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Rb25 Det Engine Issues

BukkaneNinja

By BukkaneNinja,
in Engines & Forced Induction

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BukkaneNinja Rookie

BukkaneNinja

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Morning guys,

One of the first tech post's ive done asking for help (As most end up in some retarded flame war)

I've recently completed a RB25det swap into a S13 silvia. Turned over first go, idle's well, after sorting out radiator issues, runs well now.

Major issue is this, I take it for a drive around the block, boost's well, runs very good, once it warms up, turns into a horrible ride. Idle is extremely rough, to the point of nearly stalling, needing to feather the throttle to keep her alive.

Not 100% sure what's going on, I've checked temp sensor connections etc, thinking it was stuffed when going from cold to hot, this was fine, replaced the fuel lines all the way into the back and fuel filter, thinking this might help, swapped to new spark plugs, still doing the same thing.

Not really sure what's going on, have checked a few forums and havent been able to find a definitive answer so helping someone here has some knowledge and may be able to help me.

Some forums mentions the CAS and timing (Which i'm not sure if this could be the issue?)

The CAS was removed when the engine was out, as I replaced the belts for higher RPM rated ones etc.

Any help would be greatly appreciated, cheers!

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https://www.sau.com.au/forums/topic/387084-rb25-det-engine-issues/
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BukkaneNinja Rookie

BukkaneNinja

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Can u try another afm

I can try another AFM, thankfully my daily is a R33 GTS-T with no issues, I can always unscrew this one and swap it to test?

What ECU?

Standard R33 GTS-T Computer - Nothing aftermarket at all.

New oil, new filter, new fuel lines, new filter, new headgasket, new plugs, new belts etc etc. Only aftermarket addons are a FMIC, BOV and a POD filter, nothing else at all. I do however... Have no exhaust atm, but I couldn't see that being the issue?

GTSBoy Grand Master

GTSBoy

Posted
Posted

Clean the idle air control valve. Take it off the back of the plenum, clean it out with solvent (carby cleaner is good). Do the TB as well (just spray it in there and wipe out with a clean rag).

What I suspect is happening is that when it's cold the auxiliary air valve (which is thermostatically controlled) is letting in air to keep you idling smoothly, but once you get the coolant warm that shuts and you rely on the idle valve. Which if it is dirty (or given that this is a conversion, not wired up properly) makes it run just like you describe.

BukkaneNinja Rookie

BukkaneNinja

Posted
  • Author
Posted

Clean the idle air control valve. Take it off the back of the plenum, clean it out with solvent (carby cleaner is good). Do the TB as well (just spray it in there and wipe out with a clean rag).

What I suspect is happening is that when it's cold the auxiliary air valve (which is thermostatically controlled) is letting in air to keep you idling smoothly, but once you get the coolant warm that shuts and you rely on the idle valve. Which if it is dirty (or given that this is a conversion, not wired up properly) makes it run just like you describe.

PM sent so I don't look like a tool. I will try both of these when I know more =P

BukkaneNinja Rookie

BukkaneNinja

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  • Author
Posted (edited)

Have u checked the timing when it starts playing up ?

I think it maybe CAS related or maybe even something like coils or ignitor

I have not checked the CAS yet, nor have I checked the timing when its playing up, as it wont idle with me out of the car. Resembles something of a massive lumpy cam lol. I'm still learning the in's and out's of the engine and slowly learning / trying to figure it out.

What sould I be checking with the CAS, adjusting timing etc? This engine used to run perfectly (Was removed and sat in a shed for 2 or so years) could the packs die over time from doing nothing? Not 100% sure why it would idle fine, then work fine under load, but not run properly when rough, thought the packs would die at higher rpm over being warm?

What could the ignitor be doing?

Edited by BukkaneNinja
kitto Mentor

kitto

Posted
Posted

Ill second it being the AAC valve being dirty or not even wired up.

If its fine under load when hot and doesnt miss fire, id say its safe to say its not the CAS, AFM, ignitor or coils, these all usually break down when hot and under load.

Check the plug on the AAC valve with the ignition on, yoi should have 12v on one pin. The 0V pin is controlled by the ecu when the engines running. This can be checked with a 12v led to see if its pulsing.

BukkaneNinja Rookie

BukkaneNinja

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  • Author
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Ill second it being the AAC valve being dirty or not even wired up.

If its fine under load when hot and doesnt miss fire, id say its safe to say its not the CAS, AFM, ignitor or coils, these all usually break down when hot and under load.

Check the plug on the AAC valve with the ignition on, yoi should have 12v on one pin. The 0V pin is controlled by the ecu when the engines running. This can be checked with a 12v led to see if its pulsing.

I'll check this wiring tonight. Hopefully can find some answers

Also check your ecu temp sender, on front of inlet manifold into water jacket, if its busted/missing/covered in sealant, could be still telling ecu to run on cold start (tune) but maybe not...

Checked all these plugs, wiring is fine, I also got a small file in and hit the terminals to make sure contact was made firmly.

BOOZTJUNKEY Proficient

BOOZTJUNKEY

Posted
Posted

Also check your ecu temp sender, on front of inlet manifold into water jacket, if its busted/missing/covered in sealant, could be still telling ecu to run on cold start (tune) but maybe not...

This ^^^^^^ was my next port of call hahaha

But as posted above CAS Afm coils and ignitor can breakdown from heat

U can test the CAS by pulling it out leaving it plugged in and turning it by hand .

U will here the injectors pulsing and be able to see coils sparking also

But after re reading the first post ( I tend to skim a lil hahaha) I would start with the iac valve an then go from there

BOOZTJUNKEY Proficient

BOOZTJUNKEY

Posted
Posted

I'll check this wiring tonight. Hopefully can find some answers

Checked all these plugs, wiring is fine, I also got a small file in and hit the terminals to make sure contact was made firmly.

There could still be a dud coolant temp sensor there it may just not do what it's suppose to be doing . If u have a spare swap it just to be safe and rule it out

BukkaneNinja Rookie

BukkaneNinja

Posted
  • Author
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There could still be a dud coolant temp sensor there it may just not do what it's suppose to be doing . If u have a spare swap it just to be safe and rule it out

Might have too, will do the AAC and IAC first, then that will be my next port of call I guess.

  • 2 weeks later...
BukkaneNinja Rookie

BukkaneNinja

Posted
  • Author
Posted

Clean the idle air control valve. Take it off the back of the plenum, clean it out with solvent (carby cleaner is good). Do the TB as well (just spray it in there and wipe out with a clean rag).

What I suspect is happening is that when it's cold the auxiliary air valve (which is thermostatically controlled) is letting in air to keep you idling smoothly, but once you get the coolant warm that shuts and you rely on the idle valve. Which if it is dirty (or given that this is a conversion, not wired up properly) makes it run just like you describe.

Hey guys,

Quick update, followed a how too guide on here, guestimated where the idle screw was and refitted after cleaning the whole thing down (gasket stayed intact).

Ive since taken it for a few laps around the block, the issue seems to be gone. Only time will tell however, after I get an exhaust and get it out for a few track days.

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