1995 stock KA24DE misfire/hesitate/stumble...I'm lost.

[Kouki4Zenki]

1995 240sx SE stock KA24DE Automatic. No check engine light.

Problem: While in drive, the car will misfire/hesitate/stumble at a stop or during slow acceleration. RPM's go from 700 to even 200 sometimes. Also misfires around 1300-1600 rpms but nothing over 2000 rpms. While in neutral, no symptoms of a misfire/stumble at all. Idles perfect at 7-800ish rpms. While in park, it'll misfire a little bit, but not as much as if it were in drive.

What i've tried soo far: Checking for a dead cylinder. Nothing. Checked injector resistance with the following: 11.6 across the board. Replaced injector #4 with brand new one because i thought this one was stuck open. Results...nothing. Swapped out injector #1 with known good injector. Same result. Replaced all 4 spark plugs. Checked firing order on distributor cap. Cap wires are relatively new. Car has spark, compression, and now injectors are firing.

Also, the coolant temp barely rises above C. Could the car think it's running cold all the time causing the car to run rich? (Replacing thermostat tomorrow with an OEM Nissan one)

What are the symptoms of a bad MAFs as im reading these are also a common problem on these...I tried cleaning the MAF and it ran alot better 1 time around the block...then back to same old thing. How do you test it? I read you can try to start it without it plugged in and what not but what happens if it starts unplugged and vise versa?

Bad fuel pump maybe? I ordered a fuel filter too i might toss in but i'm getting tired of figuring this thing out....

Any input would be appreciated...i'll be reading posts till my eyes bleed tonight.

[jr_ss]

Unplug your MAF while your car is idling and see if it clears up. If it does, you've a dead MAF on your hands.

[veeates36]

Sounds like a MAF issue.. Know anybody with another KA that you can swap with just to troubleshoot..? Good Luck

[Kouki4Zenki]

Update: I pulled the thermostat housing off to see if there was a thermo in it in the first place...Low and behold nothing! So i put one in from Nissan and bled/or tried to bleed it out...the car got almost to Hot. Couldn't get a good bleed cuz of the hesistate/misfire it was doing the whole time. (It'd shoot the coolant up out of the radiator making it damn near impossible) So i pulled the thermo back out and put it all back together. I have to figure this mis/hesistate out first before the heat issue...

I also installed a new Coolant Temp Sensor too just incase it was that.

The car still drives the same if not worse...Fuel filter will be going in tomorrow...

Also tried to get a datastream on all of the info but the scanner couldn't hook-up to the car...epic fail.

As far as the MAF goes, no i don't know anyone with a spare one i can test out...are SR20's the same? I have a buddy with a SR20 in a S13 though...not sure if that'll work. And i didnt try the unplugging the sensor yet...although i believe the last time i did, the car seemed like it was going to die.

What i don't get is this: What will cause the car to misfire/drop rpms or cause a hesisitation while in drive? Only in drive too, not in neutral and only a little bit in park.


HELP!

[Kouki4Zenki]

Also about the Fuel Pump...if i do end up having to replace it, could i replace it with a Walbro 255 and be fine with the stock FPR and injectors? I don't plan on doing anything major w/the KA but may go SR in the future...(not near though...) The cost for an aftermarket off brand stock fuel pump and a new Walbro 255 is about the same. Just don't want to run into fuel problems like it running too rich, etc...

[orion::S14]

^^^ It will be fine.

If you have a working, stock FPR...then it will regulate the pressure just like a stock pump.

- Brian

[Kouki4Zenki]

Update: /Sigh....ok. So we checked the timing on the vehicle. Everything seems to be in specc. The lobes on the cams both face out and the timing marks on the camshafts line up where they're supposed to. Reset the distributor thinking it may have been off a tooth or two...Nothing. Still misfiring under load ie drive/reverse. I shouldn't say only under load though...it's just worse under load...misses once in awhile in drive/neutral but not as bad.

Checked the timing again with a timing light. Marks are where they should be at -20 BTDC on the gun.

Checked all the resistance at the injectors (all at 11.6)

Checked for vaccum leaks...found one at the thing that the EGR feeds to (forget the name of it) The almost 90 degree bend that's tucked back almost to the firewall. Replaced/fixed and still...misfiring.

Checked the resistance and voltage at the MAF sensor...reads out fine. (note: there is a hole in the screen on the inside of the MAF though...not sure if that'll do anything)

Replaced the Fuel pump with a aftermarket one from Advance Auto and resused the old sock from the stock fuel pump.

Still same old thing. I'm very very confused...stumped on this. I want to keep this post alive because im sure others have encountered this. PLEASE i need the Guru/Nissan gods to help me!!!

EDIT: We also checked the compression in all 4 cylinders and they all read 160-170 psi across the board. Spark plugs were kinda white indicating its running too lean?!

[mxexux]

Have you changed the fuel filter yet? Also definitely fix the cooling problem as it does affect the controlled fuel delivery. Does your check engine light work? Light will turn on for a few seconds when you first turn the car on as a bulb check.

[Kouki4Zenki]

Yeah the fuel filter was replaced and the check engine light has not been unplugged or replaced. It comes on/lights up but just doesn't stay on indicating a problem.

The coolant cannot be bleed properly with the OEM thermostat because of the misfire. It'll toss the coolant back up threw the radiator everytime the engine will misfire causing more air to be forced back down threw the radiator. It's damn near impossible so i just took the thermostat back out and rebled it without it installed. Funny though that it doesn't misfire when i'm bleeding it without the thermostat installed. Seems to run alot better with it out at first but don't get me wrong, it'll still misfire/stumble after the coolant is in.

Kinda wierd too i got heat now finally...with the thermostat out of the car, the needle is in the middle...indicating the motor is running at normal temperature when before, it'll barely move up from C. Weird?

[mrmooseman]

try checking to see if your injectors are leaking

[lkristoefur]

check the vacuum hose to the brake booster i bet you have a tear somewhere on one of the hoses. I had the same problem on my s13 before. either that or the guy before you took the stat out for a reason?

[Blacksilvy]

shot in the dark but does the car have a hard to start condition when it has sat overnight and is cold ?

[Kouki4Zenki]

A friend an i checked the hoses there with carb cleaner too at the brake booster. Nothing. As far as the thermostat goes, i can't know that unless i figure out this misfire/hesitation. Like i said, with the thermo installed, i cannot bleed the coolant system properly because of the misfire.

There is no hard start in the mornings. She starts right up but stumbles right away and idles like a harely sometimes.

[Kouki4Zenki]

If an injector was leaking, wouldnt it be running rich? How do i check? I already power balance checked it and compression tested it. Unpluggin the injectors also.

[RJayS.]

Could be a EGR problem, or maybe by chance a throttle position sensor. Just a few more things to check out.

[illvialuver]

All I can say is maybe it is your distributor going out, mine did the same thing when it was going out, but it seems like you could have other issues. Check the main vein.

that is what I refer to the big vacum line that is in the back of the engine, kinda in between the engine and the brake master cylinder. It has a few bends in it, alot of older kas have dried out or crack main veins and they make it run like shit.

that is just my two cents. good luck.

[RJayS.]

Looked into it a little more and lots of poeple have problems with the EGR Backpressure Transducer. It will be circle looking over by your intake manifold. Ill try and get some pics for you if you need more help.

[Kouki4Zenki]

The EGR will cause it to run like this under load? Make it misfire and backfire on occassion? I'll look into that a bit more. As far as the main vein goes, i sprayed that whole vaccum line on that back firewall and it doesn't change anything. Even sprayed around the TB and EGR vaccum lines.

Another thing is too, when i unplug the vaccum to the EGR, isn't my car supposed to shut off or change idle? When i unplug it, it does nothing :P

Also if you can get pics of where the EGR transducer is located that'll be awesome. Is it by the EGR/Swirl thingys?

I'm going to check out the ohms on the TPS sensor next too...btw how do i check the distributor to see if it's on the way out?

Edit: Do you mean the EGRC or something like that for the transducer? I did find a vaccum line that was broke/cut back there that i taped up because the bend in the hose was at such a degree that the replacement line i put in seemed to be just cut off anyway i replaced it.

[Pacman]

Your EGR is stuck partially open. It would defineitly make the car stumble/mis/run badly. make sure that its clean.

[Kouki4Zenki]

When i unplugg the vaccum hose on top of the EGR, isn't the idle supposed to change or the car supposed to shut off? It does nothing. No suction like theres vaccum or anything. Car stays the same...

[Kouki4Zenki]

Update: So i took the EGR off...well half of it (the part with the big exhaust pipe i couldn't get a cresent wrench behind it so i left it and took the piece off of the manifold) and cleaned it all out. Ran some seafoam threw the brake booster that feeds into the IM and ran it for a bit...still has a misfire!!!

I found some frail/slightly damaged vaccum lines as i was doing the EGR and replaced them all...still nothing. Only other thing i can think of is MAF/TPS or distributor.

Lately, its been getting hard to start too now...meaning i have to hold the key while cranking and allow it to crank till the engine is actually running...i know its not good for the starter but still I'm stumped on this one guys....

[RJayS.]

Sorry i have been busy latly but im still trying to get pics for the EGR backpressure Transducer. Other wise i would def look into your CKP. If your computer doesnt know where the Crank is then it would be hard to control the rest of the cars electronics. Should be Approx. 185 ±19 ohms. Hope this helps.

[Iron_Zenki]

So basically mine does the same thing its your MAF really pointless you went through all that lol

[Iron_Zenki]

oh and make sure your not a idiot and check if your OBD1 or 2 :]

[fullmetalx]

check for fuel pressure. make sure its up to what FSM says. the pump can be working or new. but the pressure should be right. sometimes new parts can be defective too. i have almost the same symptoms as yours. 89 s13. fuel pressure should be ~33 psi i believe. but checked it with a gauge, read only 23 psi. replaced fuel pump. symptoms disaapeared. car runs perfect now. checked pressure again, read ~33 psi.

[Kouki4Zenki]

How are you certain its my MAF? The resistance and everything on it read out fine and cleaning it with carb cleaner doesn't do anything.

I'll try and get a fuel pressure tester to check my pressure. I'm sure it'll be good concidering i replaced the pump already and fuel filter. It feels as if it's something electrical...like it cuts out the injectors or something.

Car's getting worse to drive now especially after a long time of driving it.

Also, now with the thermostat out, the temperature goes up to middle. It used to just stay at cold. Seems to go up and down a bit while im driving...

[xSoCalxRiderx125]

Same synonyms as my car, know exactly how you feel dude shitty stuff. Try Checking all your grounds. I have been messing with all my grounds cleaning the surface area and my car seems to have been getting progressively better after I have been doing that. After changing the fuel pump, fuel filter and the fpr I had no change. Felt like I was riding a machanical bull or some shit with all the bucking and rough idling. I don't know if you checked them yet because it's kinda that one thing everyone tends to overlook sometimes. I dk let me know how that goes I'm curious if you find anything I may have overlooked. Good luck bro.

[s14j]

its your maf i had the same problem
used my brother maf and it was oky
really try borrowing or buying a cheep good maf

[nissan racer]

yea its ur maf sensor i dont if u didnt try this but unplug the maf sensor while its not runing for a min or 2 and then plug it back in it should work i had the same problem but now its doin it again so my altima is doin the same thing now but it only does it when its warmed up so i dont know what it could be.

[240sxdd]

Dont want to sound stupid but i found the reason for that is the spark plug wires. How so? Auto S14, running fine with ngk wires. I wanted to keep the wires for another car and replaced them with cheapo stocks. Car began to miss and run weird. Put Ngks back on and it was like clean again....I now have another s14 doing the exact same thing.