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XJ Ask the Question Thread
CF Veteran
Join Date: Jul 2010
Location: 802
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Year: 99
Model: Cherokee
Engine: 4.0
Seasoned Member
Join Date: Oct 2012
Location: Minnesota
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Year: 1998
Model: Cherokee
Engine: 4.0 Liter Inline 6
91 octane vs. 87 octane
I posted a few weeks back about having cold start issues. Jeep would stumble and sputter up to a start instead of just starting but, ran and drove fine after that. Long story short, I tracked it down to me running a different fuel. I thought I'd try 91 octane (because it didn't have any ethanol in it) and well after using up all that 91 I filled the Jeep back up with 87 (10% ethanol) and what do you know, back to normal and all is good.
Just thought I'd share that because I had a hard time believing that just a few more octane would do that. I think it maybe has something to do with the 4.0L's relatively low compression ratio and maybe spark plug gap? Any other ideas?
Just thought I'd share that because I had a hard time believing that just a few more octane would do that. I think it maybe has something to do with the 4.0L's relatively low compression ratio and maybe spark plug gap? Any other ideas?
CF Veteran
Join Date: Jul 2010
Location: 802
Posts: 4,930
Likes: 0
Received 3 Likes
on
3 Posts
Year: 99
Model: Cherokee
Engine: 4.0
I posted a few weeks back about having cold start issues. Jeep would stumble and sputter up to a start instead of just starting but, ran and drove fine after that. Long story short, I tracked it down to me running a different fuel. I thought I'd try 91 octane (because it didn't have any ethanol in it) and well after using up all that 91 I filled the Jeep back up with 87 (10% ethanol) and what do you know, back to normal and all is good.
Just thought I'd share that because I had a hard time believing that just a few more octane would do that. I think it maybe has something to do with the 4.0L's relatively low compression ratio and maybe spark plug gap? Any other ideas?
Just thought I'd share that because I had a hard time believing that just a few more octane would do that. I think it maybe has something to do with the 4.0L's relatively low compression ratio and maybe spark plug gap? Any other ideas?
Moderator of Jeeps
Join Date: Jul 2011
Location: Frederick, MD from Cleveland, OH
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Year: 1993 YJ Wrangler
Engine: 4.0 I6
Ask the Question Thread
I feel like I'm overlooking something really simple here.
Theoretically, why can't I jumpstart a jeep by putting the positive lead on the dead vehicle's starter terminal?
Theoretically, why can't I jumpstart a jeep by putting the positive lead on the dead vehicle's starter terminal?
CF Veteran
Join Date: Jul 2010
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Year: 99
Model: Cherokee
Engine: 4.0
Moderator of Jeeps
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Year: 1993 YJ Wrangler
Engine: 4.0 I6
Senior Member
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Year: 1997
Model: Cherokee
Engine: 4.0 Inline 6
How hard is it to install a crankshaft senor and a camshaft senor on an automatic 97 XJ? Dealership robbed me of $240 the just check it and wanted almost $900 to replace them. I just ordered the 2 and waiting to be delivered.
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Year: 99
Model: Cherokee
Engine: 4.0
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Year: 1991
Model: Cherokee
Engine: 1999 4.0L
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Year: 1991
Model: Cherokee
Engine: 1999 4.0L
crank sensor requires about 3' of socket extenders, and some creative thinking
Moderator of Jeeps
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Year: 1993 YJ Wrangler
Engine: 4.0 I6
I'm just trying to understand the fundamental flaw here.
Would it fail to start? If so, why?
Is it a bad idea because it would overtax the alternator?
Would it damage anything?
Moderator of Jeeps
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Year: 1993 YJ Wrangler
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CF Veteran
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Year: 1991
Model: Cherokee
Engine: 1999 4.0L
The main power lead to the starter motor is on a bridged circuit that is closed by the starter solenoid. If you activated the solenoid, then the power from the jumper would pass through the bridge to the battery and provide power that could be used by the other circuits. However the key is still in the OFF position so the RUN circuit would still be inactive. As such the computer could not make the engine run, and thus it would not start
Last edited by ehall; 08-12-2015 at 05:31 PM.