Missing issue. Runs good until the headlights are turned on.

[TJH88]

I bought an 86 the beginning of the year. I had a used one from 87-91 and have been out of the business since. This 86 is in pretty decent shape but hasn't been drove much since 05. Ran like a champ with new plugs, wires and all the easy goodies. It had an aftermarket radio hardwired in. I replaced the radio with a new aftermarket, replaced the stock plug and used the wiring adapter that came with the radio. I developed a miss that lasted about 3 months and a couple of thousand dollars. I wanted to send my digital dash to Casper to have the flashing 85 mph removed and all the new stuff they do. I took the dash apart and sent it in and started digging on the wiring. I cleaned up a lot of connections, but never actually found anything I could determine was a problem. My cluster comes back, get it installed and the car runs perfect. I decide to drive it to work a couple of days and misses out all the way to work with the lights on and is fine on the way home with them off. My voltage is good and I can't pinpoint any reading that look out of place. Just a shot in the dark here, does anyone have a good place to start? I'll find the problem I'm sure but thought maybe someone had some experience. I appreciate any help.

Just for a side note, I'll be heading to BG on Saturday. I traveled down last year and everything was pretty much rained out. Bummer. I hope for better weather this year. I'm not showing or racing but looking forward to seeing some cars, parts and racing.

Tim

 

[mikestertwo]

Never heard of that one before but I would start by checking all your grounds. Do you have a good ground from the negative battery terminal to the body? All the grounds good on the back of the right head?

 

[TJH88]

I've worked on the ground from the head to the firewall. I'll double check the negative battery terminal to body. I've checked it before but early on.
I found during a search on here last night a thread from way back when that had a similar issue. Can't find it again to save my life. I don't believe there was much resolution in it but wanted to read it again. That's the only other I've seen.
Thanks!

 

[mikestertwo]

All the computer grounds good on the back of the right head?

 

[Chuck Leeper]

What does "voltage is good" mean?
Koeo, batt reads?
Engine running, no lights?
Koeo, lights on?
Any data logs?
Volt drop tests run?

 

[TJH88]

Yes, I've cleaned and tightened the grounds on the back of the right head. Good voltage, I'll run some numbers but they are 13.0-13.7. I'll log it and make sure nothing drops below that number but have been watching and haven't seen anything lower than the 13.0. I'll try to work on that tonight. Also, Koeo, key on engine on? Trying hard not to be an idiot but want to make sure I'm thinking right.
Thanks again,
Tim

 

[TJH88]

I ran it around the block, about 4 miles, and logged from idle to full boost, marked the data file, turned the headlights on and ran from idle to full boost, then turned the lights on bright. Of course it didn't miss like normal but my voltage was no lower than 13.1 with no headlights and with headlights and I saw 3 blocks that had 12.9 with the brights. I will add, probably pretty important info that I failed to mention, that two different days going to work with the headlights on the headlights and dash lights went completely out. About 2-3 seconds and they were back on. Only had this happen twice. The radio stayed on. That's the latest info. Feel free to offer suggestions and questions.
Thanks,
Tim

 

[TexasT]

I'd be looking for a corroded connection somewhere in the line, and could be a bad cable, ground or power can get corroded under the insulation and not be seen. Or the Alternator needs replaced as I could be a little long in the tooth and just not keeping up with the electrical needs of the ignition, stereo, and the lights. You did say it sat a long time and corrosion doesn't wait, it just corrodes.

 

[michael evans]

I would look at the 8-gauge wire form the alternator to the battery or the alternator itself.

I would take the alternator off and have it tested.

 

[salvageV6]

Start by checking the positive (and negative) battery terminals on the battery for any corrosion and tightness, and all the fat +12 wires and fusible links on the starter.

 

[KC87]

Would be funny if it were the battery and running down the road the jarring was shorting it out internally.

 

[michael evans]

Could be that the battery is bad. The extra load of the headlights on might be to much.

Good news is that it can be tested with it still in the car.

 

[~JM~]

A battery load test is not a bad idea.

I've had at least 3 "new" batteries fail on me in less than 10 years.

 

[mikestertwo]

Does your car have Twilight Sentinel?

 

[TJH88]

New battery about 2 months ago. I cleaned the connections, battery cables, really good at that time. I'll check the other ends of the cables at that time. I'll test it to be sure it's good. I bought a good one. Yes, I do have the Twilight Sentinel. I've had the switch off and have just been using the headlight switch off and on. What are you thinking with it?

 

[Chuck Leeper]

Also, Koeo, key on engine on?

Key on, engine off.

 

[mikestertwo]

Yes, I do have the Twilight Sentinel. I've had the switch off and have just been using the headlight switch off and on. What are you thinking with it?

Disconnect the Twilight Sentinel module and see if you still have the problem. It's located behind the dash between the radio and the glove box I think.

 

[TJH88]

Key on, engine off.

Gotcha. Thanks.


I'll look into the twilight next week. I'm heading to Rose Hulman Friday and Notre Dame Saturday and Sunday to visit my boys. I should have an evening or two next week to dedicate. I'll keep everyone informed.
Thanks

 

[TJH88]

Well I'm finally getting back to giving this some attention. Since the last post, I've cleaned up all the grounds that I can find, I've yanked the alarm system and unhooked the twilight box. In the process of all this I found the negative battery terminal bolt was stripped and wouldn't tighten. I replace the bolt and was hoping for the best. I ran it around the block and it fell on it's face completely. I did get a low maf reading on the scanmaster. I've tried the tests before tapping with a screwdriver and unplugging it and nothing changed. After this these tests showed the signs of being bad. I've now installed the LT1 MAF with the translator. So far all it good. I've plugged the twilight back in and it's working fine and no problems with the lights. The twilight didn't work when I got the car and I replaced the photo eye to get it going. MAYBE the unplug and plug got a good connection, just a wild guess. As most of my troubleshooting goes, I'm not sure what fixed it but it seems to be fixed. I think I had 2 problems going. I just installed new body bushing and I'm now getting ready to put on new Highway Star seat covers, new carpet and I'm dropping the Astroroof the see what's making the noise in it. I'm a bit nervous about the astroroof project along with putting the new headliner in. I'm trying to be ready for the GS Nationals in BG. I'd sure like to drive it this year! Thanks for all the help. I'll be glad when the search is working again. A lot of knowledge on here.

 

[DR BOOST]

if you had a aftermarket computer that uses a 3 bar map, check to make sure you are not using the factory map power wire. the factory map sensor is only for the gauge and uses a unregulated 5v power that fluctuates when the lights turn on.