Help! Replaced fuel pump and filters and can't keep it running.

[two50below10]

Hey guys. I purchased a '76 280Z that had sat for a long time, although it has been driven some the last few years. I am in the process of changing out all the fluids and filters and such and have run into a problem with keeping the car running.

Some backgropund info on what has been accomplished so far. I have changed out the brake fluid, coolant, oil and filter, differential fluid, with only the automatic transmission fluid to go.

A few weeks ago the car began to sputter and then quit. Fortunately it quit as I pulled back into the driveway (had to push it into the garage though). When restarting the car again it ran real rough for about 2-3 seconds and then quit. If I wait a day and then try again it will stay running for awhile then quit. While it is running rough I could hear the fuel pump struggling so I figured the fuel pump was about to quit. So I have since removed and reinstalled the fuel tank to clean it out (the fuel smelled a little like varnish). I have replaced the fuel pump and even installed one of those clear inline fuel filters between the tank and the pump so as to not ruin the new fuel pump with any debris left in the tank. I have also replaced the fuel filter under the hood.

Last night was the first test run with the fuel system put back together. The car ran great in the driveway so I decided to take it around the block. Well, it left me stranded and had to push it back home.

So after this lengthy post I am wondering if there is there a fliter or screen inside the tank that could be clogged and causing the fuel pump to be starving for fuel? If there is, I sure didn't see any access to one when I had the tank out of the car. Please help if you have any ideas.

Thanks!

Chad

P.S. This is the same car I received some great responses to about a possible wheel bearing making a growling sounds. As you can see I haven't had a chance to address that problem now that I can't even keep it running.

[two50below10]

After doing some more reading on the forum here, I am wondering if it could be a bad coolant temperature sensor. The car will start and run great for a few minutes while it is cold. After a few minutes it starts running rough and then eventually quits. I am then unable to get it to start until hours later or the next day. Any help or ideas would be much appreciated please. Thanks!

Chad

[280]

Im sort of remotely on the same boat as you. There is no filter inside the tank as far as im aware. There is a mesh filter right on the inlet of the fuel pump that gets clogged, it may also be on the hose connected to the inlet if it somehow came loose. As far as the coolant temperature sensor goes. You can do an ecu pin test to see if its working correctly. All u need is a temperature sensor ( a cooking one would do fine) to measure the water temp. Then you would take a volt meter and check the resistance i believe between the two pins.(cant remember exactly which two pins its in the efi bible or fsm) But if you need to go and buy those two things it would be just cheaper and going to your auto parts store and just buying a new sensor its only around 15 dollars. Then you would rule that out. Make sure your current or new sensor doesnt have teflon on the threads because it could prevent a good ground. Besides that Check and/or reconnect all your bullet connectors in the wires just to make sure youre connections dont have corrosion on them preventing them from making good contact. I am a noobie so im just telling you what i would do.

[FastWoman]

Hey Chad,

I know the '78 has a large intake screen in the tank, probably about the size of a small coffee can lid. I don't know about the '76. If you didn't see tons of debris in your tank and didn't try coating the tank with epoxy, the screen should be fine. Some people acid wash the tank and then coat it with epoxy. (Because the acid wash would eat out the screen, there's probably nothing left to clog with the epoxy.)

I suspect the coolant temp sensor is a more likely cause for your problems. Keep in mind it might not be the sensor, but rather the connector it's plugged into. This connector sits at the front of the engine and gets REALLY dirty, crusty and brittle. If you were to unplug the sensor, your engine would be choking in fuel and blowing black smoke, if running at all.

BTW, 280, teflon on the EFI's coolant temp sensor wouldn't affect functioning, as it doesn't use the body as a ground. However, the temp sensor that feeds the instrument panel (that has a 1-wire connector), does use the body for ground, so I suppose teflon tape would be a bad idea (although electrical contact would probably be made anyway, depite the tape).

[Nutz]

you may try replacing the rubber fuel hoses in the ingine compartment. I have a 72 and my hoses were so old they were letting air in the lines and the fuel pump couldn't draw enough fuel. I figured it out after replacing my fuel pump.

Hope this helps

[Zed Head]

You should check your fuel pressure before you do too much more work. Hook up the gauge, start the car and pull the vacuum hose off of the fuel pressure regulator. Pressure should sit at 36 psi. Reconnect the vacuum hose and pressure should drop to ~26 - 30 psi depending on intake vacuum.

Without knowing that you have good fuel pressure, you risk spending a lot of time and money on the wrong things. Testing will tell you if the pump and FPR are working correctly, whether your lines or tank inlet are clogged, whether or not pressure is changing over time, etc. A few less things to guess at...

[two50below10]

Thanks guys for the input! I will have to do some reading on how to check the fuel pressure. What kind of special equipment is required? I also decided to go ahead and order the coolant temp sensor ($20) and the temp gauge sensor ($10, which wasn't working either). I will let you all know how I make out. Thanks again for all the great info!

Chad

P.S. One more question. Could the fact that I installed one of those clear inline fuel filters between the tank and the inlet of the pump make it too hard for the pump to draw fuel from the tank? I am thinking that it's probably not a factor because the car runs really great for 5-10 minutes before struggling and finally quitting.

[FastWoman]

Chad, I think an inline filter such as you have is a good idea. Several of us run them without any problems. I'm running a similar filter myself. I think the fact that your car runs fine for 5-10 min indicates you have no fuel flow problem, but of course we could both be wrong about that. Hypothetically you could have a pump delivering the needed pressure, but with not much flow rate. Pressure from such a pump would bottom very quickly if fuel demand picked up.

You can buy a fuel pressure gauge at your local auto parts store or put together a cheap (and not too accurate one) from hardware store components. You'd need a gauge connected to a "T" fitting. Insert the "T" between the fuel filter and the fuel rail.

[two50below10]

Ok, so here is what I have come up with so far. I did replace the temperature gauge sensor and the gauge is now working. I have determined that the coolant temp sensor is still good. I have verified this in two ways. 1) checked the resistance vs. a new one, and both read the same resistance and both match what the FSM says the resistance should be for given temperatures. 2) I then plugged the sensor connector into the new coolant temp sensor which is not installed on the car (just hanging there out in the air). It started and ran for about five minutes, and then as with the original coolant temp sensor that is still installed, the car started to struggle and finally quit.

Here are some other observations. As you probably know, if you unplug the coolant temp sensor while the car is running it will run for just a second or so and then quit. I think I remember reading that it quits because it makes the mixture to rich when unplugged. So, with that logic in mind, I decided to unplug the coolant temp sensor when the car was sounding like it is about to quit. I could then keep the car running by toggling back and forth with the temp sensor plugged in and then unplugged.

This leads me to believe that once the engine is up to normal operating temp then something is making the engine starve for fuel. Because when it is about to quit and I unplug the temp sensor it comes back to life with the added fuel but then will quit if left unplugged for more than about a second because of being to rich.

Next, I intend to try and check the fuel pressure as suggested by a couple of you guys, to see if the regulator is bad. If fuel pressure checks good, do you guys have some other suggestions for me? Could it be a bad air flow meter? Starting to scratch my head here. I would really like to get this running now that the weather is getting nice. I am anxious to drive it!

Thanks again for all the help so far, I truly appreciate it!

Chad

[5thhorsemann]

Drink a bear and controll yourself. I can gar-un-tee if you get impatient with this problem cause you want to drive the car in the nice weather, you will brake something. Take your time and go through the paces, you'll find the problem. Stop jumping around and put a pressure gauge in the system and check your pressure as stated above, Eliminate posabilities one by one.

[FastWoman]

Chad, I think you've established now (with the coolant sensor unplugging) that your fuel pump, filters and lines can supply the volume of fuel needed to keep your engine running.

At some point when I was in the process of getting my engine straight, I could get it to start and run OK when it was cold, but as it warmed up, it would run really roughly. I would also increasingly get backfire through the intake as the engine warmed up. This would happen sometimes when I would goose the accelerator pedal. My engine started running this way when I removed a fixed resistor that some mechanic had put inline with the coolant temp sensor. This was a field fix used to richen the mixture. In this state the cold enrichment was just enough to run the engine relatively smoothly when cold, but when the enrichment ended the engine ran very poorly.

I ultimately fixed my system by adding resistance back inline with my coolant temp sensor, which scales the fuel delivery up throughout all operating conditions. Search my profile for my "purs like a kitten" thread, which describes everything I went through to get my engine straight. It turns out that the (probable) culprit in my engine was an ECU that had drifted in its operating characteristics over the decades. This seems to be a common problem, and the added resistance seems to be the preferred field fix for that problem.

But before you get to the point of diddling with the resistance of the coolant temp circuit, you need to go through your engine with a fine tooth comb to make certain you don't have some other problem, like a massive vacuum leak.

[two50below10]

Here is the latest. First of all the problem has gotten worse now. I can no longer keep the car running for more than just a few seconds before is quits. So whatever part is going bad it has started accelerating its demise.

I am however narrowing it down a bit. I borrowed a vacuum gauge from a Friend and in just the few seconds I can get the car to run the vacuum checks good at around 16 and then even stays up after the car quits so I don't believe I have any vacuum leaks.

I also purchased a fuel injection pressure gauge and have checked the pressure with the engine not running. I wired the fuel pump directly to battery. When activated it produces about 38-39 PSI and then when deactivated the fuel system remains pressurized at about 34-35 PSI. I also did the pressure test with the return line disconnected and paced in a container. The test returned the same results with a nice steady stream of fuel going into the container. The pump runs nice and smoothly and quietly. When the car is struggling to stay running the pump make noise and sounds like it is cavitating or failing. This leads me to believe that the fuel pump, fuel damper, fuel pressure regulator and filters are functioning properly and that I don't have any restrictions to flow. Although now I cannot check the pressure with the car running. However I don't think that matters now that I know pressure and vacuum are fine.

So more questions for you all. Could it be the fuel pump relay? I don't know how these things fail. Are they either good or no good or can they fail slowly and possibly give the symptom that I have experienced with the sound of the fuel pump struggling and making noise? Although the relay wouldn't make sense if, when I unplug the coolant temp sensor it runs rich and comes back to life.

I have even connected a volt meter to the terminals of the fuel pump to verify it is receiving twelve volts. It does receive twelve volts while the engine is running smoothly but can see the volts start to drop or fluctuate when the car begins to struggle. However I don't know if this voltage drop is the cause or the symptom. Could my problem be with the airflow meter or the ECU? Any more ideas guys?

Thank you all for the info so far. I am definitely narrowing it down, but I sure could use more help.

Thanks again,

Chad