Surging and fuel mixing drifting rich

[Sorude]

Hi

Ok I'll try and be as descriptive as possible.

My 1978 SC has been drifting.

It gets set up and then progressively gets worse with time, these are my issues:

Starting - car take a couple of turns to start when cold but nothing really bad, warm start is easy.

Hunting

1) The idle was initially low, it is now set to around 850 revs on cold start and hunts about 3 or 4 times before it settles. Low revs to nearly cut off and then just over 2K as it sweeps.

2) This will continue when you come to a stop but again, only about 3 sweeps until the engine is warm ish.

2) When at operating temp is idles around 1.1K ish which seems a little high. But if I adjust this the cold start rev level drops and then I get massive hunting

3) Idle drops very slowly when coming to a stop when warm, for example at traffic lights. It seems to hang around 1800K rev range and drops slowly back to 1K ish.

Running Rich

I've had the mixture set with a computer sniffer but the fuel mixture drifts and the car over a long drive or a week or so will drift and become very rich again. So much so it set the CO sensor off in our apartment building underground carpark which obviously isn't good.



Idle seems to be an issue but the moving richness is bad. When driving the car hard it seems to run ok but obviously smells rich.



I think this is too much for bad injectors so I'm thinking the fuel distributor and WUR? I don't think its pressure as the car starts well and seems to drive well.

Any suggestions as I think I might need to get my WUR and distributor rebuilt.

Thanks

Scott and my first post.

[silverlock]

When I had some idle surging (and stalling) on my '78 SC — and *only* prior to it coming to temp — I ended up running some fuel system cleaner (Liqui Moly) through it, which resolved the issue after I'd gone through the tank.

The car ran extra rich on startup as well, as evidenced by the black spot on the wall in my apartment building carpark as well :-)

My next step was to pull out and inspect the WUR, but it's never returned. Vacuum lines from the WUR were all (visibly...) OK in my case, but are also another good point of inspection.

[PeteKz]

Do you drive it fairly often? Did the problem start recently, or getting worse over time? How long?

How familiar are you with the CIS? It's not terribly complicated, and is mercifully free of electronic controls, but you do need to understand how it works. Your car, being a 1978 SC should not have the OXS system, unless some previous owner swapped engines and stuff.

DO NOT throw parts at the problem. That will only complicate the troubleshooting and waste money. You MUST diagnose first.

This type of problem is frequently caused by air leaks in the intake tract. That's what I'd look for first. Two methods: first and best is a smoke tester; second is squirting starting fluid around the intake manifold gaskets, boots, and the injector holders, hoses, throttle body, etc. Another cause of the problem is the parts that increase idle during warm up (AAV, AAR) not shutting completely off when the engine is fully warm.

If you can't find any leaks, then get a pressure gauge set ($60-ish on Chinazon), to check your cold and warm pressures.

[Schulisco]

I agree with Pete!

I also suppose the car sits a longer?

The idea with the fuel system cleaner is good, it's easy and a quick and pragmatic approach. Todays fuels mostly contains ethanol, this is the worst case scenario for a CIS equipped car, even when the car sits longer...in this conjunction I always recommend to use a fuel with as less as possible or even without ethanol if available. If that's not available always use a fuel stabilizer on every tank stop. It makes sure the gas won't detoriate and that the ethanol won't get separated from gas which causes corrosion and serious damages on the CIS system incl. the steel gas tank.

The behaviour is not that strange on your car. Keepo in mind: A good running CIS car must start immediately after few cranks, run without any hazzle and proper idle. Idling between 950-1000rpm is normal for CIS cars (engine warm), when engine is cold, a higher idle is expected about 1200rpms, slowing down in a few minutes. No surging, it must idle stable!

If not, then there are one or more issues for sure. The problem is - even with several issues a CIS engine will always run somehow...This makes it harder to identify them. Furthermore it mimics symptoms which could lead into a wrong direction of troubleshoot.

When the engine starts rightaway when being cold and then it starts surging I say it's a too rich mixture. The question is: Why? Mostly a vacuum leak can be hidden by increasing the mixture, either with the CO screw and/or in manipulatiing the sensor plate height and idle screw. If that happened most mechanics get irritated and continue to "adjust" the CIS without solving its problems...

Mostly it begins on a CIS with a vacuum leak, which is the most common issue on a CIS. To find it or them(!) a smoke generator is mandatory! They can pressurize the whole system with smoke and then you see easily if there are some leaks. The check of the fuel system pressure and the control pressure (from WUR) is the next step. When CP is too low (=too rich mixture) then let it overhaul and adjust.
When control pressure is okay, then a previous mechanic "tuned" the CIS as described. It makes no sense to hunt for his things he did, I recommend in this case to make a basic adjustment of the CIS:
1. Check sensor plate height, mostly it's way out of factory specification


2. Check the basic adjustment/injection begin/starting point (that is the operating point when sensor plate is slightly lifted and the fuel pump starts so that the injectors start to spray), this can be done with the CO screw and the FP jumpered, procedure is described in the Porsche 911 workshop manual and the Bosch K-Jetronic manual as well:

Afterwards make a basic setting of the idle screw: Close the idle screw and open it again by unscrewing it by 2 turns

With these settings the engine must start rightaway if the rest of CIS works as designed. If not, then you know that you got one or more issues.

If engine starts and idles, make a test drive to warm it up and check the mixture / CO value to make suere that the engine won't lean up or runs too rich:

3. Check and adjust the CO mixture, procedure as follows:


Thomas

[PeteKz]

Ditto what Thomas said, plus this. CIS engines do not tolerate lack of use well. Drive it regularly, and you won't need to add gas stabilizer to the fuel, as you will keep putting fresh fuel in it.

[Sorude]

Sorry been away

Injectors have been replaced as they were leaking and dripping. They were actually wet!

My car was set up again and my idle has dropped a little over a week or so and has needed a little tweak up again (started hunting a little again). Not much but I had to turn it up a little. Probably a 5 degree turn so not much.

Interestingly my cold idle is around 800 revs and my running warm idle is around 900-1000. I'll check this again tonight as the car would have sat for 6 hours since the last start.

I'm going for a drive tonight and I'll remove the oil cap when the car is warm to check if the idle drops at all.

I'm thinking that it might be my WUR if my cold start idle is low? Car takes a few cranks to start on a cold start but then starts every time first time after the cold start.

Terrified of my mixture dirifting again as it got so rich it set off my gas sensor in my apartment building! 15 appartments were not very happy.

The car has sat for a very long time and has only just recently started being driven again. When I say a long time, I mean 8 years.

I also think I have a "lazy" cylinder but I don't think this should mean my mixture changes over a couple of weeks?

[Schulisco]

Originally Posted by Sorude

Sorry been away

Injectors have been replaced as they were leaking and dripping. They were actually wet!

My car was set up again and my idle has dropped a little over a week or so and has needed a little tweak up again (started hunting a little again). Not much but I had to turn it up a little. Probably a 5 degree turn so not much.

Interestingly my cold idle is around 800 revs and my running warm idle is around 900-1000. I'll check this again tonight as the car would have sat for 6 hours since the last start.

I'm going for a drive tonight and I'll remove the oil cap when the car is warm to check if the idle drops at all.

I'm thinking that it might be my WUR if my cold start idle is low? Car takes a few cranks to start on a cold start but then starts every time first time after the cold start.

Terrified of my mixture dirifting again as it got so rich it set off my gas sensor in my apartment building! 15 appartments were not very happy.

The car has sat for a very long time and has only just recently started being driven again. When I say a long time, I mean 8 years.

I also think I have a "lazy" cylinder but I don't think this should mean my mixture changes over a couple of weeks?

I still suppose at least one massive vacuum leak. When mixture is (way too) rich and engine starts without surging is pretty clear to me that there must be a leak. Otherwise it will surge from start. You car doesn't. And when the gas sensor set off than it's pretty obviously ...

Good that you already replaced the dripping injectors. But did you also put in new rubber seals and cups? Heavily recommended! You have to work out step by step every potential culprit for vacuum leaks! Otherwise you go nuts in adjusting the mixture ... CIS is very sensitive on leaks, pressures, etc.
For sure the WUR needs an inspection and I suppose it needs an overhaul fur sure after sitting that long. Also the fuel distributor. It also suffers on too long sitting and gums up over time. At the end some cylinders run too lean, others too rich. TGhis can also cause the supposed lazy cylinder. In extreme cases it causes the cylinder ran that lean and hot that you can hear the exhaust valve tickering ... this was the case on mine...
In sum the mixture might fit somehow, but it's bad for the engine, performance and mileage. Not to speak about the environment...

Use a smoke generator to hunt for vacuum leaks...

If you pull the oil filler cap the rpm must fall a bit and the engine must begin stumbling a bit. With vacuum leaks and other issues on the CIS the rpm won't fall or it even stalls...

Vacuum leaks can mimic a tight system until it's either warm/hot or cold. Saying a vacuum leak can be tight in some situations ... this can also irritate the mechanic....that's why I'm saying you urgently need a smoke generator to find all leaks.

Thomas

[Sorude]

Yep, when I replaced the injector I replaced the o rings and everything.

I removed the oil cap tonight and the idle dropped and the car started to hunt/drop and recover when it was warm. I put the oil cap on again and everything ran smoothly again.

[Schulisco]

Originally Posted by Sorude

Yep, when I replaced the injector I replaced the o rings and everything.

I removed the oil cap tonight and the idle dropped and the car started to hunt/drop and recover when it was warm. I put the oil cap on again and everything ran smoothly again.

[injector seals and cups]
Good.

[oil cap]
The shown behaviour is good, but does not prove the absence of any other vacuum leak!
You can only be sure when testing with a smoke generator and pressurizing all lines.
Reason: The vacuum on idle or revving the engine with no load mimics in some cases a tight CIS system. On load and at higher rpms then indeed leaks can be shown etc.

These smoke generators have small air pumps giving a slightly pressure to the examined system which is high enough to identify (tiny) leaks. Every leak messes a CIS up in some situations.

Does the car bangs in the exhaust when releasing the throttle while criuising?7

Also check the deacceleration and the start valve if they work properly. In some cases they won't and remain opened creating a massive vacuum leak.

How many turns do you need to close the idle screw (how many turns clockwise)? (remember the actual setting for setting it back!)

Thomas

[boyt911sc]

Originally Posted by Sorude

Yep, when I replaced the injector I replaced the o rings and everything.

I removed the oil cap tonight and the idle dropped and the car started to hunt/drop and recover when it was warm. I put the oil cap on again and everything ran smoothly again.

Scott,

You need to know your control (cold and warm) and SYSTEM pressures. A CIS pressure gauge is a mandatory tool for fuel injection troubleshooting. Without one, you are just doing a guess-work troubleshooting and will lead you no where. Another important tool is a home-made smoke generator to locate your hard to find air leak sources.

A properly maintained CIS car does not NEED TO BE DRIVEN REGULARLY. That is a FALSE excuse. I have several CIS motors on Engine Test Stands that start and run after sitting for weeks or months. I just got back from a 5-week out state vacation and came back home the other day. The ‘89 Carrera 3.2 started on the first attempt, ‘78 SC started after 2 attempts, and the other ‘79 SC motor on an Engine Test Stand took 2 attempts to run it. This morning, all started after only 1 turn of the ignition switch.

During the warmer weather the CIS motors in the garage could pass the 4-week test consistently even longer but at this of the year (December), they needed a second or third attempts after sitting for a month. But if you primed the system, they all start on the first attempt.

If you need some help with your CIS, send your WUR with a RSL (return shipping label) preferably a UPS. The testing and evaluation are FREE for members of this community.

Tony

[Sorude]

It was about 4.5 turns clockwise to closed.

I think I've had a single pop in the exhaust occasionally when the engine has been warm and I take my foot off the accelerator but coming off 5000revs

[Schulisco]

Originally Posted by Sorude

It was about 4.5 turns clockwise to closed.

I think I've had a single pop in the exhaust occasionally when the engine has been warm and I take my foot off the accelerator but coming off 5000revs

The idle screw is way too wide opened!

The basic setting (after sensor plate height setting and injection start managed by the CO screw) is 2 turns CCW from being fully closed/turned in (CW)...
Your setting indicates pretty clearly to me that the mixture is way too rich. To compensate it they opened the idle that much.
My experience is that the idle screw on a sealed and proper working CIS only needs half turn CW/CCW to adjust the idle rpm.

My approach/suggestion: Make the basic setting of the CIS as described above, make sure the idle screw is opened by 2 turns from being fully closed and then continue with the hunt for problems. I have to admit that this can get frustrating because engine might won't start and run anymore as long as the problems are not solved...
One of the first things to be checked is the control pressure from the WUR. So proceed as Tony said, get a CIS pressure gauge to measure the control pressure and the systems pressure. Also go and get a smoke generator as I described above. I'm pretty convinced that your CIS has one or more vacuum leaks. Why else do they enriched the mixture before ?

Thomas