Trouble,trouble,trouble............

[cmiulius]

Hello Z Fanatics........

I post a few weeks ago about my 1976 280Z. The problem........backfire in the air mass meter. Car idle beautiful, has fuel pressure, no vacuum leaks, timing is good, I try to run it around the block, no power, backfires. Sometimes feels like she want's to go but she cannot. Anybody any idea? I will be more than thankful for any kind of help. If anybody in LA area is willing to help me I am willing to pay:):):).

[SteveJ]

Did you change your fuel filter? Is there any chance you have rust in your gas tank?

[cmiulius]

Yeap. The car was sitting for 13 years in a garage when iI bought it. I finaly make ot run but..... I have new injectors, neu spark plugs, new injector connectors(actualy I replace all the connectors on the engine)new cap, rotor, air mass meter,EGR valve, auxiliary air valve,wires, all the sensors, TPS sensor. Runs but no power with load.

[Evil Turkey]

I'm really not very knowledgable about this kind of stuff but other than the rust in the fuel tank/fuel filter issue, couldn't it be an issue with the valve timing/ valve clearance?

[Zed Head]

The symptoms are the same that I had when my Air Flow Meter (AFM) was bad. But you show that you have replaced yours. Did you get a new/rebuilt one or just a different one?

[cmiulius]

The air mass meter was purchase rebuild by Phyton. When I empty my gas tank(dump almost 10-11 gallons) everything came out clean, no rust or other crap. i am not to familiar with Z's. I just want it running by all means.

[Zed Head]

Did you measure the fuel pressure or just see that the pump is working? Low fuel pressure could give a lean condition, which could cause backfires, and lack of acceleration.

Edit - another possibility is timing too advanced. Are you the damper pulley has not moved, and that your timing is truly relative to Top Dead Center?

Edited January 21, 2011 by Zed Head

[cmiulius]

I will check it tomorrow and I will let u know. thank u. U give me something to think. By the way, the air intake boot bet intake and mass meter is a little squeezed. from the mass meter and air box missing. u think this can cause misfire? not enough air. car runs rich.

[FastWoman]

I don't understand your last post, but a squeezed boot shouldn't affect the engine's running.

It's still possible you have a vacuum leak between the intake manifold and cylinder head. (I had a big one.) I finally verified I had no vacuum leaks with what I call my "yogurt cup test." Very simply, remove the AFM, and stuff a yogurt cup onto the boot, plugging air flow. Then pull off the brake booster vacuum line, and put a short, clean hose on it. Put the other end in your mouth, and blow. You'll be able to blow a bit of air into the manifold, pressurizing it. If you blow hard enough, you'll pop the yogurt cup out of the boot. At some fairly pressurized point, just stop blowing, and hold the pressure with your mouth. If the pressure takes maybe 10 sec to leak down, your intake system is probably pretty tight. To establish a frame of reference, you can pull off a small vacuum line and repeat the test. You'll hear/feel air escaping much faster. One small, completely open vacuum fitting is enought leakage to affect engine operation a little bit, but not dramatically.

Then if you're SURE of all of the following...

*NO vacuum leaks

*correct fuel pressure

*correct timing

*a good distributor without the common frozen breaker plate problem

*all your sensors within spec, as measured at the ECU connector

*AFM within spec

... then your ECU components might have drifted, resulting in too short an injector pulse (hence lean running and intake backfire). More and more of us are discovering this. The cure for this condition is to add resistance in series with the temperature sensor. You can look up my "purs like a kitten" thread to read the long saga that led me to this fix. The coolant temp circuit adjusts the length of the base pulse, so this correction takes place over all operating conditions.

In my own case, I estimate I was running with about 25% too little fuel. I corrected this condition by adding about 2.6 kOhm in series with the temp sensor. Cozye did the same thing, but he wasn't running as lean as I was and added a bit less resistance. We both used variable resistors, so that we could adjust and fine-tune our mixtures. I added the 20-turn variety of trim pot. Ideally I would have used a 5kOhm trim pot, but I didn't have one in the 20-turn variety, so I used a 10k pot.

[olzed]

Sarah. I am amazed at your skill with the fuel injection problems on your Z. and helping other folk out.Great stuff. I can diagnose problems with carbs on my 240, and I can do any of the mechanical stuff, but electronics has me stumped.

Brian.

[cozye]

What was the results of the tests and suggestions we made in your previous thread ? A bunch of suggestions were made and results of specific questions were never posted ?

http://www.classiczcars.com/forums/showthread.php?t=40507

[FastWoman]

Brian, you're making me blush. However, the truth being told, carbs puzzle the @$#% out of me! I mean, I know how they work in theory, but all those tiny little passages in a Holley double pumper, for instance... geesh! So I feel pretty lucky whenever I manage to keep a carb'ed engine running.

Edited January 21, 2011 by FastWoman