CIS fires, but won't run

lazyeyedog · 08-19-2010, 10:58 AM

79' CIS 911.
The engine will fire briefly while cranking, but will not stay running.
I recently removed the injection system to repair vacuum leaks and a light cleaning. The car started and ran good, save the rough idle and lack of power due to the vac leaks before. I was carefull not to "adjust" anything before putting it back together. The distributor was not touched. It seems to fire up readily, but immediately dies.
Any help would be greatly appreciated as I would like to drive this car before the weather gets bad.
Many thanks in advance!

john walker's workshop · 08-19-2010, 12:01 PM

start and die is a sign of a big intake air leak. go over your job again. is the brake booster hose attached?

lazyeyedog · 08-19-2010, 01:25 PM

Thanks for the reply.
Doesn"t appear to be a vacuum leak.
With the fuel pump relay jumpered, the car starts and runs better than ever, so something is preventing the pump from running. The relay is good.

Pazuzu · 08-19-2010, 01:37 PM

Quote:

Originally Posted by lazyeyedog

Thanks for the reply.
Doesn"t appear to be a vacuum leak.
With the fuel pump relay jumpered, the car starts and runs better than ever, so something is preventing the pump from running. The relay is good.

If you remove the relay, jumper the connector, and it runs better, then the relay is NOT good.

Put one of the black relays in the place of the red one and try that.

Superman · 08-19-2010, 02:07 PM

What about the sensor in the airbox that tells the fuel system whether the engine is running or not? I believe it is located at the top of the airbox system, to the rear (facing toward the passenger cabin), behind the throttle body or airflow sensor plate. CIS systems have a circuit that shuts off the FP unless the engine is running. It either looks at the ignition system, or it looks at a throttle/sensor plate position, to determine whether the engine is running. For starting, there is a circuit that defeats this safety feature temporarily.

lazyeyedog · 08-19-2010, 02:18 PM

With all due respect, the relay is good. I get the same result with a black relay. Terminal 85 on the relay plug is grounded, preventing the fuel pump from running. I isolated term 85 on the relay with electrical tape, plugged it in and the car ran. I also unplugged the airflow switch, (breaking the ground) and the car still did not run (relay normal, no tape). Could it be possible that the two blue electrical connectors (one on the sensor, one on the throttle) got mixed up? would it run at all like this?

Scott R · Scott R's Garage

Did you get the sensor plate switch and the one of the other plugs reversed?

Superman · 08-19-2010, 02:52 PM

Quote:

Originally Posted by Scott R

Did you get the sensor plate switch and the one of the other plugs reversed?

That's what I'm thinking. In fact, the sensor I am thinking about is (I believe) not like the regular square Bosch plugs. I believe it's just a regular spade connector. But yeah, it seems to me that this plug grounds the FP relay. Something like that. Somebody's got to know more than my guesses, but I would suspect that sensor is not plugged in.

john walker's workshop · 08-19-2010, 03:27 PM

the sensor plate switch is simply a ground contact that grounds the 86 terminal of the fuel pump relay, disabling it. the plug for the switch is green, and the cold start plug is blue. check with a mirror and flashlight. if they are on the correct items, try pulling off the green sensor plate plug, which will cause the pump to run with the key on. see if that keeps it running. i've had this problem before when the brake booster hose was rotted and leaking air, which caused a high idle, so when the idle speed screw was turned in to slow it down, the sensor plate contacts met and killed the engine. this was because of the false air leaking into the booster hose kept the sensor plate from rising enough at idle. pinch off the booster hose at the left side of the engine for the hell of it.

lazyeyedog · 08-19-2010, 04:12 PM

Aw, schucks, the two blue wire connectors were switched. 5 minute fix that I spent all day on because I didn't label them.
Thank you greatly to all those who replied, and to Pelican Parts. Without you I would have been sunk many times!

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by lazyeyedog

Aw, schucks, the two blue wire connectors were switched. 5 minute fix that I spent all day on because I didn't label them.
Thank you greatly to all those who replied, and to Pelican Parts. Without you I would have been sunk many times!

lazyeyedog,

Good job!!!! But what puzzles me is that after all these discussions about FP tests, air sensor switch, FP relay stuff, etc. you could have detected this anomaly right at the very beginning by testing the FP using the air flow sensor switch. I had committed similar blunder in the past and prompted me to find simple test to locate the culprit.

You are not alone, we all get into this situation regardless of age or experience!!!! And others benefit from your experience by remembering this episode.

Tony