Blind Freddie

How can you tell if an ECU is fried aside from other things in the car?
I accidentaly grounded the positive battery terminal, doing god knows what to everything.
Now the car is backfiring terribly, and it stalls if i turn the headlights on. Is there something i can do to test if the ECU specifically is stuffed. The cars turns on and idles ok with the lights off seemingly, but it backfires really really badly if you drive it, but doesn't seem to backfire just idling it on the spot.

Thanks for any help, Dan.

Project84

easiest thing to do would be to replace the ECU and see if the problems go away.

88seAQ

Have you checked your alternator it sounds like to me you got a low voltage problem. Get a volt meter and start the car let it Idle check voltage at the battery you should have some where near 14 v but any thing above 13.5v should be good then turn your lights and other accesories on see if there is a drop in voltage if you don't have at least 13v with acc. on then you probly fried your alt. or the wiring for it you can test those wires too. The specifices on the I am not sure of, but you need 12v (car off) at the bolted on wire in the back and at the plugin connector you should have 12v at one of the wires and I think that the other is is signal for the gauge (not 100%sure about those at the plugin though) Well best of luck to you hope it is something simple and not the ecu. Let me know how it turns out

ajsuper7

open up the ecu and smell it, if it smells like burnt circuts then it most likely is gone, you can also check and see if any of circuts are burned out, when my mop went out it fried the ecu and i found exactly what it fried b/c the circuts had that black carbon all over them...and it smelled awful when i opened it up.

Blind Freddie

hmm k. I hope it's just the alternator, but i don't think that explains the terrible backfiring...
I'll probably open up the ECU, and also test the alternator.
Could the backfiring be caused simply by a lack of power so that the spark plugs aren't firing and heaps of fuel is being pumped into the exhaust, or is the only thing that explains the backfiring that i've lost the fuel maps on the ECU. Because the car will still start and idle, and even rev seemingly fine in idle with a fried ECU?

HAILERS

The alternator idea sounds promising. I've seen low voltage cause odd problems.

Maybe a timing light to see if the LEAD coil assy is working?????

If the tach is working I'd say the trails are working.

No new ideas here....but I have doubts about the ECU being shot.

Might check to see if the bac is working by pulling its plug off at idle and see if there is a change in the idle speed when you take it off/put it on. Bad bac might accouont for the rpm drop with the headlights on. Might have fried the transistor in the ECU for the bac. Buck fifty fix for that.

88seAQ

The reason that the back fireing is happening is because the ignition (spark) is an electrical charge and without enough voltage (as in the situation when you turn your lights on) it can not spark as it is supposed to so this is most deffinatly where I would start looking any more questions go ahead and ask

88seAQ

also your would most likely have a poor idle or a no start condition if the ecu was fried and it would probly run pooly at all times, where the voltage situation is most likely only going to be noticed under a load when voltage is demanded most keep in mind the stock ignition system on a rotary engine is one of the most power hungry systems there are if not the most so before you go pulling out the ecu and smelling it you should simply hook up a volt meter and see if you have a voltage problem or check your volt gauge if equiped with one if you got a lot of drop in it when you turn on your acc then you probly hurt the internals of the alternator.

Blind Freddie

Ok i finally got my hands on a working multimeter today. Ok trying to test if my alternator is broken; according to my haynes manual, you can test if there is a short in the circuit by disconnecting the negative battery clamp from the negative battery terminal and putting a test light between them, and the light SHOULDN'T go on. I don't have a test light, however if i put a voltmeter from the disconnected - clamp to the - terminal, i get a reading of 13 volts. This is all with the engine off. So, this is a short right? Also, could this short be the ECU? I havn't opened up the ECU yet, as it's still got the Panspeed warranty stickers on there, and if they have a lifetime warranty i may have a slim chance of being able to ship it off and get it replaced (very slim though). I'm going to try and get my hands on a standard ECU in the next couple of days. My battery seems fine, reads 13 volts while car is off, and 15 while car is on. THe car still starts, but pours out a fair bit of grey smoke when it starts now, and it has trouble starting and staying on. As before, if you do anything that increases the voltage in the system, the engine stalls. And it even stalls if you just rev it. Before it was idling fine in neutral, but now it sounds like it's struggling. Funny thing is, nothing has changed from then until now, aside from the car sitting for a couple of days. But anyways, could my reading of the voltmeter from - clamp to - batt terminal indicate a short? And could this short be a fried ECU??

Thanks alot, Dan.

88seAQ

What you are testing for with the battery cable disconnected is called a parasitic draw and that will only cause your battery to go dead while you are not running it, basically it is an electrical acc. that is using current all the time sometimes just a blown domelight will cause this (also this test is best done with + cable off and a light between it and the battery +) as far a testing for a short to ground from the battery a short can cause a draw. Well sorry I can't give you anymore helpful info. I would give the ecu swap a shot now. I think you do have a draw and it could possibly be caused by a short. I would check grounds at the distributor that may be bad. I am going to try and give this one some deep thought and I may come up with something. If you get anywhere or nowhere with more info let me know whats going on or what ya find out.

J-Rat

iTrader: (2)

Hows about you make the ECU tester lights and check it that way. Thats just about the easiest way I have found to check and see if the ECU is online.

Blind Freddie

Hey,
Ok I will update you all on what's going on. I havn't done much yeh aside from print out all the tests for the alternator from the FSM. The Haynes manual is a little tricky with how to test if the alternator is bad, so anyone know an easy way? There's about 20 tests in the FSM too, half with the car running, and the car doesn't seem to like being run atm, so i'd rather stick to tests that do'nt require the engine to be running. I'm pretty worrying, i think i've really fuked something badly. It's really hard to start and a fair bit of grey smoke comes out when it finally starts, so i guess that's the just the fuel pouring through it. It stalls really easy, i just find it weird that it idles so badly now when the other day, just after i sparked it, it was idling fine in neutral, just as soon as u drive it it'd backfire really badly. Yet revving in neutral sounded exactly as it always did, but now it sounds pretty horrible, and i'm not game enough to keep my foot on the pedal to try and warm it up, it just sounds so unhealthy. Anyways, i've emailed a mech, and i'm going to ring a local rotary workshop to ask to lend an ECU and also ask them what they think has happened, maybe they know another moron that's done the same thing. Thanks alot for all the help, and i'll let everyone know how i go with diagnosing what's dead, i'm sure i'll have lots more q's.

Just the main thing i need to know now is, an easy way to test if the alternator is dead?
An easy way to test the coil packs? (The resistor method in the hayens manual is a little dodgy, i take the plastic cover off the lead coil, the one at the front of the engine bay, and then i try and measure the resistance between the two terminals, but i can't get a steady connection, if i try and measure the actual bolts on the terminals at the top, i get no reading at all, and i have to try and touch the metal under the terminals, and then i get a reading but it varies, so i just havn't got a steady connection, so is there some other way to test if the coil packs are ok, without a coil with ignotor check thing like they use in the FSM? Or should i just take the terminals off completely and measure the resistance that way?)
And what's this ECU tester light? The car still starts, so i guess the ECu couldn't be completely dead, but the fuel maps may be gone...

Once again, thanks for all the help.
I just found out that the suspension on my car is Panspeed Ohlins pro suspension, 3,150 dollars american from one website ! So at least the car is worth all this trouble.

88seAQ

In my newly found opinion most 7's are worth the money (my opinion only) love them ever since I bought mine almost 2 yrs ago for more than it was worth 2k for an 88 high mileage with an engine that was supposed to be rebuilt right 30k ago and I am currently rebuilding the engine. I still think it was worth my money, i love mine would not trade for any soupped up post 78 car on the planet, unless it was superduper sweet. I do know this the rx7 is the most picky problematic car that I have yet to find out there. I had to put a starter in mine two weeks after I bought it and then a tps a month later totaling over 300 bucks and that is at a on job discount (new parts). A few weeks before I had the motor go an me I put a new slave and master cyl on it so I have had my far share of problems with it. I know this if you love yours like I love mine it will be worth the time and $$$$$$$$$$$$$$$$$$$$$$ (lol) to fix yours. This is coming from a formerly diehard chevy man (and family). I wish you good luck from here on out with yours the biggest problem is I can not get my hands and senses on it and help fix it. I can give you this much though. You say you now have a working volt meter. If the car is idling and you have 14+ volts the alternator should be working correctly I say should because unless you have an amperage reading on your volt meter you can not be sure of this. An alt can give you voltage and not amperage but not usually. If there is a (good) shop near you and you have the confidence in the car to make it how ever far (hopfully close) take it there and let them do a starting and charging test on the car if everything checks out ok then you will be sure that the trouble is not in the alt or shorted battery or wiring in the charging system only (if you can not find an ampmeter). I wish you good luck from here on out and I still want feed back any problem that you have now I may have in the future and I want to know how things go with you and yours. Hope I can help!! That is my favorite part helping somone in need.!!

Blind Freddie

Hey,
Well i've got an ampmeter, just tell me what tests are the best to do. I've got a multimeter, so that measures current, resistance and voltage. So no insights as to what damage i might've done aside from the alt? I still have a feeling it's voltage related, by the stalling as soon as any electrical load is placed on the engine, and even the difficulty starting now i think is voltage related. But i guess i could've still fried the ECU... Well, what amp-meter tests should i do?
And remember i've got the FSM tests for alternator printed out, is there any easy one's that show alot you could recommend?

Thanks, Dan.

powrdby13B

if you really fried your ecu would the car still start?
I spose you could just test voltages and stuff

88seAQ

look for resistance in the grounds in the ignition system next

WAYNE88N/A

There are not a whole lot of electrical components on our cars that are polarity sensitive, but the one for sure is the alternator, due to the diode bridges contained within. The ECU? I would guess it is, because of the transistor circuits. Probably the CPU and a couple of other micro circuit "boxes", as well...

In theory, everything else on the car doesn't care which way the polarity is, as long as the current's flowing (except maybe the starter).

That being said, you MUST check the alternator...Hook everything back up, and put the meter probes across the battery terminals, observing correct polarity. Got something 12.5 volts or over? Good...

Now leave the meter across the battery terminals (find something to keep them there, such as "alligator clips", and place the meter in a position that can be seen from the driver's seat. Start the car, I don't care how it runs, as long as it's running...What's the voltage now? Anything over 13.5 volts is good, 14+ even better...If you're seeing that, the alt is good, if not, she's bad...

This is the easiest way to ops check your charging system, you're making this harder than it should be...The FSM checks are mainly "bench checks", i.e. something you'd be doing if you were overhauling the alt yourself...

If the alt is good, now start looking at the ECU...One step at a time, that's how troubleshooting is done

hugues

just adding to WAYNE's post ...

The FSM tests for the alt are pretty complete: they test for voltage and amperage .. but usually most pple will only do the voltage check which is better than no test at all (the 1 wayne is talking about).

Check here:

http://www.geocities.com/huguesdc1/charging.html

Tests 2 and 6 are very easy to perform and take about 5 mns.

You could also bring the alt to a parts store to have it bench tested but you have to hope the person that operates the machine knows how to correctly use it.

Once you have determined the charging system is ok, then you may want to look at the output voltages of the ECU, in particular, the one for the BAC ... see info here:

http://www.geocities.com/huguesdc1/idlecontrol.html

or you could just swap ECU and see if it solves all your problems (they can be had on ebay for $25-30)

Hugues-

Blind Freddie

Hey,
Hmm yeh i check that,
volts when car is off across battery is 12.9
Volts when car is on is around 14
So unfortunantly it's not as simple as the alternator.

I've organized to lend an ECU next tuesday from a local rotor workshop, so i'll let you know how it goes after i plug it in and fire it up. When i asked them what i would've done, they said the main fuse, but the fuse is fine, when i described the symptoms he said just lend an ECU and check it out. He's a nice guy, has helped me a fair bit. Anyways i'll let you know how it goes with a standard ECU. I'm not sure how much they're worth either, a second hand one that is.

Thanks again.

Blind Freddie

I just noticed that final reply there. I'll test my bac ECU connection tomorrow, thanks.

88seAQ

Its good to have friends fred and we have been racking are brains here like I said hard to tell without being there and using our senses, but if not the ecu since you have one that you can check it with, I would start at the grounds and check for resistance at coil and ignitor grounds. The distributor (hall effects sensor.....whichever) grounds may also be a problem. Man fixing a vehicle without being there takes for ever lol Once again good luck and I hope you don't lose the love for your 7 don't worry it is worth it once you are back on the road eating up curves and Mustangs HAHAHA!!! you will know it was well worth the time and money that you have put into this precious oddity that we call an RX7......!!!!!!!!!!!!!!!!!!!!!

ilike2eatricers

I may have a problem with a defective ECU and this may not be the easiest way to check. There may have been a problem that caused the ECU to go bad. If one didn't fix that problem first they may be going through a few ecus.

Blind Freddie

Yeh good point, i'll warn the guy at the workshop before i test the ECU.
Also, just wanted to say, thanks again for all the help and advice. I was shattered when i realized i'd damaged the car even more, but hopefully after this is fixed it will run better than it did, maybe even without a hunting idle!
Ok i havn't tested the ECU bac valve connection yet, i think what i'll do is just wait and try a standard ECU before i test mine. But what i would like to test is the coil packs.
Ok in the Haynes manual, it says to take the little plastic cover off (this is the leading coil pack, the one at the front of the engine bay next to the battery), and test resistance across the two wires. For some reason i get no reading when i touch the probes to the bolts that hold the two wires on; i can get a reading if i try and shove the probes under the bolts to the metal terminal underneath, but the reading doesn't stay steady, so it can't be that accurate. Can anyone think of anything wrong with just unbolting the two wires and measuring resistance across the two terminals that way? I don't think you're meant to be measuring resistance through the wires anyway, but maybe you are? I'm not sure. This test is meant to determine if the coil pack is bad, it's the only test the haynes manual has, and the FSM uses some coil with ignotor test pack... I'm worried about testing voltage or amps across these coils because the FSM clearly states that if you don't connect a resistor in certain places etc. when testing voltage on the coil pack you can damage it.
So in addition, does anyone know an easy way to test if the coil packs are working properly, both leading and trailing?
Thanks heaps, Dan.

Blind Freddie

bump
anyone know if taking those wires off the leading coil terminal and measuring the terminals will give me an accurate reading?
Or anyone know an easy test to check if the coil packs aren't working properly?

Dan.

WAYNE88N/A

OK, what are you doing? Coil resistances?

You can remove the nuts & terminals if you want, but be careful- those are small studs, and are easily broken if the nuts are corroded on & you give it a lot of "oomph" to remove them.

In fact, you'll get a better reading with at least one terminal off because then the meter won't have a tendency to read back through the circuit.

Put the two meter probes together- you should get a steady 0 ohms. If not, your leads are on the fritz (it happens), and everything you try to read on the car will be inaccurate (also "zero" the meter with the leads together, if yours has that function).

You don't need to test voltage on the coils...It's just a bunch of wiring wrapped around a magnet. If it's reading 1 ohm or less, it's good. The ignitors, however, are a different story, I usually check the input voltages from the main relay at the black/yellow wires at the connectors (2 for trailing, 1 for leading), or, you could follow that wire down to the actual ignitor terminal, then check the triggering signals at the ECU itself (pin 1V on the S4's, should be .8 volts).

There is no reason to check amps on this circuit...