Thread: Vapor lock
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356-930 356-930 is offline
Acceleration Junkie
Join Date: Aug 2007
Location: Laguna Beach, CA
Posts: 263
Originally Posted by TDH888 View Post
Hi fellow 930 enthusiasts,

My 89 930 is having vapor lock issues accdg. to my mechanic. Im from the Philippines and the weather here is hot and humid all year round .the car starts at once when cold but when the car is hot the car immediately starts right afrter shut down but after 15 to 20 mins after the car would just crank and would not start. the car starts easily the next day.When this symptom apppeared at 1st I brought the car to my mechanic and what he did was to disconnect the electrical connection of the cold start valve and then problem solved. the mechanic advised me to get a new thermo time switch.I was able to use the car for a month w/ out any problem while awaiting arrival of my TTS. When the TTS arrived we installed it and everything went well for a month then the symptom recurred.brought it to my mechanic and what he did was to disconnect the electrical supply of the cold start valve and problem solved except when the the oil temp is the 3/4 mark the engine will have difficulty starting 20-30 mins after shut down and will start only if you make several 5-7 second long cranking then the engine starts w/ some hesitation and some popping sound until it settles to a normal idle.I was thinking that the fuel accumulator is at fault my mechanic disagrees.
Sorry for the long letter.

thanks in advance,

First, it helps to understand how the thermal time switch (TTS) works and how to work around it. It is indeed a switch. It has two wire lugs. One receives +12v and the other is wired directly to one side of the 7th injector which is located on the back of the intake manifold just below the throttle body. Both the TTS and the 7th injector receive their +12v supply from an auxiliary power terminal on the starter motor solenoid. This +12v power is applied to the auxillary terminal only when the ignition switch is turned to the start position.
If the engine is cold enough, the +12v applied to the TTS grounds the wire going to the 7th injector thus completing the circuit to the injector, it turns on and fuel flows. And, if an engine is cold and fails to start after cranking for 10 seconds +/-, the TTS open circuits and stays open for up to a minute. Until the TTS resets itself, +12v will not be applied to either the TTS or the 7th injector and fuel will not flow. Dropping power to the 7th injector is intended to prevent flooding during/with excess starter motor cranking and when engine is hot, the TTS is open circuited to prevent the 7th injector from turning on. No extra fuel should be needed when the engine is hot.
If one wants the 7th injector to fire and add fuel whether the engine is cold or hot, just tie the lug/wire going from the TTS to the 7th injector to ground.

Your hot start issue can be an accumulator issue, a WUR issue or a check valve in the front pump issue. Suggest to your mechanic to check the WUR pressure cold and after the engine is well warmed up. Then check system retention pressure to see that it stays in spec for 20-minutes. If not retaining pressure to spec, could be the accumulator or the check valve in the front fuel pump.

To assure yourself that vapor lock is not probable, get the engine warm to the point you have experienced the problem in the past and when you turn the car off, open the deck lid to reduce the effect of heat soak. See if it starts better after 20-minutes with ‘deck lid cooling,’
Chris Toy
356-930 Gone

Last edited by 356-930; 09-19-2009 at 12:48 PM..
Old 09-19-2009, 12:42 PM
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