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87 d21 automatic 2wd


Dansun

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Got the truck about a couple weeks ago with the problem, the transmission, when at high RPMs will just hit the limiter and not shift until I let off the throttle. I wanted to swap it with a manual transmission but that’s a project for the future. I was just seeing if anyone had a suggestion on what the problem is before I send it to a mechanic. It also sputters after it goes down in rpm when at idle and sometimes when in drive. Thanks 

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Just now, datzenmike said:

What about part throttle? Does it up shift by itself?

Yeah shifts perfectly when just giving 1/4 of throttle, as soon as I wanna pull out or make a lane change using more than that it just hits limiter until I let off of it

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On the driver's side is a vacuum modulator diaphragm. It's job is to sense engine load via a vacuum hose connection to the engine's intake. Engine vacuum is low under load and higher at cruise and slowing down. A low vacuum signal will be interpreted as having the gas pedal floored and will delay the up shift. It's the thing in the middle but will have a rubber hose elbow  to the center of it connected to a metal line to another hose at the intake manifold. Make sure the hoses are not split, cracked or disconnected. This is a bit of a guess.

Modulator with kick down solenoid to the right.

lzlhkbd.jpg

 

Here is a similar set up with the vacuum diaphragm and the solenoid. You can see the metal vacuum line up to the engine. Yours won't be exactly the same...

 

2DwxAGo.jpg

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34 minutes ago, datzenmike said:

On the driver's side is a vacuum modulator diaphragm. It's job is to sense engine load via a vacuum hose connection to the engine's intake. Engine vacuum is low under load and higher at cruise and slowing down. A low vacuum signal will be interpreted as having the gas pedal floored and will delay the up shift. It's the thing in the middle but will have a rubber hose elbow  to the center of it connected to a metal line to another hose at the intake manifold. Make sure the hoses are not split, cracked or disconnected. This is a bit of a guess.

Modulator with kick down solenoid to the right.

lzlhkbd.jpg

 

Here is a similar set up with the vacuum diaphragm and the solenoid. You can see the metal vacuum line up to the engine. Yours won't be exactly the same...

 

2DwxAGo.jpg

Alright I’ll check this out tomorrow, appreciate the detailed information. 

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If a Z24i an L4N71B if a VG30i an E4N71B, I think. From '89 on a re designed automatic was used which again, I think, used some electronic controls that integrated it into the emissions system. It moved the shift points around or prevented them in order to reduce emissions.

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1 minute ago, datzenmike said:

If a Z24i an L4N71B if a VG30i an E4N71B, I think. From '89 on a re designed automatic was used which again, I think, used some electronic controls that integrated it into the emissions system. It moved the shift points around or prevented them in order to reduce emissions.

http://www.usatransdoctor.com/foreignnissan.htm described the issue perfectly, so like you said it’s most likely going to be that modulator 

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15 hours ago, datzenmike said:

Just for fun tomorrow, with the ignition OFF push down on the gas pedal slowly with your hand till it hits the floor. Just before it does you should hear a click from the 'kick down switch'.

Ok I did and it clicked just as you said 

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12 minutes ago, Dansun said:

Also I can’t find the modulator you’re talking about on the drivers side. Is it under the truck?

When I got the truck they had some foil on the EGR line that’s on the exhaust manifold going to the egr valve, I took it off and there’s some exhaust leaking out when I give it gas. You think this could be a problem that’s assisting in the transmission not shifting properly?

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Won't affect the automatic.

 

I would either replace that pipe or remove it and seal the manifold, then disconnect the hose to the EGR valve.

 

 

 

The modulator should be on the driver's side just above the oil pan. Maybe take a picture of that side and post it. Yours is the last year for this transmission.

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3 hours ago, Dansun said:

Ok I did and it clicked just as you said

3 minutes ago, datzenmike said:

Won't affect the automatic.

 

I would either replace that pipe or remove it and seal the manifold, then disconnect the hose to the EGR valve.

 

 

 

The modulator should be on the driver's side just above the oil pan. Maybe take a picture of that side and post it. Yours is the last year for this transmission.

I’m on a iPhone, how would I attach an image on here?

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On 3/10/2019 at 6:27 PM, datzenmike said:

No idea. Usually download to a picture hosting site copy the picture information and bring here and paste.

Mike after I get this trans modulator, I was looking at the Dorman exhaust header, would you recommend something else?

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