Engine bogs at ~2500 RPM. PLEASE HELP!

[yoshi280zx]

Hey, all!

Well, this is a new one for me. Last night as I was driving home, the engine started bogging out when I hit about 2500 RPM. I drove almost the whole way home at 2250 RPM and 50 MPH.

This morning, I started the car and headed for work. The engine revved up fine. There were no issues - UNTIL the car reached operating temperature. After reaching temp., the car bogged out at ~2500 RPM all the way to work. As I came home, same thing. The car runs fine until it reaches operating temperature.

Here's what I've checked. Please let me know if I'm missing something!

Fuel pressure: Normal. I upgraded the FPR in February of this year. Gauge reads fine...

Fuel delivery: Good. I replaced the fuel pump and filters in February, too.

Fuel injection: Good. All injectors are less than a year old.

Intake: Optimal with a clean K&N filter element.

Spark Plugs: Only about 10,000 miles on them. I cleaned and re-gapped them a few months ago. It is the last time I ever buy SplitFires, though. NGK for life!

Ignition Coil: Replaced at same time as the plugs with new, 7mm silicone wires.

Catalytic Converter: Replaced with Hi-Flo (well, hollow ) unit a couple of years ago. I really doubt it's clogged. Everything sounds great behind the car (nice clean, exhaust).

Temperature Sensor: Fairly new. Replaced a few years ago. This car is driven often, but not many miles.

O2 Sensor: Could this be a culprit?

AFM: I cleaned this not too long ago when I installed a new throttle body.

I just dropped a bunch of coin on a new transmission for my daily driver (Jeep). I still have another week (at least) before I finish it, so I really need my Z because it's the only running car I have right now. Because of my transmission woes with the other vehicle, I also don't have a lot of money to throw parts at the Z. Just to clarify, this is a normally aspirated engine. Any suggestions? PLEASE HELP!

Thanks in advance for your replies!

James

1980 280ZX

[zbane]

Welcome to the forum.

I have a couple thoughts on your particular issue... it sounds to me as though you are having a fuel starvation issue; that it occurs once the engine is warmed up may be a coincidence. A common problem for our Z cars is rust in the gas tank, our s130s have a fine mesh filter on the end of the fuel sending unit. If you've a significant amount of rust/crud in your tank, it will get sucked into the mesh and restrict flow. When you shut the car off, and the pump is no longer pulling fuel from the tank, the rust/crud is released as it's no longer being pulled to the mesh, and it resettles/disperses.

If you've never taken a peek into the tank, you might want to do so. The access panel is located in the hatch area, under the foam mat. Two screws to remove, then multiple little bolts on the tank (that like to break if you're not careful). You'll have to remove the fuel lines in order to pull the sending unit out.

If you've already done this, and the tank condition isn't an issue, then I'd be inclined to suspect the air flow meter. Fender side of the unit, you'll see a small black plastic cover. Carefully remove it and check the contacts for wear or corrosion.

And of course, while you're in the engine bay, doublecheck all your connectors to ensure everything is seated well.

[Ted.]

Its probably not the tank if its still running. I had the same problem with my 240, and it would run fine for a few minutes, enough to reach operating temp and completely die after sputtering feebly in an attempt to keep going. I did all the ignition and fuel (from the coil to the cap and rotor and from the pump to rebuilding the carbs, and everything in between), before throwing in an extra clear inline fuel filter, which if you still want to check is a cheap way to find out. If it turns rust colored, thats probably your culprit. If its clean, its probably the air flow meter, as David said.

[Zed Head]

yoshi, you didn't say if your ZX is a manual or automatic transmission. If it's a manual, and you have a fuel supply problem, it wouldn't be so RPM specific. Try changing gears and see if the problem is speed or RPM related.

You mentioned a new throttle body. Why did you change the stock one? Did you go for a larger TB for "more power"?

Upgraded FPR? If you're running the stock ECU, what features of a different FPR would be an upgrade?

Seems like there might be more to your story. Have you been upgrading for performance, or is this a stock 1980 280ZX?

Ted, you didn't really say what the solution to your problem was. Did you have EFI on your 240Z?

[yoshi280zx]

Welcome to the forum.

If you've already done this, and the tank condition isn't an issue, then I'd be inclined to suspect the air flow meter. Fender side of the unit, you'll see a small black plastic cover. Carefully remove it and check the contacts for wear or corrosion.

And of course, while you're in the engine bay, doublecheck all your connectors to ensure everything is seated well.

ZBane,

Thanks so much for the reply! Was in the fuel hatch earlier this year... I also cleaned the AFM when I replaced the throttle body. Double-checked all vacuum and connections. Starting to wonder if it might be TPS...?

[yoshi280zx]

I had the same problem with my 240, and it would run fine for a few minutes, enough to reach operating temp and completely die after sputtering feebly in an attempt to keep going.... I did all the ignition and fuel (from the coil to the cap and rotor and from the pump to rebuilding the carbs...

Ted,

Thanks for the info! Might try a new filter, just in case... Hard to tell if mine is FI and your is carbed...?

[cygnusx1]

Here is my first guess and I am almost sure this will work. Unplug the O2 sensor wire and go for a drive. It should fix the drivability issue. If not, simply unplug and replug the ECU and the AFM connectors. Clean them with some contact cleaner if you have some.

Here is my thinking. The car drives without reading the O2 sensor until it warms up. When it is warm, it begins reading the sensor, and tries to correct mixtures. If the O2 is reading improperly, you will get stumbling, or poor fuel mileage when the car is warm and under load. I find that typically they will run "better" with the O2 sensor disconnected. They run on a "fixed fuel map" with no o2 sensor, which is richer than when they run in closed loop (O2 sensor mode). You should feel more torque with it unplugged.

Edited December 10, 2011 by cygnusx1

[yoshi280zx]

Zed Head,

Yes, it's a manual. Sorry - pretty important info. The problem is RPM specific - with the same results in every gear. Consequently, I'm in 5th by 40-45 MPH. It sucks...

I bought the MSA throttle body years back for better performance. This upgrade was coupled with a MSA intake, K&N, ported intake manifold and new exhaust system. The car definitely breathes better and sounds great.

I scrapped the old fuel rail earlier this year to go with one I made. A new FPR seemed logical. I grabbed a rising-rate Aeromotive unit. I didn't change the system's displacement, just the way the fuel was fed. It seemed better to have it go straight to the injectors instead of traveling above the manifolds forever...

The car has run fine with all the upgrades. This just started happening out of nowhere - no recent mods...

I think it's the TPS. There was a little moisture in it (was super rainy this week). I still haven't put it back in. We'll see.

[Ted.]

Sorry, I completely spaced on this thread, . I ended up pulling the tank and had it cleaned out, then chemically cleaned, then relined and sealed. Costs less then a new or used one shipped. Set me back about 150 bucks, but it was essentially a brand new tank. Typically shops won't do it much anymore, so try finding an old school radiator shop to do it for you.

[BaTora]

I had this exact problem this week. I have a 77 280z, four speed...

I didn't read through all the threads (sorry), but I scanned to see if someone mentioned what I'm about to. I don't think so, but apologize for repeating if I do.

The problem was in the TPS. I didn't have to open it, just pop off the clip and use a q-tip to get it dry. You should also check the injector clips, because they too have a cup-like shape that holds water easily. Once I dried out all of these, my car ran great! If that doesn't work you can google the TPS to find out how to open and service it.