Hesitation during acceleration

[rcb280z]

Yeah and good luck on your search. Mine is plugged off because I can't find a replacement. Was hoping to find a new one, maybe universal. After plugging off my advance canister I no longer have a hesitation. I assumed it was my problem. Maybe not?

I used a vacuum pump to determine mine was bad, would not hold vacuum. As a matter of fact I remember saying, "thats my problem" because of how fast it leaked down. That is the reason I assumed it was my problem.

[rcb280z]

4 minutes ago, Zed Head said:

A little work with a timing light would be illuminating.

Actually a good idea

[Captain Obvious]

4 hours ago, siteunseen said:

I couldn't see it because Photobucket SUCKS.

What he said!!! 

[rcb280z]

And I don't claim to be an expert, thats for sure. Some people on this site are definitely much more knowledgeable than I, or at least I feel they are. I'm still learning.

Edited December 28, 2017 by rcb280z

[Zed Head]

1 minute ago, rcb280z said:

And I don't claim to be an expert, thats for sure. Some people on this site are definitely much more knowledgeable than I, or at least I feel they are. I'm still learning.

Everyone has their own way of problem-solving.  Getting things back to factory settings is always a good way to start.  I suggested the fuel tweak as an "in the mean-time" test.  It's completely reversible, and/or you can just set the potentiometer to zero resistance.

Besides that, we need something to discuss while he's waiting for the canister.

[rcb280z]

So actually, the "pot" really is only for "lean" conditions? To "en-rich" the system so to speak?

[DC871F]

At work, I work overseas, so nothing new to add. My advance doesn't move period, its like sucking on a soda straw, just air.

I'll plug it at first chance to see if there's a change. Resistor will be here next week. May be able to get to the car Thursday, maybe.....

 

[Captain Obvious]

11 hours ago, rcb280z said:

So actually, the "pot" really is only for "lean" conditions? To "en-rich" the system so to speak?

Yes, adding resistance to the temp sensor(s) adds fuel.  It's easy to add fuel. It's more difficult to reduce it.

@DC871F  So there is a lot of help already being provided here and I'm not going to get in the middle of that, but I would like some clarity about the problem being chased. The original problem was described as "hesitation during acceleration. Runs fine at highway speeds and intermediate speeds other than acceleration."

So what does "acceleration" mean? Are you talking "normal gradual speed increase up to a typical cruising speed", or are you talking "I put my foot hard into it and it sputters at or near wide open throttle?"

Reason I ask is that (as Zed Head alluded to earlier) the distributor advance signal is a port vacuum source and only exists at cruising pedal positions. At idle and at WOT, there is no vacuum presented to the distributor. If the problem is at WOT, it sounds more like a TPS or fuel pressure issue (fuel pump or a dirty filter(s) or plugged lines). Yes, you need to get your vacuum advance fixed, but that small vacuum leak should not have much of an effect on anything beyond cruising gas pedal position.

Oh well... So much for not getting involved.  

[DC871F]

2 hours ago, Captain Obvious said:

Yes, adding resistance to the temp sensor(s) adds fuel.  It's easy to add fuel. It's more difficult to reduce it.

@DC871F  So there is a lot of help already being provided here and I'm not going to get in the middle of that, but I would like some clarity about the problem being chased. The original problem was described as "hesitation during acceleration. Runs fine at highway speeds and intermediate speeds other than acceleration."

So what does "acceleration" mean? Are you talking "normal gradual speed increase up to a typical cruising speed", or are you talking "I put my foot hard into it and it sputters at or near wide open throttle?"

Reason I ask is that (as Zed Head alluded to earlier) the distributor advance signal is a port vacuum source and only exists at cruising pedal positions. At idle and at WOT, there is no vacuum presented to the distributor. If the problem is at WOT, it sounds more like a TPS or fuel pressure issue (fuel pump or a dirty filter(s) or plugged lines). Yes, you need to get your vacuum advance fixed, but that small vacuum leak should not have much of an effect on anything beyond cruising gas pedal position.

Oh well... So much for not getting involved.  

OK, so I read Zeds post about when the VA operates, and I hear what your saying. So lets talk about what the car is doing in a little more detail then. 

Starting from a red light, you accelerate normally until about high 2000's RPM an then a hesitation sets in running through each gear at around this RPM range. In 3rd, 4th gear, you can stand on the gas peddle and the car just acts as if you are disconnecting a plug wire or two, or grounding out, and will do this until you let off the gas, with anemic acceleration. New plug wires, plugs, and they are routed as to not ground out on anything, because at first thats what I thought it was. I guess I was hoping for an easy fix.

If you get on the highway, 70 MPH for example, it cruises fine.

New gas tank (NOS) from a donor car, fuel pump, filter, lines (engine bay only), fuel rail, injectors.

New EGR(manual transmission), 02 sensor, PCV, cap, rotor.

New battery, Hitachi alternator (overhauled), New belts.

I have been through the wiring harness at all the plugs around the engine hoping for some corrosion, but nothing really notable.

About 25 years ago, I had an 81NA, and it did this sort of thing but 10 times worse, and it was the AFM. I have not done anything with this car regarding the AFM. 

Thanks for all the replies.

Added a few pics, just for SAG's. Driver seat is the only thing really bad with interior, everything else was nice. A tiny hairline crack in dash, thats it.

 

Edited December 28, 2017 by DC871F

[siteunseen]

14 hours ago, rcb280z said:

So actually, the "pot" really is only for "lean" conditions? To "en-rich" the system so to speak?

The easy way to "kinda" test for lean I learned from a Nissan certified mechanic.  He put some taped up vise grips on the return line to build more pressure and my car ran better.  He didn't know about the "tweak" and said I needed a new FPR or pump or injectors...blah, blah, blah.

$5 dollars at Radio Shack and 30 minutes later it ran better than ever.

But I would think, just for smog test not everyday driving, you could lean one out the same as make one richer.  I know I played with mine for months while driving.  I could change the Temp, gas mileage and how it ran up top and from take off.  It was fun for awhile. 

[DC871F]

Plugged advance inlet, cleaned TPS connection. No change.

I go back through the fuel system and I'll start looking at the FSM for testing components.

Thanks guys.

[madkaw]

might think about putting a fuel pressure gauge on there to see what’s going on . I had a zxt that was giving me a fits and it was a clogged return line. Showed almost 100 psi at one point - don’t know how things didn’t explode -