Help!..89 with 3vze runs great for an hour

[RVdaytrader]

My 89 Seabreeze with the 3vze engine runs great with ample power for about an hour...then it bogs down and has to downshift for any incline!...I don't think its an engine problem or it would do it all the time. Could it be a sensor or something?? Seems to roar when it gets boggy. Any ideas??

[WME]

Any check engine light??

Off hand I would say low fuel pressure, or high exhaust back pressure

[linda s]

First thing to do is check your codes and see if the computer will help you diagnose the problem.

Linda S

[5Toyota]

hi ext back pressure as in bad catalitic converter

[DanAatTheCape]

or possibly a fuel tank that is not venting -- this is a closed system so it may be a bit involved to figure out where it gets air into the gas tank to replace burned fuel....

might be an interesting test to wait until it is running poorly & remove the gas cap -- if there is a lot of vacuum you might have reason to follow this "theory" (really a guess). Also if there is a lot of vacuum relieved by opening the gas, I would think that the engine would start performing better - for a while.

[RVdaytrader]

Thanks for the ideas...now yesterday I drove from Show Low, AZ to Durango, CO and it ran good until the last hour maybe. Then seemed boggy again. I did notice that there was no pressure (or vacuum?) when I took gas cap off when it was running good. The last fill up after it was starting to bog down, there WAS air rush (in or out) when cap was removed. The converter did come to mind, but would a bad converter problem be hit or miss, run good then bad?? Will have to check codes, maybe today, but it is time to prep Yoda for his long winter sleep!! *sigh*

[Firedawg]

Just a quick 2 cents, for starters, the converter is either plugged or it isn't. If you feel the need to check it anyways, there is a simple method. Drill a small hole in the exhaust pipe before the converter, and one after it as well. Using a pressure/vacuum gauge with the appropriate fitting, take a reading in each hole and compare the results. If there is significant back pressure before the converter, then it's plugged. A properly running converter, will create very little back pressure at idle.When finished, screw in a short metal screw with exhaust sealant on the threads to seal the holes. Now something else simple to check the next time it acts up. Pull over, shut engine down, and check the resistance on your radiator fan. You should be able to rotate the fan by hand fairly easily with some minor resistance. If this is not the case and the fan won't move easily, then replace your fan clutch. The only reason this came to mind for me was the fact that you mentioned that it sounds as though it begins to "howl" when acting up. If your fan clutch is locking up once it gets warm, this would produce a significant howl as the fan itself is now operating at engine rpm and trying to draw more air than it is designed to, thus, creating a large load on the engine as well. Maybe this helps, maybe it won't, but it's simple to check, and it's the only thing I can think of off the top that would produce an audible howl.