2 replies to this topic

[crx_rogus]

Folks -

My '86 Civic ZC Si appears to need a replacement MAP sensor (three separate probably-good ECUs agreed on that), but a used assumed-good replacement from an old friend made no difference... My Book of Helm, A.D. 1986 does not give a resistance range to check the sensor with. It gives an operating return voltage to expect, but now that I currently have two possibly perfectly good MAP sensors I would like to be able to do a resistance check. The local NAPA won't allow electrical part returns and they're asking $350 for one (unavailable from Honda or any even semi-local junkyard), so...

Does anyone know what resistance range a MAP sensor should have at idle vacuum vs. WOT so I can localize the problem more reliably?

It shows all the normal "MAP sensor is bad" symptoms - rich and unstable idle, bogging under low vacuum / heavier load conditions. The fuel : air ratio gauge shows the PGM-FI operating in too narrow a fuel delivery range; too much at idle, goes lean before more than maybe 20 - 25 hp can be generated. The gauge has an integrated potentiometer that (user-adjusted variably) cons the ECU into thinking the coolant temperature sensor is showing a cold engine when it's hot, enrichening the mixture, which in turn allows me to keep up with around-town traffic at least when otherwise climbing up over a wide, crowned road from a standstill would be ooooooooooooogly (slip that clutch!). I could guess at the expected resistance from the expected return voltage, but that's only under one operating condition, not realistically variable.

TIA,
Roger
'86 ZC Civic Si
(preceded over 15 years by '86 CRX Si, '85 CRX Si, '85 CRX DX, and an '81 1500DX as my intro Honda)

[crx_rogus]

I just found a MAP sensor -related error in my Book of Helm A.D. 1986 that my old Chilton's "All Hondas Ever Made" book does not have. The former got atmospheric pressure sensor readings confused with much less fixed MAP sensor readings... From Chilton's of all sources: 0.5V between C11 and C14 at vacuum with only the ignition on (not the engine itself), 4.5V at atmospheric (vs. 2.76 - 2.96 from the atmospheric pressure sensor). My original sensor, plus the replacement, both have constant resistances regardless of vacuum levels, so both are therefore bad. The ECU is also supposed to supply 4.75 to 5.25V across it vs. the 4.2V being delivered, but the now known-bad MAP sensor gets replaced first, then the ECU if need be.

Constant 3.65k ohms between R and W (left and top) on the original sensor, 3.55 for replacement.
Constant 2.74k ohms between R and G (left and right) on the original sensor, 2.99 for replacement.

Roger
'86 ZC Civic Si

[DEIVIONCRX]

Yep youll need some way to pull a vacuum on it, and a Volt/Ohm's meter.