Intermittent driveability issues

[J Shara]

Ok so here goes. I've been trying to drive my Z around lately because I just got it road legal and I thought I had it running beautifully. But it seems that after 20 or 30 mins. of driving, or after the car warms up, it falls on its face, loses power, stumbles and the exhaust note changes. What I cant understand is how one minute it'll have full power and sound/ drive amazing, and the next minute, it becomes lethargic. Also noticed that the temp gauge flies up past the red mark,  the amp gauge freaks out and when I have the lights on and step on the brakes the dash lights dim. I also noticed that when I rev the engine with the lights on they get brighter. Could I have a failing voltage regulator or alternator. The regulator is new, or it was 2 or 3 years ago but the alternator is original. I tested voltage at the coil and it read between 14 and 15 volts. Static battery voltage with the engine off was 14 volts as well. 15 seems a little high to me. Car has a pertronix installed too. I couldn't get it to act up while it was idling though. Its like it only happens when the car is moving. Car will sit there and idle all day long. But then a couple runs through the gears and bleh. Any thoughts would be appreciated. I just installed an airtex electric fuel pump or the rx-7 fuel pump on it today thinking it would solve my " failing fuel pump issue but I don't think that is it. Unless I have a clogged fuel line, but that wouldn't explain how the car runs fine sometimes. I am really stumped on this one.

[beermanpete]

Your charging system sounds fine. 15 volts in normal on older cars, especially if still has the mechanical regulator. The lights getting brighter when you rev the engine is normal and shows that the alternator is working.

 

The meters going crazy indicates a short or intermittent connection. Check the wire that connects to the temperature sensor at the thermostat housing. If it has a bare spot and touches ground the meter will pin.

 

The ammeter problem and the poor running could be related. You could have a bad ignition switch or a bad connection in the main power feed to the car, after the ammeter.

[J Shara]

Well the ammeter kind of flickers between 0 and what I'm guessing is like 10 or 20 amps cause the scale is from -60to60. What should a normal reading be when the engine is running?

[beermanpete]

Normal depends on the conditions. Immedeatly after start-up you should see a moderate charge that tapers off as the battery recharges. This will only last a few minutes. After that it should sit on 0 while driving. At a stop, while the engine is idling, you should see a small to moderate discharge until you start off again. Flickering could be from a regulator issue or an intermittent connecction. If you still have the mechanical regulator it can be adjusted if needed.

[J Shara]

Yea that is what it does. Ok so I can rule out the alternator, and battery cause I tested the battery, and swapped the alternator with the one from my parts car. I also put a new fuel filter on it today, and it looked like to me, even with the electric pump running, the filter fills slowly and stays  relatively empty. Im thinking clogged fuel line. After the car was turned off I noticed the filter filled. Also before I installed the electric pump, I verified with my meter 11.5 volts at the factory pump wires.

Edited September 14, 2015 by J Shara

[Patcon]

Is your return line hooked up? Have you tried pumping fuel into a container to check volume and flow?

[Zed Head]

Yea that is what it does. Ok so I can rule out the alternator, and battery cause I tested the battery, and swapped the alternator with the one from my parts car. I also put a new fuel filter on it today, and it looked like to me, even with the electric pump running, the filter fills slowly and stays  relatively empty. Im thinking clogged fuel line. After the car was turned off I noticed the filter filled. Also before I installed the electric pump, I verified with my meter 11.5 volts at the factory pump wires.

You can get a pressurized air bubble in the filter that doesn't really matter.  The float bowls will still fill and that's what counts.

 

But the 11.5 volts is not good at all.  12.6 is standard lead-acid charge.  11.5 is almost dead.  But once the engine is running you should be on alternator voltage and that's when your problem happens.  But you might be just running on battery power.  Verify voltage while running.  Low voltage can case weak spark.

 

Found this interesting chart via the Google, post #2 - http://www.solarpaneltalk.com/showthread.php?20997-SLA-Battery-Possible-Discharge-Problem

[beermanpete]

11.5 volts at the pump is low. If the voltage measured at the battery is different (higher) at the same time you have voltage drop in the wiring somewhere. This is most likely due to loose and dirty connectors in the circuit that feeds the fuel pump. To locate the source of the voltage drop use your volt meter and measure the voltage across each connector and wire segment in the circuit while the pump is running. A good connection will not have any appiciable voltage drop. A good measurement will be less than 0.1 volt. Ideally it will be zero but it will never truely be zero. The best we can hope for is approching the limit of your meter's resolution. You are lossing about 3 volts but it is probably distibuted among the various connections and circuit elements rather that all at one location. Don't forget to check the ground side wiring as well. It is part of the circuit and can cause voltage drop just the same as the positive side wiring.

[J Shara]

Good point. Thanks beermanpete. I'll definitely have to check my connections and grounds. But the car suffered this problem before the electric pump was installed too. I think I could have a few things going on electrically and fuel related.    Back to the garage