The car is a 97 Dx motor currently is a d15 bottom with a z6 head and will bog only after driving for 20 to 30 min. I've swapped everything out under the hood, new distributor, wires, head, fuel injectors and finally now I've converted to obd 1 with a p28 and still bogging. Could blown rings leaking a lot of oil cause a bog. I'm changing the main relay and fuel pump this weekend but I don't have any other ideas what it could be.

 

Was this motor freshly rebuild or it has been beaten by some one else ???
any history on the motor??
before the 20minutes how does the motor runs??

 

Bogging when hot is usually either the coil or the ICM. Their performances are affected considerably by heat.

 

Sounds like you have a problem with your o2 sensor, have you tried replacing it ??
sometimes they work fine could since they are running in open loop, but ones they heat up they cant adjust the air/fuel ratio

 

The O2 sensor doesn't begin to function until it is hot. That is why they are made with built-in heating elements and why a cold motor starts out in open-loop mode. It would be very unusual for the sensor to work fine after it heats up but stop working 15 minutes or so later.

 

Any CEL codes? Have you replaced the fuel filter? The engine should switch to closed loop faster than 15-20 minutes, unless there's no thermostat installed.

 

The engine has good compression, but I don't know its history. The oxygen sensors have been replaced and it has a new distributor, so that should rule out those. It drives okay not perfect but no bogging until about 20 min. The car is usually warmed up to operating temp in less than 5 min and doesn't bog till 15 min later.

 

CEL codes? Fuel filter?

 

maybe a cat, disconect the cat from the mani, take it down the road

 

No codes and new filter and cat has been replaced with known good cat.

 

Mechanical and ignition timing set to spec?

 

Set timing with a gun and the wierd thing is if I advance the timing one tooth it runs good, but detonates going up a major hill. It seems like its running really rich and I've swapped injectors also. Swapping main relay and fuel pump over the weekend.

 

Is the service connector jumped when you are checking and adjusting the ignition timing? Another possibility is that you got some bad gas.

 

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