Slight back fire and stumble!

[280m]

I am new to the forum and have read tons of great information. But before I start checking everything I thought I would run my problem by a few of you folks first. My 1977 280z runs strong and accelerates as it should, however when I try to accelerate quickly the car sometimes slightly back fires and always stumbles then as the rpm's climb its smooth. If i give it gas say 1200 to 1500 rpm's and ride the clutch out....no back fire and very little stumble. Anyone experience this before?

[Gary in NJ]

It's a lean condition. Fast Woman will be here soon to tell you how to fix it

[grantf]

Yes fastwoman can help, She helped me out big time. Look up her purrs like a kitten thread and my mpg thread. As well as downloading the FSM and searching the EFI section. How long have you owned the car? Check all vacuum lines for leaks, Check all electrical conections pertaining to your EFI system and be nice to your clutch.

Edited October 7, 2011 by grantf

[280m]

I am great to the clutch...trust me...It seems to be worse when cold...I have to get in touch with her or him.

[280m]

Also, i have had the car for 2 weeks, and she has had tons of work done to her...

[grantf]

try testing the water temp sensor and its conections. Have you downloaded the FSM yet or the EFI bible?

[cozye]

Just make sure you do a thorough diagnostic and eliminate any obvious things like vacuum leaks, fuel pressure issues, water temp sensors, etc. before going with the lean condition fixes. If you richen up your fuel mixture without doing the due diligence first, you could just mask the real problem (i.e vacuum or intake leak, etc.) I also had the lean condition, spent 6 months troubleshooting and trying to find a cause before I resorted to the same solution fast woman documents. I have quite a lengthy thread over on zcar.com that documented it.

[FastWoman]

My reputation preceeds me!

It sounds like everyone else has covered it so far. Go through your entire fuel/intake system to find any vacuum leaks (there are probably at least a few), anything out of spec, and parts that don't work, etc.

After you think you have your intake tight, you should leak test it. Find a way to stuff up your air intake air-tight. The easiest way I've found is to remove the AFM and stuff a plastic yogurt cup into the rubber boot. Then pull off the brake booster hose, attach a clean hose to the manifold, and blow into it like you're inflating a balloon. You'll be able to feel how tight the entire intake is by how fast the air leaks back out. You can compare to a controlled leak by pulling the little vaccum hose next to the power booster hose. Air will come shooting out of it as you blow. You should notice a very large difference between air leakage rates with and without this controlled leak. If there is a very obvious/large difference, your intake is probably tight (enough).

Check that your vacuum advance is not stuck by removing the distributor cap and giving the breaker plate a twist. It should rotate smoothly under spring tension. This feature is weakly engineered. Rebuilt distributors are available at your local auto parts store.

With your distributor working, set your timing.

Adjust your valve lash, and check your timing chain alignment per the FSM, using the marks on the cam sprocket.

Go through all your engine wiring to ensure that your connectors are clean and good and that your wiring hasn't been creatively altered. (Mine was altered.)

Once you get to this point, then we can start diagnosing the AFM and ECU for the proper mixture. If your engine is running lean, the fix is both mechanical (AFM adjustment) and possibly electrical (adding resistance to the coolant temp sensor circuit).

[280m]

Thanks for the information I will begin my work tonight.

[280m]

Well, I checked everything out...new vacuum lines and checked all the connections, i mean all, timing and it all checked out. Took the car to a mechanic that works on imports, known him for a few years. Told me it was the

themostat or thermotine sensor, said its a very common problem with datsun engines in general. Anyway he put

that in and adjusted the valves to smooth out a little rocker arm noise. Anyway cold starts perfectly and runs like a dream, just have to drain the synthetic oil the guy I bought it from put in the engine and I ready to start on the

suspension.

[FastWoman]

Cool! That was pretty fast!

[280m]

Yeah he seems to be very knowledgeable about these engines, too he works on Sunday's. Plus I had replaced all the vacuum lines and most of the fuel lines, new TPS, PCV valve, plugs, distr and rotor button, wires, fuel filter, air filter and cleaned every

electrical connection I could get to.