Ken-chan's car blog

C: Likely cause – drained battery / short circuit in the system.

Solution:

Test voltage on the battery – anything below 12v is bad news – try to charge it up. (some notes coming on how to verify battery’s charging ability based on amps)

To test for short circuit in the system, do the following:

1. Visually inspect positive cables leading away from the battery.

2. Unplug the negative terminal of the battery.

3. Wire up a 2-5 watt 12v light bulb.  Place one wire on the negative terminal of the battery and the other on the disconnected negative terminal.  With car off, if you get the light bulb to light up even a little, you got a short circuit somewhere.  Intensity and the bulb you choose can indicate roughly how much drain there is – brighter = more flow / less resistance. 

3. To further test where the short is, uplug one fuse at a time until the bulb shuts off.  When it goes off, inspect the system or wiring associated with that fuse.

S: Your gauge shows low vacuum idling.  Car feels very shaky – may stall if revved & throttle is released.

C: There could be several causes why vacuum is low.

Starting with the easiest to the more painful to fix, here they are:

1. vacuum leak(s) on the intake piping (usually via vacuum hoses or cracks in the piping)

2. vacuum hoses on the intake manifold (past throttle body)

Usually the greater the difference between good vacuum level and bad vacuum level indicates how big the air leak is.

3. EGR – the diapraghm is known to leak.

4. Leak around throttle body.

5. Intake manifold gasket leak.

6. BLOWN PISTON RINGS or BENT VALVES / Head Gasket (?) ***  (check compression / leak-down)

Solution: To diagnose vacuum leaks – visual inspection helps but it can be hard to trace in a maze of hoses & cracks almost impossible to see.  Instead opt for air compressor – just ensure it is set to moderate pressure levels.  Do not worry 100 psi will not blow away your manifold right away or create leaks if you only have a 1/4″ hose – but pay attention to your boost gauge or whatever gauge you have on the large piping to ensure you do not run over pressure it is rated for.  I am checking my stock ka-t setup to 20 psi and can easily spot if something is not right – I found that my EGR leaked past 4 psi so that got fixed

Once you find out you do not hear audible leaks and haven’t found the reason for the leak, do a compression test.  And if it looks good – and you are sure there’s no leaks, it’s probably your timing that’s off – a symptom of that would be really bad uneven idle.

S: On a hot day, you start to lose brakes after boosting for a while.  Brake pedal will get spongy and start to travel closer and closer to the floor as if there was a leak somewhere in the brake lines.  Brakes come back to normal operation few hours later once car is cool again.

C: Very likely problem with Master Brake Cylinder heating up. 

Here is what happens – usually occurs with boost past 9 psi.   Please note that ballpark measurements over time were taken with infra red meter.  With car boosting a lot especially during hot weather, manifold on T25 can reach close to 280 degrees C and on the underside of the turbo near wastegate / turbine close to 380 degrees (tested on non-water cooled t25). 

As long as you are driving, the flow of air through the engine bay will keep the air moving preventing the hot parts impacting the Master Brake Cylinder (MBC).  The problem often occurs once car stops and is either turned off or sits idling for a while – about 10 minutes later, you start car, drive off but notice the brakes are really weak and travel further to the floor.  What happened was that due to the lack of moving air through the engine bay – the manifold and turbo started cooking your mbc – I’ve seen temperatures close to 98 degrees C on the MBC housing and 110 on strut bar above.  Then when you let car sit for few hours, brakes return to normal operation once temperature of the MBC cools.   I haven’t looked into why exactly the problem occurs inside the MBC – from looks of it oil rises towards top of MBC plastic container and seems like less oil / lubrication is available in the actual cylinder – if you push pedal on hot MBC, you can hear bit of scraping and lots of pedal travel indicates there is just no oil in the cylinder when you push on it.

I noticed that anytime the MBC housing reaches over 65 degrees, you will start to see degraded braking performance such as spongy pedal, etc.

Solution: Make a brake heat shield & replace fluid in MBC with synthetic fluid.  Issue went away for me just by heat wrapping the MBC & just draining fluid from mbc & refilling with synthetic dot 4 fluid.

S: Car backfires after light throttle is applied and then applied soon after. It also backfires when boosting and letting off – it experiences rich condition and it starts to dip rpm. Sometimes it goes so low that it stalls.

** ONGOING: STILL WORKING ON RESOLVING THE ISSUE **

Observation / Tests:
-BOV is recirculated.
-New distributor was put in.
-The distance between maf and compressor is now over 15 inches (air tight extension was put in).
-IACV was replaced & spare one was cleaned & installed. On first start it blew lots of smoke (hard to tell if blue or black at night) – probably from KA-T#1 (maybe had some oil in it). I will check if it still throws a code.

-If SAFC is setup to subtract more fuel near the idle rpm, car doesn’t dip as much / backfire because (my guess) as it passes that rpm and slows down, the reduced maf signal causes injector pulse to decrease and not much fuel is dumped in. So technically the DEC-AIR function would work here except that doesn’t solve the original problem – it would only serve as a band aid solution. Let’s find the real cause…

-Determining whether fpr had broken down and car sucked fuel via vacuum diaphraghm, I unplugged it – started the car – revved it – appeared to have no leakage from the vacuum line. I went for a ride and discovered it had backfire even after I retuned it.

To be tested:
-INJECTORS: FPR appears to have been fine with vacuum line unplugged, so it could be injectors.
-FUEL PUMP?
-MAF? or MAF in/out setting on safc (It appears that it hits lean right before it backfires, I will try 2 in 6 out and subtract fuel)?

S: Car bogs, sometimes chokes when driving, runs rich.  SAFC cannot seem to subtract enough fuel, CONZULT shows rich mixture always below 0.5v (RICH) for front o2 sensor (OBD1).

Replacing front oxygen sensor seems to help temporarily but quickly after it starts causing issues again.  O2  sensor voltage never goes above 0.5v when throttled & released, o2 sensor value seems to stick and not update on conzult.

*** NOTE: ON OBD1 CARS, front oxygen sensor (usually single wire) tends to be responsible for helping ECU control AFR (Air-Fuel Ratios) and operation.  The rear o2 (lambda) pre-cat sensor is usually just used for on-board diagnostics and emissions testing, etc. but doesn’t affect the running of the motor. ***

C: Problem may be electrical: O2 sensor wire possible not having continuity near the firewall.  This is especially easy to spot if o2 sensor seems to stick in value on CONZULT instead of providing feedback.  With heat from exhaust and o2 sensor wiring loose, often the wire isolation can become grounded or connector loose – look for loose broken section from exhaust manifold / downpipe to along firewall

Solution:

Once you find a potentially problematic section – start the car – don’t burn yourself but move wire around and see if you can get reliable voltage feedback from the sensor.  If you find it, turn off motor, replace the bad section of wire along with heat wrap.  Test it.  Afterwards your o2 sensor voltage should fluctuate between 0 and 1 volts (at least past 0.7v) on warm car if you give heavy throttle and let off.

***
Recently I found that when unplugged, the ecu generates steady 0.30-0.31 volts internally on the ecu pin #46 (front o2 sensor) if unplugged / wire cut off near ecu (was testing wideband->narrowband simulation). While unplugged, this causes car to run super rich obviously.

S: When you rev the motor, car cannot go above certain rpm (often over 3k rpm).  It is indication of open loop as far as measuring air input.

C: No signal from MAF or MAF voltage static low ~ 0.2v for example (ecu sees it as error and runs open loop based on throttle input and other sensors).

Solution:

Inspect & replace MAF.

S: Car would bog down with idle hovering up and down especially after car warmed up.

KA-T bad idle – video #1

C: 1 or 2 issues.

Found:

-Clogged IACV (Idle Air Control Valve) sticking on return

-TPS (Throttle Position Sensor) out of spec — was 0.78v @ no throttle — changed to 0.45v

-Another issue was MAF.  Performed diagnostic using SAFC 2 sensor check screen – every time car would bog down – at same time the voltage from maf would drop to 0v and return.  Culprit turned out to be a bad z32 mafs.

After some changes…

Swapped 480 cc injectors, ecu, maf died (0 volts)

ka-t #2 after some changes

After maf and ecu change.. car runs good again.. One thing that keeps coming back since beginning is that I cannot get better than 10 BTDC — it seems to have happened ever since I put on SAFC 2.  It’s not so bad since I am running around 14 psi almost so timing’s safe but it would be nice to get the extra 2 or 3 degrees advance.

*******
Please note that in some cases, I found that the rpm going up and down can be caused by ecu sending incorrect signals.  Also if you replaced IACV with another one but it doesn’t seem to respond or ecu code 25 keeps showing up (IACV mulfunction), check the pins on the IACV connector – if you have swapped the IACV without pulling the manifold, chances are the pins could be bent.  You can check & if they are bent, you can straighten out the pins very easily with a mirror and small screwdriver without removing the iacv off the motor.
*******

LIKE WITH ANYTHING ELSE ON THIS SITE – EVERYTHING YOU DO IS AT YOUR OWN RISK – I WON’T BE RESPONSIBLE IF YOUR CAR DIES, EXPLODES OR YOU GET HURT OTHERWISE – USE YOUR COMMON SENSE!

For those of you who want to verify that indeed it is IACV / AIV that is affecting your idle…

Here is quick and $free$ way to check if the issue with rpm going up / down is IACV / AIV related.  On KA24DE, there is a 5/8″ hose which leads to intake pipe bypassing throttle body.

If you are running stock setup on KA (non-turbo), you will find this is the biggest hose running into your plastic intake pipe coming from the airbox.

1. Unplug the 5/8″ hose end from the intake pipe.

2. Take an old clean spark plug and plug the thick end of it into the 5/8″ hose to prevent vacuum leak and block up the line going to IACV / AIV.  Clamp the spark plug to prevent air leak (see photo).  Make sure that you also block up the nipple on your intake pipe with piece of 5/8″ hose and spark plug again – otherwise, if your intake has a 5/8″ hole that’s open, your car will run very rough (rich) since it will dump metered air.

3. If you were to turn over your car now, the car will stall because throttle body plate is closed and it has no way to get any air since you blocked up IACV / AIV.  So raise the idle rpm by opening up the throttle body plate a bit, simply by adjusting the cable or the stop point on the throttle body spring – both nuts are 14mm – do 1 or the other only.
I would recommend adjusting the cable tension as that is easiest to return back to factory state after testing.

*** Rule: to open up the throttle plate, you must tension the throttle cable – to do that – move both of the cable tensioning nuts down a bit at a time.  Start car – see if it turns over – if not, hold the gas a tiny bit and when it starts let off.  All you need is to get it started and see whether idle is still moving up and down.  If it doesn’t stay and dies, tension it a bit more so that there is enough air going into the motor but not too much or you could reach about 2500 rpm – if so – turn off the car immediately and loosen up the tension a bit.

Once started – check idle – if it’s not moving up and down anymore, you’ve isolated the issue to either IACV or AIV or ECU.  Afterwards, you can set the cables back to factory state and deal with the issue – could take off iacv/aiv and try to clean them, or try spare iacv/aiv if you find them cheap, etc.