1985 El Camino 4.3 TBI running rich (Solved)

[N2UN]

Hi everyone. Working on an 1985 El Camino, 4.3L TBI. Having trouble with the engine running rich. All the sensors and injectors are relatively new, replaced within the last year. Runs better with one injector disconnected. Fouls plugs within two weeks. Engine stumbles dies when decelerating, as if getting too much fuel. BLM is at 108, 98% of the time in closed loop. Any and all suggestions appreciated. Anyone have a similar issue that was resolved? TiA.

 

[N2UN]

Hi everyone. Having trouble with my 4.3 TBI running rich. All the sensors and injectors are relatively new, replaced within the last year. Runs better with one injector disconnected. Fouls plugs within two weeks. Engine stumbles dies when decelerating, as if getting too much fuel. BLM is at 108, 98% of the time in closed loop. Any and all suggestions appreciated. Anyone have a similar issue that was resolved? TiA.

Followup. Replaced the TBI unit late last year after a high idle issue. Drove the car sparingly over the winter and when I started driving it again this spring, this issue appeared. Checked fuel pressure yesterday and had 24 PSI at the fuel filter. The fuel pressure is supposed to be 9-13 lbs. That appears to be the problem, so switching the fuel pressure regulator today. Hope that solves it. I will follow up again after replacing the FPR.

 

[stew86MCSS396]

That would’ve been my first incline verify before you trust your Never Ever Work parts. In your other thread...you said you replaced everything with oe stock. TBI fuel pumps typically will not go over 18 psi if you totally restrict the return line. Mere fact that you're getting 24 psi tells me your pump maybe used for a higher psi application. Iirc your 45 pph injectors at 12psi will behave like 63pph injectors at 24psi.

Scroll down to the calculator at the bottom of this link… https://www.witchhunter.com/injectorcalc1.ph

Fuel pressure regulators are often rebuilt with a kit and will come with a replacement spring. As in your case it should be of the 9-13 psi flavor but who knows what you have in there now. Do you know if you're getting any return fuel from the return side? If not, this may indicate a return spring that is too strong that the pump cannot over come the spring pressure or there is some kind of restriction blocking the return fuel going back to the fuel tank.
Aftermarket spring offerings.

 

[N2UN]

That would’ve been my first incline verify before you trust your Never Ever Work parts. In your other thread...you said you replaced everything with oe stock. TBI fuel pumps typically will not go over 18 psi if you totally restrict the return line. Mere fact that you're getting 24 psi tells me your pump maybe used for a higher psi application. Iirc your 45 pph injectors at 12psi will behave like 63pph injectors at 24psi.

Scroll down to the calculator at the bottom of this link… https://www.witchhunter.com/injectorcalc1.ph

Fuel pressure regulators are often rebuilt with a kit and will come with a replacement spring. As in your case it should be of the 9-13 psi flavor but who knows what you have in there now. Do you know if you're getting any return fuel from the return side? If not, this may indicate a return spring that is too strong that the pump cannot over come the spring pressure or there is some kind of restriction blocking the return fuel going back to the fuel tank.

Thanks for the reply and the link. I'm with you on the aftermarket parts, nothing seems to work right for very long.

The fuel pump that is in it now is a Delphi FE0115 (OEM replacement), which specs (GP) at over twice system pressure and is somehow comforting for me. My mechanic sat it up to test fuel pressure at the fuel filter. We disconnected the fuel return line at the TBI to test presence of return fuel and rule out a blocked return line. We got bypass fuel during the prime function and with the engine running, which was encouraging, but no change in dynamic pressure. The TBI came from a professional rebuilder which shipped as a unit. We thought they may have installed the wrong regulator spring, so that's our current path.

Going to try again today and see what we can figure out. My mechanic mostly works on newer cars but has a vintage technician on call, so we have to wait for him sometimes.

I will update as we figure this out to add to the knowledge base.

 

[N2UN]

Solution!! We were able to solve the running rich issue. As it turns out, it was the Fuel Pressure Regulator. It had a heavier spring in it than required so it was pushing fuel through at almost twice the system requirement. We're back to 13psi and all seems right with the world. It will take a few road trips to blow all the soot out of the engine and exhaust but I'm more than happy to make that sacrifice!! Thanks to stew86MCSS39 for the interest and reply. Hope this helps someone with their G-Body journey!

 

[melloelky]

I'm glad you figured it out and thanks for coming back and reporting how you figured it out,it may help someone out someday.