Could this be Oxygen Sensor or Intake Manifold problem?

Question

1993 Dodge Caravan 3.0L V6 problem started with blown head gasket. I replaced and torqued head. After assembly and started vehical, it ran like it has a terrble misfire. It ran absolutely great and smooth before all this happened to me. Then a relative told me the intake bolts had to be torequed in sequence to the book. I tore it all apart again to torque the bolts on lower part of the MFI Intake to 15lbs. then realized I did this after the permatex gasket sealer had dried...Do you think this would have made a difference? and The Oxygen Sensor wire was cut when I tried to hack saw the manifold studs off to replace them. So the Oxygen sensor isnt connected, after reading lots of stuff online about Oxygen sensors making cars run rough, and rich, etc. I'm now wondering is the cause of all this the Oxygen Sensor, or the Intake Gaskets being re-tightened after permatex dried overnight? I did spray some WD40 all around the intake seal while running it, and there was no change in idle, as checking for air leaks etc. I know its not a misfire, we timed it correctly, and gave it full tune up as well?

Answer 1

I don't know what the problem might be, but the PCM (Powertrain Control Module) ignores the HO2 (Heated Oxygen) sensor until three things take place. 1. The HO2 sensor is heated to a certain temperature. 2. A certain time has elapsed. 3. The engine gets to a certain temperature as indicated by the ECT (Engine Coolant Temperature) sensor. I would make sure the spark plug wires are on the correct plugs and that you haven't disconnected any of the other sensor wires. ...Good Luck...

PS You might try to retrieve any code that might be in the OBD (On-Board Diagnostic) unit. You might be able to retrieve them with a method explained at the following site. It also has some of the code meanings.  http://www.allpar.com/fix/codes.html

Answer 2

A compression check rules out head issues. When replacing heads if the alignment pins are not shortened for the thinner shaved head, the head won't seal. It  doesnt sound like a intake sealing problem, use a bit of starting fluid instead of the wd. Fix the O2 first some newer cars wouldn't even run like that. Check vacuum lines(egr valve).good luck  

Answer 3

Ya! make sure the Oxygen Sensor is connected properly as this might  very well cause the problem.

If I can remember correctly the test for a leak in the intake manifold is to use gas from an acetylene torch, But I can not remember if the oxygen or acetylene was used. Most any mechanic shop could give you the correct answer to this question. They could check this easily at little or no cost. DO NOT QUOTE ME ON THIS, but I believe they use the acetylene as it blocks the oxygen that leeks into the system allowing it to smooth out the engine If the WD40 is supposed to do the same thing it may not have a sufficient amount to block all the leaks.

vacuum leak will also cause a rough running engine so check the hoses and plugs at the vacuum tree as well.

good luck, hope you track down the problem as I  know how frustrating this kind of problem can be! Have had all three of the above mentioned problems including an Oxygen Sensor that for some reason worked intermittently on a 1992 Dodge Caravan 3.0L V6

Answer 4

Your check engine light should be on if the 02 sensor is bad or if you have it unpluged.The 02 sensor will make it run with a miss and it will be running to leanor rich causing it to put out a misfire. Have you try to put the cut wire's back together it might not have shorten the 02 sensor out so you might want to try to wire them back together'

Answer 5

Fix the oxygen sensor and it may run OK.Being disconnected will cause problems.