hupp

Just to add to the CIS threads already posted...

My '79 stumbles and backfires when I try to accelerate. If I accelerate slowely she does fine, but try to rev-up and "spitter sputter" above 3000rpm. Most of my CIS is new (replaced last May) with exception to the fuel distributor. The car has been running fine until recently. This problem did not occur slowly, it was a sudden change. All system pressures are within spec.

Cold Control - 2.1 bar at 65 F
Warm Control - 3.8 bar
System - 5.4 bar
Leak down - stays at 3.0 bar for 45min.

The air plate and piston move freely. The shark starts fine and idles well. This issue only occurs when under load above 3000 rpm.

Could this be a fuel flow rate issue? I have not checked the fuel delivery yet - should this be checked at the fuel distributor? Could other non-fuel delivery related issues cause these problems?

Rich9928p

Hello Scott,

I had a similar problem with my '79 Euro track car. After going through everything, the only thing remaining was the fuel distributor. A friend of mine has a hanger queen 79 and I borrowed his fuel distributor, it ran like a top.

What was the cure ... a rebuild by a reputable vendor.

PorKen

Rev-limiter rotor bad? Green wire? Ignition box?

(I had a bad Permatune box that would not rev over 5000rpm.)

Pfunde

Hi Scott

Rich is right, I had simular problem, it ran like a 60 HP version of a 928. A friend ( read race mecanic ) of mine took the destributor apart did ?!?!?!, put it back together and ...voila !

:-)

hupp

I've heard that the fuel distributer is usually not the likely cause. Maybe I'm wrong - I'll continue to troubleshoot and field other ideas and save the distributer until last. AND hopeit isn't the distributer...$$$$$

PorKen,

Green wire is new. The ignition box is original. Not sure what you mean by rev-limiter roter?

Would a bad ignition box cause poor running all of the time of just at higher rpm's? My shark idles smooth and runs fine at low rpm.

Rich9928p

Scott,

The chain of "least cost" items are
- fuel filter\in tank screen
- fuel pump
- fuel injectors
- WUR
- fuel distributor

In my case I followed this chain, and did all the pressure tests, flow tests, did swaps of the coil & spark box, pulled the distributor and checked the Hall effect transducer, test test test.

In the end, it WAS the fuel distributor. My symptoms were cut-off starting around 4000 RPM and when the car got hotter it wouldn't rev above 3000 RPM. The failure was sputtering and popping, like running out of fuel. Well it was running out of fuel - if crud plugs up the channels, the fuel doesn't flow properly.

I wrote a quite lenghty white paper that illustrates what the guts of the fuel distributor look like and what a person may do to clean it up, drop me a note and I'll send it. In my case I didn't clean it well enough and a rebuild by a specialist cured the problem.

PorKen

Some Euros (without cats?) had rev-limiting ignition distributor rotors, which ground the spark over a certain rpm. US models use the special fuel pump relay with tach input.

You might check if the ignition distributor is centrifugally advancing. Twist the rotor by hand, to see if it rotates about 15 degrees and springs back easily.

Dennis Wilson

Scott,

Another possibility is a plugged cat. Had you been running rich before?

Dennis

Fastest928

if it pulls well up to 3000 rpm, check the cat ....if it has one

Marc
DEVEK

Dennis Wilson

Scott,

Forgot to mention other possibles. Lacquered upper cylinder in the fuel distributor and sticking/binding air sensor plate.

Dennis

JP Rodkey

When my '79 did that, a rebuilt fuel distributor fixed it.

hupp

Marc/Dennis,

My cat is gutted on my shark. Also, my air sensor is moving freely, I've checked multiple times. Would a laquered fuel distributor be a something that would get progressively worse? This problem seems to have developed overnight. The shark did run a bit rich before, but my WUR was bad. I had ordered another WUR, but before I could install this problem suddenly developed. I've installed the new WUR and adjusted the CO as best I could and she starts much better but still cant rev her up.

I checked the fuel delivery rate a couple of hours ago. I checked in two places and the results are as follows:

Fuel supply at distributor = 1.6L in 30s
Fuel return to tank at distributor = 1.15L in 30w

Pretty big differance. Is this ok?

Dennis Wilson

Scott,

Have you checked the relief valve at the back of the distributor to make sure the o rings are OK and nothing is plugging the ports. You could also have a vacuum leak which is masked by your adjustment of the AF mixture so at higher rpm's the mixture would be too rich. It doesn't sound like the distributor/WUR as their operation is linear. i.e. if they are OK at the lower rpm's they should be OK at the higher rpm's.

Dennis

Randy V

Ah - we love the tempermental CIS system.

My OB would exhibit the same symptoms - after taking on a tankful of bad gas. Try adding a bottle of Berryman's or other quality fuel additive.

If that doesn't help, I'd start scowling at the fuel distributor.

jpitman2

Warm control at 3.8B(55psi) sounds high to me - Watson gives 41-46psi for all 928 CIS. Mine went max speed 20mph no acceleration with control at 60psi due to clogged screens in WUR, now runs beautifully at 50 psi warm. Is this a fully hot reading? I ask because I found some soak occurs between warming up from cold (50psi control, running ok), and then do some work driving a few miles - went up to 60, lost power.
jp 83 Euro S AT 49k, BTDT