280zx (s130) Running way too rich

349 Views 18 Replies 5 Participants Last post by destabilized1887, 7 d ago

destabilized1887

Discussion Starter · 14 d ago

well i was driving my zx then was met with the issue of it running way rich shooting black smoke and then eventually shutting off
the car only would restart once we pulled some vacuum lines but wouldn't idle by itself

i yanked the engine apart last night because what better time to fix some other issues, did timing chain, valve seals, full gaskets except for rear main, o2 sensor, starter, coolant temp sensor, fuel pressure regulator

got it all back together and it ran but not very well, it still wouldn't idle by itself, and looked like a 2 stroke with how smokey it was

when you pull some vacuum lines it runns ok but idles arround 2k

im suspecting a bad maf or ecu at this point

1 - 19 of 19 Posts

bonfire79

· #2 · 14 d ago

were any of those items you replaced actually faulty? did you test them first before tossing parts at them? chances are they were fine and not causing the issue

is it a turbo or non-turbo Z?

your ecu is fine, but it can be checked. you don't have a MAF or a sensor. AFM is king here.

first thing I would do is check fuel pump function and fuel pressure at idle, then once you know you have good fuel delivery, I would do a compression check. make sure you have spark, fuel, and air on all six cylinders.
it could be somethings as simple as bad and corroded electrical connections too.

here is a gift: www.xenonzcar.com, s130 section, the FREE factory service manual for your year car. get it.
read it. read it again. then some more. then start the troubleshooting process there within.

destabilized1887

Discussion Starter · #3 · 14 d ago

bonfire79 said:
were any of those items you replaced actually faulty? did you test them first before tossing parts at them? chances are they were fine and not causing the issue is it a turbo or non-turbo Z?

your ecu is fine, but it can be checked. you don't have a MAF or a sensor. AFM is king here.

first thing I would do is check fuel pump function and fuel pressure at idle, then once you know you have good fuel delivery, I would do a compression check. make sure you have spark, fuel, and air on all six cylinders.
it could be somethings as simple as bad and corroded electrical connections too.

here is a gift: www.xenonzcar.com, s130 section, the FREE factory service manual for your year car. get it.
read it. read it again. then some more. then start the troubleshooting process there within.

sorry i forgot it was a afm not a mas
its a non turbo 1983
i have all the parts that were replaced, i dont mind throwing some money at the problem

the o2 sensor was bad for a while because of leaking valve seals and burning 2qt of oil a week
the starter had intermittent issues where it wouldn't stay engaged when cranking so i swapped it when i had everything apart

pressure when the pump is on and engine off is 37psi, it should be at 36 i believe

compression was good
#1 152
#2 155
#3 149
#4 150
#5 147
#6 145

i have spark, i replaced the cap, rotor, plugs, wires when i got the car
im going to get new plugs as its been 7k miles and the oil burning cooked them

tonight im pulling the rail and injectors to make sure nothing is leaking and to re seal the injectors and injector to rail hoses, spark plugs

when i get it running ill let you know the running fuel pressure, i need to make it run without a vacuum leak so the regulator is working properly

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steve240Z73

· #4 · 14 d ago

One source for excessive fuel could be the cold start injector. If it's feeding fuel all of the time, you definitely go rich.

How did the plugs look? Wet? Carbon fouled? Fuel soaked? Oil soaked?

destabilized1887

Discussion Starter · #5 · 14 d ago

steve240Z73 said:
One source for excessive fuel could be the cold start injector. If it's feeding fuel all of the time, you definitely go rich. How did the plugs look? Wet? Carbon fouled? Fuel soaked? Oil soaked?

fuel soaked/ wet it looks like a diesel truck rolling coal when it actually starts

destabilized1887

Discussion Starter · #6 · 14 d ago

steve240Z73 said:
One source for excessive fuel could be the cold start injector. If it's feeding fuel all of the time, you definitely go rich.

How did the plugs look? Wet? Carbon fouled? Fuel soaked? Oil soaked?

wet/ fuel soaked
looked like a diesel rolling coal when it actually starts

steve240Z73

· #7 · 14 d ago

If all are wet, definitely check fuel pressure & the cold start injector. If the fuel pressure is high, in addition to the FPR, verify that nothing is blocking the return line. Also, don't wait too long to change your oil. It may be getting diluted with gasoline.

destabilized1887

Discussion Starter · #8 · 14 d ago

steve240Z73 said:
If all are wet, definitely check fuel pressure & the cold start injector. If the fuel pressure is high, in addition to the FPR, verify that nothing is blocking the return line. Also, don't wait too long to change your oil. It may be getting diluted with gasoline.

im going to try routing the return into a bucket to make sure there's no blockage in the return
i have all the stuff for a oil change I just want to sort out the running issues before I ruin another 5qt of oil with gas

steve240Z73

· #9 · 14 d ago

Oil & filters are cheap, even with inflation, compared to an engine rebuild.

kickstand80

· #10 · 14 d ago

When you said you replaced the coolant temp sensor are you talking about the one in the thermostat housing?

destabilized1887

Discussion Starter · #11 · 14 d ago

yeah the one that isn't a bullet connector on the housing
top right one if I remember correctly

kickstand80

· #12 · 14 d ago

That sensor is for the engine temp gauge in the dash.

So the MOST important sensor in the EFI system is the cylinder head temp sensor (CHTS) It is located in the cylinder head between spark plug 5 & 6. You need to check this connection and the sensor. The sensor can be removed from the head, it is not in the coolant but actually reads the metal temperature of the head. If this sensor is bad, or the connection is corroded the engine will run super rich. Use an OHM meter to check it. Remove it and put it in the freezer. The OHM value should be about 7,000-11,000 ohms. Put it in boiling water and the OHM value should drop to 100-300 OHM.
And if the connection at the AFM is bad/corroded it will mess thing up as well.

Reactions: 1

destabilized1887

Discussion Starter · #13 · 13 d ago

ok so I did some troubleshooting but not as much as I would like to have

fuel pressure is dead on 36 while cranking
have spark and cleaned the plugs up a bit
clamped off the cold start line

the fuel pressure drops to 20 once the pump stops making me think injectors are leaking

currently has a crank no start

tomorrow I'll pull the injectors to see which ones leaking and check the ohms on the chts

destabilized1887

Discussion Starter · #14 · 9 d ago

destabilized1887 said:
ok so I did some troubleshooting but not as much as I would like to have

fuel pressure is dead on 36 while cranking
have spark and cleaned the plugs up a bit
clamped off the cold start line

the fuel pressure drops to 20 once the pump stops making me think injectors are leaking

currently has a crank no start

tomorrow I'll pull the injectors to see which ones leaking and check the ohms on the chts

alright I finally got around to doing some tests

chts in the freezer got me 12k ohm
chts in boiling water got me 237 ohm

no injectors are leaking and I replaced the seals while I was in there

the car decided to start today also, fuel pressure at idle is 30

it's idling at about 600rpm and blowing black smoke
when oil cap it removed it dies
when brake booster line is unplugged it idles at 1900 and no longer shoots black smoke

bonfire79

· #15 · 9 d ago

thats good the engine dies when the oil cap is removed, that means your vacuum is good. sounds like things are running better now?

destabilized1887

Discussion Starter · #16 · 9 d ago

bonfire79 said:
thats good the engine dies when the oil cap is removed, that means your vacuum is good. sounds like things are running better now?

the car is actually running now bit the condition hasn't improved,
still blowing black smoke and rough idle at 600 rpm

i just ohm tested the afm and it checked out

so that leaves the ecu left to be tested

destabilized1887

Discussion Starter · #17 · 8 d ago

destabilized1887 said:
the car is actually running now bit the condition hasn't improved,
still blowing black smoke and rough idle at 600 rpm

i just ohm tested the afm and it checked out

so that leaves the ecu left to be tested

i ordered a new chts last night and it will be here Wednesday, ik it tested good but I still believe that it is the issue it's also 60$ with shipping so it's not a huge deal

im going to see if I can get my hands on another ecu from a parts car just to test that also

sockeye

· #18 · 7 d ago

I know you looked at the fuel system but did you vacuum test the fuel pressure regulator? Or just remove the vacuum line while the fuel pump is pressurizing the system? If gas shoots out the vacuum line when the system is under pressure or the FPR won't hold a vacuum then the diaphram is bad and will allow gas to flow through unchecked into the intake system. Kind of weird but some small leaks will still hold pressure while throwing extra fuel through a hole or crack.

destabilized1887

Discussion Starter · #19 · 7 d ago

sockeye said:
I know you looked at the fuel system but did you vacuum test the fuel pressure regulator? Or just remove the vacuum line while the fuel pump is pressurizing the system? If gas shoots out the vacuum line when the system is under pressure or the FPR won't hold a vacuum then the diaphram is bad and will allow gas to flow through unchecked into the intake system. Kind of weird but some small leaks will still hold pressure while throwing extra fuel through a hole or crack.

i did check for gas in the vacuum line/ regulator it was completely dry
i believe the regulator is perfectly fine but I replaced it with a aftermarket adjustable one as I plan to turbo the car in the future and go aftermarket ecu

1 - 19 of 19 Posts