odd sputtering, burn out ecu?
 

well today i went to drive my car and it wouldnt start. so i pulled th eplugs to do the oil in the spark plugs trick and it got it to fire off. but since i was already there i put in a fresh set of plugs.. the old ones were quite fouled, although they had roughly ~600 miles on them. not sure why they fouled so fast

well prior to swapping out the plugs i noticed if i took it up to redline in second gear it would just stop at 6k. wouldnt go a hair more. it felt and sounded like it was sputtering. seems kinda odd. but this was the first time driving it this hard since the rebuild. after swapping the plugs it didnt do it in second but now in third gear. stops right at 6k. this seems very odd to me. so while driving home from work i pulled off the freeway to try and see if i could get it to go passed 6k. well when i got to the stop sign on the off ranp it died. i just compression started it this time as i was still rolling.
when trying to get up to highway speeds again it was sputtering and whatnot while in second and all the way thru 5th gear. just completely mind boggling because it was running so good before i decided to push it a bit harder.

now that i've given you such a long story im almost thinking that this has something to do with the over charging issue i just realized i had.getting upwards of 18.5 volts when above idle. could this have fried something?


also the motor is a s5 with s4 internals. no emissions, stock catless downpipe. and open intake.

after doing tons of reading it almost sounds like fuel cut. but i thought that you would only hit fuel cut if you went over a certain boost level. im only running 5 psi so not sure why it would be hittin fuel cut:scratch:

18.5 volts is WAY TOO MUCH. Yes, you could have fried just about anything. Time to start checking for burned up circuit boards. I'd start with the ECU.

Fuel cut is at 8.6 psi.

yea i know its a lot:/ i couldnt figure out why my boost gauge and amp would stop working till i got to a stop sign. then i tested the alt. it was putting out wayyyy too much. is there a way to put in a regulator to lower the voltage significantly? well i guess i know what im doing tomorrow..
is there a way to see if the ecu is indeed bad without a backup? that wont be here till saturday/.

No, you need to get a new alt or get the old one rebuilt.

oh shitty deal. looks like i got something else to replace

could be the voltage issue which could be either the alternator or battery but not likely the battery if it is cranking over fine.

the RPM cut issue sounds like an injector is dead, with only 3 injectors firing you will not be able to go past 6k RPMs without running severely lean. the old OE wiring harnesses especially on the turbo cars are notorious for having bad injector plugs, i would check them out or put a wideband on the car to see if it is in fact running lean before you hit that 6K RPM "wall".

well i know the injtectors are not dead, just got them back from witchhunter. but the wiring could be bad, i've already found a could wires on my harness that were toast. before i attempt to load the pfd there is a proper way to test the wiring at the ecu or something right?

also after gettin home yesterday i pulled the plugs and looked at them. well only the leading plugs. but the front plug was white on top and the rear was black. what would something like this mean?

so i was tinkering around testing all my electrical parts and started with the cas. first thing i noticed was it was lose. silly me. so i re-timed it. got it to fire up after de-flooding it. took it for a spin same thing.


well i noticed that i had an exhaust leak at the d/p-turbo. looks liek the gasket is shot. while investigating this leak i got out a piece of wood to help listen for wierd sounds cause i heard one from the turbo. i was listening with the wood and runnin the throttle with my hand and the son of a bitch shocked me which is leading me to think i have a grounding issue. am i right? how else would the throttle get juice?

Sounds a little like the MAIN GROUND points are not connected up right/good.

Main ground points are the LARGE cable from the batterys neg post which terminate at the long bolt of the starter (might be bolted to another nearby transmission bolt instead) and the same cable gets grounded to the CHASSIS just below the left strut tower. Those two gnd points are the ones I mean. NOt the flimsy gnd strap from the area near the wiper mtr to the transmisson.

well i got the sputtering issue figured out. cleaned the hell outta the MAIN GROUND,. thanks for tht advice hailers! but now i cant seem to ever get the car to start,. it just cranks and cranks and cranks. really irritating. and also it dies on me now when i go to stop at a stop sign. only way i cna get my car to start is to pull the leading plugs and put oil in there. doesnt make a difference if the car is stone cold cold or nice and warmed up.

Is your ECU grounded? I was testing mine one day and just had it sitting on the carpet, I got a very similer effect as you did. It stalled out about half way to work, so i pushed the the connectors back in and it got me to work. Long story short. It wasnt bolted down so it was picking up ground just by sitting on the metal. When i broke (braked?) the ecu wasn't grounded as good because it moved. Putting just one nut to hold down the ECU fixed the whole deal.

so your saying that by making sure the ecu was bolted down to the car made the difference? cause now that i think about it somehow i ended up with a extra bolt when i put it in. maybe ill have to check that and add another one in.

well i pulled up the carpet and sure enoughi was missin 2 nuts. stuck them in and nothing.. de-flooded it and still nothing.. almost as if the car isnt getting enough spark or something.

Please spare us the details!

oh sorry i read from augiedogie above saying he was having issues similar to mine and it turned out his ecu wasnt bolted down all the way. i looked and seen mine wasnt bolted down all the way so i fixed that, but that didnt fix my issue:/ it seems as if im not getting enough spark to ignite the fuel. so new plug wires will be here tomorrow and im going to test the coil packs now.

I was joking. Just reread the highlighted text until you see what I saw. Also, I don't believe the ECU grounds out externally but more like internally.

yea it seems almost everything i read it grounds thru that damn wire that hooks to the block under teh uim.

well i checked the wires and the coils. dont have a way to test the ignitors, unless there is a different way not described in the FSM

here is was i got for the coils. leading - 0Ω trailing 1 - 0Ω trailing 2 - .4Ω
and the wires seems pretty consistent. leading wires were ~8kΩ and trailing were ~5.5kΩ. not sure what they should be cause the FSm says 16kΩ per 1 meter of wire.

well im completely stumped now:/ i've checked every single electronic part that has to do with the engine. everything is testing out good. i've restabbed the cas about 59230745 times. nothing different. just spins over and will somewhat act as if it wants to start, but it doesnt. really irritating as this is my dd and is kinda keeping me trapped at home. anybody have any suggestions?


ok well i was poking around and seen this https://www.rx7club.com/showthread.p...e+motor+whales and it says run 1/2 oz per gallon, im running ~1oz per gallon. maybe slightly more. can this be the issue with it not starting? as the gas would be more diluted than it needs to be. im really just looking at every single possiblility right now because nothing seems to be working.....

after adding in my spare ecu that came today i was able to get it to start up on the 3rd turn of the key. was really happy so i let it idle in the driveway. when i got back to it after it had warmed up i sat in the driveway and just free revved it to see if i had indeed fixed the high voltage coming from the alt. turns out its still there.... i noticed that when i would rev it up if the voltage got higher than what appears to be 15v on the stock gauge it would drop the idle down to ~500 rpms and act as if the car was off. then the car died on me so i attempted to restart it and all it would do is crank and not even attempt to start. im at the end of my wits and teh next step that i see coming with this car is to sell it:/

This is what you need to do and should have done in the first place.

Buy or rebuild the alternator. The internal voltage regulator is fried and that is what caused the ECU damage.

Replace the ECU again. It is very sensitive to voltage variations, specially over voltage. Most internal components are only rated to 16V.

That will allow you to drive your car again.

You can figure out the rev limit problem afterwards.

so your saying that for the very brief half second the voltage was higher than normal it fried the ecu? sweet. i love giving this car all my fucking money. and i take it there is no way to repair the ecu myself is there?

Short ansewr is NO. You most likely won't be able to fix an ECU that has been fried by high voltage. 16 volts is the maximum voltage for a lot of internal components. A car should not have a voltage going that high anyway.

If you wish to have your rex back on the road you need to FIRST replace the alternator with a new or rebuilt one, then replace the ECU with a used one from a well known seller on e-bay. They go for about $100 - $250 depending on availability.

If nothing else failed, (your car did start when you replaced the ECU), that should do it.

Good luck

well i got the new alt today. jesus that was an adventure in itself.
the quest for a new ecu has begun. yea i figured trying to repair it was outta the picture, but always good to at least try. thanks for your input kenneth!!

..... wekk the problem still persists. had a hell of a time getting the car to start today, ended up using oil.. runs fine till i start to boost in the high rpms. just seems to cut out and im up against a wall. i think i barely got the car up to 90. didnt really act like it wanted to go faster. but when i get to thei "brickwall" i still have full boost, a whole 5.5psi, while its going on. now i just realized my turbo to downpipe gasket is, well gone. so i have an exhaust leak right there. hopefully this is my issue