Anti-siphon installation, T.I., and judging

[Richard M.]

Re: Anti-siphon installation, T.I., and judging

An anti-siphon solenoid valve which has failed open won't prevent an FI engine from starting. Quite the opposite. The engine will start TOO easily.... if it doesn't bend a rod first.

Jim, He had no power during CRANK with it connected to the ACC circuit, yet he said the engine still started. Since it's impossible to get fuel flow through it under those conditions, my brain was trying to figure out how fuel got through the spider to the nozzles to run without power on it to open, a possible case being if the valve was stuck open it might be a way for the engine to run. Yes I follow, it'll start too easy in that scenario as it's like there's no ASSV there at all.

Bend a rod? Because the valve is stuck open? You mean if the fuel meter check valve is stuck open or missing, too, and the thing dumped raw fuel down and filled some cylinders? No anti-siphon solenoid valve means plain stock, no?

Rich

[Richard M.]

Re: Anti-siphon installation, T.I., and judging

For those that are unsure what goes on inside the ignition switch of a '63-'67, a simple test sequence to see how it is internally configured is to use your test light or ohmmeter and connect it up in the various configurations and turn the key and see results on your test instrument. This is what you'll get....

Key Position Test Result
============================
Key CW to RUN ---- BAT = IGN = ACC

Key CW to START ---- BAT = SOL = IGN

Key CCW to ACC ---- BAT = ACC only


Here's a repro ign switch I had leftover from our '63 coupe. Note the GRD(lower right) is unused on Corvette.
BacksideTerminals.jpg

On the backside of the contactor is the associated contact for each terminal. The BAT terminal is underneath on the right side of the contactor(left side of photo).
InsideSwitch.jpg

When the switch is rotated by the key, the internal oval contacts make or break with the rotating brass disk. Note the 3 "nubs" on the disk. Those rotate to the various contacts for operation. When Key = START, one of those nubs on the disk goes past the ACC oval contact(upper left in photo), breaking the path it had from the BAT terminal.
InternalContacts.jpg

Test meter with Key to RUN(Meter leads BAT to IGN) - BAT=IGN=ACC closed
BATtoIGN_KeyToRun.jpg

Test meter with Key to RUN(Meter leads BAT to ACC) - BAT=ACC closed
BATtoACC_KeyToRUN.jpg

Test meter with Key to START(Meter leads BAT to ACC) - BAT=SOL=IGN closed, BAT to ACC open
20231116_084943.jpg

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[Jim L.]

Re: Anti-siphon installation, T.I., and judging

Jim, He had no power during CRANK with it connected to the ACC circuit, yet he said the engine still started. Since it's impossible to get fuel flow through it under those conditions, my brain was trying to figure out how fuel got through the spider to the nozzles to run without power on it to open, a possible case being if the valve was stuck open it might be a way for the engine to run. Yes I follow, it'll start too easy in that scenario as it's like there's no ASSV there at all.

Bend a rod? Because the valve is stuck open? You mean if the fuel meter check valve is stuck open or missing, too, and the thing dumped raw fuel down and filled some cylinders? No anti-siphon solenoid valve means plain stock, no?

Rich

I missed that detail about Tim's engine starting even with no cranking power to the solenoid valve.

There are three possible reasons that could happen:

1. The solenoid valve has failed open. Being a brand new valve, this seems pretty unlikely. I think we can dismiss this possibility.

2. All solenoid valves installed on 7375 and 7380 FI units (Tim which do you have??) have to be installed such that fuel flows thru the valve in the reverse direction. In the reverse direction, valve closure depends on a spring inside the valve. The force of this spring can be over powered by sufficient fuel pressure..... typically 18 psi - 25 psi. This is necessary to prevent breaking the pump drive cable at the instant the ignition is turned off. During cranking of an engine with a Cranking Signal Valve (7375 FI), it's conceivable fuel pressure could rise high enough to force the solenoid valve open, initiating fuel flow and resulting in engine start.

3. If Tim's FI is a 7380, it has a starting fuel bypass solenoid valve (totally independent of and distinct from the anti-siphon valve), which opens during cranking and, while open, bypasses ALL of the internal FI mechanism to initiate fuel flow. To put a finer point on that, the FI unit can be completely inoperative but the engine will still start and run for a few seconds because of the fuel bypass path. Of course that path closes at the instant the ignition switch leaves the START position.

If Tim's unit is a 7380 and if his anti-siphon valve receives power when the ignition switch returns to the RUN position, he's got a workable way to start the engine: During cranking, bypass valve is open and fuel flows. Once engine fires, bypass valve closes and anti-siphon valve opens, continuing fuel flow.

So, Tim, whacha got?

[Richard M.]

Re: Anti-siphon installation, T.I., and judging

Jim that was a awesomely education post.

Thank You.

[Jim L.]

Re: Anti-siphon installation, T.I., and judging

Just need to know now what FI model Tim has. If it's a 7380, with the starting fuel bypass path, and if he still takes power for the anti siphon valve from a point which has ACC power, he's good to go.

[Dan H.]

Re: Anti-siphon installation, T.I., and judging

Jim, what happens if he leaves it in ACC mode for some reason ?
Dan

[Jim L.]

Re: Anti-siphon installation, T.I., and judging

Jim, what happens if he leaves it in ACC mode for some reason ?
Dan

If the internal anti-siphon check valve has failed and if the serially-connected electric anti-sphon remains open, then all anti-siphoning protection is turned off. That risks a bent connecting rod.

[Richard M.]

Re: Anti-siphon installation, T.I., and judging

Just need to know now what FI model Tim has. If it's a 7380, with the starting fuel bypass path, and if he still takes power for the anti siphon valve from a point which has ACC power, he's good to go.

If the internal anti-siphon check valve has failed and if the serially-connected electric anti-sphon remains open, then all anti-siphoning protection is turned off. That risks a bent connecting rod.

If my unit, no way would I want it on the ACC circuit. IGN for me.

Since it's a atypical hit in judging, it'd be the same deduct if it's on a brown circuit or a pink circuit splice.

I vote pink.

[Tim S.]

Re: Anti-siphon installation, T.I., and judging

Just need to know now what FI model Tim has. If it's a 7380, with the starting fuel bypass path, and if he still takes power for the anti siphon valve from a point which has ACC power, he's good to go.

Thanks guys for the interest in the discussion. Jim, it is a 7380 unit. The siphon valve is working, as you can hear it open and close with the ignition switch. The car started in character (if that makes sense to you) with pulling power from the wiper motor.

[Tim S.]

Re: Anti-siphon installation, T.I., and judging

Jim,

In addition to the response I provided to your question, the only time the engine would not receive fuel is in a warm / hot start procedure when the pedal is to the floor (cutting power to the enrichment valve). Am I correct in my thinking?

Thanks again,
Tim

[Jim L.]

Re: Anti-siphon installation, T.I., and judging

Jim,

In addition to the response I provided to your question, the only time the engine would not receive fuel is in a warm / hot start procedure when the pedal is too the floor (cutting power to the enrichment valve). Am I correct in my thinking?

Thanks again,
Tim

Your understanding is correct, Tim, as is your hot/warm starting procedure.

When you shut off a hot or even warm FI engine, there will be some residual fuel in the nozzles which, from engine heat, will vaporize and create a slight flooded condition. Preventing the starting fuel bypass valve from opening during cranking keeps the flooded condition from becoming worse.

Note: If a warm engine doesn't light off immediately while cranking with the throttle open, it's telling you that it needs fuel. So close the throttle and continue cranking.

[Joseph S.]

Re: Anti-siphon installation, T.I., and judging

You should get no points deduct for an added anti siphon valve. Any knowledgeable judge will understand the "Safety" aspect of that item.

FYI to everyone! Overlooking deducts for safety items is not always for personal safety. It can also be the safety of the car. Protecting a FI engine from catastrophic damage should be a priority.

Happy Thanksgiving to all! Joe

[Jim L.]

Re: Anti-siphon installation, T.I., and judging

See the note about halfway down the page from the '58 - '60 judging manual. It clearly sez retrofitted anti-siphon valves should NOT receive any points deduct. If the manuals for other years do not have similar verbiage, they should. It would be foolhardy to chase a couple of extra judging points for which doing so could otherwise jeopardize the well being of a factory installed engine.

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