Hot Start Woes: Maybe NOT Fuel Pressure?

[David T]

The next time you have a hard hot restart, do the plug swap. If that gets it going you have a fuel system problem, probably related to rest pressure. If it doesn't start you may have an ignition system problem. In that case check for spark. The impulse coils are known to fail temperature sensitive but not quite this way. Just because you changed some parts can't rule out that you may have done the swap improperly or the part you put in is faulty. The best test for rest pressure is to observe the rest pressure with a fuel gauge. Very easy to damage the "O" rings on the PPR when putting it back together. Once damaged you won't hold rest pressure long enough. The way to test that is to use the pressure gauge and block off the return line to the fuel tank. That way even if the PPR leaks you won't lose pressure. That will confirm if the PPR leaks. Bottom line, if the plug swap gets you going you will need to get a pressure gauge and do some troubleshooting.

[Bitsyncmaster]

If it takes one hour of shutdown to have the start problem you need to verify you hold rest pressure for at least that one hour.

Your problem will get worse in the summer if the problem is caused by loss of rest pressure. My car would pass the 10 minuet specification rest pressure test but still would have hot start problems in the summer months.

Was your replacement fuel accumulator a NOS part?

[DMC5180]

When you are attempting too start (hot), is your foot On or Off the gas pedal?


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[ASquared150]

If it takes one hour of shutdown to have the start problem you need to verify you hold rest pressure for at least that one hour.

Your problem will get worse in the summer if the problem is caused by loss of rest pressure. My car would pass the 10 minuet specification rest pressure test but still would have hot start problems in the summer months.

Was your replacement fuel accumulator a NOS part?

It usually takes anywhere from 15-25 minutes for the hot start issue to show itself. My low-rent finger tap pressure test yesterday took me all the way to 20 minutes with no sign of it even losing a little bit of pressure - at which point I stopped testing and moved on to trying to start it again.

The replacement fuel accumulator I got isn't NOS, it's the newer and smaller unit I got from DMC MW.

When you are attempting too start (hot), is your foot On or Off the gas pedal?

Off. At least for the first few attempts. After first try I usually turn everything back off and then turn just the ignition on to let the fuel pump run a little bit before trying to crank it again. When that doesn't work I'll try tapping the gas pedal a bit to try and give it some fuel, but none of that ever works.

[DMC5180]

I Generally use the foot off the pedal method, which typically works fine for me.
The Owners manual starting procedure recommends you hold the pedal down about 1/4 travel when starting.

The theory behind it being the extra airflow helps push the air metering plate down a bit more. This helps purge any vapor that might be present in the injector lines quicker. Under normal circumstances when the engine fires it will do so with vigor.


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[Delorean Industries]

Replace the fuel accumulator with the correct sized unit. After seeing the post regarding the smaller unit installed that is most likely the culprit. We see hot starts all the time here with small units installed. Rarely does replacing this unit not correct the problem.

[ASquared150]

This helps purge any vapor that might be present in the injector lines quicker.

Funny you should mention that - I just got off the phone with Mike at DMC MW. Went through everything I did this weekend since the last he'd heard from me was when I was there getting the check valve and o-ring. He gave me a few more things to try. First and foremost was trying to hot start it with the gas pedal to the floor (and immediately letting off if it actually starts haha).

His thinking is that the injectors (or distributor) may be leaking after shut-down, causing flood conditions when I try and start it up again too soon. The theory is that it's taking ~35 minutes not necessarily for the car to cool back down but for that extra fuel to evaporate and clear itself. Holding down the pedal would help clear that as well.

Also suggested I check for spark because if it's not a fuel pressure thing it has to be an ignition thing.

Hopefully I can make it out to the car soon to test all this out!

[Rich06]

That sounds good but maybe the problem is still there under other conditions? Depending on the time you take between shutdown and hot restart you may get varying results. If you wait less time after shutdown the rest pressure may still be above minimum, the fuel won't vaporize in the high-side lines and it will hot-restart. But in other circumstances with longer dwell time the fuel pressure may drop further and you get stuck.

You mentioned it is now holding rest pressure. Did you measure it? If so was it above 25psi 10min after hot shutdown?

Hoping it is indeed back to normal somehow...

Not trying to take over this thread but thought I should answer. You were correct the problem was still there. I used the flashlight test when checking the pipe of agony. I really wasn't careful enough. Today I looked a little closer and found it wasn't sealing most of the time. I must have moved it somehow when working in the pontoon so that it seemed everything was okay.

I took out the pipe and put in a new o ring (using the brass retainer). I was able to do it with only removing the idle speed motor and bracket so it wasn't too bad. The pipe is nice and snug now and the problem seems to be fixed as I was using the car most of the day and had no problem.
Thanks

[DMCMW Dave]

I've seen a couple where the fuel mixture was set just a tiny bit too lean (not lean enough to run bad, but lean enough not to get enough fuel to start without assistance from the CSV). CO adjustment fixed it. Unusual problem. Exactly like a small unmetered air leak - the problem that you found.

[ASquared150]

So obviously I haven’t made a ton of progress on my hot start issue in the last few weeks. Weather in Chicago has been less than conducive to working on the car. In the meantime I’ve been researching some other stuff and reading James Espey’s Illustrated Buyer’s Guide. At the section for the Idle Mixture Adjustment Screw I noticed plug with metal hoop and didn’t recognize it. The guide says, quote, “unplugged, this is a source for a large vacuum leak.”

Ah ha! I thought maybe I’d found my problem. So I went out to the car to take a look. Where I found this:
E5DBC6A4-907B-4271-AAED-5CDD83EB5B90.jpg

What. The. Shit.

I guess PO thought shoving a sheet metal screw in there was somehow a good idea?! Also - a little disappointed this wasn’t caught during the inspection I had done at DMC Midwest.

I haven’t investigated any further, like by removing that beast of a screw, but I’m hoping whatever damage may have been cause by it is minimal...