturing defect on the line.

have you checked the fuel delivery of the fuel pump?

has your car run like this since the rebuild? am i correct, the engine only has about 14k miles on it?

Yes, I will do that at some point.

Good to know. I have steel lines which should be easy to clean out, if anything is amiss.


No. The way I figure it, the car runs fine at high rpm, which is the 'maximum fuel delivery' point, so if there was a low-output FP issue, it would show itself at that time, which it doesn't.

No, it has not. It has always run ok, but this detonation/pingy sound is a few months new. I was looking for a "My SC runs hot" kind of issue before this, but I'm hopeful that it was due to the extremely dirty #5 injector/mixture off/etc. issue.
SmileWavy

i use techron with a half a tank, and i try to keep the RPM's up for longer periods when i do.
it cleaned up my BMW real nice.


i was going to say go back to the lean theory. but if it was lean due to lack of fuel, i would think it would show up in the upper RPM's (too). (man, this is dejavoo. i had ALL these same thoughts with my problem) you dont know how many times i started to pull the FD off and take it apart looking for corrsion if the fuel chambers or replace the FP. glad i didnt.

if you suspect there is stuff in the FD, you dont want it clogging those new injectors. pull the injectors off and check fuel flow out of the lines.

you could pull a vacuum on the advance to check the amount of advance to make sure it is not to much. you know, someone else was having this problem a while back. maybe i can remember who.

do you think it could have anything to do with closed loop to open operation? fuel pressures ok?

try going rich and see if it stops the ping, it may not idle right, but it is just a test. i would run mine wildly rich, or excessive retarded timing trying to figure out if was at least fuel or ignition.

Flow test
 

Here's the results of a baby-bottle test I performed today. No huge problems IMO.

Note: I did this just using the fuel lines, as I have 6 brand-new injectors.

Even thought the flow is 'even', is it possible a gummy fuel distributor piston could make the mixture "lean" on WOT from a relatively low RPM? Like, the gummy piston slowly moves to where it should be? Sorry if it's that's a dumb question.

http://forums.pelicanparts.com/uploa...1291156382.jpg

Even a new injector can go bad, but probably not your problem. The fuel distributor plunger has to move when the air plate moves up. They are mechanically linked (sort of).

Thanks Souk; that's something I didn't know.

that looks good.

lets go over what you have now.

your control pressures are good. (rechecked?)
your timing is correct.
fuel delivery is even. (what about system volume?)
no air leaks.- are you sure about the air leaks. have you checked the plumbing in the rear? what about the vacuum line to the booster that JW did a write about? i put a vacuum gauge on mine, pulled a vac and let it sit to see if it held.
replaced the lambda relay. (frequency valve working properly? checked it with dwell meter?)
new injectors.
new wires. (MCA had a problem with his new wires, dont remember the brand)
fuel filter? (even though my fuel filter was VERY old, it made no difference for me, but my tank is also clean). (how is your tank and pickup screen?)

fixed:
your engine temps are down.


problem:
detonation at low RPM and at high RPM?

did i miss anything?


put an LM2 on it and check the mixture across the RPM range if you suspect it is lean.

you know, someone else had a lean issue in the low 2k rpm's, wish i could think of who it was.

From your description, this sounds like ignition not fuel. You said you swapped distributors, how about your green wire? I once had very similar conditions(pinging/pre-detonation)and the cause was shorting of the green wire at the plug connection. I cleaned and applied some of that liquid electrical tape to produce a fresh insulation around the wires as the exit the plug and the problem went away. Worth a check. These wires are very sensitive and live in a harsh environment.

I did examine the green wire when I cleaned my distributor, and it 'looked' ok to me, but I can always look again, maybe stick a meter on it.

I'd be taking up Todd on the offer to use his LM1 to check your afrs and get some hard data about what is going on.

Interesting...

If I roll open the throttle from lower RPM climbing hills in my 930, my J&S Safeguard (individual per-cylinder knock sensing/retard) almost always pulls 1,2 and 4 degrees of timing at 2,600 RPM.

Only place in the RPM range it does it - never detects knock at lower or higher RPM - and the knock goes away long before there's enough manifold pressure to enable the WUR boost enrichment circuit - so as far as CIS is concerned, this is N/A mode.

I kind of suspected that either CIS goes momentarily lean under those circumstances, or that there's just slightly too much advance in the picture right there at that engine speed. Or both.

Watching this, I’m going to repeat my admonition in Post #21:

This is THE WAY to confirm or eliminate detonation as a cause.

For the additional cost of a few more $/gal it does no harm.

If you take your cat off, you can use the leaded 114 octane for the test. :D

Best,
Grady

Thanks, Grady. It's my next step, as soon as I get through this tankful of Techron.

SmileWavy