Need advice on AFR

[30KFT]

My original early 930 motor has been fitted with a K27 & Carrera cams & a PowerHaus muffler & is otherwise stock but freshened. After having all the major components of the original CIS fuel system rebuilt by reputable vendors (pumps, lines, FD, CPR, injectors, filters, throttle body, on & on) & the distributor, CDI & engine wiring harness(es) when warm my AED AFR reads 10+/- @4K, 11+/- @3K, 12+/- @2K & jumps to 14-15 @ 1.5K. Below 1.5K rpm it won't idle & won't re-start until it cools a bit. Since I have read about everything I can find here & elsewhere but have still been wrestled to the ground by the CIS I'm hoping for some suggestions on why, as my rpm increases, the mixture richens when it should be roughly in line with all the ranges I see listed here. It seems like I am overlooking something simple. It wouldn't be the first time on this project but this is making me lose my enthusiasm. I could use a hand if any of you have ideas. Thanks & I really enjoy following y'all-

[Black_Hat]

You need a set of CIS gauges to measure:
Warm and cold control pressure
absolute system pressure
and
enrichment pressure (careful not to use too much air pressure or you will ruin your WUR)

the post numbers here or over at the 930 turbo forum

an Air leak will cause over rich condition

[30KFT]

Thanks BH- my CIS pressure measurements are within spec according to my gages; all intake seals & injector blocks are new. Part of the mystery;

[Black_Hat]

get a can of starter fluid and spray around any seams on intake while idling look for change in idle speed.

a leak can suck in air under vacuum
and
blow out air under positive manifold pressure - causing an over rich condition.

does your car hold system pressure for the spec time after ignition off ?

[30KFT]

BH
After CPR fully warm (.8 > 2.85 bar in 5 minutes) then switched off, system pressure bleeds off to zero in 7 minutes

[boyt911sc]

Originally Posted by Black_Hat

You need a set of CIS gauges to measure:
Warm and cold control pressure
absolute system pressure
and
enrichment pressure (careful not to use too much air pressure or you will ruin your WUR)

the post numbers here or over at the 930 turbo forum

an Air leak will cause over rich condition

Please post your control and system fuel pressures. Your residual pressure loss is too quick and would affect your hot start . How is your cold start?

Tony

[30KFT]

Cold control pressure @ 63F = .8 bar/12 psi
Cold control pressure @ 63F w/ WUR fully warm = 2.85 bar/42 psi
System pressure @ 63 F = 5.9 bar/ 87 psi

Cold start is prompt once sys pressure comes up but hot start is unreliable
thx

[boyt911sc]

Originally Posted by 30KFT

Cold control pressure @ 63F = .8 bar/12 psi
Cold control pressure @ 63F w/ WUR fully warm = 2.85 bar/42 psi
System pressure @ 63 F = 5.9 bar/ 87 psi

Cold start is prompt once sys pressure comes up but hot start is unreliable
thx

What year/model is your engine? What are the last 3 digits of your WUR? Without knowing the engine configuration we are discussing, we will be all just guessing. Need specific information about the subject. This is not a one-size fits all solution. Thanks.

Tony

[Black_Hat]

as @boyt911sc pointed out "Your residual pressure loss is too quick and would affect your hot start"

as shown by the system pressure bleed off after shut down

you need a new fuel pressure accumulator

or as Porsche calls it a fuel pressure reservoir

[30KFT]

CPR = 0438 140 054 w/mild enrichment to accommodate K27 & Carrera cams
engine number 686100
series 51
case # 930 101 104 OR
thx, Tony

[Manda Racing]

How about a 14.26 reading at 5k rpm. ?

[356911930]

The OP's engine looks to be a 3.0L, 930/51 with updated wur, originally a 022, to a 054.
Hope this helps,

Rahl

[30KFT]

Is there a listing of the correct, original CPRs (and other 930 CIS components) by year or engine series available somewhere? This would be helpful when trying to ID used items. as they become more and more scarce.
Thanks to everyone for your help here-

[Walt Fricke]

As to fuel pressure bleed off, the other possible culprit when it is too fast is the check valve in the fuel pump. On some older pumps this was a separate piece screwed in between the pump and the output fitting. Later, it was internal to the sort of output tower on the pump - it could be screwed out of its housing, as I recall, but I don't know if it is available as a separate part.

But perhaps failure of the check valve is much less common than failure of the fuel pressure accumulator?

[30KFT]

When measuring system pressure with the engine running will a faulty accumulator affect system pressure readouts? If so, what do I look for?

[Walt Fricke]

No
The accumulator dampens out pressure fluctuations from the pump or otherwise, but that not working quite as much as it should shouldn't change the system pressure significantly, as it is set in the pressure setting valve in the fuel distributor. Control pressure is quite a bit lower than system pressure as the WUR lowers system pressure to control pressure.

Getting residual pressure to where it should be may not solve your other issues, but at least the engine should start when hot like it should.

[30KFT]

Thanks Walt; since my FA (3 port) is 45 years old I've decided to replace it but I'm skeptical that it is the problem. My check valve is part of the banjo fitting instead of the banjo bolt at the front pump so it is a little more difficult to test but I'll check it while replacing the FA.