jeep pcm bypass for "real" alternator

thnx i'll try this and see if i can get a little closer to fixing the problem finding an open circuit would be nice

I think the deal is to install one of those "one wire" alternators and live with the Check Engine light. Seems the regulator is built into the PCM on that model(same one I have). I got lucky and it was just the brushes on mine.

-- Old Crow "Yol Bolsun!" '82 FLTC-P "Miss Pearl" '74 XLH chopper(gone but not forgotten) BS#133, SENS, TOMKAT, MAMBM

Jeeps are very known for bad grounds. They get real sneaky ones too like the alternator bracket is no longer grounding to the engine block type of sneaky ones.

I look for these by walking a multimeter looking for the voltage drop.

I start with the engine running and headlights and heater fan on for circuit draw and get a volt reading at the battery 'posts'. I then leave the meter on the battery positive post and put the negative on the alternator case. I should have almost the exact voltage.

I would suspect on yours I would find a difference so I take the negative meter probe and put it on the cable clamp at the battery post, then on the cable, then on the engine block, then on the alternator bracket, then on the alternator case, then on the body of the vehicle. If I find a voltage drop at any of these points, I have found a bad connection.

I also walk the positive meter probe along leaving the negative on the battery post. Same thing, from the post to the clamp then the cable then the cable's other end, then the bolt it is on.

If I was to swap a real alternator in, I would go for the AC Delco one the CJ and GM uses. They are everywhere and easy to get parts for. It is a 'one wire' setup but runs best with 2 wires coming to it, one to the battery and one key switched trigger to turn it on.

I have no experience wiring the others but would figure the main output from your alternator would just feed the regulator. The regulator would need to be wired properly, but a schematic for it should outline it or knowledge of the old Ram.

You might run into trouble with emissions though.... That check engine light has to work and it will likely be left on with the alternate alternator.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > hey, ive got a 95 wrangler with a charging problem. i swapped out the

ok heres the deal.. im getting a high field coil voltage (around 11) all the time.. lights, wipers and heater blower on or off makes no difference.. but charging voltage is always low. so that points me back toward the alternator, only problem is I had the alt. tested at autozone before i installed it.. so now im stuck again.. i guess ill take the alt. back off and have them test it again... if it comes back fine what would be my next logical step to getting this thing running? thnx again for the help j

You are under the impression 11 Volts is 'high'?????

Did you check the ground paths like mentioned earlier?

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 (More Off Road album links at bottom of the view page)

yeah the site

says that"Check to see if the regulator is functioning by starting the engineand turning all accessories off. The voltage across the alternatorfield coil terminals (two small terminals, below the positive outputterminal) should be less than about 5V (roughly). Turn allaccessories on (headlights, brights, fan, rear defrost, radio, etc.)and measure the field coil voltage again. It should be above about10V (roughly)."

so i took the alt back up the autozone and had it tested (again) it passed (again) but the guy said something about the machine doesnt test the amps the alt is putting out. (which i didnt know) so it could pass and still be bad. i thought if it passed then it was good !?!?! so i guess ive got a lot to learn. looks like im in the market for a new alternator.. at least its probably not the pcm.. i dont get paid for about a week but ill bump this when i get the new alt on.. wish me luck! and thanks for the help so far..

Bill, i checked those connections with the meter and they look good. thanks j

6 months back I had the same thing going on with my BMW. Alternator tested good (at Autozone, no less) but battery would not charge. Replaced the brushes and it worked great. Did the same thing in my '95 Dodge van a month or so later. For the van it cost me $2 and about an hour. If you are at all handy with this sort of thing or if there is an shop around that would replace them I would look that way before I dished the cash for a new alt.

Matt

Ok, I will try just once more then I will leave you be....

I suspect a bad ground path giving your symptoms just because I have seen it soo many times before including my own Jeeps.

You have positive cables to the alternator which appear to work, but it also needs a ground path to complete the circuit.

I would recommend you run a battery booster cable from the battery negative to the alternator 'case' to see what happens to the charging voltage as measured at the battery posts with a meter.

I then would recommend you run this same booster cable to a clean bolt on the body of the vehicle and check the charging rate with a meter at the battery posts.

If the charging doesn't change, then your grounds are likely ok.

Mike

i had a problem posting yesterday.. i posted a reply but it didnt go through.. and when i re-replied i forgot to mention that i did what you said.. the volts across the batt terminals and then move the negative lead of my meter to the alt case.. i got the same volts as across the batt terminals.. so if im getting the same volts from the alt case and positive battery terminal that im getting from the both battery terminals the batt terminals, the ground would most likely be good right? but ill try the booster cable thing.. ill take any help i can get and try anything free. lol j

where is everyone getting the brushes?? everywhere i call doesn't have them.

The other spot would be the body to see if the volts are there too.

Mike

where is everyone getting the brushes?? everywhere i call doesn't

I get them at a local alt/starter rebuild shop. You should find one close to you in the phone book, I would expect. Auto parts stores don't usually deal with them, they like to sell whole parts.

Matt

oh ho, I see.. those autozone cheaters! TO THE PHONE BOOK!!

it was the brushes after all.. go figure.. thanks everyone. j