jacobcartmill

iTrader: (6)

i grounded my ecu to try to get rid of my 3800 rpm hesitation. it is still there. i have not tried to add one on my pressure sensor yet. which wire to i add the ground to? there are 4. 2 red and 2 black ones.

NZConvertible

Check those wire colours again, three of them should have stripes. The four wires should be brown (might look red) with a white stripe, brown with a red stripe, black with a white stripe and plain black. The black one is the ground wire, which is the one you want.

If the colours don't match up, get a multimeter and check for continuity between each wire and the chassis (with the ignition off). Only one will have continuity, and that's the ground wire.

BTW, I added extra grounds to the ECU, boost sensor, battery and engine, and I still have a small stumble at 3800rpm, so don't hold your breath...

jacobcartmill

iTrader: (6)

Well, to add to this; since i grounded the wire at the ECU, the stock boost gauge is pegged right in the middle of the meter. before it was stock on full vacuum then would go up and down when i hit boost... is this a problem? also, i have an FCD. the word on the street was that the FCD disabled the stock boost gauge, but mine was working fine til i re-grounded the ecu.. whats the deal?

HAILERS

Not good. The brown/white should have 5 volts on it. Its ref voltage.

The black/white should have 12v.

The brown/red is the input to the ECU and the boost gauge.

The pure black should be the ground.

Back to the brown/red wire........with the key to on, you should be able to stick a meter lead up the back of that wire and see 2.3 to 2.7 volts.

I'd take the fcd out of the picture and do the above in original configuration.

As a general rule, if the boost sensor does not respond to boost inputs, then the ECU isn't seeing the boost either. Not good at all.

Put the word out on the street......the fcd does not disable the boost gauge. The only exception is if some clot set the clamping voltage to some obscene low voltage. I've used a RB and three home built fcd's on my car(87) and the only limit it has put on my boost gauge is that it won't go past the last click on the boost gauge because that's where I have the clamping voltage set.

I also don't have any hesitation. Must be due to the U.S model having the extras, like a egr valve, 3000 rpm starting gig, thermowax etc. humor.

With some luck, the fcd is the only thing that went bad. So do disconnect it(and reconnect the wiring harness to the boost/pressure sensor) and see what happens.

jacobcartmill

iTrader: (6)

ok i think i know which wire you are talking about now on the pressure sensor, but why would grounding my ECU pin my stock boost gauge in the middle of the scale?

here is what i did.

HAILERS

Pardon me. Functional illiterate here. Head up my dark spot etc. In my mind I was thinking you grounded the wrong wire in the boost/pressure sensor. Oh well.

Grounding the right wires at the ECU should not have effected your boost sensor. Unless you grounded the wrong wires. Which pins did you ground????? Give letters please.

600HP CLUB

in FC3s-pro.com, it states if your pressure sensor isn't working then the boost gauge wouldn't go to ZERO when ignition is pointed on "ON" position, mines does go up but doesn't reach to the ZERO, prolly because the boost gauge is messed up. I test my pressure sensor and i don't remember the number but i remember it was good enough resistance.

I cut the black wire on pressure sensor and put back my battery, and check with the ignition on ON position and it doesn't move, until i re-attached it goes up again but doesn't reach zero, about 80% of the way, when ignition is on ON position, so does this mean my pressur sensor is fOOked? or is my gauge messsed up?

-mike

HAILERS

600HP CLUB......just try this experiment with you boost gauge. Go to the sensor and take the vac hose off and plug it. Now go start the car and let it idle. Does the needle now come closer to the zero mark???????

The reason I mention this, is that my gauge only gets within two needle widths of the zero. I did the above experiment and found that with the vac hose off and plugged, the needle will hit the zero. I suspect the extra voltage with the alternator running is bringing the gauge up to speed, so to speak. Try it and see what happens.

jacobcartmill

iTrader: (6)

hailers: i know you were talking about the boost sensor. i was just showing you how i grounded the ECU to make sure i did it correctly.

i fixed the problem (the plug fell out. i plugged it back in and still have hesitation when the secondaries come on)

HAILERS

The wires that should have been grounded should have been 2C, 2R, 3A, 3G.

I notice that 2B is the pressure sensor. Is it possible that you got 2B grounded instead of 2C??????????

Also about the hesitation.......I think it was SixRotors who said he did not rid himself of the hesitation until he regrounded the ground at the tps. He did the pressure sensor and it did not work, so he pressed on to the tps.


EDIT: I see you were writing when I was posting. You fixed it. Good. Hesitation? See the words in this post above. Be careful. By the way. I've been distracted while messing with the ECU and left a plug off. Later went to start it and it would start and really idle crummy and die. Scared the heck out of me.

dr0x

If you live at a high elevation, your boost gauge will sit a little below 0 because of the thinner air. Everyones will do this.

jacobcartmill

iTrader: (6)

actually, that could be a problem for me... when i was setting my TPS i had it set on Ohms and it kept saying open load. so i put it on volts and got it to 1.00.
could that open load ohm reading be because of a bad ground at the TPS? if so, do you think this could be my problemo?

whoa, thats cool dude. you live on mars?

HAILERS

It seems to me you could check the ground on the tps first by just getting on the ground wire with the meter and the other lead on the battery negative lead and see if its under say .2 or .3 ohms.

Do you have a orifice in the boost/pressure sensor line???? Or pill if you will?? Lack of can cause the hesitation problem. It did on my n/a when I changed vac hoses and left it out.

Altitude??? I've thought about that and did blame the needle being off to that until I found that with the alternator putting out the needle would go to the zero mark(vac hose off the pressure sensor while doing so). Not much altitude in Ft Worth, Tx. I think its 550-625 ft above, something like that. 600CLUB is in the bay area which to me means sea level. A good thought about the altitude though.

dr0x

Im about 3700ft above sealevel. My boost gauge is off quite a bit while the car isnt running. But once it starts up I get normal vacuum/boost readings.

NZConvertible

Someone thinks they're a comedian... Since my car's in a million bits (UIM's off) I'll to this tomorrow. Fingers crossed...

Jacob, have you read this?

600HP CLUB

where can i get this orifice????!!! i can't find it anywhere

HAILERS

This thread has the part number https://www.rx7club.com/forum/showth...oost+and+pills This is a fix for some, not for others. Cost about three bucks. What do you have to lose. Look for hailers on that thread.

600HP CLUB

ok took it off and it goes to zero, sooo? what does that mean? but for somereason i think i hear PINGing..sounds like water drops on a can... i plug it and it dissapeared...

Amur_

RE: the stumble.

There was a post this past fall from one guy who eliminated his 3800 stumble after changing his O2 sensor...

NZConvertible

I mentioned above I've installed all the recommended additional earths and still had a stumble at 3800rpm. Well I've just had my injectors professionally cleaned and the stumble has completely gone! There's not even a hint of the secondaries coming in. I expected the engine to run better after the cleaning (and it does), but this was an unexpected surprise. I guess the dirty injectors were sticking for a fraction of a second when they are first fired. If you have this problem and you've never had the injectors out, put it on your "to do" list.

silverrotor

iTrader: (1)

Most definately. Have your FI'S machined cleeaned. I noticed a difference too. But the big gain was after I regrounded my ECU and directly adding an additional 4 gauge wire from the (-) terminal of the Battery directly to the stock Engine Ground. That Is without the orfice In the line running In the Pressure Sensor line. I am now currently and for the last year, hesitation free. Even In the coldest of mornings.

wrxfc3s

I have suspected my car as not richining the mixture after 3800 thing. My boost gauge doesn't function normally, it acts similar as if you remove the connector all togather (the gauge doesn't move to 0 when you tap on the gas and doesn't move w/ boost until around 8-9psi and even then it goes to about 3/4 way up) I removed my FCD and the car will never go to fuel cut (even w/ 10psi) Supposedly the boost sensor is good, but I've been thinking the cable between the ecu and sensor is bad somewhere. I haven't looked yet but does the wire from the boost sensor go through the harness in the front of the car and wrap around the drivers side into the compartment or does it go the other way?

My car doesn't hesitate but I noticed a serious lack of power on the top end, I saw the boost gauge and stopped driving the car. I have an older HKS sport turbo kit on the car w/ TO4B.

A few really wierd things on my car:

1) I have a constant small drain on the car that I haven't been able to isolate.
2) I had a horrible engine noise problem that no car stero place could fix, they said somehting is malfunctioning in the car.
3)I have the boost/fuel enrichment problem.

The engine noise problem started after swapping my ECU out for a test unit from RP that had been remapped. When I swapped mine back in the car I started getting this engine noise?

HAILERS

About the wire path for the boost sensor wire (BrR). It goes from the boost sensor, into the car on the passengers side, where it splits off. One wire goes to X-15, a fifteen socket plug. When it split off from the BrR wire, it became a LW or blue and white wire and gets inserted in the far end of the X-15 plug. From there it goes inside the cabin to a plug called CO-3, a 21 socket plug below the meter gauges, and from there to C-02 a round plug on the back of the combination meter.

So, no it does not route like you thought.

And its probably too late to answer 600HPCLUB, but if you did plug the vac line to the boost sensor, and then turn the engine on and now the needle hits the ZERO mark, whereas it did not before, then its I'm assuming a voltage drop that is screwing up the reading when the engine is off. Evidently when the alternator is on the boost gauge is reading right because there is not the voltage drop that is present with the engine off. Make sense???? Does to me.

HAILERS

wrxfc3s
Why not try what I suggested to 600HPCLUB??????
Take the vac hose off the bottom of the boost sensor. Plug the hose with a screw or whatever. Now start the car. How close to the O does the needle come??? If you turn the engine off, and then turn the key to ON, engine not running, does it read the same??? Or is the needle further below the O than when the engine is running??

Have you checked the vac line for the boost sensor for leakage???

Do you really mean that the factory gauge does not move until your aftermarket gauge hits 8-9 psi??? Does not move at all????????? I'd be looking for vac leaks in the boost sensor hose or the connection. orwonderaboutheaftermarketgauge.

600HP CLUB

makes too much sense too me. i get it hailers, because the alt doesn't power up until engine pulley makes it work..

-mike