'76 280 running rough

[JohnnyP]

I had a thread going in the "Help Me" section, but felt it appropriate to move it over here…

Here is the dilemma: My car starts and will move and all that. On start up or whenever I depress the accelerator, I get next to no power. The best way I can describe it is by saying that when I press the accelerator the car makes a sputtering sound, like its about to stall. It doesn't go away if I give it some gas and just try to ride it out. This problem has been haunting me for a few weeks now. Here is what I have done as far as trying to diagnose/treat the problem…

EFI troubleshooting for "lack of power"

Checked and adjusted timing

Checked/tested vacuum advance and replaced its hose

I tried plugging the cold start (as suggested by ZtylerZ)

Checked the fuel/air filters

I did a compression test, yielding the following results:

Cyl#1: 155

Cyl#2: 160

Cyl#3: 155

Cyl#4: 160

Cyl#5: 160

Cyl#6: 155

1976 280z FSM compression range: Compression pressure kg/cm2 (psi)/at rpm: 11.5 - 12.5 (164-178)

Pulled the spark plugs and compared them to the Haynes manual for spark plug diagnosis

What am I missing? What else could be the source of the problem? Thanks to any and all who lend their advice on this one, and to everyone whose helped me out thus far.

John

Edited July 6, 2010 by JohnnyP

[S30Driver]

It is possible the TPS is bad or poorly adjusted & contributing to your problem. If it is sitting on the idle contacts too long, or those contacts are shorted, it will be telling the ecu to not give the injectors more fuel, hence no power.

There is a simple proceedure in the shop manual to adjust it correctly. All you need is a vom to set the 3 contacts, idle, cruise, & wot.

As a quick test to see if it is an issue, disconnect its electrical connector temporarily & drive the car. See if the problem improves & report back.

[Zed Head]

Have you checked your fuel pressure? I looked at your other thread and did not see any numbers.

It doesn't take much fuel to get your engine to idle but under load you won't get anywhere if you don't have the pressure to feed the injectors.

If you have disconnected your cold start valve, you can use that hose off of the fuel rail to connect the gauge to. It's right where you want to measure. I put one there permanently (made for underhood permanent use - from JEGS) and it's pretty convenient.

Ideally, you would measure with the starter disconnected to check the pump and regulator, then with the engine running to see if those components and the fuel lines can keep up with engine speed.

Edited July 6, 2010 by Zed Head

[JohnnyP]

Where can I get a fuel gauge like the one your talking about?

[S30Driver]

As ZH said, Jegs has them, also Summit Racing.

Many people use a liquid filled gauge to prevent vibration damage.

[turbo 260]

Sounds like fuel to me also. You can help the situation by using vice grips to pinch off the fuel RETURN line. This will slightly help a weak fuel pump and help diagnos a lean condition. This isn't a substitute for getting a fuel pressure gauge. If the pump is original, you could just swap it out and see if that fixes the problem. Chances are that if it is old, it's going to go out soon anyway.

Jim

[Zed Head]

If you have disconnected your cold start valve, you can use that hose off of the fuel rail to connect the gauge to. It's right where you want to measure. I put one there permanently (made for underhood permanent use - from JEGS) and it's pretty convenient.

.

Just fixing old posts with new knowledge. The JEGS liquid-filled gauge I discussed actually turned out to be very inaccurate once it got warm. It read low, disguising a high fuel pressure problem for quite a while. Stay away from liquid-filled gauges in hot environments, especially the inexpensive gauges.

[cygnusx1]

Making it run that badly, I would start thinking about an AFM, the AFM connector, or ECU connector, IF the fuel pump and pressures are good.

Edited October 23, 2010 by cygnusx1

[Pomorza]

Where can I get a fuel gauge like the one your talking about?

I'm not positive if were talking about the same thing here, but I have a fuel pressure gauge mounted on my Z right past the fuel filter. I just went to the local race shop and picked up a standard FP gauge. It does the job just fine for me.

I do have a suggestion though as I've met someone that had a similar issue. When your first start your car and it runs like car, pull on the harness going to the computer (and by pull I mean GENTLY TUG). A friend of mine had an issue where the solders on the inside of the computer (the FI one that is) were loose causing the thing to loose connection with the rest of the car.

I would personally start with the basics. Make sure your have enough fuel in the car and that your AFM and TPS are set correctly. Also check all the connections and connection points to see that they are on tight and aren't covered in crude. Remember these cars are 30+ years old. Even the best wires and connectors will have issues.

Jan

Edited October 23, 2010 by Pomorza

[Mikes Z car]

...I did a compression test, yielding the following results:

Cyl#1: 155

Cyl#2: 160

Cyl#3: 155

Cyl#4: 160

Cyl#5: 160

Cyl#6: 155

John

I am curious about how many miles are on your car as my compression tests out similar to yours and I am wondering how many miles might be on my engine.

Thanks,

Mike

[shaneish]

i have a 76 280z. i too had issues similar to what you are describing. i tracked my down to vaccum line issues. vaccum plays an intricate roll in how the engine performs.

hope you got your problem lined out.

[Zed Head]

I am curious about how many miles are on your car as my compression tests out similar to yours and I am wondering how many miles might be on my engine.

Thanks,

Mike

Reply to this old slightly off-topic post - The compression values can vary a LOT depending on which gauge you use and with what adapters, etc. I bought a screw-in type gauge recently and got 120 psi with the adapter tube and 180 without it. The volume of the gauge hoses, adapter tubes and the gauge itself become, in essence, part of the combustion chamber volume when the test is done.

As I've read many times on these forums, it's the comparison between cylinders that matters the most.

Back to the point of your question, in my case, my odometer says 46,000. Could be 146,000 or 246,000. But I got five 180s and a 179. I was surprised, especially considering that my engine burns a little oil and shows some signs of a hard life.