L28 Problems - Will not rev over 3.5k - Possible Air Flow Meter Prob

[SugarFreeGum]

Ok,

Car was running well a few months ago.

1981 280zx N/A (n42 head) EFI

Current problem.

10-20% throttle engine runs fine. When throttle is half way the car chuggs and strugles, when its pressed to the floor it takes off and runs fine up to 3500 - 4000rpm, Once it gets to about 4k it struggles to get any higher.

Engine idle is good usually around 800-1000rpm (althought i have seen it idle high at 1200rpm)

All injectors & electrical connectors have been checked and are fine

Injector seals, rubbers plasitc caps have all been replaced.

Fuel Filter is clean

Fuel system has been cleaned

Rebuilt distributor

new spark plugs & leads

My mechanic seems to think it may have something to do with the air flow meter? As if its not getting enough air, or getting to much prehaps?

I've taken the cap of the AFM and reved the engine, and the AFM seems to be opening & closing ok.

Any suggestions would be much appreciated.

[sblake01]

Throttle position sensor?

[SugarFreeGum]

I havn't checked any of the sensors as i'm not too sure how. I've searched and read for many hours through many posts but still unsure.

My mechanical knowledge is very limited.

Where is the throttle position tester and how can i test it?

thanks!

[GunnerRob]

Have you checked the hoses for holes and/or cracks? Try feeling around both of the large corrogated hoses that are attached to the air flow meter and the throttle body. Also, there should be a smaller hose, about 1" in diameter, under the intake manifold that runs from the manifold forward to (I believe) the throttle body. This smaller hose probably has a foil covering on it that makes a person think it could be a metal tube. I found a hole in this one that caused problems. I know your Z is a later model than my '75 280, but I would think the intake system hoses would be basically the same (no need to change what works well!)

Hope this helps,

Rob

[SugarFreeGum]

thanks rob, all hoses have been checked and a few replaced.

I've have checked the big hose/boot from the AFM to TB but maybe i should double check it again.

[sblake01]

I havn't checked any of the sensors as i'm not too sure how. I've searched and read for many hours through many posts but still unsure.

My mechanical knowledge is very limited.

Where is the throttle position tester and how can i test it?

thanks!

It's located on the side of the throttle body. It's the black box secured with two mounting screws. Remove the connector and you'll see three numbers on the throttle position sensor that correspond with the three terminals. Check for continuity between terminals 29 and 30. If it's good but needs to be adjusted that is kind of a hands-on thing but it's outlined in the FSM.

[SugarFreeGum]

thanks i'll check it out.

What does FSM stand for?

[SugarFreeGum]

Ok checked the throttle body sensor, theres no corrosion on the pins or plug, both seem to contact well.

What is the part thats connected to the radiator hose and manifold, it has an electrical plug on it as well?

[sblake01]

FSM=Factory Service Manual. I believe the other part your are referring to is the thermotime switch. It sends the signal to the cold start valve.

[SugarFreeGum]

Any more suggestioms anyone?

I've just ordered a service manual, hopefully that will give me some ideas also.

In the mean time i'm driving around with little power

[SugarFreeGum]

Ok, after playing some more, i tightened up the boot in between the AFM and TB. I just took it up to 5000rpm with no probs, it still seems to hesitate a little after. The boot had a few smal cracks but they only looked like surface cracks. I might get the boot replaced, at least it seems to be running alot better.

[FRLDYZPIMPN]

I had same problem. Couldn't get passed 3500 rpm on any gear, always hesitated. I had the AFM tuned and both boots from air cleaner to afm and afm to TB replaced. Now it runs great.