Turbo that doesn't run-on

[gtu935]

Trying to figure out a problem with a turbo (1987) that doesn't run on after the key is turned off. The run-on relay is good (replaced anyway) The CDI box is good (also tried another one to compare). Now we are trying to locate the capacitor that should be in the harness between the Run-on relay and the CDI box. Maybe some one has a part number?

Any help at all is appreciated.

Bill Rudtner

[RarlyL8]

You are trying to find a problem because the engine does not run on after shut down?
Why is this a problem? Run-on means there is unburned fuel after shut down which is a problem.

[gsxrken]

Originally Posted by RarlyL8

You are trying to find a problem because the engine does not run on after shut down?
Why is this a problem? Run-on means there is unburned fuel after shut down which is a problem.

Yep. Porsche thought to leave the ignition on for a second or two after key off to burn off the fuel that the CIS injectors continued to spray in until the pressure dropped below the injector's pintle valve spring.
Part #: 930-617-117-01-M504

Pelican Parts - Product Information: 930-617-117-01-M504

[gumba]

Should this relay be left in or left out?

[gtu935]

I'm not looking for the relay. The relay, when the key is on, powers a Capacitor that feeds the stored current back to the CDI box when the key is turned off. THis is how the system works.

I'm trying to find the capacitor or part number for it.

Thank you fellow pelicaners.

[mark houghton]

I don't believe there is any such capacitor as you've mentioned. Instead, the capacitor resides within the ignition shutoff delay relay...said capacitor storing enough energy to keep the relay contact points closed for a couple of seconds after you shut off the ignition (thus keeping power flowing to the CDI). As far as I know, that's how the system works. There isn't some huge capacitor that keeps the CDI energized in and of itself.

Regardless, it's not really a necessary item to have in my opinion. I never ran with one, having bypassed it when installing MSD ignition.

[wgwollet]

Your correct Mark for that guy.

But for me I think now I have a bad ignition switch because I get no voltage to fuse #12 in front, which feeds the Delayed action relay (which I jumped) and then the CDI.
So I do have unswitched 12 v in the DAR connector, how would you get voltage or jumped voltage to CDI so I can test the engine?

[RarlyL8]

The fuel pressure drops below injector cracking pressure spec (40psi) immediately when the ignition is cut. Injectors are prone to leak which is what the delay relay burns up. I cannot imagine spending one minute's time or money trying to fix this system if broken. Many folks disable it as it is so annoying. However, if you wish to fix it then replace the relay.

[gtu935]

Problem here is it's the complaint from a client that wants it to work. The car is an 87 with 12,000 original miles. The only problems with the car are where past mechanices have touched. There is a place in the harness where someone removed something. According to the original wiring schematic there is such a capacitor not incorporated in the CDI box or the relay.

[gtu935]

The client wants it fixed... Read above, The relay was replaced, the CDI box was replaced.
I've been fixing, servicing, modifying Porsche cars for over 30 years. Not a DIY guy here. I'm trying to gain insight from some one out, a fellow Pelican who actually knows.

Thank you for your help.

[T77911S]

Originally Posted by gtu935

Problem here is it's the complaint from a client that wants it to work. The car is an 87 with 12,000 original miles. The only problems with the car are where past mechanices have touched. There is a place in the harness where someone removed something. According to the original wiring schematic there is such a capacitor not incorporated in the CDI box or the relay.

the 86 does not show a capacitor and i doubt they changed that circuit just for the 87.
mark is right on how it works. it would be a very easy wire splice to bypass the relay.

i think it is a needed feature. for one, why would porsche go to the trouble to put in such a circuit if there was no reason.
here is MY reason for it, other than burning off excess fuel when turned off, and BRIAN, if it was not still burning off fuel after the fuel pumps are off, why does my car and my brothers continue to run for 15- 20 seconds?
well, here is my reason and i know you all will think i am CRAZY and all to go by is what happened.
i was working on my car. i had the CD unit unbolted so i had a ground clip from the CD to ground. (it should not be needed since there is already a ground). i was driving down the street and the car cut off. the pumps kept running so i thought the ground came off. got out, reconnected the ground, there was a spark and the engine started running again. at first i thought i imagined it. i removed the ground, it stopped, connected the ground, there was a spark and it started.
i think with the low compression engine, fuel dumped in the cylinders and not burned off and the heat, it does not take much to fire the engine back up. all it would take is for the spark to jump from the rotor to the cap and off it goes, and again with unburned fuel left in there and it easy to turn over due to low compression off it goes.

[RarlyL8]

If your engine runs on for 15-20 seconds there is something wrong with it. That is NOT normal operation. When 930s were new they didn't do that, but when 30 years old with neglected systems they do. Normal run on should be 1-2 seconds tops.

[zcoker]

Off topic: doesn't the yellow relay do the opposite, turn on the pumps for a few seconds when key is first turned on?

[DSPTurtle]

Crazy clients!!! I feel your pain. Anyway, does it backfire after shutting down? If not, then the relay is working just fine. Can you here the CDI whine for a few seconds after shutdown? If so, then it's working. Means the CIS is actually in good shape!

[mark houghton]

Originally Posted by zcoker

Off topic: doesn't the yellow relay do the opposite, turn on the pumps for a few seconds when key is first turned on?

It will fire up the pumps for just a scant second when you first turn the key to ON. Just a short little vvrrrrrtt. Before I replaced mine (which turned out not to be necessary) my old "original" one never did that. The new one gave me a spit second hint that the pumps were working.

[Ronnie's.930]

Originally Posted by zcoker

Off topic: doesn't the yellow relay do the opposite, turn on the pumps for a few seconds when key is first turned on?

Are you referring to the overboost relay that is part of the overboost (fuel pump cutoff) protection system? If so, I did not have the faintest idea that it did anything at startup (as Mark mentions above).

[T77911S]

Originally Posted by RarlyL8

If your engine runs on for 15-20 seconds there is something wrong with it. That is NOT normal operation. When 930s were new they didn't do that, but when 30 years old with neglected systems they do. Normal run on should be 1-2 seconds tops.

never timed it, probably more in the 3-4 seconds. its long enough that i always expect someone to say something but not like the old dodge we had that ran on for 30 seconds or more. i always heard they were running backwords when they did that. but no, not a problem with my car.