MPI installed...Electrical Issues - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 02-08-2004, 09:53 AM
Xburn3
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MPI installed...Electrical Issues

Hey Jeepers, I finally got the MPI kit installed, she starts up nice, sort of, and runs ok. The thing thats bothering me is when I turn the headlights on, the gauge checking the charge and oil pressure drops. When I turn the lights off again, they jump back up. Any ideas what it could be. Obivously I took a big chuck of wiring out installing it but I dont think I touched anything that affects the lighting, seems to run on a different set of wires coming from the fuse block.

Also I understand I dont need the old ignition module, so I should be able to just cut those wires and take it out right? Was mounted behind the Drivers side fender.

And theres also wires from the ignition coil and old distributor plug I shouldnt need either I think.

Just dont want to cut something I will need later. Ill dig around and see if I can find anything, but I figured I would ask and see if anyone knew. Thanks
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post #2 of (permalink) Old 02-08-2004, 10:09 AM
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Re: MPI installed...Electrical Issues

Yes, you can remove those wires. In fact, you can remove the computer that is in the cab..it's just above the heater duct.

As for your eleictrical problem...make sure you have a good ground. This is a good reason to have a good volt meter. Measure the voltage between the negative terminal of your battery and the body. You should have almost no voltage difference. Anything more than .2-.3 volts is an indication of a bad ground. Check the braided straps that go from the engine to the body and from the negative battery terminal to the body.

Plase let us know what you find out.
post #3 of (permalink) Old 02-08-2004, 01:14 PM
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Re: MPI installed...Electrical Issues

yes I already have removed the old CPU, and cut a bunch of the wires off from the old emission controls.

Ive been diggin around all morning and I dont really have any improvements, I am wondering if it had something to do with the diode you have to install on the alternator wire. Not sure. One of the braided wires was off, the one that mounts to the rear of the engine. But i put it back on with no change. I dont see any braided strap from the battery to the engine though.

While I am here I should ask this:

Where is this plug supposed to connect to, its the first plug from the harness, but there is no mention in the instructions from the kit, and no where for it to connect to.



And what am I supposed to connect here, I am thinking it it the red vaccum switch from the 4WD, maybe someone knows.

Other than that, no luck on elertical...Ill keep tryin
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post #4 of (permalink) Old 02-08-2004, 03:44 PM
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Re: MPI installed...Electrical Issues

I'm pretty sure the disconnected plug in the first photo orignally went to the PCV cutoff valve...something that never worked right on the 258 and was even recalled on later models. The valve shutoff the vacuum to the PCV valve when the key was turned off primarily to prevent dieseling. You should be fine just leaving it disconnected.
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post #5 of (permalink) Old 02-08-2004, 04:08 PM
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Re: MPI installed...Electrical Issues

well that plug is from the MPI wiring harness that came with the kit, why would they put that on a fuel injected setup?

I am still at a loss as to the electrical problem. About 20 minutes ago she wouldnt even start up, no juice even to the starter, then a second ago she started up no problems. Something is definitely wrong, and I suck at electrical...
post #6 of (permalink) Old 02-08-2004, 04:58 PM
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Re: MPI installed...Electrical Issues

well I just drove it around again. I tried turning on different things to see how they affected the charge, and it seems to be the accessories. My radio has no effect on it at all, I am assuming because I have it directly charged from the battery and ground to a location on the tub, so I would assume the groundings on the tubs are fine. But the heater and the headlights drain it for some reason, I dont get, and I dont know why it wouldnt start before, Im baffled...
post #7 of (permalink) Old 02-08-2004, 05:47 PM
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Re: MPI installed...Electrical Issues

</font><blockquote><font class="small">In reply to:</font><hr />
But the heater and the headlights drain it for some reason, I don't get, and I dint know why it wouldn't start before, I'm baffled...

[/ QUOTE ]1. OK something changed...
2. Don't just check the grounds,
3. Refurbish them.
4. The items you are telling us about,
5. Are the highest current drains,
6. That the electrical systems supplies...
7. The grounds are the single points of faiure...
8. A Fuel Injection System won't run reliably,
9. When the voltage drops below about 10.7 volts...
10. If that threshold is breeched,
11. Lots of bad ju-ju is gonna happen.
12. So, now do a few things: [*]Replace the battery cables (positive and negative)[*]Make sure the battery post/clamps are burnished.[*]Replace the frame to engine block braid/cable[*]Replace the frame to tub wire/braid[*]Run BIG, separate grounds to the Lights and the heater motor.
13. These fixes don't cost much,
14. And the benefits are wonderful.
15. Then you know what's not broke,
16. That's often as valuable as knowing what is broke.
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post #8 of (permalink) Old 02-08-2004, 07:16 PM
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Re: MPI installed...Electrical Issues

where are the braids located, I know of one behind the engine.
post #9 of (permalink) Old 02-08-2004, 07:38 PM
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Re: MPI installed...Electrical Issues

and I suppose the general consensus is that its a bad ground...
post #10 of (permalink) Old 02-08-2004, 09:23 PM
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Re: MPI installed...Electrical Issues

I believe that the block/frame braided cable is bolted on around one of the motor mounts. -- Mike
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