Cold Start Issue - Video - Page 4

Paulporsche · 09-14-2007, 01:30 PM

mca,

The things psalt is talking about are just the items I'm afraid I have no knowledge about. I know they are covered in Bentley.

BTW have you checked for broken head studs? About 2 yr ago I had a warmup condition that seemed to be due to a broken head stud. I say seemed. I am not entirely sure. Maybe someone else has experience w/ this. When you check for leaks it wouldn't be a bad idea to check for exhaust leaks too. As I said before, my speakers aren't so hot. Do you detect any exhaust not changes as the car warms up?

mca · 09-15-2007, 01:58 PM

UPDATE:

Today I decided to plug in the vacuum hose at the deceleration valve (never had it connected since I have owned it - 2.5 years). It had previously been plugged with a screw. Unfortunately the vacuum hose was too brittle and cracked while trying to fit it over the decel nipple.

I thought it best to replace the entire hose not knowing that there was a third connection behind the throttle body. For those unfamiliar with this hose (like I was until today), it runs from the cruise control servo (back left of engine) to the throttle body where there is a 'T' connection and then it continues to the deceleration valve at the right/back of the engine (for an 82 SC anyhow).

Anyhow, I got the hose back in place and all of the connections made and was pleasantly surprised at the results.

HOW DECEL VACUUM LINE CHANGED MY CAR:
1) Revs ease down between shifts instead of dropping off hard. I really like this - just seems so much nicer.

2) No more blap blap blap popping which I have always experienced in my car no matter how lean or rich the mixture. I really like this too.

3) No more smoke on decel. Well, I need to drive it super hard for a bit in order to really determine if this is true. But so far so good.

I will see how she cold starts tomorrow and report back. AAR seems to be working fine too.

Thanks,
Craig

mca · 11-19-2007, 01:57 PM

Haven't done much more as far as troubleshooting this since I recently spent most of my time changing oil lines and adding a new oil cooler.

Again, she starts up fine and idles around 1800 then dies off. On the second try, everything is perfect. Idles high for a bit and then settles to 950 just like she should.

There HAS to be an easy answer here. She runs perfectly otherwise - cold, hot, you name it.

It is just the first crank ... gets plenty of fuel and starts right up ... after 3 seconds or so the idle tapers off and struggles to hang on (or dies). Second crank is perfect.

I can live with it but I hate to start my car twice everytime I want to cold start it.

BRB-83-911SC · 11-20-2007, 08:02 AM

This thread is of great interest to me, as I have the exact same cold start symptoms you have (your video's sound just like my car). Warm start is fine. I do have a new WUR installed, new airbox, pressures in spec, etc. The symptoms I experience do have a twist, though:

1 - Cold Start during summer temps - intitial rev, then severe stumbling at the verge of stalling, then after about a 30 - 60 seconds return to normal 950 RPM idle. I still need to let it idle for a few more minuted before I can drive off without stumbling.

2 - Cold Start during colder temps (below ~45F) - initial rev and immediate smooth idle at ~1200RPM, slowly settling back to 950 RPM after several minutes. I can drive off immediately with no stumbling.

3 - Warm Start at all temp is perfect, engine idles and runs out perfectly with no hunting or hesitation.

Is my understanding correct on these components?

AAV - provides for initial "blast" of fuel for initial start (seems to be working as it should in my case).

AAR - provides for temporary fuel enrichment during cold start and warm up (seems to be working in my case when ambient temp is below ~45F, but not during warmer temps)

So, a comment by "psalt" has me thinking: "There is a temperature switch on the right timing cover that is closed below 59F for cold starts, but this is too low for some climates and there is a replacement Bosch switch that is closed at 78 degrees."

Does this switch control activation of the AAR?

I have been learning as much about the CIS system as possible, but don't mess with it myself. I had a reputable shop do the previously mentioned CIS repairs and set up, and it was done during colder weather.

Good thread, and looking forward to the resolution of your issue.

mca · 11-20-2007, 08:13 AM

Quote:

Originally Posted by BRB-83-911SC

This thread is of great interest to me, as I have the exact same cold start symptoms you have (your video's sound just like my car). Warm start is fine. I do have a new WUR installed, new airbox, pressures in spec, etc. The symptoms I experience do have a twist, though:

1 - Cold Start during summer temps - intitial rev, then severe stumbling at the verge of stalling, then after about a 30 - 60 seconds return to normal 950 RPM idle. I still need to let it idle for a few more minuted before I can drive off without stumbling.

2 - Cold Start during colder temps (below ~45F) - initial rev and immediate smooth idle at ~1200RPM, slowly settling back to 950 RPM after several minutes. I can drive off immediately with no stumbling.

3 - Warm Start at all temp is perfect, engine idles and runs out perfectly with no hunting or hesitation.

Actually, we have the EXACT same problem. Although I can't say for certain about the temps being below 45F, I do recall starting her up on a rather chilly morning without issue. Usually here in Charleston, SC it is warmer than 45F.

Your #1 comment perfectly describes what I am experiencing - verge of stalling ... now I just cut her off and restart without problems. What happens when you immediately restart in this scenario?

psalt · 11-20-2007, 08:30 AM

Is my understanding correct on these components?

AAV - provides for initial "blast" of fuel for initial start (seems to be working as it should in my case).

AAR - provides for temporary fuel enrichment during cold start and warm up (seems to be working in my case when ambient temp is below ~45F, but not during warmer temps)

So, a comment by "psalt" has me thinking: "There is a temperature switch on the right timing cover that is closed below 59F for cold starts, but this is too low for some climates and there is a replacement Bosch switch that is closed at 78 degrees."

Does this switch control activation of the AAR?

Hello Brian,

No, both of these handle air not fuel. The AAR is the main CIS device to increase idle speed on a cold engine to overcome friction. The AAV is an add on throttle bypass to add air for starting and stablize the sensor plate. Unfortuantely these terms are swapped in several places and if you want to get a CIS education, stick to the Bosch manuals, "Gasoline Engine Management" is a good one.

The final version of CIS is a collection of band aid separate components that do not speak to each other like spoiled little children that will not cooperate.
You have to understand each one separately and how they effect the overall operation of the engine. The final CIS version is widely misunderstood and you usually get part swapping advice from people who have never sorted one out. Before attempting anything, you should check the ignition timing and the dwell reading of the frequency valve cold and hot.

In my experience, the initial stumble and stall is usually caused by the vacuum retard kicking in and has nothing to do with CIS. You can easliy test this by disconnecting the grey hose at the back of the distributor and resetting the idle speed with the larger bypass screw. You do have to wait a day to test a cold start.

Paul

BRB-83-911SC · 11-20-2007, 09:24 AM

mca - mine does sometimes stall, and when it does, it starts up on second try fine, without stalling again. However, it restarts and idles at low RPM's until it levels out. Still have to let it idle a bit once leveled off before I can drive off. I think it is a lean condition in this instance. When starting in cold ambient temps, and I get the "fast idle", I can drive off right away with no stumbling, which seems to me that in this situation (colder ambient temps) the mixture is richer. This is what led me to ask whether the "temperature switch" activates the AAR during cold temps (below 59F). If so, maybe the 78F switch would be a solution.

psalt - sorry, I do realize that the AAV and AAR handle air, but don't they in effect cause the sensor plate to react, effectively introducing more fuel? I guess my question to the point is, does the temp switch cause the AAR to come into play only at ambient temps below 59F? It seems in my case that I get the idle speed boost (and I would guess fuel enrichment) only in cold ambient temps, when I could actually use that enrichment in warmer conditions as well.

Anyway, I will pull out my Bentley to brush up on this some more. I'm not necessarily looking to make any changes right now, as the car is running better than ever, but have been curious about this cold start issue.

Paulporsche · 11-20-2007, 09:46 AM

If you go back to the first page, you'll notice that vac leaks were mentioned as a possible source for this problem. Since a new vac line to the decel valve helped, maybe new lnes are needed elsewhere, say to the dizzy or AAR.

I did what psalt mentions recently. I disconnected and plugged the vac retard line to the diz. Warmup and idle are greatly improved.

BRB-83-911SC · 11-20-2007, 10:29 AM

OK, I should have gotten the Bentley out BEFORE posting!

- Cold Start Injector - sprays extra fuel into the intake during initial cold start cranking. Thermo Time switch controls how many seconds the Cold Start Injector operates. (works for me)

- AAV - Provides additional bypass airflow to the sensor plate during starting. Default position is open, valve is closed by engine vacuum once the engine is running. (works for me)

- AAR - Provides additional bypass airflow to the sensor plate to raise idle speed. Valve is slowly closed by electrically heating a bimetallic strip. (Should "fast idle" occur on a cold start, regardless of ambient temp?? Or, does the ambient temp have an affect on the bimetallic strip? i.e. if above, say, 55F, AAR remains closed.)

- Temperature Switch (15C/59F) - Forces closed loop operation of the O2 system when OIL temp is below 59F, allows open loop operation once above 59F. (does not affect operation of the AAR, as I had questioned)

Sorry for the confusion.

PS - just went out to the garage, 39F here today. Started, stalled, re-started and idled smoothly at ~1200RPM, slowly dropping back to normal 950RPM.

psalt · 11-20-2007, 10:30 AM

psalt - sorry, I do realize that the AAV and AAR handle air, but don't they in effect cause the sensor plate to react, effectively introducing more fuel? I guess my question to the point is, does the temp switch cause the AAR to come into play only at ambient temps below 59F? It seems in my case that I get the idle speed boost (and I would guess fuel enrichment) only in cold ambient temps, when I could actually use that enrichment in warmer conditions as well.

Hello Brian,

No, the temperature switch is for the lambda system. The AAR has no switch, only a heating element to help close the throttle bypass within a consistent time. Idle speed is controlled by air bleed around the throttle plate through several devices, not fuel enrichment. The CIS lambda was calibrated to meet a specific set of emission tests, drivability was "adjusted" with band aides and add ons. The system is too lean by default and the FV richens it up to almost OK on a new engine with no vacuum leaks. They got the calibration wrong on the 80 version, improved it abit on the later version, then dumped it for Motronics before it was fully sorted.

If it takes two attempts to cold start, there are several factors in play. The lean condition is caused by engine wear and vacuum leaks at the injectors, sleeves and plumbing, resulting in a lower sensor plate deflection than on a new engine with perfect compression. As soon as vacuum builds and hits the distributor, the loss of 5 degrees of timing is often enough to stall the engine. The second attempt fires the CSV again, making the mixture rich enough to get through the transition. You can put up with it, or disconnect the retard and reset the idle. The retard was added solely to met the curb idle HC test and has the side effect of raising the idle temperature on a hot engine. They run much better without it. The CIS lambda cars also tend to run lean and a better compromise for drivability can be found by setting the FV dwell to 35-40 instead of 45-55. This results in a richer mixture on cold starts and WOT, but the system will correct to stoich below 35% throttle.

Paul

BRB-83-911SC · 11-20-2007, 11:09 AM

Thanks Paul. That all makes sense to me. Even if I live with it as is, at least I understand it!

mca · 11-20-2007, 11:27 AM

Quote:

Originally Posted by psalt

In my experience, the initial stumble and stall is usually caused by the vacuum retard kicking in and has nothing to do with CIS. You can easliy test this by disconnecting the grey hose at the back of the distributor and resetting the idle speed with the larger bypass screw. You do have to wait a day to test a cold start.

Paul

So, to do this I get my car up to operating temps, pull and plug the grey hose, adjust idle accordingly and then shut her down and wait until the next day to see what happens?

psalt · 11-20-2007, 12:00 PM

Yes

mca · 11-20-2007, 02:58 PM

Quote:

Originally Posted by psalt

Yes

Didn't notice any change in idle speed when pulling and plugging the vacuum retard line (mine is orange). Is that normal?

psalt · 11-20-2007, 03:18 PM

Didn't notice any change in idle speed when pulling and plugging the vacuum retard line (mine is orange). Is that normal?

Not normal, you probably pulled off the wrong line, the advance line is orange. There are two lines to the distributor canister. The front hose is for the vacuum advance, it uses ported vacuum and is irrelevent at idle. The grey hose at the back of the distributor is for the vacuum retard, it uses manifold vacuum and is active at idle. If you remove the distributor cap and look at the direction of rotation, the operation of the vacuum canister should be obvious. Put a few drops of oil under the pad and snap the rotor against the advance while you are in there.

Paul

mca · 05:02 PM

Quote:

Originally Posted by psalt

Didn't notice any change in idle speed when pulling and plugging the vacuum retard line (mine is orange). Is that normal?

Not normal, you probably pulled off the wrong line, the advance line is orange. There are two lines to the distributor canister. The front hose is for the vacuum advance, it uses ported vacuum and is irrelevent at idle. The grey hose at the back of the distributor is for the vacuum retard, it uses manifold vacuum and is active at idle. If you remove the distributor cap and look at the direction of rotation, the operation of the vacuum canister should be obvious. Put a few drops of oil under the pad and snap the rotor against the advance while you are in there.

Paul

The line nearest the distributor adjusting bolt is the retard line right? If so, mine is blue. The line towards the back of the distributor (closer to fuse panel / driver's side rear) is orange.

Removal of one, the other, or both had no effect on my idle. I do feel suction through the blue line.

psalt · 11-21-2007, 03:08 AM

Removal of one, the other, or both had no effect on my idle. I do feel suction through the blue line

If removing the grey braided hose at the rear of the distributor has no effect on the idle speed, you have other problems. Idle speed will increase several hundred rpm on a correctly functioning engine. The first thing to do is to check the timing with both lines disconnected with a timing light. It should be 5 degrees BTDC. When you hook up the retard line the timing should be pulled back to TDC. Also check that the advance mechanism is not frozen, the timing should advance to 25 BTDC when you rev the engine to 3000 rpm. If the distributor is OK, check the routing of the line against the emission decal, it may have been replace incorrectly.

mca · 11-21-2007, 06:13 AM

Quote:

Originally Posted by psalt

If removing the grey braided hose at the rear of the distributor has no effect on the idle speed, you have other problems.

Such as a bad canister? Any other areas?

Quote:

Originally Posted by psalt

The first thing to do is to check the timing with both lines disconnected with a timing light. It should be 5 degrees BTDC. When you hook up the retard line the timing should be pulled back to TDC.

Timing at idle remains the same whether lines are connected or disconnected and plugged.

Quote:

Originally Posted by psalt

Also check that the advance mechanism is not frozen, the timing should advance to 25 BTDC when you rev the engine to 3000 rpm.

I will double check this. As of a month ago when I had someone providing throttle, the timing advanced correctly and checked out ok at 6000 rpms.

Quote:

Originally Posted by psalt

If the distributor is OK, check the routing of the line against the emission decal, it may have been replace incorrectly.

You mean where it connects to the back of the throttle body? I tried to get a good look at both connections with a mirror ... still tough to see.

I did notice that the retard nipple on the distributor has a little wiggle. I assume that can't be good.

Thanks for the help Paul. It is much appreciated.

Scott R · Scott R's Garage

Quote:

Originally Posted by mca

Such as a bad canister? Any other areas?

Timing at idle remains the same whether lines are connected or disconnected and plugged.

I will double check this. As of a month ago when I had someone providing throttle, the timing advanced correctly and checked out ok at 6000 rpms.

You mean where it connects to the back of the throttle body? I tried to get a good look at both connections with a mirror ... still tough to see.

I did notice that the retard nipple on the distributor has a little wiggle. I assume that can't be good.

Thanks for the help Paul. It is much appreciated.

You can have advance via the mechanical weights in the distributor, and not have retard. More than likely the distributor advance/retard mechanism is bad. Test it by pulling vacuum on the back/retard side and watching for the rotor to move. If not, order a new unit from our host, and replace it.

psalt · 11-21-2007, 08:37 AM

Timing at idle remains the same whether lines are connected or disconnected and plugged.

You can have a frozen plate in the distributor, a torn diaphragm, or an incorrect vacuum source. An open manifold vacuum line will create a lean condition at idle. If the timing is 5 BTDC with the line disconnected and plugged, test the advance side by watching the timing marks with a light with the throttle open slightly (w/vac and without). If the advance side is working OK and not frozen or leaking, leave the retard disconnected and plugged and move on to the dwell setting for the FV. There is no reason to want a vacuum retard unless you fail an emission test at idle. Remove the plastic cover at the left side of the engine compartment and connect an analog dwell meter to the green/white stripe wire terminal in the test plug. The meter should read steady 58 dwell cold during warm up, and start fluctuating between 40-55 dwell when it goes closed loop. If the lambda system checks out, adjust the mixture to the rich side, 30-45 dwell ,with an allen wrench and retest.