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1987 MAF circuit test

Vettetime

Member
Joined
Jul 27, 2020
Messages
8
Location
California
I have a 87 that I'm getting codes 33 and 36 so I replaced both MAF relays (burn off and power relays) still getting a 36 code after I start car up again from driving it! And occasionally a 33.
I unplugged harness at MAF sensor and turned on ignition.i checked for volts on the purple wire no volts. I do have ground on the BLK/wht wire. I plugged harness back into sensor and start engine
Then probe purple wire and with car running I have the battery voltage.when I probe the dark/grn wire (censor wire) at idle I have 0 volts.when I ground annolog wire BLK/pink car stalls!
Does this mean ECU has bad circuit for mad?
Any help is appreciated...
Thank you
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
As you know, you have two faults, one in the MAF sensor circuits and one in the burn-off relay circuits. The diagnostic info for those two faults is too lengthy to repost here.

Do you have the Factory Service Manual? If so, the first thing I'd do is look for the diagnostic and repair information for those two fault codes. If you don't have the Manual, you'd be best served if you got one.

If you unplug the MAF and probe the purple wire, you're not going to see voltage there unless both the MAF power and burn-off relays are closed. The black/white wire is the system ground and a chassis ground. Zero volts on the dark green wire at idle may indicate a faulty MAF or a relay problem.

I could not find a black/pink wire in the diagram for the MAF circuits on an '87. The wires which go to the MAF should be: dark blue for the burn off signal, black/white for system ground, black for analog ground, purple for 12V and dark green for MAF signal

Lastly, if you get an FSM and start diagnosing according to it, you need a 12V test light and a DVM with at least 10Megohm impedance.
 

Vettetime

Member
Joined
Jul 27, 2020
Messages
8
Location
California
As you know, you have two faults, one in the MAF sensor circuits and one in the burn-off relay circuits. The diagnostic info for those two faults is too lengthy to repost here.

Do you have the Factory Service Manual? If so, the first thing I'd do is look for the diagnostic and repair information for those two fault codes. If you don't have the Manual, you'd be best served if you got one.

If you unplug the MAF and probe the purple wire, you're not going to see voltage there unless both the MAF power and burn-off relays are closed. The black/white wire is the system ground and a chassis ground. Zero volts on the dark green wire at idle may indicate a faulty MAF or a relay problem.

I could not find a black/pink wire in the diagram for the MAF circuits on an '87. The wires which go to the MAF should be: dark blue for the burn off signal, black/white for system ground, black for analog ground, purple for 12V and dark green for MAF signal

Lastly, if you get an FSM and start diagnosing according to it, you need a 12V test light and a DVM with at least 10Megohm impedance.

Thanks for the great info I'll pick up a FSM ��
 

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