Hey guys, I've got an '87 TII, I am wondering which wire on the boost sensor needs to be grounded to fix the 3800 hesitation.

Thanks in Advance,
Aaron

 

bizump

 

The brown/black one on the early versions and the pure black on later versions, is the grounding wire.

Do not EVER ground the brown/white wire. Its the ref voltage from the ECU and you'll fry the ECU. The brown/red is the feedback from the sensor to the ECU, and the black/white is 12v.

One thing you might do to see how good its grounded right now, is to put one of your meter leads on the brown/black wire and the other lead on the battery negative post. You should have less than .1 to .5 ohms. If not, ground it better.

And just a note: when you ground that wire, you ground a number of other sensors like the tps, afm and water thermo sensor. They are all spliced together inside the harness. Only problem with that concept, is that bad solder joints at the other sensors spliced joints, will not make them work any better thru your added ground at the pressure sensor. See the wiring diagram in the fsm for what I'm talking about (splices).

 

I don't have a brown/black wire... just a brown/white, brown/red, black/white, and black. So would it be the black then?

Thanks,
Aaron

 

Yes, black on the newer cars.

 

HAILERS: thank you so much for the info. I did the ground and also put a pill in the vacuum line to the sensor. The car runs flawlessly!!! *knock on wood*

 

so you splice into that wire and run it to the chasis to ground it?

 

Yup, not sure if it was that or the pill that did it, but no more hesitation

 

Probably the pill/orifice. Only way to find out for sure is to remove the hose and put a hose on that has no pill/orifice. I wouldn't touch a thing if it runs good now.

 

hailers you are a really smart man!!

 

Ok well that solved it for only TWO DAYS!! Now it has come back so I don't know what to do. Any help would be much appreciated.
Thanks,
Aaron

 

More grounds! Add grounds to the battery, alternator, engine block and ECU.

P.S. I like it when the Aussies call it "earth."

 

HAILERS--just went and checked the '91 TII ad there are no solid black wires at the pressure sensor. The car is a 1/91 build, could be different, eh?

 

That's odd. I'll look at the 91fsm later. About eight hours from now, and let you know what the deal is. I only own a 86-87 cars and don't have a series five to look at. Could be different. Seems they would have fixed the grounding problems by the time they made series five cars.

 

I'm looking at a 91 schematic. There are three wires. The one that is ground should be the BROWN/BLACK wire. Brown with a black stripe.

The G/Y is the input to the ECU at pin 2H on the ECU.

The Brown/White is ref voltage of approx 5 volts.

I'm talking about the pressure sensor on the right front strut tower. 100 percent sure.

 

HAILERS-- I can concur the three wires. Br/Bl, Br/Wh, and G/Y. Just wanted to clear it up for others that there my not be a solid black ground lead for 91s.

Brian

P.S. Our BBQ is on the 24th here in Jax, and I still owe you a steak!

 

The goofball Mazda people irritate me. The ground for that sensor is brown/black on the 86/87 then they changed to a pure black for a few years, it seems, then I now find out that the 91 is back to brown/black. Goofy, but not serious goofy. Mmmmmmm.. steak! Someday.....

 

Yeah, I'm pretty sure all s5's are running brown/black for ground. Kind of strange why they keep changing.