: Can bad ECM cause 85 fleetwood brougham ht4100 miss bad, backfire and barely run?



dhuberasu
11-09-10, 09:00 PM
I have changed whole distributor, distributor cap and coil and others...

anyway to diagnose bad ecm? Does ecm control each spark or just advance and retard?

Read where you can disconnect 4wire connection to distributor and will run in bypass? is this correct?

codes are 23 34 52 53....

thanks in advance
david

drewsdeville
11-09-10, 09:10 PM
I'm going to assume codes 23 and 53 are due to you fiddling with the distributor, which is now new.

Code 34 is most likely your concern, MAP signal out of range. This will definitely cause some severe running issues. Make sure the wiring and vacuum line to the MAP sensor are plugged in and in tact. If everythings good, replace the MAP.

dhuberasu
11-09-10, 09:35 PM
made sure all connections good and clear codes......started car....barely will run and backfires rhythmically.....almost like out of time.....very bad.....brand new engine...was fine....all of a sudden current problems....I have checked the mechanical timing and all looks good....should not be mechanical.....after starting since codes were cleared.....no codes shown....

very puzzled
does the ecm control every spark on this model or just retard and advance?

thank you

drewsdeville
11-09-10, 09:39 PM
ECM applies a static spark curve to the base timing that you set traditionally. There's a catch though - in order to correctly set the timing, you have to prohibit the ECM from adjusting the timing while you are setting it. If you did not know this, your timing is way off.

To correctly time the engine, jump pins A and B on the diagnostics (ALDL) connector under the dash. You can do this with a piece of light gauge wire or a paper clip. Then, time the engine by rotating the distributor, using a timing light. When you are done, pull the paper clip or piece of wire from the diagnostics connector.

Are you sure the MAP sensor is good? Where did that code 34 come from that you listed above?

dhuberasu
11-09-10, 09:51 PM
the codes must of been from before the rebuilding....car set up for 15 years....and dont really know history.....

I feel stupid now....did not think this car had the aldl connector....had read about it.....think I have spotted it over the hump....forgive me....but use to race and build cars all of the time.....is the jumping of the pins that critical? I know laugh at me....I hope that is it.....would be great.....about $5000 into this thing.....

thank you very much!
david

drewsdeville
11-09-10, 09:57 PM
Yes it is critical. If you don't, the ECM is adjusting the timing at the same time you are. It's impossible to get the timing correct without doing this.

dhuberasu
11-09-10, 10:02 PM
good gracious....I wont tell you all the parts I have replaced.....lots.....

can the connector's orientation be inverted on the car compared to the manual? It is the 12 pin thing but only top row has contacts....maybe one in bottom.....

thank you again ......can't express enough gratitude on here....

dhuberasu
11-09-10, 10:06 PM
good gracious....I wont tell you all the parts I have replaced.....lots.....

can the connector's orientation be inverted on the car compared to the manual? It is the 12 pin thing but only top row has contacts....maybe one in bottom.....

thank you again ......can't express enough gratitude on here....

drewsdeville
11-09-10, 10:19 PM
I think the pins are labeled on the side of the connector...I can't remember. Grab a flashlight and have a look.

Otherwise, I'm pretty sure the A and B pins are the two upper right pins:

http://www.2carpros.com/trouble_codes/obd1_trouble_codes/img/gm_obd1.jpg

Use the notch on the connector body for orientation as to whether or not you are looking at it upside down or rightside up.