Hi there,

I've got a chipped 1995 WRX RA that has of recent developed a problem where sometimes the engine just cannot rev. During these times it is possible to coax it to go to maybe 4k rpm by pressing very lightly on the throttle, however at any real amount of throttle input (enough for the car to move if in gear), the engine misfires and just can't get above about 1500rpm. At those times it feels and sounds like a car with launch control would sound.

The problem can be fixed by shutting off and restarting the engine and if it's really stubborn by resetting the ECU. It can re-occur within 5 minutes or can be fine for a few days. The current chip I'm running is the stock Z5 ECU map with modified boost and timing only. I have swapped the chip out with 2 others I have with the same symptoms, however all these chips used to work fine about a month ago. I have also replaced cam and crank sensors without any improvement.

The next step I will take will be to swap the ECU. If anyone has any other ideas I can try, please contribute. Thanks.

 

More info after some more troubleshooting.
Swapping ECU and MAF makes no difference.

I have verified that when the engine refuses to rev, it cuts off spark. So basically at idle, the spark is fine, as soon as I attempt to rev the engine, it cuts off spark and spark resumes when I lift off the accelerator.

I have also logged MAF, RPM (in case of dodgy cam/crank sensor) and TPS while this is happening and their values are fine and change linearly as expected.

The problem occurs almost exclusively when the engine has been idling for example at traffic lights. It's almost impossible for it to happen when the car is actually moving, especially when on boost.

Anyone have any ideas on what this could be?

 

How sure are you of the condition of your:
- plugs
- coil-packs
- fuel pump
- injectors

What fuel is the car normally run on, and how long have you had it?

Besides plotting MAF voltage values, what else have you done to rule this out as the problem? Have you swapped it over with another, opened it up to check for dry solder joints, visually examined the wire element for obvious signs of fouling/wear/damage? I can try and take a close-up picture of mine for comparison, which is nearly new and fixed some atrocious running problems I had recently, despite the voltage gradients from the old one looking more or less 'normal'.

 

I've had the car 3 years, I have no idea what octane of fuel we get.

Coil packs - car is converted to single coil, have tested with another single coil and have also connected a single coil pack and a spark plug - this was when I saw that the car totally cuts off spark when I attempt to rev.

Fuel pump, injectors, plugs - the car is cutting off spark totally as soon as I put my foot down, I don't think these items can cause that problem. However the plugs are 6 month old Denso IK22s and I have verified that fuel flow is sufficient when this problem happens by checking the flow of fuel from the fuel return line. When the car is not acting up i.e. after a restart, it will boost to 1bar perfectly without a misfire till I go back to idle for some time when it might decide to start acting up.

I am currently using a MAF borrowed from a friend of mine whose car is off the road, same thing. I didn't know that you could actually open up the MAF sensor to check for dry joints, I thought it was a sealed unit, how is this done?

I also thought a MAF would cause fuelling issues. What I'm getting is a total spark cut if I put my foot down to the extent the engine can even go off, if I feather the throttle I can get it to 4000rpm or so. It also idles perfectly.

 

throttle sensor?

 

The TPS does read linearly from 4.5V (closed throttle) to 1V (full throttle). I've tried with the TPS unplugged - same symptoms. However this is one item I havent swapped out. I will try that out this weekend as well.

 

I'd re test your MAF. unplug it and start car if it starts your maf is duff if it doesn't start maf is fine.

Also change your spark plugs for new ones i know its a lot of money for new sparks after 6months i had issues with starting like on 3cilis but changed my sparks and was fine.

Also i take its an import if so you need to run it on 99octan fuel. 95 will kill the engine.

 

I'd re test your MAF. unplug it and start car if it starts your maf is duff if it doesn't start maf is fine.

Also change your spark plugs for new ones i know its a lot of money for new sparks after 6months i had issues with starting like on 3cilis but changed my sparks and was fine.

Also i take its an import if so you need to run it on 99octan fuel. 95 will kill the engine.

 

Lewak: The unplug MAF test is not conclusive, if you search for recent MAF related threads, you will come to the same conclusion. However one thing I have not tried is driving with the MAF disconnected (off boost of course), I will try that and see if there is an improvement.

I have a set of new NGK coppers arriving next week, for sure I will swap out the plugs then.

The timing map has been modified to cope for the fuel we get, so no issues on that front.

 

alright mate when you put the ignition on to start how many clicks are you getting,reason i say is that there is arelay up behind the dash on the drivers side which i swapped out on avehicle in my garage not so long back with similar problems,when the problem occured and you switched ignition off then on there was 1 less relay click which can be easily over looked.

 

prodriverules: The relay sounds like a possible avenue for investigation. Do you know the name of the relay? For example is it the main ECU relay? Or how many pins it has? This would be very useful for me to know so that I can start with the most likely suspect.

I will count the relay clicks in about 2 hours when I get to the car and post back.

 

dont know the actual name but it has 5 terminals and is to do with the ignition system,you should hear pardon the words lol 2 clicks and 1 clunk when all is running fine and one less click if the relay is getting stuck/not working,let me know how you get on cheers.

 

I can confirm that I only get 1 click (fuel relay) and one clunk (must be main relay). I will open up the dashboard tomorrow and find the non-working relay. Thanks for the help so far.

 

Problem solved.

It was the MAF, I had borrowed a MAF sensor off a friend of mine which apparently was not so good, so the problem occurred less often but was still there. Another MAF totally cured it. Thanks for all the replies.