S14 SR20 running rich, possible coolant temp sensor?

[1988montecarloss]

Recently bought another s14 with an s14 SR swapped into it, have spent some time fixing a bunch of the previous owners fuckups and have it running better than it was but it’s still running rich to the point where black smoke runs out of the exhaust

Have replaced all vacuum lines and rerouted intercooler piping and have no vacuum/boost leaks

CAS has also been reinstalled correctly and timed to 15°

It also runs best right when I start it and gets worse as it warms up which is leading me to believe it’s the coolant temp sensor but would like to get some other opinions/possibilities, I didn’t think it would affect it this much but who knows

The ECU also doesn’t have the little LED in it to pull codes for some reason and I don’t have an obd2 scanner so haven’t had a chance to pull any codes

Setup is as follows

98 240sx
S14 notchtop SR
Motor is stock other than
FMIC, exhaust and intake
Still has stock WC ecu, injectors, maf etc

[S14rebuild]

Vacuum leak (verify with pressure tester)
Maf
Engine coolant temp sensor(for ecu)
Fuel pressure jacked high
Faulty injector(s)

There ya go....find which is the problem

[1988montecarloss]

Originally Posted by S14rebuild

Vacuum leak (verify with pressure tester)
Maf
Engine coolant temp sensor(for ecu)
Fuel pressure jacked high
Faulty injector(s)

There ya go....find which is the problem

No vacuum leak
Car runs much worse when maf is unplugged so I’m assuming it’s working
Running a stock FPR and have switched to a second known good one
Injectors have also been relaxed with a known good set

[1988montecarloss]

Replaced coolant temp sensor, no difference

S14 ka24 is the same correct? It fits and plugs in and have read online they’re interchangeable

[S14rebuild]

Did u confirm the maf is reading properly?

[1988montecarloss]

Originally Posted by S14rebuild

Did u confirm the maf is reading properly?

Haven’t actually tested it with a multimeter yet but that’s my next course of action also going to borrow another maf from a friend in the next couple days

[S14rebuild]

Sounds good keep us updated

[1988montecarloss]

Originally Posted by S14rebuild

Sounds good keep us updated

What should the maf read at idle? 0.8v? Know which pin I need to pull the voltage from? My car has the 3 pin stock Sr maf

[mint40]

if you unplug a injector while its running does it die or do nothing? I just had a similar problem with mine and it turned out to be the lower o rings on two of the injectors shit the bed. I had to order a new set from nissan because they were leaking pass the o ring and dumping fuel in cylinder.

[jedi03]

have seen where the stock maf causes engine to run rich, would suggest enthalpy tune to help...

[1988montecarloss]

Originally Posted by mint40

if you unplug a injector while its running does it die or do nothing? I just had a similar problem with mine and it turned out to be the lower o rings on two of the injectors shit the bed. I had to order a new set from nissan because they were leaking pass the o ring and dumping fuel in cylinder.

It doesn’t shut off but the cylinder obviously dies when you pull the plug on each one, I put a second set of injectors with good o rings in it already before posting so that’s not the case

[collegekid]

I would order a cheap ~$25 consult port adapter if you have a working consult port and check for codes before doing anything else. This is based on the assumption that you have a laptop and a working consult port.
The OBD2 connector won't work in your car, unless you have a parallel ECU install (KA24 ECU still in the car with the SR20 WC ECU controlling the swap).

Could also be a crappy O2 sensor

[1988montecarloss]

Originally Posted by S14rebuild

Sounds good keep us updated

Bench tested MAF and TPS, maf has 0.8v at idle and goes up when I blow across it, TPS ranges from 0.7 closed to 4.20 open which is just out of spec but I’m also using a cheapy multimeter so it might be that little bit off

Unplugging o2 while it’s running makes no difference though so possibly that? But I can’t imagine an o2 affecting it this much

[1988montecarloss]

Originally Posted by collegekid

I would order a cheap ~$25 consult port adapter if you have a working consult port and check for codes before doing anything else. This is based on the assumption that you have a laptop and a working consult port.
The OBD2 connector won't work in your car, unless you have a parallel ECU install (KA24 ECU still in the car with the SR20 WC ECU controlling the swap).

Could also be a crappy O2 sensor

This is the consult port correct? Can I jump two pins on it to get codes like on some other cars? If so which ones?

[Kingtal0n]

The engine should run fine without the maf plugged in.

Limp home mode should give a rock solid idle that stops at 2500rpm~

I suggest the ecu or injectors are the problem if it won't idle without a maf
And it's got fouled plugs now if you've been running rich for a while. Which means misfires no matter what you do or fix.

always disconnect O2 sensors when diagnosing fuel issues
always pressure test with 15psi+ frequently, every month or at least every few months until satisfied nothing is changing.

[1988montecarloss]

Originally Posted by Kingtal0n

The engine should run fine without the maf plugged in.

Limp home mode should give a rock solid idle that stops at 2500rpm~

I suggest the ecu or injectors are the problem if it won't idle without a maf
And it's got fouled plugs now if you've been running rich for a while. Which means misfires no matter what you do or fix.

always disconnect O2 sensors when diagnosing fuel issues
always pressure test with 15psi+ frequently, every month or at least every few months until satisfied nothing is changing.

Have since tried it in limp mode and runs about the same as with it plugged in before it warms up

On the 2nd known good ecu and injectors out of a friends car before making this thread so that’s not it, when swapping to second set of injectors it did run better than it was before but it’s still far from 100%

Have also swapped/cleaned plugs a bunch of times after trying something new to get a “clean” test and no difference

Anyone know of a place in the us that stocks consult adapters? All the ones I’m finding online are in China and take 3 weeks for shipping

[Kingtal0n]

If you
Compression test
leak down test
swap injectors, check O-rings & fuel pressure
pressure test
swap ecu
pressure test
swap the maf
pressure test
check fuel pressure while engine is running & not running
install brand new copper NGK plugs heat range 7 BKR7ES iirc
check the battery grounds, engine ground cable, add a ground to the engine->chassis
Check the coil pack ground on the back of the engine
changed the cts
unplugged the O2
unplug the tps

These engines are among the simplest to diagnose in the world.
Fueling goes:
maf -> ecu -> injectors

Either you have the wrong maf (has it ever run properly in the past with that maf?)
Or the timing was set incorrectly (common mistake)

Or it has an obscure wiring issue, perhaps a bad cas or some bad cas wiring.
You need a wideband to see what is going on with the fueling

[1988montecarloss]

Pulled the codes off the ecu, just got 55 which is nothing wrong lmao So it’s either a mechanical issue or something isn’t hooked up right, fuel pressure and compression test is my next move

[1988montecarloss]

Originally Posted by Kingtal0n

If you
Compression test
leak down test
swap injectors, check O-rings & fuel pressure
pressure test
swap ecu
pressure test
swap the maf
pressure test
check fuel pressure while engine is running & not running
install brand new copper NGK plugs heat range 7 BKR7ES iirc
check the battery grounds, engine ground cable, add a ground to the engine->chassis
Check the coil pack ground on the back of the engine
changed the cts
unplugged the O2
unplug the tps

These engines are among the simplest to diagnose in the world.
Fueling goes:
maf -> ecu -> injectors

Either you have the wrong maf (has it ever run properly in the past with that maf?)
Or the timing was set incorrectly (common mistake)

Or it has an obscure wiring issue, perhaps a bad cas or some bad cas wiring.
You need a wideband to see what is going on with the fueling

Have done everything above other than fuel pressure and compression test which will be the next things I do

Car has the correct maf, maf also gets correct voltage and reads correct voltage at idle and rises with airflow

Valve cover was pulled to verify correct CAS installation and was timed to 15°

Had a wideband temporarily installed and read 10:1 all the time which is as rich as the gauge could read

Car was purchased as a project and I’ve been fixing things wrong with it done by the PO, it was barely running when I got it and I at least have got it to run better but still nowhere near 100%

[Kingtal0n]

whelp fueling goes
maf -> injector -> ecu

simplest engine in the world , the right tune with the right injector = fuel

If it's sitting on 10:1 you missed something huge. Like wrong size injectors or the wrong chip in the ecu, massive boost/fuel leak or something huge

[mint40]

How did you check timing on the motor?

[1988montecarloss]

Originally Posted by Kingtal0n

whelp fueling goes
maf -> injector -> ecu

simplest engine in the world , the right tune with the right injector = fuel

If it's sitting on 10:1 you missed something huge. Like wrong size injectors or the wrong chip in the ecu, massive boost/fuel leak or something huge

Stock 370cc injector, stock untuned ecu, checked compression yesterday and all was good, couldn’t find a fuel pressure tester locally to rent so when I find one I can use I’ll check that as well, also going to try a known good set of coilpacks

Originally Posted by mint40

How did you check timing on the motor?

With a timing light on a plug wire on the #1 cylinder with the motor in timing mode

[1988montecarloss]

Checked fuel pressure, makes 42.5psi and holds it steady at idle

When initially turning the key to ON without starting the car just to prime the fuel pump it will make the initial 42.5psi and then the pressure very slowly drops down to 30-35ish, could this be an injector leak or is it just fuel running back to the tank because the pump turned off?

When I installed the new injectors the o rings looked fine and I used lube to install them to keep the o rings from getting pinched or turned over so I don’t think it’s them unless it’s the actual nozzle itself leaking

[mechanicalmoron]

Originally Posted by 1988montecarloss

Checked fuel pressure, makes 42.5psi and holds it steady at idle

When initially turning the key to ON without starting the car just to prime the fuel pump it will make the initial 42.5psi and then the pressure very slowly drops down to 30-35ish, could this be an injector leak or is it just fuel running back to the tank because the pump turned off?

When I installed the new injectors the o rings looked fine and I used lube to install them to keep the o rings from getting pinched or turned over so I don’t think it’s them unless it’s the actual nozzle itself leaking

As long as it holds 30 or so when it's off, should be fine.

I didn't see where and if anyone said it's not the coolant temp sensor, but that's a good instinct - Coolant temp can make motors flood so badly they won't run, or start. Check it out.

[1988montecarloss]

Originally Posted by mechanicalmoron

As long as it holds 30 or so when it's off, should be fine.

I didn't see where and if anyone said it's not the coolant temp sensor, but that's a good instinct - Coolant temp can make motors flood so badly they won't run, or start. Check it out.

Coolant temp sensor has been replaced with one from a parts store so who knows if it works or not as hit or miss as they are, is there any way I can test the sensor to know if it’s working and in range??

[mechanicalmoron]

Originally Posted by 1988montecarloss

Coolant temp sensor has been replaced with one from a parts store so who knows if it works or not as hit or miss as they are, is there any way I can test the sensor to know if it’s working and in range??

Oh, I'm afraid I missed that.

Unplugging it generally about half fixes a bad temp sensor.

You'll have to excuse my ignorance, but I assume an sr has no provisions for US evap gear? You could be sucking tank fumes, depending how your vent situation was handled.

[dct223]

Originally Posted by 1988montecarloss

Coolant temp sensor has been replaced with one from a parts store so who knows if it works or not as hit or miss as they are, is there any way I can test the sensor to know if it’s working and in range??

why not buy an OEM temp sensor? Check your connector to get the correct SR temp sensor

sometimes there is corrosion on the harness plug as well. You can buy replacement harness plugs if needed

[1988montecarloss]

Originally Posted by dct223

why not buy an OEM temp sensor? Check your connector to get the correct SR temp sensor

sometimes there is corrosion on the harness plug as well. You can buy replacement harness plugs if needed

Was trying to get car going ASAP and the parts store had one in stock will probably order an OEM to try since the car is still down anyway, plug looked okay