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UPDATE SOLVED TBI Running Poorly Code 42 & 44

C

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77 Chevy Truck with new 91 TBI motor swapped in. Used TBI parts, new painless harness with all correct sensors including VSS.

Took it for the 1st real drive today as part of the engine break-in period. I drove about 10 miles and noticed the ALDL check light (painless wiring harness) had come on. When I came to a stop to check it, the light went out. So I continued on my merry way. After another 5 miles the ALDL check light returned and stayed on, except when I would come to a stop and idle for a minute. Then the check light would go out. As soon as I'd start driving for a few miles it would come back on. I ended up driving about 68 miles roundtrip and it sucked up 8 gallons of fuel.

So, on the way home I dropped by Autozone and got a code key. When I got back home I checked the ALDL and pulled up a code 42 and code 44. Now I know each code can be a number of things but I thought I'd get a group opinion to help narrow it down.

The truck was running doggy. If I tried to accelerate normally it acted as if there was a lean running carb on it. If I accelerated very gently it ran okay. Also the mileage was horrific, between 7 and 8 mpg.

Whatcha think?
 
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Kinda sounds like the VSS or O2 sensor. On my 89, I have an O2 that is going bad, and the VSS is not hooked up, so when you drive down the road, the light will come on, and will go off when you stop, or after awhile driving. It sucks alot of gas too (454 doens't help any). Code reader should tell you what codes are what, not just what the number of the code is.
 
44, lean exhaust...oxygen sensor? Maybe a bad sensor is incorrectly reading lean and causing the ECM to try and dump fuel in to richen it up (which might make it too rich and trash your fuel economy).

Have you shut down and pulled a spark plug for visual inspection when the CE light is on? If so, does it look like it's loading up? Is this the stock TBI cam?

(edit: b454rat beat me to it!)
 
Code 42 is the ESC circuit (module) and it seems like a pretty darn common problem, as I had it when I first did my conversion. Ill look for the flow chart for code 42, its around here somewhere.
 
42 is the ESC
44 is lean at the O2

Just thought somebody might recognize the problem off the top of their head. I'll work on getting it diagnosed tomorrow.
 
if you want to try another computer let me know I seem to have a few...
 
Thanks Toby, appreciate it!

If it ends up being the computer I will give you a holler. Should know within the next day or so.
 
Okay, all sensors are good. The problem is fuel delivery, it's intermittently running out of fuel. This was a dual tank 77 carbureted K10.

Right now it's running off just one tank with a carter electric in-line pump. The pump cycles and runs properly. The fuel pressure after the in-line filter is a steady 11 and goes to 12 when throttled up. The tank is 3/4 full.

Today the fuel starvation became worse to the point it was barely running. Limped it in to the shop and parked. Let it sir for a few minutes then cranked it back up. It would run fine for 5 minutes and then suddenly starve for fuel while idling. If you throttled up at the lean points it would stall. Crawling underneath and switching to the opposite tank feed did not make a difference.

The pump cycles up when you turn the ignition on, but when your cranking the engine it barely cycles. When running the fuel feed is intermitant and we still get a code 44 "Lean O2". My buddy the wrench thinks it's a fuel pump issue.

Any ideas from the peanut gallery? I think I either need a stronger pump than the stock carter unit or there is an issue running TBI off carbureted tanks.

:1zhelp:
 
code 42 you get when you unhook the tan wire to set the timing. did you clear the codes after setting the timing? did you plug that wire back in?
 
Hey James, sounds like you have a clogged tank venting issue. Leave the gas cap off, try running it like that. Also, with it running bout 5 minutes, unscrew the gas cap, listen for the hissing sound of air entering a vacuum. Along those same lines, find the hose that goes from the tanks to the charcoal cannister. Unhook it and blow air(10-15psi) back thru to the tank, to check for clogs. Leave the canister unhooked and see if that makes a difference. Wish you were closer, I'd be there playing Mr. Whatwrench.:D
 
3 on the tree said:
Hey James, sounds like you have a clogged tank venting issue. Leave the gas cap off, try running it like that. Also, with it running bout 5 minutes, unscrew the gas cap, listen for the hissing sound of air entering a vacuum. Along those same lines, find the hose that goes from the tanks to the charcoal cannister. Unhook it and blow air(10-15psi) back thru to the tank, to check for clogs. Leave the canister unhooked and see if that makes a difference. Wish you were closer, I'd be there playing Mr. Whatwrench.:D
Click to expand...

I don't have a cannister, never did. Tried running with the caps off, didn't make a difference. There is absolutely no pressure differetial when the caps come off.


big83chevy4x4 said:
code 42 you get when you unhook the tan wire to set the timing. did you clear the codes after setting the timing? did you plug that wire back in?
Click to expand...

42 never came back after the 1st reset. We figured it was the ESC trying to compensate for the ultra lean condition. Today it just threw the code 44 "Lean O2.
 
This might sound off the wall, BUT. Hook up a 5 gallon gas can to your elec fuel pump,see if that makes a difference.Use a long line first, approx same length as pump to gas tank. Then try as short a line as possible. If the short line improves fuel flow, then your fuel pump is going south.
 
I believe that was on tomorrow's agenda, will let you know what happens Mike. Thanks for the wisdom, you old dudes are smarter than I thought. :rotfl:
 
Do you have a fuel return line plumbed up to the regulator? The stock regulator Will NOT work without a return line plumbed back to the tank/s. Your pump should not cycle it should run all the time.
 
sounds like you might need more fuel pressure. I had a similar issue turned out my return line was to big. Pinch off the return line some wich will ceate more pressure and see if it makes a differance. How close to the tank is your pump??
 
Thunder said:
Do you have a return line plumbed up to the regulator unless you have done some deastic changes the stock regulator wont work without a return line plumbed back to the tank. Your pump should not cycle it should run all the time.
Click to expand...

I'll double check that tomorrow Thunder and let you know.

moneypit said:
sounds like you might need more fuel pressure. I had a similar issue turned out my return line was to big. Pinch off the return line some wich will ceate more pressure and see if it makes a differance. How close to the tank is your pump??
Click to expand...
The pump is on the frame rail opposite the saddle tank. It's sitting about 1/2 the way up the total tank height.
 
I have nothing useful to add. I'm just real tempted to say something about TBI being overrated and carbs rock the house.

However, I know that's not really true, but it's still tempting just because. :tongue1:
 
Come on now, using a non-stock pump in a non-stock TBI tank, even THINKING it's the fault of the system isn't fair. Carbs suck because when I tried to use diesel, it didn't run! :)

If the external fuel source deal helps, you COULD be dealing with a tank issue, others have. Clogged filter sock, crud in tank, broken pickup, etc.
 
Okay, problem solved and a big thanks to Thunder for solving the mystery. :waytogo:

The fuel pump being used for the swap was a pulsating type electric unit, what you'd find on most typical carb applications. The TBI/MFI systems require a different style pump called a Gerotor. See the following link for a description. Specifically there is a Carter #5001 series made for the Carb to TBI swap. Worth it's weight in gold.

www.carterfueldelivery.com/fuelpumps/electric.php

Once the Gerotor pump was installed and the fuel pump lowered to the base height of the fuel tank the intermittant starvation issue was fixed. The truck runs fantastic. Like night and day, I can't believe the difference.

Big thanks to Thunder for 3 days worth of coaching, fuel pump recommendation, and helping on his own time. :saweet:
 
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