The ECU is fried OR not getting its power fed to it.

The 0.4 vdc means just that. It should be appox 4vdc or four volts dc, Not .4. I've seen a bad or fried ref voltage ECU and it read about 1volt if I remember right. No Ref Voltage equals no start, no spark and probably no fuel injector pulse. The radio should work. Find a station you like to listen to and contemplate what your next move is.

Personally what I'd do, is NOT buy a ECU until I back probed a couple of the wires on the ECU plugs. The ones I'd have an interest in are pin 3I (THREE EYE) and 3J (car will run without that one, but check anyway).

Then I'd backprobe pin 2A. That is where the Ref Voltage exits the ECU to the sensors. It should be about 4vdc. Not .4vdc.

That's with the key to ON. Also you might pull just the middle plug and check pin 2A on the ECU side for voltage. Leave the small plug and big plug on for this checkout.

Pin 2A is the middle plug, far right, top row. You count the pins from the wire side starting from the far right of the plug and in a up/down fashion.

Come on, Grab that sparkplug wire and touch ground with the other hand. Spin that engine over. J-Rat would. Step up to the plate!

 

im avoiding the shock if i can. ok tongiht if I get a chance ill start probing the ecu for voltages. are there any other pins I should check?

 

No. With just the small plug to the far left on the ECU connected, you should get approx 5vdc from pin 2A. But that said, leave all the plugs on at first and backprobe 2A looking for approx 5vdc.

Check your meter out first, either at the battery terminals or by backprobing pin 3I. That 3I is a Black/White wire and should have battery voltage on it.

If 2A has what you said earlier, .4vdc, then you need to wonder what it was that blew the output device in the ECU. Pin 2A feeds several things. The TPS, AFM, ATP, BOOST SENSOR, VARIABLE RESISTOR. Maybe a dead short on one of those wires?

I checked one of my cars this morning. It's right at 5vdc on pin 2A with just the key to ON.

Just to ease your mind, you can remove the other two plugs on the ECU and just leave the small one connected. Now measure 2A. If it's still .4vdc, then the ECU has gone **** up. There's no hope for it. By doing that you eliminated those items that 2A feeds, so they can't be pulling the 5vdc down to .4vdc.

You might, before putting in a new/used ECU, check the items 2a feeds for dead shorts.

 

Here's a couple of jpgs of the ECU plugs. Note how the plugs are viewed from the WIRE side of the plug. These same views are available in a free download from the internet.

 

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alright thanks hailers... ill go start pulling back carpet!

 

just as an update.. im currently right in the middle of checking the ecu.

ive pulled the carpet back. its wet. its wet and it smells light sweat, its not dripping, but all the yellow foam is wet and smells like old sweat.

weird.

I popped open the ecu, checked all thesolder joints, none look brun, looked quickly inside, saw no burn resistors or transistors or anything.

examining the harnesses, the wires out of 1B and 1C have some hackjob job done on them. its now become obvious that the carpet has been pulled back before.

1b and 1c look like they were split, then reconnected with friggin tape. there are loose wires coming out, so it seems 1B and 1C are now connected? gr. im going to go peel backk the electrical tape around the harness a bit to try and figure out why the wireees were split.

gahh it stinks!

 

measuring 2a (backprobing) I got 0.08 volts. a bit away from the needed 4.

I checked 3I like you said, read 12.4 volts. grr whats going on

 

for the record the shock isnt...that entirly bad...if i get pissed off enoguh when checking for spark ill joyfully grip a spark plug in hopes of a shock

 

yeah I know. Ive built plenty of shockers in electronics classes etc. Just dont want to go through the touble since its not going to shock me anyways

 

To check for spark, you unscrew a spark plug then reconnect the spark plug cable. Hold in hand and have someone crank.

 

yeah this thread title isnt accurate anymore. and its become way to big. lets let it die. switching to here:

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/help-ecu-problems-465634/