1985 Other Nissan Models LOOPING IDLE \ ENGINE SURGES

Tiny
MRKMX1
  • MEMBER
  • 1985 NISSAN
Engine Performance problem
1985 Other Nissan Models Two Wheel Drive Manual 166000 miles

I HAVE A 720 NISSAN 2.4L WITH THE 8 SPARK PLUGS. MY ISSUE IS THAT IF I SLOWLY BRING THE THROTTLE UP TO APPROX 1800 RPM FOR ABOUT 1 SEC IT WILL DROP RPM TO APPROX 1000. IT WILL KEEP DOING THIS IF PEDAL IS KEPT AT SAME 1800 RPM POSITION. STILL THERE AT IDLE AS WELL JUST VERY SUDLE. IT WILL NOT START DOING THIS UNTIL VEHICAL IS WARM, SO IF CHOKE IS OFF THERE IS NO PROBLEM. VEHICAL HAS NEW EGR, BPT, VACUUM LINES, VVT, O2 SENSOR, CAP AND ROTOR. ANY SUGGESTIONS? VERY KNOWLEGLABLE ABOUT THIS CAR SO YOU CAN BE TECHNICAL WITH ME PLEASE I JUST WANT THIS FIGURED OUT THANK YOU.
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Thursday, March 12th, 2009 AT 3:52 PM

14 Replies

Tiny
MERLIN2021
  • EXPERT
To be able to look up any specs we need the model the 2.4 is in. Get back to us!
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Saturday, March 14th, 2009 AT 8:21 AM
Tiny
MRKMX1
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1985 NISSAN MODEL 720 PICKUP TRUCK 2.4L SINGLE CAB REG BED, STANDARD SHIFT VIN IF HELPS JN6NDO1S3FW029392. CALIFORNIA MODEL. BUILT IN 01-1985 UPDATE TO RPM RANGE. RAISE TO EXACTLY 1900 RPM AND HOLD THERE FOR 1-2 SEC, AND I WILL DROP TO 1500 RPMS AND BOUNCE BACK AND FORTH BETTWEEN THE TWO. THERE IS A RYTHM TO THE FLUCTUATING IT IS VERY CONSISTANT.
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Monday, March 16th, 2009 AT 12:23 PM
Tiny
MERLIN2021
  • EXPERT
Have you checkk the BCDD? Heres how and what of it...
ARTICLE BEGINNING DESCRIPTION The Boost Controlled Deceleration Device (BCDD) is installed to control HC emissions during deceleration by reducing the engine's consumption of lubricating oil. The BCDD is mounted under the throttle chamber as an integral part. This device supplies additional air to the intake manifold to maintain manifold vacuum at proper operating pressure. OPERATION The Boost Controlled Deceleration Device (BCDD) contains 2 diaphragms. When vacuum in the intake manifold exceeds a pre-determined value, diaphragm No. 1 opens the vacuum control valve. This allows manifold vacuum into a vacuum chamber in the BCDD and actuates diaphragm No. 2. When actuated, diaphragm No. 2 opens the air control valve, allowing additional air into the manifold to maintain required operating pressure. The amount of air entering the manifold is controlled by the servo-action of the air control valve and vacuum control valve. This servo-action maintains manifold vacuum at the predetermined operating pressure. Fig. 1: BCDD System (Maxima) ADJUSTMENTS BCDD OPERATING PRESSURE 1. Turn adjusting mechanism as necessary until specified operating pressure is obtained. Turning the adjusting mechanism clockwise decreases operating pressure and counterclockwise increases pressure. 2. Turn adjusting mechanism in or out with lock spring in place. Also, always set lock spring properly to prevent changes in operating pressure. 3. After setting pressure to specification, accelerate engine and check adjustment. If lower than specified, turn adjusting mechanism until correct. 4. Accelerate engine again and check adjustment. If engine speed cannot be decreased to idle when checking BCDD operating pressure, proceed as follows: 5. Turn adjusting mechanism counterclockwise so BCDD operating pressure is .79 in. Hg higher than specification on Maxima models or .98 in. Hg higher than specification on Pickup models. 6. Turn adjusting mechanism 1/4 turn clockwise so pressure drops to specification on all models. If operating pressure cannot be observed in step 5), turn adjusting mechanism counterclockwise so BCDD operating pressure is 1.97 in. Hg higher than specification. 7. After setting pressure to specification, accelerate engine and check adjustment. If lower than specified, turn adjusting mechanism until correct. 8. Turn adjusting mechanism 1/2 turn clockwise so pressure drops to specification. If pressure cannot be adjusted, unit must be replaced as an assembly.COMPONENT TESTING BCDD OPERATING PRESSURE 1. To check pressure, engine should be at normal operating temperature, idle speed set to specifications and transmission in Neutral. Connect a tachometer to engine and a vacuum gauge to intake manifold. 2. Run the engine under no load and note vacuum reading. Increase engine speed to 3000-3500 RPM on Maxima models, or 2000 RPM on Pickup models, then quickly close the throttle. 3. Manifold vacuum should increase 23.6 in. Hg or more on Maxima models, or 24.0 in. Hg or more on Pickup models. Gradually decrease to idle level. Operating pressure should be 21.6- 23.2 in. Hg on Maxima and 23.8-24.2 in Hg. on Pickup. If pressures at idle are not to specification, proceed to ADJUSTMENTS . Fig. 2: BCDD System (Pickup)
NOTE: The BCDD operating pressure must be set to specifications after previous adjustment procedures, even if engine speed cannot be decreased to idling RPM.


http://www.2carpros.com/forum/automotive_pictures/62217_BCDD_1.jpg

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Monday, March 16th, 2009 AT 1:26 PM
Tiny
MRKMX1
  • MEMBER
I HAVE ONE OF THE NISSAN TECH MANUELS THAT THE DEALER USES. IS ONLY DISCRIBES HOW TO ADJUST ITEM BUT NOT HOW TO FIGURE OUT IF IT IS NO GOOD. ANY IDEAS?
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Saturday, March 21st, 2009 AT 12:13 PM
Tiny
MERLIN2021
  • EXPERT
Tetsing info is in my post, if it cant be adjusted and stay in proper range, it's no good. Read the bottom of the post!
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Sunday, March 22nd, 2009 AT 10:39 AM
Tiny
MRKMX1
  • MEMBER
NOT MUCH CHANGE WHILE ADJUSTING BCDD. SO I REMOVED THE BCDD UNIT ALL TOGETHER AND PLUGED THE ENTRY HOLE, AND THE ENGINE STILL HAD SAME PROBLEM NO CHANGE. ANYTHING ELSE YOU SUGGEST I TRY?
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Monday, April 6th, 2009 AT 3:19 PM
Tiny
MERLIN2021
  • EXPERT
Check for vacuum leaks and plugged exhaust, the converter may have broken up.
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Thursday, April 9th, 2009 AT 5:01 PM
Tiny
MRKMX1
  • MEMBER
Just got smog test done on vehical. Pass the test, at 15 mph recording it was lower the the average by far. However at the 25 mph recording it did great on everything but "NO". That it almost didnt pass. Max was 1153 and my truck was 1132. I asked him about the cat if it was good and he said that it was fine. What would cause such high NO I thing if I find that then it might solve my other problem.
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Friday, April 17th, 2009 AT 4:32 PM
Tiny
IDAHOGEARHEADS
  • MEMBER
MRKMX1,

I stumbled on this thread, I know it seems to be long dead but I was wondering if you ever figured out what happened with your Nissan 720. I have the clone to your truck, and it has the exact same issue!
I hope this message finds it was to you,
Thanks, Idahogearheads
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Saturday, February 11th, 2012 AT 4:59 AM
Tiny
RIVERMIKERAT
  • MEMBER
I don' think he's going to reply gearheads.
What have you done to try and fix your problem?
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Sunday, February 12th, 2012 AT 7:20 AM
Tiny
IDAHOGEARHEADS
  • MEMBER
Well, I have replaced the cap, rotor, plugs, wires, oil, set the valves and timing. I started the truck cold and verified that the ECC did not start changing the mixture via the air fuel mixture solenoid in the Carb. The truck runs better on the cold start circuit (before the computer starts to take control) after the system goes into a closed loop computer controlled mode it starts to surge. I just replaced the O2 sensor but have not tested the result yet. Given the fact that the only inputs to the computer are the O2 sensor, and the temp sensors, the only factors left would be a faulty computer or air fuel mixture solenoid. Any other good theories would be appreciated.
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Sunday, February 12th, 2012 AT 5:06 PM
Tiny
RIVERMIKERAT
  • MEMBER
It could also be a faulty temp sensor. Low fuel pressure (runs better in cold start than closed loop; cold start increases the amount of fuel).
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Sunday, February 12th, 2012 AT 8:40 PM
Tiny
PHULKRUM
  • MEMBER
Have the same issue. Poped up one month prior to me having the engine rebuilt, long story short. This issue is still remaining, though I have passed smog this looping issue is driveing me nuts and giving me whiplash. Lolz
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Wednesday, April 11th, 2012 AT 11:47 PM
Tiny
RIVERMIKERAT
  • MEMBER
Vacuum leaks. Fuel pressure. If carbureted, check needle seat and float valve. Check for play in throttle shafts. If injected, try injector cleaner. Check fuel pressure.

And check the rest of the thread for ideas.
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Thursday, April 12th, 2012 AT 12:25 AM

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