I have an 89 formula 350 with TPI that has been running like a top... Until this past friday. The car won't stay running, has a terrible miss it sounds like, and the throttle is pretty much non-responsive. I put the code puller into the diagnostic port, and it now starts and idles fine. No codes are stored btw. So the problem is obviously with a sensor somewhere correct? Closed loop the car won't run, but open loop it will, albeit rich. Before I start forking out money for sensors, etc. I would like some assistance in making an educated guess as to which ones to go after. My first thought is the O2 sensor. Anyway if there is a propellor head out their that can steer me in the right direction, I would appreciate it. Remember, open loop it stays running, but closed loop it won't. NO REPORTED CODES! Thanks in advance ...

 

DJD,

Welcome Aboard!

Since it apparently runs acceptably in open loop, the factory fuel calibrations must be close enough to get the engine running. The BLM tables are apparently not close enough. Since you have no stored error codes, remove the battery power for a few minutes (long enough to clean the battery cables and terminals) and reconnect. This should clear the BLM tables.

I'd go with your first impression, especially if the O² has more than 30K miles on it. While there, check the connector and wire harness lead.

 

Ok, I replaced the O2 sensor, and did the computer reset as suggested. The problem apppears to have improved somewhat, but now I have a definate stumble when applying throttle from a standstill or low speed. Also, when at idle, such as at a traffic light, the check engine light is coming on after about two minutes. The code is, Guess what, CODE 44. Lean ... Bla Bla Bla. What now? I thought maybe a bad sensor, so i returned it for another one, which was a miracle in itself. Installed the new one, reset the computer again, and same result. What next? My next thought is fuel filter maybe?

 

You guys think maybe its just bad gas? I've got about 2/3 of a tank, so I'm gonna go run it out on the interstate and put some new in. I'll let ya know if it helps. I read that it may be water in the fuel somewhere

 

Check the fuel pressure.

 

Problem solved ... Mass Air Flow Sensor ... No reported code though ... very weird. Took a snapon diagnostic computer to figure it out.