I've been having a werid issue with my engine sporadically falling on its face since I swapped in the HO 305. I used all the sensors from my old engine, which worked fine except for the spun rod bearing So when I first start it up, it idles fine and drives fine for anywhere from 5-15 minutes, then it begins to seriously bog down under light acceleration. If I give it more gas it wakes up again and is fine, but I've had it stall a few times now in a parking lot or similar situation.

Here's the weird part. Once it warms up, I have no issues. I can also shut the car off and re start it immediately which gives the same result. I always get a code after driving over 50 mph for a bit and then slowing down to 35. It's always exactly 35 mph when it comes on, but the code doesn't store, when I shut off and re start it's gone. The problem has also been MUCH worse when the weather got colder. Would I be correct in assuming it's getting a really cold false reading and dumping fuel in to compensate? What sensor would do that? MAP?

EDIT: I should clarify that I ditched the quadrajunk from the HO (which came from an 84 if that hels at all) and re used my TBI setup

 

Check the fuel pressure. Might have a bad tps also.

 

The TPS is within spec, don't really have a way to to test the fuel pressure, but with the problem being so intermittent I wouldn't think that would be it anyway. I'll get it checked as soon as I can to rule things out, though. Another reason I think it might e mechanical is because my old engine used every sensor and accessory I have now and it worked perfectly, minus the spun bearing. This is bugging the hell out of me!

 

Sounds like a problem I had with a TBI truck. It was a clogged fuel filter.

 

If you're going to work on it yourself, buying tools (and learning how to use them correctly) is part of the pain and the glory.

Don't rule-out fuel pressure. If the pump is failing - as in: spins most of the time, but occasionally freezes - I would expect sputtering to be a symptom. Of course, there are things other than the fuel pump that could cause sputtering. Example: faulty vacuum line that leaks more under some conditions than it does under other conditions, ...or center distributor button that is not making proper contact, ....or a bad relay, ...or bad gas

I don't like the "just throw parts at it" method of fixing anything. But, whether its intermittent issues, or constant issues, the process of diagnosis always requires elimination of suspects.

HOW OLD is that fuel pump?

HOW MANY more hours of service (and months of just sitting there getting old) do you expect to get out of it?

I'm of the mind that when a car gets more than 15 years old, you aren't just maintaining it. You are restoring it. If you aren't restoring it, there are bunches of parts deteriorating as certain as the sun rises, and will one day leave you on the side of the highway. Make sure your AAA Premier premiums are paid.