1989 Oldsmobile 98 After warmup the engine runs rough and s

Tiny
MLANTZ
  • MEMBER
  • 1989 OLDSMOBILE 98
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 168,000 MILES
The car starts fine and runs fine until it warms up and goes into closed loop mode. Then it does not die but chugs, surges, pauses, runs rough. It started out minor and now is getting worse.
What I have replaced so far:
Plugs, wires, EGR, IAC valve, Ignition control module and coils, fuel filter, O2 sensor.
About 2 years ago the dealer put in a remanfactured ECM assembly.
I cleaned the throttle body and checked for vacuum leaks and bad hoses. I checked the fuel pressure and it runs steady at 35psi (within spec).
I am suspecting a bad catalitic converter or maybe it's the Crank or Cam position sensors. What do you think?
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Sunday, May 31st, 2009 AT 7:38 AM

7 Replies

Tiny
RACEFAN966
  • EXPERT
Ok I would like you to check the coolant temp sensor. If you could unplug it and do an ohms reading on the sensor (not wire harness). If you do this cold then get back to me with reading and what setting it was on and the air temp at the time of the test. Then get it warmed up when it is having its problems and do the test again this time provide the reading the engine temp. Thanks.
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Monday, June 1st, 2009 AT 9:52 AM
Tiny
MLANTZ
  • MEMBER
Since it was hard to get to I just installed a new one. It read 2.1K at 85deg F. Did not solve problem. Also, I have yet to get a fault code. I even tested the system by disconnecting the TPS and it set code 22 correctly. On Sunday I drove it 20 miles in city and hwy with no problem. I then stopped and shut it down for 5 min. When it started it immediately started cutting out and did so all the way home. Really a puzzle. I suspected bad gas but all the samples I took from the fuel rail are fine. Why no codes?
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Monday, June 1st, 2009 AT 6:51 PM
Tiny
RACEFAN966
  • EXPERT
Ok I would like you to do the same test on the air charge temp sensor. This sensor is in the air intake tube should be easy to get to. You do the test just as you did the coolant sensor. Let me know what you find ok. Thanks.
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Tuesday, June 2nd, 2009 AT 10:38 AM
Tiny
MLANTZ
  • MEMBER
It appears to be OK also, 1745ohms at 105 deg and 960 ohms at 135deg (I checked the actual temp with a laser temp.
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Tuesday, June 2nd, 2009 AT 6:52 PM
Tiny
RACEFAN966
  • EXPERT
Ok I would like to check the cam and or crank sensor. But I need to know what engine you have as the 3.3 the sensor does both and the 3.8 ltr they are seperate sensors. Get back to me and we will take it from there.
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Wednesday, June 3rd, 2009 AT 10:48 AM
Tiny
MLANTZ
  • MEMBER
This model only used the 3800 engine. I thought about these but since they are a required signal for the spark and the engine runs fine cold I assume these are OK. I don't have the diagonstic equipment to read the pulse signals, is there an easier way?
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Wednesday, June 3rd, 2009 AT 5:53 PM
Tiny
RACEFAN966
  • EXPERT
Ok lets run some tests on the camshaft sensor. Now what I have read the car will run if the signal is bad just not well. It is on the timing cover refure to pic below. Now here is what I need you to do first.
Unplug it and hook up your volt meter (on the plug) between term a and b and check voltage and then check voltage between term b and c with key on engine off votage should be between 8-11 volts. Let me know what you find. Also is the engine light on and is there any codes? The first pic below is so you can locate the camshaft sensor. The second pic is so you know what term is what in the sensor harnes so you can test the voltage, if you look in the lower right hand corner of that pic you will see the camshaft sensor plug with the term labeled let me know what you find.


http://www.2carpros.com/forum/automotive_pictures/249564_Graphic_88.jpg




http://www.2carpros.com/forum/automotive_pictures/249564_Graphic1_13.jpg

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Thursday, June 4th, 2009 AT 10:21 AM

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