RKeats

Long story short, my car runs perfectly with no codes stored but only for a fairly short drive, If I take the car out for the day, after about 3 hours of consecutive driving, car will start bucking, engine light comes on, and it will stall. Come back the next day, code is gone, and it'll drive perfectly again for a few hours. Luckily last time I had a paper clip handy so I could check the code at the side of the highway, which was 44 (Lean exhaust). I'm assuming it's an o2 sensor since it hasn't been replaced in the last 10 years of the car being in my family, but the issue is that I can only really test to see if it'll die by going on a long drive, and if the test fails and the car dies then I'm towing it home again for the 8th time this summer. How can I test to make sure I'm not just replacing random stuff?

92RS-HeritageEd

iTrader: (2)

I've had an ongoing issue w/ this...


Hope they help!

ULTM8Z

Definitely sounds like something heat related... My guess is the O2 sensor is not malfunctioning and is reporting a real lean condition.

Only, everything under the hood reaches full operating temperature long before 3 hours, so that leads me to discount the stuff under the hood.

Maybe something with the fuel system out back? If the fuel tank is somehow heating up over time with warm fuel being cycled from the fuel rails back to the tank... Fuel lingers in the rails for a little bit until the unused fuel is sent back to the tank (meanwhile having absorbed some heat off the engine in the process). Over time, the heat can build up in the fuel tank, warming up the fuel...

Maybe an issue with an old fuel pump not able to operate at higher temperature? Fuel pump basically uses the fuel as a coolant. If the "coolant" temperature is getting too hot for an already-faltering fuel pump to keep itself cool?

If you had a fuel pressure gauge on the car, you may notice a steady drop in fuel pressure before the issue manifests into a full blown stall condition?

Or some sort of fuel tank evap system issue perhaps?

RKeats

If it stalls again I'm going to try unplugging the MAP sensor, that's one of the only things I haven't tried. It's tough to diagnose because the car is perfect until it dies, so the only time I can diagnose is at the side of the road which is easier said than done.

RKeats

The pump is a new delco, the filter is new as well, the injectors are new and pressure shows well. I should have included this part previously but I have a decent passenger side manifold leak and it sounds like I may have a driver side beginning as well. I'd imagine that could have an impact on the o2 readings but wouldn't it be more immediate? Or could air be getting sucked in at the manifolds and clogging the catalytic's? I have 2 and who knows when or if they were ever changed

92RS-HeritageEd

iTrader: (2)

I understand, see 1st hand experience.

https://www.thirdgen.org/forums/tbi/...n-exhaust.html

ULTM8Z

then maybe inspect the evap system and make sure you're not getting over or under pressure conditions in the tank.

again this appears to be heat related to me... and the only thing that I can see that would take that long to manifest would be something with the fuel tank.

might also want to check the voltage and ground at the fuel pump... a lower voltage may cause the pump to work harder to maintain fuel pressure.

GeneralDisorder

iTrader: (1)

The O2 isn't the issue - if it was reading lean and the engine wasn't actually lean it would be adding tons of fuel and the exhaust would likely be black, etc. Since you have bucking and stalling we can safely assume that the engine is indeed lean. Find out why it's leaning out and you find your problem. You need to invest in some live data/logging equipment for this. Also probably should install a fuel pressure gauge. Need data - you can't collect this from the side of the road - we need data leading up to the event so you can track the delta of all the engine sensors, and the cruise BLM's over time.

GD