I have been researching and trying ideas from multiple sites on how to get my Fuel trims correct. I have a 1954 Chevy that is riding on a 1999 Chevy Silverado 1500 frame and powertrain. Original donor engine blew up and I have put a rebuilt 5.3 in it. I keep fuel trims because gas mileage has been terrible and more black soot than expected on tail pipe. Long Term fuel trims averaging -(7-15). Was hard to start after driving so replaced fuel regulator. No change in numbers. I then replaced the MAF and MAP sensors. No change. it is a cone filter but it is clean and no oil residue, even took the filter off to see if there was a restriction and no change. Then changed all oxygen sensors. No change. Had an error on new oxygen sensor and pulled and was completely covered in black soot after about 30 miles of driving. I have checked for exhaust leaks. I have checked for vacuum leaks both with gauge(read 16mmHg) and by propane test, no change in speed of engine. Bought an Autel MS906BT to check injectors and they all balance to 42-44 psi. Original fuel pump averaged 52psi. Replaced it and new fuel pump, Delphi, reads 52psi also. Previously I had changed fuel filter. It had the original 896 PCM and I just recently changed it to a 411 with EGR delete, so I can clean up engine bay, EVAP delete, rear O2 delete, and VATS delete. Still with long term trims reading rich. I replaced spark plugs when I replaced engine so about 350 miles on plugs. New ECT when I replaced engine and it appears to be reading correctly. The injectors where cleaned about 1400 miles ago. Truck runs good except the running rich and will not start when warm. I don't know what else to check or replace. Will lose about 6 psi over 3 minutes when doing a fuel pressure check. Other times though fuel pressure doesn't budge for 10 minutes.

Thanks
DrHicktown

 

Are you running a stock tune? Is the MAF clean? Is the PCM calibrated for injector size?

 

Yes it is a stock tune. Yes the MAF is clean. I am running stock injectors and the PCM is calibrated for the stock injector size.

DrHicktown

 

The 99 had a smaller injector. The later ones had larger injectors...

The 99 was like 21 lbs injectors
The later used a 24 lbs injectors

Are you sure they are scaled correctly in the tune?

Was the MAF and MAP Genuine GM or parts store brand?

Where is the MAF mounted on your swap?

 

With the original PCM that came with the donor truck it ran with the same injectors it came with from the factory with the rich condition. I forgot to mention I replaced the cam sensor when I had to motor out. The new 411 PCM is tuned to a 2001 so that could be a possibility I guess but numbers on long term trim are similar to the original PCM. The new MAF is Delphi and MAP is AC Delco. The MAF is located just behind the filter. I had looked into the location of the MAF to see if that is the issue but it appears near the original location. If I need to change injectors I will, just have held off doing that after they seemed to be working correctly per the injector balance test.

 

Was the intake off the engine? Have the Intake gaskets been replaced?

Maybe see if there is knock retard pulling timing

If everything checks out electrically and mechanically, Then you may need to just have someone adjust the tune.

 

Yes intake was took off and put new gasket on. Like mentioned before I tried the propane trick to see if my gasket wasn't seated and i got no change in RPM. Not familiar with what you mean knock retard pulling timing. Could you explain that. I live in the middle of nowhere so I am on my on in this situation. Finding somebody to adjust tune unless on the internet would be difficult

 

The propane trick doesn't always work due to the intake design. This is why I asked if the gaskets were replaced. If there new, you should be good.

When the motor senses knock, it pulls timing. This is something you need a good scan tool to see and monitor.

If you have your own tuning software there are people that can assist you remotely. Atomic Performance and Fabrication can get you set up whether have the equipment or if you need to purchase some. He offers remote tuning service as well.



@Atomic Performance

 

My advice is to buy HP Tuners (with two credits) along with a wideband (AEM 30-0300). I was having similar issues shooting the "parts canon" at my build with no success. I was able to fix the issue(s) and slowly tweak the tune and trans shift points as I learned the HP Tuners software. It's payed for itself 10 fold even with gear and tire size changes, not having to mail order out or make appointments with expensive tuners. As posted above Atomic can help with remote tunes.

 

I wanna know what the fuel trims are doing under load while you are driving.

Are the short term trims really positive and adding fuel or are they negative as well. In all honestly even with the what you say about the long term trims the computer should be able to adjust and make it run pretty close to stoich. If the trims were completely maxed, that is another story.

If the injector information is wrong, that is a for sure problem for how it's running. Injection timing, flow rate, offsets, injector pulse would all be wrong if you still has smaller injectors installed but had larger injectors in the calibration.