Hard to start when warm - ideas?

[GrimJack]

When my car is dead cold, it starts on the first crank, absolutely every time.

When I shut it off, it will start again just as easily immediately.

If I leave it for a while - 10 minutes to several hours, but not enough that it will cool completely, it's hard to start. It will take several tries at 5 seconds each attempt to catch. Of course, it spits out no codes.

I found a procedure for testing the fuel pressure up VSV on the SONiC site, I'll give that a shot and see where it gets me.

Any other ideas?

 

[Nick M]

Ive seen the cold start injector bleed down into the intake. Putting the acclerator to the floor and how quick it starts would be an indicator.

 

[Supraholic]

If I leave it for a while - 10 minutes to several hours, but not enough that it will cool completely, it's hard to start. It will take several tries at 5 seconds each attempt to catch. Of course, it spits out no codes.

Any other ideas?

does the starter turn over? or it just cliks?? mine was the starter..

 

[Loki]

My old car would never start when it was hot, I would have to let it cool down for 30 min to an hour and then it would start fine. Replaced the CPS and never had the problem again.

 

[GrimJack]

does the starter turn over? or it just cliks?? mine was the starter..

It cranks fine, it just won't fire.

 

[GrimJack]

My old car would never start when it was hot, I would have to let it cool down for 30 min to an hour and then it would start fine. Replaced the CPS and never had the problem again.

That's odd. I didn't think there was anything that changes in the CPS with temperature?

 

[Loki]

That's odd. I didn't think there was anything that changes in the CPS with temperature?

I don't know if there is, but I do know that my car would crank just not start. I could tell when it wasn't going to start cause the tach wouldn't move when I was cranking it. Then when it would move it would start, I think one of the wires going to the CPS was fried.

 

[GrimJack]

Hmm... thanks for the tip. I'm going to keep an eye on the tach when I start it at lunch today.

 

[IJ.]

Grim: The way our cars are setup is the pump requires an Ign Signal before the pump will run.

My "Theory" with hard hot starts is the fuel in the rail boils when you shut the motor down expands enough to return to the tank then when you go to restart you end up cranking enough to get a signal to run the pump enough to get pressure/cold fuel in the rail.

You could test this by trying a 12v source through a switch to the pump relay, power the pump just before you crank to prime it and see if it starts.

With the Wolf ECU I can tune the initial activation time and it made a HUGE difference to hot starts.

 

[MDCmotorsports]

Grim:
I had the same problem with my old car and fuel setup - stock with no VSV hooked up.

On my new car, I have no pulsation dampner, Aeromotive AFPR, -6 lines, walbro pump, and no VSV.

Starts up great hot, some times a little sluggish cold - maybe 2 cranking times.

 

[IHI-RHC7]

Grim, are you pre 89 or post?

 

[GrimJack]

Post 89 here.

 

[mrnickleye]

Sounds like 3 possibilties. 1) Spark. Next time its gonna sit hot for 30 min, check for spark at the plugs when you try to start it. no spark?? May be a component that gets an 'open circuit' when overheated, then works again after it cools down. Check or swap the EFI relay (just had an 89 Cressida with this problem).

2) Fuel. You need to run a 'full' fuel pressure test. You may have an injector that is bleeding down when it sits for awhile. The pump only runs in the 'start' position, until it does start, then the ECU keeps it running. The pump relay may also be the cause, as it is under the hood, and may be weak when overheated.

3) Heat soaked intake valves that have too much carbon on them. The carbon gets totally dried when a warm engine sits for 30 min or longer. Then, when you try to start it, the carbon soaks up, like a sponge, the fuel coming in. After cranking for a while, enough fuel gets into the cylinder to keep it running.

I have never seen (nor personally been told of) a fuel rail boil the fuel out on a supra thats in 'otherwise' good condition.

 

[GrimJack]

Well, it won't be #3.

I just rebuilt the engine... it's only been running again for 2 weeks. Valves are cleaner than an engine out of the factory.

I rather doubt it will be #2, either. I had all the injectors cleaned and tested when they were out for the rebuild.

 

[Jason T]

Sounds like 3 possibilties. 1) Spark. Next time its gonna sit hot for 30 min, check for spark at the plugs when you try to start it. no spark?? May be a component that gets an 'open circuit' when overheated, then works again after it cools down. Check or swap the EFI relay (just had an 89 Cressida with this problem).

I have had this happen with a faulty CPS worked 100% cold tested in spec once running temp would not start again till engine stone cold

Check the specs on the CPS see if way out of range

Link to CPS specs

 

[GrimJack]

I haven't been trying much on this recently, I was paying more attention to getting my power steering back online. Now that that is fixed, this becomes my highest priority again. This is slow to diagnose, because I have to let it cool down between attempts - as soon as it fires once, it will start perfectly again.

A few more things to add.

My tach registers that I am cranking the engine, so it doesn't sound like Loki's problem.

I jumped the fuel pump and it still does the same thing, so it's not boiled gas in the fuel rail. (This was where I had my money too, thanks IJ!)

I unplugged the CSI sensor at the thermostat housing just for kicks, and no difference there. I'm interested in Nick's idea... I guess the theory is that too much extra fuel in the intake causes the mixture to be so rich that it won't fire for a bit? And eventually the fuel evaporates, explaining why it will start when dead cold... and trying with the throttle at WOT would just flush the intake faster, allowing it to start quicker... I'm going to try this one at lunch.

All in all, this is quite puzzling. I like the challenge!

 

[IJ.]

Grim: Very welcome it all becomes a process of elimination and after you rule out the obvious step by step you should be left with an answer that will help us all!

 

[mk3supreme]

Grim do you think it's a bad ground connection? Or the efi main relay? code 43? I think you should look into that. I am getting that code with my car and it does the same as yours.

 

[GrimJack]

No codes for me.

 

[Supra7MG]

This is slow to diagnose, because I have to let it cool down between attempts - as soon as it fires once, it will start perfectly again.


Cold Start Injector Time Switch. When they fail the Cold Start Injecter activates at all Temperatures therfore flooding the cylinders with unwanted fuel when engine temp is warmer that ambient. This is a pretty common occurence with the origional switch. Mine went out at 20,000 miles. Check the resistance per the Toyota manual.