j.kenzie@sbcglobal.net

Hi,
Over the past week or so, it's taken longer to start my cold (70*F.) vehicle. Normally, it starts in 2-3 seconds. Now it is 6-8 seconds. I have 12V at the coldsart injector and the thermo-time switch is new. My fuel pressure goes to 36psi instantly on turning ignition key.
I'm tempted to say my CS injector is malfunctioning and drop in a new one. On my 84 L-jet my CS injector is in the rear of the engine under the airbox.
The car runs great in all other conditions. Plugs look great, distributor cap and rotor are new.
What can I do to support the idea of bad CS injector?
Thanks in advance.

John Speake

You could replace the coldstart valve with a small wattage (like tail lamp bulb) to check that the thermo switch is working at the ambient temps you have in summer. It may only operate for a few seconds. (it operates for about 8 sec at -20degC ambient)

You would need to measure the dc resistance of the coldstart valve, and then use a bulb that would draw a similar current.

If the thermo switch circuit can switch the required current, then it might be possible to check that the cold start injector is spraying with a pressurised fuel rail. I will leave that to your imagination, but please be careful !

I wouldn't think the amount of fuel sprayed is critical.

j.kenzie@sbcglobal.net

Thanks John,
I always respect your opinion. After my tinkering and voltage checks, the car is starting much better. I may have rubbed aways some contact oxidation on the CS valve. Also, it occurred to me that at 70-80*F., the CS valve make not get enough input to quickly light up the engine. I'm a little scared to spray gas to check so I think I'll either wait and see or replace the CS injector.
What would happen if I grounded one side of the CS injector and let the starter relay supply 12V while the starter is running? I could do this by grounding the G terminal on the thermo-time connector and eliminating the thermo-time sensor. Would this flood the engine? Just curious.
Thanks again.

John Speake

Hello Dave,
Glad to hear it is running better now ! I don't have the US L-Jet circuit handy, so I can't comment on how you might energise the CS valve directly. Usually power is fed (often via a relay) to the thermoswitch and then onto CS vlave which completes the seires circuit to ground.

You will also get a second or so closure of the thermoswitch before its bi-metal contact goes open circuit. Is it powered direct off the igntion switch, or is it only energised when the engine is turning ?

I suspect the latter...you could always experiment with the bulb idea to find out :-)

j.kenzie@sbcglobal.net

John,
The CS only gets 12V from the starter relay via the thermotime switch. It occured to me that while the TT switch limits the CS injector to 2-8 seconds, that is about the same amount of time I have the ignition key in the Start position. Then in hot weather I would have the CS injector to light up. Just an idea.
Thanks again

John Speake

.............so you suspect a little flooding when hot start ?

j.kenzie@sbcglobal.net

I don't really suspect hot start flooding. I was just trying to figure out why Porsche controls the CS injector this way. The 12V to the CS inj. is switched by the starter relay and the ground is switched by the therm-otime switch. Seems like either one would be enough and maybe even better. I'll just try it and report.
Thanks

PorKen

With all these cold start threads, I've been wondering if maybe the cold start tubes and the passages in the head can get clogged up over time? You've got gas, oil vapors, and low air flow, in hot 10mm bored passages the length of the head. I'm sure noone ever cleans them.



(Thinks out loud...) To clean them, you'd have to remove the TB covers to get to the front plugs on the heads. Then remove the plugs and the cold start plumbing off the rear of the heads, and use a gun barrel brush and carb cleaner, followed by a blast of compressed air.

granprixweiss928

where does the air/fuel mixture that is injected into the back of the heads route too?

anyone have a diagram?

does it only go to cyl 4 and 8?

Tampa 928s

? On cold start injector
If one was to convert a CIS to L-jet and elimanate the cold start injector on the L-jet "as per Porken" can you keep the Cold Start injector circuit location from the Cis system. Does the csi location matter with the two different systems?