WUR again.

[soren.911]

I have cis form a 76 carrera 3.o on my RoW 3.2
It runs very well, but i have to run 1.9 bar i warm pressure (0.8bar cold). It runs too lean in part load if i go over 2 bar warm pressure.

The low warm pressure results it canīt hold the pressure when I shut the engine off. Thatīs no problem when I set the wp at 2.7bar.

Is there any way to adjust the warm holding pressure?

[kiwi 911]

Hi, I assume being a 3.2 it's are Carrera 3.2?

Interested to know the storey behind back-dating to CIS system?

[soren.911]

The carrera 3.2 came in the shop as a short block without exhaust, intake and fan. It has been running out of oil, resulting in a broken rod bearing and crank.

The CIS came from a carrera 3.0 which had to be rebuild for historic racing.

[prebordao]

Originally Posted by soren.911

I have cis form a 76 carrera 3.o on my RoW 3.2
It runs very well, but i have to run 1.9 bar i warm pressure (0.8bar cold). It runs too lean in part load if i go over 2 bar warm pressure.

The low warm pressure results it canīt hold the pressure when I shut the engine off. Thatīs no problem when I set the wp at 2.7bar.

Is there any way to adjust the warm holding pressure?

I will be interested in any replies as I have a similar problem. I recently adjusted my WUR for a 2.8 warm pressure, but with engine off pressure goes quickly.
I guess it's down to the relation between bimetal / plug height and spring tension.

[T77911S]

how are you checking the AFR at part load and what is it?

i hate to ask this really dumb question but i dont know how much you know about CIS, so, you have adjusted the fuel mixture using the 3mm adjustment? again, not to insult you, but sometimes you have to ask the obvious.

with the bigger motor, you should have to run higher warm CP. here is why.

the AFM(air flow meter) chamber is devided into 3 sectons. the idle or lower section, the middle section, for mid RPM cruising which BTW is suppose to lean out the mixture, and the upper section or high RPM section.
if the airflow is increased due to a bigger motor( i dont know how much of an increase 3.0 to 3.2 ould be) the transition points from the 3 sections will happpen at RPM's other than what the ssystem was designed to do, with the idle to mid RPM being the most critical and probably where you would see poor porformance, kinda like too small a carb on a big engine perhaps.

so, if your WCP is low, the plate is probably in the mid RPM section at idle, which means you are not seeing the rich idle mixture to lean cruise mixture change. i would think like this, you would have some hesitation off idle.


another thing, your WUR should also have vacuum enrichment. is that connected and connected to the correct port?

using an LM2, my mixture at idle is in the low 13's, with mid RPM mixture around 14.6-15 and then it starts to go rich again around 4k RPM, transition from mid RPM to upper RPM.

[soren.911]

If I set my wcp to spec. (2.7bar) I have stumble and backfire between 2200-3200rpm and I can not richen it up enough up to run probably and still having and acceptable idle.

Carrera 3.0 are famous for running a bit too lean part throttle.

[Gunter]

I wonder if it would be better to replace the Carrera 3.0 CIS with a CIS from SC 3.0 Euro 1978-83 or US 1978-79 non-Lambda?

A complete used CIS costs about $400.

Do you have large intake runners?
Did you replace the points with Petronix or similar?
Ignition distributor serviced and the curve checked?

[soren.911]

The car is running great and I have no cold start problems with my low pressure settings, but it is the residual pressure (warm) i miss now.
The question is if there is any way to adjust the residual pressure in the WUR.?

[Gunter]

Do you mean system pressure?

AFAIK, residual pressure is maintained by the check valve on the pump and the accumulator.
It keeps pressure for a while to enable hot-starts.

[soren.911]

With my pressure gage I can see how the change in residual pressure is affekted by changes in warm or cold pressure adjustments.

With WUR adjusted to spec. residual pressure is 1.1 bar for more than 20 minutes.

My check valve is fine (system pressure 5.2bar) and I have a new fuel accumulator and check valve in fuel pump.

[prebordao]

Soren i have the same problem.
People usually mention mostly the accum and the check valve as the culprits of low resid press, but that's on the supply side !
The wur when warm is responsible for holding pressure for some time when the engine shuts down. If it doesn't there goes the warm starts..

[boyt911sc]

Soren,

What fuel pressures (control, system, and residual both COLD & WARM) are you getting now? Could you post these numbers? What WUR ( 0-438-104-???) do you have now? Is your engine a 3.2 CIS (Euro) configuration? Thanks.

Tony

[soren.911]

Originally Posted by prebordao

Soren i have the same problem.
People usually mention mostly the accum and the check valve as the culprits of low resid press, but that's on the supply side !
The wur when warm is responsible for holding pressure for some time when the engine shuts down. If it doesn't there goes the warm starts..

Yes that is the problem.

[soren.911]

Originally Posted by boyt911sc

Soren,

What fuel pressures (control, system, and residual both COLD & WARM) are you getting now? Could you post these numbers? What WUR ( 0-438-104-???) do you have now? Is your engine a 3.2 CIS (Euro) configuration? Thanks.

Tony

It is a 017 WUR and the specs are: cold 1.3 bar warm 2.7 bar

As mentioned before my settings are: cold 0.8bar warm 1.9bar

It is a Row 1986 3.2 engine.

[T77911S]

i dont know what the 017 WUR is, but the 76 CIS system has a vacuum enrichment WUR, and based on your WCP(2.7), that is too low, as in the vacuum is not connected. this will cause the poor mid band performance you are talking about. when i removed my vacuum, as a test, i had the same problems, steady speed was fine, but when i tried to give it gas, it ran like crap, bucked, popped, hesitated.
the vacuum enrichment will give about another .8 bar of pressure to lean it out, then it removes the vacuum to richen it up when you give it gas and go WOT.
which opens another can of worms, what is your WOT AFR? are you too lean now? you really cant modify pressures without some kind of analyzer to verify what is going on.
i think you are causing other problems by covering up the real problem.

my car ran bad for years. i tried wild ignition settings, overly rich fuel mixture settings, even considered taking apart my fuel distributor until i found a fuel injector line that was partially clogged, now it runs great, but in the mean time, i was covering up the problem even though i new something else was wrong. (i also found my cams 15 degrees advanced by the PO).

you also need to verify that your ignition advance, both mechanical and vacuum, are working.
you also need to verify the mid RPM AFR.

in your first post you said you are running 1.9 bar warm. do a search or ask others, there is NOBODY here running that low a pressure on a properly running car, the key being a properly running car.

set the pressures to spec and figure out why it runs bad at spec.

[Gunter]

Originally Posted by soren.911

It is a 017 WUR and the specs are: cold 1.3 bar warm 2.7 bar

As mentioned before my settings are: cold 0.8bar warm 1.9bar

It is a Row 1986 3.2 engine.

Yes, but your CIS is from a 76 carrera 3.o on your RoW 3.2 and may not be sufficiant to supply the larger engine?

Or you may need a different WUR, or an adjustable WUR.

When I built my SS 3.2, I used the non-Lambda CIS from 1978 and an adjustable WUR with a 1982 engine.

[prebordao]

By mixing a 3.2 (originally motronic) with a 3.0 CIS, I think you can't rely on any "predefined" specs.
You'll have to do some trial and error, or better adjust-measure-test !

[T77911S]

both above have good advice, but you need to start from spec and work from there. like i said earlier, you should have to raise the control pressure, not lower it, and actually, probably just a few tenths of a bar....if any. i would go with the upper end of spec.

the 78-79 would be my choice for a 3.2

how about air leaks? injector seals/sleeves, intake runner boots, intake gaskets, vacuum lines, are they all good? how about popoff valve or cracked air box?

[boyt911sc]

soren,

Test and confirm that the system does not have a significant vacuum/air leak/s. Not being able to find any leak does not mean you don't have any. A pressure test will once and for all, tell you the integrity of the vacuum in your engine. The test is very simple and takes a few minutes to do it. Why do this? Looking at your cold and warm control pressures, tell me that the engine is SET rich even when warm. A 1.9 bar WCP is too low for CIS. Even with a bigger engine (3.2) like yours.

I suspect unmetered air into the system making it LEAN and inappropriate mixture adjustment was made to compensate for the unbalanced mixture. To support these assumptions, you need to test and confirm the settings. Keep us posted.

Tony

[soren.911]

I have no air leaks and the car is running great and pulls hard over all rpm. Runs smooth at part throttle and starts first time cold without touching the gas pedal.

Ignition is new or rebuild, timing and advance is spot on.

4% CO at idle, 2% CO part and 5% CO at WOT.

My only problem is my residual pressure loss.

I have tried to make a new and shorter pin in my wur, so I could tap the valve house further down in the house of the wur to make the distance between the valve in top and the spring in bottom shorter. But that did not solve the leak.