My car has been having this hot restart problem. I can get the car to start from cold with no issues, but if I park and let it sit for a while, but not long enough to fully cool down, it will not restart very easily. Instead, it will crank and crank and crank and not fire. It's kind of like vapor lock, like the fuel pump is getting a bubble in it or something and fuel can't pump past. Or maybe the fuel pump impeller is slipping when it gets hot?

Anyway, I decided to drive the car today and parked the car and went into Summit Racing to get some things for the Civic. When I come out sure enough to stupid car won't start. So I rap on the relay, which is fairly new, and check the fuse, and smack the DME, and rap on the fuel pump and check its connections, all to no avail. Still no start. Then for no reason I decide to pull off the vacuum lines from the FPR to see if it hisses when I remove the line, which it does. I put the line back on and go back to try to start the car, figuring it will not fire and would you believe it, it fires immediately.

So is there any correlation? Was it just a fluke that letting of the vacuum pressure allowed the car to start? Bear in mind the FPR is less than 6 months old.

And remember, the relay is almost new. I put it in when I first started having this problem and it has not helped. And the relay it replaced was also only in for a short period.

 

I have nearly the same problem, also a nearly new FPR, and new fuel pump.

 

The other thing I thought of was that you are letting a lot of heat out of the engine compartment by opening the hood, right?

 

from what i have learned, if you have a hot start problem, it it almost always because of a rich a/f mixture. i would double check those FPR's. new parts can be faulty.

 

it might be the check valve downstream from the fuel pump is leaking pressure.

87951

 

There should be a gassy smell then, no? I don't get any kind of gassy whiff, but maybe I'm just not catching it. Also, the notoriously innaccurate Autometer A/F meter doesn't seem to bear that out either. BUT, the issue did start a few months after replacing the FPR, so who knows.

Yeah, I did have the hood popped for a few minutes while I checked things. What under the hood would get heated and cause this?

 

I was wondering about that. It is fairly new, but I imagine sludge from the tank could jam it up. I may just put the car up for the winter and fettle it in the spring.

I should note the car restarted without a hitch an hour or so after I got home, which would have given whatever time to cool off if it is a heat issue.

Oh, and other than the hot restart thing, the car runs great (knock on wood).

 

it is like the old vapor lock with carbs. you could trick it by putting clothes pins on the fuel line to dissipate heat rather than having the fuel vaporize.

it depends how much it cools off.

if it starts good after sitting all night the check valve is holding pressure and something else is allowing the pressure loss, the hiss your heard.

i've got a lot of insulation on the lines as they come from the fender well over the ex manifold and engine.
87951

 

Does the tach move when it won't start?

 

Bearone,

I assumed the hissing I head was the vacuum pressure releasing when I pulled the vacuum line. It does the same thing if you pull the line off the brake booster. Is it bad that there was still vacuum in the system?

Also, on the 924S the fuel line fortunately don't go over the exhaust manifold like they do on the 951, so I at least don't have that heat issue to contend with as directly.

Zero10

I'll try to pay attention next time it doesn't start. I think it does, but I wasn't really paying attention, just spouting a string of profanities.

 

it is vacuum unless you see something.

87951

 

Just wiggle the reference and speed sensor wires coming from the bell housing at the back of the engine whenever that happens. It always works for me!

 

leaky injectors may cause this problem, if holding the accelerator down while starting (giving more air) helps start, or clears it up this would further point to injectors. maybe do a compression check, my dad said bad compression can cause bad hot starts too

 

Funny Michael, Hot start issue- I immediately think bad FPR> Thanks for the heads up brother!

 

Well, I want to think it is electrical, but the temperature variable has me thinking it is something getting heat soaked after the car sits for a few minutes and either causing vapor lock or ?

To review:

Car starts perfect when cold.

No gas smell at any time

Car runs perfect when it starts or restarts. No hesitation, idle is perfect.

Car will restart just fine if I shut it off and then restart it within a couple minutes. I forgot to mention that.

Car will not restart if it sits for maybe 10 minutes or more until something cools down. The cooling occurs by some means that I am not sure of, whether opening the hood or what. Then once whatever cools down the car starts as if nothing happened. So if I drive to the office and let it sit there while I am at work I can go out at the end of the day and it starts right up, no problem.

What is new-ish on the car, for the most part from me wanting to replace old stuff as it comes to mind.

Injectors - less than 2 years old
DME Temp sensor - 1 year old
O2 sensor - 4 or 5 years old
check valve - 2 years old
Fuel filter - maybe 2 years old
ISV - almost 2 years old
All vacuum lines - 4 months old
FPR - 4 months old
speed and ref sensors - 2 years old
Relay - between 4 and 6 months old
all solder joints have been checked and resoldered if suspect on the DME within the past 6 months

The only thing that is not new is the fuel pump.

Off course any of the new stuff could be bad. I will have to take the car out and drive it then part it for a few and see what happens, then diagnose from there.