1995 Estate Wagon - Cold Start Help - Service Engine Soon Light

[91olds98]

Hey all - need a little help on this one.

Car:
1995 Buick Roadmaster Estate Wagon - 5.7L LT1.

Few days ago my engine started surging occasionally. "Service Engine Soon" light came on but car still ran ok. Shut it off and started back up several times. Parked it overnight (in sub-zero weather) and the next morning it wouldn't start. Would turn over, just wouldn't fire. Engine light was still on.

Started pulling sensors one at a time: pulled MAF, Temp, CPS, Knock... got to MAP sensor, pulled the connection, engine started right up. Engine light was still on. Replaced MAP sensor: car ran great for about 30 min - then started surging again, and engine light came back on.

Parked overnight again, and next morning (warmer this time) engine started, but wouldn't rev - when accelerator was pressed, engine just choked and almost died. Pulled MAP sensor plug - engine ran ok again. Engine light still on.

Tried getting ECU trouble codes - jumpered terminals 5-6 to get codes to flash on dash (ODB1) but nothing happened. Also tried jumpering 6-12 - still nothing. Now I cant get any trouble codes at all.

Still runs, but engine light is still on. Cant get the trouble codes. When I insert the jumper into the correct plugs, the check engine light goes off - no diagnostic "12" code, nothing at all.

Any ideas? I could really use some help with this one.
Thanks in advance.

[bennylw]

Hi 91olds98,
regarding the trouble codes I don´t think the shorting of pins work on the -95. I have a 95 RMW and it didn´t show anything on my car either.
About Your real problem, I guess that it works better when You took off the MAP connector just because it goes into some kind of limpmode when it loses a sensor reading. Then it just uses preset tables for ignition, injectors and so on.
Have You checked for vacuum leaks? From what I´ve read on most forums, it´s a common problem when leaks tricks the PCM to wrong settings.

Another part that gives these problems more than not is the Optispark (it gets moist and just stop working), I had startproblems intermittently and when I cleaned and sealed the opti it worked like a charm. Many would say "buy new, maybe MSD replacement", but I´m on a budget so I just fixed the original Opti. Google for LT1 + optispark and You get plenty to read. impalaSSforum is a good place to be when You have an LT1

If You´re into electronics, or have a friend that is, i recommend that you fix a ODB <-> computer cable and download some freeware to get the error codes read. I haven´t got the links on this computer but I´ll put some links to software and hardware for OBDI LT1:s in another thread when I get to the other one.
I just got my AutoXray EZ-SCAN 6000 which is a great help but maybe a bit costly for just checking trouble codes.

Just some ideas to get other, better than me, guys to post