Highly upset,HELP!!

[Happyone]

I recently bought a 78 911SC. The car starts fine at times and then other times it idles rough. It will run well and then just die for no apparent reason. Starts back up sometimes right away, other times after it dies, it has to crank a bit to start up. When it runs rough while driving it will backfire or hesitate and pop, then it runs better. I have replaced the fuel pump,fuel filter, fuel pump relay, distrib cap and rotor,plugs, had new wires on it , distrib signal cable and coil. I would guess the ICU is next right?? Any idea what could be the issue??

[kerthunk]

Have you just been replacing parts or are you running tests first? Have you tried checking your system and control pressures? They need to be calibrated and it doesn't just "fix itself" by replacing the fuel pump for example. After checking your pressures (system, control cold and warm, and leak), you need to pull your injectors to verify the spray pattern and delivery amounts. Once all that is good, you can check out the ignition system...

The '78 has no computer control, it is all machine. You need to make sure all of the individual parts are working right. Just replacing stuff is going to prove VERY expensive!

I would recommend picking up a CIS pressure test kit and reporting back here with the results. Also, where are you located? There may be a Pelican around you that can give you a hand.

Good luck!

[tharbert]

Welcome to the forum (un)Happyone. You will find lots of great info here. It would help if you described you car setup in detail and maybe post a few pictures of the engine. The original 78 SC engine has the CIS fuel system. Use the search button and look at some of the posts concerning CIS and poor running. Search for CIS and Warm Up Regulator or WUR, "air leaks" and/or "control pressure". For instance, CIS is greatly susceptible to air leaks in the intake. There are lots "how to fix" threads. You will finds hours of reading and I suspect you will come across the answers to questions you haven't even thought of yet.

[gshase]

cracked air box........massive vacuum air leaks

[pete3799]

Is this a stock 78 motor,CIS and ignition set up (Bosch ICU)?
Could be fuel related also.
Got a fuel pressure test gauge?
Did you clean the in tank filter (screen) located in the bottom of the fuel tank?

[airbil]

BTDT
Bad ground. Engine will start. Car will run. Car will warm up. Warms up and resistance at a bad ground, probably underneath the car, builds up and kills the electrics.
If I recall there is a grounding strap from trans. to body that is open to the elements and corrosion that is the most likely suspect.
Good luck! Report back what you find.

[ivangene]

slow down on part replacing...speed up on reading, asking questions and testing

welcome to the forum!
keep in mind, these cars need work, and part of the joy (or frustration) of ownership is the solving of issues

all the best - post some pics

[Brown747]

..also go through your fuse panel contacts. Replace all fuses that are looking 34 years old and cleanup the contact points on the panel with a piece of fine sandpaper. Also cleanup the pins on the 14 pin connector where the engine wiring harness goes onto the panel at the left rear of the engine compartment.
Good luck.
Thor

[theiceman]

Cold control pressure checks and base CO adjustments after verifying no unmetered air entering system due to craked intake sleeves or cracked airbox.. go from there..

[groovzilla1959]

years ago one of my 911sc's ran really bad as you describe - it turned out to be the fuel distributor

[wwest]

Make sure the battery isn't being overcharged....

[zotman72]

Classic CIS fuel accumulator failure symptoms

[rusnak]

I'm no CIS guy, but is there a pickup coil in the distributor? Maybe you can pull it, and check for wear, clean and lube the advance mechanism, etc.

Is the backfire in the intake, or out the tailpipe?

[RWebb]

recent buy, so what exactly did the PPI say & what tests did they run?

[timmy2]

13 offers to assist with questions and suggestions and no response from the poster.
Guess he fixed it...

[Cairo94507]

He may have a job and family.....

[aadrew10]

He may have a job and family.....

Impossible