Rich and Surging on Highway

[adamputz]

It idles fairly high at warm up (around 1600 rpm's), then the check engine light only comes on once i've driven for a bit. It's running rich and surges on the highway. I've replaced the O2 sensors, spark plugs, fuel filter, injectors, and cleaned the MAF. Does anyone have any idea what this could be? I'm also getting about 11 MPG.

 

[Twizzler09]

I'd check your fpr (fuel pressure regulator) first.

If the diaphragm in the regulator has ruptured its going to let tons of fuel into your cylinders. Easy way to check your regulator...is to pull the vac line off the side of it and see if theres any raw gasoline in it. If there is, then you found your problem.

Hope this helps ya

 

[adamputz]

I think that did it, replaced the one bad injector and the fuel pressure regulator, took it on the highway and no more check engine light!

 

[Twizzler09]

Nice.

Hopefully it stays that way, eh? =p

 

[adamputz]

after I made the changes I disconnected the negative for 10 minutes to reset the computer. I drove it for 20 minutes and my check engine light came on for a minute then it went off. I took it on the highway and now it's loading up so much that it backfires. It runs really rich at half throttle, then if I put it to the boards it will acclerate really hard. Do I have to use a code reader and reset everything?

 

[Wicked_Sludge]

resetting the PCM by unhooking the battery is never a great idea. you can clear codes using the same proceedure you use to pull the codes with a simple paper clip (check the tech library for details).

 

[dorman68]

Try cleaning out the throttle body, sometimes they get gummed up from carbon deposits.

 

[adamputz]

I'll take a look at that, I ran the codes on it and this is what I got.

114 - (O,R) IAT sensor out of range - IAT (intake air temperature)
522 - (O) Park/Neutral Position (PNP) or Clutch Pedal Position (CPP) circuit fault - PNP transmission MLP sensor out of range in park - Transmissions

 

[Wicked_Sludge]

the IAT is a problem. make sure the sensor is plugged in and installed in the air box as it should be. if it is, you can measure the OHMs accross the sensors 2 terminals and compare the readings to a chat of resistance vs ambient temperature.

 

[adamputz]

Ya i'll check that with an ohm meter tommorow. Is the IAT located on the throttle body on the 4.0? I also got these from the memory codes.

172 - (R,M) Oxygen sensor not switching - system is or was lean - Single, Right or Rear HO2S - Fuel control

173 - (R,M) Oxygen sensor not switching - system is or was rich - Single, Right or Rear HO2S - Fuel control

176 - (M) Oxygen sensor not switching - system is or was lean Left or Front HO2S - Fuel control

177 - (M) Oxygen sensor not switching - system was rich Left or Front HO2S - Fuel control


Could the IAT sensor be causing these O2 sensor codes to be coming up? I had 2 of the O2 sensors replaced already

 

[Wicked_Sludge]

it could be, its a good place to start anyway.

the IAT should be located in the lower half the the air cleaner box.

 

[adamputz]

Ya good call, it's easy to test anyways. How many O2 sensors does the 4.0 have?

 

[Wicked_Sludge]

its been a while since ive been under that generation of 4.0. id guess 2.

 

[adamputz]

haha that's good to hear, thanks for all the help!

 

[Twizzler09]

93 is 3rd gen....

If thats the case... I think theres 3. I know my '96 has 3. One on either side of the Y-pipe and one behind the cat-converter. Dont think the o2 is your problem though.

Thinkin Wicked is on the right track with the IAT.... def knows his stuff