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sailracr 10-14-2013 08:59 PM

Electrical issue
 
Just picked up an 85 CJ7 I6 (all stock and mostly original) that is having an electrical problem. I believe I have two related but separate electrical issues.

Firsts issue, starting, the jeep will crank but not start. I have been able to work around this issue by running a wire directly from the battery to the positive terminal of the coil. Without this wire the jeep won't start. Clearly there us a problem with the start position of the ignition switch. I'm sure I can track this down but for now my starting wire work around is keeping me rolling.

The bigger problem is that the jeep starts to sputter and stall when reaching full throttle. This could be the carburetor but given the other starting electrical issue and the fact that the jeep runs really well at all other speeds I'm inclined to exhaust the electrical possibilities first, unless anyone has a stronger opinion. This issues as more of a struggle because it seems to come into play any time I reach speeds requiring fifth gear (highway speeds). What could cause the jeep to want to cough and sputter at/near full throttle?

Thoughts, ideas, many thanks.
~Jason

LeePrather 10-14-2013 09:39 PM

A) ignition switch replace

B) vacuum leak was causing my similar sputtering under load. Could also be accelerator pump in the carb or your fuel line setup?

FishnWishn 10-14-2013 10:08 PM

Had a stalling sputtering problem under load when my v6 had a gasket leak and antifreeze was going into my # 2 cylinder. it fouled the plug and basically ran 5 cylinders when in 4th or high rpm accelerations.

airjeep 10-14-2013 11:11 PM

Dude, I'm pretty sure you have 2 seperate issues. You have voltage drop at start, you could have a bad battery,a bad coil, a bad starter, or bad wiring... you need to do voltage checks at componets to isolate the voltage drop.. something is dragging the voltage down. The cutting out at high rpm may point to a coil. but b4 you go that far you need to isolate the problem. I can help if U need it,

LumpyGrits 10-15-2013 01:18 AM

Quote:

Originally Posted by airjeep (Post 16846137)
Dude, I'm pretty sure you have 2 seperate issues. You have voltage drop at start, you could have a bad battery,a bad coil, a bad starter, or bad wiring... you need to do voltage checks at componets to isolate the voltage drop.. something is dragging the voltage down. The cutting out at high rpm may point to a coil. but b4 you go that far you need to isolate the problem. I can help if U need it,


Then why can the OP start the eng with a jumper wire?:confused:
This is a classic sign of a bad ign switch.
LG

sailracr 10-15-2013 05:33 AM

Thanks all, what would be the process to isolate a possible voltage drop issue at various components. I checked the voltage at the coil and it's 12 v in Run and 9v at start (I'll verify that again this morning it may be the other way around), but that was in spec as far as I have read. I'm on a road trip at the moment (of course this is when these things happen) so I don't have access to my FSM. Thanks for the help.

shadoow 10-15-2013 06:55 AM

does your jeep have a OEM tach? The power for the run circuit goes thru the OEM tach so if the tach isn't working right the jeep won't stay running when you release the key from START. It's easy to bypass the OEM tach by unplugging the 2 connectors on it and plugging them into each other.

sailracr 10-15-2013 07:16 AM

Yes I have an OEM tach and it's working well. I've just warmed up the jeep and checked the voltage on the O2 sensor and it's fluctuating between nothing 0.5. I can't see the metering pins moving at all. I tried as suggested on another site to throttle up a bit and then close the choke butterfly to force a rich condition after which I should observe the metering pins moving back, but I can't see any movement. It seems the O2 sensor is working but maybe not either the stepping motor or the computer? Any idea how to troubleshoot those?

Matt1981CJ7 10-15-2013 07:31 AM

The O2 sensor should fluctuate between .1 V and .9 volts. See here.

The computer is suppose to move the stepper based on which side of .6 volts the O2 sensor is reading.

If forcing a rich condition by closing the choke had no affect on the stepper location, then either the O2 sensor is bad, the computer is bad, the stepper is bad, or there's a wiring problem.

Good luck,

Matt

texasdave 10-15-2013 09:03 AM

Or all of the above. 28 year old wires and computers, sensors and associated problems make it a joy to work with.

sailracr 10-15-2013 09:13 AM

I've read through the under the hood site diagnostic info and the three major players pages. I'm not seeing any stepper motor movement, I'm always getting less than .5 volts from the O2 sensor, and the diagnostic A0 and B0 are constant 12v while the engine us running (should be fluctuating based on what I gave read). I'm thinking to just replace the O2 sensor as they are cheap but I fear I may have a larger wiring problem based on my new requirement for a jumper wire from the battery to the coil for starting which I'm just not sure how to track down. Sigh, I just want to get back home where I have access to my manual and my tools. Thoughts?

John Strenk 10-15-2013 09:58 AM

Don't forget the engine has to be warmed up first before the pins start to move. THat's based on the temp sensor in the intake manifold. Not the one in the block.

So many things to keep the carb out or the RUN mode.

sailracr 10-15-2013 10:08 AM

I was just reading about that so I'm trying to figure out how to test it. I think because it opens at 65 degrees I can just disconnect it to trick the computer int thinking it's open, correct? Also, I read where the computer should initialize the stepper upon startup by moving the pin in and out. I've had a helper start the jeep and I still can't see any movement at startup. Doesn't that indicate maybe a bad stepping motor or computer? I haven't found yet how to test those components. Any thoughts?

LumpyGrits 10-15-2013 10:24 AM

This site may help.
http://home.sprynet.com/~dale02/list.htm

AGAIN-IF you can start your jeep with a jumper from the battery to the coil.
You do NOT have a voltage drop issue. You have a open circuit/no contact issue. They are NOT the same thing.

The engine's 'sputter'n spit'n issue. Replace the O2 sensor.
When the O2 dies, your fuel mix goes full rich.
LG

jimdubose 10-15-2013 11:09 AM

bad ignition switch and possibly a gas tank full of sludge


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