As the title says, I have a new engine in, it was started and driven around the block, wouldn't start the next day, it seems to have had an intermittent short in the injector/ignition circuit previously as well. I have power at the coils and the injectors, I have had the CAS tested with an ohmmeter and it falls within parameters, between 120 and 200, it registers 168 or so. I could hook a labscope up and see if I get a squarewave pattern, but since I read that the fc has problems with cold-solder points inside the ecu I pulled it and checked. There seem to be three transistors on one side and one large one on the other side screwed into the case, and all three solder-points at the legs in the board of ALL OF THEM are either broken/corroded or burnt (doesn't smell burnt and the traces aren't buckled and wrinkled, no scorch marks either, so I am skeptical about it being BURNT). I am stuck on this, and before I am blasted about not searching, believe me, I did, but couldn't find anything definitive. So my question is this:
Should I try to resolder these points and just trial and error it, or should I look away from the ecu and do more tests with the CAS? Or, conversely, do you think my ecu is bad? Is there any way to test the functionality of my ECU?

 

See if you have approx 4.5 vdc on the brown/white wire at the boost sensor. IF you do, then get a spare cas and connect it to the harness. Key ON. Spin the bottom gear of the cas. Spark should happen and clicking of the injectors should happen (primarys).

Burnt parts in a ECU........suck. Get another if there is no 4.5vdc on any of the brown/whtie wires with the key to ON. Got 4.5vdc? Then you should have spark also if the cas is plugged up and the ECU is plugged up.

 

It is naturally aspirated. Is there still a brown and white wire? Is the test still valid? BTW, I don't know for sure if these points are burnt or just failed..I can't see why the base (middle) leg on a transistor would ever burn, I guess stranger things have happened..

 

Boost sensor = pressure sensor .

 

for education's sake, if i do not have 4.5vdc at the pressure sensor what does this mean. I am going to post some pics of those solder points too and lemme see if you guys think it is a cold-joint or a burnt ecu..thanks for the input guys!

 

here are some pics...

These are the ones on the sides here that are messed up..the five(yes all five) on the right and the big one on the left. I assume since there are three legs on each that they resemble transistors, if anyone knows what they are responsible for...I'm all ears..


I tried to get good pictures, and from these I am MORE convinced that it might be spiked..

 

should I bother cleaning this solder off and resoldering? or should I be so sure that this is the problem...I bought the car running and the engine blew..and now after the swap and the initial startup and test drive it wont start again...you think this is my culprit?

 

Those points all look re-soldered already. The brown 'crust', if you will, is the flux from a rosin-core type solder, rather than the original solder seen elsewhere on the board.

Have you checked for codes? Malfunctioning equipment will register and be reported when you check...

And yes, those do appear to be transistors.

 

hmmmm....I don't think it had registered any codes..they would have thrown the check engine light up right?

 

I'll have them scan it again anyhow..now that I'm going over the diagrams, I am thinking BIG transistor=ignition, cluster of three/two smaller transistors=fuel injectors(2 secondary, 2 primary, and maybe the fuel pump or a retard mech.?)
just a theory...

 

ok guys, the scan tool won't communicate with the computer, there is no voltage at my pressure/boost sensor. I'm leaning towards this being my ecu, am I right?..I was going to get the CAS hooked up to a scope to see if it produces a square-wave pattern, any other tests that may be beneficial to pin this down? Thanks!

 

The ENGINE fuse has to be good for the Main Relay to pull in and feed the ECU and the coils.

 

The coils and the injectors are getting power but the pressure sensor is not..

 

No 4-5vdc ref voltage on the brown/white wire at the cas or afm etc, means there will be no spark or injector action. No ref voltage.........no start.

It's possible something is pulling the ref voltage down. Pull the plug off the afm and check the brown/white wire at the boost sensor again. If it now shows up, then something in the afm is bad.

PUll all the sensors getting the brown/white ref voltage and see if with all those plugs off the sensors, if you now get the ref voltage.

You sure the ECU is getting power? On 3I and 3J? Series four pins. It helps if the year of the car is in the thread and whether turbo/non turbo, series four/series five.

No ref voltage means this car will NEVER start with the ECU that is in the car. NEVER EVER.

 

It is in the post, its on my signature. Its an 88 Naturally aspirated, I guess that's series four if I am right. Well it had started, and it ran and was parked and it no longer would start the next day. When it was checked there is reference voltage at the coils and the injectors, but like I said they just aren't firing, not getting grounded by the ecu. There is no reference voltage at the pressure sensor, and like I say, the scantool will not communicate with my ecu or vice versa. What color is the wire that supplies power to the ecu and what voltage should it register when checked? Thanks you guys, this car has been in the shop since the fifth of august, and I desperately need it by the 14 of november of I am SCREWED!! All your help is greatly appreciated!

 

Pins 3I and 3J are on the small plug and if looking at the wire side of the plug, they are the last two wires. One above the other on the end. The Left end.

The FUEL SECTION of the FSM has a section called CONTROL UNIT and there you find the function of each and every wire on the ECU plugs. 3J is White/Blue and 3I is Black/White.

Pin 2A supplys the 4-5vdc ref voltage to the sensor.

If the EM harness is NOT grounded to the engine, the ECU won't work. Its two wires on top of the rear rotor housing on a series four car. They can be checked by pulling the plug off the ECu and checking the gnd wires to ground using a simple digital meter. Gnd wires are pure black. Pins 2R, 3A, 3G and I THINK 2B. Just pull the plug of and meter to the stated wire and the neg lead to gnd. Should be less than a ohm. Might be a touch higher depending on what you used for a meter neg gnd.

 

Just get another ecu, s4 NA ecu's are literally a dime a dozen and easy to find. You can get 2 or 3 spares of every electrical part on your car for under 100 bucks.

 

Anyone have any ecu's I can get? N327..88 coupe, as in my avitar. I am going to check out my engine ground, I see how it could have slipped loose and caused the symptoms, yet I need to know, there is power to the injectors and the coil ignitors- does the ecu supply the power to them too or just the ground? I have the Haynes manual, not the FSM, I think I see here that power is supplied by the relay anyhow, so the ground is missing. And no reference voltage at the pressure sensor, haven't checked for reference voltage at any other sensor yet, but if my ground is off it would definitely cause these problems. And if it were a pre-existing condition I would have to pay extra for extra tests and diagnosis fees, but I hope they just left the ground off and it can be fixed. If the computer has power and ground at the connector though...I think I know what the next step is- so, if you guys have any extra n327s laying around give me a price- I found one online for 60 shipped, if anyone can beat that I may get one just in case...

Thanks for your help!

 

The ECU does not supply power to the injectors. Power is supplied by the Main Relay to them and then the OTHER wire on the injectors get a pulsed Ground FROM the ECU. So you can see how you can have power at an injector and even have the ECU out of the car in the shed in the backyard.

The CAS gets spum by the engine. The CAS MAKES an AC signal to the ECU. The ECU uses this information to pulse the ignitors in the coil pack and to pulse a gnd on the fuel injectors. The ECU must have its grounds wires ....grounded for the electronics in the ECU to perform.

N326 or N327 will work in your car. A used one for, what??? thirty to fifty bucks?? Go look on EBAY or this forums FOR SALE section.

Sixty shipped isn't so bad.

 

Pull the plugs off the sensors that use a brown/white ref voltage wire. The TPS, AFM, VARIABLE RESISTOR, BOOST SENSOR, ATP. Then go to one of those brown/white wires and see if it has 4-5vdc or not. You do this in case one of the sensors has *a internal problem* causing the ref voltage to be pulled down.

Seems you'd get some small voltage of some kind. I bought a bad ECU and it had something like 2vdc max output. ALL the plugs on the EM harness connected up? The two orange ones near the firewall with fifteen pins and thirteen pins in them??? Probably since you have 12vd at the injectors.

 

yeah that's where I looked was ebay. I'm getting to understand the rx7, I understand a generic concept of the computer in a car, I learned obdII back in school and briefly examined the older systems, I know there are inputs and outputs, inputs will have reference voltages that vary i'e potentiometer, hall-effect switch, or the piezoelectric crystal-type ect sensors, etc. and the compter monitors it and changes the outputs accordingly, which changes the input which changes the output etc. I know that mazda used hall-effect sensors for the ABS and I assumed as well for the CAS. I have just been a little confused about the wiring, what supplies power to where and what will have power/ground if this or that sensor is functioning/malfunctioning. It's getting much clearer now thanks to you guys, I knew that you would help me and I can't thank you enough..

 

yeah everything's plugged up from what they say, of course I'm gonna have them stop what they are doing tomorrow AM and have them check the engine ground, I think I have it narrowed down to those two, either the ecu or it's ground. Would I get reference voltages if the ground on the engine is loose?

 

hey i have a issue with my car and i have been following these steps and my pressure sensor reads 8.5 volts but no spark or injector pulse i have tried 3 differend ecu's 2 cas and 2 of each coil

 

ok well duh read it wrong lol i do have 4.8 v on the pressure sensor but no spark or injectors and my main relay works fine

 

where does the ecu ground on the car??