1995 ORVIS 5.2 stumbles when hot then runs fine - JeepForum.com
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post #1 of 23 Old 05-24-2020, 08:16 PM Thread Starter
88formula
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1995 ORVIS 5.2 stumbles when hot then runs fine

1995 ORVIS 5.2 when hot (over 215) starts fine if I start it in 10 min...but if I wait for 30min to an hour, then starts shaking seconds later like it wants to stall, or like it has a vacuum leak, put it in gear, start driving and bam it straitens out like nothing happened.. plenty of power ...

I changed the fuel pump
ECU
MAP sensor
full tune up
injectors
TPS
IAC
coolant temp sensor (for computer)
air intake temp sensor
New coil
fuel pressure is fine, could it be the O2?

no mechanic can figure it out... im out of answers... please help me!!!


Last edited by 88formula; 05-24-2020 at 09:24 PM.
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post #2 of 23 Old 05-24-2020, 08:50 PM
jeepjeepster
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Unfortunately without doing a little diagnosing, you're blinding throwing parts at it. Gotta get some sort of scanner that will let you see some data. Have you checked fuel pressure while its stumbling? Its more than likely heat soak on a sensor. What brand of sensors are you using?

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #3 of 23 Old 05-24-2020, 08:55 PM Thread Starter
88formula
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Quote:
Originally Posted by jeepjeepster View Post
Unfortunately without doing a little diagnosing, you're blinding throwing parts at it. Gotta get some sort of scanner that will let you see some data. Have you checked fuel pressure while its stumbling? Its more than likely heat soak on a sensor. What brand of sensors are you using?
yes, checked it... its fine .. had a scanner on it while it stumbled .. nothing... That is what I was figuring.. I know its a heat soak issue... but what sensor? I have zero codes, BDW sensors from AutoZone

This was my Father in laws Jeep... im the second owner.. he passed on and I loved him and this Jeep... I have 175K on it and it still looks new!

would a crank position sensor or cam position sensor do this when hot?

Last edited by 88formula; 05-24-2020 at 09:54 PM.
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post #4 of 23 Old 05-24-2020, 10:37 PM
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If the plenum gasket is bad, which they all go bad on almost every magnum V8, that is a vacuum leak.
02 sensor can do that too.

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post #5 of 23 Old 05-25-2020, 06:35 AM Thread Starter
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Originally Posted by PolkaPower View Post
If the plenum gasket is bad, which they all go bad on almost every magnum V8, that is a vacuum leak.
02 sensor can do that too.

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wouldnt it do it all the time with a plenum leak? and the O2 sensor would throw a code? its an intermittent problem
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post #6 of 23 Old 05-25-2020, 07:53 AM
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I'm talking about a scanner that shows live data, like a snap on 2500. It should show you if, for example, its starts to stumble when the O2 goes into closed loop. Try to find an NTK O2 sensor if you do replace it.

1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #7 of 23 Old 05-25-2020, 09:07 AM
jtec
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AM I reading this OK - when hot it stumbles on restart, starting HOT is the concern?


Have you tried a fuel pressure drop, just KEY on, engine not running.
What is fuel pressure, high should be in @ 3seconds. Then check in 5minutes.

Plugs - correct plug and heat range. How do they look any clues? WET, black, tan, damaged?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #8 of 23 Old 05-25-2020, 09:41 AM Thread Starter
88formula
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Originally Posted by jtec View Post
AM I reading this OK - when hot it stumbles on restart, starting HOT is the concern?


Have you tried a fuel pressure drop, just KEY on, engine not running.
What is fuel pressure, high should be in @ 3seconds. Then check in 5minutes.

Plugs - correct plug and heat range. How do they look any clues? WET, black, tan, damaged?
the plugs look normal... and are the champion direct replacement. im going to pick up a fuel pressure gauge... this was doing it before and after a new fuel pump... it starts fine revs down and then starts to stumble... and then will straiten out when I start driving... only when its really hot and has been sitting for at least 20-30 min...
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post #9 of 23 Old 05-25-2020, 09:52 AM
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before the vapor lock suggestion where are you located - death valley?

Will your scanner let you look at live data?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #10 of 23 Old 05-25-2020, 09:55 AM
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Any issue with AIRBAG light, it does come on for 3seconds then go out?
You are seeing correct ECT?
I am unclear did you change IAC - if so did you clean any air bypass ports?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #11 of 23 Old 05-25-2020, 10:34 AM
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Originally Posted by jtec View Post
AM I reading this OK - when hot it stumbles on restart, starting HOT is the concern?


Have you tried a fuel pressure drop, just KEY on, engine not running.
What is fuel pressure, high should be in @ 3seconds. Then check in 5minutes.

Plugs - correct plug and heat range. How do they look any clues? WET, black, tan, damaged?
Ahh, good point. Could be a fuel injector issue.


1994 ZJ-I6 w/270,000 mi
1998 ZJ 5.9 w/66,000 mi Slate Black
2004 KJ w/108,000 mi
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post #12 of 23 Old 05-25-2020, 07:03 PM Thread Starter
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please guys read what I wrote... new injectors.. proper pressure .. did a leak down test.. all good
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post #13 of 23 Old 05-25-2020, 07:03 PM Thread Starter
88formula
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Originally Posted by jtec View Post
Any issue with AIRBAG light, it does come on for 3seconds then go out?
You are seeing correct ECT?
I am unclear did you change IAC - if so did you clean any air bypass ports?
yes on all.. cleaned out the ports when I changed it
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post #14 of 23 Old 05-25-2020, 07:31 PM
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trying to help, those were my 1st thoughts

Fuel pump all you said was replaced - is it NEW IDK is it good IDK.
Fuel pressure test and leak down you did not mention either. good leaves a bit of guessing.
replaced IAC did not have me thinking clean IAC air bleeds.

Are you loosing coolant?
you did not say anything about vac leaks,
>> did you try the carb spray vac leak ck - esp when HOT? to easy to dismiss.
When you had the scanner did yu look at ECT and IAT?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #15 of 23 Old 05-25-2020, 10:42 PM Thread Starter
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Quote:
Originally Posted by jtec View Post
trying to help, those were my 1st thoughts

Fuel pump all you said was replaced - is it NEW IDK is it good IDK.
Fuel pressure test and leak down you did not mention either. good leaves a bit of guessing.
replaced IAC did not have me thinking clean IAC air bleeds.

Are you loosing coolant?
you did not say anything about vac leaks,
>> did you try the carb spray vac leak ck - esp when HOT? to easy to dismiss.
When you had the scanner did yu look at ECT and IAT?
no loss of coolant...zero vac leaks...I did the carb spray check....did not get good readings.. will be doing that on Friday...this is an intermittent problem and straitens out when it cools just a little .. I did not mean to be snippy.. I have been dealing with this for a month.. and im at my whits end
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