My Z bucks like a bronco???

[Guest Anonymous]

Hello all of you fellow Z owners!

 

I have a 1983 280zx in mint condition and has been garage kept it's entire life.

But I am having only one problem.

 

Here is the problem before I start rambling.

In high heat (meaning if its hot outside) or the engine is very hot and also when it is low on gas it starts to buck like wild horse. If it is cool outside or the engine is cooling nicely and it has $10.00 worth of gas in it then there are absolutely no problems. The two are independent sometimes. If the car is hot and has a full tank then I get the problem. Also if the car is cool but the gas is sorta low then I get the bronco horse but not as bad as the heat. If its both then forget it I will be sitting on the side of the road waiting for it to cool down and keep doing this until I get to a gas station and fill it up and let it cool all the way down. It also seems to have terrible gas milage.

 

The worst is the heat. It happened last year about this same time. I went to Vegas and it did it all the way there and back. IT SUCKED. Luckily most of the time I was able to get to a town or something and sit in a bar for two or three hours while it cooled...

 

Thing is the car isn't overheating in the sense the temperature isn't in the red. Its at it's normal hot operating temp and no higher so I know the cooling system is working properly.

The symptoms are like low gas or something. The engine just cuts in and out. Sometime I can downshift and run high rpms and that will get me a little further down the road.

 

Could this be the oxygen sensor. I read in my manual that this sensor needs to be replaced every 30,000 miles no matter what. In my car I bet its only been changed once.

 

Anyway any help from anyone would be great. It sucks being stuck on the road in 90 + degree weather and have to wait until you car cools to drive it. If I don't do something soon I won't have any U joints or a tranny left.

[Pop N Wood]

Fuel delivery problem.

 

I will bet my left nut.

 

You either have a weak fuel pump, clogged fuel filter or some other restriction.

 

With a full tank you have a nice pressure head at the inlet to the pump. As the take gets low, the inlet pressure drops and the pump is not capable of making it up. When the engine and/or fuel heat up, the pump doesn't work as well (maybe starts to vapor lock?) and it becomes even less tolerant of a low tank.

[Tim240z]

Could also be fuel percolation/vapor lock. With a fuel tank full, the fuel is likely staying cool enough (I'm assuming this is a FI stock I6), but when it's hot the underhood temps are heating up the fuel lines. Try (if the above suggestions don't work), either rerouting your lines away from the heat or wrapping them in heat shielding.

Shot in the dark, but something to think about.

Tim

[Guest Anonymous]

I'll pass on betting a nut I may still need them, but I'd vote maybe vapor lock as well, check to make sure the line is not close to any exhaust or heat sources. A fuel pressure gauge in the car might also let you know whats going on. Thats a sucky thing for the car to do, I'm sure its no fun rattling your brains out when it does it. Fuel problems suck. Good luck finding it.

 

Regards,

 

Lone

[Guest Anonymous]

OK. Now I have my temp gauge working thanks to Wayne.

 

I was wondering where to check the vacuum pressure at. I can't seem to find it in the book. Does anyone know all the points to check the vacuum pressure? Also what the limits are supposed to be at? If it is in the Hayes manual or chilton manual then can ya give me a page number. I can't seem to find it but know it has to be in there somewhere.

 

Could my probs listed in my first listing be my EGR valve? I did what it stated in the manual on how to check it and it seemed to do just fine. I also noticed that the manual has a heat shield under the EGR in the picture. Mine does not. Could this be the prob.

 

After I check the vacuum pressure and it turns out OK I am gong to check my fuel pump pressure. I can't help think that it has to be a fuel problems or maybe the fuel pressure regulator is bad.

 

I have been doing some driving around and it seems to have problems only AND I DO MEEN ONLY! when it is under load with a real low tank of gas or the engine is at a high temp. This would tell me that if it was a outside temp or engine temp then i would think it to be the AFM air temp sensor. But I don't believe that it is the AFM for the fact that if it was it would do it more often or all the time. It wouldn't have anything to do with a low tank of gas or a load. If it was just under load then I could maybe think it was the fuel pump or something with that system. But with both heat and low gas / load happening its hard to tell.

 

So I can only guess and think that it is the fuel pump that is the culprit. I come to this conclusion because when it is under load and the gas is low then the pump has to work harder to pump the fuel out of the gastank. When it is hot out or the car is very hot, I should say. Then the pump over heats and has to work hard again.

 

One of the tests I tried was putting cool gas in it:

I drove the car out to the dessert on about 3g of gas. Once it got a tad above normal operating temp then it started its bucking bronco crap so I pulled over. While pulled over I even let it get hotter by revving the engine while it sputtered and grumbled. I also turned on the air conditioning. After I turned off the air and revved a few more times I noticed the clicking behind the glove box again. It died probably 5 times in about 30 minutes during of all of this. Anyway It was pretty hot. I then put in about 2.5g of gas that I had in a gas can in the back. Right after that I tried to create the same thing by driving around the area and NOTHING. I drove it all the way home without a sputter. STRANGE HUH?

 

Well, that is my theory anyhooooo..... I will check the fuel pressure tomorrow and if its bad then I will replace it and hope that solves my problems. If the pressure is good I will probably change the fuel pressure regulator first.... UNLESS ANYONE AS ANY BETTER IDEAs, SUGGESTIONS or OBJECTIONS??????

 

THANKS

 

P.S. I am starting to be the Z. hummmmmmmmmmmmmm

[Mike kZ]

Are you sure you don't have dirt or rust in the tank? It sounds like the pickup is getting clogged, and when you put new gas in, it moves everything around in there, clearing the pickup.

[Guest Anonymous]

I pulled the sending unit out of the top of the tank and looked at it and inside the tank and saw nothing. Not even little particals at the bottom. Infact it looked brand spanking new. I also checked the filter on the end of the sending unit and it was like new alos. Is that what you were talking about when you said PICKUP?

[Mike kZ]

Ya, that's what I meant by pickup. Well if the tank is that clean, I would say your electric fuel pump is at fault. It sounds like it's overheating, and when you add cool gas, it keeps the pump cool for a while. Your regulator shouldn't make a differnce hot or cold. It's just a diafram. Now vacuum to the regulator(if yours has vacuum), or a pin hole leak in it could cause problems, but my guess is the pump.

[Lockjaw]

A couple of things. First, you do need a fuel pressure guage to see what is happening, or an air fuel ratio monitor.

 

I would check the little filter on the inlet to the fuel pump. That could be clogged. The other thing I would do is disconnect the factory ground wire on the pump, make your own wire, find a spot to connect it, and make sure you scuff up the metal there so it gets a good contact.

 

I cannot rememeber if the ZX's control fuel flow thru ground or positve, i think it is ground.

 

A Zx with a clean tank should have no problem running around with low fuel in the tank.

 

I can't remember if you said you replaced your fuel filter up by the engine, but I would replace it if you haven't.

 

I have heard of people having vapor lock problems with ZX's, but I have not ever personally experienced any with my ZXT, although I do have a much stouter pump than stock. with a stock fuel rail.

 

Also, how about checking your fan clutch to make sure it is in good shape. When the car is cold, and you start it, it should couple up and pull alot of air, and then back off. As the car warms up, you should hear the fan couple back up and pull more air.Helps if you manipulate the throttle with the hood up. You can feel the fan air flow pick up and drop off. That is a long shot, but your fan clutch could be going bad.

 

Good luck and check back to tell us what is up.

[Guest Anonymous]

OK here goes. I installed a permanent fuel pressure gauge and did quite a nice job if I must say so myself. Anyhoooo, I also hooked up a vacuum gauge ($15 at auto zone). Its actually a vacuum and a fuel pressure gauge in one put the fuel pressure gauge PSI side of it only goes up to 10 PSI.. USELSS on that end of it.

 

The results were great. The fuel pressure at idle was at 30 and the vacuum was at 21. When I revved the rpms up the fuel pressure rose to 38 and the vacuum dropped almost completely. As soon as I let down the throttle they went back to were they were.

 

I also disconnected the FPR vac hose and the fuel pressure rose to about 37-38. Just like the book said it should. So as far as vac tests and fuel pressure tests every thing seems within spec.

 

So after all came out dandy. I thought I would go ahead and put a new fuel pump on and while I was at it I went ahead and changed the PCV valve. Only because I figured it was old and what the hell.

 

So here is a list of all the things I have done in order.

 

1) Pulled the sending unit and inspected it for a abnormalities, dirt, grim or deposits

Results: Looks great. Like new. Doesn't seem to be bent nor did it have any grim nor was it dirty at all.

 

2) While the sending unit was out I inspected the tank with a flash light.

Results: Looks like new. No dirt of any kind.

 

3) Removed every vacuum hose in the car and replaced it with new hose.

Results: Seemed to make no diff but they needed changed anyhooooo.

 

4) Replace rubber fuel hoses in engine compartment.

Results: None to speak of but they needed it also.

 

5) Installed a pressure gauge

Results: Now I can read my fuel pressure anytime I want. Also pressure met the specs per Haynes manual. 30 at idle and 38 at high rpm.

 

6) Test vacuum pressure with a vacuum guar.

Results: Vacuum pressure met the specs per haynes manual. 21 Hg at idle and dropped at higher rpms.

 

Note: The fuel pressure and vacuum pressure stated above were done at the same time.

 

7) Replace the fuel filter

Results: Not sure but may have been the prob

 

8) Replace the PCV valve

Results: Not sure but may have been the prob.

 

9) Put a heat shield under the EGR like in the book

Results: I gues it will keep the heat from bothering the EGR

 

So that is all I have done to the car to this point.

 

I took the car for a test drive. Well I barely made it out of the drive way. I only had a couple of lines of gas. (I have a digital dash) I assume a couple of lines is about 2 to 3 gallons of gas. NOT SURE. Luckily my local gas station is down hill from my house. So I put about $5 in the tank. The symptoms coming from my house were as follows.

 

I couldn't get any RMPs up. I could idle fine but anytime I would push on the gas it would sputter terriblely. Well after I put some gas in the same thing happened. Then I figured well I have to get it home somehow so I just decided to sputter back home. WELL, as soon as I left the gas station lot everything smoothed out slowly. But the time I got to my first light it seem to run pretty good. I just figured it must have been air in the lines for all the stuff I did to it. So I daringly told myself lets go for it. Well I took off to the dessert. It wasn't as hot today as usual but sorta hot. I drove around for about an hour. In stop and go traffic, up hills and in the heat. I down shifted, up shifted and basically gave it some hell. NOT ONE DARN BUCK NOT EVEN A SPUTTER!

 

So, I am still dumbfounded.

 

I surely don't think it was the PCV valve

I surely don't think it was the installation of a pressure gauge

I surely don't think it was the EGR heat shield.

I surely don't think it was just the fuel filter????????????

 

I guess the fuel filter seems to be the most logical. I put a couple of bottles of FI cleaner in it a while back and that was about the time I had probs. I could have swore I changed the filter when the probs started. The only reason I put the FI cleaner in the car in the first place is because the car sat in a garage for about six years and was never driven. (not me! The former owner) So I figured it needed it. Hell, the FI cleaner may have cleaned the fuel lines and made both fuel filters bad and now that I have run numerous tanks of gas threw the car and now have replaced the filter it solved the probs.

 

We will see. I will get to a lower tank of gas and take it out to the dessert on a hotter day and really test it. I just can't see that it was just the filter.

 

Next I will also check out the entire fuel pump. Filters, wires and the works.

 

If it continues then I will test the sending unit for probs. Also is there a way to adjust the fuel gauge. Meaning I may be running out of gas and the gauge is still showing I have gas. Also I used to get an audible womans voice when I was running low on gas. Now I don't????? Maybe she is mad at me and doesn't want to talk to me anymore. She is behind it I know it? HAAAAAA

 

ANYHOOOOO! I have another question here...

While installing my nifty little fuel gauge I disconnected the wires going to the AC vac pump. In my hastiness to get the gauge installed I didn't mark the wires and don't remember what goes where. I looked in the manual and again couldn't find a thing.

 

one wire is yellow, one is blue with a red stripe and the other two are black.

 

I thought I had them hooked up right. This is the order from top meaning sky and bottom meaning ground. At top I put LR under that I put black. On the other one I put black top and yellow on bottom. So the order from top to bottom is LR, B, B, Y

 

If anyone know the order please let help me know

 

I tried the AC hoping I wouldn't burn anything up and it seemed to work but only the bottom vents toward the floor board worked. I couldn't get the dash front or upper and side vents to blow and no matter were I set the air conditioner it seemed to sound the same. Except at off, economy and defrost??????????????????????

 

Thank you

[Pop N Wood]

Whew! Looks like I get to keep my left nut for a few more years anyway.

 

FI cleaner could very well have broken enough crud loose to clog multiple filters. I have heard of the same thing when a car that is use to plain old gas gets a tank of ethonal blend. The alcohol is a very good solvent. My buddy had to change his filter several times before it finally stopped clogging.

 

BTW, a fuel pressure gage makes a pretty good back up gas gage. As your tank gets low, so will the fuel pressure.

[Guest Anonymous]

WEll, It still does what it always did. Got very hot yesturday and again buck and jumped and yet again I spent about an hour on the side of the road.

 

Pulling and inspecting the Fuel pump today.

 

Does anybody know were all the filters on thc car are so I can inspect, clean or replace??

 

Also I have another question here...

While installing my nifty little fuel gauge I disconnected the wires going to the AC vac pump. In my hastiness to get the gauge installed I didn't mark the wires and don't remember what goes where. I looked in the manual and again couldn't find a thing.

 

one wire is yellow, one is blue with a red stripe and the other two are black.

 

I thought I had them hooked up right. This is the order from top meaning sky and bottom meaning ground. At top I put LR under that I put black. On the other one I put black top and yellow on bottom. So the order from top to bottom is LR, B, B, Y

 

If anyone know the order please let help me know

 

I tried the AC hoping I wouldn't burn anything up and it seemed to work but only the bottom vents toward the floor board worked. I couldn't get the dash front or upper and side vents to blow and no matter were I set the air conditioner it seemed to sound the same. Except at off, economy and defrost??????????????????????

 

Thanks

[DAW]

Make sure your vapor canister hoses are intact and hooked up right. This is how the fuel tank is vented while engine is running..if the diaphram in the lid of the canister were cracked I think you'd have an occluded tank vent which could cause the type of fuel delivery problems you have. Is your injector/fuel rail cooling fan operating correctly?

 

Sounds like your AC vacuum pump isn't hooked up right or you switched one of the small vacuum lines to a check valve, etc. If you don't have a factory service manual, and Haynes/Chilton is not detailed enough, your city library may have the Mitchell Manual series for reference and these are very thorough.

 

Does the fuel pressure monitor you hooked up show erratic when the car acts erratic? DAW

 

P.S. Confirm that your fuel return line is not crossed with the fuel supply line under the hood if you haven't already done so.

[Guest Anonymous]

I will check the things you stated. As for the injector cooling fan I ma not sure. When is it supposed to come on? It does work I know this because I let the car get really hot in the garage the other day and after I shut the car off the fan kicked on for a while. But to me it seemed very hot before it did so.

 

As far as the canister goes would I have to replace the entire canister or just the filter and the diaphram.

 

I am wondering about this becuase just the other day while testing the very same idea crossed my mind about improper venting. It seems when I have the problem and end up putting gas in the car when I unscrew the gas cap I get either a huge sucktion of air or a huge release of air (not sure which). I hadn't really paid much attention to it really becuase I have had or put gas in other cars that have done the same thing. But maybe with a Z its a bigger deal.

 

THANK YOU

[DAW]

You'd only need to replace the diaphram. You can test it to see if the diaphram is ruptured by sucking on a hose connected to the vacuum port (labeled "dist."); if it holds vacuum it's OK, if you can't create a vacuum, it's bad. There's a kit (diaphram, spring, & retainer) if it's bad. DAW

[Pop N Wood]

Robert, what did your fuel pressure gage read when the car was bucking? Can you recreate the problem on the side of the road where you can get a visual on the gage?

 

If your pressure at the engine is 30+ when the problem is happening (doubtful given the symptoms) then you don't have a fuel problem.

[Guest Anonymous]

YEEEEEEEEEEEhoooooooo

 

ALL is back to the way it should be!

 

I did what you stated Wayne. Here are the results.

 

"empty" 12 ohms

"full" 78 ohms.

 

I also did the full and empty check and that is what it was.

 

The only reason I even run my tank low is because gas prices are outrageous and I live in a very hilly mountainous area in California. So I tried to make the car light for climbing hills and to save on gas. STUPID HUH?

 

Anyhoooo... After running all of your tests and even before reading this post, believe it or not, I came to the same conclusion. I originally thought they were separate problems but finally deduced that one caused the other.

 

So to prevent my stupidity in the future I pulled the sending unit out and bent the metal rods that hold the floats up about a half an inch. Actually the floats were below the lowest point on the pick fuel line. about an half inch. So I put the bottom of each float close to even if not a little above the lowest point of the pickup line.

I think maybe this was a problem to begin with. Like I said before when I started to have problems initially I took it to a shop. They said they pulled the sending unit. I also pulled it out about 3 times. As you probably well know the unit just doesn't pop out easily. I pulled it out very carefully and am pretty sure that I didn't bend the float rods. But the shop I took it to probably didn't and therefore the rods were bent a little to far down because of it being pulled out so many times.

 

I figure I have a huge tank so why not. Now when my gauge reads close to empty I know I am not and know that I won't burn up my fuel pump.

 

All tests ran great. As a matter of fact since I have a new pump my Power has greatly increased. Feels like it is brand new again. Runs like a beast. I guess I didn't notice the power loss due to the slow deterioration of the pump.

 

Thank you very much everyone for your help. Who every bet there left nut can keep it now.. HAAAA

 

Here is a link to my problem and fix.

 

http://www.geocities.com/gussgrissom/My_280ZX.html

 

THANK YOU

[Guest Anonymous]

Well it seems all in not well.

 

Every thing has been working fine.

 

Please read previous posts for things I have done and problems I have fixed.

 

For those of you following these posts it seems I have yet a third problem that could only be figured out by fixing the other problems. ({1}low tank usage which caused {2}fuel pump wear).

 

When turning on my air-conditioner and letting it run for about 2 to 5 minutes I get the bucking again. Once I turn it off then it goes away. There is a clacking sound behind my glove box when it happens. I looked in the manual to find out what it was and it seems it maybe the #1 fuel pump relay. When the clacking starts the bucking starts. When I shut off the air-conditioner the clacking goes away soon after and then the car runs great again and stops bucking. I can repeat this at anytime but at least I wont be stranded on the side of the road. All I have to do to get rid of the bucking is turn the air-conditioner off.

 

I tried to locate the #1 fuel pump relay but the manual states it is under the passengers side foot guard under the glove box which would verify where the sound is coming from. But the picture of what it looks like in the manual is not the same as it is in my car and I am not sure what it looks like and were it actually is. I would rather not guess. But I do know that it is in that area Also to be honest I don't think there is anything wrong with the #1 fuel relay. I think it is making that noise from some other cause with my air-conditioner.

 

Again for those of you who have followed these posts. You will notice that I stated that sound and problem before I did anything to the car. So I can only assume that it was from nothing I did and was a pre existing problem. Also I thanked Wayne for giving me the right configuration on the electrical wires on the vacuum pump and for my air-conditioner working. But the only thing I did was turn it on in the garage and noticed the cold air was coming out of the write vents and that it worked.

 

Now, thanks to Wayne, I know the wires are correct. Now could someone give me the right configuration on the vacuum tubes on the same unit. The tubes I speak of are the four smaller vac lines. Two go into the top of the fuel manifold and two go threw the fire wall to the air-conditioner system. All these lines come from an vac pump next to the built in inspection lamp.

 

The vac pump arrangement is as follows:

 

The black or red (in my car it is black) cap with wires is on top and the yellow cap with wires is on bottom. Then there is a port on top next to the black cap and a port on the bottom directly across from the port on top next that is next to the yellow cap. These ports are on the housing itself.

 

OK, if that is understood then the vacuum lines come out of these ports and go to specific locations. The black cap with wires vac line goes into the firewall to what I assume an air-conditioner component. The lower vac line from the air pump housing also goes into the firewall.

 

The vac line coming from the yellow cap goes to the a location that is located close to the center of the fuel manifold and it connects to a valve of some sort. The line above the yellow cap from the air-pump housing goes to another location on the fuel manifold right next to the EGR with other vac lines splitting off from a T fitting.

 

Is this correct? Or is my description to crazy to follow?

 

If anyone knows what it is I can do to test, arrange, fix, replace or repair please let me know. I wouldn't worry to much about it since I am in California and really don't use the air-conditioner but in a few months I am moving to Phoenix Arizona and I am definitely going to need my air there.

 

Thanks