mas sensor burnoff control relay

[Jay James]

mas sensor burnoff control relay
Hi, I have an '86 c4 which has a dead short which is blowing the fuse to the MAS SENSOR BURNOFF CONTROL RELAY and does not allow the car to start or run.  When the relay is disconnected and new fuse installed the car starts and runs.  What is the long term effect of having this relay and circuit disconnected.  The short has been traced to the large wiring loom that runs behind the distributor.    The fault will be found when I have more time and patience.  Any help will be appreciated.  Thanks

[Vettech]

Have not got the book in front of me, but you can run disconnected. In the thottle body there is a fine wire that is fed juice when engine runs, the wire heats, this represents a resistance value, the ECM sees this and converts to an equivalent amount of air flow (sets air/fuel mix ratio), open throttle = equals more air = cooler wire = changed resistance value = ECM adds or subtracts fuel = best possible fuel/air mix etc etc - even though you have an air cleaner, dirt etc will get thru the throttle body, and just loves to stick and burn onto the wire, therefore at the end of your drive when you turn the engine off, the controll relay will activate for "x" seconds, switching on the "MAF burnoff relay" which applies a full 12v to v wire, heating it to a trillion or so degrees, which vapourises any sh#t stuck to the wire. Next startup means you have a clean wire and perfect air/fuel mix. There are three relays, inter-related, they are a P in v A. I'll find my books and see if i can give u some more clues but, it is easy to confuse between the relays. Disconnection should be ok for the short term, but obviously as the wire gets crappier, then fuel economy and perormance will be affected. VP

[Vettech]

When you say fuse, do you mean "a fuse or a fusible link" - reason  i ask is, I cant see one in one of my cct books, there is a fusible link which feeds - Mass  burnoff relay, oil pressure switch, Mass burnoff control relay, fuel pump relay (contacts). The block diagram is convoluted, since some of the wires come out of the ecm, so the exact sequence of operation is not straight forward, but I know Ive read it somewhere, will keep looking.

[Jay James]

Hi, it was the fusible link and I replaced it with a 20amp inline fuse.  It is located just before the mas burnoff relay located just behind the battery on the far right hand side of the firewall ( USA passenger side ).  Thanks.

[Jay James]

Thanks VP that helps a lot.  Regards, Jay

[Vettech]

OK, yours has been modified differently to my 87, batteries are on RH side guard, but my +pos is a large cable going back under the LH side A/C, back to the original positive tie point for a multitude of fuseable links, your fuseable link "H" has been moved and wired to the batt and then run thru the loom to the relays etc. This means it has been cut and joined, then wrapped, could be crimped or soldered, (but I have seen so called professionals just twist the wire together) and if they did several joins close, then the insulation could move/slip with inevitable shorts, seems the best place to start looking. I recently had the oil sender leak which is at the back of the engine under the dissy squeezed by the fire wall, an abolute bastard of a place to get to - best of luck

[Jay James]

Thanks Vettech that is a great help.  Regards Jay