SureShot

My weekend projects:
Ground the pressure sensor.
Rewire the fuel pump.
Battery relocation?

Madrx7racer

i put it in the Passengers bin, under the carpet, through the firewall running parallel to the firewall into the starter.......

Etrips

dude you changed your avatar... change it back

SureShot

Do you mean run both the primay (+) and (-) under the right side carpet, past the ECU to the fire wall, then through the fire wall & left across the tunnel, directly to the starter?
I like that since the fuel pump wiring can follow the same path by the right seat.

I was thinking of using the origonal cables at the old battery location to terminate in jumper cable hook on posts.

RETed

You entire chassis is (-) negative ground.
You don't need to run a (-) negative cable back to the front.
Just connect the shortest length of cable to a secure point to the chassis.


-Ted

Madrx7racer

no, the negative stays in the bin. The wire does not go under the seat, it goes along the side of the interior(covered partly by the MAZDA plastic cover at the bottom of the door.) I used a kit with new battery cables. I will take a pic to show you!!!!.....this reminds me I need to bolt it on before I go driving it for the first time.

rxse7en

I went the simple route, Bill. Grounded to chassis in the bin and ran the positive to the starter and then another positive lead to the fuse block in the engine bay.

SureShot

I see.
Then I only need a short ground strap from the body to the starter.

RETed

Starter grounds through the engine.
Unless you removed the main battery ground wire totally, this is not necessary.


-Ted

WAYNE88N/A

You could leave the 3' negative run between the left strut tower and the starter, OR just install a brand new 3' negative run between your new chassis ground point and the starter. That way you'll know for damn sure the same potential exists between the chassis and the starter...

I keep making attempts to try to explain why NOT to ground the boost sensor to you guys, so here I go again- The sensors send very small voltages to the ECU, and any difference in potential between seperate grounds on the car will affect these voltage signals, it's not much, granted, but there is no such thing as a perfectly bonded grounded chassis, every wire has resistance, and your chassis metal has resistance. Resistance affects current, as we all know. This is why Mazda designed a common ground for each of these sensors, so that the potential is the same for all, therefore all voltages can be compared with each other more accurately for fuel scheduling.

OK, did I explain it so it makes a little more sense now, lol?

NZConvertible

It's done because the Mazda TSB says to. I assume they had a reason...

WAYNE88N/A

There must have been some extenuating circumstances, specific year cars, something? I've had more than a few PM's from guys asking me why their cars were running like $hit after they grounded that sucker. And, lo and behold, as soon as they removed it, everything's all better. Have you read the TSB, NZ, I haven't, if you have give me a "reader's digest" condensed version please...I'd like to know WHY they wrote it, just to satisfy my curiosity...There must have been something that wasn't designed or installed quite right, maybe at a harness connector, I would guess...

The strange thing is, some guys claim this helps (adding the ground), yet for some it obviously hurts...

NZConvertible

I've seen the TSB posted here before, but it was ages ago. Mazda issued it as a cure for the 3,800rpm hesitation, and in many cases it does work. It didn't for me, but it had no negative effects either. Icemark would probably have more info.

WAYNE88N/A

So you don't know if it was issued for a specific series, or even year, of our cars?

Knowing you from your inputs here in the forum, I would bet you have immaculate OEM grounds on your car, which is probably why the TSB didn't help you. I've never had a bad hesitation problem, but did have a "quasi-hesitation" back when my 5th & 6th ports opened too early after the "airpump" mod I did to them...That really screwed with the boost sensor's head, lol...

RETed

There's a cut-off date when Mazda actually fixed the problem, so this only affects EARLY FC build dates...

I have the exact VIN # posted on my website, but the bitch isn't responding right now.

I'll reply post when it comes back up.

The TSB actually shows the diagram of the plug and recommend adding a ground wire to the black/white wire.


-Ted

NZConvertible

Are you sure it's the black/white wire? Unless earlier models had different wire colours, the B/W wire is switched 12V from the main relay (88 FSM). I wouldn't ground that one... The ground should be black, like all ground wires in the car.

j9fd3s

iTrader: (3)

theres a second tsb about the 3800 hesitation, they want you to tighten the gound on top of the motor, the rear bolt of the emissions rail

NZConvertible

That would makes sense, given what Wayne said above. The MAP sensor's ground wire goes back to that nut along with most other EFI components.

And FYI Wayne, I've never touched that ground on my car, so I doubt it's immaculate. It's on the list of things to do next time I lift the UIM.

HAILERS

I posted the TSB. Do a SEARCH. Yes, it was for the early versions only. The extra ground was supposed to go to the water filler neck. Go to ALLDATA.COM for all the TSB'S. Small cost involved. Very small.

WAYNE88N/A

Someone with "the power" needs to remove this grounding step from that "grounding how-to" thread, I should think, since it's obviously not applicable to the majority of our cars. Either that, or add a disclaimer in there somewhere.

I'm shocked, Jason, lol, you haven't "cleaned up" the most important ground on your car? 3 of the 4 ECU grounds use that spot. It's probably responsible for a lot of the "my car is running like crap" threads we see on here...Mazda did a ****-poor job of engineering the physical placement and mating surfaces of this ground....

HAILERS

My, my. On early 86/87 cars the ground is BROWN with a BLACK stripe....BrB. On later cars it was pure black.

The worst thing that will happen with grounding the BW wire is a blown fuse. BUT if you ground the BROWN/WHITE wire.....you've just toasted your ECU for good.

The hesitation fix on my 87 was only finally fixed by installing/soldering a extra ground wire to the ground wires at the ECU. My ECU grounds on top of my rear housing are/were perfection. I can remove the EXTRA ground I installed on the ground wires at the ECU and make the car hesitate at will. Other people have different results/no results/bad results.

The Emissions harness has more crimp splices than a dog has fleas. These crimp splices are also in the ground wires for the ECU which run to the top of the engine. They also exist in the brown/white reference voltage wire that runs all over the engine. In my opinion......on some harnesses some of these splices were not done very well.

Frankly I look with a jaded eye at some of the grounding suggestions on this forum......just as they look with a jaded eye at my regrounding of the grounds at the ECU. I mean, really, putting a ground wire on the coil assy's????? Gotta be kidding. They're bolted to the chassis with four nuts.

WAYNE88N/A

Hailers, your engine-to-chassis bonding is shot (that little piece of crap "clip" on your firewall, with the wire going to the tranny) if you can remove your 'new' ECU grounds and cause hesitation again, pure and simple. I noticed the irony of Mazda's grounds the first time I had the UIM off, and installed my own bonding jumper between that rotor housing ground and a new firewall spot. Try it, maybe your "jadedness" will decrease.

NZConvertible

Yeah, I know. I just can't be bothered removing the UIM just for that. Last time it was off was so long ago I didn't even know of that ground.
And a whole lot more besides. The AFM, TPS, MAP sensor, water thermosensor, intake air temp sensor, variable resistor (S4), atmospheric pressure sensor (S4), knock control unit (S4), knock sensor shield wire and O2 sensor shield wire all use that same ground point. It's importance can't be overstated. Hmm, perhaps I will check it...

RETed

http://fc3spro.com/TECH/FAQ/3800.html

Oops, you're right - it's brown/black.
It should NOT affect any of the later cars according to Mazda.
It should not affect ANY Kouki or S5 FC's.
The last affected VIN is listed above.


-Ted

SureShot

Along with what you guys are saying:
I found why my sensor signals were inacurate.
The cheesy primary ground clip had slipped off the firewall spade.
I had installed a backup ground from the battery to the alternator, but witout the firewall clip, the pressure sensor was giving erratic readings.