2002 wrx does not start when warm

[jonerbob]

I have completely stock 2002 wrx wagon. It starts up and runs fine when it is cold. But if I go for a drive to the store and come back out it wont start. It cranks and turns over. So far I have replaced the cam sensor, crank sensor, spark plugs, and a fuel pump. I have no idea what to do now and was wondering if anyone has any ideas. Thanks

[Obeisance]

I'm curious about your problem and interested in learning how to troubleshoot these cars. I'm gonna take a shot in the dark and make up a suggestion; does giving extra gas during a warm startup help/change anything?

Since it starts when cold I assume that you have air, spark and fuel in the combustion chamber.. I don't see how any of this should change when warm, but maybe there's not enough fuel.

Also, you say that the car runs fine when cold. Does that mean that it has the acceleration and rev-response into the high rpms of a healthy engine?

I am also curious to know if the engine even sputters when it turns over when warm (i.e. is there conclusive evidence of a spark in the chamber).

[jonerbob]

I'm curious about your problem and interested in learning how to troubleshoot these cars. I'm gonna take a shot in the dark and make up a suggestion; does giving extra gas during a warm startup help/change anything?

Since it starts when cold I assume that you have air, spark and fuel in the combustion chamber.. I don't see how any of this should change when warm, but maybe there's not enough fuel.

Also, you say that the car runs fine when cold. Does that mean that it has the acceleration and rev-response into the high rpms of a healthy engine?

I am also curious to know if the engine even sputters when it turns over when warm (i.e. is there conclusive evidence of a spark in the chamber).

Thanks for the help.
It does run like a good healthy engine when it is running. It has the normal acceleration. When I try to start it warm giving it gas has done nothing for me and there is no sputtering. It just turns over with no start.

[Obeisance]

My best guesses for troubleshooting are fairly crude. I think that with my limited knowledge I would just start taking things apart to see if they work from the outside. I would try to take out the fuel injectors and see if they are spraying:

South Coast Speed & Sound / Subaru WRX Fuel Injector Replacement Instructions

and I would try taking out the spark plugs and see if they are arcing.

All of this is a really time consuming way to see if the problem is with fuel delivery or with the electrical system. Or can you confirm that all of that is working well when warm?

[jonerbob]

I would assume that they all work fine when warm because I have driven the car over 100 miles straight and had no issues. But then when I go to start it when its warm it wont start. I have been looking all over online for answers. I have seen people with similar problems that replaced the engine coolant temp. sensor. But I am not sure if that would be the issue.

[Obeisance]

Well, if you don't mind my meandering replies and shoddy guesses I'll keep going. Does the car push/hill start when warm? This may be able to distinguish between problems in the starting circuitry (I can't imagine this changing with engine temperature) or problems with the computer controller (or the attached sensors). (I found this suggestion on an iwsti thread: Please help engine turning over but won't start - Page 3 - Subaru Impreza WRX STI Forums: IWSTI.com , but in that thread I think the cars didn't start at all.)

Also, since you're wondering about the coolant temperature sensor, does that appear to function well in the dash gauge?

[jonerbob]

Well, if you don't mind my meandering replies and shoddy guesses I'll keep going. Does the car push/hill start when warm? This may be able to distinguish between problems in the starting circuitry (I can't imagine this changing with engine temperature) or problems with the computer controller (or the attached sensors). (I found this suggestion on an iwsti thread: Please help engine turning over but won't start - Page 3 - Subaru Impreza WRX STI Forums: IWSTI.com , but in that thread I think the cars didn't start at all.)

Also, since you're wondering about the coolant temperature sensor, does that appear to function well in the dash gauge?

I will try the push/hill start and hopefully have an answer by tomorrow. Thanks again

[jd92677]

I have seen people with similar problems that replaced the engine coolant temp. sensor. But I am not sure if that would be the issue.

This seems like a pretty good guess. If the ECU can't tell what the engine temp is or is reading the wrong temp, it won't be able to calculate the proper amount of fuel and could give you a crank, no start. If you can source out a scantool that has live data, you could look at coolant temp and compare what the ECU sees to what the gauge is reading.

[jonerbob]

Sorry it took so long to find an answer. But I brought my car to a mechanic friend at a dealer and he went through and checked all my sensors and looked at the issue. He said that I need a new ECU. So I am ordering a new one this week hoping to have it by next week. I will let you know if the problem is fixed.

[MainFrame]

New ECU? That sounds very unlikely.. but I have seen stranger things. Did your ECU get wet or something?

[jonerbob]

it overheats and has trouble sending a signal to sensors. The guy I brought the car to has been working on Subarus for over 20 years and said he has seen similiar problems with imprezas before. I believe the person who owned the car before me messed with the ECU.

[MainFrame]

That still seems pretty strange to me. I've been on here and several other Subaru forums for ten years now, owned a WRX for just as long, dealt with thousands of issues on hundreds of cars and I have never heard of an ECU over heating. I know one guy in Alaska who was having strange issues with misfires that turned out to be a bad ECU, but it was because the plug in his firewall was missing and when he drove through a puddle it drenched the ECU.

I had a similar issue with my car not wanting to start when it was warm and it ended up being bad injectors. I just don't know what someone could have done to the ECU to cause it to over heat. He could have messed with the tuning..


If the cranking enrichment tables have been messed with that would explain your issue. The ECU has different throttle tip-in enrichment tables for cold start vs. warm start. That's one of the things that has to be adjusted for cold starts on e85. If the car was improperly tuned that could easily cause your issue.

Did you try pulling the map on the ECU and comparing it to a stock map? Or maybe even flash a stage one map and see if that fixes your problem?




I'm not saying it's not a bad ECU, I just think that seems unlikely.

[jonerbob]

You were right. It was not the ECU. I got a new one put it in and went for a drive. It runs great. Then I drove home let it sit about twenty minutes and once again it turns over but wont start.

[MainFrame]

Sorry if you've already answered this, I'm on my phone.. when it's warm and won't start, have you tried pumping the gas, or flooring it while the engine cranks? Just about every car I've dealt with that didn't want to start warm would fire up if you gave it plenty of fuel while cranking.

[jonerbob]

I have tried that it does not work. I also noticed I am getting around 13 mpg too.