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Old 05-19-2020, 09:51 PM   #1
haut92
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Default Car dies when warm, no CEL

Hey there,


tl:dr Car dies when it is warm and then won't start again despite turning over. No CEL, runs fine when cold.


This problem evolved from another thread on the of mine on the forester forums but wanted to re/cross-post here to see if anyone has any ideas.

I flashed the car to stage 1 on an AP OTS map and that is when these issues started. I have since flashed the car back to stock and the problem is getting worse.

2004 FXT 4EAT, 160k on the clock with all regular maintenance done except the spark plugs (we bought it at 100k and have not done them, I assume they have 160k on them..). Fuel filter has less than 10k miles on it. Car ran fine until flashing the new map about a month ago. I did do an oil change recently and went from 0w30 to 0w40 of the same brand since that is what I had but I doubt that is the issue. I just replaced the battery hoping that would help but no luck.


The car hesitates then dies in various rpm ranges once warm. It will die eventually if I leave it idling. It will drive ok while cold but then dies when the engine reaches temp. Once it dies, I have to wait 15 minutes or so to drive it, otherwise it will turn over but not start. The longer I wait, the further I can drive, but it will die again. I have tried flooring it while I turn it over and it does not seem to help.

I had a CEL for misfire in cylinder 1 and 4 and one later for cam positioning sensor but those only came on once each and never again. The problem stabilized and now happens routinely when the car is warm and I have not had a CEL since then.

I've checked for vacuum leaks, think we are good. Pulled the cam sensor (bank 1) and it looks fine but who knows. I wanted to test it but turns out it is a three prong and I have no idea how to test it.. The coolant temp sensor appears to be reading accurately based on the AP (warms up to about 180-190 before the problems start).

Haven't ruled out the fuel pressure regulator since it is hard to get to on this car but seems wierd it would only have an issue while warm??

I am going to have a shop do plugs asap and am praying that is the issue but figured I'd post up here to see if anyone else has any ideas where else to look.

Thanks for any help!

P.S. Anyone have a recommendation for a good independent subie mechanic in south Seattle/Burien area? I've never come across a problem on this car I couldn't fix and it looks like all the recommended shops are up north
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Old 05-20-2020, 01:41 AM   #2
Zmanwrx23
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Not sure if I can be of any help however I did experience a similar problem under different circumstances.

When I finished building my 2006 WRX it would do exactly as you described. Ran great cold and would start right up. Once it got up to temperature it wouldn't idle and if I let it idle it would die. It would turn over again but once warm you had to keep your foot in it to get it to idle. I traced my issue through some AP logs to a grounding issue for my front o2 sensor. The values it was showing on my logs made no sense and my tuner said the same thing. I looked and had forgotten to bolt back down a ground strap by the passenger side strut tower. I bolted it down, unhooked my battery and drained power from the car, then hooked it back up (I did this so my car could relearn how to idle) and I haven't had a problem since. Maybe a ground strap is loose or corroded to the point its no longer actually grounding? I'm not sure this is the case given this started after you flashed your tune but at least something to look at.

Also.......change those plugs
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Old 05-20-2020, 11:24 AM   #3
haut92
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I'm on the plugs!

Thanks for the info, I suspect it is either the front O2, a cam/crank sensor or the FPR/filter. My theory is that resetting the ECU (flashing to stage 1) brought out the issue. I flashed back to my stock map with memory (uninstalled AP) and the car was fine. Then I messed with it and reset the stock ecu and the issue came alive without the AP installed. Nothing quite like the feeling of causing your own issues on the car...

I was going to fiddle with the AP tonight to check out the O2 sensor readings but I really don't know what I am looking for so will have to do some research on that too.

Cheers!

Last edited by haut92; 05-20-2020 at 11:44 AM.
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Old 05-21-2020, 09:49 PM   #4
igoiks
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Crankshaft position sensor tend to fail this way
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Old 05-22-2020, 06:01 AM   #5
bp05obxt
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Default Car dies when warm, no CEL

Sounds very similar to something I have seen before. I would advise a compression test.

The situation I am aware of the car would get to temp and die somewhere on the road. Pull over cool off and go again. The engine would lose compression at operating temp due to a ringland failure. The engine generated enough compression as the cylinders cooled, around the piston, to start and run, but eventually the same thing would occur as the heat expanded the cylinder wall away from the piston/ring/etc.

A cold compression test showed 30% in the worst cylinder which is terrible; upon removing it was evident that the piston, rings, and debris had actually ground away into the cylinder wall. It was hard to imagine the engine could run with the damage that was there.

Last edited by bp05obxt; 05-22-2020 at 06:47 AM.
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Old 05-23-2020, 02:56 PM   #6
haut92
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Just did the front O2 sensor with a Denso (OE) sensor, threw on an OEM air filter and cleaned the MAF again. Disconnected the battery while I did it so the ECU reset.

It seems to run rougher and the car still dies when coolant reaches 180. So no benefit.

I want to believe it would be the crank or cam sensors but I feel like they would be throwing a consistent code (or at least more than one time). I found a good deal on an OEM CPS so I am going to put swap it out for no other reason than there was a code for it one time.

I do notice a thumping sound coming from the fuel tank area after the car dies at idle. Looking in to doing a fuel pressure test to see if maybe it is the pump. Is that a common symptom of a pump failure? Don't see much about it online.

edit: I just datalogged an idle. at the end, i tapped the throttle and the car died as he RPMs came down. It goes way lean and misfires in cylinder 1 before dying. This is after it has idled for about 10 minutes post ecu reset. Never drove on it so I suspect that is the issue with the a/f when it is reved. Here's a link if it helps at all :

https://drive.google.com/open?id=1hB...MHeShhbAAPuF4l

Last edited by haut92; 05-23-2020 at 03:40 PM. Reason: https://drive.google.com/open?id=1hBdnPDmI4YamzG8hHDMHeShhbAAPuF4l
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Old 05-23-2020, 03:12 PM   #7
Jp925
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Buddy had similar issue and it turned out to be a fuel gremlin, pump was Going bad but not all the time. He tore his hair out trying to figure it out; but replaced that and everything was fine.
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Old 05-23-2020, 11:41 PM   #8
haut92
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Looking in to just replacing the pump. Found a guy selling an open box walbro for cheap locally so might be an easy thing to rule out.

Curious if the minimal extra load from a stage 1 tune might have been too much for the old stock pump.

I pulled the MAF and the car throws a code immediately so I don't think it is that. Running out of cheap fixes here...
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Old 05-25-2020, 05:40 PM   #9
haut92
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Replaced the pump with a walbro 255. Car seems to run better but the car still dies when the coolant temp reaches 185 or so. Then it won't start up again until it cools down.

I have a cam sensor on the way, after that, I think I'll pay a mechanic to figure it out and pray for the best.
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Old 05-25-2020, 06:43 PM   #10
IRSLOSTI
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Quote:
Originally Posted by haut92 View Post
Replaced the pump with a walbro 255. Car seems to run better but the car still dies when the coolant temp reaches 185 or so. Then it won't start up again until it cools down.

I have a cam sensor on the way, after that, I think I'll pay a mechanic to figure it out and pray for the best.
had the sam eissue with my g35. the issue was the pump wasnt fully seated so it was losing pressure when at operating temps. check your pump and the orings
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Old 05-25-2020, 09:27 PM   #11
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Quote:
Originally Posted by haut92 View Post
Replaced the pump with a walbro 255. Car seems to run better but the car still dies when the coolant temp reaches 185 or so. Then it won't start up again until it cools down.

I have a cam sensor on the way, after that, I think I'll pay a mechanic to figure it out and pray for the best.
Im wondering if it is some sort of vapor lock issue, have you checked the pressure at the rail when warm?
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Old 05-26-2020, 02:19 PM   #12
haut92
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Quote:
Originally Posted by IRSLOSTI View Post
had the sam eissue with my g35. the issue was the pump wasnt fully seated so it was losing pressure when at operating temps. check your pump and the orings
The issue popped up with the last pump which worked fine for 160k miles and I am pretty sure the new one is snugged up good but the same issue. I kept reading about the o rings but there were none on my OEM pump and none came with the Walbro or install kit. The part number for fuel o rings from subie shows it isn't made for an 04 XT. I don't think I need them???

Quote:
Originally Posted by Jp925 View Post
Im wondering if it is some sort of vapor lock issue, have you checked the pressure at the rail when warm?
I don't know much about vapor lock but, looking in to it, it seems plausible. I'll check to make sure no lines are out of wack or too close to something hot. I don't have a fuel pressure gauge so I probably can't fully diagnose that. I am going to run it till it dies then try starting it with starter fluid in the intake to see if I can confirm it is a fueling issue.

Thanks yall
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Old 05-27-2020, 09:23 PM   #13
danger1138
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Sounds like it may be some kind of electrical gremlin.

Check coolant temp sensor.
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Old 05-27-2020, 09:29 PM   #14
Jp925
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Quote:
Originally Posted by danger1138 View Post
Sounds like it may be some kind of electrical gremlin.

Check coolant temp sensor.
Would a coolant temp sender kill the motor? It should only affect the gauge reading.
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Old 05-28-2020, 03:20 PM   #15
haut92
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I've read it can cause some issues similar to what I am experiencing.

I actually pulled the trigger and just ordered one since they are only like $30 OEM. I figure it may be the issue because the car was consistently dying at 185 degrees on the AP coolant temp reading. Should be here in the next day or two. Anyone happen to know where it is on the EJ255? I think I see it in the forward center just under the intake manifold but would like to be sure before I start pulling wires.

Funny thing though, the car was low on coolant. Still had fluid in the resevoir when cold but it was VERY low. I finally got some subie coolant and topped it off last night. Afterwards, I ran the car to check vacuum leaks and ultimately to try an start it with starter fluid once it died but the car ran JUST FINE. It heated up to operating temp and fans kicked in. reving to 2k and taking foot off the pedal was no problem (used to kill it or at least stutter it). I could never get it to die to try the starter fluid, even turning it off when hot it would fire right back up.

May be the car learning the new O2 sensor and idle? Maybe something goofy with the coolant being low throwing it off? Probably no actual change and I will take it out and get stranded on the road as soon as I test it....

In no way do I think the low coolant was causing this issue, the car was definitely not overheating and the res was above half full when it got warm. But, as of last night, it seems the car is working fine. I'll take it for a drive tonight or tomorrow and update.
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Old 05-29-2020, 03:24 PM   #16
Jp925
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Following this thread out of sheer wtf because Im so baffled now.
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Old Yesterday, 04:22 AM   #17
bp05obxt
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As mentioned before I had experience with something similar. A coolant temp sensor was considered a possible cause. One was bought but never used, due to finding the compression was bad.

A compression test can only further negate or confirm an issue.
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Old Today, 04:29 PM   #18
haut92
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So I warmed it up the next day and the issue came back, but this time, it finally threw a CEL.

Once again it was P0340 Bad cam positioning sensor on bank A (passenger side).

I already had one in the mail, swapped it out yesterday and drove it today. 10 miles on the stock AP map, no issues, logging looked good. I said **** it and flashed to stage 1, 15 miles more, logging, everything looks great, no issues. I did do the idle relearn procedure on both of these before driving them.

Car seems to run better and idle smoother. DAM goes straight to 1. Only one instance of feedback knock going to -2, otherwise, all 0s.

So at this point, I think the initial flash was the last stand for the CPS. Swapped it out and I am good to go. I'll update if anything changes.

Thanks y'all!
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