buttsjim

Can someone who understands the ECU advise me on how it controls fuel injection?

I just put a new rebuilt engine in my 87 RX7 TII, but it won’t start due to a “no fuel” condition. I have spark, the fuel pump operates, and I have fuel flow in the supply and return fuel lines. The resistances on all my sensors check out. My grounds (checked with switch off) and voltages (switch on) at the back of the ECU plugs all appear good, with the exception of the heat hazard sensor (which always reads 12 volts unless I short it). I checked all my fuses visually, and with a meter.

When I turn the crank angle sensor by hand, I get spark, but nothing else—no clicks from the injectors, no smell of gas, no gas on the spark plugs. Just for kicks, I put my meter test lead in the back of the solenoid resistor plug (injector side) and watched the reading for the front primary injector. When I turned the CAS by hand, the reading cycled between 10.4 and 11.9 volts. In a similar way, I got a duty cycle reading of 3.5 milliseconds for the same injector. Finally, I went back to the ECU to re-check the output voltages for the injectors. Pins 3C, 3E, 3F, and 3H all read about 11.9v from the back of the plug, but if I took the plug off and read the value directly from the ECU pins, it was only about 0.3v.

According to the chart in the FSM, there should be an output signal of 12v from the ECU, so it seems like I should see it if I read directly from the pins, right? I don’t—I think the 11.9v I’m seeing at the back of the plug is actually in the circuit coming from the main relay. Also, if I’m reading the chart on page 4B-32 and schematic Ba-2 in the FSM correctly (and I’m not sure I am), it appears that the injectors have 12v feeding them from both sides, so that it would take a voltage drop on one side of the injector to make it fire. Is that the way it works? If that’s true, then since my ECU isn’t providing the 12v output, wouldn’t my injectors be constantly firing?

Can someone give me a clue here? Everything I’ve checked other than the ECU seems ok, and I think I’ve checked everything. I’m hoping I missed something big, easy, and cheap to fix, so I’d appreciate anything you guys can tell me. By the way, my ECU is an N332. I've had the car since new; it is factory stock, 140K miles, and was running perfectly when the O rings went. It then sat for 2 years. Thanks!

HAILERS

Your right and wrong in some of the things you said.

The voltage for the injectors comes from the MAIN RELAY, thru the solenoid resistor (series four), to the injector and out the other pin on the injector to the ECU.

The ECU pulses a GROUND on that circuit to make the injector pulse.

You should see battery voltage on the small plug of the ECU but you should not be looking for voltage coming out of the ECU.

You saw a duty cycle when you turned the cas, so I'd think the ECU and wiring is good.

I can't help but think that the fuel lines are crossed somewhere.

I posted the diagram for a series four this day somewhere. You might look at it.

And I did read what you said about the fuel lines flowing. That seems at odds with what I just said above about fuel lines being crossed. It's a puzzler (sp?).

Buy a can of starter fluid and spray for a moment into the airfiler. Just one or two seconds, then crank the engine and see if it will fire for a moment. That'll show it is a fuel problem. Later. I'll attach those jpgs to this thread.

Question: is this the same engine as came out or a JAP engine?

You seem to have done more trouble shooting than the average grease monkey.

HAILERS

If it's a USA engine the fuel should follow this path. The red dots are pressure from the filter and the green dots the return. JAP engines are different. Sorry, I know what you said about the fuel flowing...but

Was this engine in a fire ever? I had a fpr that was melted internally and had the same type problem til I worked it out.

buttsjim

Hailers:

Thanks for your quick reply!

You gave me really good news regarding the voltage source. I do see battery voltage on all 4 injector wires in the small plug, so that's good. I'm just totally confused that everything checks out, yet my injectors don't work. I saw the duty cycle with my meter in parallel with the back of the ECU plug for the front primary and ground, but since I was rotating the CAS by hand I wasn't sure if it meant anything.

I'll re-check the fuel lines. In searching this site for clues to my problem, I've noticed that it's pretty common for people to cross these. I don't have a fuel pressure tester, so I temporarily put a hose clamping pliers on the return line to make sure I had supply pressure. When I did that, I could actually hear the flow in the lines slow down. But, I'll visually check them to be sure. I'm tied down at the moment, but will get some starting fluid later and see what it does.

The engine isn't my original, but a brand-new rebuild from Hayes Rotary Engineering. I'm pretty sure it's domestic. As I recall, the serial number indicated it was an early TII motor. I still have my original motor, but I thought the housings might have warped. My o-rings went bad when I was on a trip, and I nursed the car 300 miles through the Texas hill country to get it home.

I'm really stubborn when I'm trying to fix something, and I've found a whole lot of troubleshooting help by searching this forum the past couple of weeks. I've just finally reached the point where I don't have a clue!

Thanks again for your help!

Jim

buttsjim

I should have mentioned... The new engine was a short block--all the externals and accessories are off my old engine. The FPR is a suspect, but I thought that clamping down on the fuel return line would bring the fuel pressure back up and compensate for a weak FPR. I don't think the FPR is blocked, because I can really hear the fuel flow in the lines.

buttsjim

OK.

I cheated--I didn't get a chance to get some starter fluid, but I sprayed a quick shot of brake parts cleaner into the throttle body via the intercooler duct. When I tried to start the car, it fired immediately, but quit firing as soon the brake cleaner vapor was burned. I tried this 3 times, and it worked three times.

So. I have spark, I have timing, and the motor is ready to start--if it only had fuel. And, my fuel line plumbing is correct. It has to be some sort of electrical problem to the injectors.

Any ideas?

HAILERS

No ideas at the moment. Just how can it be an electrical problem if it fired up. It's gotta be a fuel issue.

How about that. Brake parts cleaner,. Never done that before. That SEEMS to prove it is a fuel delivery issue to me.

If your seeing 12v on the ECU plug, then you KNOW the injector plugs are attached.

You can hear the fuel flow so it would SEEMthe fuel pipiing is good.

I think you must now realize that it is a fuel problem. If I come up with another idea I'll post it.

Anyway, since I'm stuck in a rut, the fuel line from the fuel filter goes to the most forward metal delivery line on the engine, on a USA version. Heck, swap them around and see what happens. Only a few minutes to do that since you/we're stumped.

buttsjim

I thought I had a problem with the ECU signalling the injectors to squirt, because it seemed like I checked everything else. But, back to basics, so I pulled the UIM off to check for flow from the injectors. I should have done that before I put it all together, but I just checked their resistances and put them in.

The car sat for 2 years, so I wonder if the injectors are so gummed up that the solenoid can't pull the needle valve free. I put 12volts on the injectors when I pulled them out last night--I could hear the current arcing from the hot wire to the injector terminal, but I couldn't hear the solenoid clicking. Tonight I will wire the injectors to the fuel rail, and see if they'll spray under pressure.

I didn't originally think the injectors were the source of my problem, because it seemed too much of a coincidence for them all to go bad at once. But, if they're gummed up, it makes sense that all 4 would gum up equally. Do you know any way of cleaning them? I was thinking of finding a small ultra-sonic cleaner on ebay, and filling it with carburetor cleaner.

I don't recommend using brake parts cleaner in lieu of starter fluid, but I was just too curious to wait and do it right. When I took the UIM off, the TB end cap and hose from the intercooler had a lot of solvent in them that didn't burn. Brake cleaner burns well, but doesn't vaporize like starter fluid does.

Thanks again for your advice. You made me realize it was time to stop chasing non-existent electrical gremlins, and re-evaluate my mechanical work. I've learned so much researching this site over the past two weeks. I'll keep you posted on what I learn.

HAILERS

I find it very hard to believe all the injectors went bad also. Not very likely.

I do like the idea of wiring the injectors to the fuel rail and spinning the cas with your fingers to see if they will spray.

No, I don't think I'll ever use brake fluid to start a car. Brake fluid is heck on paint and I'm clumsy enough to spill it all over the place.

Be careful. I once started a fire around the injectors while playing around. I got the area wet and accidently arc'd a wire and poof. Had a fire extinguisher handy so no real damage. I think an extinguisher can be had from the auto store for around ten/fifteen bucks.

I'm used tie wraps to hold the injectors on the rail before. Let us know what happens.

HAILERS

Here's a thought. The brake fluid has a consistency of a light motor oil.

This is a fresh rebuild? Low compression.

What actually caused the car to fireup was the brake fluid acting as a light oil and giving you enough compression for the fuel mixture to ignite.

If things are all together, put some light oil in the sparkplug holes while hand rotating the engine. Reinstall the plugs and try starting the engine again.

buttsjim

Whoops...not brake fluid--brake parts cleaner! So it's probably cleaning the oil off the housing surfaces and reducing compression.

I think the car has good compression, and it builds up oil pressure nicely if I turn it over with the fuel pump turned off. Also, when I pull the spark plugs to check for gas after my attempts to start, I always find them coated with assembly lube.

I know I have a fuel delivery problem, and I'm really curious to see what the injectors do when I check them tonight. I thought about having them cleaned and flow-tested while the car was down, but I was too cheap. What a wise investment that would have been!

buttsjim

For those interested, my problem was that both primary (and one secondary) fuel injectors were gummed up, and not spraying. I was able to clean them using carburetor cleaner under 10 psi pressure, and intermittently applying battery voltage to the terminals. I also drained all my old fuel from the tank, and put in fresh.

When done, the car started right up, filling my garage, driveway, and half the neighborhood with white smoke. I thought it was wonderful, but neither my wife or the neighbors were all that impressed. The smoke cleared after awhile, and the rebuilt motor idles beautifully.

Hailers, thanks so much for your advice. I was barking up the wrong tree trying to figure out the ECU, and I probably would have ended up burning it out if I kept fiddling with it. The problem was definitely with the injectors--I should never have put them in without cleaning them in the first place, as the car had been sitting for over 2 years.

HAILERS

Yeah. I goofed with that brake fluid remark! I don't work on cars for a living, but from my view point, you did one of the most intense and reasonable troubleshooting processes ever posted on this forum for a non-starting car.

I've just rebuilt an engine for a fellow and I plan to start it up looooooong after the neighbors go to work.

buttsjim

I guess that was a pretty thorough troubleshooting process, but only because I was desperate! I'm cheap and stubborn, so I typically try to troubleshoot a little at a time and learn as I go, rather than take the car to the shop and pay someone else. I'll check this or that, think about the results, follow up, check some more, etc. In this case, when I ran out of ideas, I started searching this forum and learned all kinds of stuff that I could do.

This site is a great resource, and I hope I can make a positive contribution to it.

Good luck starting your rebuild (I noticed that when Bruce Tarrantine started the project engine at the end of his rebuild video, his garage didn't fill up with smoke like mine did--do you suppose maybe he forgot to put oil in it?)