kingsizetech

I have a 1990 RS 305 TBI,and having a problem with the ses light...while driving around town sometimes ill get a slight surge from the car like its going to die out...and the ses light will come on for less than a min and then go out and then the car will run fine...when I get home to retrieve any codes, is were I have the problems...when I turn the key on "engine off" the ses light will go on for about a second then shut off and not come on anymore...so I cant retrieve any codes using the aldl A&B jumpers...If I wait from 20 min to about a hour ill be able to turn the key on and the ses light will come on for a sec then off for a sec then back on like normal...but when I am able to check for codes all I get is 12 12 12...I would like to find out why it surges and the ses light comes on and try to retrieve a code telling me what the problem is...anyone out there that can help me out.

Billy_Bob

I think you are saying you can not connect a code reader to the car connector and get any sort of reading until 20 minutes has elapsed after you have had it running?

And that if you shut off your car, then turn it to ignition on, the check engine light does not come on (which would be a normal ignition on bulb test)?

If this is the case, it sounds like you have a bad ECM or you are losing power to it.

I would get a factory wiring diagram (in a factory service manual set) and find the wires which provide +12 and ground to the ECM and monitor these with a multimeter to see if you are losing power to the ECM. Also see if there is a separate +12 for ignition on and check that as well.

kingsizetech

well in the past two months I replaced the ecm twice and the car will run fine...and then their will be days when the car will start surging and sometimes the ses light will flicker on and off...but when I try to pull up any codes,all I get is code 12...

Billy_Bob

Well I would start by monitoring the voltage to the ECM.

What you would be looking for is not only loss of power, but an unusually high voltage too. Basically should be 12, 13, 14 volts.

What I would do is connect test wires to the wires powering the ECM, then connect those to a voltmeter and keep that next to me while I drive. Then if the problem occurs, look and see what the voltage is.

kingsizetech

Well a few hours ago I was checking the wiring to the ecm and found a blue wire going to pin #B6... On the wiring diagram it goes to the Pass-Key Decoder Modual,and from there it goes to ECM Fuse 10A.and on diagram is reads "Hot in run,bulb test or start"...Well anyways the wire was previously cut and taped together...I guess it wasent taped together securly,cus when i put everything back together the car wouldnt start...It would crank over but no fuel at the injectors...So I went back and removed the ecm again and found the blue wire to be disconnected...So I connected it with a but splice "which I should of done in the fist place...and the car started right up, Do you think this poor connection at the blue wire could of been the proublem thats been causing the ses light not to function properly...

Billy_Bob

I don't know if that would be the cause of the problem or not???

If it was the cause of the problem, It would have taken me a LONG time to track that down!

Anyway good catch! It is things like this wiring problem which can cause "weird" things to happen with computers.

If you notice any other wiring problems like this, fix them as you did above. I like to make the wiring "look like factory". That is wrapped in electrical tape and that black plastic tubing over it. This protects it from rubbing against a sharp metal object and grounding out.

And as you learned, never twist and tape wires. Cars vibrate a lot and these will come loose. Always crimp connect them so the have a good solid connection.

Otherwise let's just wait and see if that solves the problem. If not, then do the voltage to ECM monitoring thing above.

Let us know if that made the problem go away please.

kingsizetech

Well I drove the car today and on the freeway it started to surge fo about 20sec and if I get on the gas it will stop surging and drive normal...But when I get home to check for any codes the ses light will not function properly,so I cant pull up any codes at all...

Out here in California the temp has been very hot, and with the windows rolled up the temp inside of the car gets extremly hot. so before I get ready to drive the car I'll check the ses light, and it wont function properly "flash for 1sec, then off, then nothing it wont come back on again... But if I pull the car in the garage and let it cool off for about 1hr the ses light will work just fine but the only code I get is 12...

And when the temp is hot in the car and the ses light is not working properly the idle on the car will be around 1700 to 2000rpm in neutral...

One day when I pulled it in the garage from the hot sun, I pulled the ecm to check the wiring and it was very hot so I disconnected it and let it cool off then reconnected it and the ses light worked fine but I only got code 12...

In the evening the car will run fine and the ses light will work properly.I dont know if the hot outside temp is doing something to the ecm or some emissions sensor to the ecm...

I guess I will have to check the power and ground wires to the ecm with a my multi meter...does anybody out there no what pins to the ecm are powers and grounds.

Parts that I've already replaced
ECM "three times already"
IAC valve
Ignition Modual
Sparkplugs and wires
Ignition Coil
Fuel Pump Relay
Fuel Filter
02 Sensor
Coolant Temp Sensor

All these parts were just replaced within a two month period.

JeepYJv8

here is a diagram id check power (when the problem is occuring if possible)




Make sure you use a meter (not a test light) with your key in on position you should be seeing simular voltages as above...good luck

kingsizetech

Well I checked for voltage to A6,B1 and C16 and getting 12v with key on.

and the grounds at A11,A12,D1 and D2 are good.

at pin B6 which is for the VATS im getting 2.5 volts,I dont know if thats within limits.

All of the voltage and ground checks were done when the ses light was not not functioning properly.

I dont know if the ses light is intermitant at times?