CIS issues again

[Jeff Alton]

I have a buddy's SC here and am trying to diagnose a running problem with it.

It starts and idles fine, but really does not take a load very well at all. It will cough and sputter and give the occasional backfire while under load when the throttle is pushed. It feels like it has about 40HP. The airbox appears to be NOT cracked and there is a pop off valve installed....

It has a steady 21 inches of Vacuum at idle, new cap, rotor and plugs. I am going to do a compression test so I can rule out the problem as being mechanical.

I am not worried about going through the entire CIS system to trouble shoot, but if I can avoid it, that would be better.

Has anyone suffered similar problems and found the fix?

Cheers

[ljowdy]

Spray carb cleaner around every possible vacuum leak, if the engine stumbles, then you have a leak
If the plunger in the fuel distributor isn't clean and moving free, that could be part of the problem.

Also, change the fuel filter, if it becomes clogged, it will make the engine act as you described.

[Jeff Alton]

Thanks, fuel filter is on my list and I have checked for vacuum leaks as well, with carb cleaner and propane both.

Cheers

[Bobboloo]

Symptoms do sound like fuel delivery. When you check the pump check the fuel lines as well. Make sure they aren't crimped or degrading.

[ljowdy]

I know this is getting to be an old thread (9 days) but I thought I'd share my problems and final solution.

When I bought my car, it ran like krap, I bought a used fuel distributor as one line was plugged up. That helped so I went out and bought a cheap sonic vibrating jewelry cleaner and dropped all 6 injectors into a bath of Motor Purr Injector cleaner and cleaned the injectors for a few days. That helped but still, it didn't run right. Then, one day, it started to run correctly and I took to my friends shop and set the CO mixture to about 3.0%. It ran great then started to krap out again. I then bought a complete 1973.5 FI system which included everything from the intake runner, fuel distributor, injectors, cold start, hot start, air box and even a K&N filter. I bolted it on and the car ran great for about 1 month then it started acting up again. During this time, I noticed a high pitch sound coming from the fuel pump so, I bought a new pump and at the same time, installed a new set of plug wires. Before I started the car, I decided to install a new fuel filter for the new pump and much to my surprize, when I removed the filter, the fuel that drained out was the same color as Ronald McDonalds hair. Next step was to remove the fuel sender and with a flash light, I looked inside the tank and saw tons of rust in the fuel. I stuck one of those telescoping magnets in the tank and pulled out a ping pong ball sized bunch of rust.

Drained the tank, and took it to a local radiator shop I've been dealing with for years and they cleaned out the tank, lined the inside and the outside and when I got it back a week later, it was like a brand new tank. During the week, I cleaned the injectors again to remove and residual rust chips or crud.

I blew out the fuel lines, installed another new fuel filter, installed the gas tank and started the car. It ran very rich. I then took it to my friends shop and using his exhast analyzer discovered that the previous CO setting of 3% was now 10%. Seems that with a clean fuel system, fuel easily flows through the lines so, re-adjusted the mixture and the car has never been so responsive in the 6 months I have owned it.

Long story, lots of money but finally, the problem is solved and the engine is far more responsive than it's ever been.

[Jeff Alton]

This car has a very lean mixture setting, loose pop off valve and a couple more vacuum leaks. Also the timing was set incorrectly.

All good now, but I set it too rich to pass emissions testing, so I still have a wee bit of work to do......

Cheers

[Paulporsche]

ljowdy,

Thanks for that writeup. Glad you got it fixed.

Jeff,

Sounds like you're on your way. Let us know how it works out.