Cold start issue with my newly refreshed CIS

[Jameel]

Thanks Walt.

I checked my pressures again this afternoon. Cold pressure was 2.5 bar, right at the low end of the spec for the temp. So, onto your questions.

Micro switch: It was working fine when I reassembled the CIS last month. But today it was a little sticky, and as it turns out, it actually wasn't clicked up in its closed position by the arm on the throttle. I pressed up on it with my finger and I heard the click of the contacts closing. The spring wasn't quite pulling it shut all the way. So I lubed the pivots and also loosened the two screws that hold it on and pushed the whole switch down a little so the throttle arm in effect pushed the switch's are up closed. It's working properly now. I did check it electrically last month when reassembling the CIS. It checked out fine. The car is warm now, so it's idling fine. But I'll check it again later this evening after its cooled off and see if that solved the problem. I'm still a little foggy on what the switch does. Jim doesn't describe its function, just has a picture of it "Throttle Switch 2"

I tested the throttle position sensor (Jim's Throttle Switch 1) electrically when I reassembled the CIS last month and it checked out okay according to Bentley specs.

I also tested the decel valve and it held vacuum.

Tested AAV according to Jim's method. Tested good.

I thoroughly cleaned my Lambda harness and connectors and sprayed them with Deoxit before reassembling. They are clean. Also running a new engine harness from Dennis, so that's clean too. I also checked the stuff under the passenger seat, but don't remember if I actually cleaned it. I would have if it looked dirty.

So we'll see if the "throttle switch 1" did the trick when I start it cold next.

Engine runs sweetly once its warmed up (minute or two) but as with many rebuilds, I'm just super anal about it being as good as it can be.

[gazzerr]

Very interested to see if that helps with your problem.

I have found that generally the WUR's tend to lean out too quickly, especially when it's warm out, so it's never a perfect cold start cycle.

Tony generously re-calibrated my WUR last week and it does start better. I'm getting 1000 rpm "cold" starts here in really warm 86 degree weather. Before my CCP was way too low and the rpm would oscillate quite badly until it warmed up. CCP is definitely a factor in your rpm during the warm up cycle.

Walt - I'll check my micro switch to make sure it's closed properly too before I start it next to see if that gives a clue.

[zelrik911]

Dont overlook the thermo time switch in the LH timing cover. It is a link between the starter solenoid and the WUR. Test it as it may be sometimes faulty?

[Jameel]

Went out first thing this AM to fire it up. 56 degrees in the garage. Here's the video. It is definitely better. You can see it idle a smidge slow, then idle a little higher right away, gradually slowing back after about a minute. Someone tell me this is just about right and I'll be happy!

My notes don't mention that I tested thermo time switch, so maybe I tested, maybe not. I think not since I never had cold start issues before (7000 miles last year) so I probably just put it back on the chain cover assuming it works. I will test today.

[rwest]

Jameel,

When I start mine, it pops up to about 1500rpm and then settles down to around idle fairly quickly in warmer weather.

Not sure if mine is correct either, but that's pretty much how it has behaved for the 27 years I've owned it.

Rutager

[boyt911sc]

Originally Posted by zelrik911

Dont overlook the thermo time switch in the LH timing cover. It is a link between the starter solenoid and the WUR. Test it as it may be sometimes faulty?

Zelrik,

Go over your post (above). Read it several times maybe you will notice what's the error.

Tony

[boyt911sc]

Originally Posted by rwest

Jameel,

When I start mine, it pops up to about 1500rpm and then settles down to around idle fairly quickly in warmer weather.

Not sure if mine is correct either, but that's pretty much how it has behaved for the 27 years I've owned it.

Rutager

Rutager,

Depending on the ambient temperature, a cold start would normally be between 1400~1600 RPM. When the temperature gets well below freezing point, my SC revs more than 1600 RPM and you could hear the engine speed gradually go down after 30 sec. and continue to go down up to 2 mins. until it stabilizes. Unlike modern engines that need only several seconds, our 911 CIS needs to wait much longer.

Tony

[Jameel]

I didn't get a chance to test my TTS today. Pretty sure though that the TTS in its cold state allows power to the cold start injector through the ignition switch. Once you turn off the ignition, the injector stops injecting. Then once the TTS warms up via engine heat the cold start injector doesn't get activated on startup. Isn't there also a time limit on cold start, such that if you're cranking the engine cold it only injects for 8 seconds so as to not flood the engine.

[Jeff NJ]

I think the RPMs at startup in your video are just fine. You can hear the rpm increase after a second or two as the solenoid closes to advance the timing for about a minute, then it idles down and runs smooth once the solenoid opens and brings the timing back.

Not sure its worth the effort to try to improve on what you have if it is consistently like that now. I say problem solved!

[Jameel]

Originally Posted by Jeff NJ

I think the RPMs at startup in your video are just fine. You can hear the rpm increase after a second or two as the solenoid closes to advance the timing for about a minute, then it idles down and runs smooth once the solenoid opens and brings the timing back.

Not sure its worth the effort to try to improve on what you have if it is consistently like that now. I say problem solved!

Ummm...what solenoid? Are you talking about the cold start injector? And where's the timing advance you're talking about? I thought the dizzy can only advance under higher rpm-induced vacuum and centrifugal force under the same conditions?

[Walt Fricke]

I had the same "ummmm". The CSV is an electronic fuel injector. The TTS prevents it from squirting any fuel with the engine warm/hot. There is a heater element inside the TTS which causes a bimetallic element to open a contact, which breaks the circuit to the CSV. Don't know the exact parameter, but 8 seconds sounds about right, maybe less.

On our Lambda cars the frequency valve makes the mixture rich when the engine is below 15 deg C. When the engine gets above that, the FV quits doing that. With the O2 sensor working, at that point the system will try to keep the air fuel ratio at 14.7 or so while you are cruising, but at wide open throttle (seldom used around town, or even on the highway) it richens the mixture up for more power.

Anyway, a higher idle right after starting, with it descending to whatever you have it set for (850?)thereafter, is normal.

Dropping low, as yours did, is not normal.

[Jeff NJ]

Originally Posted by Jameel

Ummm...what solenoid? Are you talking about the cold start injector? And where's the timing advance you're talking about? I thought the dizzy can only advance under higher rpm-induced vacuum and centrifugal force under the same conditions?

My bad. The solenoid I was talking about is a vacuum solenoid plumbed into the vacuum hose to the distributer, but that isn't the case on your car. It advances timing for a bit when cold, which increases the rpm, which I thought I heard it do on your video because it sounds just like my 930, which has that solenoid.

Regardless, if your cold start idle stays the way it is now, congrats!

[T77911S]

that started pretty good. good idle....smooth. low but that would not bother me...too much
started to sound bad at the very end of VD maybe???
did not read first page, is the AAR doing its thing? could be a matter of it not opening as far as it should or not closing as far as it should. (if it does not close as far as it should the idle setting compensates for this).

could just need a minor mixture adjustment. try lift up and pulling down on the sensor plate as soon as you start it cold to see if it idles up/better. if warm mixture is good then adjust CCP.
if its too rich I would just leave it. no not a hi idle but it starts good and idles smooth.

TTS has nothing to do with the WUR

[rwest]

I would agree that it starts real quick and nicely. Just seems that at 56 degrees out it should idle higher for at least awhile.

What components are responsible for the higher idle at start up? More than just the WUR?

[Paulporsche]

From your video it looks to me that your mixture is just ever so slightly rich during that phase of warmup. You are getting just a little bit of a hunt. If you do a quick rev to 4000 and snap the throttle shut, does the idle try to dip down or does it go right back to 1000?

How is the idle once fully warmed?

Also, and you may not get to try this until the fall when things turn colder, how does it act under a colder cold start situation?

[Walt Fricke]

In an SC with the FV, the FV is what gooses the cold idle - 65% duty cycle when engine temp is below 15 degrees C. Plus, of course, the residual from the CSV. Above that temperature, idle is always at 50% duty cycle, so there is no idle enrichment.

[T77911S]

the AAR is what increase the idle.

the drop in CP from the WUR and change in DC with the FV increases fuel enrichment for the cold starting and initial running when cold.
if the mixture is too lean when cold then you get the backfiring.


hey paul. I was just thinking about you yesterday. thinking I had not seen you here in a while.

[Jameel]

Originally Posted by Paulporsche

From your video it looks to me that your mixture is just ever so slightly rich during that phase of warmup. You are getting just a little bit of a hunt. If you do a quick rev to 4000 and snap the throttle shut, does the idle try to dip down or does it go right back to 1000?

It will settle back to 900 if I blip during the high idle warmup. But I pretty much never do this, rather letting the system bring it back down before I get underway.

Originally Posted by Paulporsche

How is the idle once fully warmed?

Great. 900 and steady in varying conditions.

Originally Posted by Paulporsche

Also, and you may not get to try this until the fall when things turn colder, how does it act under a colder cold start situation?

Not sure yet, but I've started it in the 50's, but not colder than that yet.

As a general update, it seems like I'm getting the low idle start more frequently now. It will struggle at 200rpm for maybe 10-15 seconds then eventually pop up to 1100. But I don't like hearing the engine struggle like this so I just shut it off at once, then restart. 100% of the time when I do this it will pop right up to 1100 on the second start, then settle back to normal idle in a minute or so. I would love to know what is changing in the system that makes it idle higher every time on the second start.

[DRACO A5OG]

If I may, you really should not be sitting at idle, just drive off so the parts get enough oil to avoid undue wear.

[T77911S]

could be fuel pressure has built up
mixture (CCP) could be off and the second start just clears things up. perhaps plugs. what heat range are you using. how do the plugs look. take a look at them when warm and after a cold start. look for wet ones.
mixture could be slightly off.

remove the connector on the top rear of the AFM. when cold, turn the key on and let pump run for 5 seconds then start