Ok, it's not a TPI but HSR. I asked in the other section but haven't got it figured out so I thought I'd ask here. Even though they are laid out differently, I think the similarities make it close enough. Please check my sig for details but it's a 400 HR 236/242 street motor.

Here's my problem, the 4 rear cylinders are running rich and the 4 front are about right. It runs ok until warm and by the time it's up to temp the rears are starting to foul and runs like crap.

I've run compression test and a leak down test and everything is pretty straight. Check cam best I could in car and there doesn't seem to be a flat lobe or any problems with the valve train.

The Bosch 36# injectors were removed and bench tested with TB cleaner under 43PSI pressure and cycled. They didn't leak and flowed ok. Not an official test but ok.

I had installed a 58mm TB a few weeks before noticing this problem. I suspect there may be a vac leak or maybe the larger TB is letting the front cyls rob air. Running EBL computer and am guessing the NB senses lean and adds fuel.

Not sure were to go from here and any comments will be appreciated.

 

I believe this is a inherent design issue with the HSR. Try doing a quick search and I think youll find several complaints about the rear cylinders running rich on the HSR. Still, couldnt hurt to check things like the FPR diaphragm for leaks ect.