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Okay so here's a strange one. Think I may have posted about this a while ago, but have some more info now and hoping for some fresh opinions.
My '97 Aero runs rough at less than full load when it's warm/hot.
It always starts easily. When it's cold it runs like a dream. When you floor it, it's smooth as silk and pulls like crazy.
But cruising, or accelerating at part-throttle, it bucks and stumbles. Not heavily, but it's noticeable. At a constant 65 with the cruise on, you can feel it a little. Every now and then it gets worse, you can see the gas mileage drop a little, and once in a blue moon it even backfires (remember, this is under steady-state conditions). Basically, it feels like it's running lean. I think the problem has existed as long as I've owned the car (~1.5 years) but is slowly getting worse.
Here's what I've checked:
Air & fuel filters (replaced 5K miles ago)
Plugs (BCPR7ES-11, gapped to 0.039", < 1 month old) insulators of old ones were consistently tan, dielectric grease used when installing
DI cassette replaced ~9 months ago, swapped the old one back in, no difference
All vacuum lines replaced with silicone and routed correctly
Hooter valve recently replaced and tests ok
Fuel pressure tests ok
Did basic checks for vacuum leaks, injector o-rings and such seem okay
O2 sensor appears fine (using computer w/OBD software) - "wakes up" quickly and cycles fast and consistently
CEL is not on and no stored codes
Engine temp appears okay
Have tried Techron & isopropyl repeatedly
Manually cleaned fuel injectors
The only other thing I can think of is the crank position sensor (how do you test this?). But seems to me if that sensor were bad, it would run poorly at full-load also?
Also, some of you may remember I've modified the Trionic software, but I swapped in an ECU with stock software and no difference.
Anyone have any ideas?
Eric Law
posted by 63.173.23...
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