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Unread 02-28-2015, 01:07 AM   #1
Haleyrz
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1998 ZJ 
 
Join Date: Oct 2008
Location: Spokane, Washington
Posts: 2,763
TPS uncertainty

I it's been a long couple months of random misfire + isolated misfire pending codes, hesitations, and rough idle bull crap. Every once in awhile I'll get a no start as well unless given throttle only to immediately die. Then like magic it will start and run for weeks, sometimes pending misfires, sometimes no codes at all. Never does the CEL actually come on. Today it did, for random and #2. Went through spark, fuel, compression, and crank sensor, all is good. Tested my TPS today just cuz. Plug has good ground, and 5V. Plug it back in and probe the wires, slowly open the throttle and it's minimum is at .82V and max at 3.89V. So super basic question. Is it bad since it's not .5V and 4.5V? I've been also monitoring it via live data for a few days and anytime idling or letting off the pedal it's jumping from 16.1%-16.5%. It's my understanding that at idle it should stay in one value?

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1998 ZJ Laredo, 4.0L, 2WD, it's boring
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Unread 02-28-2015, 05:23 AM   #2
PolkaPower
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1998 ZJ 
 
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I never bothered testing them. It's easy enough to go to a JY and pull a bunch of TPS sensors and try them out. I always grabbed a bunch of extra sensors when I went just for spares.

98 was a notoriously bad year for 4.0 computers. When those fail they give the same symptoms as you are describing.
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Unread 02-28-2015, 12:37 PM   #3
Haleyrz
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I had that thought. I wish there was a way for me to know for sure I had a bad PCM without taking it to a shop.
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Unread 02-28-2015, 01:52 PM   #4
ZeeJay1997
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Did you put another IAC on it? You said yours was rattling.

It sounds like you have more that one problem external to the PCM or a bad PCM. I cant think of a scenario where the TPS or IAC would cause a misfire.

Most shops will fall short when it comes to diagnosing these things and so do most armchair mechanics on the internet, myself included.

The pending misfires codes come from having a single incidence without a consecutive repeat. The PCM looks at the crank sensor signal to monitor for misfires if that helps any.

Mine was acting very similar to yours and it was the cam sensor connector. I got in there with a scribe and tightened the contacts up and fixed it.

What kind of plug wires are you using? If you have those solid core or wire wound wires, I recommend you ditch them and get some OEM style carbon core wires. Once these type wire age a little, they cause misfires on these engines.

On a 97 4.0, the correct TPS voltage range is > 350 mV and < 900 mV at idle. <4.5 volts at wide open throttle, so yours seems to be good. The jumping could be due to variation in reference voltage so that's something to consider.
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Unread 02-28-2015, 03:41 PM   #5
MrRoundel
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Quote:
Originally Posted by ZeeJay1997 View Post
Mine was acting very similar to yours and it was the cam sensor connector. I got in there with a scribe and tightened the contacts up and fixed it.
If I remember correctly, the OP had replaced her distributor, but had not taken the Mopar cam sensor from the core. I probably confused the issue, as I had stated that the parts book for my '98 did not show anything called cam sensor. I believe the FSM did reference the part, however the parts book referred to it as a "switch plate". I believe that the OP may have been unsure of the brand cam sensor that came with the rebuilt distributor.

Maybe I'm looking at the wrong part in the parts book?
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Unread 02-28-2015, 04:10 PM   #6
ZeeJay1997
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Quote:
Originally Posted by MrRoundel View Post
Maybe I'm looking at the wrong part in the parts book?
No, you're looking at the right thing in the parts book. If you look in the FSM, it's called a camshaft position sensor. I guess the tech writers didn't have a meeting one day. You'll also see abbreviations like CMPS CKS and other such garbage that people like to argue about to prove their automotive knowledge. To keep it simple, I'm stuck on cam and crank sensor. .. cuz I'm a pretty simple person...
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Unread 02-28-2015, 04:18 PM   #7
MrRoundel
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Originally Posted by ZeeJay1997 View Post
... cuz I'm a pretty simple person...
Thanks for keeping it simple for me. I thought it might have something to do with a lack of communication. Certainly is a lack of consistency. Oh well, at least now I know that we're talking about the same thing.

Cheers.
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Unread 02-28-2015, 05:05 PM   #8
ZeeJay1997
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Originally Posted by MrRoundel View Post
T I thought it might have something to do with a lack of communication.
Only amongst the folks at Chrysler.
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Unread 02-28-2015, 05:50 PM   #9
Haleyrz
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Yeah, I had replaced the distributor, cap, rotor, wires, plugs, coil, crank sensor (which I actually don't believe is bad and coincidence that it started after replacement lol, but I still have my old one). Brand new wires are BWD wires from my work (O'Reilly's). Everything new was BWD, plugs champion copper, and distributor A1. I should have kept that original cam sensor. I've been thinking a lot about the PCM, because my fuel trims will be normal one trip, then erratic the next trip. Misfire, not misfire. Pending codes, or like now, confirmed code P0302 only. So idk wtf to do with spark, fuel, and compression being good, and the readouts being so hit or miss. I'm gonna be heading over to Seattle next weekend hopefully, to buy two 5.9's from a friend. One is a parts jeep, other is low miles with rebuilt title. Then sell this 2wd 4.0L off, but hopefully fix it so the next person doesn't have to deal.

So, getting a junk yard PCM. Good idea or no?
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Unread 02-28-2015, 08:16 PM   #10
ZeeJay1997
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Originally Posted by Haleyrz View Post
So, getting a junk yard PCM. Good idea or no?
it depends on if it an as-is sale or if they offer a warranty. the latter will likely cost more. it's like box of chocolates.
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Unread 02-28-2015, 08:37 PM   #11
Haleyrz
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Does it matter that mine is 2wd? Or just make sure I get it from a 4.0L?
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Unread 02-28-2015, 08:39 PM   #12
ZeeJay1997
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same engine and drivetrain. 2wd and 4wd are not interchangeable. must be a 98
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Unread 02-28-2015, 10:24 PM   #13
Haleyrz
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Well damn, that makes it incredibly difficult lol. The chances of finding a 2wd in the junk yard.
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Unread 02-28-2015, 11:15 PM   #14
ZeeJay1997
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I was going to refer you to Car-Part.com. Went on there and got the choices in the screenshot below. According to them a 4.0 makes no distinction between a 2wd and 4wd. So either I'm wrong or they are wrong.
98-pcm.jpg

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Unread 03-01-2015, 12:36 AM   #15
RedRiverT
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I seem to have gotten rid of the 0300-0306 codes I was getting every few days after I cleaned the PCM pins and sprayed the PCM plug connections with electronic parts cleaner. Of course, now I have another problem (maybe more than one actually) and one day it was causing very definite missing and I got some 300-306 codes. But that is one day in over a month, whereas I was getting them every 2-4 days for I don't know how many months. Soon after getting it, I read that aftermarket plug wires will cause misfire codes, and I had just put BWD's on it, so I figured that could be the cause and didn't worry about it. It was running OK then, not perfect but not dying randomly like now.
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