RAT454

I've installed the LT1/tranny/computer/wiring harness etc from a donor
95 roadmaster into a 75 Monte Carlo. Used the factory 3 book service
manual with updates to do the wiring. Runs drive great.

However, when I hook up the switched 12 volt wire to the "F" terminal of the
alternator to energize the alternator, the engine loads up, stumbles
and dies. I tried going direct to the battery, still the same. The
alternator is new, and was re checked, I pulled the one off the wife's
95 roadmaster, and it does the same thing. The new alternator works
fine on her car....I went back through the wiring again to make sure I
didn't miss anything...I'm not blowing a check engine light or a
security light. When it stumbles and starts to die, the fuel pump is still
working and I have 45 psi at the manifold so I don't think the VATS is
screwing up. With the engine on and the f terminal disconnected I have
12.4 volts....when I hook up the f terminal and run the motor up, I
get about 14.6 volts. I have no other driveability or operability
problems. I flat runs great. shifts great, lock up works, temps and pressures are good. Fries the tires with the 3.55 posi. We reworked the opti spark when it was out. New plugs, Wires. The donor roadmaster was ours and it ran great.
I ran it up to the school shop yesterday. Plugged in an analyzer. They got no codes...we cleared the memory and still the same...
>
Any Ideas?

> Thanks
>
> Greg Johnson
> Las Cruces, New Mexico

briand069

Hi,
I don't think you need to use the "F" terminal on this alternator. Try looking at this link http://novaresource.org/alternator.htm and see if this wiring helps.

Brian

RAT454

Thanks for the reply, an interesting site....

It's actualy connected to the I terminal not the F terminal We have a 300ohm resistor (simulating the idiot light) in series with the L terminal and the I teminal is factory connected to the underhood fuse box to the secondary cooling fan fuse...we disconnected this wire and installed a new gm delco alt. still the same problem..and no codes.. we think it has something to do with the increase in voltage (12.8 disconnected to 14.8 connected) applied to the system when the alt kicks in. I picked up another roadmaster last week, also a 95 so this weekend we are going to start swapping parts and see if we can't find something amiss...


Greg

Live for TAs

Sounds similar to the situation I had with my LT1 Datsun. I found out (the hard way) that the small (sensing) wire from the alt goes to the idiot lamp. There are no other small wires to hook up on the LT1 style alternator (CS144 model). I had wired mine to a fuse that was hot with ignition on and got no charge and apparently damaged the alternator. I added a 470 ohm resistor in the line to simulate the idiot lamp and it still does not charge. I'm going to either rebuild or replace it and see if it is OK now.

RAT454

I also installed a resistor in series to simulate the light, I installed another new altenator and still having the same problem. I've been kinda tied up with school and cranking out a few engine rebuilds and haven't gotten a chance to get back to it in a month or so. One thing that we did do was hook the battery up to a variable power supply. with the alt harness disconnected the engine ran fine on battery voltage, however when we increased the applid voltage above 13 volts, the engine started missing, and stumbling. My plan is to trace back all wiring again and vertify the voltage required in in curcuit. I'm studing the curcuits and I'm thinking I may have a low voltage line hooked up somhow to a 12 volt supply. the kicker is I've done these swaps with no problems before.

I'm also considering sending the computer off and having it checked/ reprogrammed..I may have screwed something up in it....

Just haven't been able to set aside any time to work on it lately..

thanks for the reply

g

kingslam

Hey you need to use a 480 ohm resistor to a voltmeter to the I terminal, that is the intergal voltage regulator signal to turn on the alternator, look in your diagram of the instrument cluster and you will see the 480 ohm resistor on the circuit panel. I swap LT1's into different cars too......at my shop

LT4orbust

I KNOW, this is an old thread, just a little FYI not to be overlooked. Make sure the positive battery terminal crimp is good, on my 97 TA it has a 3 cable crimp, I tested for voltage drop and it shows less than a tenth of a volt on one side of the crimp and over half a volt on the other( the half that has the alt feed has over half volt).
I tested for v drop a week ago, it tested good (only because I didn't check at more than one point at the crimp), so... before you replace the voltage regulator, diode pack, and battery, make sure all the crimps are good. After running for about 10 minutes my volt gauge would slowly go into the red zone, voltage would go to approx. 11.5 volts.
Feel the crimps for warm spots, a bad crimp will heat up. I've been doing this too long for a problem like this to get by me, idk ....getting old.