Jadz928

Edit: Into fuel system R&R, see Post #18
_____________________

Finally had a chance to drive #6 ('77 928, 5 speed) after some maintanence - new fuel pump, fuel filter, fluids, etc.

Runs good at idle... appears rich at startup, but settles down alright.
Revs freely thru the RPM range.

While driving, as I applied throttled it would take it only to 1/4" throttle, then it would take a "nose dive" and sputter and buck. It just can't handle any load.

This is new to me, the CIS cars. I'm checking here to see if there is a common sympton, with hopefully a rather isolated fix.
However, I'm prepared to dig in, if it requires something more systematic.

I have the WSM to review. I can take video if that helps too.

Any help would be much appreciated. Thanks!

BTW, it was really nice to be able to drive this thing for my first time.

SeanR

I'd start with the fuel delivery pressures.

Jadz928

Sean,
Do you know where I can get that kind of testing equipment?
Is this something a Napa might supply locally?

Dave928S

+1 ... check fuel delivery volume and pressures are to spec ... sounds like it's not getting what it needs. Roger has a good affordable CIS kit.

Jadz928

Do these CIS cars not like low volume of fuel the tank?

After having drained the tank, it was refilled with a gallon or maybe two.

Wonder if it would help to put a couple/few more gallons in there...

Jadz928

I nice RL'r pointed my toward this recent CIS thread. Reviewing now...

Dean_Fuller

Bad spark plug wires.

Dave928S

Shouldn't make any difference. The pump draws from the tank, pushes out through a check valve on the outlet of the pump, through the filter, to the motor, via the fuel accumulator in the right rear wheel well .... then the return loop comes back and discharges to the tank. One test you're doing will be to check that the pump delivery is at the specified rate through that loop. Level of fuel should have no effect on the ability of the pump to push fuel through the circuit ... that is the head of fuel in a full tank will not assist the pump.

Jadz928

Got it. Thank you, sir.

Jadz928

Interesting, Dean.

Apparently, the car was driving fine before the PO sold it to me. Mentioned taking it on a long trip.

When going thru the engine bay last February, I noticed the vacuum advance on the ign. dist. was disconnected. Naturally, I reconnected it, but didn't ask why it was that way to begin with.

I may have to do some vacuum system testing and throw a timing light on this one.

SQLGuy

I had a CIS Golf GTI that had similar symptoms. In that case it was caused by a tear in the hose that connected the CIS metering unit to the intake manifold. I don't think the 928 has such a hose, but if there's someplace that false air could be getting pulled into the engine without lifting the plate, or if the plate is getting blocked somewhere in its movement range, I think that would be a cause of the behavior you describe.

Dean_Fuller

My 89 did the same thing when I first bought the car. Drove home fine some 200 miles....but over the next 2 or 3 weeks started to miss, sputter and buck UNDER LOAD only. Idle was fine and steady. Changed wires and all was fine up to this date. No telling how old the wires are since new is so much money. I think a lot of folks run them WELL past their prime because they just don't see spending hundreds on a set of wires.

There is a lot more required from the wires when under load so that is where the weakness will show first IMHO. May not be the answer but again...new would be good to have anyway and it may fix this issue.

Dennis Wilson

Since it appears to be running rich, try disconnecting the cold start valve to see if the problem goes away. If it does, the thermo time switch is probably bad.

Dennis

vze2jshn

I suggest you get the CIS testing gauge and fittings and the large blue soft cover Bosch book on CIS and go through the trouble shooting section for early CIS K basic. Sounds like it may be your control pressure regulator aka: warm up regulator(WUR). Also consult WSM.

ROG100

We sell the complete CIS pressure test kit - sell tons of them to the 911 guys.
$66 plus shipping.