car is missfiring at low revs under load

pretty much as the title says, when i first start the car up & drive when it's cold, it drives okay for about 40 seconds, then when in the low rpms, any slight load i put on the motor makes it miss fire lots till about 1500-2000rpm then it just shoots off like vtax and runs mint above those revs. This started happening about a month ago, it's gotten worse lately to the point where it bothers me a lot

here's what I've done:
got spark plugs brand new about 10000 - 15000 km ago.
i've been through numerous amounts of spark plug leads (matching sets & mismatching sets) though all used, they work fine in other cars.
tried 3 distributors, used, but worked fine on other motors.
replaced the fuel filter, used, but same as above.
this is also the 3rd motor in the car that's been doing this.
tried quite a few ECU's as well

wat do?

[B][/what kind of gas are you using?
B] get some higher octane mixed in there and see if it makes any difference in where it runs differently.
our hatch does this and Ive done all sorts of things to no avail. I am going to try a compression check next I guess I have borderline valve seating issues. I also suspected the map sensor at one time but never looked closer at that.

I use 95 in it all the time, which is the highest I can get in this town I believe. Haven't had 91 in it for a very long time either.

how are your valve clearances?

I honestly don't know, don't know how to check them either. If the next motor that goes into the car does the same thing then I'll add that to the to-do list.. just wondering if there's anything car related that's causing it to act up

what kind of plugs?
cap and rotor. matching set?
any wire leads tied together or lying on manifold?

try pulling the coil lead slightly out of the dizzy (but still fairly secure so it wont pop all the way out) and run it to see what difference it makes.. if it gets worse then I would say new leads were needed, if it gets better then plugs or coil (if it is even an ignition problem)

They're NGK plugs, don't know what sort though, I forgot.
I only have 1 b20a dizzy rotor, but a few caps. they appeared to be in good condition.

I use a f20 dizzy in the car though (internal coil) I've replaced the coil, rotor & cap on it too (used but good). I don't know how to do the test you're saying to do though? but normally when i mess around with the leads while the car is running i get a shock lol

maybe I should try adding a ground straight from the dizzy to the cars body? I'll try that tomorrow

you couldnt do that "test" with an internal coil:rolleyes:

I guess you check for carbon tracking inside that cap, red, black, or white marks or debris

i swear by ngk v groove or u groove whatever, nothing fancy just dam good plugs

I figured that lol. The cap that's on it now is in good condition, I replaced a couple cause one was soaked in oil (that was my own fault) and the other had lots of that white corrosion in it. the one on there now is good though.

I just added some thick ground cables from the motor & dizzy to the frame of the car, didnt make any difference

and the spark plugs are BCPR6E-11 (NGKs recommendation)

I had the same thing happen with mine and it turned out to be the rotor...it was loose or something don't remember exactly. But new cap and rotor fixed it. I tried everything fuel filter, plugs, wires the whole 9 yards.

It's gotta be electrical if it runs fine in the upper rpms IMO

That's what I was thinking too. I'll put my F20 dizzy back in & try more rotors. I'm poor ass and can't afford to buy stuff lol.

You could also try bleeding the cooling system; air bubbles may throw off the readings from the TW sensor, which can affect timing and fuel/air mixture.

i took off the intake manifold and stuck on a carb one and the motor ran good, didnt missfire under load, but the carb leaks petrol every where and i cbf sticking another carb on. so the missfire can't be from the ignition system, as I left the efi stuff on there when running the carb. The fail with it running like shit must lie within the intake manifold/fuel pump/fuel filter/injectors. I'll go swap all those and see how it goes

i forgot to mention that the car hasn't idled properly in the last couple weeks. well i just reinstalled all the IACV hoses, even bled the coolant system properly, still doesn't idle like it should, actually stalls most times. I also replaced the fuel pump, fuel filter, injectors and FPR. The fuel in the tank is nice and yellow like it should be, heaps of fuel pisses out both fuel rail ends with hoses off & it looks clean and such. I've tried 3 ECUs again after this, nothing has changed. WHAT THE FUCCCK!!!

so just a quick recap of what's been swapped:
new spark plugs
3 engines
many different ECUs
3 dizzys
many different leads
2 O2 sensors
2 fuel filters
1 fuel pump
1 set of injectors
2 FPRs

this is really pissing me off cause it's not improving at all. and it's fucking terrible on fuel (like 11mpg) wat do???????????????????????

i also forgot to mention that it runs really really rich. you can add the ect, injector resistor box and map sensor to that list of stuff replaced. it's still running way too rich

Quote:

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Originally Posted by A18A

i took off the intake manifold and stuck on a carb one

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Sounds like a fun day. Have you ohmed out the injectors? Maybe you have a bad one that's leaking fuel. I would think you'd get a CEL code when the O2 sensor couldn't lean it out, but who knows?

Tps?
Map?
try swapping any / every thing you can from the manifold till you find it

well I grounded the wire that goes to the o2 sensor to make it run lean, it made quite the difference. I guess I need yet another O2 sensor. that's shitty how they just randomly fail. it still misses every now and then though and still doesn't feel like a proper running b20a, but at least it idles now!! and drives somewhat smoothly

Quote:

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Originally Posted by Dr_Snooz

Sounds like a fun day. Have you ohmed out the injectors? Maybe you have a bad one that's leaking fuel. I would think you'd get a CEL code when the O2 sensor couldn't lean it out, but who knows?

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lol you should have seenn my fuel tank for the carb, i emptied the window washer tank and put fuel in it then ran the line that goes to the squirters to the carb. worked good lol. anyway nah i dont have any electrical testing devices except for a volt meter. I'm confident the injectors are good though as they're from a motor i pulled from a different car a couple months ago, which ran fine. I didnt get a o2 sensor error from the ecu, but i guess that wont happen till I run the car for a while with a faulty one/none. It hasn't given me any error yet for grounding the wire that's supposed to go to it. i do get egr error after about 5 minutes of running the car though, which is probably related. or maybe i forgot to plug it back in

disregard this post.

actually now it's running okay, just misses slightly when cruising

no, you can't just end it like this! :eek5:
You still have the annoying misfire?
Now that it has warmed up some here I am going to look back at mine because it annoys the shitotta me. The car runs out great with plenty of power and no misfiring really but a odd sound in the exhaust. The misfire is definatley there at idle and just above idle taking off then it seems to disappear. The car never really chugs or skips like a dead skip misfire though.
Ive done all the things you have done in this thread except O2 sensors. ( or switch over to a carb) I dont think it runs rich but I do get a strong gas smell only in the afternoons, never in the morning????
No injector or rail leaks either, all that is replaced.

Wow... too bad I missed this thread from the beggining.

I'm sure it's the O2 sensor.

Try disconnecting it. The car will run like crap until it realises there's no O2 sensor. Then, it should run without missfiring.

Yeah I'm sure it was my faulty O2 sensors as well. Running without it (for probably over a hour of driving) didn't make the car start running without missing though, i eventually got a O2 sensor error. when I grounded the O2 wire (cause now i don't have any o2 sensors lol) it started to not missfire. the idle is still shitty and won't stay still, and it feels pretty damn slow (0-100kph in like 12-13 seconds) but I'm hoping that's soley cause of the grounded o2 wire