83SC multiple symptoms possibly running lean?

[zje]

Back in May I took the car to a very reputable shop to have CIS settings tuned as I do not have a CO meter. The mechanic said he heard some predetonation and asked what kind of gas I used. I had been going out of my way to get ethonal free 90, and he said I really should use 93.

After getting the car back, the idle seemed low on cold starts. Once the car warmed up, rpms were at a nice stable 950. However, the rpms got so low when cold that the engine died a few times. I turned up the idle and it stays running but warm idle is now at around 1200.

The thing that has me worried is that oil temps are higher than I remember them getting last summer in similar weather.

I am wondering if the car is running lean. Combination of low cold idle, running hotter, and predetonation... One thing I did not mention to the shop was that the PO had the cat bored out, would that affect mixture settings?

I don't want to mess with the mixture without a CO meter, is there any more troubleshooting I can do? I've read a little bit on pulling/pushing the plate in the airbox, but that doesn't seem to be deterministic either.

Thanks again for all the help and sorry for the rambling!

[Bob Kontak]

Predetonation is a primarily a function of timing.

Where is your's set?

[zje]

I actually asked that shop to set timing as well, I had set it myself previously but haven't checked since they set it.

I can dig out the light and see where we're at, but the same person who set it is the one that told me I have predetonation.

Another thing: when accelereating today, I heard a weird noise around 3.5k. Hasn't come back, sounded like a flutter.

On the spark side, I have a msd 6al (not digital), and replaced the green shielded wire last year.

Thanks!

[zje]

Finally was able to dig the timing light out. It looks like it was just to the right of the 5 degree mark at idle. I was alone so I couldn't check the higher rpms.

I've put a couple hundred more miles on the car and I noticed that same flutter noise yesterday under hard acceleration. I'm still thinking it might be predetonation.

When I was looking around the engine compartment, I noticed a loose green wire (picture below). There was also a boot with nothing plugged in (my picture didn't come out and I'm not with the car at the moment to take another). Is the O2 sensor disconnected (I remember reading that the O2 sensor is a green wire between the fuel filter and accumulator)?




Thanks!

[pmax]

Check if your O2 relay, under the seat, is working. If it's not, the car runs lean.

81 SC Oxygen Sensor Relay

[T77911S]

adjusting the idle for cold running is NOT how you do it.
adjust the idle for running hot.

there is a device called an aux air regulator (AAR) located on the right side of the engine between the runners,. it has to vacuum hoses and one elec connector. the connector should have 12v on it. check it with a test light. the AAR opens when cold to let more air into the engine to raise the idle. then is closes as it is heated by 12v.

did your mech check fuel pressures. if so find out what they are. this is a MUST before setting mixture.

are the oil temps higher just at idle. if so does it come down with steady driving.

you don't have to have 2 people to check timing,. just rev it until it stops advancing.


it usually will not run if the O2 relay is not working. check the frequency valve and make sure it is vibrating with key on.

[Bob Kontak]

Originally Posted by T77911S

you don't have to have 2 people to check timing,. just rev it until it stops advancing.

Newer SC's have the wimpiest timing advance of the bunch. 18-23 BTDC maxed out and that happens before 3.5k RPM.

You don't have timing marks on the wheel for max advance but what you can do is use the timing light and make sure the timing is advancing when you blip the throttle.

If you did not pull/plug the retard hose off of the vacuum unit and you read say 7 degrees BTDC at idle you are about 10-12 degrees more advanced than you should be. That could be as much as 34 degrees max advance at 3k rpm on up. That will cause detonation with 87 pump gas.

You should read almost 5 degrees ATDC with all hoses attached at idle.

[Bob Kontak]

Originally Posted by pmax

Check if your O2 relay, under the seat, is working. If it's not, the car runs lean.

Originally Posted by T77911S

it usually will not run if the O2 relay is not working. check the frequency valve and make sure it is vibrating with key on.

They will spin but not really drive-able. Intake backfires with throttle blips and no response. Nothing robust to speak of.

Here's a vid I made several years ago before and after pulling the O2/Lambda relay. All old timers here have seen it. It goes south in a hurry.

[zje]

Here's a link to a video of my timing measurement with all hoses connected at idle. It's hard to see because I couldn't get my phone closer, but at around 7 seconds you can get a pretty good idea of where things are at.

https://www.youtube.com/watch?v=AMy2GBgVoCU

Here is a freeze frame that I think captures it. Based on Bob's comments, it looks fairly advanced. That other mark off to the side was a paint pen marking I tried to make last year for the advance. Looks like I need to retard timing possibly? Bentley says to disconnect hoses, so I'll try and see if I can measure it again with hoses disconnected...




Will ask about fuel pressure, the mechanic I used believes the symptoms I've been seeing are due to a dirty injector. I do prefer to DIY, I only brought it to a shop to have the mixture adjusted since I don't have a CO meter. The reason I was originally thinking lean mixture setting is that I have symptoms at cold idle and with harder throttle - which are both situations under which CIS runs open loop.

When it comes to the FV relay I will test it later, but I did unplug it last year and the car ran like complete garbage, definitely sounded like it was going to stutter and die.

Thanks all for the help!

[zje]

I hopped into the garage to get a photo of the boot that was unplugged. Should that little green wire in the bottom of the photo be plugged into the boot in the top of the photo? Definitely don't want to randomly try stuff like this, but what I've been reading indicates this might be the O2 sensor.

[pmax]

Originally Posted by zje

I hopped into the garage to get a photo of the boot that was unplugged. Should that little green wire in the bottom of the photo be plugged into the boot in the top of the photo? Definitely don't want to randomly try stuff like this, but what I've been reading indicates this might be the O2 sensor.

Yeah, that female end is from the O2 sensor. There should be a matching male plug, long disintegrated I say, with the green wire inside.

That green wire goes to the O2 computer and it's exposed. Who knows what random signals it's sending to the lambda control ?
Tape it up or add a connector. O2 Sensor Connector Crumbled, $1300 Replacement Part???

[zje]

Re-plugged in O2 sensor, as expected cold idle didn't improve. Didn't see much difference in my short test drive to warm up the car before timing measurement, but it's good to know that was addressed.

Speaking of timing, here is a video of the timing light with the vacuum hoses to the distributor disconnected and plugged:
https://www.youtube.com/watch?v=93KsgKnePng

And a relevant still image:


Note that there are three marks, the factory TDC and 5 BTDC and the one all the way to the right is a paint mark I made for max advance.

So it looks like the timing is advanced. Only thing I've done to the distributor since the mechanic set timing in May was replace the bosch rotor with a GB330 since I have an MSD box, but I assume that shouldn't change anything. What could cause the timing to be so far off?

[Tylermelvin]

I’m dealing with a similar issue. 15 minutes of driving has the temp gauge near red, stop, then restart ~dies once, then turn over and starts w/a puff of smoke sometimes. One day at high temp off a longer drive the fuel pump I had replaced last season started buzzing like crazy, but only for that day and haven’t heard it since. Coincidence but I also have exhaust coming in through the interior vents after hot running and shut down.

I’m also thinking flooding/dirty injectors or possibly could it be something with my fuel pump?

[Bob Kontak]

Originally Posted by zje

What could cause the timing to be so far off?

Folks get a little too aggressive.

The timing is not horribly off. Let's say you are at 12 BTDC vs 5 with hoses disconnected.

I would adjust it to 5 and take it for a ride and see if strange noise occurs.

What octane are you running?

[zje]

Originally Posted by Bob Kontak

Folks get a little too aggressive.

The timing is not horribly off. Let's say you are at 12 BTDC vs 5 with hoses disconnected.

I would adjust it to 5 and take it for a ride and see if strange noise occurs.

What octane are you running?

Won't have time to mess with this and drive the car again until Tuesday, might reach out to the shop who set the timing and see what they say too.

Been running 93 (with ethanol) since the mechanic recommended it due to detonation that he heard, before that I always went a little out of my way for 90 octane ethanol free (but probably with a worse additive package).

One issue that still bothers me is the low cold idle, I've been tempted to check the mixture as well, as I've seen a lot of folks on here run much richer than what the decklid says.

Thanks again for all the help!

[Bob Kontak]

Originally Posted by zje

Won't have time to mess with this and drive the car again until Tuesday, might reach out to the shop who set the timing and see what they say too.

Yep.

I can say I would not know the difference between a broken head stud noise and detonation. I know a little bit of stuff about a lot of things but I am not a Porsche wrench.

I will tell you one trick. Put a golf tee in the retard hose at the distributor and let it hang. Nothing on the vacuum pod tube. Leave the advance hose intact. It made a world of difference on start up with my car (81 - pretty much same as yours). Retard is inboard closest to fan.

The deal is all of the CIS bandaids (e.g., AAR/AAV) get a little tired. Bumping advance at idle (by eliminating the retard vacuum) gives it a little more vitality when starting.

You can adjust timing with a wrench and your light. Get it to 5 BTDC with retard hose plugged. Advance is non functional until off idle. It works in conjunction with mechanical advance to establish your advance curve as RPM's increase.

All that said, do what you feel comfortable with. A trusted mechanic is a good sounding board.

Enjoy the rest of the weekend and keep us posted.