83 280ZX accelerating problem

[jmw_man]

So, as mentioned in another thread (http://www.classiczcars.com/topic/50200-83-280zx-wont-start-wont-fire-just-turns-over/page-4), my Z is doing something weird. I recently had intermittent starting problems and I finally purchased a rebuilt Cardone distributor from Rockauto.com. So far so good it seems to be starting, but I noticed it started accelerating weird.

 

First off, what I experience while the engine is "warming up" is largely different from what I experience after the engine is hot. The below is confirmed as it's happened to me twice.

 

While the engine is warming up:

At idle, if I press the gas pedal, the RPMs move up fairly smoothly (as smoothly as they could for a 32 year old car). When I put her into 1st, the car has slow acceleration before hitting 2000 RPM. As I approach 2000 RPM I notice the needle kinda bounces up and down a tiny bit, but once I get over 2000 RPM, everything smooths out real nice and all of a sudden I get a huge burst of torque and get pinned to my seat. Amazing acceleration at 2000+ RPM. I will admit though, this Z car has ALWAYS felt like it had low torque plus some hesitation at lower RPMs, it just almost seems exaggerated now.

 

While the engine is hot:

So here's the dilemma, once the engine get's hot, it's a different story. I feel like I'm going to break something if I push it to hard to get past 2000 RPM. Heck, even 1500 RPM is impossible to pass at this point. It's really weird, I hear noises that sound like gargling and I also hear a lot of throaty noises coming from the rear coupled with some pops here and there. Maybe it's backfiring or something but they sound faint and frequent when I gas it to accelerate. If I throw it in 5th gear and just cruise it's fine, it's just when I try to get past 1500 RPM. edit: Oh, I forgot to add, when the engine is hot, even sitting in park the engine won't get past 1500 RPM and I still hear the popping/throaty/gargling noises.

 

I'm not really sure where to start to troubleshoot. I have the FSM but I don't really see a section that could help me. Any pointers?

Edited April 20, 2015 by jmw_man

[jmw_man]

You know, everywhere I look in other posts I see people mentioning "the bible" and I keep thinking they are referring to the FSM. Then I finally saw a post where someone separated the two out. There's the bible, and then there's the FSM. I've had the FSM for a number of years now but I reviewed "the bible" for the first time last night (also called the Electronic Fuel Injection (EFI) Guide). First off, let me point out that there are two download links at Xenon130, the second larger one doesn't seem to work for me. The first one is the one that works for me but it says that it's for the "earlier" model 280Z/ZX car so I'm not sure if much has changed between the info in that one and my 83 280ZX. Anyways, I reviewed it last night, and I got to say, while experiencing my new acceleration problem, I've been ready to blame the new remanufactured Cardone distributor I bought through Rockauto but after digging around in the EFI manual I'm ready to move on to other culprits. 

 

My problem with the acceleration occurs when the engine gets hot. This leads me to believe that it's something electrical in the engine compartment (which is why it was easy to blame the distributor) but when I reviewed the EFI manual, it never pointed in that direction. In fact, it looks like it's pointing me towards the AFM or the injectors. I do have an injector leak so I think I'm going to go ahead and replace them. Are there a specific set that you guys recommend for injectors?

[siteunseen]

I've been happy with the Standard FJ707Ts I put in my '77 a few years ago.  The original ones had cracked at the pintle end going into the intake manifold.  The 707Ts are designed different so that can't happen again.

 

A couple of hours cleaning all of your electrical contacts and grounds is a good start and doesn't cost much.  If the ground isn't good the electrical part will overheat.  Here's a look at the Zs, http://atlanticz.ca/zclub/techtips/electricalconnections/index.html

More information, http://atlanticz.ca/index.php/tech-tips.html

 

You're going to need to pull the plugs and see how they look, it's like blood work to a doctor, they'll show a lot about how the car is running.  Borrow a vacuum gauge from an auto parts store, post the results.  Also you need to know your fuel pressure so finding a gauge to borrow or buy would help.  Lowes hardware has one that goes on a swimming pool filter that'll work for about $10 bucks.  Your pressure should be around 30psi so make sure the gauge is for high pressure, usually 0 to 50psi. 

[Zed Head]

One problem people new to cars have is terminology, not enough words in their brains to convey the message.  Reading back through your post I think what you might be describing is a "lean" fuel air mixture.  Not enough fuel for the quantity of air entering the engine.  It's controlled by the AFM vane position, so will be tied to engine RPM.  

 

But, before you go crazy on the AFM, one cheap thing you can try, that might be enough, is to add resistance to the coolant temperature sensor circuit.  It's fixed the problem for many of us here, and it's pretty simple.  You can either buy a few resistors and wire them in or get a cheap potentiometer (volume control) from Radio Shack and use it as adjustable resistance.

 

The sensor has a bullet connector on each wire coming and going to the ECU.  Put a male and female bullet on your resistor, find one of those connections, and slip it in there.  If "lean" is the problem, a little bit of extra resistance will have immediate effect.  If it does, you can focus on fuel supply - fuel pressure, clogged injectors, bad AFM, etc.  At least it wil give you a better focus.

 

And the second "Bible" is really the one you want.  It might be available from another web site somewhere, or maybe you can find a way to get it on a thumb drive or something.  It covers the ZX's.

 

http://www.xenons130.com/reference.html

[siteunseen]

That second link I posted has all the info on adding a potentiometer to your coolant temp sensor. Look under "EFI & FUEL"

Mine was lean so I added the volume knob from Radio Shack and it fixed mine but it did it at all temperatures, cold and hot.

Is your accordion rubber boot in good shape? If it's cracked you'll have unmetered air going in the throttle body, maybe making the gargle and popping sound, a vacuum leak.

Put a vacuum gauge on it.

Have you checked the Throttle Position Switch? It could be out of adjustment or damp inside. You can pop the cover off and roll the throttle rod to see if it comes off low speed contact as you go up in the RPMs, then at high RPMs it should contact the opposite side.

I'll quit now, don't mean to throw too much at you all at once and it's beautiful outside.

Can't stop, sorry. If it gets worse when it's warmed up it be the cold start valve is stuck open dumping fuel in the intake. Unplug it and see if it still does it.

Edited April 22, 2015 by siteunseen

[jmw_man]

 Look under "EFI & FUEL"

I think you meant cooling system. Correct me if I'm wrong.

 

Oh and Radio Shack went out of business didn't they? Is there another option other than Fry's Electronics, .

 

Can't stop, sorry. If it gets worse when it's warmed up it be the cold start valve is stuck open dumping fuel in the intake. Unplug it and see if it still does it.

When you say unplug it, you are saying to unplug the connector right? I tried that, I drove around with the connector unplugged and there was no change. BUT, that doesn't mean it's not stuck open right? I did a power check, get's power when you crank it over and not all other times but that still doesn't mean it's not dumping fuel.

 

 

Have you checked the Throttle Position Switch? It could be out of adjustment or damp inside. You can pop the cover off and roll the throttle rod to see if it comes off low speed contact as you go up in the RPMs, then at high RPMs it should contact the opposite side.

I'm not sure the cover comes off. It felt like the bottom edge of the cover unclipped or popped off or whatever but the top part is still physically connected to the connector pins. I feel like if I pry it off any further it's going to break.

 

One problem people new to cars have is terminology, not enough words in their brains to convey the message.  Reading back through your post I think what you might be describing is a "lean" fuel air mixture.  Not enough fuel for the quantity of air entering the engine.  It's controlled by the AFM vane position, so will be tied to engine RPM.  

 

But, before you go crazy on the AFM, one cheap thing you can try, that might be enough, is to add resistance to the coolant temperature sensor circuit.  It's fixed the problem for many of us here, and it's pretty simple.  You can either buy a few resistors and wire them in or get a cheap potentiometer (volume control) from Radio Shack and use it as adjustable resistance.

 

The sensor has a bullet connector on each wire coming and going to the ECU.  Put a male and female bullet on your resistor, find one of those connections, and slip it in there.  If "lean" is the problem, a little bit of extra resistance will have immediate effect.  If it does, you can focus on fuel supply - fuel pressure, clogged injectors, bad AFM, etc.  At least it wil give you a better focus.

 

 

Inspecting the AFM would have been my next step but I'll try adding resistance to the coolant temperature sensor circuit first. When you say add resistance though, how much are we talking? 20 ohms? 200 ohms? etc?

 

Edit: Nevermind on that question. Went to Fuel Tweaker as you mentioned below and saw that they used a 1k potentiometer.

 

 

 

 

I've been happy with the Standard FJ707Ts I put in my '77 a few years ago.  The original ones had cracked at the pintle end going into the intake manifold.  The 707Ts are designed different so that can't happen again.

 

A couple of hours cleaning all of your electrical contacts and grounds is a good start and doesn't cost much.  If the ground isn't good the electrical part will overheat.  Here's a look at the Zs, http://atlanticz.ca/zclub/techtips/electricalconnections/index.html

More information, http://atlanticz.ca/index.php/tech-tips.html

 

You're going to need to pull the plugs and see how they look, it's like blood work to a doctor, they'll show a lot about how the car is running.  Borrow a vacuum gauge from an auto parts store, post the results.  Also you need to know your fuel pressure so finding a gauge to borrow or buy would help.  Lowes hardware has one that goes on a swimming pool filter that'll work for about $10 bucks.  Your pressure should be around 30psi so make sure the gauge is for high pressure, usually 0 to 50psi. 

 

 

Yea, I saw how expensive replacing injectors is going to be. I think I'm going to hold off until the current problem is fixed. Heck, I don't even know if they need to be replaced.

 

I spent a lot of time last summer and prior doing work on the Z, replacing ignition components including the plugs (they probably have 300 miles on them, and they probably have 10 miles on them while driving in the current condition. I'm not sure pulling the plugs will tell me much because of that.

 

I also did a CRAP load of tests on the car in the last couple years. Two years ago it all started with tracking down what was draining the battery. Turned out to be a part to an alarm system. I've clean so many electrical connectors with my electrical contact cleaner (although, there's still discoloration, and it seems like some connectors could technically be too loose but I'm a bad judge of what might be considered too loose), I've tested vacuum and fuel pressure. I've checked resistances and battery voltages at the ECU. Everything I tested always tested good. I've also invested probably close to a grand in testing equipment already.

 

There's a gremlin in my car...

 

 

 

The sensor has a bullet connector on each wire coming and going to the ECU.  Put a male and female bullet on your resistor, find one of those connections, and slip it in there.  If "lean" is the problem, a little bit of extra resistance will have immediate effect.  If it does, you can focus on fuel supply - fuel pressure, clogged injectors, bad AFM, etc.  At least it wil give you a better focus.

 

 

It turns out my water temperature sensor doesn't have the bullet connectors near the sensor. Going from the sensor, it immediately enters the harness. I didn't look at where it comes back out of the harness near the ECU yet. I'm a little hesitant about cutting anything to add a potentiometer in there. I know it's only temporary as you said because it would help us pinpoint my problem. I guess it doesn't really matter. If I find time to run across town, I'll purchase one and will go from there.

Edited April 23, 2015 by jmw_man

[Zed Head]

Click a few times.  It's called "Fuel Tweaker". 

 

Radio Shack restructured, but didn't liquidate.  Dallas is probably big enough to support one.

 

 

How's that for "dead"?

[jmw_man]

I did pull the cover off the AFM, there's no binding that I could see or feel inside the AFM. To my untrained eye it appears to be operating as it should.

 

Tomorrow I'm going to check the water temperature sensor resistance at the ECU. I'm also going to check for continuity on the throttle position switch. I wonder about not being able to pull the cover off the throttle position switch. could that be common with some aftermarket TPS's? I'll have to take a second look at this.

[Zed Head]

Sorry, I got my years mixed up (again).  Your engine has a cylinder head temperature sensor (CHTS), in place of the coolant temperature sensor used on the 280Z's.  It's on the right side of the engine, above the spark plugs, between 5 and 6 I believe.  Same style of connector, and you should fine the bullet connectors, I think.

 

As site said, a vacuum leak after the AFM would cause a lean condition also.  Easier to find and fix that, if that's the case.  Even the PCV system, the hose underneath the intake or the one from the valve cover, can cause a lean condition if it leaks.

[jmw_man]

Number 5 spark plug wire isn't transmitting a spark above 2000 rpm while engine is hot.

[Zed Head]

Number 5 spark plug wire isn't transmitting a spark above 2000 rpm while engine is hot.

Doesn't really fit your acceleration weirdness, does it?  No pickup from idle to 2000 RPM with six sparks, and awesome acceleration after 2000 with five?

 

You're testing for spark with a timing light or tester of some kind?

[jmw_man]

Doesn't really fit your acceleration weirdness, does it?  No pickup from idle to 2000 RPM with six sparks, and awesome acceleration after 2000 with five?

 

You're testing for spark with a timing light or tester of some kind?

 

Timing light.

 

Like I said, the awesome acceleration after 2000 rpm only occurred before the engine got hot. The number 5 quits when the engine gets hot.