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Vapor lock

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,


tdh88
Old 09-18-2009, 05:34 PM
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I had a problem similar to this and was able to immediately correct it by:

lowering my WUR cold start pressure. it was too high at cold start and that was causing a "too lean" condition when attempting to start when cold. what little fuel was evaporating before combustion could take place... [my best guess]

there are three pressure settings for the WUR: cold, warm, and boost. the first two can be checked with a CIS test kit and to check boost, you would need to hook up a mighty-vac to the bottom of the WUR to check boost.

Oh yeah, I too thought it was my accumulator... still got the same accumulator, and she starts right up cold/warm/or hot...
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Old 09-18-2009, 06:36 PM
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I also doubt vapor lock. With two pumps there should be enough pressure that vapor isn't a problem.

The popping you mention leans me to think WUR issue.
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Old 09-18-2009, 07:08 PM
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no vapor lock...its a bad fuel accumulator... had the exact same symptoms on my car a long time ago. check into it.
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Old 09-18-2009, 11:08 PM
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Quote:
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,


tdh88
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,’
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Last edited by 356-930; 09-19-2009 at 11:48 AM..
Old 09-19-2009, 11:42 AM
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Quote:
Originally Posted by mooney265 View Post
I had a problem similar to this and was able to immediately correct it by:

lowering my WUR cold start pressure. it was too high at cold start and that was causing a "too lean" condition when attempting to start when cold. what little fuel was evaporating before combustion could take place... [my best guess]

there are three pressure settings for the WUR: cold, warm, and boost. the first two can be checked with a CIS test kit and to check boost, you would need to hook up a mighty-vac to the bottom of the WUR to check boost.

Oh yeah, I too thought it was my accumulator... still got the same accumulator, and she starts right up cold/warm/or hot...
Thanks Mooney for you reply and advised. Is it possible to lower my WUR's cold start pressure if my 930's WUR is stock ? Is the stock WUR adjustable?My mechanic agrees that its not vapor lock after he did some additional test.

thanks,

TDH888
Old 09-20-2009, 02:27 PM
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Quote:
Originally Posted by 356-930 View Post
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,’
Thank you Cris. My mechanic had rule out vapor lock .Is the stock warm up regulator adjustable.?

TDH888
Old 09-20-2009, 04:38 PM
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Ok, mine has been doing the same thing, ever since I got the car.

I have changed out the accumulator, the front pump check valve, the fuel head check valve!

I've changed out the infamous green wire, I've changed out my distributor pick up coil, I'm on my second new ignition coil, my second new C.D.I. box!

Mine did it with the stock WUR, amd still does it with my Brian Leask adjustable WUR.

It ONLY does it when the car is up to full temp. & sits for 10-45 minutes. Dead cold it always fires right up. After sitting for 45+ minutes it also always fires right up.

I've tried turning the pumps on via pushing down on the fuel head CO adjuster plunger screw, which works great and gets plenty of gas into the system. When I crank the engine after pushing down on the plunger screw, I can smell raw gas coming out the tail pipe, but it does not fire up.

If it is some where near the 45 minute mark when I try to start it, it cranks forever then very reluctantly fires, it labors to gain rpm no matter how much throttle is applied. After a few seconds of labored running it cleans up and is fine.

The problem seems heat related to me, and it seems more ignition related, is there any switch or sensor that could cut out the ignition, or at least cause a heavy voltage drain?

Could it be as simple as an overheating ignition switch?

Overheating starter solenoid?

Man I'm grasping at straws here, We cannot be the only 2 guys that are having or had this problem.

As you can all see, I've tried damn near everything that everybody has suggested.

I've been told that it might be a leaky injector, but how could a leaky injector cause all 6 cylinders to flood? And why if it is a leaky injector, will it not fire when I manually start the pumps. Even if 1 cylinder is flooded, the rest should fire off!

I've resolved myself to planning my starts & stops around a 1 hour window, simply to avoid this crap! But one can not always do this, mine is my daily driver.

Beyond frustrated.....
Mark
Old 09-20-2009, 04:54 PM
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mark,

you say you have an adjustable BL WUR... Have you hooked up some CIS gauges and checked your pressures? If so, have you attempted to adjust your cold and warm control pressures?

I too have a BL WUR and used it "as shipped" for a couple of months... Started having all sorts of starting issues. then, broke down and got some CIS gauges and started checking readings. turns out that my cold control pressure was way too high [like 3.75 BAR]. When i lowered it to 2.9, the car started right up!!

hope this helps...
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Old 09-20-2009, 05:01 PM
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Quote:
Originally Posted by TDH888 View Post
Thanks Mooney for you reply and advised. Is it possible to lower my WUR's cold start pressure if my 930's WUR is stock ? Is the stock WUR adjustable?My mechanic agrees that its not vapor lock after he did some additional test.

thanks,

TDH888
tdh: the stock WUR is adjustable - - but, way beyond my pay-grade!!
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Old 09-20-2009, 05:03 PM
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Hey Mooney,
I have not hooked up any CIS gauges yet. Like I said though, mine has done this exact same thing ever since I've owned the car. That has been with both the stock WUR & with Brian's WUR. The chances that both were adjusted exactly the same to cause exactly the same problem is very unlikely.
Looking at a picture of the Thermo-tine switch from our hosts catalog, I seem to remember re-attaching a loose wire form that switch when I did my first valve adjust, then when I did my last valve adjust, I noticed that the wire was again loose.
So if that switch is not hooked up properly, could this cause a hard/no start when hot condition?????
Mark
Old 09-20-2009, 06:10 PM
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This could be carbon fouled CIS injectors leaking fuel after a hot shutdown until the accumulator spring loaded diaphram is back to it's relaxed state and flooding the motor in the process.
The hot start symptoms are exactly what you are experiencing.

[I posted this the other night but my post was deleleted during all the server timeouts and later the database transfer to the backup server]

All CIS injectors will eventually do this because they stay open continuously while the engine is running.
Electronic injectors do not do this because they are constantly opening and closing and because of this they are self cleaning.

A can of techron or seafoam may help, but usually they have to be removed and cleaned to be succesful.
Old 09-20-2009, 06:30 PM
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TDH888 and full quack

For full quack's problem, I like JFairman's leaking injector theory best. Sounds like a fuel issue, but there's NO WAY I'd rule out an ignition problem. I doubt it's a heated ignition switch or starter solenoid.

I'd try...ground the white wire to the over boost switch so you're taking it out of the system. Maybe the heat's causing it to go open circuit? Wiggle/clean the wires TO the CDI box. Wiggle/clean the 14 pin connector that goes into the rear fuse panel (will cause a no-start if not connected). Check the connections to the fuel pump relay sockets. Yellow relay okay? Jump it and take it out of the loop to see if that helps. Same with "delay relay". Dizzy cap okay? Does your tach needle jump around when trying to start it?

These are thing I'd check now that the more obvious stuff has been done. Maybe the heat is opening up some electrical connections or soldered joints.
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Old 09-21-2009, 11:30 AM
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I've tried grounding the over boost switch, jiggled every wire bundle known to man, swapped out each & every relay, dizzy cap is great, rotor is great. I have no yellow relay(mine is euro if that makes any difference).
I'm thinking it's time to send my injectors out for cleaning & spray pattern balancing. It's just that getting to back 2 drivers side injectors out while the engine is still in the car, is a real *****! Then I'll also be down for the better part of 2 weeks for turn around time.

Sighhhhhh......guess I'll have to drive my truck for a couple of weeks.

Mark
Old 09-21-2009, 11:58 AM
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Quote:
Originally Posted by full quack View Post
. . .So if that switch is not hooked up properly, could this cause a hard/no start when hot condition?????
Mark
No. When hot, the thermal time switch is open circuit, does not fire the 7th injector. Only time it acts to turn the 7th injector is when engine is cold and then only for about 10-seconds of cranking as it's got its own heater that makes it let go of ground. There's a reason its called a "Thermal Time Switch."
Find the lug on the TTS that goes to the 7th injector, i.e. not the +12v wire. Hard wire that lug and the wire attached to it (the one going to the 7th injector) to ground. When cranking the engine, the 7th injector will fire regardless of engine temp. If this 'fixes' your hot start issue, definitely a fuel related issue, not ignition.
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Old 09-21-2009, 04:24 PM
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Fuel Accumulator

I own an 87-930. Same exact issue and it was my accumulator. Changed it and have not had problem since. Very easy to do.

Best of luck in the fix,
Bryan
Old 09-21-2009, 07:34 PM
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Originally Posted by TDH888 View Post
Thank you Cris. My mechanic had rule out vapor lock .Is the stock warm up regulator adjustable.?

TDH888
Dear 356-930 and other responders to this post,

I would like to give you an update as to whats happening w/ my car in the hands of my mechanic. First of all we replaced the ignition coil because the original coil was already leaking w/ oil at the top edges. I replaced it temporarily w/ a working Bosch coil and the car idles & run better. I ordered the proper one from pelican & it will arrived next month. I believe the ignition coil we replaced was w/ the car since 1989. We also discovered that the socket that connects to the CDI was loose. We discovered it when we were trying to start the car 30mins after shutting down then restarting it. While I was cranking car what he did was to wiggle the connector going to the CDI and the car started at once. We reconnected the cold start valve . The mechanic tightened the CDI connector. He tested the car bringing it to operating temp. We shut off and restarted the car after 30 mins ,the car refuses to start . He disconnected the connection immediately going to the cold start valve and the car immediately started. My thermo time switch is new it was replaced 2 months ago and its specific for the 89 930 USA version. Do you think my cold start valve is the culprit?


TDH888
Old 09-25-2009, 02:33 PM
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Check the residual pressure in the fuel system after you shut the pumps off, and see if it is to spec for that time period specified. If your pressure drops off real fast, you can flash the fuel into vapor in the lines. Vapor lock is fuel boiling.
Pat
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Old 09-25-2009, 02:41 PM
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Quote:
Originally Posted by TDH888 View Post
Dear 356-930 and other responders to this post,

I would like to give you an update as to whats happening w/ my car in the hands of my mechanic. First of all we replaced the ignition coil because the original coil was already leaking w/ oil at the top edges. I replaced it temporarily w/ a working Bosch coil and the car idles & run better. I ordered the proper one from pelican & it will arrived next month. I believe the ignition coil we replaced was w/ the car since 1989. We also discovered that the socket that connects to the CDI was loose. We discovered it when we were trying to start the car 30mins after shutting down then restarting it. While I was cranking car what he did was to wiggle the connector going to the CDI and the car started at once. We reconnected the cold start valve . The mechanic tightened the CDI connector. He tested the car bringing it to operating temp. We shut off and restarted the car after 30 mins ,the car refuses to start . He disconnected the connection immediately going to the cold start valve and the car immediately started. My thermo time switch is new it was replaced 2 months ago and its specific for the 89 930 USA version. Do you think my cold start valve is the culprit?


TDH888
No, I do not believe the cold start valve or the thermal time switch is the problem. Re-read my information on how the thermal time switch (TTS) works. Bottom line, if engine is cold, TTS turns the cold start valve on and fuel flows into the intake manifold. If engine is hot, TTS does not turn cold start valve on. If the TTS were "bad" meaning it turns the cold start valve on even when the engine is hot, the engine would most likely sputter to life because it was too rich but it would sputter to life. If so rich it couldn't start, you will smell raw fuel in the exhaust pipe.
The minute you let go of the starter motor, (i.e. stop cranking the engine) the TTS and the cold start valve, whether good or bad, are out of the circuit. Neither will have a +12v supply. If you're cranking and cranking and it's not starting hot, you probably don't have fuel.
As suggested by Pat Keefe, "Check the residual pressure in the fuel system after you shut the pumps off, and see if it is to spec for that time period specified. If your pressure drops off real fast, you can flash the fuel into vapor in the lines. Vapor lock is fuel boiling."
Lastly, since fussing with the CDI connector yielded good results, visit that component again when the engine refuses to start.
Good luck and let us know what Gremlin caused the problem once you've gotten it resolved.
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Old 09-25-2009, 06:46 PM
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Chris

As usual, a ton of knowledge and great advice packed into one paragraph. You are welcome to come to Fresno and drive my car anytime if you miss it too much. Or heck, why not an automatic?

Be well,
Bryan
Old 09-25-2009, 06:55 PM
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