Hot start problem - what do I need to check?

[ianhid]

Hi guys, I've been having trouble with hot starts since Dragonball. I've got a feeling this is probably because I don't rag the tits off it in the UK, so something that was marginal is now a bit borked. Basically, what should I be taking a look at?

 

It starts fine cold, no problems with cranking speed either hot or cold. It just doesn't catch for a bit when hot, then splutters into life. It doesn't need to be very hot at all to have problems, 3 mins round the corner at 30 to Sainsburys was enough to cause. The car does smell like it's running a bit rich, so the two may be related. (Fouled plugs?) I haven't noticed a misfire at speed, but that doesn't necessarily mean all is good.

 

It idles a bit above 1krpm when first started and in the first couple minutes, then drops down to the third mark above 0 (stock tt auto gauge, whatever rpm that actually is), sometimes getting right down to the point I'm worried it'll stall out. Hasn't stalled on me yet, it's come close enough for me to blip the throttle once or twice though.

 

I'm handy enough with a multimeter and tools to check readings/pull things out if I know what I'm looking for and how tight to put them back on... I'm still running the stock ECU and stock twins, jap import car, non-vvti.

[Ric]

I sometimes have this issue, although it's not happened for a while. While I was reading up on it leaky injectors seemed to be the most popular theory

[Chris Bailey]

Idle control valve could possibly be causing the idle issue, could just need a clean. Might be worth checking the spark plugs for the hot start issue.

[Chris Wilson]

If you had a wide band O2 sensor it would be useful, but i am guessing you do not. My advice would be to suspect leaking injecors, especially if they are none stock. I would also consider an issue with fuel rail pressure not holding due to a faulty fuel pump (internal one way valve leaking), again especially if it's a none stock pump.

 

The reason a wide band would help is it would show if the initial hot start period was rich or lean.

[Scooter]

Chris could he bridge the diagnostic port to run the fuel pump prior to starting, to test the fuel pump possibility?

[Chris Wilson]

Chris could he bridge the diagnostic port to run the fuel pump prior to starting, to test the fuel pump possibility?

 

 

Yes, that would prime the rail effectively, good idea!

[ianhid]

If it's a non-return valve that's the problem wouldn't I have problems from cold as well? It's an aftermarket pump, not 100% sure exactly which one though (Adi told me, I just can't remember). The injectors are stock j-spec ones as far as I'm aware.

 

I don't have a wideband fitted at the moment. It's on the list for things to add along with a full suspension overhaul, Syvecs and a small single...

[Chris88]

Does the Supra not have a Hot Start Vacuum Switching Valve? The Soarer 1JZ does.

 

On the Soarer the HSVSV switches the reference for the FPR from the manifold to atmosphere (remember that the manifold pressure is below atmosphere when starting) when the engine temperature is hot. The purpose is to increase the fuel rail pressure for hot starts to reduce the lean mixture which would otherwise be caused by the percolated fuel which has been sitting in the hot rail.

 

With exactly your symptoms on a Soarer 1JZ I would pull the reference pressure hose off the FPR with the engine idling, stop the engine and see how it starts 5 minutes later.