Hot Start Woes: Maybe NOT Fuel Pressure?

[ASquared150]

So I’ve completed the holy trinity of fuel pressure-related hot start issue fixes:

New Fuel Accumulator ✓
New Check Valve ✓
New Primary Pressure Regulator O-Ring ✓

...all to no avail. Nothing’s leaking, the car starts just fine cold and runs well too. But if it gets warmed up and turn it off it still refuses to start back up until it’s completely cooled down again.

So - if it’s not a fuel pressure problem, what else could it be? OR is it still a fuel pressure problem and there’s something I’m missing?

[Bitsyncmaster]

You need to test how long you hold rest pressure. Just take the air cleaner off and lightly tap the air plate to know if there is still pressure. Then you time how long you hold pressure after engine shutdown.

Of course using a pressure gauge is better but it sounds like you don't have one.

How long you need to hold rest pressure depends on what the air temp is that day. I found in the summer above 90 deg. F I would get a hot start problem at 3 hours after shut down. Now if I could hold rest pressure for 3 hours or more I would not have that problem.

[ASquared150]

You need to test how long you hold rest pressure. Just take the air cleaner off and lightly tap the air plate to know if there is still pressure. Then you time how long you hold pressure after engine shutdown.

Of course using a pressure gauge is better but it sounds like you don't have one.

How long you need to hold rest pressure depends on what the air temp is that day. I found in the summer above 90 deg. F I would get a hot start problem at 3 hours after shut down. Now if I could hold rest pressure for 3 hours or more I would not have that problem.

Once I have that figured out though what do I do with the information? Do certain time ranges of holding rest pressure point to different problems/solutions?

[PJ Grady Inc.]

So I’ve completed the holy trinity of fuel pressure-related hot start issue fixes:

New Fuel Accumulator ✓
New Check Valve ✓
New Primary Pressure Regulator O-Ring ✓

...all to no avail. Nothing’s leaking, the car starts just fine cold and runs well too. But if it gets warmed up and turn it off it still refuses to start back up until it’s completely cooled down again.

So - if it’s not a fuel pressure problem, what else could it be? OR is it still a fuel pressure problem and there’s something I’m missing?
You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
Rob

[Michael]

Had the car been recently worked on before this hot start issue(for anything)? There is a reason I'm asking.

[Bitsyncmaster]

Once I have that figured out though what do I do with the information? Do certain time ranges of holding rest pressure point to different problems/solutions?

Your result will tell you if it is a rest pressure problem or to look elsewhere for the problem.

[ASquared150]

You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
Rob

Yup that’s the one I changed the other larger one was fine. Honestly the one on the plunger cup looked like it was in good shape too but I had the replacement so I made the switch.

Maybe I should also mention that I did all three separately. I did the fuel accumulator last week. When that didn’t work I made the trip out to DMC Midwest and picked up the check valve and o-ring. Did the check valve this morning and still had the hot start problem so did the o-ring this afternoon.

The car has a new (old-style) fuel pump as of last October and a fresh fuel filter. Seriously grasping at straws for what the issue is. Maybe something weird with the cold-start injector?

[sdg3205]

You mentioned the PPR Oring. Are you aware there are are two orings? One is on the regulator and one is on the plunger cup which is not apparent until you remove the cup with either momentary fuel or air pressure or with a small forcepts.
Rob

I've had an issue with the 3rd o-ring. on the base of the needle, which you can only find after complete disassembly! Check your CSV and injectors for leaking out your rest pressure too.

[DMC5180]

Maybe something weird with the cold-start injector?

The next time you go to do a Hot start and it doesn’t, unplug the blue CSV connector and try again. IF it starts, this is an indicator that the TTS has been bypassed to ground and the engine is getting too much fuel when hot.



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[Rich]

Maybe something weird with the cold-start injector?

About initial diagnosis question: If you or DMCMW can verify that the system holds at least 25psi for 10 minutes after engine shutoff then you'll know if you need to keep troubleshooting for fuel leakage or work on non-pressure causes. The air meter plate test is a good starting point but you can't get a number from that.

About your CSV question: Agreeing with Dennis on the TTS check and adding this. Among the potential leak points, most of which are mentioned in the thread already, is the CSV. If it leaks enough - or if any of the injectors leak - then the system won't hold rest pressure. So, is it possibly a leaky CSV? Yes, but not likely. You could pull it and look for fuel leaking with ignition ON, engine off, TTS & CSV plugged in as usual.

Be safe around pressurized fuel components.

[Michael]

Had the car been recently worked on before this hot start issue(for anything)? There is a reason I'm asking.

I'll ask again.

[ASquared150]

I'll ask again.

Haha sorry Michael - your original comment got lost in the fray. I just bought the car in September of last year. Brought it out to Mike at DMC MW in October and they did a make-run and first-timer's inspection. Post-inspection there was a lot of work to be done in the fuel system, namely a new pump and cleaning out the gas tank. Also replaced the fuse box and and a ball joint and got all new brakes. Also had the Eibach springs installed (which certainly wasn't necessary at the time but I couldn't stand the front wheel-well gap). And a few other things like new door/hood struts etc.

But the only work done on the car since October has been me doing the accumulator, check valve, and o-ring.


Your result will tell you if it is a rest pressure problem or to look elsewhere for the problem.

The next time you go to do a Hot start and it doesn’t, unplug the blue CSV connector and try again. IF it starts, this is an indicator that the TTS has been bypassed to ground and the engine is getting too much fuel when hot.

About initial diagnosis question: If you or DMCMW can verify that the system holds at least 25psi for 10 minutes after engine shutoff then you'll know if you need to keep troubleshooting for fuel leakage or work on non-pressure causes. The air meter plate test is a good starting point but you can't get a number from that.

About your CSV question: Agreeing with Dennis on the TTS check and adding this. Among the potential leak points, most of which are mentioned in the thread already, is the CSV. If it leaks enough - or if any of the injectors leak - then the system won't hold rest pressure. So, is it possibly a leaky CSV? Yes, but not likely. You could pull it and look for fuel leaking with ignition ON, engine off, TTS & CSV plugged in as usual.

Be safe around pressurized fuel components.

I'll take a few taps on the air meter plate and check out the CSV connector next time I'm with the car (I keep it parked in my dad's garage about 30 minutes from my apartment). Possibly later today.

Thanks everybody for the advice/assistance/etc!

[Rich06]

Hello,

I've been having the same problem with 1246 since I bought it in December. I've driven it about 800 miles. It started fine when cold but it wasn't holding rest pressure and I had to crank and crank to start it again if it sat for more than a few minutes after shutting it down when hot. I replaced the o-rings and fuel check valve, and checked the POA to no avail. The accumulator is less than 3 years old.

Yesterday I decided to look at the vacuum reservoir in the driver's side pontoon. There is a rubber cap over one of the fittings and it was completely rotted. I replaced it with a new one (3/8") and today for the first time I've had no problem. I was stopped for a while doing errands at two different places. The car started as soon as I turned the key even though it was not completely cooled off. I checked and it is now holding rest pressure.

I hope this helps.
Rich

[sdg3205]

Hi rich. That vacuum bung has nothing to do with rest pressure. Just a stroke of luck. Your issue is probably unresolved.

[Rich06]

Hi rich. That vacuum bung has nothing to do with rest pressure. Just a stroke of luck. Your issue is probably unresolved.

Thanks Dave,

I kind of thought that but wasn't sure. It just seems strange that the car had no hot start issue for the first time today and is holding rest pressure. The outside temp was not any different than what we've had. I've had the problem for almost 3 months. I have done some other things such as replacing the fuel lines, etc., but didn't do anything else yesterday.

[Rich]

....today for the first time I've had no problem. I was stopped for a while doing errands at two different places. The car started as soon as I turned the key even though it was not completely cooled off. I checked and it is now holding rest pressure.
Rich

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...

[ASquared150]

Thanks for the tip Rich06 - here's hoping your issue really is fixed. Also sorry to kinda take the thread back... but I did make it out to my dad's today and ran all the tests/checks I could in the short time I had:

First thing I did was pull the cold start injector to make sure it wasn't leaking. It was a bit dirty but I cleaned it up and turned on the ignition, no leak. Had my dad crank the motor briefly and it sprayed a nice little mist of fuel just like it should.

So I re-installed it and took the car out for ~20 minutes to get it warmed up. Came home, started a timer and pulled the air box. Tapped the air plate a few times every minute and after 20 minutes it still had back pressure so I put the air box back on and went to start the car. Which is where this gets a little sticky.

Normally 20-25 minutes is the perfect amount of time for vapor lock to set in, but the car started right up. Idled a little rough but steady, and got smoother if I gave it a little gas. Shut it down and unplugged the CSV. Started right up again. I figured the 20 minutes spent tapping the air plate must've been enough for it to cool down (even though it usually takes more like 35-45 minutes to get over its vapor lock.)

Waited another 5-10 minutes and tried starting it again with the CSV still unplugged. This time it didn't start, but that's probably because it was cold at that point. Plugged the CSV back in and it started - though it idled rough. Unplugged the CSV again for the hell of it and started right up again, but this time idled smoother.

...So, I have no idea what's wrong at this point. Any thoughts?

[DMC5180]

Well, you’ve had positive results, but you’ll need to run the test again. But, let the engine get hot so the Fans cycle at least once.

Then do your typical delayed hot start routine. Don’t unplug the CSV this time. If it doesn’t start right away, then and only then, try it with the CSV unplugged.


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[ASquared150]

Well, you’ve had positive results, but you’ll need to run the test again. But, let the engine get hot so the Fans cycle at least once.

Then do your typical delayed hot start routine. Don’t unplug the CSV this time. If it doesn’t start right away, then and only then, try it with the CSV unplugged.

So - went back out in the car for a 30-minute drive. Fans cycled multiple times. Came home, let the car sit for 20 minutes and went out to try and start it up again (for the first time hoping for vapor lock.)

On my first attempt (CSV still connected) the car cranked and turned over but immediately died. That actually happens somewhat frequently with my hot start issue. Tried it again immediately afterwards and nada. Just starter motor, no turnover.

Then I pulled the CSV, turned the key, and still nada.

So I think we can rule out the CSV malfunctioning. Yay?

[Rich]

So - went back out in the car for a 30-minute drive. Fans cycled multiple times. Came home, let the car sit for 20 minutes and went out to try and start it up again (for the first time hoping for vapor lock.)

On my first attempt (CSV still connected) the car cranked and turned over but immediately died. That actually happens somewhat frequently with my hot start issue. Tried it again immediately afterwards and nada. Just starter motor, no turnover.

Then I pulled the CSV, turned the key, and still nada.

So I think we can rule out the CSV malfunctioning. Yay?

Sounds like the CSV is fine. It isn't leaking per your observation.

The better news, if you can call it that, is that you can more or less replicate the hot-start issue. Is that correct?

If only you can get a fuel pressure reading to go with the repeatable hot-start issue....if you can know from data taken before/during hot-start-fail events that fuel rest pressure is below spec then you'll know focus on finding the leakage.

[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:
55953

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...

[DMC5180]

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:
55953

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...

It may not be what you think. The metering housing left the factory with a tamper-proof sealing plug in that hole. To remove the plug, you drill a small hole into it then thread a small screw in and pull the plug it out. Once removed you could, in theory, just stick the plug with screw back in the hole if you did not have the removable rubber plug to replace the original sealing plug. It does not take much to plug the hole. I’ve seen golf Tee’s used or even a old school lead ✏️ .

You will need too look closely at it to determine if the screw is threaded into the plug or directly into the housing. if in the housing you could have a leak around The threads. Nonetheless, it has been tampered with.


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[David T]

People use all kinds of things. On one car I found a golf tee!

[Michael]

Advance (or about any auto parts store) sells universal vacuum plugs in the "Help" section. I used one from that pack.

[DMCMW Dave]

It may not be what you think. The metering housing left the factory with a tamper-proof sealing plug in that hole. To remove the plug, you drill a small hole into it then thread a small screw in and pull the plug it out. Once removed you could, in theory, just stick the plug with screw back in the hole if you did not have the removable rubber plug to replace the original sealing plug. It does not take much to plug the hole. I’ve seen golf Tee’s used or even a old school lead ✏️ .


I've also seen that hole drilled out so big that the original or rubber plug won't fit any more. In that case, the only thing that will work is something like what you see, and such things may be better left alone as long as they are tight.

[ASquared150]

So, over the past week or so I've been able to put a good amount of time into the car. The very first thing I did was pull that screw out of the mixture adjustment screw access hole. It wasn't driven too far in but it left the top of the hole pretty marred. So until I get back out to DMCMW for the proper part, I plugged the hole with an M4 bolt that fit pretty snug and then covered it with some adhesive aluminum tape - not entirely ideal, but it should hold vacuum WAY better than the screw did.

Since I had the airbox off I also took care of my high idle - it'd been idling around 1500 RPM for a while. Long story short I adjusted the idle speed screw and microswitch screw and now it idles around 750 as it should.

And finally while adjusting the idle I noticed the car was getting way too hot - pretty quickly moving past the 220 mark on the temp gauge. Radiator fans weren't turning on. Jumped the otterstat, fans still worked. Turns out at some point the driver's side coolant pipe had started leaking at the hose junction heading up into the engine bay. So I tightened all the hose clamps I could easily reach, opened up the bleeder valve and added coolant until the overflow tank was half full and the bleeder was leaking, then replaced the radiator cap on the overflow tank with a new one. Coolant system is working properly again.

Now then, back to the hot start stuff:

After adding the coolant I took it for a quick spin to get gas (added a can of Techron as well). When I got back I let the car run until the fans had cycled 2 or 3 times and shut it down. Waited 15-20 minutes, and it started right back up and went straight to idling at 750. Very promising.

Then today I took it out again and drove around town for about 45 minutes. Got the engine plenty warm, fans cycled multiple times. Then I shut it down and set a timer for 45 minutes. Came back to the car, and it started right up again, first try. Idled a little bit rough but then smoothed out. So I drove it around a little more, let the fans cycle 2 or 3 times again, then shut it down and set a timer for 30 minutes. Again, started right up, first try.

So, is my hot start problem solved? Of all the work I did recently the only thing I can think of that would affect it would be sealing the mixture screw port off better. But even that seems like a somewhat insignifigant change to solve my hot start issue. Would adjusting the idle screw possibly make any difference? I'm worried I just happened to get lucky today on my tests and that the issue isn't actually solved...

[DMC5180]

Time will tell.

Is your Car largely stock in the relay compartment ? Meaning original fuel pump relay.


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