Solved: 3.0SC with CIS bucking / surging, bad idle....
 

Gents,

I finally installed a wideband O2 sensor and gauge in my car last night (3.0SC with CIS) and *boom* engine issues solved in 15 minutes. The car was running extremely lean. I've searched the threads on this site for years trying to figure this out and Im so happy to have it fixed that Im going to shout it from the rooftops.

A few things I've learned:

While running lean:
- the car would buck and surge badly around 2K rpm.
- the engine was extremely sensitive to pedal movement in the 2-3K range, especially in traffic
- the engine struggled to hold idle and was difficult to start
- I could hear the engine missing / misfiring / stumbling in the exhaust note while at idle and cruise,

With the gauge was installed I was able to fatten up the mixture and saw:
- as the mixture became more rich, the idle went way up
- I adjusted the idle down using the large idle screw on the side of the CIS
- Car now idles perfectly, bucking @ 2K is gone, and misfiring is gone, and the engine starts much easier

I did attempt to over-richen the mixture and experienced:
- lumpy idle, or "seeking" idle, 850 to 1200 rpm
- backed off the mixture by 1/4 turn and it smoothed right out

The engine is now at a point where the idle is stable, not lumpy, and the bucking issue is resolved. However, my LM-1 gauge is telling me that my full-throttle / acceleration AFR is ~15.4. Cruising AFR is better at around 14.5. This is a bit more lean than I was hoping to see. Like I said above, I did try to fatten it up but it negatively effected the idle behavior. So still a bit of work to do, but I feel like Im on the right track.

So, in short: Buy a LM-1, haha.

i found that my 2.7 like the mixture set just lean of the surging at idle. when I put my LM on it after years of setting it like that I found it was pretty much right on spec.

what CIS system does it have
also what WUR is on it
does it have lambda

you might check for air leaks.
check the intake bolts, injectors and sleeves

Its a 3.0 block with an older non-lambda CIS.
The intake bolts and gaskets are new, as well as the sleeves.
I did check the box just a few months ago, replaced old hoses, etc, so its all looking good.
Not sure about the WUR.

I agree on the LM 1; You can post a data logging file that would help.

14 at WOT is a bit of a problem....that is too lean.

I am guessing you have a Euro SC with a 089 WUR?
If that is the case you might have the vac ports switched around which could explain perfect behaviour at idle part load and wrong behaviour at WOT.

My 83 euro SC with 089 WUR cruises around 15.7 and wot around 15.2. Idle is smooth at 950rpm and around 13.9afr fully warmed up. Not to hijack but should the cruising and wot be much richer?

I have a 001 1973.5 WUR on my system. The CIS is not original to the block unfortunately.

This is roughly what Im seeing as well. I wonder if its a problem...

Cruise is perfect. The Euro SC s need to be tuned lean. Idle at 13.9 is also very good. Recommended setting is 05-1% co. Unlike US where people go 3%.

I do not understand why you see 15.2 at WOT.

I am seeing 12.9 low 13s at WOT. Also with LM1 and RPM data logging option.

I had the same issues you are describing. My fix turned out to be a bum relay under the passenger seat that supports the Jet-Tronic brain box. You may have solved the issue with some changes to your CIS settings, but would def encourage you to take a look at that relay (assuming you have this set up!).

@garment : The relay & CIS brain only applies to the later models with lambda.

15.4 at WOT is too lean, and you need to take care of this running lean at WOT will give detonation.
Your engine (and wallet) won't like it. You should be between 12.5 and 13.5 at WOT.

Before playing with the mixture settings, make sure you don't have any vacuum leaks. Does your idle change when you open the oil filler cap ? If it does, that's already a good sign.

The mixture screw is only one part of the equation.
The warm control pressure (-> WUR) is the other one. Get a CIS pressure gauge, and measure all your pressures.
Make sure they're within specs, especially the warm control pressure.
Since your engine is lean, your control pressure must be on the high side.
If your pressures are OK, check again for vacuum leaks or cracked airbox.

If your WUR has a vacuum port on the side, make sure it's plumbed properly (check that you have vacuum on the hose at idle).
The vacuum actually makes it leaner (higher control pressure), and so when the vacuum goes away at full throttle, the engine runs richer. So if you have a vacuum, you can try to plug the hose and run without it. Cruise should be richer. WOT should not change much.

I wouldn't worry too much about not having the right WUR. Ideally, you want the exact WUR your system was designed to work with.
But all they do is go from one pressure (low @cold) to another (higher @warm) in a certain time, and eventually you can have that extra vacuum hose to lean the low / mid range a bit.
So you should be able to tune any WUR to work decently on your engine.
The cold pressure and transition time to the warm pressure are not that important, as long as the engine starts runs OK at cold, it's good enough. It's just a transition state, it doesn't have to be perfect.
The important part is the warm pressure, where your engine will operate most of the time. So get a good warm control pressure and then fine-tune your mixture screw so that you get good readings both at idle (13.5 ~ 14.7) and WOT (12.0 ~ 13.5).
Then adjust the cold pressure if needed so that the car starts OK when cold.
There are a few threads that explain how to tune the WUR by pressing in or out the large "plugs". Some sockets and a vice can do the job.
The adjustable WUR only adjusts the cold pressure, which isn't that important to me, but it's still nice to have, so that once you've tuned your warm pressure you can easily fine tune the cold pressure.

While you're working on your WUR, clean the fuel ports with compressed air, there's a little screen that can be clogged, and when clogged it will make the engine run lean.

This is likely the problem. The -001 used a throttle position switch as it had no vacuum port. If the throttle switch is not functioning (there would be no provision for it in the '75 wire harness) then it cannot enrich the mixture on throttle. If you also have the '73.5 FD the system is inadequate to fuel a 3.0L engine.

Has this engine ever run properly with the current CIS system? I ask to see if something has malfunctioned or if it never functioned properly in the first place.

.

RarlyL8 is right. You can't just arbitrarily mix and match components like the WUR. Porsche used several different ways of enriching the mixture under acceleration. The early CIS system used a very different and short-lived method.

If this were my car, I'd look at all of the components of the CIS system, to see what's actually on the car. If most of the components were not from a 3.0 CIS system, I'd probably try to find a complete used system.

For anybody that owns a CIS car, it's a really good idea to study the operation of the system on your specific car. There were so many changes from 73-83, that generalities about the specifics of CIS operation are almost worthless.

JR

This is probably what I need to do too. I know that I have a vacuum leak, well, an un-metered intake air leak, so it idles too high when warmed up, like at 1100 or so.
So, I need to find that leak.
But then today, after not driving it for a couple of weeks, it popped at idle, and popped accelerating, and popped at cruise throttle, 2-3 k rpm.
It was like the pop sometimes heard while quickly decelerating, but this was much more frequent. So, I took the car home. I have a mixture gauge already installed, but with the vacuum leak it's probably way off anyway.
Could the popping be related to air leak and mixture? Or do I have something much more serious going on that I need to check?

If you have no lambda then your WUR controls enrichment under throttle by vacuum. I've an '83 Euro 3.0 with a wideband AFR gauge in place of my clock.
I cruise at 14.5 to 14.7 ( I like it a little fat due to the Az heat)...however, under wot it drops down into the 11 range as it should.
Most older WURs need a rebuild and have been compensated for by simply fattening up the AFR...that works ok for cruising but it will simply lean out at wot or under aggressive driving.

I suspect that the entirety of the system is all from 73.5. The injector lines are metal, the WUR is 001, etc.

I can test the throttle switch in the morning, but I think I've done this before. *If* its working, what else can be done (other than replacing the system)? Can the system be fattened up with a different adjustment? Like I said above, Im fat while idle (~13), stoic on cruise (~14.5), and lean on WOT (~15.5).

Clearly the engine needs a real solution, just wonder if theres a temporary bandaid to toss on it in the meantime. Thoughts?

The '73.5 CIS is rather crude and typically swapped out for a -129 WUR and the switch eleminated. You really need the WUR/FD from a 3.0L engine for things to work well and support the power level.

get the WUR from the 78-79 SC or even the 76-77 2.7. they have a vacuum controlled enrichment that will fix the lean WOT.

Not true of his WUR. See RarlyL8's comments.

Don't assume anything. Check it, component by component. As an example, the steel lines were first used around 1981.

Here's the bottom line. If the majority of the system is indeed from 1973, toss the whole thing and buy a system appropriate for your engine. The 1973 system didn't work all that well and changes came fast and often. There are a bunch of things in a 1973 system that won't mesh well with your car and were fixed in the later years. If you don't run a cat, I'd choose a '78/'79 US system or any ROW 911SC system.

There really isn't a bandaid fix. That's how these systems get ****ed up in the first place, by people swapping out one component or the other. Even if you fixed the mixture problem, a '73 system is way too small for your engine. Why give away horsepower, for no upside?

JR

he needs an 033 or an 045 WUR. with vacuum enrichment.
it even provides a quick enrichment with an increase in throttle much like the accelerator pump on a carb

I don't know what the 129 one is off of.

Not to derail the thread, but I have lean running issues with my USA 80 SC.

When cold, and accelerating from 1-2.5k RPM, AFRs jump into the 15s, then drop right back into 13s after I hit about 2800 RPM.

When warm, my idle is at 13.9 with WOT at about mid 12s as it should.

What would cause the instance of cold lean running operation only in the beginning phase of acceleration?

I suspect my cold CP is off... Hence the lean condition only when cold. But that doesn't explain the 2500 RPM window of lean, then back to normal rich after the RPMs increase. Or does it?

:confused: