Low RPM/misses on cold start

Jeff NJ · 03-12-2017, 04:58 PM

So I have been starting to get the 930 ready for spring over the past week and one of my goals was to get rid of a miss at idle and low RPM/stumbling on cold start.

The low rpm has really been there since I did all my upgrades, including Leask WUR, K27 HFS, TK IC, Rarlyl8 headers and muffler. Last year I blew the turbo and at the time tested compression, leakdown and fuel pressures (system, CCP, WCP, boost enrichment). Compression and leakdown were great and pressures were in spec (cant remember exactly the numbers, but they were right there).

Last week, I pulled the injectors and checked fuel flow without the injectors at idle and WOT and then with the injectors connected and all tests were amazingly even. I did find that 5 of the 6 injectors weren't totally tight (could move the crush washer before loosening the injector) and #2 was definitely leaking air (see evidence of rust from the moisture below). So they are now tight and the miss is gone when warm! So that is a good thing.

Fuel flow through the injectors at WOT

Very loose injector:

However, it still runs lousy when cold. I have tried adjusting the CCP so that the cold AFR as low as 10 and as high as 13 and while I can detect differences in how it runs based on how rich/lean it is at startup, the RPM basically doesn't change until the AFR is way out of spec. It is about 700-750. If I give it some throttle, it goes up no problem and I can hold it at 1200 or so with the foot and it runs better (still some misses until it warms a bit, but far less than at 750rpm), but I cant get it to start at that rpm level. I can drive it immediately, but it obviously isn't happy. It will typically stall once or twice if I don't touch the throttle since it is too low and definitely missing frequently. Once warm, it runs perfect.

I checked the AAR and it is open when cold:

I put ice packs on it for a bit to get it to open some more and then started it and it didn't change the idle speed, so I think it is open enough on its own. After warming up, it is completely closed, so it works. RPM eventually rises and settles at 950 when warm, so I cant adjust the idle speed.

What else can affect cold start rpm? I am confident there are no more air leaks. I have gone through it multiple times and the injectors being loose was the last issue for air leaks. Hoses are new and perfect, TK injector blocks are tight, good hose clamps, and new orings ensure the IC is not leaking.

How can I get the cold start RPM up a bit so that it runs better at idle and then I can tweak the CCP to get cold AFR in spec?

Thanks!

As an aside, anyone want a 15yr old girl that doesn't listen to anything I say? I found this today. Grrrr.

T77911S · 03-13-2017, 03:51 AM

aw that's not so bad. just smile and appreciate that she leaves you a note.
I got a 17 yr old boy. things are not any different.
last night he HAD to go with his friend to best buy to return something, did not ask us, we did not know where he was. claims he called but he cant find the record on his phone that he tried to call. 3 days home wont do any good but makes us feel better.

you did not say year

great looking fuel flow.
did you check injectors for leaks, FP on and no air flow.

which way out of spec does it have to be to run better? richer?

the AAR should be changing the RPM.
set everything to spec.
WCP and CCP based on temp.
then set idle mixture when warm.

it really sounds like you have an air leak
check for air leaks.
intake manifold. check bolts. spray some water on it.
check the IC sealing. lots of places for air leaks.
I had problems with the intake manifold not being flat. the plastic ICB's and the improperly fitting gaskets made it concave,. I had it machined flat.
also had problems with intake bolts coming lose.

verify ignition timing, advance and retard.
plug wires

one thing you can do,
there is a termo time valve on the block behind and under the intake.
Porsche ran the vac advance to this. I don't agree because it can block the timing retard when on boost and engine cold.
connect the vac retard to it. this will up the RPM a little more when cold.

Bucketlist · Bucketlist's Garage

As an aside, anyone want a 15yr old girl that doesn't listen to anything I say? I found this today. Grrrr.
^^^^
I think of kids and cats about the same.....keep a cover on it and they will never know i'ts there.

My car has always had some roughness or miss when cold, the 30 year old manual fuel injection system is in the cold, rich warm up cycle. My rpm is not that far off which may point to a ccp that is too low. I keep mine at about 2.3 bar year around and it always starts and idles pretty good. I think I ignore most of the roughness or missing until it has been running for a few minutes.
From here I would play with the idle mixture a click or 2, and maybe start it in my dark garage and see if there are any sparks jumping between plug wires.
Good luck!

Jeff NJ · 03-13-2017, 08:20 AM

Quote:

Originally Posted by T77911S

aw that's not so bad. just smile and appreciate that she leaves you a note.
I got a 17 yr old boy. things are not any different.
last night he HAD to go with his friend to best buy to return something, did not ask us, we did not know where he was. claims he called but he cant find the record on his phone that he tried to call. 3 days home wont do any good but makes us feel better.

Yeah, its not terrible, and I need a detail anyway, but it still annoyed me.

Quote:

Originally Posted by T77911S

you did not say year

great looking fuel flow.
did you check injectors for leaks, FP on and no air flow.

which way out of spec does it have to be to run better? richer?

Year is 88.
I did check for leaks as you described. None at all.
It seems to be a bit better on the rich side, probably around 11 AFR.

Quote:

Originally Posted by T77911S

the AAR should be changing the RPM.
set everything to spec.
WCP and CCP based on temp.
then set idle mixture when warm.

How much should it change it? Last fall I did exactly as you suggest. Everything set to spec and then idle mixture.

Quote:

Originally Posted by T77911S

it really sounds like you have an air leak
check for air leaks.
intake manifold. check bolts. spray some water on it.
check the IC sealing. lots of places for air leaks.
I had problems with the intake manifold not being flat. the plastic ICB's and the improperly fitting gaskets made it concave,. I had it machined flat.
also had problems with intake bolts coming lose.

Did all of the above. I have the Aluminum TK injector blocks. Double checked for tightness again when I did the fuel flow tests. Sprayed carb cleaner all around to listen for rpm changes - nothing.

Quote:

Originally Posted by T77911S

verify ignition timing, advance and retard.
plug wires

I did check timing in the fall again and timing is perfectly in spec per the service manual.

Quote:

Originally Posted by T77911S

one thing you can do,
there is a termo time valve on the block behind and under the intake.
Porsche ran the vac advance to this. I don't agree because it can block the timing retard when on boost and engine cold.
connect the vac retard to it. this will up the RPM a little more when cold.

This is interesting. I have removed the emissions crap, including the vac retard solenoids and capped the lines, so maybe I can run the retard line to the TTV? How much will it retard the timing when cold? Anything I need to be aware of, or do I simply run the line and see the difference?

thanks!

kevin930t · 03-13-2017, 11:48 AM

Hey Jeff,i was wondering if you read the article by Bob Tucker cis fuel injection operation,its pretty good full of trouble shooting probs.I googled fuel injection operation.I hope it helps.

Sent from my SM-N910T using Tapatalk

T77911S · 03-14-2017, 03:10 AM

there is a solenoid that blocks the retard vacuum when line you go on boost. if it is not there and you hit boost the timing WILL NOT retard.
if you removed the solenoid you may not want to do this.

what the TTV will do in my configuration is keep the timing from retarding when cold. its only about 5 degrees but it will bump up the idle a little.

you have been very thorough in what you have done but I think you may have missed something in one of your tests.
you have done everything I would do and have done.

are you venting your BOV to atmosphere or recirculating it back into the intake.

heliolps2 · heliolps2's Garage

are you running an oxygen sensor ? May want to check that also, With your mod's I would run a deg or two more advanced timing.

Jeff NJ · 03-14-2017, 09:57 AM

Quote:

Originally Posted by T77911S

there is a solenoid that blocks the retard vacuum when line you go on boost. if it is not there and you hit boost the timing WILL NOT retard.
if you removed the solenoid you may not want to do this.

what the TTV will do in my configuration is keep the timing from retarding when cold. its only about 5 degrees but it will bump up the idle a little.

you have been very thorough in what you have done but I think you may have missed something in one of your tests.
you have done everything I would do and have done.

are you venting your BOV to atmosphere or recirculating it back into the intake.

So this is the way I understand the solenoids: One is strictly emissions based and affects the air pump. The other retards timing when cold, but opens when warm to have no effect then. So removing it, as long as you run the line from the distributer to the throttle body, should have no effect on timing (off or on boost) once the solenoid would have opened up.

So after some advice from OSI930 (thanks Todd!), I crimped the vacuum line from the front side of the distributer to the throttle body and the rpms went up to about 1100 on a cold start!! So I am thinking I just need to put that solenoid back, plug it in and run the vacuum hose from the front of the distro to the solenoid and then to the TB (port I) as shown on this diagram.

So what logic determines when this solenoid is powered (cold obviously) and when does it open to stop affecting idle? Is it the TTS?

To add to my confusion, I found a thread by 16Volt regarding these vacuum lines and he ran the vacuum from the same front of the distro to the temp switch up by the crankcase breather and back to port I on the TB. So the Temp switch (#38 in the diagram above) basically replaces the solenoid and opens on its own schedule based on temp.

Cruise surge/boost issues

So which is better, or does it matter?

Certainly, I can be completely wrong in my understanding of what it does and how it works, so happy to hear from the experts.

Jeff NJ · 03-14-2017, 09:59 AM

Quote:

Originally Posted by heliolps2

are you running an oxygen sensor ? May want to check that also, With your mod's I would run a deg or two more advanced timing.

O2 sensor is disconnected.

I know that stock timing is probably not ideal for me, but frankly, I understand it just enough to be dangerous. What will advancing as you suggest do for me at cold start, at warm idle and at WOT?

T77911S · 03-14-2017, 10:44 AM

what do you mean by "front side"
I always look at the ports as left or right.
right side points towards the dist. this should be the vac retard.
the other is advance/ boost retard.
note, if boost is applied to both ports there is NO timing retard. this is bad.

my car did not have any of the emissions crap when I got it so what I know is from reading.
the electrical solenoid should be on the vac retard side. this blocks boost going to the retard side and is controlled by the throttle switch.

if you removed a vac line and the RPM when up then that should be the vac retard port.
this port ONLY has vac at idle.
the advance port ONLY has vac above idle and pressure when on boost.
you can connect that vac line to the other port to TEST the advance at idle (if it has vac on it at idle). the RPM should go up again.

try removing and plugging the vac retard side and only using the advance port at see how it starts.

personally I like having the retard at idle, it makes the idle sound deeper and smoother, on my car.
you can run without the retard port but not the advance port

Jeff NJ · 03-14-2017, 12:19 PM

Front side is the port closest to the front of the car, which is also the port that points to the right, so in your description, that is the retard port and that is the one I crimped closed to test.

My advance port is connected to port V on the TB on the diagram I posted earlier, so that should be fine?
Ideally, I would like the retard line to be closed when cold, then opening at some point to lower the idle back to stock 950rpm.

What is the throttle switch that you mention?

And so I understand, you are saying it isn't a cold start aid, it is always retarding the timing at idle, but the other port (left side) is advancing at idle, so they offset at idle? And then when off idle, the advance/boost retard port is the only port active and it advances on throttle, and retards during boost? Would that be why 16Volt ran that retard line to the temperature switch next to the crankcase breather tube on the top of the motor, so that it was closed when cold and then opens when it warms up?

Am I close?

Jeff NJ · 03-14-2017, 12:20 PM

Quote:

Originally Posted by T77911S

try removing and plugging the vac retard side and only using the advance port at see how it starts.

That's exactly what I did earlier today and got 1100 rpm on cold startup.

JFairman · 03-14-2017, 05:22 PM

Try advancing the timing. Stock timing is retarded for emissions to heat up the catalytic converter.

Jeff NJ · 03-14-2017, 05:42 PM

Quote:

Originally Posted by JFairman

Try advancing the timing. Stock timing is retarded for emissions to heat up the catalytic converter.

Jim, how much advance?

I'm deep into the ultimate distributer, timing, msd mod thread. you have a lot of great posts in there and I am getting a much better understanding how the two pots work and the system that controls timing.

I'm on page 7, but it seems that connecting the timing retard pot (blue hose on yours) directly to the correct port on the TB can defeat some boost retard? If so, I really need to put that solenoid back in.

JFairman · 03-14-2017, 06:01 PM

If there's room in the slot under the nut and washer that holds the distributor in place mark it's position with a black sharpie. Loosen the nut and turn the dist clockwise a little and see how it runs. Idle will probably be a little higher.
It helps to connect a timing light so you can see what it says down on the crank pulley.

Jeff NJ · 03-14-2017, 06:11 PM

Quote:

Originally Posted by JFairman

If there's room in the slot under the nut and washer that holds the distributor in place mark it's position with a black sharpie. Loosen the nut and turn the dist clockwise a little and see how it runs. Idle will probably be a little higher.
It helps to connect a timing light so you can see what it says down on the crank pulley.

Yeah, I can do that and quantify it with a timing light. But are you talking 1 or 2 degrees advance, or more than that?

JFairman · 03-14-2017, 06:29 PM

Mine runs real nice around 15* btdc at idle. I bent the centrifical advance weight stops inwards a little to limit full advance to compensate for more static advance so full advance wouldbn't be too far advanced and possibly hurt rings and stuff. If you remove the small oval pressed in shiny metal cover in the side there is a way to do it crudely without taking the distributor apart.

Jeff NJ · 03-14-2017, 07:16 PM

Don't you also have the MSD boost retard installed? I don't have that. I'm not really comfortable tweaking the weight stops since I've never touched them or tweaked them in the past. I don't want to guess. I am thinking just a couple degrees advance and re-install the solenoid to get it to idle higher cold.

JFairman · 03-14-2017, 08:20 PM

I do but it's not hooked up so it's not doing any thing.

mark houghton · 03-15-2017, 04:26 PM

Definitely add timing as Jim has suggested. You may not be able to get more than a few degrees cranking the dizzy to the stops, depending on how it's been indexed. My current 930 I have cranked as far as she'll go and only got a couple-three more degrees out of it but it did bring the rpms up and did help with the overall running of the beast. Don't be concerned about over advancing at boost with just a few static degrees added. I think you'll find it gives a measure of adjustability to your idle rpms, allowing you to fine tune (down, if needed) with the idle speed adjustment screw on the throttle body. That darn idle timing retard is just to heat up the catalytic converter anyway, if I recall, per US emissions BS. Mo' advance mo' good....to a point.