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RB25DET Neo hot start issue (unplug water sensor starts)

ifixedit

By ifixedit,
in General Maintenance

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ifixedit Enthusiast

ifixedit

Posted
Posted

Hi

Since the rebuild of the engine, 

Was running fine. Until I fixed a oil leak on a brand new cam seal! My luck!

 

Anyways car not exhibits a hot engine starting gremlin.. turns over and hesitate to start..

 

Unplugging the water temp sensor makes it start instantly.

 

I checked voltages at ECU and ohms on sensor.

It's fine.. 0.3kohm 1.2 /v hot 2.5k cold 3.5v

 

So I am hesitant to think a bum sensor. But interesting the unplug of that starts engine fine.

The engine didn't exhibit this behaviour before stripping the front on engine to get to camshaft seal.

 

Dunno what else to look for..

 

Re.

Shaun

 

ifixedit Enthusiast

ifixedit

Posted
  • Author
Posted (edited)

There is something else I find slightly different.

 

Every time I race the revs. It like they lock to say 1000-1100 rpm for a split second then drop to idol.

 

I don't specifically remember it doing that before.

I remember it doing it slightly more subtle 

Edited by ifixedit
GTSBoy Grand Master

GTSBoy

Posted
Posted
28 minutes ago, ifixedit said:

Where do I get a consult commander thinggy?

 

Do ecus on skylines have led flashes like old Sr ecus

 

Might find a fault that way?

Someone is selling a Consult cable and ECUTalk setup on these very forums, for not much $$ at all.

Otherwise, you go to a mechanic who has a scan tool and plug in and investigate.

Fault codes aren't all that helpful if there's not a big enough fault to actually raise a code. What we're looking for here is what the ECU thinks the temperature is when hot, cold, plugged in and unplugged, plus what it might be doing to injector pulse widths while cranking under those circumstances.

KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Disconnect the sensor overnight and see if it starts and runs ok. If the sensor is not sending a signal the ecu reverts to a cold start map which will work until you turn the engine off. A new sensor was about $30 from an auto electrician (its not a Nissan specific part) so not too hard to replace.

ifixedit Enthusiast

ifixedit

Posted
  • Author
Posted (edited)

It's odd when disconnect the sensor, that the a/C fan turns on.. 

It appears when disconnecting the sensor tells ecu engine is hot! And runs additional a/C fan.

Which is odd. Considering lower resistances mean higher temps. And open circuit would be lowest resistance! Haha

None the less this area is an area I want to investigate.

The other thing is I might take off all the piping. (Intercooler pipes) it might be a loose , broken tube somewhere with a slight vac leak.

As I said the time right after rebuild. Assembling everything. The car ran absolutely beautiful.. no issues like this.

Wasn't until I dismantled it again (pipes , crank pulley and timing belt) this started happening.

I will take a good look to try and figure it out.

I will look at the main block grounding wire to.

I also want to check the ignition wiring ground. (Back of engine I think there is a cable)

Edited by ifixedit
ifixedit Enthusiast

ifixedit

Posted
  • Author
Posted (edited)

I have tested with friends water sensor, it's not the problem.

I got a feeling my battery is shit!

My battery goes a bit flat after a few days of not driving.. not dead flat but a very slow turn over.

I was thinking I have some sort of parasitic load. I still need to test this. None the less. If I charge the battery for a few hours. The car starts a little bit easier when hot. But not like when it's cold! (Instant start basically)

Is a low crank voltage a high possibility that might be a problem to start a skyline?

 

If it is the battery, a bad cell might drop too much volts at higher heat

Edited by ifixedit
KiwiRS4T Grand Master

KiwiRS4T

Posted
Posted

Got a multimeter and a charger? Fully charge the battery, disconnect it it, measure the voltage and then retest after as long an interval as possible and see if it is holding the charge...or fully charge it and take it to a battery shop for testing.

 

tridentt150v Grand Master

tridentt150v

Posted
Posted

Fully change the battery and then use the headlights on high beam for 60 seconds and see if the battery handles it or drops down to say under 10 volts.  If it stays above 12 volts its OK, if it drops, its had it.

niZmO_Man Grand Master

niZmO_Man

Posted
Posted

Weird, your first post said hot start issue. So when it was cold, it started fine?

The battery died on my car last week (cells were half dry), couldn't jump start it, not enough volts. Replaced battery, fired up straight away.

ifixedit Enthusiast

ifixedit

Posted
  • Author
Posted

I agree this was a weird situation.

It made me pull hair out!

 

The battery shows 12.4v-12.8v after settled after each use. Light made it dim to 12.1 not the best..

 

But cannot believe the difference in starter speed with replacement battery!!

I'm happy the issue is gone. And it wasn't a wiring nightmare to sort through. Haha

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