TBI Rich and Off-Idle Stumble

tobyw · Feb 2, 2008

I know lots of you guys bash AFI and their TBI conversions, but I have had good luck with mine thus far so let's just treat this as any other troubleshooting session, and not a pissing match about what I "should" have done, OK?

I'm running a 350 SBC with a TBI conversion on an Edelbrock manifold, HEI distributor, and headers. Up until now, it has run wonderfully. However, it has recently started running extremely rich and has a hesitation/bogging under load right off idle. It is far worse when the engine is cold, as this hesitation/bogging will go away once it reaches a reasonable operating temp. However, the richness persists no matter what. I have inspected all the vacuum lines and fittings, verified my inlet fuel pressure is a steady 13psi, and have tried to let it warm up both with and without the air cleaner to take that out of the equation as well. Again, these are all recent developments. Where do I go from here?

superglock · Feb 2, 2008

Check the temp sensor (for the computer) and see if it is reading right, I had one freek out and it was reading -45degrees and to was 70 out, The truck wouldnt run hardly. If you cant check it try just unpluging it and see what it does.

GaryTJ · Feb 2, 2008

also the temp sensor grounds at the T/stat housing. Make sure the wire is good and solid to ground.

tobyw · Feb 3, 2008

Forgot to mention I've got WINALDL, but don't have much idea what to look for in the readings... It does have a temp readout though, so I'll definetly check that next!

super samurai · Feb 3, 2008

comp. test it also,i had one do that and it turned out to have a dead cylinder.

GaryTJ · Feb 3, 2008

if you have winaldl you have it made.

Look at the map sensor readings too. remember that the map sensor is the difference between atmospheric pressure and manifold vacuum.

I would run rich if you had a bad intake valve. It would be pushing compression back into the intake, lowering manifold vacuum thinking it was under load the map signal would enrichen it.

Also, if your motor has a bit of blowby, the lower section of the TBi unit will fill with carbon and choke off the signal to the map. Pull the hose off the map and make sure you have a real good vacuum signal. Not a bad idea to clean the tbi unit by spraying carb cleaner into the hose leading to the tbi unit.

Blueleader · Feb 3, 2008

Take a look at the fuel spray pattern out of the injectors. It should have a nice even cone shape. I've had a couple injector failures where the fuel is just kinda dribbling out. Both times, the rig still ran but was rich as hell.