420A Not cranking when hot

[sinisa]

First of all car is forged 420a with ms3. I want to get rid of this problem before adding turbo.

Engine runs good, idles good and does not overheat or die anytime. Fans run and stop with the temp.

After some driving with few pulls and shut it for short time (for gasoline etc..) it does not crank until it fully cool down. It starts if we push start or jump start it.

Its not battery because it cranks normally when engine cools down (battery is relocated to back). Everything seems fine when i looked from tunerstudio. So i changed the starter and solenoid but the problem continues.

Any suggestions?

 

[Mech Addict]

So you’ve concluded it’s not the battery, but you can jumpstart it when this happens? How are you attaching cables to jump: under hood or on battery in rear?

 

[sinisa]

We attach cables to the battery in rear

 

[AWD-Tony]

I would check power to the starter solenoid when this happens. Possibly an issue with the starter relay

https://www.dsmtuners.com/threads/starter-relay-location-wont-turn-over.358809/

 

[sinisa]

I would check power to the starter solenoid when this happens. Possibly an issue with the starter relay

https://www.dsmtuners.com/threads/starter-relay-location-wont-turn-over.358809/

I hear that fuel pump turns on when ignition on. Does it mean starter relay is ok?

 

[AWD-Tony]

I hear that fuel pump turns on when ignition on. Does it mean starter relay is ok?

Sorry. IDK what triggers the fuel pump on a 420a. It probably has its own relay for the fuel pump and same for starter.

My guess would be you’re not getting starter signal when it’s hot. Easy test. Pull the starter solenoid signal wire and put a multimeter or test light. Have someone turn the key. Test light will light, multimeter should read battery voltage.

 

[BLACK'98DSM]

Could also be the coolant temp sensor. Check it's signal

 

[AWD-Tony]

Could also be the coolant temp sensor. Check it's signal

420a needs a functioning CTS to crank?

 

[sinisa]

Could also be the coolant temp sensor. Check it's signal

Actually i want to ask this
Is there any protection mechanism in stock ecu that when ecu thinks engine is overheated it prevents cranking?
I can see the temp in tunerstudio its normal
I tried unplugging the one that controls the gauge in cluster nothing happens
is there any other sensor than this two?

 

[Mech Addict]

that’s worth considering, and I don’t know the 420 ( or ecu function) well enough to answer it. I’m still puzzled that it won’t crank on its own, but can be jumped. That describes a simple lack of voltage from the battery. Seems like somewhere there is a thermo switch that is staying on and stealing power, so there is not enough to crank. Are fans running while you’re attempting to start? A/c mag clutch? Check voltage at the starter while starting, both cold and hot conditions. Not that that’s easy, but that would confirm that it’s not a relay or other circuit gremlin.

 

[BLACK'98DSM]

Is there any protection mechanism in stock ecu that when ecu thinks engine is overheated it prevents cranking?
I can see the temp in tunerstudio its normal
I tried unplugging the one that controls the gauge in cluster nothing happens
is there any other sensor than this two?

There is not. It should start regardless of temp if everything is functioning properly.

The smaller sensor is for the gauge only. It won't affect anything if it's bad.
The larger one is what told the stock ecu to enter/exit closed loop. If it were bad you would be getting too much fuel for a hot start. It's odd that it isn't even hitting though. With too much fuel you'd at least get backfires or something.

 

[AWD-Tony]

Does your car have an alarm?