wierd shutoff at 4k rpms '90 SOHC

[Nuisance Crew]

I have a problem every once in a while where at about 4,000 rpms or so the fuel (i'm assuming) will cut off until the rpm's either drop to (exactly) 3,100, or I can push in the clutch for a moment and that seems to bring it back as well. it feels just like a speed govener kicking in. It seems to happen mostly when I'm trying to accelerate heavily, but not as a rule. I'm stumped on this one, any ideas would be helpfull, thanks in advance!
JD

[Nuisance Crew]

I guess the shutoff comes as low as 3500 rpms, but it always comes back on at 3100...

[Ricks15]

I have the same F**king problem too I think you outta check you're speed sensor and see if its either loose or damaged and then go from there.

[TougeNinja]

my friends dohc was doin the same thing at 3k but its cuz the maf plug came loose lol

[projekt_s13]

my friends dohc was doin the same thing at 3k but its cuz the maf plug came loose lol
I had a similar problem for about a week, the car would redline at 4500. Changed the MAF and it went away.

[Nuisance Crew]

Aaaah, I'll try swaping out the MAF and see if that helps, thanks!
I don't think it has anything to do with the speed sensor, I've had the problem with a few different trannies in, but anything is worth a shot!
JD

[Nuisance Crew]

What's the best place to get a new MAF? should I get a 240 one, or one of the other options?

[kandyflip445]

You have a 240 right? Go to the junkyard or to an autoparts store (dunno if the parts stores carry them may have to go to Nissan).

With a MAF from another car you would need a reprogrammed ECU.

[Nuisance Crew]

With a MAF from another car you would need a reprogrammed ECU.

Thanks, that's what I needed to know :)

[Nuisance Crew]

Swapped out maf, and no change, not throwing any codes... TPS voltages seem to be in line... any other ideas? I'm wondering what's so special about 4200 rpm's, there must be something that happens around there that would give a clue

[kandyflip445]

Make sure there is power to the plug on the MAF.

[Nuisance Crew]

Yeah, forgot to say I did check the maf per the FSM and everything checked out, I didn't check continuity the ecu, so faulty wiring somewhere may be a possibility, i have a spare engine wiring harness snake, I'm going to try hooking that up temporarily and see if that works. I have my speedo wire clipped at the ecu, and my 4+5 gear sensors unpluged to eliminate rev/speed limiting, but I'm wondering, if the harness for the gear sensors was really oily/dirty, then maybe the ecu would think that the car was always in 4th or 5th gear, and rev limit, but then again, if i push the clutch in, it will redline just fine. Hmmm maybe I'll just clip the gear sensor lines at the ecu to eliminate the question.

[Nuisance Crew]

Ok, just clipped 5th gear wire at ecu, couldn't find a 4th gear wire on the ecu diagram I have, cleaned my air filter, cleaned my intake, air regulator, i.a.a. unit. still no change, 4th gear cutout at about 4k, 5th at about 3.5k, and some intermitent sputtering when accelerating in lower gears.

[UNITEDMASTER]

Hello I have developed the same problem,Im suspecting either the FPR or the fuel pump is just old & tired in my case cause it revs fine. But under heavy load it goes limp for a second ,then when I back off it comes back in,and also at cruising speed under light throttle its OK . Check those things out. PEACE

[Nuisance Crew]

Yeah, that could very well be, I can get to higher rpms if I just feather the gas and let it creep up, heavy load and it falls on it's face. can anyone explain what part the vacuum source plays on the FPR? I'm wondering if too much/not enough vacuum can be causing the FPR not to function properly. Is there any way that a faulty PCV valve could cause any of these problems?

[Nuisance Crew]

swapped out FPR, no change, tried it with no vacuum, no change. checked timing, ok, rechecked tps, smooth voltage increase within specs. checked pcv bah. also according to one of the ecu's diagnostic modes it's running rich. maybe I'll try swapping out injectors, or yet a different maf

[Nuisance Crew]

I have the same F**king problem too...

Did you figure out your problem?

[ILoveJDM]

I have the exact same problem.

highway driving around 4k rpms is fine, but once i romp on it and increase the load this happens:

rpms drop slowly like letting off the gas when car is in gear
mashing on the throttle does nothing still decelerates as though your off the gas in gear.
pushing the clutch in and taking it out clears up the problem.

happened to 2 of my sohc's now.

daily driving and everything is else, its only on the highway under heavy load it does this.

[kandyflip445]

Weird.


..........

[Nuisance Crew]

I have the exact same problem.....

Everything you described is right on, and the ECU doesn't even throw a code. It seems like anyone who has this problem has tried replacing everything with no luck. I'm sure the magic answer is out there somewhere. one of my nieghbors suggested maybe the coil pack is getting old and just can't keep up, but with the clutch in (no load), it redlines just fine. and usually 1st 2nd and most of the time 3rd gear will redline as well under load. we should take one of our cars to nissan headquarters and ask them what they did! lol
It almost seems like when it cuts out it's going into the failsafe mode, and comes out only after the rpm's drop back below 3k by either letting the car slow down while still in gear, or pushing in the clutch in for a second. I wonder if the problem would be solved by swaping in an ECU from an automatic?? Is there anyone who has an automatic with a similar problem? or is this just us 5 speeder's?

[UNITEDMASTER]

Hey my car is runing the auto ECU,even though I did a 5sp swap ?? And I got the same problem its got me kinda stumped,I already checed my coil & the resistance is in spec. LMK what you all find.PEACE

[carkid0007]

Maybe this isnt just a 240 thing, my buddy has the same exact problem with his Jetta and has no idea.

[kandyflip445]

I just thought of another case like this on another car. It was a partially clogged catalytic converter. Under load the partially clogged cat would restrict the exhaust flow and not allow the car to rev and would loose power. If you can use a buddies or try a new one it MIGHT clear it up. Or you could just try it without the cat at all but it will be very loud and watch out for exhaust fumes!

Hope that helps!

[Nuisance Crew]

Hmmm, good suggestion, but I have a "high flow" cat, well actually it's a test pipe, lol. MN has no emissions anymore :)

[kandyflip445]

Well crap.... :rofl:

[EchoOfSilence]

Mine does this.

It only happens when my guage cluster doesn't light up, which is because the speed sensor circuit shorts. Might be a faulty VSS, or power unit to the guage cluster....

[bik]

same happend to me on my dohc i look for the truble for weeks... it was the same problem and was the IACV (dont remember the spalling) the valve then is under the intake manifild. u dont have to take it off, just use carbclenner in the little vaccum pipe

[Dirtylepp]

same thing happens to me. I have a sohc with an auto ecu.

[Nuisance Crew]

OK everyone, reconnect the the speed sensor wire that you clipped at the ECU to defeat the speed govener, clear your codes, make a run and tell me what happens.

I did this and now i can redline in 4th, and get up to the 115 mph or so in 5th , don't remember the rpm's. (4th + 5th gear sensor disconnected at tranny)

The only other think I did today was replace 2 spark plug wires that were kinda fried, and checked the gap on my plugs (only minor adjustments needed)

Here is my guess: at some point nissan made a revision to their SOHC ECU's to kick in the failsafe if the VSS was clipped, or malfundtioning. The ecu in my '90 is actaully a remanufactured replacement, I got the idea from another thread where srdetman i believe was asking for help with the speed limiter on his SR and ran into a similar problem.

So, unless replacing those plug wires made the difference, it's the vss wire. the next experiment is to wire a toggle switch, and try to flip it a bit before hitting 115, or see how long it takes for the ecu to "enforce" it's limit once the switch is flipped. So the guy above who said to check the VSS was actually right on.

[Nuisance Crew]

Anyone tried this yet? does everyone having this problem have your vss wire clipped, or a malfunctioning vss?

[DriftSpecial180]

Same problem. I have a '90, but i know its my cluster cause it doesn't work. most likely the same problem for you as well. Getting a new cluster this week.

[EchoOfSilence]

from where ?

[ILoveJDM]

OK everyone, reconnect the the speed sensor wire that you clipped at the ECU to defeat the speed govener, clear your codes, make a run and tell me what happens.

I did this and now i can redline in 4th, and get up to the 115 mph or so in 5th , don't remember the rpm's. (4th + 5th gear sensor disconnected at tranny)

The only other think I did today was replace 2 spark plug wires that were kinda fried, and checked the gap on my plugs (only minor adjustments needed)

Here is my guess: at some point nissan made a revision to their SOHC ECU's to kick in the failsafe if the VSS was clipped, or malfundtioning. The ecu in my '90 is actaully a remanufactured replacement, I got the idea from another thread where srdetman i believe was asking for help with the speed limiter on his SR and ran into a similar problem.

So, unless replacing those plug wires made the difference, it's the vss wire. the next experiment is to wire a toggle switch, and try to flip it a bit before hitting 115, or see how long it takes for the ecu to "enforce" it's limit once the switch is flipped. So the guy above who said to check the VSS was actually right on.



well for one. I didnt cut my wires, and the car is stock..no ecu swappage
secondly my speedo is fucked, it goes to 20km/h in neutral when its cold but works fine in gear.
third, my other coupe did this, but the speedo was working properly

[ranger240]

a month ago my car did stuff similar to this.... it later developed into an ungoldy amount of engine buckling....

gave it a tune up; oil plugs wire, no distributor though, got lazy, that made it a noticable improvement though it it would still barely rev past 3500 at speed.. next i cleaned the MAF which caused a some improvement.

what it finally turned out to be when i gave up and took it to a shop was the fuel injectors... they cleaned the injectors and replaced the seals...

check the injectors after a tune up... hope that helps

[Nuisance Crew]

Yeah, I'm guessing there's a few different problems that could cause these symptoms, so it's just a matter of trial and error. So far we have Vss, speedo, or any of the associated wiring; injectors; and MAF.