85 Cougar 5.0 CFI running rough. Suggestions?

Topic: 85 Cougar 5.0 CFI running rough. Suggestions? (Read 1640 times) previous topic - next topic

85 Cougar 5.0 CFI running rough. Suggestions?

April 17, 2011, 05:42:54 PM

I am trying to get my 85 that I just bought in good running shape. Right now it runs rough at idle, dies when put in gear, and bogs down for a second when accelerating from a stop.

I ran the KOEO codes and got trouble codes 23 and 31. According to the fordfuelinjection website, those codes correspond to TPS voltage and EVP voltage.

I checked and had the correct 5 volt signal to the TPS and then check the output voltage and it was 1.93 with the car off and varied between 3v and 5v with it on due to the bad idle.

Next, I checked the EGR. The EGR held vacuum and seemed to operate correctly. The vacuum line to the solenoid was uncracked also. I confirmed 5 volts at the EVP connector and then tested output voltage at at several vacuum readings. At 0" HG I got a reading of 1.89. At 5" I got 3.92, and at 10" I got 3.96. The EVP voltage with the car running remained at 1.89.

I would rather replace parts that don't need to be replaced. Can anybody help interpret these results or suggest what to do next. Thanks!

85 Cougar 5.0 CFI running rough. Suggestions?

Reply #1 – April 17, 2011, 05:56:24 PM

The EGR valve has to close completely at idle, if not it is a vacuum leak and will give an unstable/stall condition. They like to carbon up. Carb cleaner + screwdriver to get the plunger clean so it can seat completely has worked for me. I don't know about the CFI cars, but the SEFI calls for 1.00v or slightly less at the TPS with the throttle closed.

85 Cougar 5.0 CFI running rough. Suggestions?

Reply #2 – April 17, 2011, 06:07:11 PM

Thanks Jim. I do recall reading about setting the TPS voltage to about .95 on the SEFI cars but wasnt sure if the CFI cars were the same also. Doing a bit more research, I read that the EVP sensor voltage should only be about .75v when it's closed, so my reading of 1.93 may be an indication that you are right about it not being closed all the way.

85 Cougar 5.0 CFI running rough. Suggestions?

Reply #3 – April 17, 2011, 10:01:19 PM

I also forgot to mention I did check the fuel pressure and came up with 39psi.

85 Cougar 5.0 CFI running rough. Suggestions?

Reply #4 – April 20, 2011, 03:08:12 PM

I replaced the TPS and the car runs a lot better now. I reset the computer and the only code now is the code 31 for the EVP sensor voltage. The car still seems to run a bit rich (kinda stinky) and hopefully I can get that sorted out this week. The car also seems to run a bit hot (on the factory gauge anyway.) Is it possible the ignition timing is off and causing this?

I also checked out the radiator fan rubbing the shroud. It is just barely nicking it right at the bottom. Possible worn out motor mounts? I will probably get an electric fan for it in the near future. Is the Taurus fan still the popular swap?