Piranha

Hey guys, I'm just wondering what the different voltages that come out of the boost sensor actually effects coming out of the ECU. It seems like my boost sensor voltages were a little lower than normal, but still linear. I was looking at it a while ago, and didn't mess with it too much, but I'm wondering, if it has a factor in how much fuel the ECU puts in, if I could lean out because my boost sensor would be sending lower voltage?

blu_gxl

if it's sending lower voltage it would make you run rich same as if it went out.

HAILERS

I believe the signal mostly effects the timing. Retards the timing at large boost pressures also.

The 89 manual on page F2-74 is a relationship chart. On that chart it says the pressure sensor effects: Fuel injection timing, fuel pump resistor relay, a/c relay, split air solenoid valve, asv and aws solenoid valve, fuel pressure solenoid valve, bypass air control solenoid valve.

Most of that would effect a 87 except the a/c relay. The aws is not called that on a 87, its a ......????? bypass air solenoid??

Didn't say a thing about the ignition timing. Hmmmmmmmmm. I'd come to believe it retarded the ignition timing at high boost. Oh well.

Piranha

You get lower voltage from it when you are in vacuum or low boost, so how could it make you run rich? Wrong...

Hm, I need to sit down and read the factory manual, well the online one I have. So fuel injector timing could mean richness in fuel.

I'm also asking this because I'm not getting full rich on my A/F meter. I get about .7 volts. I'd rather have it running a bit higher for safety sake.

blu_gxl

well, it would make more sense if it made to high a voltage to make you run rich that might be why they want you to ground it when you get hesitation.

Piranha

I don't get hesitation...

HAILERS

Uhhhhhhhhhhhhh. I think I read the chart *** backwards. Its attached. What do you think??????

Piranha

Yeah, you definately read it backwards. Hm... Hailers, do you have your pressure sensor voltages written down anymore?

HAILERS

No I don't. Give me a list of where, what and when and I might be able to do it before it gets dark. P.S If anyone damaged there engine with any bad info I put out, just bill me. The check will be in the mail.

Piranha

Just the pressure sensor signal voltage, at full boost, maybe 3 or 4 psi, atmostpheric, and some vacuum, if you can. Thanks! AND MY BILL IS ALREADY ON THE WAY!

Barwick

so how hard is it to rewire this sucker? I hear Piranaha has done it already. What did you do, can you do a writeup?

HAILERS

Back. It takes a while to find a good piece of road with no traffic. IDLE: 1.14 @750rpm........First gear at 4000 and let off the throttle: .40 volts(full vacuum I guess). FUEL CUT: 3.60 volts. The 0 on the factory gauge is approx 2.45 volts.

I'll do more tomorrow. Here's the deal. I have a Fluke 88 automotie meter. When I went for the full boost I was looking at the meter and driving. When I got fuel cut, I saw the first time 3.54 volts. A touch low. Later as I was playing, I realized that I could put the meter on min/max, then drive the car to fuel cut. It would then register the minimum voltage and the maximun. Seeing as how at fuel cut thats as high as it will get, I did just that with the meter on min/max. Hit fuel cut. Page thru min, max, and avg. The max showing was 3.60 volts.

So what I can do tomorrow is put the meter on min/man and boost to each mark on the boost gauge, then let off the gas. The meter should read on the max, the reading I was at when I hit the mark on the boost senor, whether the 1st, 2nd or which ever mark. Tomorrow for accuracy.

No, I don't have a aftermarket gauge. Foot control.

Piranha

Thanks Hailers! I'll be checking that tomrrow. Wow, 3 volts.. I don't think I ever got that high. Hmmmm :|

Hey Barwick, it is very easy, infact it realy doesn't need a writeup, but I'll write what I did.

I just bought some wire from radioshack. I ran a few feet through where the cabling for the ABS goes through the firewall, since it is very easy to grab cables. I then cut the wire going into the ECU. The boost signal wire is pin 2B. Its a brown wire with a red stripe. With the plug connected, its on the bottom row, far right. I attached the wire to that, then by the boost sensor I put a new female spade connector on the wire, pulled the old one out of the plug, and put the new one in the plug. All done. I also spliced in the stock boost gauge again, because I love it. :P

HAILERS

Another hmmmmmmmmmmmmm. I thought you had the volts vs boost chart at http://www.teamfc3s.org/info/articles/fcd/diy_fcd.htm I'm running a Mazdatrix 2.5 downpipe with presilencer coupled with a DynoMax cat back from Rotary Performance in Dallas. I was pretty safe prior to the Dynomax. It would have to be below 50 degrees before I'd hit fuel cut. With the Dynomax and 95 degree days like today I will hit fuel cut, but it can be controlled with common sense.

Piranha

Oh yeah, I did Looks like we both forgot. There are sooo many webpages..

Barwick

excellent, great information. Thanks.

Barwick

Okay, i just went out and checked it. At the pressure sensor itself, the voltage is fine. At the ECU I'm not sure yet, I haven't checked it, it started raining, and it's friggin' dark.

RexRyder

iTrader: (10)

hey guys, jus wondering, will grounding the Boost Sensor bypass fuel cut? Will it **** up ur engine also, by running to rich or lean?

Piranha

Uh... dude... grounding ANY sensor or anything that isn't supposed to be grounded is stupid... the boost sensor puts out a voltage, so you'll be telling it that there is no voltage. I fried an ECU accidently grounding the reference voltage.

HAILERS

Piranha........how about reading this thread: http://www.haltechforum.com/showthre...5&pagenumber=1

In specific, the post by HITMAN regarding narrow band 02 sensors and their accuracy. This is in reference to your remark about seeing .7v on your 02 sensor under boost.