84 Laser Turbo - dead logic module?

[Neat Hedgehog]

I was having an issue with a code 24 (TPS) with two TPS that checked out good. It would stall when the "power limited" lamp was on, and idle at 3k when it started without the lamp on. Only code I had was 24, consistently.

Now it's doing something completely different. The lamp is on constantly, it idles and drives ok enough to be reliable, but won't flash trouble codes anymore. I can switch the ignition on and off like always, but the lamp just stays on solid now, no flashes at all. Never seen this before. Is my computer basically dying on me, or having a stroke? I have disconnected the battery to clear things, and it made no difference.

[ScottD]

I would check the logic module plugs and make sure there is no moisture in there. Maybe clean with electrical contact cleaner. If it is dry and the contact cleaner has no effect, then I would say the logic module has died. I had a problem on my GLHS where it was in limp mode and wouldn't rev. It wouldn't return trouble codes either. I put another LM in and the problem went away.

[Neat Hedgehog]

I have the glovebox out so I can play with the LM. It was covered in sand, and probably full of it, too. I can clean up the plugs, but I'm not hopeful. I have been chasing tuning gremlins since I bought the thing, and have always suspected the LM of having mental issues. I have wanted a performance ECU for a while, but i have never been able to find a reliable listing for a performance module for an 84. 85's and up, sure, they're like popcorn.

[ScottD]

The electronics on the 84 are different than all the other years. You could always put a grainger valve on and manually turn up the boost, though I think the boost limit in the LM is lower for an 84. On the later stuff over boost cut out is 14.7psi.

[85boostbox]

Contact warren stramer. He was selling one a year or so ago and from his thread looks like he might not have sold his. PM him to find out if he still has it laying around.

[Neat Hedgehog]

The electronics on the 84 are different than all the other years. You could always put a grainger valve on and manually turn up the boost, though I think the boost limit in the LM is lower for an 84. On the later stuff over boost cut out is 14.7psi.

Yeah, the boost limit is a straight 7 on the 84's, with no overboost. 85's had a computer controlled gate and could overboost to 9 psi. If I ever get her tuned up enough to play with the boost, it's going to have to be with tricks like that.

Hmm.. I'll check out that lead. Thanks, 85boostbox.

I could pick up a regular computer, I guess, but if I'm going to the trouble of it, I may as well make it an upgrade, however minor it may be.

[mpgmike]

I have the glovebox out so I can play with the LM. It was covered in sand, and probably full of it, too.
Was this a flood recovery vehicle?!? How did sand get there?

Mike

[Neat Hedgehog]

The previous owner did a cobble-job sandblast on her to repaint the body, but didn't remove or even properly cover most or any electronics. The gauges are full of sand, as were the vents.

[Neat Hedgehog]

Well, I managed to straighten the computer out for now by cleaning up the connectors. It's still rusty and rough looking, I don't trust it to last too much longer. The circuit board was sandy, and there's a little corrosion.

I have an '84 Performance ECU that I grabbed from FWD that's in way better shape. I'm assuming I can't just plug-and-play, and that some adjustments will be needed (timing, and such). Any good guides or suggestions so I'm not playing it completely by ear?

[Xtrempickup]

the 84 mopar performance logic module is good for more boost when installed with a grainger valve (manual boost controller). its plug and play. the 84 has a more agressive spark curve than the new 85 then 86 Turbo1, but the block uses 10mm head bolts to mate the head to it. the 84 is stronger than a 86 tho as it has the better rods i read some place. 7psi is stock boost, i had mine wired shut as the wastegate actuator is a 2 nipple one, different than 85 and later. i ran over 7psi no problem, but overboost causes it to jerk a little.

[Neat Hedgehog]

Ok, that's good to know.

Yeah, the 84 was overbuilt, probably because it was the first year with the turbo. The rods were heavier than later T1's that had them lightened up to match expected performance; less mod friendly.

I might wait on the grainger until I get my new exhaust with my tax return. I'd feel silly bothering with overboost until I ditch the crappy stock pipes and cat; poor thing is suffocating as it is. Haha