L Jetronic FI, Idle Good, WOT Not Good, But Only Sometimes! Options

[Cjllong]

Alright,

I have L-Jetronic FI and the motor starts and idles. When I hit the gas, it dies at a certain RPM. I'm no stranger to the FI in my car and I have diagnosed many problems, but this one is killing me. The mystery is.... Sometimes it runs like a top, other times it dies. About a month ago, it died at the curb in front of my house. Today, I took it for a ride and it died at the curb again. I took apart the throttle body and checked the Throttle Switch.... it's good. I checked all the other components... All good! I fired it up.... Damn thing ran like a top all over town! I didn't do anything different! I'd like to think I fixed it, but I'm not that good! Any ideas on how to find the actual problem and make it reliable?

Chris

[jim_hoyland]

How is the distributer ? Is the vacumm can still working ? Points ?

[zonedoubt]

Flaky wiring somewhere? An intermittent open circuit can be difficult to track down.

[914Mike]

Alright,

I have L-Jetronic FI and the motor starts and idles. When I hit the gas, it dies at a certain RPM. I'm no stranger to the FI in my car and I have diagnosed many problems, but this one is killing me. The mystery is.... Sometimes it runs like a top, other times it dies. About a month ago, it died at the curb in front of my house. Today, I took it for a ride and it died at the curb again. I took apart the throttle body and checked the Throttle Switch.... it's good. I checked all the other components... All good! I fired it up.... Damn thing ran like a top all over town! I didn't do anything different! I'd like to think I fixed it, but I'm not that good! Any ideas on how to find the actual problem and make it reliable?

Chris

My '74 would die at random, I finally figured out that the Dual Relay had come partially unplugged. (IMG:style_emoticons/default/headbang.gif) Had to re-tension some of the spade lugs in the harness block and all was well. Dieing at a certain RPM is probably a sticky flap in the AFM or worn contacts on the resistor in the same component.

[zonedoubt]

I have been encountering some stumbling on slow increase of throttle the past couple weeks. Today I popped the cover off the air flow meter and found that the AFM flap "rotor" (not sure what it's called -- I labelled it "2" in the photo below) was catching on the fuel shut off contact arm (labelled "1"). I bent it back to where it should be and observed that it was clearing OK when applying throttle.

I'm not sure how the contact arm bent in the first place, maybe was riding a bit close to the rotor.

Having the cover off the AFM is a good way to visually check that things are working as they should in the AFM (at least mechanically). Just don't mess with the adjustment screws. (IMG:style_emoticons/default/wink.gif)

[Cjllong]

The distributor cap and rotor are new. The problem started, then I replaced the cap and rotor thinking that would solve it. The AFM is also new. I blew the last one with a bad backfire while working on it a while back. The dual relay is also new. (Can you tell I've done some work here?) I'm not so sure about the vacuum on the distributor though. I don't recall a manual test for that one. Can you tell me how?

I'm wondering if the Fuel Injection Resistors could cause this problem? I had to re-solder new wires to the resistor pack and it's entirely possible my soldering job didn't hold up. Any thoughts?

Chris