Have been having a big issue with starting the car when it's hot.

When cold, the car fires right up. But when hot, the starter will crank super slow, or if only kind of warm, it will crank OK, but the car won't restart until I come back later. This happened yesterday:

- drove 45 minutes toward home in rush hour. Distracted at stop light and stall out
- starter chugs super slow when try to start. Gets worse as battery gets weaker
- cop pulls behind me and I ask for jump. Starter cranks really well with the CA coming off his battery, but car won't start at all
- tow truck comes but he can't get under bumper, so the three of us start pushing car to get it out of the way of traffic
- I jump in while it's moving and drop it into first - it fires up immediately and I drive off


So what gives? Alternator and battery have both been tested as good. I suspect heat soak either in cables or starter itself are causing massive resistance, which might explain why my little battery can't get starter to crank well, but cop's Ford Explorer battery could. But why would it not start with good cranks, but would start when it was pushed? Possible issue with ignition switch too, where I'm not getting power to Run circuit when key in the Start position?

Thanks guys

 

Check the main 80 amp relay for signs of heat damage

 

I had a similar problem with my Miata. It ended up being the starter was on the way out , it was drawing so much current that it was dragging the battery voltage down below what the ECU needed to fire the coils. Fredb

 

Guys - much appreciated. Looks like I had two problems going on at once:

- Starter was indeed on the way out. Replaced that and it cranks well even when hot (good ol' O'reilly lifetime warranty).
- Cranking pulsewidth at 160F was too low. I had it at 1.6, and 2.2 seemed to be about right (which is where I had my 130F PW set).

Thanks again!

 

Very interesting, I have the same problem. Yesterday the car left me sitting. It ran fine to my destination but upon trying to get back in the car and leave which was about 15 minutes later, the car simply would not fire. After a few unsuccessful attempts the battery/starter began cranking slower and when that happens it's just not going to happen. In my car either it starts quick after the key turn or it doesn't start at all. I got a jump thinking this would be the ticket and I cranked for quite awhile off and on with no luck. I came back hours later and it started and ran fine. I must have started that car (warm) 25 times last evening and it fired every time.

This problem began for me after changing my fuel system/. Datalogs from the Hydra showed tons of injector time at high RPMs which was a result of a dropping fuel pressure from the original 99 fuel pump. And so began my nightmare that I won't delve into. At any rate, I now have a 300 Liter/Hr pump, 3/8 fuel line supply and return to the existing hardline, an external adjustable pressure regular, a GM style fuel filter and an inline check valve and a car that intermittently won't start when it's warm. When I was cranking yesterday I noticed that my fuel pressure gauge was reading zero or dashes. The gauge HAS misled me before so I can't be 100 percent certain whether that was actual or not. The problem has occurred at autocrosses as well, make a run, come back, shut the car off and it may restart and it may not. I had several pushes at the past autocross which seems to make it fire right up.

I know this is too long but it's like a vapor lock situation is happening and short of changing the "dead head" fuel system I am not sure what I can do. Interesting, I too have COP with 700cc Injectors

 

Aint not starting when hot normally a CAS sensor issue? solved me both times. Or heatsoaked air intake sensor?

 

Get your laptop on it the next time it happens , watch the battery voltage while cranking . The Hydra positively won't fire the coils if the voltage drops below 10 volts . I just solved this on my car after being stranded multiple times in the last month. If you're running an NB starter like me , it will crank the car fine at a lower voltage. ,

 

I bought my Miata non-running, with PO swearing it was just because the starter was out. Price reduced enough to take the chance on it, replaced the started with new one PO had included, and it fired up. However, not reliably, and sometimes it would take a ton of cranking. When (if!) it finally would start, a bigass cloud of smoke would come out the back, but then would run totally clear. Finally put 2 and 2 together and realized I was getting waaayyy too much fuel during cranking. Brought the cranking fueling curve way down, and got it to start first crank from then on. However, all of the cranking I'd done did a number on the starter, and it would turn SUPER slow when the car was hot, which I learned is a symptom of a starter on the outs. I have a feeling this is how the PO burned the old starter up in the first place.

Couple of things I learned/now believe that might help you:
- if starter turns slow when car's hot, replace it
- if car will fire up immediately when being pushed, but not while cranking (at normal speed - see point above), then there's probably something wrong with your cranking fueling, warmup enrichment, etc. The engine doesn't know whether it's being pushed vs being cranked - only the ECU does.

Your fuel gauge thing is weird. Might rent an analog one from the parts store to double-check.

Good luck!

 

Tonight I started the car up after cleaning the intake with Carb Cleaner and changing plugs. After the car got warm I shut if off and sat there with the key on and I noted the following. The fuel pressure which is set at 60psi slowly began climbing. Within 10 minutes it was up to 85, in 15 it was 93 and I had shut the car off before it even hit 180 degrees of water temperature. I was in the shade in my garage with the hood up and it still climbed that high. At the autocross with the payment being 100 degrees I can only image what pressures are happening between runs.

Now then... the issue from stock appears to be the inline check valve that I placed just before the hardline that runs up the car body. Apparently the fuel gets hot, starts expanding and the check valve does it job and holds until some extreme pressures are reached. Cycling the fuel pump does nothing since it simply pushes all the new fuel back through the return system at the back of the car which is before the NOW higher pressure fuel forward of the check valve.

FWIW. I did check cranking voltage which seems to not go below 11 volts. The check valve was added because I was having hard start issues due to no or very low fuel pressure on initial start-up. I removed the factory fuel pressure regular that was in the tank ( Which I now feel was a huge mistake).

So now I'm wondering what the EASY fix would be. I need an adjustable check valve or one that I can release pressure? Or do I remove the check valve and just let the fuel pump run longer? I'm not really sure at this point. Opinions?

 

Put them back in?