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Unread 08-22-2013, 11:29 PM   #1
iflypa28
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1988 YJ Wrangler 
 
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Odd pinging problem...

So I noticed this the other day, when I was driving with my top on and was actually able to hear something other than wind! It seems my engine is pinging pretty bad but only in very specific circumstances. The engine must be completely warmed up to temp, at HWY speeds (above 50mph, so 4th or 5th gear), and only at mid throttle. It seems that under really light or full throttle it doesn't do it (of course its still loud as crap and hard to tell).

This is what I do know:
Timing is set right at 9*BTDC
Both vacuum and mechanical advances are working as specified in the FSM.
So I don't think its a timing issue.
New plugs, wires, cap, rotor.
Choke is working properly
Vacuum powered air intake doors are functioning correctly (i just fixed them)
stock carb that otherwise runs great!
Stepper motors appear to be functioning as far as I can tell.

Any idea what would cause this problem or how to diagnose it from here??? I have no problems under any type of acceleration (light, moderate, or heavy) from slower speeds in any gear or RPM, I find this really odd! I may be trying the nutter bypass in the next few days when I get some time, don't know if this will help or hurt.

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Unread 08-23-2013, 12:05 AM   #2
Luuca
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Quote:
Originally Posted by iflypa28
So I noticed this the other day, when I was driving with my top on and was actually able to hear something other than wind! It seems my engine is pinging pretty bad but only in very specific circumstances. The engine must be completely warmed up to temp, at HWY speeds (above 50mph, so 4th or 5th gear), and only at mid throttle. It seems that under really light or full throttle it doesn't do it (of course its still loud as crap and hard to tell).

This is what I do know:
Timing is set right at 9*BTDC
Both vacuum and mechanical advances are working as specified in the FSM.
So I don't think its a timing issue.
New plugs, wires, cap, rotor.
Choke is working properly
Vacuum powered air intake doors are functioning correctly (i just fixed them)
stock carb that otherwise runs great!
Stepper motors appear to be functioning as far as I can tell.

Any idea what would cause this problem or how to diagnose it from here??? I have no problems under any type of acceleration (light, moderate, or heavy) from slower speeds in any gear or RPM, I find this really odd! I may be trying the nutter bypass in the next few days when I get some time, don't know if this will help or hurt.
I have no answer for you, but that's about the best written post/question on here I've ever seen. Not only did you explain the issue, you have situations and events leading to it AND what you have checked and fixed. Thank you!

Posted via my pretentious iPhone.
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Unread 08-23-2013, 12:29 AM   #3
iflypa28
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Haha...I hear ya! Thanks
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Unread 08-23-2013, 05:24 AM   #4
Old4X
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Two things to try/

First, turn the vac advance adjustment out 2 turns and see if it still does it.\

Or:

Run the fuel out and fill up with ethanol free fuel and try again.
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Unread 08-23-2013, 10:13 AM   #5
Luuca
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Quote:
Originally Posted by Old4X View Post
Two things to try/

First, turn the vac advance adjustment out 2 turns and see if it still does it.\

Or:

Run the fuel out and fill up with ethanol free fuel and try again.
I was going to suggest a octane boost fuel additive, but I know nothing. Just know that's what the bottle claims to solve.
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05 LJ Rubi "Ghost" 4.0L Auto NV241 Rock-Trac D44/44 lockers, 4" Currie Lift, 1" BL, 33s, hardtop
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Unread 08-23-2013, 11:15 AM   #6
EABiker
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Quote:
Originally Posted by Old4X View Post
Two things to try/

First, turn the vac advance adjustment out 2 turns and see if it still does it.\

Or:

Run the fuel out and fill up with ethanol free fuel and try again.
X2 on taking out a bit of vacuum advance. It sounds as if your engine is running at just just about it's perfect air/fuel ratio since it does not ping under other conditions.
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Unread 08-23-2013, 09:18 PM   #7
iflypa28
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Quote:
First, turn the vac advance adjustment out 2 turns and see if it still does it.\

Or:

Run the fuel out and fill up with ethanol free fuel and try again.
I had no idea you could adjust the vacuum advance! Where is the adjustment? You can't buy ethanol free fuel anywhere around here that I have found unfortunately or I would have been using it a long time ago!
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Unread 08-23-2013, 09:25 PM   #8
iflypa28
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Quote:
X2 on taking out a bit of vacuum advance. It sounds as if your engine is running at just just about it's perfect air/fuel ratio since it does not ping under other conditions.
I think you are right about this...I did a bunch of work to it when I bought it and it went from an average of 12.3 mpg to 16.5mpg. I was actually concerned it was running too lean but im not sure how that can happen unless the ECM is shot. I am currently mid-nutter bypass so we will see what happens after that!
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Unread 08-24-2013, 06:50 AM   #9
Old4X
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Quote:
Originally Posted by iflypa28 View Post
I had no idea you could adjust the vacuum advance! Where is the adjustment? You can't buy ethanol free fuel anywhere around here that I have found unfortunately or I would have been using it a long time ago!
Remove vac line from advance unit on dizzy.

Stick an 1/8 inch allen wrehch into the snout and turn the screw.

I usually turn it in all the way first counting the turns so I know where I started. 8 or 9 turns out is normal factory setting.

Methonol laced gasoline burns leaner than real gas (stoic is different) and is likely what is causing your detonation. Delaying the advance should help.
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Unread 08-24-2013, 07:17 AM   #10
iflypa28
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Great thanks! I never would have found that by just looking at it. Ill give it a try, I bet it will work too.

I wish I could find real gas around here I'm sure that would help a lot. Every time I go to Tennessee to visit my dad there is a station there that sells it, so I fill up. That was with my Grand Cherokee though, it actually improves my mpg considerably on the trip home.
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Unread 08-24-2013, 07:46 AM   #11
Old4X
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The boat marinas near you should sell it. Down near Sharron Harris, Jordan Lake, and whatever that lake is called up 85 from Durham. Kerr Lake?
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Unread 08-24-2013, 08:40 AM   #12
iflypa28
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That's a good point, I didn't think of that.
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