Cold start/idle issue. 77 911S

[AndreasK]

Hi. Recently bought a 77 911S. Has the original 2,7. Rebuilt some time ago, with SSI headers and 964?? cams. Sweet car and engine. Starts and runs great when warm.

Starting cold, not so good. Very predictable, but, I have to give it some throttle and it fires up. Wonīt idle for about a minute. Shuts right of. With the throttle i can keep it steady at 1000 rpm. After about a minute, with the same amount of throttle it suddenly (takes about 5 seconds) revs up to about 2000 rpm. I can then let the throttle go and it idles fine. Rides a bit jerky until fully warmed up. Especially around 2000-2500 rpmīs. Some backfires, especially when changing gears at lowish rpmīs.

Porsche shop, checked fuel pressures, when i bought it. Not so good. Changed accumulator and fuel pump. Pressures fine after.

Where do I start looking?

[Knockdown]

If you plan to work on your CIS yourself, then I would recommend getting a fuel pressure gauge set so that you can perform the cold/warm fuel pressure test. My 77 performs somewhat like yours and I know my cold pressure is a bit high, not much of an issue in Florida. The warm up regulator controls the fuel pressure during warm up. Lots of good threads on this forum and info on the web.

[AndreasK]

Originally Posted by Knockdown

If you plan to work on your CIS yourself, then I would recommend getting a fuel pressure gauge set so that you can perform the cold/warm fuel pressure test. My 77 performs somewhat like yours and I know my cold pressure is a bit high, not much of an issue in Florida. The warm up regulator controls the fuel pressure during warm up. Lots of good threads on this forum and info on the web.

Thanks! I do plan om getting the fuel pressure set. But I havent found one nearby yet. Ill probably have to order one. My plan for the weekend is to take out my WUR and clean the intake screens. I was hoping my specifick and predictable cold issue would help you experienced guys pinpoint where to start.

[Tarek307]

might be fuel accumulator..

[AndreasK]

Originally Posted by Tarek307

might be fuel accumulator..

Accumulator and fuel pump is new.

[boyt911sc]

Originally Posted by AndreasK

Accumulator and fuel pump is new.

Without a CIS pressure gauge, you will be spending a lot of time doing guess-work troubleshooting to identify your problem/s. Do yourself a favor and invest on a good pressure gauge kit. Search for a recent post by 'Antares', he bought a set of pressure gauge that I would recommend to people to have. Keep us posted.

Tony

[T77911S]

the gauge set will pay for itself if it saves you ONE trip to the shop

[al lkosmal]

Also....a wideband o2 to measure the A/F mix is a handy tool.

[dfhtrhjn]

I have a 77s as well. If you have to give it throttle to fire up then your cold start valve is bad; it's not squirting the fuel in at startup. You don't need throttle to start CIS, even if the car dies right after, it should start and run for a second only the cold start gas.

That being said, it sounds like there's more going on here. You may also have issues with your WUR.

I hate CIS personally, and the minute I have a problem with mine I'm ripping it out and putting in the x-faktory ITBs

[AndreasK]

Originally Posted by dfhtrhjn

I have a 77s as well. If you have to give it throttle to fire up then your cold start valve is bad; it's not squirting the fuel in at startup. You don't need throttle to start CIS, even if the car dies right after, it should start and run for a second only the cold start gas.

That being said, it sounds like there's more going on here. You may also have issues with your WUR.

I hate CIS personally, and the minute I have a problem with mine I'm ripping it out and putting in the x-faktory ITBs

Thanks! That's the sort of thing I'm after. Mind you. Didn't want to hear about CSV problems. I know where it is, but I haven't seen it 😂 I'll be getting the fuel pressure gauges, but the ones I can find locally I'm not sure are any good. Will probably have to order one. No secret. I'm very new to this CIS thing. It's a strange and mysterious thing😂

[ossiblue]

Originally Posted by AndreasK

Hi. Recently bought a 77 911S. Has the original 2,7. Rebuilt some time ago, with SSI headers and 964?? cams. Sweet car and engine. Starts and runs great when warm.

Starting cold, not so good. Very predictable, but, I have to give it some throttle and it fires up. Wonīt idle for about a minute. Shuts right of. With the throttle i can keep it steady at 1000 rpm. After about a minute, with the same amount of throttle it suddenly (takes about 5 seconds) revs up to about 2000 rpm. I can then let the throttle go and it idles fine. Rides a bit jerky until fully warmed up. Especially around 2000-2500 rpmīs. Some backfires, especially when changing gears at lowish rpmīs.

Porsche shop, checked fuel pressures, when i bought it. Not so good. Changed accumulator and fuel pump. Pressures fine after.

Where do I start looking?

The bold in your post needs a bit of clarification.

Without using the throttle, will the engine start and immediately die? If so, your CSV is working. It's not clear in your post that you are using the throttle to get initial firing of the engine or to just keep it running. This is an important distinction.

Even if the CSV is not working, once started and running, your use of the throttle to keep the engine at idle is indicative of another issue, likely out of spec cold control pressure--that's why you need a gauge set before anything else. The CSV only works when the start circuit is engaged, meaning when the engine is being rotated by the starter motor. Once you let the key move from the START position, the CSV stops injecting fuel.

Let us know about the cold start without the throttle. Does the engine fire and immediately die?

[Tony V]

"Recently bought a 77 911S". Not sure about the '77 but is there the cold start lever between the seats like my '74? Maybe something basic like the cold start procedure? Lift lever, start car. No insult intended. Just checking.

[ossiblue]

Originally Posted by Tony V

"Recently bought a 77 911S". Not sure about the '77 but is there the cold start lever between the seats like my '74? Maybe something basic like the cold start procedure? Lift lever, start car. No insult intended. Just checking.

Hand lever ended with the 75 model year, as did the fuel pump running with ignition switched to ON, before start. From '76 on, cold start was "automated" and the fuel pump relay was added.

[AndreasK]

Originally Posted by ossiblue

The bold in your post needs a bit of clarification.

Without using the throttle, will the engine start and immediately die? If so, your CSV is working. It's not clear in your post that you are using the throttle to get initial firing of the engine or to just keep it running. This is an important distinction.

Even if the CSV is not working, once started and running, your use of the throttle to keep the engine at idle is indicative of another issue, likely out of spec cold control pressure--that's why you need a gauge set before anything else. The CSV only works when the start circuit is engaged, meaning when the engine is being rotated by the starter motor. Once you let the key move from the START position, the CSV stops injecting fuel.

Let us know about the cold start without the throttle. Does the engine fire and immediately die?

To clarify. Yes, I have to give some throttle to get it to start, when cold. (No throttle needed when warm) So I most likely have a CSV problem.

But, like you say, there is most likely another issue. I have to give some throttle to keep it running for the first minute or so after starting. With the throttle I can keep it steady at 1000 rpmīs. After about a minute, while keeping the throttle in the same position, it revs up to about 2000 rpmīs. I can then let go of the throttle and it idles fine. Runs a little jerky on low rpmīs until fully warm.

I will be getting fuel pressure gauges, but if there is anything I can try until then, (without changing expensive parts at random) advise would be appreciated

[ossiblue]

Originally Posted by AndreasK

To clarify. Yes, I have to give some throttle to get it to start, when cold. (No throttle needed when warm) So I most likely have a CSV problem.

But, like you say, there is most likely another issue. I have to give some throttle to keep it running for the first minute or so after starting. With the throttle I can keep it steady at 1000 rpmīs. After about a minute, while keeping the throttle in the same position, it revs up to about 2000 rpmīs. I can then let go of the throttle and it idles fine. Runs a little jerky on low rpmīs until fully warm.

I will be getting fuel pressure gauges, but if there is anything I can try until then, (without changing expensive parts at random) advise would be appreciated

Thanks, this helps.

While you're awaiting the gauge set, you might try to see if you are getting voltage to the CSV--don't know if you've checked for that. Remember, you will get voltage only if the key is in the START position. If you get voltage to the CSV connector, next check that you are getting a ground connection from the thermo-time switch when engine is cold. You need both readings at the CSV for it to work.

[T77911S]

giving it throttle to start really does not mean anything especially if you have to keep giving it throttle to keep it running.
if you have to stay on the throttle after starting you have a mixture problem, period. if you have a mixture problem it will be hared to start, period.

trouble is figuring out why you have a mixture problem

[AndreasK]

Finally ready for some garage time. Winter has arrived
Had to drive it home, after an alignment, on summer tires, in this;

Scary!

Havenīt really done anything to the car as it runs fine after warm-up. What Iīve learned; Had fuel pressures checked, warm and cold is ok. I have a new fuel pump and accumulator. CSV is OK, wur has power. I DO have one or more air leaks. At least at one or more of the injectors. (Ordered new seals and sleves) No change to idle when removing oil-tank lid.

Problem has been getting worse as the weather has become colder. Starts ok, but wont hold idle unless i feather the throttle. Lately its been running rough until warm, sometimes not on all cylinders. Backfires more. But stil fine when warm.

Could my problems be caused by air-leaks alone?

[rwest]

Removing the oil cap on a 77 won't make a difference in idle- if you look at the hoses going to the oil fill, you'll see that one hose is going right to the unmetered air filter side of the air box. It's only later model cars were the idle changes.

Yes, air leaks can and are a huge determination on how well the system works. Air leaks will cause a lean condition. It would be prudent to find and fix all leaks before you worry about pressures.

Do a few searches and you'll find procedures for hunting down leaks. Here's a great thread- second post has some links for trouble shooting.

CIS Troubleshooting for Dummies

[AndreasK]

Originally Posted by rwest

Removing the oil cap on a 77 won't make a difference in idle- if you look at the hoses going to the oil fill, you'll see that one hose is going right to the unmetered air filter side of the air box. It's only later model cars were the idle changes.

Yes, air leaks can and are a huge determination on how well the system works. Air leaks will cause a lean condition. It would be prudent to find and fix all leaks before you worry about pressures.

Do a few searches and you'll find procedures for hunting down leaks. Here's a great thread- second post has some links for trouble shooting.

CIS Troubleshooting for Dummies

Thanks a lot Mr. West So changing my oil-cap was futile

[T77911S]

Originally Posted by rwest

Removing the oil cap on a 77 won't make a difference in idle- if you look at the hoses going to the oil fill, you'll see that one hose is going right to the unmetered air filter side of the air box. It's only later model cars were the idle changes.

Yes, air leaks can and are a huge determination on how well the system works. Air leaks will cause a lean condition. It would be prudent to find and fix all leaks before you worry about pressures.

Do a few searches and you'll find procedures for hunting down leaks. Here's a great thread- second post has some links for trouble shooting.

CIS Troubleshooting for Dummies

if I remember correctly my hose on my 77s went to the "turtle" or rubber boot going to the TB. I think I replaced the seal on the oil cap to prevent air leaks.