Need some help diagnosing engine troubles... that come up only during rallys.

Ok, this popped up at STPR last year. After about 25 stage miles, the car starts to sputter in the high RPM range. Starts at the very high rpms to the point where you barely notice it... then it slowly works its way down, to the point where I have to shift at about 4000 rpms just to keep the car accelerating.

I replaced the entire ignition system.... at sno*drift the same issue popped up. After stage 4 or 5, I noticed it (last stage before service). Said I started to feel it again. After we went back up by the 2nd stage it was really bad.

Soo could be a heat/heat soak issue right? No... 2nd day after the car was sitting in -10 degree weather all night, it started after only 4.5 miles; much quicker than the day before. If I let the car sit for long periods of time it will go back to I get about 25 miles in before the issue starts.


So, so far I've replaced the ignition system.
Installing an aftermarket fuel pressure regulator now, with a gauge to watch the fuel pressure.


Any other potential causes i'm missing? o2 Sensor possibly screwing with the computer??? Seems like something is being learned by the computer almost. I have no OBD in the car.


Here's a picture of the spark plugs, after one rally. The igniter? on the 4th plug looks brand new with no soot on it at all, not sure if that means anything, but other than that they look ok to me. Need to get this resolved, STPR will be miserable again if I dont... sno*drift I could kinda get away with not having upper rpms for the most part.



Edited 2 time(s). Last edit at 04/22/2013 06:30PM by czwalga.

Also the car has no crank/cam sensors.

Distributor is a mechanical connection to the the cam shaft.










Edited 1 time(s). Last edit at 04/22/2013 06:30PM by czwalga.

Don't know about your ECU but many ECUs have progressive rev limiters that reduce max RPM based on oil temp inputs....

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Kinda looks like the end plugs are fairly normal, maybe a tad lean. The center two, especially the dull black one are running on the rich side. Could be ignition but also could be bad injectors maybe a head gasket issue? Check valve clearance just ofr giggles, do a leak down test. Maybe pull injectors and have them flow checked.

Anything else acting wonky?

My RX-7 had a bizarre issue last year that was extra fun to try to diagnose. After driving for 30-40 minutes, it would start to run progressively worse. No real symptoms other than "complete dogshit" especially under heavy load.

The problem was the alternator would get hot and start to get electrically noisy, which made the MSD (or the Megasquirt) unhappy. Replaced it and all problems vanished.

I only noticed it after getting somewhat fed up with trying something and then driving it for an hour that night, iterated over a week, and then went driving for much longer, and after a while other things started going loopy like the stereo. That's when it clicked in my head that I was chasing the wrong system.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.



Edited 1 time(s). Last edit at 04/22/2013 09:40PM by Pete.

If you have a pressure regulator with a gage whats the fuel pressure like at high rpms when that's happening? Are you sure its not a soft pump going dead or clogged fuel filter? Worth a check.

I'm just installing the fuel pressure gauge/regulator now, waiting on a fitting i forgot to buy.

I've swapped pumps already, although havent ruled out a faulty stock regulator yet. No oil pressure/temp sensors.



It doesn't feel like a miss. It's just hesitation and won't rev any higher. I guess this is why I feel like I dont think it's a single fuel injector, or single plug.

Feels exactly like when I had a fuel cell with no surge tank, fuel starvation around the corners. It would just hang, only difference is once the fuel settled I could actually accelerate again.

I think those dizzys had two and sometimes three pickups in them. I've had some wierd stuff with Japanese dizzys. What brand of spk plugs?

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heymagic
I think those dizzys had two and sometimes three pickups in them. I've had some wierd stuff with Japanese dizzys. What brand of spk plugs?

You're right it has two pickups. NGK

Theres no ecu timing adjustment? Subarus will pull timing if it sees Knock (Detination). the more knock the more timing it will pull. If it doesnt see knock the ecu will add timing back over a period of time. Your simptoms sound the same as a subie with a bad ecu map. If you cant adjust ecu. try finding out what the timing is and back it down a degree or 2. The hotter the intake air is the more chance of knock. If you dont want to pull timing try race gas and see if it stops. If it does then pull timing or buy race gas.

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First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
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I can adjust the timing by turning the distributor, and having two ECU pins shorted together.

Sounds the same as a dsm, talon. How much timing is there you know? the ecu must be able to change timing then. Thats why you have to jump the wires to take the ecu out of the picture. The reason I believe you only see this in rally is because your every day driving doesnt build enough intake heat to cause knock. Does it have a maf or a map sensor?

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First rally 2013
Rally car type AWD subaru
Total rallies as driver 6
Total rally cars built 2
Total rally cars caged 3
Total rally cars repaired from offs 4
Total years racing exp other then rally 19 yrs
Like 31motorsports on FB!
Check out 31motor sales on ebay for used Subaru parts

Quote
Reamer
Sounds the same as a dsm, talon. How much timing is there you know? the ecu must be able to change timing then. Thats why you have to jump the wires to take the ecu out of the picture. The reason I believe you only see this in rally is because your every day driving doesnt build enough intake heat to cause knock. Does it have a maf or a map sensor?

MAP/Vacuum Sensor. No MAF.

If it is infact pulling timing from a knock issue (though the spark plugs sure don't show any signs of it), you might have an issue with the knock sensor itself. Most knock sensors are just a microphone that pick up a certain frequency, or the ECU looks for a certain frequency.
With a race car, this can cause problems as they are usually louder mechanically. Even something as simple as a rattle can throw off a knock error. If you can bypass/dissable the knock sensor, this might point you in a certain direction.
My thoughts are that all the noise from running down stage might be causing the ecu to pull timing.
Stock ECU or aftermarket? Also, contact John Reed (or PM him). He is very knowledgeable in this area.

Had an issue with my Evo where it would start stuttering as the car got bounced around. Washboard was more problematic than say a hard landing. Turned out to be a bad electrical connection from (inside?) the MAP sensor to the ECU so it was getting 'max' reading spikes in the middle of normal readings. Replaced the MAP sensor and the problems went away.

Dave