Stumble troubleshooting advice - Infamous Nissan

KivPanther · 02-19-2021, 02:15 AM

I’m having a bastard of a time tracking down this intermittent stumble in my V6 so I need to pick some brains.

It only happens when under light acceleration or cruising; doesn’t do it coasting under power, idling, or under heavy acceleration.
It seems to only do it around about 3k RPM.
It does it both cold and hot with no seeming change in frequency.
It happens very quickly, often a couple times in succession. Not enough to cause the tach to jitter even.
It also does it while cruise is active and doesn’t seem to affect its performance.

I have replaced many vacuum hoses and couldn’t find a leak using smoke. The O2 sensor has been replaced. I cleaned the MAF while the manifold was off the truck. All the injectors are brand new and have brand new o rings and seals. The distributor is new, the spark plugs are new, and the plug wires are new. Any thoughts?

Deerhurst · 02-19-2021, 03:10 AM

Any codes? How old are your plugs and wires?

KivPanther · 02-19-2021, 03:32 AM

No codes. Plugs and wires are brand new. NGK iridium plugs (real ones) and NGK blue wires.

Ftown · 02-19-2021, 03:50 AM

It happens while in cruise control? Maybe the cruise mechanism is going out. Try smoking the cruise control mechanism. It also runs off vacuum

Ftown · 02-19-2021, 03:55 AM

Also, I'd check your injectors. I have an f150 that I chased a miss I thought was a vacuum leak. Turned out to be a bad injector

KivPanther · 02-19-2021, 05:08 AM

Sorry, I should clarify: It doesn't happen ONLY while in cruise control, it happens ALSO while in cruise control. I actually just replaced the ASCD vacuum hose since it had rotted, but it has its own vacuum pump separate from the engine control system. The fuel injectors are, as mentioned above, all brand new, tested working, and getting pulse.

89'HBV6 · 02-19-2021, 08:31 PM

If you replaced the vac line to the cruise, what condition was it in? Could be some smaller particulates got pulled in? ...from the inside of the old rotted hose? (thinking outloud)

KivPanther · 02-19-2021, 09:46 PM

The ASCD itself is old it in good shape. The only thing bad was the vacuum hose. Still though, since it does it regardless of whether I’m in cruise control or not I doubt it’s related.

LugNut1990 · 02-19-2021, 10:57 PM

So no change between before/after the new injectors?

It seems that the problem would be more evident under hard acceleration if fuel-flow was the cause, but did you change the fuel filter too?

If it is repeatable, try cracking the gas cap open and trying it again. Might generate an error code, but is the miss gone?

KivPanther · 02-20-2021, 01:01 AM

Correct; there was no change after the injectors were replaced. I did replace the fuel
filter at the same time. I had bought a new TPS but hadn’t gotten around to installing it yet since I wasn’t sure it would need it. I also haven’t been able to get the idle to drop all the way to 750 after warming up even after adjustment. I might just go ahead and swap them just in case.

I’ll give the gas cap thing a go on my way home from shift tonight and see what happens.

02-19-2021, 02:15 AM	#1
KivPanther Furball Join Date: Oct 2020 Location: North Carolina Posts: 112 Vehicle: 1994 XE King Cab Thanks: 3 Thanked 21 Times in 18 Posts	Stumble troubleshooting advice I’m having a bastard of a time tracking down this intermittent stumble in my V6 so I need to pick some brains. It only happens when under light acceleration or cruising; doesn’t do it coasting under power, idling, or under heavy acceleration. It seems to only do it around about 3k RPM. It does it both cold and hot with no seeming change in frequency. It happens very quickly, often a couple times in succession. Not enough to cause the tach to jitter even. It also does it while cruise is active and doesn’t seem to affect its performance. I have replaced many vacuum hoses and couldn’t find a leak using smoke. The O2 sensor has been replaced. I cleaned the MAF while the manifold was off the truck. All the injectors are brand new and have brand new o rings and seals. The distributor is new, the spark plugs are new, and the plug wires are new. Any thoughts? __________________ Last edited by KivPanther; 02-19-2021 at 09:47 PM.

02-19-2021, 03:10 AM	#2
Deerhurst 4/86 SE-V6 2 tone 4x4 HB Join Date: Apr 2013 Location: Oregon Posts: 7,374 Vehicle: 1986.5 SE-V6 4WD D21, 2003 Audi A4 Avant 3.0 Quattro Thanks: 891 Thanked 903 Times in 822 Posts	Any codes? How old are your plugs and wires? __________________ 1986.5 SE-V6 4X4 D21 Hardbody Pacesetter Long Tube Headers Morimoto Mini D2S HID Projectors and Hella 500s VG33i

02-19-2021, 03:32 AM	#3
KivPanther Furball Join Date: Oct 2020 Location: North Carolina Posts: 112 Vehicle: 1994 XE King Cab Thanks: 3 Thanked 21 Times in 18 Posts	No codes. Plugs and wires are brand new. NGK iridium plugs (real ones) and NGK blue wires. __________________

02-19-2021, 05:08 AM	#6
KivPanther Furball Join Date: Oct 2020 Location: North Carolina Posts: 112 Vehicle: 1994 XE King Cab Thanks: 3 Thanked 21 Times in 18 Posts	Sorry, I should clarify: It doesn't happen ONLY while in cruise control, it happens ALSO while in cruise control. I actually just replaced the ASCD vacuum hose since it had rotted, but it has its own vacuum pump separate from the engine control system. The fuel injectors are, as mentioned above, all brand new, tested working, and getting pulse. __________________

02-19-2021, 09:46 PM	#8
KivPanther Furball Join Date: Oct 2020 Location: North Carolina Posts: 112 Vehicle: 1994 XE King Cab Thanks: 3 Thanked 21 Times in 18 Posts	The ASCD itself is old it in good shape. The only thing bad was the vacuum hose. Still though, since it does it regardless of whether I’m in cruise control or not I doubt it’s related. __________________

02-19-2021, 03:50 AM	#4
Ftown Join Date: Dec 2020 Location: Lakeland, FL Posts: 30 Vehicle: 1995 Hardbody XE V6 Thanks: 4 Thanked 1 Time in 1 Post	It happens while in cruise control? Maybe the cruise mechanism is going out. Try smoking the cruise control mechanism. It also runs off vacuum

02-19-2021, 03:55 AM	#5
Ftown Join Date: Dec 2020 Location: Lakeland, FL Posts: 30 Vehicle: 1995 Hardbody XE V6 Thanks: 4 Thanked 1 Time in 1 Post	Also, I'd check your injectors. I have an f150 that I chased a miss I thought was a vacuum leak. Turned out to be a bad injector

02-19-2021, 08:31 PM	#7
89'HBV6 Ol'school Geek Join Date: Mar 2020 Location: Washington State Posts: 481 Vehicle: 89' D21 KC SE V6 5spd 2WD - 87' D21 KC SE V6 5spd 2WD Thanks: 499 Thanked 123 Times in 106 Posts	If you replaced the vac line to the cruise, what condition was it in? Could be some smaller particulates got pulled in? ...from the inside of the old rotted hose? (thinking outloud)

02-19-2021, 10:57 PM	#9
LugNut1990 Join Date: Jul 2015 Location: N.E. Kansas Posts: 730 Vehicle: 1990 Nissan Hardbody Thanks: 0 Thanked 99 Times in 87 Posts	So no change between before/after the new injectors? It seems that the problem would be more evident under hard acceleration if fuel-flow was the cause, but did you change the fuel filter too? If it is repeatable, try cracking the gas cap open and trying it again. Might generate an error code, but is the miss gone? __________________ Original owner 1990 Nissan Hardbody, Aztec Red Standard cab, 4x4, KA24E, 5-speed Intentionally near-stock Mods: Second OEM horn, stereo/speakers/sub, mud and snow tires, HD trailer hitch (cat 3+), liquid bed liner, G1W dashcam Definitely not for sale!

02-20-2021, 01:01 AM	#10
KivPanther Furball Join Date: Oct 2020 Location: North Carolina Posts: 112 Vehicle: 1994 XE King Cab Thanks: 3 Thanked 21 Times in 18 Posts	Correct; there was no change after the injectors were replaced. I did replace the fuel filter at the same time. I had bought a new TPS but hadn’t gotten around to installing it yet since I wasn’t sure it would need it. I also haven’t been able to get the idle to drop all the way to 750 after warming up even after adjustment. I might just go ahead and swap them just in case. I’ll give the gas cap thing a go on my way home from shift tonight and see what happens. __________________

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