RxTodd

Hey friends,

Thankfully, my engine turns fine, seems to have compression, and wants to run. Only thing is, there is NO gas flowing to the engine. I've changed the fuel pump, filter, pushed compressed air thru the lines, but no fuel. There is a little less than a gallon of gas in the tank. Should I put more in? Does anyone know if there is a strainer inside the tank? It doesn't add up. Any input is welcomed and appreciated.

mazdaverx713b

iTrader: (91)

There is a pickup filter on the pickup assembly. I typically start with 3-5 gallons on a project car. Less than a gallon may not be enough to get the system primed with fuel pressure.

Can you verify that the fuel pump is receiving source voltage when the engine is cranking over?

RxTodd

Yes, I made sure the pump was hot. I even got under the car while someone tried to start it to hear the pump engage, which is new by the way. I hear you about more fuel and that makes perfect sense. I think I'm going to drop and clean the tank first because the pickup you mentioned might have a clogged strainer/net/bag or whatever it's called.

Thanks for the speedy response!

Seniorchief

RxTodd welcome to the forum, and always try and add the year/model of your car when asking questions as it usually helps others who may want to respond..

RxTodd

I'm sorry, I thought all of that information was visible with my post. I own an '85 GSL-SE.

LongDuck

Ooooookay, that helps, because the -SE is the only fuel injected version of the FB series, and has completely different fueling systems than the carbeurated cars. Here's what I'm going to ask you to do; your fuel pump may be just fine and building pressure at the fuel rail, BUT, the ECU won't fire fuel injection based on Trailing Ignitor operation unless you have both spark at Trailing Coil AND air coming in as registered by the Air Flow Meter. The AFM has a switch that is closed (*passes current) only when the air door is open, as occurs when the engine is gulping air. When that switch is closed, it allows the fuel pump to run. This is designed to prevent flooding, and to prevent high pressure fuel flow without engine operation, such as after an accident.

The Ignitor which runs the Trailing Ignition is mounted to the side of the Distributor, the Leading Ignition is run by the Ignitor toward the front of the Distributor. The ECU receives a trigger from a white wire which is connected via spade to the hot side of the Trailing Coil. This trigger allows the ECU to know when and how often the ignition fires so that fuel can be mapped to a simple graph for Fuel Injector timing and duration. Without a working trigger, the Fuel Injectors will never fire, and the engine will never start - even if you hear fuel pump operation at the pump and the Fuel Rail.

Lack of spark on Trailing Ignition, leading to lack of trigger to the ECU, is typically caused by a failed Trailing Ignitor. You can test this by swapping that white trigger wire from the Trailing Coil to the Leading Coil, and if the car starts and runs, you have a bad Trailing Ignitor (*and no Trailing Ignition). Alternately, you can swap the Leading and Trailing Ignitors on the Distributor, but it's a lot quicker to move one wire than swap both Ignitors...

Read this a few times, maybe do a quick search on my name and "gslseforme" and "SE Fuel Injection", and see what you get. There have been many hreads on this over the years.

Also, please create a signature line with information about your car, trim level, mileage, any modifications you've made, as this will help us to help you. Good luck,

mazdaverx713b

iTrader: (91)

LongDuck smacked the nail on the head with his response. I will add one thing however. I came across the same issue you are having once and the fault that I had found was that someone had the dynamic chamber off and somehow managed to unfortunately the ground wires for the injection system. I don't remember if it was one or two stacked, but the wires were black and I believe bolted to or around the rats nest. Its been nearly 20 years so I don't remember exactly. Once I secured those ground wires, the injectors started working properly and the engine ran fine. I was chasing my tail because I had good fuel pressure to the rail and I had good spark and the mass airflow meter tested well within spec. This is just something else to check in case you get stuck where I was stuck many years ago.

RxTodd

Thank you both, I will have to read both of your post a few times to make sure I know what to do. I don't know if I mentioned before but I'm not getting fuel to the engine at all. After replacing the pump, filter, and cleaning the lines, I took them off the nipples leading to the rail and there is no fuel pumping through.

The flap or door that Longduck mentioned moves freely with hand manipulation but wondering if it malfunctions while trying to start,, would that stop the flow of fuel from the tank all together?

LongDuck

In order to get fuel pumping, you need the following:
1) Fuel in the tank - more than a gallon is plenty
2) Power to the Fuel Pump - a strong, well grounded battery with a positive that's attached to the starter properly. Check fuses, too.
3) Air coming into the engine - as metered by the Air Door on the Air Flow Meter (*or using the Fuel Pump Test Jumper- search...)
4) Trigger Signal for the ECU to fire Injectors - white wire from Trailing Coil AND working Trailing Ignition - meaning the Ignitor, the Coil, and the wiring in between is connected
5) Working ECU - the N304 ECU is known for being robust, as it's simple. I've never read about a failure.
6) Clear path for Fuel - there is a mesh screen on the in-tank pickup, a high pressure Fuel Filter before the Fuel Pump, and metal screen in the inlet to the pump. The Fuel Rail has a pulsation dampner and a Pressure regulator - these rarely go bad.
7) Working Fuel Injectors - check connectors, including the pigtail wiring which connects to the front engine harness. These can degrade over time and not carry current to the low impedence injectors. In your case, both may have failed.

This should get you started, but search as instructed before, as theres a TON of info on this very board about SE Fuel Injection. Good luck,

mazdaverx713b

iTrader: (91)

If the mass airflow meter is not good, the fuel pump will not activate. There is a test procedure for it in the FSM. I'll see if I can find it and post it.

mazdaverx713b

iTrader: (91)

Mass airflow meter test procedure from the FSM:

RxTodd

Well, I dropped the tank and I see a MAJOR problem! It has reddish brown sludge throughout. The pick-up assembly tubbing(the metal L shaped part) is completely clogged with hardened sludge. I literally don't know where to begin. The pick-up assembly filter that Mazdave 10AE Restoration Guy mentioned, seems to be attached to the floor of the tank. Is that normal? I've seen several tank cleaning/resurfacing kits online but there also seems to be a compartment in the tank that I cannot access. The overall integrity of the tank looks good so it is a small positive to my otherwise negative discovery.

It's funny because of all the units I've owned, this is the first to have me go completely through it. Guess I've been spoiled but it's all good. I'm learning so much as I go and I'll appreciate it it more when I'm cruising on a warm summer night with the roof out.

Happy Holidays to all!

RxTodd

Hello all,

So in reading several fuel tank related post, I learned that the strainer does not stay in the tank. It may sound like I'm a dumb *** but I really did not know. It was stuck in the tank with goo from aged gas. I see where lots of members are cutting their tanks in half at the seem, cleaning the inside thoroughly, the weldding back together. I don't have that skill set so that method is out for me. I'm going to try and see what a local radiator shop can do it for.

Thank you for all the help you guys always offer.

Ckforker

If the shop can clean it, POR makes a great kit to seal the tank and prevent it from happening again.

RxTodd

Thank you, I'll check it out. Any tips on cleaning out the pick-up tube? I guess I'll try to soften the sludge and use a pipe cleaner to get it back to free flowing.

PJPilot

I inherited a 1980, had been sitting in my Uncle's garage for probably 15 years. I had it trucked to a shop near me in CA, the guys that worked on it found the gas tank and fuel system loaded up with sludge like you described. They sent the tank to a radiator shop to be cleaned out and refurbed. Might be an option for you?

RxTodd

Yeah PJ, it's looking like that will be the option for me. Again, there are several DIY kits and videos showing the process but it concerns me that the tank has baffles or compartments that I would only assume they were cleaned, etched, and sealed properly. Too much leaving to chance you know...

Thanks for sharing your experience.

mazdaverx713b

iTrader: (91)

The pickup assembly can be cleaned once removed from the tank. The filter slides over the pickup tube as you learned. Pretty simple little filter. If yours is able to he cleaned and reattached, do so as they are no long available new from Mazda.

The fuel sending unit may need replaced as well. The sender is available new and comes with a new gasket. I recommend ordering the securing screws when you order the new sending unit. They can be tough to remove and can round. Sometimes though you get lucky and they come right out.

As for the tank, it can be soaked and pressure washed clean. I did this with a tank on a 10th Anniversary RX-7 a couple years back. It took some time but turned out nice. Once its cleaned internally you can coat it with the POR15 kit mentioned above. I also chose to undercoat the outside as well.

PJPilot

@mazdaverx713b

Where can one get a new fuel sending unit as you mentioned above? My 1980 SA fuel tank was cleaned up really well, it's in good shape. But somewhere in the process the fuel sensing got jacked up, fuel level now reads constantly 1/2 tank low. I think I need a new sending unit. Thanks for any info.

mazdaverx713b

iTrader: (91)

Unfortunately I believe the sending unit for the 79-80 is no longer available. The 81-83 and the 84-85 senders are available but do not interchange.

Toruki

Might be worth troubleshooting the gauge and the sender. This is a good thread re: the gauge, https://www.rx7club.com/1st-gen-gene...oting-1122629/

You can read the resistance of the sender with an ohm meter, should vary smoothly from ~ 110Ω to 0-ish as you move the float assembly through its range of motion (I'm assuming it's removed at this point).

RxTodd

Well,
I got a quote for having my tank cleaned and resurfaced today...$300 bucks the tech said which included me purchasing two, $30 a gallon, solvent to soften the crud in the tank, then bring it back to him to cut it open, sandblast and re-coat the inside. Being that my only other option is doing it myself, this is probably the best route to take. The baffle inside the tank is the only thing stopping me from trying to do this on my own. I'll tell you how it turns out with pics when it's finished.

Thanks for all the suggestions!

mazdaverx713b

iTrader: (91)

Cutting the tank open scares me to be honest. The tanks can be boiled out and most radiator shops will do the job. Once the tank is dipped and cleaned you can coat it internally and it will be as good as new.

KansasCityREPU

iTrader: (9)

There are a lot of videos on YouTube that go through the process of cleaning and sealing a tank with the POR15 tank sealer kit.

RxTodd

I agree,
It's hard to rationalize purposely breaching a tank that has great overall integrity. Yeah, you would think a radiator shop could handle this job but for some reason, here in Central N.C., I can't find a shop that is willing to do it. Its been frustrating to say the least. I'm going to give this a go myself. I really appreciate the encouraging words from all of you. As always, I'll try to keep you updated on my progress.