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Unread 09-24-2009, 10:40 AM   #1
PT's93
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1998 ZJ 
 
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Posts: 58
Will zero oil pressure = Limp Mode?

'97 ZJ, 4.0

Oil pressure gauge reads zero. Coolant temp normal, Engine runs fine for a few minutes, then looses power & 35mph becomes top speed. No ticking or knocking.

Will zero oil pressure indicated put the engine into Limp Mode after a period of time?

This is brother-in-law's ZJ. He noticed lack of oil pressure after third power loss (he was assuming tranny problems). Three power losses in a three day period, and still no ticking, knocking, or running hot. Before I start looking at the oil pump and its drive, wondering if all it needs is a sending unit.

Thanks!

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Unread 09-24-2009, 11:28 AM   #2
greasefingers
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No neither the PCM nor the TCM get readings from the oil pressure sensor. It only goes to the dash board gauge.
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Unread 09-24-2009, 11:59 AM   #3
PT's93
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Quote:
Originally Posted by greasefingers View Post
No neither the PCM nor the TCM get readings from the oil pressure sensor. It only goes to the dash board gauge.
Thanks!!

I was afraid of that.

Yet, one of the computers knows that there's something wrong. Brother-in-law reported that a "Check ???" light was flashing on last run. I'll pull the ScanGauge out of my Explorer and check his codes before yanking the pan off. I'll also check for a broken pump drive shaft. Can you tell that I'm not looking forward to taking the oil pan off!

Thanks Again!
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Unread 09-24-2009, 03:37 PM   #4
acidspit86
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i dont know about the zj but on the wj it wont bring you down to limp mode
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Unread 09-26-2009, 11:49 AM   #5
Kota04SXT
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Flashing CEL is no good. Usually indicates a knock/bad miss in a cylinder. Does the oil pressure gauge move when he gives it gas?
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Unread 09-26-2009, 06:17 PM   #6
PT's93
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Quote:
Originally Posted by Kota04SXT View Post
Flashing CEL is no good. Usually indicates a knock/bad miss in a cylinder. Does the oil pressure gauge move when he gives it gas?
Talked to brother-in-law - It was a "Service Engine Soon" light on the Information Center, not a CEL. They probably didn't do a reset at last oil change.

Do not know about pressure rise on rev-up. I'm going to wait till he gets it to my place for further diagnosis (the only in-law that's mechanically inclined was the father & now that he's passed away I seem to have been voted the family mechanic).
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Unread 09-26-2009, 07:47 PM   #7
simidrm
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limp mode

I would say that your oil pressure sending unit has gone bad because if you had 0 oil pressure that engine would self destruct in less than a min,as far as limp mode that is a transmission issue where when the gov pressure sensor goes bad the tranny goes into limp mode which will usually only give you 3rd 4th and over drive and starting out in 3rd gear will make the engine work hard to get moving resulting in slow speed until rpm get up to normal range this is a protection for the tranny that also lets you get vehicle to a service station.
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