ECU bad?????

[sano86323]

Need a sanity check here guys, so please chime in if you can.

Engine cranks but will not start. Sprayed starter fluid into the vacuum box and engine started and ran for a while.

I have verified that there is fuel pressure, that all 4 injectors fire fuel, and that there is nothing wrong with the rest of the wires/components in the injector circuit.

Is there any other reason for this "run with starter fluid" behavior other then the ECU being bad???? Someone PLEASE save me from spending the bucks for another ECU when the problem lies elsewhere.

[Turpro]

Where are you spraying the starter fluid? Is your vaf plugged in?

[sano86323]

Starter fluid into the port where the break booster is normally attached. Yes, the VAF is plugged in and passes the diag testing in the shop man. All wiring has been verified 3 times now (continuity and no shorts checked) as well as tested twice for the correct voltages at the ECU.

[progt91]

sounds like a fuel issue. where did you check the fuel pressure from? what was the pressure at? are you sure there are no restrictions in the fuel line. if it starts with starter fluid then the fuel system is where i would look first.

[sano86323]

Fuel system was my thinking as well (including ECU and distributor.) Fuel pressure checked between fuel filter and injector rail. Between 60 and 70 psi if I remember correctly (was in line with the number from the shop manual.) I also flow tested the injectors and they were in spec. Lastly I checked that the injectors spit fuel when the appropriate ECU pin was grounded (with ECU disconnected.)

The flow test was done with the injector turned on for 15 sec. It would be nice to figure out a way to test flow volume with the engine cranking but have no clue what the number would be.... so all I am going to be able to check is the timing and duration of the electrical signal to the injector (I have an o-scope).

Any suggestions on more fuel system tests?

to all: any suggestion on it being something other than the fuel system? I still cant see how it could be something else, but I will admit that I dont know what I am doing.

[sano86323]

progt91: I think the flow test (done using car's fuel system excluding ECU) being in spec means there is not a flow restriction. Let me know if this is not the case. thanks.

[Racerboy]

The ecu controls the fuel system. Therefore, if the ecu is damaged, the fuel system may not work.

[sano86323]

RB: sorry if I have offended you by asking this question. I cant see a way in the world that the problem could be outside of the fuel system (including ECU and distributor)... but I just wanted to try and make sure we (I) am not missing something. Its $300+ bucks IF I can find one.... dont want to goof. Dont be pissed.

[Racerboy]

RB: sorry if I have offended you by asking this question. I cant see a way in the world that the problem could be outside of the fuel system (including ECU and distributor)... but I just wanted to try and make sure we (I) am not missing something. Its $300+ bucks IF I can find one.... dont want to goof. Dont be pissed.

no problem. I understand completly. I'd do the same thing.

But you can find a used ecu on car-part.com for about $50. And you can sometimes even get them cheaper than that. Every so often I see them for $20 and snap them up in case mine every goes out again. Also, people have them on here every so often.

[Mazda_Powered]

Are your fuel lines to the rail backwards? Car won't run if they are lol.

Also I would check all your under hood fuses, as we as the in cabin fuse labelled "engine".

[sano86323]

fuel rail: I will double check, but I dont think it would have passed the flow test or the pressure test if I had.

There is not fuse labeled "engine"... all the labeling is in Japanese.
Joking aside, I have ohmed out the entire emissions harness (and parts of the front and rear as they are related to ECU function) TWICE, and a significant portion of it a 3rd time. No way we got a blown fuses.
Now I am off to find the fuse that is labeled engine in Japanese.

[Mazda_Powered]

Top fuel line coming off the filter will flow to the injectors first, not to the fuel regulator. That'll save you some work.

As for the fuse, I do believe it's in the lower 2 rows of the fuse box, I'll go check for you right now.

EDIT: yea it's in the lower row of fuses.

[sano86323]

MP: Fuse is fine, so is fu.... oh sh*t. How did that happen?

I had checked that twice... apparently both times were before we pulled the rail to check the injectors. duh. (I love my boy.)

Sadly we are now back to the will run for 10-15 sec and then dies.

HELP guys!!!!!!

[Mazda_Powered]

so it now starts for a bit??

what VAF are you using? If it's a B code or anything other than a Y/U code it'll need to be adjusted before the car can idle properly.

When it starts, is it running on 4 cylinders?

[sano86323]

Injector signals do not look right... given that G and NE are good, that means we will be forking out some $$$$... not nice.