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Old 12-24-2019, 03:07 PM   #1
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Default bucking @ 2000 rpm only

hi im new to the forums and honestly new to nissans. im trying to keep this pickup alive from neglect of previous owner. its a 1987 king cab D21 pickup with the 2.4 and 5 speed. the truck seems to only buck at 2k rpm. if you power through it it goes away. if youre on the highway it doesnt do it or accelerating it doesnt do it. just seems to be while cruising around 2k. the truck has new fuel pump about 50 miles ago along with new fuel filter and air filter. the truck seems to have alot of vacuum lines capped off which after reading some of your forum pages is common with deleting emissions. the truck runs great down the highway and starts right up and idles great. which is why id love to get this problem sorted out and fixed because its such a good pickup compared to my 99 gmc 2500 454. i am mechanically inclined but due to alot of these parts not being held at my local parts store id like to have atleast a direction to take to try and solve this problem. im guessing with the electric fuel pump that the truck is some what of a fuel injected engine. thanks for any advice in advance.
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Old 12-26-2019, 12:50 AM   #2
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Check the ECM for stored trouble codes. See what that says. It wont hurt to unplug the throttle position sensor harness and the MAF harness. The connections are known to corrode and cause all types of drivability problems.
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Old 12-26-2019, 02:37 AM   #3
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thank you i will try that tomorrow and see what i find. so far ive never seen a check engine light come on. appreciate the direction.
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Old 12-26-2019, 03:02 AM   #4
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The 87 doesnt have one. I have an 87....it is a toggle switch. You have to pull the seat out. The ecm is under the passenger side. Bench or bucket seats are held in with 4 bolts.
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Old 05-07-2020, 04:47 PM   #5
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im having the same issue. idle-good, acceleration-good. 2000 rpms-no good. when i sit at idle and rev up to 2000 slowly it hunts/pulsates/bounces the RPM around. if i dont sit there at 2000 im good. i read on here before to swap out the ECU but it didnt help. i have tried the MAF cleaner with no change. i really hope i can find someting on here cause i continue to search. any help would be greatly appreciated.
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Old 05-07-2020, 08:21 PM   #6
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On my '90 KA24E, a failing fuel injector would only become apparent while accelerating through about 2300 RPM.


If not done already, first do a tune up (plugs, wires, cap/rotor, timing), replace the fuel and air filters, the PCV valve, the upstream O2 sensor, and maybe the EGR valve. And do a smoke test for vacuum leaks.
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Old 05-07-2020, 08:31 PM   #7
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A sticking, or slow to react, EGR valve can cause this. I had a similar issue on my new truck and after capping off the valve itself (and the control solenoid of course) I have not had any more issues. Truck runs fine, screw the polar bears.
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Old 05-08-2020, 02:15 AM   #8
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Anyone having engine issues in the 2000 to 2500 RPM range should check their codes.

The Service Manuals state that Fail Safe Mode (i.e. Limp Mode) is indicated by difficulty in the 2200 to 2400 RPM range, but the tachometers on these trucks are not guaranteed to be that accurate.

If there are no codes, trucks older than 1992 or so should look into this thread:

FIX: erratic idle, low speed driveability, possibly more
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Old 05-08-2020, 11:17 AM   #9
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JP, i checked my codes and what i get is P1130 and P1400. ive had this problem since i bought it. i recently just did the DOHC Frontier engine swap and i have deleted the EGR system and all the extra unknown vacuum lines. the only vacuum remaining is the fuel reg and brake booster. she runs just like before but now with one more cam! she isnt the quietest timing is alittle off and im still trying to understand that. thought i was off a tooth but idk. maybe i can get a video up on youtube and link it here so you and the others can see my problem. where in the FSM does it state "limp mode" and why would it only limp at roughly 2000 rpms? how do you get it out of "limp mode"?
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Old 05-08-2020, 05:09 PM   #10
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Fail-Safe mode is detailed in EC-76.

For the MAF error P0100, it says engine speed will not rise over 2400 RPM due to fuel cutoff. Further down on the same page, it says the ECM will not rise above 3000 RPM.



The ECM behaves slightly differently with the different years of Hardbody trucks. I didn't comb through the entire 1997 service manual, so there could be something else that causes a specific 2000 RPM issue or the bucking at that speed could be the onset of it preventing the engine from reaching 3000 RPM.

P1130 is for the Swirl Control Valve, EC-243
P1400 is for the EGR System, EC-176

As shown in the image below, the EGR system and the Swirl Control Valve work together and rely on the vacuum hoses.



I'm not saying you should never do that, but you should consider making the engine work without the ECM if you are going to eliminate systems that the ECM uses to control fuel pulses to the fuel injectors.
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