MFI warm start issue

[chiroracer]

Was there a real " factory kit" for an enrichment button?

[edmayo]

I have never seen or heard of such.

[Haasman]

Boulder Bob- Did you solve your problem?

[socalozzy]

years ago I had a problem with my '73S with stock MFI - acted like vapor lock. when cold, the car starts OK. when warm (doesn't have to be a hot day), after sitting for 15 minutes the car won't start (just cranks normally). If the car sits for a few hours, it starts normally. I fixed the problem by replacing the "check valve" (overflow valve 901 110 915 00). I got a used one and and it fixed the problem.

As I understand it, the fuel system from the pump under the car to the injection pump needs to hold pressure and if it doesn't the injector pump will not deliver fuel to the injectors. Is this correct? I also understand that there is another check valve in the pump.

So now the problem is back. Pelican wants $242.75 for this part. Is the valve getting gunked up? Can I soak it in solvent? Can I test it? Is the one at the pump under the car accessable?

Has anyone else had this problem?

Why does letting the car cool off solve the problem?

If there is already a thread on this sorry to be asking, maybe someone can provide the link - it's a tough one to search for.

Thanks.

Hi, im having the same issue, i went for a drive came back parked, and wouldnt star back up no matter what i did. came back 6 hours later and it fired up.
what soulution did you fine for this issue?

thanks.

[Boulder Bob]

Hi, im having the same issue, i went for a drive came back parked, and wouldnt star back up no matter what i did. came back 6 hours later and it fired up.
what soulution did you fine for this issue?

thanks.

Hi Socalozzy

I put an inline fuel pressure gauge in the line from the console to the MFI pump. I haven't looked in there in a while, but I believe around 15 psi is the right number. If the pressure in that line bled off due to a check valve malfunction I can monitor it. I haven't had the problem since then so I can't confirm my theory. I also carry a clamp for the fuel line so if the check valve fails presumably I could clamp off the appropriate line and the fuel pump would hopefully generate enough pressure to get fuel to MFI pump and allow the car to start.

MFI experts: does this make sense?

[socalozzy]

Hi Socalozzy

I put an inline fuel pressure gauge in the line from the console to the MFI pump. I haven't looked in there in a while, but I believe around 15 psi is the right number. If the pressure in that line bled off due to a check valve malfunction I can monitor it. I haven't had the problem since then so I can't confirm my theory. I also carry a clamp for the fuel line so if the check valve fails presumably I could clamp off the appropriate line and the fuel pump would hopefully generate enough pressure to get fuel to MFI pump and allow the car to start.

MFI experts: does this make sense?

thanks for the tip, is the line with the blue arrow the one i need to place the inline gauge in?
is the check valve is pricey?
i was told the pump does lose pressure.

[Boulder Bob]

I put the gauge in the line that comes out of the bottom of the fuel filter. I bought the gauge at a store that caters to hot rodders. not expensive. let us know how it works out.

[Rusty]

Years ago I purchased a double banjo bolt so you could check running pressure and residual pressure following shutdown. I can’t remember where I bought it, maybe someone else can chime in. Try 5 gallons of race gas. To see if that helps.

[BURN-BROS]

The problem is indeed Vapor lock. The injector is mounted to the cylinder head and when you turn the engine off, heat soak gets the injector up to head temperature. It then gets the hard lines hot all the way up to the injection pump. I am now replacing the steel fuel lines with plastic ones to combat the issue. You can actually see the bubbles forming when you install the plastic lines! This issue has been around for years, but recently something has changed in regards to formula of the fuel, here in California the powers that be have increased the allowable ethanol content to 10 percent.

[gled49]

Even when gas was good this problem existed. On a hot re-start, I full throttle crank and slowly release the throttle until the throttles are about to to close, car starts. I’ve just got use to it.