Tired of searching ...testing pressure sensor
 

Ok, sick of searching thread after thread of absolutely nothing. I need to test the pressure sensor on my s4 TII....the fsm says to unhook the vaccum line and pull 100whatevers of vaccum on the sensor and check the voltage of the sensor with the ignition on....WELL...that's not possible for me, as I have no way to pull 100mmhg or whatever of vaccum. Is there anyway to test this other than with pulling a vaccum?

Here's why I ask...my car has been having random hesitations throughout the rpm range...sometimes 3500..sometimes 4500 or so...sometimes in the lower rpm's...around 2500. Well, I've been messing with the S-AFC on the car and have just recently been advised to change the THR wire from the tps signal on the ecu, to the pressure sensor output up front before the FCD....well...with the THR hooked to the tps signal...I could sweep through the rpm range in neutral and watch the thr increas from 0-100%...but it was hitting 100% at like 20% pedal.

HOWEVER, now that it is wired to the pressure sensor...I am getting absolutely NO reading from the THR on the AFC. Should I be getting a reading at all sitting with the car ign on/car off...or with the car idling, or will I not get a reading until I'm actually boosting?

Find someone with a vacuum gauge and do it...

Or if you want attach a piece of vacuum hose to it, suck, and check the voltages to what they should be per the FSM.

Good luck, I've got a N327 pressure sensor if it's any help... I thought mine was bad and I checked pricing on the fuckers from NAPA, $380 :o

Glad mine was still okay :)

James

EDIT: Also make sure your TPS is set, and your AFM is good.

Use a multimeter to check the MAP sensor output voltage at three points; at the sensor, at the ECU loom before the S-AFC wire and directly at the ECU (i.e the other side of the tapped wire). With the ignition on and the engine not running it should be 2.2-2.5V. With the engine idling it should drop to ~1V.

You should always be getting a reading when the ignition's on.

Doesn't really sound like a MAP sensor problem though...

Did you remember to reinitialize the SAFC?

Alright...i just tested the pressure sensor with a DMM. I think this may be the problem.

Ok, all the below was done with the ignition on, and the car off)
Testing right off the sensor...there is an fcd plugged in. coming right out of the sensor, there are 3 wires...white, red, black. Tracing the wires back, the white wire matches to the brown w/red stripe on the factory harness, which is the pressure sensor output. This wire is only putting out .02 volts...it's the same right at the sensor, before the fcd, and after the fcd. The red wire, right at the sensor puts out 5volts...Now I'm assuming the black wire is suppose to be ground (please correct me if I'm wrong there). Testing this wire for continuity...I can't get a tone (my meter makes a buzzer sound when you get continuity). I had my meter ground on the battery...and I checked a couple other points under the bay and was getting good continuity. So, if that is a ground...where is the harness coming off the pressure sensor grounded? Where should I go from here?

The grounds for all the sensors in the engine bay plus the atmospheric pressrue sensor in the car, are all spliced together inside the harness and meet up at pin 2C of the ECU. The actual ground for those sensors I'm pretty sure comes from the ring terminal on top of the REAR rotor which feeds ground to pins 2R, 3A, 3G.

If the key is to ON, I'd go to the harness connector at the boost sensor. The plug with the brown/red, brown/white, black/white and finally either a pure black wire OR a brown/black wire which are ground.

I'd remove the FCD first thing and connect the boost sensor up like it came from the factory. The brown/white will have approx 4.5 to 5 vdc. The black/white will have battery voltage. The brown/red will have 2.3 to 2.7vdc and the ground wire will be of a value of .....oh, say 0.5ohms IF the key is OFF and the meters negative lead is on the battery negative post.

That's for a series four turboII. And the voltage checks above are with the key to ON and the connector on the boost sensor. Just unbolt the sensor and flip it up so you can backprobe the wires in the connector with the plug on the sensor.

It sounds like a honked up FCD or one made for another series car. Try without the FCD in the circuit like I mentioned above.

The pressure sensor should have a connector with four wires going into it. The one I'm looking at on my desk has four, and the one on my 88 base has four as well. That 5v wire is your signal wire, the others I'm unsure about, I'll see if I can find a wiring schematic for you, and let you know. But IIRC the voltage should sweep with vacuum. Give me a few minutes.

James

Couldn't find a wiring diagram for you, hope this helps though.

So - you have an S-AFC.
Guess what - It will tell you the TPS (gray wire), AFM (white wire) & PRS (blue wire) sensor volts in test mode.
It's in the directions.

In dial display mode, you can even verify if your TPS is bad (drop outs, or non-linear)
I'm betting you have a worn/dirty TPS. A drop out in the TPS swing will make the ECU give randon fuel cuts.

Again, the brown/red wire is the output to the ECU from the boost sensor. It splices off and also feeds the boost gauge if you have a turboii.

The black/white is 12vdc for pwr.

The brown/white is the Ref voltage.

The pure black is ground. It could be a brown/black if its a early 87 car.

The SERIES FOUR FCD made by RACING BEAT.........has two plugs with FOUR wires in each plug. It's got your yellow, blue, red and black colored wires and I don't really care what they do in life becaue I RIDDED myself of FCD and SAFC and got a RTEK 2.0 Whiz Bang modified N332 ECU which does AWAY with safc/fcd AND also lets you monitor the inputs/outputs of the ECU either while you drive down the road or later in your eazy chair looking at the graphs etc.

By the way, I notice that I had spliced into the white wire on the RB FEMALE connector to feed the SAFC. I ran a wire. BUT, and I agree, you don't have to do that for the reasons the NZ stated in a post above .....somewhere. You look at your boost gauge and when it hits about zero or just above, you then look at what percentage the THROTTLE (really boost now) is at and THAT will be your high setting on the SAFC. Mine was in the sixty whatever percentage range when I had the obsolete/has been FCD/ECU/SAFC outfit on the car (RTEK2.0 owners are a proud lot). humor

The Rtek is the main advantage to an S4, but us S5 owners are proud too.

I put a SPDT switch on my gray wire to switch between the TPS & pressure signal.
I use the pressure to select the high/low map, and only switch to TPS to test it.

That SPDT is a unique angle to this sort of thing. High five to you.


Darn. That requires me to show you my JACAR Simple Voltage Switch that I cobbled together last week. It's going to be used to cut off the START signal to the ECU when the water thermo temperature switch voltage falls below 1.5 volts in order to give me no HOT START problems EVER again. JPG below. Bought a box for it today at FRYs

Ok...i think my FCD is fubared. First off, comparing mine to the one pictured above...mine has NO blue wire....the first plug (that goes into the boost sensor) has only 3 wires:red, black, & white....the fourth hole on that plug is empty (this is where the blue wire in the picture above is located)

Anyway, I plugged the factory harness back in to the sensor, and I get all the correct readings

brown/red~2.3V

brown/white~5v

black/white ~12V

black = ground

Now when I hook the fcd back in...the only wires that go into the sensor now are

red=5v (reference)

black=ground

white=0.02 (this is suppose to be the signal wire for the AFC...but coming out of the FCD, only has 0.01Volts)

As far as the Rtek 2.0 goes...i've been talking to mike maltavo at digital tuning. I'm testing the software on the palm zire 72 for him, and he may have to "hand make me a cable", but there's a very good chance I'll be getting the rtek 2.0 in the near future...but, in the meantime trying to figure out this issue....could this fcd with that low voltage be causing random hesitation problems throughout the rpms?

bueller? Anybody know what FCD doesn't have this 4th wire? Or is this FCD just been hacked to death or something?

Series five *5* do not use the black/white 12vdc wire.

I HAD a FCD on my car. Both a RB and a home made one. Each put out the required voltage on the brown/white wire which is the output signal to the ECU.

Some say a series five FCD will work on a series four. I'm neutral at best on that subject.

well, if this one is any good...then I still can't use it with the AFC correct?

The signal wire I'm tapping into only shows 0.02 volts.

If it's an s4 pressure sensor, and it's suppose to be getting 12v...then how would it work when it's not getting that voltage now? Was the s5 pressure sensor different from the s4 as far as not needing 12v?

If this is a problem, and the pressure sensor isn't working properly....could it be causing random hesitation at different points in the rpm range?

The FCD you have is of no use to you. I'd get another. One for a series four car.

If the thing wasn't putting out a signal, then it might very well have caused driving problems.

A FCD should put out the same signal as just having a regular boost sensor without a FCD. That is until you start boosting above 8-9 psi, then the FCD will peak out.

Hailers, would you say the pressure sensor is in correct working order if I measured those same voltages you posted? What would be the effects of a broken pressure sensor? Thanks for any help

Unbolt the boost sensor so you can access the wires.

Turn the key to ON.

Meter negative lead to a known ground like the engine. Positive lead up the backside of the BROWN/RED wire.

Key to ON. The voltage should be 2.3 to 2.7 vdc. If it reads that, key ON, engine OFF, then it's probably ok. That's for a Turbo car. A non turbo reads different.

Thanks Hailers. Thats what I thought, I got 2.31 vdc at that terminal- brown/black wire (Series 4 turbo). I'm just trying to localize the source of my stalling problem.

In short, new rebuilld with 300 great running miles on it, and now it justs stalls out after 4 seconds of running. AFM resistances all check out per the FSM, but I'm going to see if I can find a good working one to swap and test. No vaccuum leaks found, not flooded, injectors don't leak, fuel pump is good-verified by swapping in another, have spark, was timed correctly beforehand. TPS unsure but set to 1 k ohm at idle on cold engine.

Im pretty much all out of ideas, so I'm going to start a thread with this problem.
But thank you for your input.

The number you got sounds good enough to me. Brown/Red wire though, NOT brown/black.

The ECU during start looks at the START signal, the rpm, and the temperature of the water thru the water thermo sensor.

After it starts it uses the afm, water thermo sensor, pressure sensor and other *stuff*.

Rebuilds usually have low compression in the beginning. Three hundred miles should have gotten you almost out of that area.

I'd check the turbo inlet duct where it mates with the turbo for cracks and the back side of that duct to see if the checkvalve has fallen out or the bypass valve hose has cracked/leaking.

I'd eyeball and see if the water thermo sensors plug is still connected to the back of the water thermo sensor located on the back side of the water pump housing. A little hared to see but can do.

You might look at this http://www.teamfc3s.org/info/articles/idle.html

The attached jpg explains the start cycle. After that is when you seem to have the PROBLEM, so it's not too relevant, but it helps to know about it.

great INFO. im having hesitation problems all of the sudden, started a day ago above 3K and up..my wideband is reading 9:2 to 9:7 above 3K RPM's i got new plug wires coming but i wanted to test my pressure sensor also...i just dont know where else to look? i got a code checker hooked up and its not throwing codes either? i unplugged the pressure sensor and the code started but i dont know what else to check?? maybe the TPS? as soon as i hit 3K and 5LBS of boost it hesitates BAD.... and i have a Rtek1.7

Thanks Hailers, it was the Brown/Red wire. I have no idea why I typed Brown/black. I did a compression test days before this problem surfaced and both rotors were at 115 or a little higher on brand new housings.

Anyway, the water sensor plug is definitely connected, verified by removing the UIM. I even pressurized the intake system to couple psi and found no obvious leaks. It has an aftermarket TID with no check valve. Maybe a faulty bypass valve, but how can that be tested?

I made a led code checker and found out the atmospheric boost sensor next to the ECU was unplugged for those 300 miles, but other than that one, there are no codes being thrown. The stalling problem is still there after that was plugged back in. The ecu has the Rtek 1.7 chip if that changes anything.

Brand new fuel filter was also put in. AFM unplugged, the car runs. Holding the flapper in the AFM open more also allows the car to run. The previous owner made a TID that positions the AFM 90 degrees off normal with the plug facing up. It has always run fine like that before, so I don't think that is the cause to this problem but I would like to correct that.

I am in the process of locating a known good AFM to swap in. I'm out of ideas...

it shouldnt run WITHOUT the AFM ???

Well that's what I thought, but something is wrong.