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Master Tech Lee
Master Tech Lee, ASE Master Tech
Category: Car
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Experience:  36 years Domestic and Import Electronics Diagnostic Tech
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IF THE RETURN VOLTAGE IS TO HIGH HOW DO I GET IT RIGHT. tHE

Customer Question

IF THE RETURN VOLTAGE IS TO HIGH HOW DO I GET IT RIGHT. tHE BAROMETRIC SENSOR LOOKS LIKE THERE IS SUPPOSED TO BE A VACUMM LINE TO IT IF SO WHERE DOES IT COME FROM.
Submitted: 1 year ago.
Category: Car
Expert:  Master Tech Lee replied 1 year ago.

Leon Davidian,Sr. :

Welcome to justanswer.com My name is XXXXX XXXXX online automotive technician. Reading your comments. I will be right with you.Thank You, Leon

Leon Davidian,Sr. :

Need the year, make, and model please; and include engine size please and thank you.

Leon Davidian,Sr. :

Leon

Customer:

1980 Cadillac Eldorado 6.0 litre TBI. I have burned two ECM's I am tring to troubleshoot before cooking another. Fuel presure at the schrader valve is 10 PSI and the fuel filter is new. Have checked and repaired bad vacuum lines. No signal to trigger injectors. Car started and ran rough for about 5 minutes after replacing ECM then quit. Have located MAP and Barometric sensors and measured reference voltage at 5 volts. With harness plugged in the third wire in the harness from the ECM to each sensor read .02 volts, with the harness unplugged still have 5 volts reference voltage but the thrid wire reads about 4.80 volts. Have unplugged TPS to see if there was a change but everything stayed the same. Reference voltage at the TPS is 5 volts. Pluged back in the TPS reads 1.4 volts at closed throttle and 5 volts at WOT

Leon Davidian,Sr. :

Thank you for the information. I am looking in into this for you. I need to look at the specs and wiring schematic. I will get back to you, Leon

Customer:

Leon

Customer:

Just Answer is asking for feed back but I have not recieved anything from you to give feedback on. Can you help?

Leon Davidian,Sr. :

thank you for your patience. I am going to be on all day tomorrow and will have your information .

Leon Davidian,Sr. :

There is suppose to be a vacuum line going to the map sensor i sent a diagram to show you where the map vacuum line at throttle body to map is routed. please check and/or replace this line and recheck voltages.

Leon Davidian,Sr. :

Thank you, Leon

Leon Davidian,Sr. :

Full Size Image

Customer:

Thanks for the diagram, it will help a lot

Leon Davidian,Sr. :

Heollo

Leon Davidian,Sr. :

sorry hello

Customer:

Long story short. Replaced burned out ECM with new one. Car ran roughly for about 5 minutes then quit. Restarted and ran really rough then quit agian, would hot restart. Fuel pressure at trottle body 10 psi, fuel filter has been replacedReference voltage to MAP and BARO sensors 5 volts, return voltage 0. No signal from ECM to injectors, Power to injectors but no pulse from test light hooked to injectors when cranking. TPS reference voltage is 5. Voltage with throttle closed 1.4, with WOT 4.8. Vacuum lines have been checked, bad lines repaired.

Leon Davidian,Sr. :

be right with you

Leon Davidian,Sr. :

ok

Leon Davidian,Sr. :

i am reading your comments

Leon Davidian,Sr. :

Fuel psi is with in spec

Leon Davidian,Sr. :

Full Size Image

Leon Davidian,Sr. :

Are you getting the same reading when the map vacuum is hooked up , correct

Customer:

Have not been able to check fuel psi with engine runnuing

Leon Davidian,Sr. :

But you have 10 psi key on correct

Customer:

Correct

Customer:

Fuel pressure measured at Schreader valve.

Leon Davidian,Sr. :

ok here is a chart to test the map/baro sensor, but what has me is no injector pulse. while you look at the map test and chart, i am going to check on the crank and cam sensor situation for ya

Leon Davidian,Sr. :

Full Size Image

Leon Davidian,Sr. :

you are going to use the ALL at top readings for testing

Leon Davidian,Sr. :

Take your test light to the terminal "R" on the 7 pin ignition module and see if this provides a reference pulse with test light. This pulse is sent to ECM indicating engine RPM and crankshaft position. With out this The ECM will not fire injectors.

Leon Davidian,Sr. :

Full Size Image

Leon Davidian,Sr. :

let me know what you find out, so i will know which direction to go, Leon

Leon Davidian,Sr. :

Do you have any questions?

Customer:

Now you find out how much I know, what do I use to test the MAP and Baro sensors. Also I take it that the "R" pin is in the harness that pluggs into the side of the ECM

Customer:

I also run into reference to the oxygen sensor. As far as I can see there is not ine on this car, should there be?

Leon Davidian,Sr. :

i thought you knew how by the readings you gave me above

Leon Davidian,Sr. :

yes you have o2 sensor here

Leon Davidian,Sr. :

Full Size Image

Leon Davidian,Sr. :

i am going to give you a schematic and connector if i can find it- to help you check the map

Leon Davidian,Sr. :

How did you get the readings you sent me from above?

Leon Davidian,Sr. :

R - is at the igniton module

Leon Davidian,Sr. :

i will see if i have diagram too, of this for you.

Leon Davidian,Sr. :

ignition mod is in the distributor just to remind you

Leon Davidian,Sr. :

this is for testing the baro/map

Leon Davidian,Sr. :

Full Size Image
Full Size Image

Leon Davidian,Sr. :

going to find ignition mod pin and electrical chart for you

Leon Davidian,Sr. :

let me slow down and ask a stupid question - the vehical does not start correct?

Leon Davidian,Sr. :

do you have spark?

Leon Davidian,Sr. :

but no injector pulse to pulse fuel correct?

Leon Davidian,Sr. :

just making sure we are on the same page

Leon Davidian,Sr. :

I ask cause we need to find why the injectors are not working to give you the fuel needed to run engine

Customer:

To get the Map and Baro sensor readings I used a multi meter. Used the ground wire in the plug and tried terminals in the plug until I got a reading.I am also using a Haynes manual for reference. The diagrams you sent, are they generic, my car is a 1980 Eldorado with a 6.0 liter TBI motor. The vacuum chart you sent me gives values for different altitudes so I think that the car needs to be running but I cannot start it

Leon Davidian,Sr. :

that is correct and we will start with the no start. I was confused due to the original comment to justanswer.com was asking us "


IF THE RETURN VOLTAGE IS TO HIGH HOW DO I GET IT RIGHT. tHE BAROMETRIC SENSOR LOOKS LIKE THERE IS SUPPOSED TO BE A VACUMM LINE TO IT IF SO WHERE DOES IT COME FROM."

 

Leon Davidian,Sr. :

I was giving you an answer to that question - then now the car does not start. I am sorry but i have to help you with the no start condition first.

Leon Davidian,Sr. :

OK I need you to check the ground

Leon Davidian,Sr. :

yes the 1980-81 are the same

Leon Davidian,Sr. :

my charts are from a professional source

Leon Davidian,Sr. :

check the ground to ecm

Leon Davidian,Sr. :

is there any codes ?

Customer:

Yeah my bad, I'm getting frusterated with this car but don't want it to beat me. Yes I have spark. Earlier testing showed power to the injectors but no pulse. When I replaced the ECM I could see fuel squirting into engine. It ran rough for a short time then quit. I restarted, it ran then quit and stopped squirting fuel. Again power at the injector but no pulse when cranking. Want to find problem before burnning another ECM.

Leon Davidian,Sr. :

yes a bad ground on this car has been a problem. Do you by your book were the ground to ecm is?

Leon Davidian,Sr. :

sorry does you book describe were the ground is

Leon Davidian,Sr. :

have you checked the fuses?

Leon Davidian,Sr. :

check this fuse

Full Size Image

Leon Davidian,Sr. :

Here is what you need to start is to check the ground to ecm.

Leon Davidian,Sr. :

2. check terminal R at ignition module for pulse this is done by looking at the ignition model for pin R and then re install cap then probe the wire to pin R and crank engine. Does the test light pulse?

Leon Davidian,Sr. :

But first check all fuses at relay box and inside car.

Customer:

Currently the ECM is just hanging under the dash. There are two ground cables attatched to the body, one goes to the bracket that the MAP and Baro sensors are mounted to and the other goes to a mounting stud on the back of the ECM. I thought the connection between the body ground and the ECM was poor but not so, however the connection between the body grond and the Sensors was poor as the mounting bolt that the ground cable was attatched to at the sensor bracket was srtipped. I replaced the bolt and the connection is now tight.

Leon Davidian,Sr. :

ok i found the ECM diagram

Leon Davidian,Sr. :

hold wjile i get this together for you and it shows the ECM ground and pin R

Customer:

I don't think I have checked this fuse. I will have to locate it and check it. Do you know what amperage it should be?

Leon Davidian,Sr. :

I see i would to check the ground strap from engine to fire wall if you do not see it near the passenger side then run a jumper wire from engine to a good body ground for ol time sake

Leon Davidian,Sr. :

in the diagram it reads 15 amp

Customer:

Leon

Leon Davidian,Sr. :

yes

Leon Davidian,Sr. :

Full Size Image

Leon Davidian,Sr. :

i am here

Customer:

Things are going good here but I have to sign off, got to go to bed, have to travel early tomorrow (my job) gone for a few days. Will you be available when I get back?

Leon Davidian,Sr. :

yes, when will you be back? and you must rate me for us to stay connected

Leon Davidian,Sr. :

three days i will be on in the evening

Leon Davidian,Sr. :

Are you there

Customer:

Yes and thank you, XXXXX XXXXX a lot of good info out there and I think I have found some

Customer:

Bruce

Master Tech Lee, ASE Master Tech
Category: Car
Satisfied Customers: 502
Experience: 36 years Domestic and Import Electronics Diagnostic Tech
Master Tech Lee and 13 other Car Specialists are ready to help you
Customer: replied 1 year ago.

Leon


Thank you for your assistance. I was able to start the car but it needed a 40 amp boost to get it going. I guess a new battery is in order. I still have issues that I think I can work out but if needed can I call on you again?

Expert:  Master Tech Lee replied 1 year ago.
OK Thank you, Leon

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