I just bought some Throttle Body Linkage Spacers and Shims from Z1 for my 1990 300zx NA because I was told by Z1 that could be causing my hesitation issues that I've been having.

I have already replaced the TPS and set it to .45 volts at idle but it still hesitates (injectors are also good and ECU reads code 55). The hesitation occurs when I jab the throttle suddenly, but when I ease on the throttle, it drives fine. The hesitation seems like it is being caused by something involving the throttle bodies because when I reset the TPS by unplugging it for 7 seconds, the car drives good for a short time.

I was wondering if anybody knew exactly how to install the Throttle Body Linkage Spacers and Shims and what is required to be done? And if anyone has any idea of what else could cause my hesitation please let me know.

Here is the link for the Throttle Body Linkage Spacers and Shims that I bought from Z1:
http://www.z1motorsports.com/product...oducts_id=4432

 

Who am I to dis Z1.. they have seen more Cars than I have.. Now that 'That' is out of the way....!!

Don't do it.. !..

You are Causing Problems, to try and Fix problems.. Not a good Idea.. Fix the problem First.. Then Modify..

Go to the Root of the Problem First..

When you Jab the Throttle, the Air Rushes into Intake Manifold before the Air Flow Sensor has time to react ( as the Air between the Air Flow Sensor, and the T-Bodies will drop in pressure for a Bit ).. then the Fuel Pressure Regulator must vent it's MAP line back into the Intake, to allow the Fuel Pressure to Rise.. Then the Fuel Pressure will start to Swell the Rubber Lines, and Compress any Vapor Pockets in the Fuel System, then the Fuel Pressure can Start Rising.. then the ECU has done a Few Calculations to send Sigs to the Injectors to start Injecting More Fuel..


I think you have a Problem with the Vac Lines being Old/Pinched on the Fuel Pressure Regulators, or a 'Slightly Weak' Fuel Pump that it not Delevering Full Flow that will Raise the Fuel Pressure Fast Enough..

But then.. I've only touched 3 z's In my Life.. So what do I know..

Cap

 

Thanks for your reply. Wouldn't it make sense that something was wrong with the throttle system around the TPS because when I reset it (unplug it for 7 seconds), it runs fine for a little? Also the TPS changes the voltage reading by itself from when I set it to .45 to around .23 . When I tried to set it back to .45, the idle switch turns off and the engine revs to about 2k rpms.

Are there other distinct signs that can tell you that the fuel pump is going bad? I hear a buzzing sound on the drivers side underneath the car when I turn it off. Not sure if that could be related to it.

 

I'd like you to try the 'Reset' of the TPS when the Car is Hot..

If the Reset of ECU/TPS works when all is hot, then I'd say it's NOT the Fuel System..

Try it and post back.. Hot..

Cap

 

When I reset the TPS the engine is always hot. It will drive fine for a short time when I reset but shortly after it starts to act up again.

 

Hmmm..

That is a Learned bad Behavior..

I'm not that Familiar with the Nissan ECU's.. So I'm learning these as well..

Unless someone with a Better Idea comes along, I'd change the O2 Sensors.. as they are used in the 'Feedback Loop' part of the learning process..

I do know that my 300 ( 95 NA ) performed Much better off the line, after the O2's were changed at 180K Miles.. they were still factory Org.. and did not give any particular problems, but we were dragging at straws trying to get it to idle better..

That part worked.. for us.. not sure about yours..

Cap

 

Could this be a Knock Response?..

Not sure how the TPS 'Reset' would do/undo a Knock Reaction or Ignition Advance Change..

Cap

 

How is your timing? If its set correctly, take your CAS off and see if the teeth are worn on the CAS and the cam.

 

timing is good right at 15 or 16. is it tough to take off the CAS? it does seem like it's related to timing but would the CAS explain my hesitation?

 

I advanced the timing a little bit and my car seems to be running a lot better. No more hesitation. I guess my car had that CAS recall or whatever in the earlier engines.

 

I'd like to know where you ended up with the Timing..

Cap