2.5 Subaru Conversion Intermittent Miss / Surge / Stall

[Jennybenny]

I have a new to me Subaru 2.5 rmw conversion in a 1989 Westfalia. Story is 2000 Impreza, rebuilt with new head gaskets, etc last year. Coolant loop is reverse flow manifold. Engine Looks immaculate - like brand new from the showroom, no loose wires, etc. New everything else. Rebuilt auto transmission at some point but older.

My issue is that at some point before the motor is fully warmed up (gauge indicating near temp light at 80 degrees ambient) it starts running like complete garbage for several minutes. Runs fine at startup. Runs fine when hot. At some point surges stalls won’t idle smells like someone is pouring gasoline in the passenger seat. Like timing off, crack in distributor cap, wrong jets in carb all at the same time bad.

Then will suddenly run for the rest of the day like the most sorted motor ever built. You can’t hear it, idle completely steady, doesn’t smell like it is running rich, etc.

Odb codes are fuel temp, coolant temp and some emissions codes but I assume those are to be ignored because it doesn’t have all of the emissions control from a modern motor. Don’t have a scan gauge set up yet to check real time.

Over my head. Took it to a Subaru conversion knowledgeable mechanic. Ran perfectly for the three days he had it.

Is there something to check when it starts running like dog shit, or even better a know bad sensor / setting that causes this behavior?

Jason

[AZ Landshaper]

Id not assume you dont have the emissions controls of a modern motor. Being 47 I consider the 2000 Subarus to be relatively modern. Deff enough so that the emissions controls send signals to the ECU. For example the O2 sensor is an emissions control item that kicks in about the time your rig starts to run like junk. Its telling the ECU to adjust this and that to curb the emissions at the same time make the vehicle run more effectively.

THose emissions codes are important
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[wesitarz]

Coolant temp code? Maybe your coolant temp sensor is old/wonky. Located midway on the coolant manifold facing the A/C compressor if you have one. DIY replacement with little coolant loss.

[skills@eurocarsplus]

[Jennybenny]

[quote="skills@eurocarsplus"]

[Howesight]

The DTC (Diagnostic Trouble Code) system on your Year 2000 Subaru is able to detect, based on how it is programmed, a failed or intermittent coolant temp sensor. Most likely, the way it detects that is by noting quick changes in the resistance sensed by the ECU. The Subaru programmers know that sudden changes in coolant temperature, for example, are not possible. A failing temp sensor or its wiring would give such a rapid change in the resistance of the thermistor inside the coolant temp sensor.

Therefore, it would be a great idea to replace that sensor. By the way, a coolant temp sensor which malfunctions intermittently would cause exactly the symptoms you have described.

If replacing the coolant temp sensor does not cure the symptoms completely, then your wireless harness may be the cause of the DTC.
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[skills@eurocarsplus]

typically when a ECT goes tits up it fails at -40*f

this would result in a pig rich condition at start up which isn't the initial complaint.

i had a 16v ECT kick my ass as it had a very similar issue. ran fine for 5 mins (long enough to get me to the gas station) and upon restart ran lie 100% shit.

ran fine otherwise

took a lot of doing, but the ECT failed in a very odd temp range. if i started it and left it running or just drove it, it never missed a beat because i "drove thru" that "segment" of the ECT.

almost sounds like that's what going on here. not sure about your scan gauge, but my scanner will do a recording session, up to 3 hours. you could note your starting ECT and go for a ride then see what is going on at the time of the fits it is throwing.

obviously easier if you can record and graph the data so you can review it without having to stare at a screen
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[Jennybenny]

Thanks to all - it was the coolant temp sensor. Been running great for a couple of weeks since replacement.

Jason

[skills@eurocarsplus]

thanks for posting the fix.

sounds like you had the same failure as my 16v ECT. it's like the sensor had a dead spot

glad you got it solved
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[16CVs]

Is it possible that a 2.2 could have the same issue? Mine runs well but has this intermittent high idle. No light as this is OBD 1.

Stacy
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