Still having idle drop, and can't think of anything else, please help.

[cuban11182]

So I upgraded the last thing that I thought could be the problem. Yesterday I added a DUI ignition. I haven't changed these things chasing the problem, they would've been changed anyway. In any case I'll try my best to explain.

So when the engine is running, the idle will drop about 100 rpm sporadically. When it does it, my voltage drops and then recovers. I thought initially it was my 3 wire alternator, so I replaced that with a higher output powermaster, but it still did it. To verify that it wasn't the alternator I unplugged all 3 wires (still had the pulley attached), and it still did it with the engine running just on battery.

Someone had suggested that the A/C compressor was kicking in (it was un-wired) and I recently replaced that with a Jeepair compressor (still un-wired).

I had found the EGR broken, so I built a plate, then I replaced the intake manifold with an Offenhauser. The carburetors are both new and they were a MC2150 and now a Holly 390. There aren't any vacuum leaks on the intake.

All vacuum lines are new. There are a Limited few: vacuum advance, PCV and brake booster. PCV rattles and mostly holds air when I blow into it, but I'm going to replace anyway.

The exhaust is still stock. I didn't look to see if there is a ground on the exhaust like there is on newer cars, should there be one?

So I'm running out of ideas on what it could be. I've attacked all the wiring under the hood and it's cleaned up and the duct tape that was used to hold things together has been replaced with electrical tape. I know I have a ground under the dash in the signal cluster since when I turn on my signals my tach responds to the indicator, but I couldn't see that being the issue since I had removed the alternator being the culprit.

If anyone has any ideas, I'd greatly appreciate it. Tell me where to look next.

Here is a video. It happens around the 15-16 second mark.
https://www.youtube.com/watch?v=yVcTYMNhQno

 

[lutry]

Any possibility that you have fluctuation in the fuel pressure
or a clogged fuel filter?

 

[cuban11182]

I pulled the cap thinking I had a vapor lock but it worked. I'll change the filter regardless

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[Fastatv]

Could you have a little water in the fuel? When it drops 100 rpms, does it immediately gain the 100 rpms back....?

 

[cuban11182]

I've filled it up so many times I would think it would've worked it's way out. In any case I'll try some sort of in tank treatment.

It does recover about 2-3 seconds later.

 

[cuban11182]

Ok boys and girls, new PCV, fuel filter (with small nipple at top), and heet added. I know it's still to soon for the heet, but with the other two things, no change.

 

[gutthans]

You stated that you had an idle drop with a corresponding voltage drop??? Suppose it's actually a voltage drop RESULTING in an idle drop?

That would mean the current ceases to flow to the ignition momentarily. I would suspect either a broken wire, malfunctioning relay, or a broken fuse board soldering.

If, when doing all the work, a wire was pulled or flexed, it may have cracked leaving a microscopic gap inside the wire insulation. Heat and/or movement will cause the wire to separate enough to break connection for a microsecond...resulting in a drop in voltage signal. A relay could suffer a similar fate internally, depending on its' construction, so too with the soldering in the fuse panel.

If you can test each ignition related circuit for continuity, that might identify which one is broken...particularly if a helper can wiggle or whack on things during the test. Alternatively, replace your 10/12 volt feed line from the battery to the fuse panel, and the ignition line from the panel to the DUI.

BTW you can also take new wire and run a HOT from the battery to the DUI. Disconnect the normal Bat In line for this. Crank the car and let it run...(you must pull the wire off for the engine to stop, since the ignition key no longer controls the DUI. This would help you identify that it is the wiring circuit that is at fault.

 

[cuban11182]

That makes perfect sense. Going to create a jumper wire now so I can test out the wiring being the problem.

Will report back.

Thanks.

*EDIT*

Just tried it and no dice. It was weird seeing it running after I turned off the key. Reminded me of Forrest Gump "I just felt like running".

**EDIT 2**
Went out and found the positive battery terminal cracked on the wire. Changed that out, and it still does it. Ughhh.

 

[cuban11182]

New video:
http://youtu.be/1oVQSVZx_xA

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[Lumpy Grits]

How old are you spark plug wires?
Same for your dizzy cap and rotor??
Spay the SP wires with soapy water and start it up.
What happens?
LG

 

[cuban11182]

New DUI and wires. Plugs have less than 3k on then.

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[cuban11182]

I just looked at them and saw they are iridium, getting some Copper ones.

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[cuban11182]

It's a circuit breaker, but when I pulled it I checked everything signals, hazards, wipers, low and high beams and they all worked! I looked at the drawings and saw that it was in the seat buzzer location. Since I don't have a seat belt buzzer I'm assuming it was trying to make noise, got frustrated, told me to pack sand and dropped the RPMS!

In any case I ran it for about 5 minutes, two times and it didn't drop!

When I pulled it after running for a few seconds she was hot.

 

[Lumpy Grits]

No CJ ever had a seat buzzer as OEM.
GOOD FIND!
LG

 

[cuban11182]

Thanks, but I can't take credit. Someone on jeepforum.com asked about circuit breakers, so I thought I'd pull it. Just went for about a 30 minute spin, and not a single drop.

 

[lutry]

WOW

 

[cuban11182]

I was told what happens is that the circuit breaker calls for voltage till it pops, then it resets and calls for more. When it resets and calls for more, it loads the engine and makes it drop.

 

[somedude922]

Wow. Talk about needle in a haystack!!!

 

[cuban11182]

Wow. Talk about needle in a haystack!!!

No kidding. Although I've changed many things since I bought the jeep in April, I have been chasing this thing for a bit. Hopefully my pain will lessen someone else's if they have the same problem.

 

[jdcaples]

Impressive sleuthing!

-Jon