Hot start - sometimes acts like it's flooded

[dmruschell]

After being turned off for 5-10 minutes after driving (just long enough to run into a store or pump gas), sometimes one of our DeLoreans doesn't want to start. It will crank just fine, but it won't actually catch and start. However, if the gas pedal is pushed all the way to the floor and the engine is then cranked, it will start up after a few seconds. It's as if it had a carburetor on it and the engine had flooded. Does anyone have any idea what could be causing this?

I do have David McKeen's hot start relay on the car. My understanding is that it runs the cold start injector whether the car is hot or cold. Could that be contributing to the issue? Our other delorean also has the hot start relay installed (it doesn't have a thermo-time switch, so it needs the relay) and doesn't have this issue.

Thanks in advance!

[NightFlyer]

After being turned off for 5-10 minutes after driving (just long enough to run into a store or pump gas), sometimes one of our DeLoreans doesn't want to start. It will crank just fine, but it won't actually catch and start. However, if the gas pedal is pushed all the way to the floor and the engine is then cranked, it will start up after a few seconds. It's as if it had a carburetor on it and the engine had flooded. Does anyone have any idea what could be causing this?

I do have David McKeen's hot start relay on the car. My understanding is that it runs the cold start injector whether the car is hot or cold. Could that be contributing to the issue? Our other delorean also has the hot start relay installed (it doesn't have a thermo-time switch, so it needs the relay) and doesn't have this issue.

Thanks in advance!

The three primary causes of hot start problems are:

1) failed check valve at the fuel pump

2) partially failed accumulator (a complete failure will prevent the car from running)

3) damaged PPR (primary pressure regulator) o-ring

As to the check valve:

Regardless of the fuel pump that you're using, I personally recommend installing an external inline check valve on the main feed line, as it makes dealing with K-Jet that much easier. The best one that I've found, and the one that I personally use, is the SMC valve manufactured in Minnesota USA. It's over spec'd, and should last a life time or more. It's readily available from US Plastics, and is the same one that DMCH now includes with all their pump/sender combo kits (based on my personal recommendation):

http://www.usplastic.com/catalog/item.aspx?itemid=85394&catid=945

Post about the installation of my valve (with pictures):

http://www.dmctoday.com/showthread.php?276-K-Jet-DMCH-Fuel-Pump-Sender-Combo-External-Inline-Check-Valves&p=3911&viewfull=1#post3911

As to the accumulator:

You can test the accumulator by pulling the hose off the back of the accumulator (the small one that's connected to the integrated barbed fitting). Block that hose (as I'm not sure if the return line that it tees into is check valved or not). Then run a length of hose off the accumulator barb and into a catch container of some sort. Jump the fuel pump on at the RPM relay. If the accumulator is good, then no fuel should flow from the back of the accumulator. If the accumulator is worn but still somewhat good, then you'll only see a few spurts of fuel flow out the back of the accumulator at the initial start up of the fuel pump. If the accumulator has suffered a complete failure, you'll get a steady pressurized stream of fuel out the back of the accumulator.

The car will run with anything less than a complete failure, but a partial failure will cause hot start issues, in which case, the accumulator will need to be replaced.

If you do need a new accumulator, I highly recommend getting the full stock/OEM sized accumulator from Summit racing or someplace similar, as opposed to the 4-cylinder accumulator that most vendors are now selling.

http://www.dmctoday.com/showthread.php?9-Important-Fuel-Accumulator-Info

As to the PPR o-ring:

This is unbolted/removed from the fuel distributor. If upon a visual inspection, the o-ring appears swollen, deformed, or compromised in any way (tear, cut, etc), then it should be replaced. Dave McKeen strongly recommends using a viton o-ring in this application, as a traditional nitrile/buna-n one will swell with today's ethanol blended fuels. Changing this o-ring is only recommended if there's a confirmed problem with your existing one, and should NOT be done as a matter of preventative maintenance.

Best luck :thumbup:

[dmruschell]

I'm not so sure it's caused by the lack of fuel or fuel pressure. When this happens, it doesn't matter how long the car is cranked or how many times it is cranked without the gas pedal pressed or how many times the fuel pump is primed; it doesn't show any sign of turning over. However, when the gas pedal is pushed to the floor, it roars to life within a couple of seconds. If it was a carbureted car, I'd say it had too much gas and had been flooded.

[NightFlyer]

I'm not so sure it's caused by the lack of fuel or fuel pressure. When this happens, it doesn't matter how long the car is cranked or how many times it is cranked without the gas pedal pressed or how many times the fuel pump is primed; it doesn't show any sign of turning over. However, when the gas pedal is pushed to the floor, it roars to life within a couple of seconds. If it was a carbureted car, I'd say it had too much gas and had been flooded.

You could always try running a regular RPM relay and see if it still happens.

[Bitsyncmaster]

My hot start relay will turn the CSV on after one second of cranking (hot or cold). If you think that could be your problem just unplug the CSV and see it that helps. You should not need the CSV in the summer months.

But a 5 to 10 min hot start problem is most likely a very bad accumulator or as Josh suggested other problems with rest pressure. When I first got my car it had that same problem and it was the accumulator. If you have an original accumulator, I recommend it be replaced anyway.

[Rich]

I'm not so sure it's caused by the lack of fuel or fuel pressure. When this happens, it doesn't matter how long the car is cranked or how many times it is cranked without the gas pedal pressed or how many times the fuel pump is primed; it doesn't show any sign of turning over. However, when the gas pedal is pushed to the floor, it roars to life within a couple of seconds. If it was a carbureted car, I'd say it had too much gas and had been flooded.

It most like is indeed the low fuel pressure. This is all consistent with a bad accumulator or a bad check valve, either of which will allow the fuel at the hot-soaked engine to vaporize in the lines because the system is not maintaining shutdown pressure. That causes the engine to suffer from vapor lock.


a. The hot start will be difficult because the fuel in the lines is no longer all liquid fuel. The injectors are metering vaporized fuel, not liquid fuel, so the engine gets a super-lean mixture that won't fire.
b. When you floor it while cranking you eventually will feed enough cooler, pressurized liquid fuel into the system that it will show up at the injectors after all of the vaporized fuel is chased out. Flooring the accelerator, for those of you who remember carbureted cars, was one way to overcome vapor lock on those things. All you're doing in either case is purging the fuel system faster than you would at any lower throttle opening. Not that it's a bad idea, but it's not addressing the root cause.

The other way to recover from the problem is to wait til the engine cools, allowing the fuel bubbles to condense and disappear when the fuel pump lights up for the cold(-er) restart. The car starts up fine when the engine isn't hot, right? Classic fuel rest-pressure problem. Not the same as a "pressure" problem in every respect, but specifically a rest-pressure problem.

[David T]

After being turned off for 5-10 minutes after driving (just long enough to run into a store or pump gas), sometimes one of our DeLoreans doesn't want to start. It will crank just fine, but it won't actually catch and start. However, if the gas pedal is pushed all the way to the floor and the engine is then cranked, it will start up after a few seconds. It's as if it had a carburetor on it and the engine had flooded. Does anyone have any idea what could be causing this?

I do have David McKeen's hot start relay on the car. My understanding is that it runs the cold start injector whether the car is hot or cold. Could that be contributing to the issue? Our other delorean also has the hot start relay installed (it doesn't have a thermo-time switch, so it needs the relay) and doesn't have this issue.

Thanks in advance!

Remove the hot start relay, do the plug swap, and if it starts up you have a problem with "Rest Pressure" and post #2 tells you how to fix it.

[dmruschell]

It most like is indeed the low fuel pressure. This is all consistent with a bad accumulator or a bad check valve, either of which will allow the fuel at the hot-soaked engine to vaporize in the lines because the system is not maintaining shutdown pressure. That causes the engine to suffer from vapor lock.


a. The hot start will be difficult because the fuel in the lines is no longer all liquid fuel. The injectors are metering vaporized fuel, not liquid fuel, so the engine gets a super-lean mixture that won't fire.
b. When you floor it while cranking you eventually will feed enough cooler, pressurized liquid fuel into the system that it will show up at the injectors after all of the vaporized fuel is chased out. Flooring the accelerator, for those of you who remember carbureted cars, was one way to overcome vapor lock on those things. All you're doing in either case is purging the fuel system faster than you would at any lower throttle opening. Not that it's a bad idea, but it's not addressing the root cause.

The other way to recover from the problem is to wait til the engine cools, allowing the fuel bubbles to condense and disappear when the fuel pump lights up for the cold(-er) restart. The car starts up fine when the engine isn't hot, right? Classic fuel rest-pressure problem. Not the same as a "pressure" problem in every respect, but specifically a rest-pressure problem.

This makes sense now. I will start investigating.

The car is 3196, a 2008 DMCH new build that was owned by Wilson Hitchings and extensively gone through by DPI before I bought it. So, the parts should be new-ish at least. Given the reputation that the accumulators have, I'll start there.

This issue only appears sometimes and is so intermittent (and doesn't happen often) that I haven't looked further into diagnosing it. But, this DeLorean is my fiancee's and it did it to her yesterday, so it's time to fix it :P