veink

can anyone tell me how to check my boost pressure sensor. I did it the way the haynes man. said to and got a whacky reading. How likely is a booost sensor to go out, and if it didi would it cause my secindaris tocut out?
Thsnks

Scott 89t2

umm.. I think I can read that....

how much boost are you running when the secondarys cut out? they are surposed to around 6psi on 87-88 and 9 psi on 89-91.

the 87-88 also requires a pill in the vac line to the sensor, if you are missing this it'll cut out too soon.

HAILERS

1. Disconnect the vacuum hose from the pressure sensor.
2.Connect a voltmeter to the pressure sensor (Brown wire with a red stripe)terminal.
3.Apply 100mmhg(3.9inHg) of vacuum to the pressure sensor using a vacuum pump tester.
4. Turn on the ingnition switch and check the voltmeter reading.
RESULT: Voltage: 2.0~2.5V at 100mmHg(3.9 inHg)
MITTYVACS are available at any reliable auto store, even PepBoys.
5. I have a meter connected to my pressure sensor. If you give me a reading of yours at say 7psi boost, I'll give you what the reading on the one I have.
6. The above is a copycat of the factory service manual that is available free online at..........You know where.
7. What was the wacky reading? Curious.

veink

at3.9 hg it was reading somthing like 5.6 volts.

veink

what exactly does the pilll do?

HAILERS

The *pill* which is an orfice, prevents *spikes* or overshooting. No orfice will cause bucking, jerking etc during hard acceleration. I have not experienced it on my turbo, but did with my na when I replaced the vacuum line without the orfice. Was very noticable. Its dark right now, and cold @4:45am, but when the sun comes up I'll put the Mittyvac on the pressure sensor and see what I get and write back. Out of curiosity I took a look while driving yesterday at the voltage output at 7psi boost and it was b/t 3 and 3 and a half volts. Related: https://www.rx7club.com/vforums/show...highlight=pill and this link has the part number https://www.rx7club.com/vforums/show...threadid=14679

HAILERS

Just put the Mittyvac on the 87turbo and the reading on the brown wire with the red stripe is 1.97. Should be 2 to 2.5 volts. Close enough for me(ice cold car, ice cold human too). I patched in a boost sensor for a n/a and its reading was 2.8(should be 2.5 to 3.5 for a n/a). It appears there is something amiss with your car if your on the brown wire with the red stripe. Sorry 'bout that. By the way, I bought that n/a sensor yesterday at the wrecking yard. That sensor plus a cable for the cruise control cost me altogether 10 bucks even, so if you do indeed need a new sensor, it should'nt cost much from a wreck yard. Might make sure the correct sensor is on your car. The turbo number is N318(could be N313, the last number was questionable on my car) and the 87 na is N327.

HAILERS

I'm always forgeting something. I meant to suggest going back and looking again at the voltage when a vac of 3.9 in/hg is put on it. It might be possible that you got on the wrong wire. One wire is a constant 4.5 volts, another a ground, one has 12v and the one your interested in is the output your interested in, 2-2.5volts. I'd double check before buying another. You've probably done this already, but I thought I'd mention it anyway.

veink

well I got the pill from my old 87n/a and put it in the line. It didnt change anything. I did read in some of those posts above that There are susposed to be more than one. My car ran fine before i replaced my manifold gasket and there was no pill In it then. The idle on the car is also somewhat imprecise. Sometimes it will idle just fine, with about 15 psi vac. other times it will idle lean and bounce. Still other times, vac. will drop to ~12 psi and it will run a little rich. I read on ons of those posts that if your vac. at idle is les than 15 your angine is almost dead. I have a street ported engine, will that affect the vac?
Also the throttle stop is not making contact, how much of a problem could this cause and will it mess anything up to change its position?

Scott 89t2

you will have less vac with a street port. if it's running fine sometimes and drops to 12" sometimes it's probably a vac leak. I had a leak on mine a few weeks ago and it idled pretty bad and only pulled 12".

my guess is you missed a hose somewhere when the mainfold was off or you didn't get the gasket on right.

HAILERS

Back to the pressure sensor. If it is reading like you said, get rif of it. The ECU is getting a wrong signal as to what load the engine is under.