Suspected ECU problems

[tyrodtom]

I've been circle track racing a 90 240SX since 2003, 23 wins so far. All of a sudden a problem has occured, the car cuts out at full power, after about 5-6 seconds, stays powerless for about the same amout of time, then comes back full power. Will repeat this endlessly as long as i'm willing to drive it.

It does this in 3rd gear, will only do it at the track under full thottle. If I put the car in 4th, it still does it, but at longer intervals. I can't similate the condition in neutral, and don't dare drive it on public roads to test it since it's a full race car, unmuffled, caged, windowless, decaled, etc.

I've tested fuel pump pressure, but not under full load. When the car shuts down, it's instant, no backfire, just completely goes away, then just as suddenly comes back to full power. It's like something suddenly is shuting the injectors off, and I would think only the ecu could do this. I've got a FSM, and have run every test I can think of, the computer will not do a valid self check, so I suspect more is wrong with it. The car is a completly stock KA24E, with all smog equipment removed, and has run fine for years this way, until all of a sudden this problem appeared.

Any thoughts on something I might have overlooked???

[del82]

What do you mean valid self check?

If it's a bad computer, many times it'll give you bad error codes, when you go to check the parts they'll be within spec, and that's what will clue you to it. The other way to check is just swap out the computer with a known good unit, and try it again, but I suspect that'd be on the pricey side, what with having to pay for a track day to test it out.

If its not a bad computer, I suppose it could be a vibration issue, since it only happens under load.

[tyrodtom]

I got another ecu from another 90 240, but evidently they're not all compatable. The engine would only start with a lot of throttle, would never idle, when I let it run at about 2000rpm for maybe three minutes, I though maybe it would "learn " the engine after a few minutes, it got about 4-5 feet of the exhaust pipe cherry red, and wouldn't rev past 4000. I think it had it running crazy rich and radically retarded the timing.

I see a pdf file of ecu compatability on this forum, but I can't get it to load on my computer.I have a A11-B17-G13 in it now, I had a A11-B16-G12 in it for years, and the hot pipe ECU was a A11-B45-G08.

It's fustrating to have a car that will only race about middle of the field, when I know if I can correct this problem it'll be back up front.

[Vegascorbin]

#1 Congrates on your wins, we are still looking for our first.

You are not alone on this problem. Let me guess, it will cut out at about 4,000 to 4500 RPM (like turning the switch off) but if you step on the clutch and take the load off the engine it will come back and go about 500 RPM higher.

There was a 3 page thread that was last updated a couple of weeks ago that covered this problem, but no one was ever able to do an exact fix. Many people will say that it is your MAF etc and while that could cause problems it most likely is fine.

Can you think back to anything that happened when it started. Had to give it ajump start, conflict with another car, differant fuel, anything that might point use to a cause and then a cure.

Are you running any type of dash? BTW as best I can figure out, this is not an unusual problem for the SOHC when they reach a certin age. Hav enot heard of it happening to DOHC.

[tyrodtom]

I don't have the factory dash, but I do still have the stock instrument cluster bolted to a aluminum dash. I race mostly at a 3/8 mile asphault track, 17 deg. banking, this happens just a little before the middle of the straights. My peak rpm, when things are right, is about 6000-6100, so this is happening well above 4000-4500, it's somewhere above 5000, because I barely get down to 4000 in the turns. I'm going to race it tomorrow. During practice i'm going to experiment with several different tricks, the clutch pop you discribe, turning off the ignition switch for a split second, and not giving it complete full throttle. If none of those tricks help, i'll just race it in 4th, and settle for another mid-pack finish. I hate to do that, cause that isn't real racing to me.

I've read the other threads with similiar problems, and Googled it too. So far, they haven't helped, but i'm gonna keep looking. And I guess i'll have to try my luck at another E-Bay computer.

[big monkey racing]

The reason why you had so much problem with the issue of the cherry red exhaust is this ecu A11-B45-G08 is for a 1991 dohc automatic. How do you have everything hooked up in your car cause I also have a 1990 240 that I race at a 1/3 mile dirt track. Do you have schematics and pics of how you have it all hooked up so I can see if I have mine wired the same as yours. If you find a fix for your 240 please let me know cause mine does exactly the same thing yours does. If I figure mine out I will surely let you know what fixed mine.

[tyrodtom]

If we don't get a rain-out i'm racing today. I'm surprized a ecu from a DE would even run my car at all, I put my old suspect ecu back in and there doesn't seem to be any additional harm done by that episode.

I'll have more time tomorrow to post my wiring changes, they're very few, it's basically all stock, and the car ran very good until this lastest problem. More later.

[Vegascorbin]

Are you still running the speed cluster? If so check this thread:

zer...miter

[tyrodtom]

I still have the cluster, but all the wires on the transmission were cut off several years ago. Maybe in my case I should get under the car and make sure nothing is in any of the empty plugs. And I have another cluster.

[Vegascorbin]

I think what is hapening is there is a signal that goes from the cluster to hte ECU. My guess is that when the ECU does not see this signal it goes into some type of "Limp mode". It appears that the ECU gets this signal even if the speed sensor is disconnected.

Try your other cluster and let us know if it works. It would be great to confirm the fix.

Our cluster was removed prior to us getting the car and the car had the problem when we bought it. We thought it would be an easy fix.

[nuts510]

it's been my experience with the older model Nissan's if you cannot go into self diagnostic mode and the car still is running ECU is bad!!!!!!!!! I have been working on nissan for many years try replacing your ECU abet the car starts run in perfect. also congratulations on getting to race a independent suspension Nissan in circle track racing every time we ran one they'd make a law against it chickens.

[tyrodtom]

I finally got another ecu, I installed it , and the engine at least seems to run fine, but I haven't put it under load. I'm going to take the car to the track Thursday and practice it with just the new ecu. But i'll also have the other cluster, and i'll have a fuel pressure gauge on the fuel line mounted so I can read it from the seat. If the new ecu doesn't change anything i'll change clusters and see what developes. The fuel pressure gauge will tell me if my fuel pump is failing under full load. So Thursday I should know a little more.

[tyrodtom]

Well guys, in my case, it WAS the ecu. Went to the track today and practiced. The only thing different was another $ 65 ECU off of E-Bay. It pulled smoothly all the way to 6000. In the past i've run both 5 speed and auto ecus and it made no difference, the car ran good with either. This ecu is from a automatic. The car felt real good, wish me luck. We race Saturday.

[big monkey racing]

What did you have to do to make the auto ecu work? Would you be willing to send me the bad ecu so I can disect it and find out what went bad.

[tyrodtom]

I did nothing but install it. I've cut or removed all 3 of the hookups on the transmission several years ago when I replaced a clutch. I think I know what's wrong with my old ecu. I usually store the car outside under a tarp, it has nothing but a Lexan windshield, and sometimes the ecu got wet and water got inside it. The #4 injector would quit firing. I'd take the ecu out,take the cover off and drain the water out, the firing circuits for the fuel injectors are on the bottom, and #4 is on the very bottom. Moisture would short out the #4 first. I would also take a soft toothbrush and clean the corrosion off the contacts. eventually this combination of corrosion and me brushing it away went thru the connections. I removed the component, and replaced it with another. Either that component was bad or my repair job with the solder sucker and solder gun wasn't so good.

[tyrodtom]

A real good night at the track. I took the pole, and won the race too.

Late last year I took the head off and lapped the valves, but the very next race the ECU problems started. I could tell the engine was making much better power off the turns, but I had the power cut 2/3 way down the straight. Lapping those valves and making sure the sping pressure was right increased my cranking pressure 10-15 psi, and I have no idea how much HP I gained.