85 MP LM bucking and cutting out

[PunKid]

So i recently got a second hand MP LM Stage 1. It was the correct part number for the weirdo 85 electronics that I have in my 85 Omni GLH-T with a MBC (8psi).

I plugged it in and took it for a ride. it seamed to start good, idle great and cruised great. I did a half throttle roll on in 3rd gear and at 3000rpm it just died. Like the ignition was switched off. I could repeat this in almost any gear with moderate load, although the rpm or boost varied. trying a WOT pass in 2nd resulting in bucking and a flash of the check engine light. When I checked the codes I got nothing but code 55. (not even code 12).

I figured it was a bad map sensor, so i swapped in two different ones with the same results. I also noticed that after checking the codes, the light would remain on and almost flicker really quickly instead of cycling back the codes.

This leads me to believe the computer is toast. I put the old computer back in and did both a 2nd and 3rd gear pull to 5500 at 8psi with no problems.

So just looking for a confirmation on my assumption.

[GLHNSLHT2]

doh, guess you should of bought mine

[86seeS]

mines doing the same.... Changed map and tps with no change

[csomni]

whats the # on the lm

[PunKid]

doh, guess you should of bought mine

Ha, well this one was real cheap,now I know why

the case number was P4532335, I think the year it was made was 99.

I looked over the board and it got some whitish residue in some areas that i can't seam to clean up with electronics cleaner.

[dwh4784]

doh, guess you should of bought mine

Indeed...I can vouch for that one. It came out of my old car which ran beautifully.

[zin]

Did you swap MAPS? If not try swapping them, I had a similar problem and that did the trick.

Basically, the map was reading higher than reality, throwing it into over-boost and yet showed no other codes to indicate where the problem was.

Mike

[PunKid]

I did replace the Map with two different sensors from factory computers.

Does anyone know if the Map sensor on the MP computer should be a different part number then the factory one?

[dwh4784]

I didn't change the MAP sensor when I used the MP computer.

[PunKid]

I didn't change the MAP sensor when I used the MP computer.

I guess what I am asking is the MAP sensor part number on the MP computer the same as the factory computer?

[ShelbyTC16v]

MAP is MAP. Just use the MAP your car came with that you know is good. You don't need a special MAP for the MP logic module. BTW, I have 3 different LM's I also posted in your thread when looking for a LM.

[zin]

I had a similar situation where my Map went bad and I was going crazy trying to figure it out because it won't necessarily set a code unless it goes totally dead. I my case it read high and would run into Over Boost while still in vacuum! I tried a number of maps that I had and even bought another LM and a "new" map, which turned out to be a mis-packed TBI unit!

It would have been easy to see if I had received the OTC 4000 I bought off Ebay, but that's just not my kind of luck. In the end, I changed to an external MAP and that fixed it...

I was SO close to "fixing" the problem with a can of gasoline and a match!

Anyway, I will also suggest replacing it with a known to be good map, and check it on a scan tool or a volt/ohm meter to be sure it is reading in the right range. The base voltage is 5V, so at 0" of vacuum it should be about 2.5V or 1/2 it's range and 1.25V at roughly 14" of vacuum, if it reads alot higher, it's likely the culprit.

Best of luck!

Mike

[PunKid]

Yes I did put in my good MAP sensor from my working computer.

I have a friend with a OTC 4000 scan tool so I will hopefully do some test with both the factory computer and then the MP unit.

[ShelbyTC16v]

Make sure there is no moisture in your MAP line too.

[JohnnyIroc]

got the same problem going on but i swiched form 86 s car computer to 87 T2