Running rich, fuel pump constantly runs

[Cethern]

I'm at my wits end with my 75 280.

On Friday I noticed the fuel pump wouldn't shut off with the key, then shortly after that it started running super rich and rough.

at first I thought fouled plugs, before I did anything I looked for vacuum leaks, lose wires anything out of place.

Then I did some searching on here and the Web, nothing I read fit so anyway I changed the plugs, water temp sending unit, fuel pump, and the ignition coil. I switched out the fuel pump relay as well. All cylinders are getting spark.

I'm limited to just a few hand tools as most are still in Colorado.

Until Friday the car was running fine.

Thanks in advance for suggestions and ideas.

Eric

[Cethern]

I'm kinda surprised of the lack of suggestions, but anyway I ran through the list of tests from the FI Bible, the only thing that showed up was a problem with 1 & 2 injectors when checking for voltage.

I don't see how that would cause it to run so rich, also I'm still trying to find out where the fuel pump is getting it's power from.

[Zed Head]

The problems you described and the actions you took don't really follow, and the description is a little confusing. You said that the pump kept running when you turned the key off then the engine started running rich. But the engine can't run with the key off....? Plus you're on the "changing parts" path, instead of the "test and take measurements" path. Nobody can recommend a new part to change until you've taken a measurement.

First, I would download the 1975 FSM and use it instead of the "bible". The "bible" is like using Cliff's Notes, when the original book is right there, and free. Read the Engine Fuel chapter.

I would measure fuel pressure and record the resistance of the coolant temperature circuit. Those are two things that can easily cause a rich condition. As far as the pump goes, the wiring diagram is in the Engine Fuel chapter also.

[Cethern]

I'm limited on resources with having to use a tablet not a lot of room data wise.

With the battery connected the fuel pump runs, even with the ignition unplugged, the only way to get to shut down is to unplug the fuel relay, which is why I changed it out, and knowing that a bad water temp sending unit can cause some fine systems to run rich and being at the parts store for the plugs is why I changed it.

I hate changing parts without knowing what the problem is, but nothing is standing out as the problem.

After going through the test list in FI Bible the only thing that didn't pass is the #1 cylinder and #2 didn't show battery voltage at the ecu, I took a 9volt battery to the injectors all of which clicked open and close,

I'm almost wondering if it is a ignition issue as now it's started to backfire out the exhaust, after that I checked the timing marks on the chain and cam, I will most likely pull the dizzy and check it.

[Zed Head]

The 75 files are 86 MB total.

Have you taken any of the resistance measurements shown from page 45 on of the "bible"? The three tools that will help you the most are a multimeter, a timing light and a fuel pressure gauge. Without those, troubleshooting will be difficult.

[SteveJ]

The positive wire for the 76 (and the 75) fuel pump comes from a green/blue wire. That wire originates at the Electronic Fuel Injection Relay pin 74. In the relay, pin 74 gets power from pin 73 (white/red wire) when the coil is energized.

The coil in the relay is energized when either pin 76 or pin 4 have 12 VDC. Pin 76 is connected to the START circuit of the car. Pin 4 is connected to the ECU. Pin 4 has 12VDC when the AFM contacts are closed. (See EF-12 and EF-15 in the FSM)

If the fuel pump stays on after you turn off the key, unplug the fuel pump relay and look for continuity between pins 73 and 74 on the relay. The attached drawing shows where the pins are on the base. Look for the green wires running to the fuel pump relay base. If you have continuity, that means the contacts are probably welded shut.

Also check for voltage from Pin 4 on the relay base to ground. Measuring 12VDC is bad. Please note that I don't know if unplugging the relay would reset the signal from the ECU.

The good news is that if you have a bad relay, apparently they are not that expensive.

[Cethern]

Zed Head, yes I took resistance measurements, they were within spec as per the manual.

SteveJ, thanks for the info, there is continuity, I put a 9 volt battery to the terminals and was able to get both coils to click, I would take that as a good sign that the coils are not stuck closed.

As of now the car barely runs if you can call it that, and is back firing out the exhaust, I picked up a timing light and haven't gotten the damn thing to light up to even see if the timing is off, but if I pull the plug and hold it about. 1/2 in away it will bridge the gap.

Thanks again for the help

[Zed Head]

it started running super rich and rough.

Other causes of running super rich are more common, but it is also a sign of a bad ECU. Some people have fixed theirs by re-flowing the solder connections from the connector to the board.

[Cethern]

Zed Head, that is an interesting idea.

I have thought of taking some video to give you and some friends an idea of what I'm seeing.

[SteveJ]

By the way, I saw this on FB in the Datsun parts and needs group in response to someone's problem.

Description

Hi Guys I have a question. I have a 78 280z 2+2 with a l28e. Im having a fuel problem. The car is flooding itself out. I have to unplug the fuel pump just to let it run otherwise it will start up and die or not even start. I have brand new injectors, fuel pressure regulator and Air Flow Meter. At first we thought it was the injectors and fuel pressure regulator then we replaced the AFM. Anybody have any ideas on what it is I've inspected all wire Connections and none are corroded.

Response

This is so simple, it's right in the EFI BIBLE. Check the connection to your Coolant Temperature Sensor for the ECU. When it's loose or corroded, the thing thinks it's -40 and floods the hell out of the car. Has nothing to do with the injectors or the AFM.

[Zed Head]

That brings up one good point about the "bible" - it shows how to take the measurements from the connector at the ECU AND has the chart of temperature versus resistance on the same page. The FSM's are vague and you have to do some figuring and page-flipping to get to the same point.

If Cethern has been using the 280Z Electronic Fuel Injection Book then he's already checked the connection when he took the coolant temperature sensor measurement at the ECU connector.

[Cethern]

I did check it at the time it was around 5deg outside and I got resistance in the number range that they had in the book, also the sending unit is new the pig tail connectors I made sure were clean.

But I'll recheck it just to make sure.