AFR Max lean to 20.6
My dad has a Chevy 454 with the 2x4/dual quad setup. It does not have fitech ignition control.
Ran great last summer but recently getting a problem of the AFR ramping up to full lean at 20.6, thus causing the system to pour fuel in attempting to compensate. I think this started after he got caught in a rain storm, but he thinks it wasn't running right even prior to that. There's a large hole in the hood with a tunnel ram sticking out, and I believe he also drove through a puddle at least 6 inches deep (submerged the exhaust for a moment). We'll take ANY suggestions at this point!
-Traded out the o2 sensor twice but the problem persists.
-Was considering a possible vacuum leak somewhere in the intake, but the idle is steady with no hunting.
- Now I'm thinking maybe an ignition problem or misfire, which would pump un-burnt air into the exhaust. Weird though because it usually idle's and runs fine until it is fully warmed up, then the problem starts (which is why we were thinking vacuum leak). I believe he has the MSD 6a, but I'll confirm and check that it is not the 6al with the spark cut rev limiter (read about an issue in another thread).
-Could it be a bad injector in the Fitech unit(s)? I'm only assuming that the system is pouring in fuel because the inside of the exhaust pipes are extremely black and sooty now. But maybe it really is going lean because of a bad injector? Fuel pressure is good and steady.
-Spark plugs are all new after the rain. He will be checking the distributor/cap tomorrow.
My first thought was the O2 sensor. But since you dropped in a couple of those already that is out. What is the rpm reading?
Rpm holds steady about 900 where it is set (no up and down that would indicate a vacuum leak). That is until the afr reading shoots up to 20.6. Then it chugs and struggles to stay running without pressing the gas pedal. This seems to start occurring only after everything is fully warm.
Pete do you have a log of when this is happening that might help with it.
If you do then use dropbox or something similar to post a link to it.
That will get you more help because ppl can see a lot on the logs
Thanks Maxx. Here's a link to the log file..
https://drive.google.com/open?id=1NDuk4ztdOMQ7OxYn8FKhyVNlsVFRSHSz
HI, just looking at the log file here are a few things.
the TPS stays pretty much at 0 but the IAC counts are very high 250+. Even at the 80 degrees the IAC counts should be lower or going lower after start up. Once at operating temp I would try the IAC adjustment instructions to get the counts to between 5-10 by adjusting the throttle blade open to see if the IAC counts go down.
you can try looking for vacuum leaks using a spray bottle of water and spraying different surfaces to hear it get sucked in and the rpm change. But a vacuum leak wouldn't have IAC counts that high.
check ignition system to make sure everything is good, plugs, wires, cap, rotor, coil to ensure no misfires that would show it going lean as a result.
cant think of anything else right now.
cheers
63chevyii327
Just yesterday I ran into this exact problem. Was cruising through the neighborhood when the afr poegged full lean and i was barely able to stumble the car home. So far here is what I have looked at and what I am thinking.
Car runs great after it warms up a bit and gets into closed loop. It was only after driving and the temp getting up that it started the trouble. I dropped the fuel filter and found it to be a bit clogged. Cleaned it real well, but also noticed that when I broke the line lose at the filter there was no fuel coming out of my rear sumped fuel line even though i had a few gallons of fuel in the tank. Deduced that the external mounted pump is slightly higher than the sump and if i get below 1/4 tank i can't draw fuel well due to the gravity feed nature of the system.
So I topped off the fuel and installed the filter. Drove the car again and it ran great for about 15-20 minutes then pegged lean again. At this point I looked into vapor lock. The throttle body unit was very hot and the steel braided fuel lines were also quite hot. I jumpered my pump and circulated fuel for about 2 minutes with the engine off. After that it cranked right up and ran fine until I shut it off.
I have ordered a 1 inch phenolic spacer. NOT METAL. And also a heavy rubber carb insulating gasket. I will install these 2 items as well as set my pump to utilize the pwm instead of being full on. Running the fuel pump at constant 100% will heat the fuel up quite a bit. After that I am hoping my issue will go away.
I believe it was a fuel heating issue. Running the pump 100% constantly, having a low level of fuel, and the heat soaking of the fuel lines and efi unit caused the fuel to just get too damn hot and give me either vapor lock at the throttle body inlet or vapor lock/cavitation at the pump inlet. Perhaps both. We shall see.
If your set up sounds at all like mine these are a few things you should check. Run the car and if it pegs lean again, turn it off and see how hot the pump and the throttle body unit are. Also check the temp of the fuel feed line at the throttle body. Good luck.
Quote from Marbles on September 30, 2019, 7:02 amJust yesterday I ran into this exact problem. Was cruising through the neighborhood when the afr poegged full lean and i was barely able to stumble the car home. So far here is what I have looked at and what I am thinking.
Car runs great after it warms up a bit and gets into closed loop. It was only after driving and the temp getting up that it started the trouble. I dropped the fuel filter and found it to be a bit clogged. Cleaned it real well, but also noticed that when I broke the line lose at the filter there was no fuel coming out of my rear sumped fuel line even though i had a few gallons of fuel in the tank. Deduced that the external mounted pump is slightly higher than the sump and if i get below 1/4 tank i can't draw fuel well due to the gravity feed nature of the system.
So I topped off the fuel and installed the filter. Drove the car again and it ran great for about 15-20 minutes then pegged lean again. At this point I looked into vapor lock. The throttle body unit was very hot and the steel braided fuel lines were also quite hot. I jumpered my pump and circulated fuel for about 2 minutes with the engine off. After that it cranked right up and ran fine until I shut it off.
I have ordered a 1 inch phenolic spacer. NOT METAL. And also a heavy rubber carb insulating gasket. I will install these 2 items as well as set my pump to utilize the pwm instead of being full on. Running the fuel pump at constant 100% will heat the fuel up quite a bit. After that I am hoping my issue will go away.
I believe it was a fuel heating issue. Running the pump 100% constantly, having a low level of fuel, and the heat soaking of the fuel lines and efi unit caused the fuel to just get too damn hot and give me either vapor lock at the throttle body inlet or vapor lock/cavitation at the pump inlet. Perhaps both. We shall see.
If your set up sounds at all like mine these are a few things you should check. Run the car and if it pegs lean again, turn it off and see how hot the pump and the throttle body unit are. Also check the temp of the fuel feed line at the throttle body. Good luck.
Fuel pressure and what does the data say?
Did you ever get your issue resolved?
Also curious, if setting it back to < 100% PWM helped.