KA24E cutting out and don't know why

[Vegascorbin]

This car is a 1990 240SX with the KA24E 5-speed. It has been converted over to a Dirt Track Race car. When we rev the engine over 3000 to 3500 it just stops running untill the RPM drops below about 1500. Then it runs fine until we hit 3000 to 3500 again.

What we have done/tried:Engine has been totaly rebuilt to STOCK specs. Total of about 1 hour on new rebuild. MAF has been both swapped and cleaned All emissions have been removed. Unused Vacum lines capped off.Plugs, wires, Cap, Rotor have all been replaced.Injectors swappedECU SwappedPower Transistor swappedDistributor swappedFuel Pump replaced with a NEW Walbro 255LPH High Pressure pumpFuel tank replaced with a Racing Fuel CellFuel Filter replaced with a stock filterNew TPSExaust is removed after the collectorTransmission Wireing and Speed Sending unit are NOT connected.Dash has been removedO2 Sensor has NOT been changedFPR was SwappedBelts, Hoses are new along with new Radiator

Best we can determin is that the ECU is cutting fuel flow by turning off the injectors but this is hard to confirm. We say it is a fuel cut off because when the engine fires again thare is no smoke from a fuel rich condition that would occur if spark was cut.

With so few sensors giving input to the ECU why would it cut fuel? We are not even getting close to the 6000 rpm area that one would expect for a rev limiter.

Sorry for the long post but I want to give a complete picture and hope that someone can give an answer. There are other simalar posts but none that either say what was finaly replaced to correct the problem or we have allready replaced what they did.

PS: Please do not sugest swapping to a DOHC or SR20 etc. We race a stock class and must run the original motor type. Turbo etc also not allowed.

Thanks in advance for your thoughts and ideas.

[T-Bird]

Check the air fow meter connection, make sure there is no corrosion or damage to itAlso check the all the other connections for the same, mine did this once and it was the air flow meter connector

[Vegascorbin]

Thanks for the info. We will check that out and post results.

[idriftnsj]

i think that the gear sensors on the transmission have some thing to do with it to but check ur tps sensor connections mine came off at half track and my car shut down at 4grand

[Vegascorbin]

Finaly got a chance to workon hte car today. We did check the MAF connection and they were not as clean as we liked so we got some cleaner and worked them over. I need to research how to take the terminals out of the housing to be able to clean them properly. Also I want to tighten them up a bit.

I did try running the car at 5000 (after cleaning) and it held RPM fine. I then unpluged the MAF and it cut out just like it did on the track. I think we are on the right track. We will know more after the next race (next Saturday)

Thanks for the sugestion. I will post more when we know more.

[Vegascorbin]

Ok finaly got a chance to report back what we found out on Saturday.

Basicly nothing changed. We did replace the MAF Connector and did not fix it. We dis find a frayed wire going to the Power Transistor and repaired that but it made no diferance.

One other thing we found out is that we can run up to about 4500 in second WITHOUT the engien cutting out but only upto about 3000 - 3500 in 3rd (the gear we need to race in.)

Can any body tell me under what conditions the ECM will decide things are so bad that it must shut down the engine? We think that the ECM is getting confused and is eather getting a signal at the wrong time or not getting a signal it is expecting and it decides that all heck is breaking out ant to sut down as an act of self preservation. Seams a little advanced for this gen of ECM but thats is all I have right now.

Any othr Ideas guys? (and gals if you are around) We are stumped.

[compression]

have you checked the ECU for codes? A CONSULT scan tool would be ideal, but not alot of people have them. When its running and revving, watch the fuel pressure, it should increase as vacuum decreases.

[Vegascorbin]

In the past we have not had codes but will check again to be sure.

I don't think it is Fuel Pressure as we did swap the FPR with another one from our non-running doner car. If fuel pressure was low, I would expect the engine to slowly die off as fuel required exceded supply. That is not what is happening. In this case it is like throwing a switch. But only under load. We can run 5000 all day long as long as we are not in gear.

[Vegascorbin]

We checked for codes again tonight and once again got the good old 55 no trouble code.

THEN.....we went to mode one to check just hte O2 and expected to se flashes 5 or 9 every 10 seconds depending on which referance you use

BUT....We say NO flashes. No error code but an O2 that is not working. Went and picked up a new O2 and we now have flashes. We are going to go to a dry lake bed on Saturday and see how it runs.

[Vegascorbin]

We took the car to the dry lake bed for some testing and found out that the new o2 sensor made NO differance. We made a few runs and weree able to find out it allways cuts out at about 3500 to 4000 (tach is a little flaky) in either 3rd or 4th. It will some times cut out in 2nd but not allways.

We swapped the MAF and it made no differance. Our best guess now is that the ECU is not getting the MAF signal for some reasion. We hafe checked the obvious and now are going to start striping doen the wire harnesses lookin for either hidden damage or an old repair that has failed.

Any thoughts or sugestions?

[Truck]

Well here comes the thoughts and suggestions.

Could it be the transmission? How does it run in 5th? You mention some wireing is not hooked up... is there a reason for that?What about timing? Have you taken it to any knowledgable people in the auto business?

It seems to me that your having problems with your transmission. Not the mechanics, just the wiring I suppose. You enjoy free reving under no load, but are having trouble when travelling. Was the car running before you made it a track car? If so, I would suggest you consider the things that you have changed first.

[Vegascorbin]

The car was allready a Race car when we bought it. The Trans was bad when we got it and it also had this cuttoing out problem. We got the race car and a parts car both for $500.

When we swapped the trans we found out that the wiring for the trans was torn and cut out. We just left the wiring dissconnected.

We have not tried the car in 5th gear as we don't have the room. This is a total race car. If we take it on the street big trouble.

I understand your thoughts but what I don't get is that when you look at the wiring, other than the speedomiter output of all of the switches are "open" unless you are in reverse, 4th or 5th. If it does not "know" what gear you are in why does it effect the problem?

Right now I will probably reconnect the trans wires just because they are not connected and should be but I don't expect a big change. I hope I am supprised.

Thanks for the input and keep the ideas coming.

[Vegascorbin]

Currently re-wireing the maf all the way from the ECU. We found a couple of splices in the wire that I didn't like.We think that both MAFs we have are bad. After re-wire if it still doesn't work we will most likely bite the bullet and buy a new maf.

[idriftnsj]

go to the junkyard and pull one out i might have an extra i gotta look in my basement

[idriftnsj]

hey man ur better off tryin to find 1 at a local junkyard un less u plan on buyin a new one from an autoparts store 109.99 with a 54.00 core charge

[Vegascorbin]

Yeah we probably will go for the $$$. We have two MAFs now and get the same result with both and we don't KNOW that either one is good. It has come down to either wires, which we did not really see any thing there, or the MAF itself. Once we finish the wire reroute and "repairs" we will voltage check the MAF (Thanks NICO for a procedure) and decide what to do. One advantage with new is that it has a 1 year warranty. about $105 plus tax and no core as we have one to turn in.

[nismopu]

i can send you one if you want one I got quite a few laying around, you just pay for shipping. OH and they work very well. peace.

[Vegascorbin]

Latest updateI think we have found the area that is causeing the problem.

After re-wireing some parts of hte harness (none of the injectors) I fired up the car and it was not running right. I pulled injector wires one by one and found that we were only running on 2 cylinders! (2 and 3)

I had been working with the ECU so I double checked the connection and all looked well. When I moved the wires the idel smothed out etc. Thought that was odd so wiht the ECU sitting on the floor I just flicked the wires with my finger and the engine died. Re-started it and tried it again. Flicked it again and the idel would change etc.

So it lookes like we have bad wires at the ECU connector even though they look good. We are going to try to swap engine harneses with one from our doner car and see what we get. I think the ECU being exposed to the eliments in this race car took its toll. Once I get it working right I am going to build a cover for hte ECU.

[NC_240coupe]

You were running on only 2 cylinders and you didnt notice that right a way i had my 240 run like that and it sounded like straight garbage lol but its not the MAF sensor because i had a problem with that and thats when the car would start and die if not it wouldnt start at all and i just had to scrape the corosion off with a pic....but can you post pics of your car i want to see that i see nothing but JDM wanna be 240's where im from and yes including mine

[Vegascorbin]

Yeah, it sound silly that we would not know it was only running on 2 cylinders but in my defence the car is running NO exaust. Header only so it is loud. And we have never had the car running correctly so have nothing to compaire to.

We did swap the ECU Harness last night. We now are running on 3 cylinders. A 50% inprovemnet #4 is not working so we have to swap that injector out and then head to the dry lake bed to test it this weekend.

I think we are getting close. When we get it fixed and win a race then I will post a picture

[Vegascorbin]

Bump/Update

Ok most recently we found that the #4 injector was not firing. We had swapped injectors before to fix this and ASSUMED it was fixed. Everyone knows what happens when you assume. first time we swapped all four but this time we swapped just #4. Still not working. Seeing as we had changed the injector and the wiring harness (for differant problems) the only thing left was to swap the ECU.

Low and behold #4 injector starts working. Reset the timing and things run great (we think). The car seams to have a lot more power (duh!)

No time for testing so we head to the track.

Start of the Heat Race my son hits the gas and to make a long story short it took the entire front stright for him to crash

Broken left front strut bearing (aka Strut Mount) and lots of fender damage for me to fix. Oh, well. Thats Racing.

Also the car still falls off above 3500 RPM. Has to be MAF. Nothing else left. Changed ECU and Harness.

I will update when I have more to report.