KA24ET – Hard to start when cold – Fuelling Issue

[Titan]

Hey guys, it’s been a while since I posted here, but this has always been the best place for technical advice.

A few years ago I turbocharged my S13 KA24E with a T3. Basic details: FMIC, SAFC, 370cc CA18DET injectors, Walbro 255. The car ran great after the build for many years.

Since then the car has been sitting for the past year as I bought a daily driver (Mazda 3... very exciting I know). I have been busy reviving the car over the past 2 months and at the very end I've run into an issue. The car was running fine before it was stored.

The engine is very difficult to start when cold and I am certain it is a fueling issue.
It will turn over, but won't catch until I return the key to accessory on. After it fires it will almost immediately stall. The process will need to be repeated several times while blipping the throttle in order for the engine to remain running. Once it warms up there is hesitation and backfiring under throttle, but at least it remains running. Removing the plugs yields a flooding scenario.

I have performed an inspection or replaced the following parts / systems:

- Fuel pressure is consistent while priming, cranking, and running (40 psi)
- Injectors have been cleaned and flow tested on a bench last week
- New fuel filter
- Fresh fuel in the tank
- Checked MAF (Hotwire is clean)
- Checked IACV (Ports are clean)
- SAFC settings same as when car last ran well
- No ECU error codes
- Resistance of ignition coil is in spec (primary and secondary)
- New rotor
- New distributor cap
- New plugs and plug wires
- Spark is present on all cylinders while cranking (checked each cylinder with a spare plug grounded to the engine block)
- SAFC reading proper TPS signal
- Coolant temp sensor resistance in spec
- Air regulator valve is getting 12v signal when key is in accessory on
- New battery
- Rebuilt alternator

I have tried playing with the SAFC and base timing, but neither has given me proper results.
I have literally tried everything I can think of in addition to following FSM troubleshooting procedures. No avail. I would be very grateful if anyone has any ideas / solutions, as I`ve exhausted all my troubleshooting knowledge.

[greenwood]

dirty maf? dirty iacv? bad cold start sensor, not sure what it is called on your car.

seems to be the answer.

[souljaseth33]

Try un-plugging the MAF and see if it runs/starts any better

[zeebrah]

^ +1 also check o2 sensor. I had similar problem on my sohc (although not nearly as bad as yours) but idk how o2 is with your turbo setup.

[Titan]

dirty maf? dirty iacv? bad cold start sensor, not sure what it is called on your car.

seems to be the answer.

I checked the MAF and IACV, all clean. I also checked the air temperature sensor and coolant temperature sensor. The resistance for both is in spec.

Try un-plugging the MAF and see if it runs/starts any better

Did that. It went into safe mode (not allowing me to exceed 2500 rpm). No difference in how well the engine ran.

[anti tyler]

02 sensor shouldn't matter if he's using the SAFC. I don't even run one on my KA-t.

what it is sounding like is an old problem I had with mine, always check the MAF, that's first and fore most. then what you want to do even though you said you've looked, is check your SAFC and make sure it isn't set to anything stupid like v6 or v8. also make sure you're using the right sensor and not on something like the karman sensor. (if that's what it's called)

last thing you can try, is replacing your ignition coil with something like an MSD blaster 2. you say you checked spark and all, but I had an issue where spark was golden, but under load my coil was acting up horribly.

don't give up hope yet

[Titan]

02 sensor shouldn't matter if he's using the SAFC. I don't even run one on my KA-t.

what it is sounding like is an old problem I had with mine, always check the MAF, that's first and fore most. then what you want to do even though you said you've looked, is check your SAFC and make sure it isn't set to anything stupid like v6 or v8. also make sure you're using the right sensor and not on something like the karman sensor. (if that's what it's called)

last thing you can try, is replacing your ignition coil with something like an MSD blaster 2. you say you checked spark and all, but I had an issue where spark was golden, but under load my coil was acting up horribly.

don't give up hope yet


Thanks for the input.
I checked the SAFC and all the settings are correct.
I will check voltage from the MAF again tonight.

I checked the ignition coil resistance (primary and secondary) versus a brand new one at the store and they were nearly identical. What are the chances of it being bad under load?

[greenwood]

Even if the maf looks clean it can still be fucked up

[Titan]

Even if the maf looks clean it can still be fucked up


Noted, thanks. I'll pickup some electrical contact cleaner ontop of checking the voltage.

Keep the comments coming.

[anti tyler]

Thanks for the input.
I checked the SAFC and all the settings are correct.
I will check voltage from the MAF again tonight.

I checked the ignition coil resistance (primary and secondary) versus a brand new one at the store and they were nearly identical. What are the chances of it being bad under load?



like the guy above just said, the maf can still be messed up. it all depends on how much you're willing to spend, your exact issue sounds like everytime my maf pigtail came unplugged and fell off. so it's up to you on if you want to go to autozone and buy the MSD blaster coil 2, which is like $40. or find a local friend that can lend a MAF to you, the worst case senario is the the pin on your ECU plug is sliding out. make sure to check that, I had a few pins sliding out of my ECU plug and it affected my SAFC.



[email protected][email protected]# if you can try and take a video, without doing too much to the car, you don't want to destroy it.

[Exas Spec D]

Set the timing back to stock and retard it a few degrees 'till it catches.

[Butcher240sx]

Maybe bad fuel in the tank. Or clogged injector. Drain the fuel filter and tank. Put new gas in the tank. fill the filter back up with seafoam or other injector cleaner. Replace filter and crank on it.

[Titan]

Maybe bad fuel in the tank. Or clogged injector. Drain the fuel filter and tank. Put new gas in the tank. fill the filter back up with seafoam or other injector cleaner. Replace filter and crank on it.

I put 30L (8 gallons) of fresh fuel in the tank. The injectors were cleaned and flow tested on a special rig in a fuel injection shop less than a week ago. Brand new fuel filter installed. No luck.

[Titan]

Cleaned the MAF this morning. No difference on a cold start. I also unplugged the MAF, no difference.

Anyone got any other ideas?

[anti tyler]

if you unplugged the maf and no difference then you just answered the question... stop cleaning the maf and replace it.

85% that's your problem

[Titan]

if you unplugged the maf and no difference then you just answered the question... stop cleaning the maf and replace it.

85% that's your problem


The thing is that once the motor is warm it runs fairly well. It will start up and idle. Whereas when it's cold it takes 20 attempts at cranking then it needs to be kept alive with throttle input.

[weirdchris555]

Check star signal fuse? Or something similarly named. Drivers side foot area. Same problem I had, corroded fuse, then wrong fuse size

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