LSx Alternator and 4L60E Problems

[78bronzechariot]

I just got my 4.8 Vortec (LSx)/4l60e running on Thursday. It has been running well, but the shift points seemed close together. I took it on its first long trip (two hours) one way today. When I got back home and was parking the truck, I had it in reverse and idleing for a few minutes while I was talking to my fiance. Then the check engine light came on. I plugged my code reader into it and it said P1810 TFP MANUAL VALVE POSITION SWITCH - CIRCUIT MALFUNCTION. I have done some looking and it sounds like the computer can't tell what range the mechanical selector is in. Has anyone had any problems with this, and what the fix is?

As for the alternator problem, When I go into wide open throttle either accelerating or to force a downshift to pass, my voltage gauge drops down to 11.5 and the headlights dim. I drive a mile or two and it comes back to 13.8. Is the alternator about to give up or is there something I don't know about like a cutoff at a certain RPM? I had it tested at the parts store and naturally it didn't do it then and tested good. Any other thoughts on the matter?

[dwcsr]

Not sure about the first question but the Alt question sound like a slipping belt or pulley.

[78bronzechariot]

Its got a new belt idler and tensioner, and i don't hear it squeal. I will double check in the morning though, maybe I got the wrong size belt. Still concerned about the trans problem

[dwcsr]

go over to LS1tech.com or LS1truck.com and ask. I remember seeing something about a bogus check engine light after the swap and a way to make it go away. It may not be the same but some one over there should have an answer

[Ackattack]

yeah, check out LS1tech.com

both problems seem oddball to me

[Hart_Rod]

+1

[eagleuh1]

What did you use for your fuse and relay center for the engine harness. If you used the fuse center for the donor truck with the 4.8, it's possible the tranny isn't getting power. It's power came from the in cab fuse center. Ask me how I know this? Mines a 2005 5.3, and I used the under hood fuse and relay center from the donor truck. The fix can be to run a jumper to power the tranny circuit, like I did. Good luck with your problem and let us know what it was and the fix.

[78bronzechariot]

Okay, alternator problem solved: New alternator. I haven't gotten any response off of LS1tech.com yet, but I did some reading. It is possible that the alternator cutting in and out can cause enough voltage fluctuations to set codes that are irrelevant. I put a new alternator on it and drove it 90 more miles. Hasn't set a code and the trans seems to shift fine except the points are still early for my liking, but I think that is a function of my tune more than a real problem. I got my harness and computer from ChevyThunder.com and it has its own set of eight fuses (I'm honestly not sure what each one does). But now that you mention it, I think I will go outside and just make sure they are all good.

On a side note, I didn't realize that the Hot Rod power tour was coming through Effingham, IL today (about 45 miles from my house, and where I took my test drive to today). I got caught in the middle of hundreds of old cars and trucks cruising on their way to Du Quoin, IL. I did happen to see a light blue 67-72 truck but it was a few cars ahead of me and I couldn't determine the year (well I know it wasn't a 67 since it had side markers).

I've also attached some pics of my truck and engine.

[78bronzechariot]

All the fuses seem to check out fine, but I hooked up the scanner for grins and it says P1810 pending so there is probably still a problem with it. eagleuh1 do you know which pin on the trans connector is the power feed to the trans so I can check it?

[78bronzechariot]

Well stupid me, I'm pretty sure I found the problem now. I pulled the plug to check for power, and since my truck is so low, I just pulled it back up under the hood so I could see it. Turns out there was a wire rubbed through the insulation. I think it was contacting the pinch weld between the floor and firewall panels. I shrink wrapped it, then I stuck a piece of rubber tubing over it to protect it and plugged it back in. Took it around the block and the shift points have improved, especially the 3-4-lockup shifts. I hope this solves my problem. I will keep you guys posted.

[D-Rat]

Nice truck BTW.

[78bronzechariot]

Thanks, I did everything myself except modify the headers!