1G 90 GSX hard cold start

[Jonerob]

My 90 GSX has a weird start issue. After sitting for an hour or more, the car needs to crank for 3-4 seconds before starting. Once it starts, even if turned immediately off, it will start again instantly. I’ve noticed that if I turn the key on and leave it on for like a minute,
It will start instantly also.

I realize that the fuel pump/prime on the 1g doesn’t start until the key is in the start position. With this knowledge I have tried bumping the key, audibly letting it prime multiple times then attempt to start but even with 42 psi of pressure in the rail, it still cranks for a long time. Here’s what I’ve tried:

new fuel pump
Fuel filter
New fuel pressure regulator
Cleaned/rescreened injectors
New maf
New copper plugs
New wires
Coolant sensor
Set base timing correctly
Boost leak tested
Recapped ECU
Vacuum line delete
New timing set/cam timing dead on

This has become an obsession to fix. I have a 93 Evo and I can breathe on the key at -20 degrees and it instantly starts so I know it’s possible . Any insight would be appreciated.

 

[sierra5]

Double check the coolant temp sensor with 2 wires on the bottom of the thermostat. I've had one of those wires break and the ecu thinks it's -40° so it dumps fuel in making it hard to start. Ik these aren't picky with cel so it's hard to diagnose easily but coolant sensor will throw a code but o2 won't .

 

[19Eclipse90]

O2 sensor will throw a code. I've read it may not if the heater goes out.

Oxygen (O2) Sensor Connector from Ohm Racing

Might check your coils and power transistor unit.

 

[Jonerob]

Double check the coolant temp sensor with 2 wires on the bottom of the thermostat. I've had one of those wires break and the ecu thinks it's -40° so it dumps fuel in making it hard to start. Ik these aren't picky with cel so it's hard to diagnose easily but coolant sensor will throw a code but o2 won't .

I actually did as well as replaced the ends and even checked the impedance at the wires themselves not the plug terminals. I was sure it was that sensor but I was fooled

O2 sensor will throw a code. I've read it may not if the heater goes out.

Oxygen (O2) Sensor Connector from Ohm Racing

Might check your coils and power transistor unit.

These are some of the last remaining items to replace and just see. I wonder if I may have an issue with them being as sitting with the key on for a minute or two before attempting will make it fire off instantly. Maybe a coil isn’t charging fast enough or the transistor has an issue internally.

 

[sierra5]

Have you tested compression when it doesn't start? My car had a fuel tank full of rust and made valves stick so it'd run once but not later once it's had a chance to cool. I have my O2 sensor cut off for a wideband and it doesn't throw any codes for 1g

 

[19Eclipse90]

Plug gap would be the other thing I'd suggest double-checking. If everything else truly checks out, it can't be anything but spark.

 

[Jonerob]

Here’s a weird new development. I always leave the keys in the ignition because the car sits in the garage. I left the keys in the trunk pop accidentally the other day. I went out the next day and popped the key in and boom instant start. I started taking the key out of the ignition when not in use and 5 times in an row it’s fired immediately after sitting a day or more. There’s no way I can conceive that the keysense circuit being energized for long periods of time would make the ecu do anything funky. I think I’m losing my mind

 

[AWD-Tony]

My car did the same thing when I first got it and from reading some threads, it seemed the fuel pump check valve leaks down after the car sits for an extended period of time. I did confirm this once I installed an afpr.

 

[RLSchwabe]

There's a sealing o-ring on the fuel pump hanger that when re-installed incorrectly may cause the fuel system to lose pressure. I have the same issue on my 1G but I haven't pulled the pump to confirm. I'll see if I can find the thread that references it.

Found it:

1g Fuel Not Priming?

Help needed please A little while back I replaced my fuel pump (Walbro 190l). Since then the car has a hard time starting after its been sitting. I thought that the fuel filter might be be causing this, since its the only thing that I have not replaced. The car turns over with ease, b...

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